From left to right: Endomorphic Jay Cutler, Mesomorphic Arnold Schwarzenegger and Ectomorphic poster-child Frank Zane
Endo-what now? Allow me to explain.
If one studies physical fitness (academically, or practically), then one is bound to come across the three main human body types. The endomorph, mesomorph and ectomorph.
Endomorphs are characterized by their ability to easily gain weight (be it fat, or muscle).
Ectomorphs are characterized by their ability to easily lose weight (fat, or muscle)
Mesomorphs are the middle ground group that appear to have the most malleable bodies.
In general, endomorphs have lower metabolisms than the other two, while ectomorphs tend to “run hot” all the time. Few people are all one way, or the other, but a notable dominance of one type, or another is usually prevalent.
The endo/ecto part can get confusing; especially if one is used to these prefixes in the context of endotherm/ectotherm. The names seem to be reversed from what one might normally hear (ectomorphs being more “warm-blooded” than endomorphs etc). The names have nothing to do with thermophysiology. They were coined after the germinative layers of the body during embryonic development. Endoderm forms the digestive tract, and endomorphs are usually stereotyped as fat. Ectotoderm forms the skin, and ectomorphs are usually stereotyped as being “all skin and bones.”
The reason I went with these specific bodybuilders (Jay Cutler, Arnold Schwarzenegger and Frank Zane) was partly to buck these stereotypes, but also to point out something that the news outlets are missing. Namely that having a lower metabolic state, does not mean one is a “couch potato” or has “forgone exercise.” Bigger, means more massive. That may mean fat, but as one can see above, it also can mean muscle and bone. Dinosaurs were not fatter than mammals. They were bigger.
Photo of estuarine crocodile by: D. Parer and E. Parer-Cook
Two new papers have recently hit the journal circuit. Both of them involve using living crocodylians to gain a better understanding of paleo-life.
The first one comes from Denver Museum of Natural History paleontologist, Dr. Kenneth Carpenter:
Carpenter, K. 2009. Role of Lateral Body Bending in Crocodylian Track Making. Ichnos. Vol.16:202-207. doi:10.1080/10420940802686137.
The study used an adult Caiman sclerops (first use of a large adult reptile for a locomotion study; at least as far as I know) placed in a small room with two 30cm walls placed on either side of it. This restricted any lateral movement, and “funneled” the animal out the singular opening. At this opening, a camera was placed. It would photograph the animal as it left the room. The room itself, had a smoothed mud covering. This muddy floor would record the tracks of the C.sclerops as it walked by.? Several runs were done, and photographs were taken for each run.
This is the first study I have seen that gave a front view shot of an adult crocodylian as it walked along. As Carpenter mentioned in the paper:
This front view is in contrast to most photographic studies which only capture pro?le and top views….
Carpenter also mentioned the potential of there being an ontogenetic change in limb stance as animals move from hatchling to adult. This is something that I have hinted at previously Hatchling crocodylians seem to have weaker femoral adductors than adults. This is understandable given the greater weight that adult femora need to bear. This can result in a skewed view of crocodylian erect stance; with most authors tending to underestimate the degree of “parasagittality.”
That said, I was surprised to read that Carpenter had found the adult Caiman sclerops to have a hip adduction angle of approximately 65? from the horizontal. Judging from figure1B, the hindlimb appears to be much closer to the midline than the forelimb. Fig1D seems even closer to, if not 90?. It is important to point out that much of the hindlimb is blocked by the body in this shot, as the animal is fully laterally extended. A concurrent shot from behind would have been very useful here; as would an x-ray series of shots throughout the walk phase (for instance: see this long video of a Crocodylus acutus walk cycle. Pay special attention to the position of the femur).
Alas, that is not what the paper is about.
The paper is about how lateral movements during locomotion, have substantial effect on trackways. Dr. Carpenter points out how, despite the semi-erect stance of the forelimbs, the track evidence would suggest an animal with a much narrower (parasagittal?) stance. This has bearing on how prehistoric reptiles, in particular: quadrupedal dinosaurs, may have stood.
One might rightfully ask if we should expect dinosaurs to have had any lateral movement to their walking cycle at all. Carpenter points out that lateral body bending, though not quite as exaggerated as that of crocs, is present in most tetrapods. Birds seem to be the sole exception, with their extremely stiff thorax. However birds are also obligate bipeds, and the avian thorax is much shorter and stiffer than that of dinosaurs.
So it would seem to be a likely bet that quadrupedal dinosaurs likely exhibited some degree of lateral body bending.
Triceratops pic from britannica.com, but originally from: Mounted Skeleton of Triceratops elatus? by Henry Fairfield Osborn, American Museum Novitiates, Sept. 6, 1933
Carpenter’s work rightfully asks us to caution reconstructions of stance based largely off of trackway evidence. A fine case study that the paper brings up, is ceratopians. This group, more than any other, has received considerable attention for how the forelimbs were oriented. Early work on ceratopians, favoured a hefty sprawl to the forelimbs (e.g.? Gilmore 1905, or Lull 1933). This was critically evaluated during the heyday of the dinosaur renaissance. Authors such as Bakker (1986), Paul and Christiansen (2000), instead favoured a fully erect stance. A large portion of the data supporting this assertion, was trackway based. The results of this study call into question that view. However this was not the first paper to have done so. Thompson and Holmes (2007) also questioned the “erect ceratopid” view, using a half scale model of a Chasmosaurus irvinensis forelimb. Their results come closer to the results from this paper. Though Thompson and Holmes felt that there was no real modern analogue to ceratopian forelimb mechanics.
In the end, Dr. Carpenter reminds future researchers of the importance in incorporating the entire animal when analyzing trackways.
The second paper comes from the Journal of Experimental Biology.
Owerkowicz, T., elsey, R.M. and Hicks, J.W. 2009. Atmopsheric Oxygen Level Affects Growth Trajectory, Cardiopulmonary Allometery and Metabolic Rate in the American Alligator (Alligator mississippiensis). J.Exp.Biol. Vol.212:1237-1247. doi:10.1242jeb.023945.
The authors embarked on a study of how previous paleo-atmospheric oxygen levels might have affected the lives of animals that would have been alive through these times. According to Owerkowicz et al, crocodylians were chosen because:
Given their phylogenetic position and highly conserved morphology throughout their evolutionary history, crocodilians are often thought to retain many characteristics of basal archosaurs.
I do take some issue with this, as prior reviews on crocodylomorph diversity (Naish 2001) coupled with many new discoveries ( Buckley et al 2000,? Clark et al 2004, Nobre & Carvalho 2006)? continually cast doubt on the old view that crocodylians have survived “unchanged” for some 200 million years. Nevertheless, the results of the study are both interesting, and relevant to reconstructions of how paleo-life would have adapted to these wildly different paleo-atmospheres.
Owerkowicz et al raised groups of hatchling American alligators (Alligator mississippiensis) under three different atmospheric conditions. A hypoxic (12% O2) condition reminiscent of paleo-atmospheric models for the late Triassic/Early Jurassic periods. Current atmospheric conditions (21% O2), and a hyperoxic (30% O2) condition reminiscent of paleo-atmospheric models for the Carboniferous and Permian periods.
The results were interesting, though not too surprising. As expected, hypoxic alligator hatchlings were smaller than their normal and hyperoxic counterparts. However, the degree of growth stunting is pretty surprising. Hypoxic hatchlings were about 12% shorter and 17% smaller than normal hatchlings.
Baby alligators pic from REPTILES mag. December 94. Author unknown.
Surprisingly, hatching time did not change under any conditions. This suggests a degree of “hard wired” embryological development inside the egg. In the case of the hypoxic hatchlings, they came out “almost done.” While all three groups had remnants of a yolk sac upon hatching, the hypoxic hatchlings actually had the yolk sac still protruding (normal and hyperoxic hatchlings just showed distended bellies). In some cases, the yolk sac was larger around than the hind legs, thus making movement clumsy and cumbersome.
Other interesting results from this study, included notable changes to the cardiopulmonary system. Hypoxic hatchling lungs were actually smaller than the lungs of normal hatchlings; which appears counterintuitive. The heart, meanwhile, showed distinct hypertrophy in hypoxic animals. The authors believe that lack of lung growth in hatchlings may have been due to the fact that lung function does not start until after hatchlings have hatched.? The heart, on the other hand, is hard at work circulating blood just as soon as it is formed; so it would have experienced the challenges of hypoxia at a very early stage.? Bolstering this hypothesis from the authors was the fact that three months after hatching, hypoxic alligators showed a distinct increase in lung growth rate (the lungs appeared to be “catching up” to the heart).? Hypoxic alligators showed shrunk livers as well. No real explanation for this was given, but it was mentioned that reduced liver mass seems to be a common trait in animals raised in hypoxic conditions. It appears to have some bearing on overall metabolic rate.
Hyperoxic hatchlings exhibited “typical” organ growth rates.? Where hyperoxic animals excelled was in breathing and metabolic rate.
Breathing rates were smaller in this group, while metabolism and growth rate were all larger. The explanation by the authors was that these hyperoxic animals were receiving such high amounts of oxygen in each breath, that they were actually hitting saturation at much shallower breaths; hence the shallow breathing. The higher metabolic rate is believed? due to a lack of right-left shunting in the crocodylian heart. This shunting is usually caused by low oxygen levels (like that experienced in diving), and tends to result in metabolic depression to conserve available oxygen stores.? Since these alligators lungs were constantly saturated with oxygen, right-left shunting never occurred, resulting in an elevated metabolism.
Incidentally, Owerkowicz et el give mention of a cardiac shunt known in embryological birds (via the ductus arteriosis). Though only analogous, one can’t help but wonder what this might have meant for all those dinosaurs that lie between these two groups.
Interestingly, hypoxic alligator hatchlings also showed a higher standard metabolic rate. Though these animals would voluntarily eat less than their normal and hyperoxic counterparts, their metabolism was more like hyperoxic hatchlings than they were normal hatchlings.? Owerkowicz et al believe the reason for the increased metabolism was due to the higher cost of breathing in these animals. Despite taking “normal” breaths, hypoxic hatchlings were taking in a larger tidal volume than their normal and hyperoxic siblings. The heart was also working harder to deliver enough oxygen to tissues.
Finally the authors give mention of growth rates in hyperoxic animals. Basically, it is faster. The authors mention that this might be caused by the persistently elevated metabolic rate, or perhaps from channeling saved energy from breathing (which is one of the main energetic costs in reptiles) into biomass.? It could be a mix of both, but I’m more inclined to think that it comes more from channeling energy reserves into other parts of the body. A high metabolism means nothing, if there is not enough free energy to go around. Just look at the hypoxic gators from this study. Despite their high metabolism, they grew slower than their peers.
The results of this study showed how modern animals can acclimate to different atmospheric conditions. They don’t show how animals would adapt and evolve in these conditions, but they do hint at the general directions, and help give us a clearer picture of what life was like millions of years ago.
~Jura
References
Bakker, R. 1986. The Dinosaur Heresies. William Morrow. New York. ISBN: 0821756087, 978-0821756089 pps: 209-212.Buckley, G.A., Brochus, C.A., Krause, D.W., Pol.D. 2000. A Pug-Nosed Crocodyliform from the late Cretaceous of Madagascar. Nature. vol.405:941-944.
Clark.J.M., Xu, X., Forster, C.A., Wang, Y. 2004. A Middle Jurassic ‘Sphenosuchian’ from china and the Origin fo the Crocodylian Skull. Nature. Vol.430:1021-1024.
Gilmore, C.W. 1905. The Mounted Skeleton of Triceratops porosus.? Proceedings United States National Museum. Vol.29:433-435.
Lull, R.S. 1933. A Revision of the Ceratopsia, or Horned Dinosaurs. Memoirs of the Peabody Museum of Natural History. Vol.3:1-175.
Naish, D. 2001. Fossils Explained 34: Crocodilians. Geology Today. Vol.17(2):71-77.
Nobre, P.N. and Carvalho, I.S. 2006. Adamantinasuchus navae: A New Gondwanan Crocodylomorpha (Mesoeucrocodylia) from the Late cretaceous of Brazil. Gondwana Research. Vol.10:370-378.
Paul, G.S., and Christiansen, P. 2000. Forelimb Posture in Neoceratopsian Dinosaurs: Implications for Gait and Locomotion. Paleobiology, 26(3):450-465.
This post took a little longer to get together than I expected. Much like the first installment of this series, I found myself writing more and more. This time, though, rather than bother with breaking the post up into a bunch of smaller sections, I’ve decided to just dump the whole thing online at once.
Don’t worry, I’ve provided lots of pretty pictures to ease the eye strain. 🙂
While an in-depth look at Tianyulong confiusci‘s filaments (or as in-depth as one can get with just photos), has left me with doubts regarding their validity, one question still lingers.
If the filaments do prove to be genuine epidermal structures, then what does this mean for dinosaurs in general?
When this little ornithischian was announced, many in the paleo community (in particular the paleo-art community) seem to have used this little guy as a license to draw feathers on pretty much any dinosaur. After all, if protofeathers are found in ornithischians and saurischians, then it seems likely that they were a basal trait for dinosaurs in general. Some have even argued that the filaments alleged for Tianyulong, along with the protofeathers of maniraptorans, and the “fur” in pterosaurs, are all homologous structures; thus making a “furry” covering a primitive (plesiomorphic) trait for all of Dinosauria.
This is where we really need to start putting the brakes on. One only needs to do a cursory examination of any archosaur cladogram to see that there is a problem with this argument.
Though it is all too often forgotten, we have found the skin impressions from practically every major dinosaur group known to science. You know what these impressions show?
Scales
In practically every case, “skin” impressions from dinosaurs show them to have been scaly. Impressions from hadrosaurs (Sternberg, 1909, Anderson et al 1999), ceratopians (Brown 1917, Sternberg 1925), stegosaurs (Xing et al 2008, and photo on the left), ankylosaurs (Parks, 1924), sauropods – including embryos (Coria and Chiappe 2007), and most theropods (Abelisaurs [Czerkas & Czerkas 1997], Allosaurs [Pinegar et al 2003] and Tyrannosaurs [Currie et al 2003]) have all shown the presence of hexagonal, or tuberculate scales. Dinosaurs were a decidedly scaly bunch. (Proto)feathers were the exception, not the rule.
A common counter-argument to this has been that protofeathers could have been lost as animals got larger, or that protofeathers were an ontogenetic thing, with fuzzy babies going bald as they reached adulthood.
The essential problem with this argument is that scales are not equivalent to naked skin.
Scales, like hair and feathers, are a form of integument. Though they form as an infolding of the epidermis, they nonetheless lie on top of it. There are certain mutations in reptiles that will produce scaleless mutants (e.g. “silkback” dragons). These mutants retain their epidermis (which often looks very loose). The epidermis can also be clearly viewed between the scales of snakes while they are swallowing a large prey item. If dinosaurs really did lose protofeathers as they got larger, then one would expect to see patches of naked skin in between patchy feathers (much like what we see in extant pachyderms), but that’s not what we are seeing.
“Silkback dragons.” A new breed of bearded dragon that lacks scales. Photo from the Bearded Dragons and Other Creatures website. Click the photo for more information.
It is often pointed out that birds have both scales and feathers, thus making it possible for scales to occur in conjunction with feathers on dinosaurs.
However, this generalizes the relationship between scales and feathers. The fact is scales in birds do not occur because of an absence of feathers, but rather from active suppression of feather formation (Sawyer and Knapp, 2003). If one has ever plucked a chicken one might notice a distinct lack of scales on the most of the body. Despite the fact that feathers form along tracts in the skin, the areas between these tracts remain bare. Ostriches (Struthio camelus) provide another prime example of this.
Ostrich pic from: T-Rat’s Dinosaur Pages. Click to visit.
Ostriches are large birds that, like most large animals living in tropical climates, have undergone a fair amount of insulation loss in order to avoid overheating. One need only look at the bare flanks, or neck of an ostrich to see that scales are nowhere to be found on these section. Scales only occur on the tarsometatarsal (ankle and toe) portion of the body. In fact there is a rather sharp demarcation where this occurs. This demarcation agrees well with embryonic studies of diapsids which show how integument formation occurs (Alibardi & Thompson 2001).
Feather ß-keratin proteins are likely homologous with scale ß-keratin. However they are also smaller than scale proteins (likely caused by a deletion to the scale ß- keratin gene [Gregg et al 1984]). Taken together all of this suggests an antagonistic relationship between scales and feathers. One that would determine integument placement based off of where one protein cascade ends, and another one begins.
To put it another way, the chances of a scaly dinosaur with a feathery mohawk, are extremely unlikely.
The ontogenetic argument seems even less likely, as it posits that dinosaurs lost one type of integument as hatchlings and then grew a completely different type as they reached adulthood. This would make dinosaurs unique among vertebrates in doing that.
To summarize then, scaly dinosaurs were not “naked” like elephants and rhinos. If we are to believe that a dinosaur group lost protofeathers as it evolved to be larger, then we must also assume that group then re-evolved scales in its place.
It is at this point where a cladogram comes in handy.
The following are three cladograms showing the possible evolution of filamentous integument in archosaurs. Each terminal group is one that we know the integument for (though not the exact member who’s picture I used). I’ve simplified things a bit with the coelurosaurs due to the nebulous nature of both Sinosauropteryx prima and the putative tyrannosauroid Dilong paradoxus. This should have little effect on the results as all these guys would do is add even more steps to the following situations. The general outcome remains unchanged.
The following are a few hypotheses that have been proposed over the last month for dinosaur integument evolution.
Hypothesis 1: The filaments seen in Tianyulong, Psittacosaurus, maniraptors, and pterosaurs are all homologous structures, thus making protofeathers the plesiomorphic trait for all of Dinosauria.
If these filaments are homologous. Blue dots indicate where filaments would have been lost, and scales would have re-evolved. Click picture to enlarge.
Take a look at our first cladogram. The blue dots indicate cases where a trait was lost, or reversed. In order for our first hypothesis to be true, then protofeathers would have to have been lost a total of 7 times! Also keep in mind what I mentioned previously. We are not just talking about protofeather loss, but also scale re-acquisition. That would also have to have occurred 7 times; making for a whopping 14 evolutionary steps!
Hypothesis 2: The filaments seen in Tianyulong, Psittacosaurus, maniraptors, and pterosaurs are merely analogous to each other. They represent yet another case of convergent evolution.
If filaments are convergent. Red dots indicate areas where filaments would have evolved independently. Click to enlarge.
As the second cladogram shows; if this position is true, then protofeathers would have evolved a total of 4 different times. Once in the theropod line, once in pterosaurs, and twice in Ornithischians. That’s still a lot, but not nearly as many as in our first case.
Hypothesis 3: Protofeathers were the plesiomorphic trait for ornithodirans (pterosaurs and dinosaurs), but were lost at the base of Dinosauria, and subsequently reacquired by various dinosaur groups over time.
If filaments were ancestral, but were lost early on and then reacquired. Click image to enlarge.
As one can see from cladogram 3 there, this situation results in a messy outcome. We see a single re-evolution in theropods, while Ornithischians show a helter-skelter pattern of filament reacquisition, and subsequent loss. The result is 1 case of evolution, 4 cases of filament loss as well as 4 cases of scale reversal, and 2 cases of filament re-evolution; making for a grand total of 11 steps.
Technically one could make the 3rd cladogram a bit different by having filamentous integument evolve twice within Ornithischia. This reduces the steps needed to 6, and makes for a cladogram very similar to cladogram 2.
A general rule of thumb for systematic paleontology, is to assume that evolution takes the least amount of steps possible (we assume Nature is generally lazy that way). As such, the evolutionary situation that produces the fewest “steps” is assumed to be the most likely situation. Nature doesn’t have to flow that way. There are cases out there where evolution might take a more complicated road, but in general this assumption that the simplest explanation is the most likely, tends to hold up.
So what does that say about our current situation?
Assuming that filamentous integument occurred a few times in ornithodiran evolution, results in a cladogram with substantially fewer steps (4). As such, it appears the most likely, or most parsimonious case.
Protofeathery integument could still be basal to Dinosaurs, and all those necessary reversals could still have occurred, but the road getting there seems unnecessarily complicated, and thus rather unlikely.
As it stands right now, it appears that if the filaments on Psittacosaurus and Tianyulong did belong to their respective owners, then they are a case of convergent evolution. Though generally frowned upon in systematics (mostly because it is a pain in the ass for phylogenetics), convergence is a rather common feature of evolution. For instance, in squamates alone the evolution of live birth has occurred a conservative 100 times (Shine 2005)!
So yeah, convergence happens; even for seemingly complicated things. That the filaments in these ornithischians, bear almost zero similarity to those of Sinosauropteryx and kin, further supports the hypothesis that they are an independent case of evolution.
There is another alternative that seems to rarely get mentioned. It is possibile that these filaments are actually scale derivatives. This would not be that surprising. Scales produce a wide variety of different ornamental structures in extant reptiles (from strange nose protuberances in certain iguanians, to flashy frills in agamids, and soft velvety skin in some geckos). In fact, the presence of the Psittacosaurus “quills” alongside scales, suggest that they are more likely to be a scaly derivative, than a feathery one.
Gonocephalus grandis, Rhacodactylus ciliatus, and Atheris hispida. Just some examples of scale diversity in extant reptiles.
What of the other major implication for basal “fuzz” in dinosaurs. Does this clinch the “dinosaurs were warm-blooded” argument?
Despite the wishes of some of the more vocal dino enthusiasts on the internet, this does not signal the death knell for bradymetabolic dinosaurs.
Both mammals and birds have an insulatory coat. From what we can gather, the role (or one of the roles) of this coat is to keep body temperature fairly constant. Therefore it is tempting to look at both feathery birds and fuzzy mammals and assume that a high metabolic rate (or automatic endothermy) must be associated with insulation.
However mammals and birds only represent two instances of insulation. As any statistician will tell you, two points make a line, not a pattern. What would help would be if there was at least one other group of critters that had insulation.
Well, it turns out that there are: Arthropods.
From the “woolly crustaceans” of the deep ocean, to bees and tarantulas, “hair” is fairly common among arthropods. This hair (deemed: setae) has a different embryological origin from mammalian hair, so it cannot be considered homologous.
So there is a third outgroup that shows filamentous coverings. Is it also associated with a constant body temperature and automatic endothermy?
Well no.
In many species, the setae appear to function primarily as touch sensors; whether it be for the legs of a fly, or the body of a orb weaving spider. Still there are a few (moths, bees, certain beetles), that do use their hair for insulation. These animals are “functional endotherms.” That is to say that they use muscular power to generate heat internally. The difference between them and the classic “warm-blooded” mammals and birds, is that heat is generated solely by “skeletal” muscle, and can be turned off.
That insulation should not automatically equal “warm-bloodedness” has been recognized before. Previous authors (Schmidt-Nielson 1975, Withers 1992) have pointed out that while insulation does seem to lead to homeothermy, it does not associate so well with a high metabolism.
So then could we say that Tianyulong and the “feathered” theropods were using their insulation to maintain a stable body temperature.
Maybe not.
If one is to use filaments for insulation, then they need to be spaced close enough that they will trap a layer of air between them and the skin. In mammals and birds this results in a notably fuzzy coat. Yet, sometimes this look can be deceiving. Consider polar bears. Despite their hairy look, polar bear fur offers very little insulatory benefits (Lavers 2000). The main use for the fur, seems to be to hide the black, sun absorbing skin underneath. Polar bears stay warm by maintaining a large layer of fat between their skin and the body core. The wide spacing of the hairs also allows them to quickly drain water from the body when the bears emerge from their icy swims (where insulation benefits of fur equal exactly zero). So if one is going to keep warm by being fuzzy, then that fuzz better be pretty thick.
For the protofeathered/feathered maniraptorans, the fuzz count appears high enough to allow for functional (possibly passive) homeothermy. This is not the case with Tianyulong. The filaments in T.confiusci are spaced too far apart to allow for much in the way of heat retention. These filaments must have been used for something else. Possibly as a means of defense by keeping attention focused on the tail, or (if backed by erector muscles) by making the animal look substantially bigger and more intimidating to a potential predator. They may have been used in a more passive sense by conferring camouflage to their owner. All are possible alternative uses for these filaments (ignoring, for now, the likelihood of these filaments being used for multiple purposes).
Besides all that, the Mesozoic is well known for being a time of high global temperatures. This doesn’t lend well to the assumption that filaments were evolved to keep their owners warm.
Now if they evolved to help keep heat out…
~ Jura
References
Anderson, B.G., Barrick, R.E., Droser, M.L., Stadtman, K.L. 1999. Hadrosaur Skin Impressions fom the Upper Cretaceous Neslen Formation, Book Cliffs, Utah: Morphology and Paleoenvironmental Context. Vertebrate Paleontology in Utah. David Gillette (ed). Utah Geo Survery. ISBN: 1557916349, 9781557916341 pps: 295-302.
Alibardi, L. and Thompson, M. 2001. Fine Structure of the Developing Epidermis in the Embryo of the American Alligator (Alligator mississippiensis, Crocodilia, Reptilia). J. Anat. Vol.198:265-282.
Brown, B. 1917. A Complete Skeleton of the Horned Dinosaur Monoclonius and Description of a Second Skeleton Showing Skin Impressions. Bul AMNH. Vol.37(10):281-306.
Coria, R.A. and Chiappe, L.M. 2007. Embryonic skin from Late Cretaceous Sauropods (Dinosauria) of Auca Mahuevo, Patagonia, Argentina. J. Paleo. Vol.81(6):1528-1532.
Currie, P.J., Badamgarav, D., Koppelhu, E.B. 2003. The First Late Cretaceous Footprints from the Nemegt Locality in the Gobi of Mongolia. Ichnos. Vol.10:1-12.
Czerkas, S. A., and S. J. Czerkas. 1997. The integument and life restoration of Carnotaurus. In D. L. Wolberg and G. D. Rosenberg (eds.), Dinofest International, Proceedings of the Symposium at Arizona State University, pp. 155?158. Philadelphia Academy of Natural Sciences, Philadelphia.
Gregg, K., Wilton, S.D., Parry, D.A., and Rogers, G.E. 1984. A Comparison of Genomic Coding Sequences for Feather and Scale Keratins: Structural and Evolutionary Implications. Embo J. Vol.3(1): 175-178.
Lavers, C. 2000. Why Elephants Have Big Ears: Understanding Pattersn of Life on Earth. St. Martins Press. NY. ISBN: 0312269022. pg 104.
Parks, WA. (1924). Dyoplosaurus acutosquameus, a new genus and species of armoured dinosaur; and notes on a skeleton of Prosaurolophus maximus. University of Toronto Studies, Geological Series 18, pp. 1-35
Pinegar, R.T., Loewen, M.A., Cloward, K.C., Hunter, R.J., Weege, C.J. 2003. A Juvenile Allosaur with Preserved Integument from the Basal Morrison Formation of Central Wyoming. JVP. vol.23(3):87A-88A.
Sawyer, R.H. and Knapp, L.W. 2003. Avian skin Development and the Evolutionary Origins of Feathers. J. Exp. Zool. (Mol Dev Evol). Vol.298B:57-72.
Schmidt-Nielson, K. 1975. Animal Physiology Adaptation and Environment. Cambridge University Press. Cambridge. ISBN: 0521570980, 978-0521570985. pg 669.
Shine, R., 2005. Life-History Evolution in Reptiles. Annu. Rev. Ecol. Evol. Syst. Vol.36:23-46.
Sternberg, C.H., 1909, A new Trachodon from the Laramie beds of Converse County, Wyoming. Science, v. 29, p. 753-754.
Sternberg, CM., 1925, Integument of Chasmosaurus belli: Canadian Field Naturalist, v.39, p. 108-110.
Given all the recent stink over a certain other documentary, I’m not exactly itching to jump back into dino docs.
Oh well.
The Public Broadcasting Service’s long running series NOVA, has a new episode out, entitled Arctic Dinosaurs. The episode is about a particularly exciting find in Alaska, and its implications for our view on dinosaurs. The researchers; namely museum Victoria’s Tom Rich and MNS Dallas’ Anthony Fiorillo, came across a fossil bed along Alaska’s north slope, that revealed the existence of hadrosaurs, ceratopians and coelurosaur theropods, all living in far North Alaska.
As I had mentioned previously, NOVA tends to get lauded for its well put together documentaries. I would argue that this doc was no different; though there were some missteps that I feel may be a sign of NOVA’s producers trying to fall more in line with the fare seen on Discovery Channel and the A&E networks.
Secondly, I would like to lambast PBS for what is probably their most egregious error with this, and other NOVA specials. Namely the lack of Firefox love. The only way I am able to watch these NOVA specials is by firing up Internet Explorer. If I use Firefox all that happens is I get a dead loading screen.
The premise of the series is fine, and as in previous iterations, NOVA has done a good job of letting the scientists talk how scientists really talk (i.e. with lots of caution and caveats).
I was far less impressed with the writing for the narrator. There were more than a few instances where the narrator resorted to straight up hyperbole. Especially in the beginning when it is revealed that all these dinosaur fossils had been found in this polar state.
The narrator said:
The startling discovery that these ancient reptiles, “thunder lizards,” lived and thrived in the arctic has taken scientists by surprise.
Then a little later:
According to conventional wisdom, it shouldn’t be here, because this is how dinosaurs are typically pictured: cold-blooded reptiles living in tropical climes, not in cold, arctic environments like this one. And the Hadrosaur is not alone.
Um, no. We have had discoveries of dinosaurs, and other reptiles from polar and paleo-polar latitudes, for decades now. The real neat thing about this find, was the sheer number of animals discovered. This doc served more as a review of what we have learned so far, rather than a breaking news story.
There was another writing snafu that occurred a little further in too that I feel needs clarifying:
Scientists long believed that dinosaur biology resembled that of cold-blooded reptiles like crocodiles, animals that require warmth to survive and cannot withstand prolonged exposure to temperatures below freezing. But not one crocodile fossil has been found along the Colville, which suggests that polar dinosaurs found a way to adapt to an environment that their cold-blooded cousins couldn’t tolerate. But how?
This statement is misleading. We do have evidence of non-dinosaurian polar reptiles. These include Cretaceous crocodylian and turtle fossils found in Victoria, Australia (which would have been closer to the South Pole) and Axel Heiberg Island in Canada, as well as plesiosaur fossils from Antarctica, and at least the assumption that Meiolaniid turtles (large, ankylosaur like armoured turtles that lived from the late Cretaceous through to the Pleistocene) had once lived in Antarctica.
Oh, and also Leaellynasaura amicagraphica was a herbivore; not a carnivore as was stated in the show.
So there were those few writing missteps. The only other thing I can fault the show for was its very lackluster CG work. As NOVA is a mostly public funded series, I can forgive the lower quality CG work, though I still think they could have afforded to make their models at least a tad more realistic (especially since they teased feathers on Dromaeosaurus albertensis before returning to scaly maniraptors (i.e. the Troodon formosus). Plus their Gorgosaurus libratus was just atrocious.
Regardless, most of these complaints are small. The writing flubs were probably the worst offenders. Short of that, the show was well put together. Though the show still fell a little more in the pro-warm-blooded camp for dino metabolism, it was the first and only time I have ever heard a documentary point out that warm-blooded and cold-blooded are opposite ends of a continuum. In fact one of the better writing moments occurred towards the end when the narrator stated:
Dinosaurs likely had their own unique solution to the body temperature problem, which allowed them to survive for millions of years in the toughest seasonal conditions their world had to offer.
It was nice to see a documentary that actually took a more objective stance on the whole thermophysiological debate.
Finally another big plus for this show was the sheer number of paleontologists that rarely seem to make it in front of the camera, including Hans-Dieter Sues and Anusuya Chinsamy-Turan (the latter of whom while being a great scientist, has one of the harder to pronounce names in paleontology).
Overall, this was another fine piece of work from the folks over at NOVA. Though there was a tendency to stray into the realm of hyperbole with the narration, and the CG work is somewhat painful to watch, the show proved informative and interesting.
In the end, that’s really all a documentary should strive for.
Okay, I know all I am doing is fueling the perpetuation of this kind of crap on TV.
That said, I was bored, and one of the few cool things about The History Channel is that it allows folks to watch their shows online.
The latest one was called: Bloodiest Battle; the story of the Cleveland Lloyd Quarry.
Well, the JFC version of what happens.
Anyway, there were, as usual, a host of annoying offenses in the show. Besides the ever annoying “loud dinosaurs” (i.e. all the dinosaurs couldn’t stop roaring), there was also the requisite rampant speculation on the social life of Allosaurus, the ecological relationship between Allosaurus and Ceratosaurus, and various anatomical flubs that continue to send out the message that The History Channel only hires the “talking heads” so they can appear scientifically legitimate.
Anyway, the only reason I am bringing this one up is because the most egregious error in the entire program (in my mind, at least) was the absolute statement from “Dinosaur George” Blasing that “all the evidence points to these animals being warm-blooded.”
That is bull-shit with a capital B.
Er…Bull-Shit.
There is no, I reiterate NO consensus on the thermophysiology of dinosaurs. That is true for all dinosaurs. All the evidence used so far has been ambiguous at best.
Furthermore, a “cold-blooded”Allosaurus is going to have the same overheating problem as a “warm-blooded” Allosaurus.
The problem has nothing to do with thermophysiology. It has to do with big animals over-exerting themselves in a hot environment. Dinosaurs were reptiles, and like all reptiles, they had a very limited means of removing heat. No sweat glands, and no real bare skin.
One thing that Allosaurus and other saurischian dinosaurs may have used to keep cool is their air sac system. Air sacs in birds do not lead to their high aerobic capacity. That is accomplished through the flow through system that the air sacs created, where oxygen is sent only one way (vs. the dead end bellows way that mammals and reptiles use). The perfusion of extra air sacs all over the body does nothing to add to endurance in birds. What it does do, though, is lighten the body and provide a spot for heat to dump from deep in the body. It is honestly quite likely that this is was the main impetus for air sac evolution in dinosaurs, and its consequent exploitation by their avian descendants.
This explanation would certainly have been a more scientific answer to how Allosaurus kept cool instead of pulling that antorbital fenestra radiator idea out of wherever “Dinosaur George” found it.
I don’t like absolutism in science programs anyway, but this type of absolutism is what lead to the general public thinking, erroneously, that scientists have discovered dinosaurs to have been warm-blooded. All this winds up doing is creating a false concept of dinosaurs that winds up getting shot down when new students enter the field and find that dinosaurs weren’t the super hot-blooded beasts they thought they were.
Plus, it’s just annoying when some fanboy says that being “warm-blooded” is one of the fundamental differences between dinosaurs and other reptiles.
Okay, I’m done venting.
Next episode involves some mythical beast called a “megalodon” (they must mean Carcharocles/Carcharodon megalodon). I hear that, at 15 meters (50ft) in length, it was the size of a jumbo jet and had to eat a tonne of meat a day to keep going.
Yeah, definitely sounds like something worth missing!
A few weeks ago the History Channel aired their first in a twelve part series on prehistoric creatures.
Now, being the History Channel – a subsidiary of Discovery ChannelA&E Networks – one would expect this series to detail some aspect of prehistoric life. Well that it does…sort of.
The series is called: Jurassic Fight Club. Many of you have probably already watched the first three, or four episodes, but for the uninitiated the premise is as follows:
Imagine all 4.6 billion years of prehistory as being one planet wide cage match somewhat akin to Primal Rage. Each week two animals (usually dinosaurs, but there are the occasional mammals) are pitted against one another.
Each hour long show is supposedly based off of a real fossil site. For instance the first episode was about a Majungasaurus skeleton that was found with bite marks of another Majungasaurus (erroneously referred to as “Majungatholus” despite paleo-consultant disapproval). One of the recent ones involved the infamous Tenontosaurus tilletti / Deinonychus antirrhopus fossils (a find with one large, dead T.tilletti and a few dead D.antirrhopus nearby. One of the first bits of evidence in favour of pack hunting behaviour in some theropods).
The show sets the “battle premise” and then seeks to justify its reasoning by cutting to various paleontologists for their take. The paleo crew is fairly diverse and include: Dr. Thomas Holtz Jr.Dr. Larry Witmer and Dr. Phillip J. Currie.
Okay, so maybe all that doesn’t sound so bad to some of you, but what may seem okay in theory has turned into an utter failure in execution.
Let me state up front that I immediately left this series for suck back when I first heard the title. It sounded like just another useless “documentary” that is little more than an excuse to watch two CG animals fight each other in order to satisfy some sophomoric need to watch things fight.
Still, there were proponents of the series (namely the paleo folks that worked on it) that urged the most skeptical of us to give the show a shot. As such, I refrained from commenting on it until now.
Four episodes in and now even the scientists who helped on it are starting to back away.
Honestly who could blame them. The show uses minimal information from the actual scientists. The shot of Dr. Witmer comparing theropod maxillae is continuously reused, and I could swear the show spends more time on the non-professional guys than they do the actual scientists.
This is a problem because it is the non-professional crowd (one fellow in particular) who really bring the show down.
The show features the likeness of one Dinosaur George Blasing. A quick perusal of his qualifications finds him to be little more than a particularly successful dinosaur fanboy. He apparently makes his living by talking about how cool dinosaurs are, to elementary school children. In effect, he is little different from Dinosaur Don Lessem, who writes books about dinosaurs for children.
Now don’t get me wrong. There’s nothing wrong with being an amateur, or a big, but non-professional, dinosaur fan. The problem I have is with History Channel essentially letting the fanboys run the show. This is supposed to be an educational program. History Channel is supposed to be the repository for all things historical. As such, it should be held to a higher standard than, say ABC, or Fox. Yet, here we get to witness the production of another terrible program that only seeks to snatch eyeballs. It offers practically no educational value.
Frankly that just ticks me off. Jurassic Fight Club is about as terrible as Animal Face Off was (another Discovery Channel property that not only embarrassed the subject matter, but also the scientists involved with it, by forcing them to give trash talk to one another).
The question that shows like JFC leave me asking is: what audience is it meant for? By seeking out professional paleontologists for their input, one would assume that the makers were looking for scientific accuracy. This, in turn, suggests that the goal is to pass knowledge on to their viewers. Yet, if one can slog through the first episode they will find themselves assaulted with absolutes left and right, tonnes of MTV style quick takes and replays, and a metric tonne of speculation. Each episode ends with Dinosaur George giving “his take” on how the whole story unfolded (complete with the CG animation). Now this sounds like nothing more than Godzilla style popcorn entertainment.
So which is it? Is JFC trying to be a documentary, or a popcorn flick?
By trying to do double duty, it comes off as more of mockumentary. A documentary that seeks to mock the subject material in which it presents. When done right, mockumentaries can be great (e.g. This is Spinal Tap), but in cases like this, where the parody does not appear intentional, the result is more of a slap in the face to those of us who do work in the field. To ask for professional advice and then completely ignore it, is a huge insult to both professions. The History Channel people should know better.
One question that is left from all this is: must we sacrifice scientific accuracy for entertainment, in order to get the knowledge across to the viewers?
As one person had mentioned on another forum: if scientists were to get the documentary that they wanted, no one would watch it.
Pardon me if I decide to call bullshit on this one. If one wants to see a documentary that is designed in a way respectful of the subject matter, one need only look at PBS’s NOVA series. Rarely does NOVA falter in their presentation style. Because of this consistent high quality the series tends to be lauded by many in the fields of science.
Okay, so maybe NOVA is a fluke. Besides, it’s on PBS and we all know how small and concentrated the PBS demographic tends to be. Are there any other examples?
Plenty.
David Attenborough – King of great documentaries
If one really wants to see how to make a series of successful and scientifically sound documentaries, one need only to look over to the UK, and the BBC. In the realm of documentaries, the David Attenborough docs reside in the upper echelon of quality. Not only are Attenborough’s documentaries well done, and accurate, but they are also popular. Planet Earth, one of the latest Attenborough docs, was the most watched cable show of all time. Discovery Channel pulled in 100 million viewers when it first aired in the United States. That is huge for a major network, much less a cable network (Discovery’s average prime time ratings are around 5 million viewers).
So not only does a scientifically sound documentary bring in the audience, but it can bring them in droves. When BBC released “Life in Cold Blood,” it was an event in England, bringing in more viewers that the average drama.
If we head back to the states, we can look at an old staple of children growing up in the 1990s; Bill Nye the Science Guy was a show that garnered a large and devoted fan following. Bill Nye was not only a great presenter and funny comedian, but he was/is also a real scientist. Though the show did its best to avoid using large words (for its young demographic), the show repeatedly and successfully showed off how awesome science was and how amazing the real world is.
Bill Nye – Champion of science education
You know why I think these shows did as well as they did? Because they didn’t dumb stuff down. There was no push to show the flashy stuff in order to maintain audience attention (equivalent to showing something shiny to distract a cat). The BBC documentaries, Bill Nye and NOVA all respected the intelligence of their audience, and the audience reciprocated by showing up in droves. People from all walks of life enjoy a good challenge. Today’s current documentarians would benefit from remembering this.
So for all those scientists who are asked to participate in the next big Sci Fi/Discovery Channel/ABC show/ whatever documentary; I say don’t fear speaking your mind on the importance of keeping the science up to snuff. If the filmmakers start bitching about having to “keep things simple” or removing the science for the sake of “the story,” just tell them:
That’s not how David Attenborough would do it.
~ Jura – who will probably never get a consulting job on one of these shows.
Actually, I’ve never thought that sauropods were grey. Mammals in general tend to be rather bland in their colour schemes. Reptiles don’t have that problem. With xanthaphores (yellow pigmented cells), erythrophores (red pigmented cells) iridophores (iridescent cells) and melanophores (dark pigmented cells), the range of colour available to reptiles, and by extension – dinosaurs, is quite vast.
That said, I always pictured sauropods as either a brownish green colour, or maybe a very pale blue (blue is generally rare in tetrapods, hence the thought of it being a weak blue).
But I digress.
I grew up during an interesting time for dinosaur research. Unlike the majority of paleontologists working right now I didn’t grow up learning about dinosaurs being slow and sluggish mistakes of nature. I also didn’t grow up with the “hummingbirds on crack” version of dinosaurs that is currently pervading popular culture. Rather, I grew up during that strange transitory phase of the Dinosaur Renaissance where dinosaurs were sometimes viewed as sluggish beasts and other times as racecars of the Mesozoic.
The result, I think, has been a slightly detached and objective look at how perceptions of dinosaurs have changed over time.
A “Brontosaurus” getting attacked by Allosaurus during a sojourn on land to lay her eggs. Ah, the classics.
One book I remember fondly was the Golden Book of Dinosaurs (shown above). It featured these beautiful drawings of dinosaurs living life as best we thought at the time. One picture that really stuck in my head, was a shot of two Brachiosaurus; one on land and the other so deep in a lake that one could only make out the crest on the head. I found that page to be so immersive and atmospheric. My knowledge of physics was not so good at the time, so it never dawned on me that this poor sauropod was basically breathing through a straw with its lungs separated by at least 2 atmospheres from the air entering (as best it could) the nostrils.
Then around the early nineties when Jurassic Park the book came out I started to note a distinct change in how dinosaurs were being portrayed. No longer were sauropods swamp bound behemoths. Now they were fully terrestrial titans that could not only support their weight on all four legs, but could even do so on 2 (well 3 if one counts the tail). It was around this time that Robert Bakker’s infamous “Dinosaur Heresies” started making the rounds.
Now, admittedly, Heresies came out in 1986 and the changing view of dinosaurs actually started in the seventies. However, it wasn’t until the early nineties that the full effects of Bakker’s work could truly be appreciated. If anything this gives one an idea of the kind of inertia one must deal when it comes to getting scientific ideas out into the public.
Again I digress.
It was around the early nineties when I first read The Dinosaur Heresies. The first few chapters were amazing. I had never seen dinosaurs portrayed this way. They walked better and were more active. In many ways they better fit the concept I had in my head all along.
Then I came up to the end of chapter 3. The thesis of this chapter was to explain why reptiles should not be viewed as inferior to mammals. In order to do so Bakker explained all the various ways in which extant reptiles outshine extant mammals. The end of the chapter features a beautifully drawn shot of the “panzer croc” Pristichampsus snatching a Hyracotherium (formerly Eohippus). The caption read:
Pristichampsus hunted during the Eocene Epoch, about 49 million years ago, but it was very rare, much rarer than big mammalian predators, proof that cold-bloodedness was a great disadvantage.
Predatory Dinosaurs of the World. Available on Amazon
That’s when the real thesis of the book hit me. The argument wasn’t: “Dinosaurs weren’t slow and stupid, because of the following.”
Rather the argument was: “Dinosaurs weren’t cold-blooded because the facts show the following.”
In order to pull dinosaurs out of the mire, Bakker had to change their fundamental thermophysiology. The general concept, that cold-bloodedness is inferior to warm-bloodedness, remained the same. This despite Bakker’s initial attempt to explain how “cold-blooded” reptiles outshine “warm-blooded” mammals.
Bakker’s book was just the start. From there, we had Adrian Desmond’s “The Hot Blooded Dinosaurs” (okay, technically Desmond was first by 7 years, but he largely stole Bakker’s work to make the book so it evens out) and Gregory S. Paul’s infamous: “Predatory Dinosaurs of the World.” Each new book taking the “dinosaurs can’t be cold-blooded” argument a little further. By the time we hit Predatory Dinosaurs of the World, Tyrannosaurus rex was running along at 40mph, dromaeosaurs were practically flapping around and every species of dinosaur was reaching adult size by between 4-10 years of age.
Sadly it was at this point that Jurassic Park was written. As hardcore fans know it was Greg Paul’s erroneous sinking of Deinonychus antirrhopus into Velociraptor that gave us the JP “raptors.” It was also at this point that the pendulum of dinosaur physiology officially swung the other way.
The thing that had always bugged me about this view of dinosaurs was the sheer lack of supporting data for it. The assumption was always that dinosaurs were so vastly different from “typical reptiles” that they had to have been doing something different. Yet when one looked at the actual data dinosaurs came out looking slightly odd at best. For the most part dinosaurs fit the reptile mold quite well. It was these elusive “classic reptiles” that didn’t appear to exist.
Most reptiles don’t fit the “typical reptile” mold at all. Yet despite numerous papers over the past 30 years depicting reptiles doing things normally thought un-reptile like (e.g. caring for their young, competing with large mammals, etc), most of this was dutifully ignored in favour of an older, more outdated view.
It was a problem that Neil Greenberg (1980) aptly called: The “endothermocentric fallacy.” Basically, the assumption that being an endotherm is inherently superior to being an ectotherm. Part of that superiority included the ability of endotherms to do everything faster and “better” than similar sized ectotherms. This problems with this way of thinking warrants an entire blog post to itself. So rather than get bogged down with this particular I’ll touch more on the endothermocentric fallacy at a later date. For now all that one needs to keep in mind is that the thinking of the time was that if dinosaurs were going to be active at all then they had to be endotherms.
By the late nineties we had the first evidence of feathers in a small branch of the theropods (Maniraptora). Birds were officially adopted into the dinosaur family tree and the fully endothermic concept of Dinosauria was completely entrenched.
The funny thing, of course, is that this dogmatic view of dinosaur metabolism was just as bad as the early 20th century’s “cold-blooded” swamp bound view. Sure dinosaurs were more active now, but the data supporting it was just as nebulous as the stuff that was used to keep dinos in the swamp.
Enter the 21st century, and the late…um, 0’s (does anyone have a name for this decade yet?). Biomechanic work on dinosaurs has started to reveal amazing insights into the physical limits of what dinosaurs could do, and the results have started to pull the pendulum back again.
Work by John Hutchinson and Mariano Garcia (2002) on T. rex showed that not only could T. rex not hit 40mph, but it technically couldn’t run either. A biomechanical assessment of theropod forelimbs by Ken Carpenter (2002) has shown that the “bird-like” dromaeosaurs could not fold their arms up like birds after all.
Work by Rothschild and Molnar (2005) on sauropod stress fractures showed no signs of rearing activity in sauropods, while work by Kent Stevens and J. Michael Parrish (2005) pulled the swan-like curve out of sauropod necks, placing things far more horizontally.
Work by Gregory Erickson and others (2001) on micro-slices of dinosaur bone has indicated that very few dinosaurs hit adult size in less than 15 years.
Now we have a new study by Lehman and Woodward (2008) which follows up on Erickson et al’s work and actually shows that even this toned down version of dinosaur growth is probably too fast as well. Lehman and Woodward focused on sauropods and studies on their bone microstructure. What they did was compare bone growth data to a well used equation for growth in animals.
Deemed the Bertalanffy equation; it states that the mass at any given age is an exponential function limited by the asymptote of adult body mass. This equation has been used extensively in studies on bird and elephant growth among others. An example of the equation is given to the right for fish.
When the authors did this they discovered something quite interesting. Instead of taking 15 years to reach adult mass, sauropods like Apatosaurus excelsus took closer to 70 years!!
Other sauropods measured took between 40 and 80 years! This is a substantial decrease in growth rate estimated before. Mind you this is data taken, in some cases, from the same piece of bone that Erickson et al had used. So one can’t suggest anomalous bones being used as the reason behind the surprising results. The authors also went to great lengths to take into account differences in mass estimations as well as allometric growth of body parts. In each case the changes had little affect on the overall outcome (in many cases, it made growth go even slower).
Now keep in mind we are talking about the time it took sauropods to reach full adult size. This is not the time taken to reach sexual maturity. Earlier studies by Erickson et al (2007) had already discovered that dinosaurs didn’t wait to grow up before engaging in sex, so there is no issue here of 80 year old sauropods finally “doing the nasty.”
What this does show is that growth in dinosaurs might not be as determinate as initially thought. An 80 year old sauropod might just have been close to the edge of its lifespan at this point (though the possibility of bicentennial sauropods does still exist). It also shows that dinosaurs had growth rates far closer to the realm of reality (before it was hard to imagine how an Apatosaurus excelsus was able to pound down enough food daily to add 13.6 kg of new mass a day. Especially given their small mouths).
Thermophysiologically what does this all mean? Were dinosaurs “cold-blooded” after all?
That’s one of those questions that will never be fully answered (short of a time machine). What this does do is pull dinosaurs ever further away from the “definitely warm-blooded” category and push them right back into the middle again. When/if the dust settles on this metabolism debate I suspect that dinosaurs will probably remain in the middle somewhere.
Of course while all of this is going on with dinosaurs we have other studies, like those from Tumarkin-Deratzian (2007) showing the existence of fibrolamellar bone growth in wild alligators, that are finally moving the rusty pendulum of reptile metabolism out of the “classic reptile” category and much closer to the middle.
So in the end dinosaurs will still probably wind up being “good reptiles.” Thankfully the exact definition of what that entails will have probably changed by then.
~ Jura
References
Bakker, R. 1986. The Dinosaur Heresies: New Theories Unlocking the Mystery of the Dinosaurs and their Extinction. William Morrow. New York.
Carpenter, K. 2002. Forelimb Biomechanics of Nonavian Theropod Dinosaurs in Predation. Concepts of Functional Engineering and Constructional Morphology. Vol. 82(1): 59-76.
Desmond, A. 1976. The Hot Blooded Dinosaurs: A Revolution in Paleontology. Dial Press.
Erickson, G.M., Curry Rogers, K., Varricchio, D.J., Norell, M.A., Xu, X. 2007. Growth Patterns in Brooding Dinosaurs Reveals the Timing of Sexual Maturity in Non-Avian Dinosaurs and Genesis of the Avian Condition. Biology Letters Published Online. doi: 10.1098/rsbl.2007.0254
Erickson, G.M., K. C. Rogers, and S.A. Yerby. 2001. Dinosaurian Growth Patterns and Rapid Avian Growth Rates. Nature 412: 429?433.
Greenberg, N., III. 1980. “Physiological and Behavioral Thermoregulation in Living Reptiles” in: A Cold Look at the Warm-Blooded Dinosaurs (R.D.K. Thomas and E.C. Olson Eds.), pp. 141-166, AAAS, Washington, DC
Hutchinson, J.R., Garcia, M. 2002. Tyrannosaurus was not a fast runner. Nature 415: 1018-1021.
Lehman, T.M., and Woodward, H.N. 2008. Modeling Growth Rates for Sauropod Dinosaurs. Paleobiology. Vol. 34(2): 264-281.
Rothschild, B.M., and Molnar, R.E. 2005. Sauropod Stress Fractures as Clues to Activity. In Thunder Lizards: The Sauropodomorph Dinosaurs. (Virginia Tidwell and Kenneth Carpenter eds). Indiana University Press. pp 381-394.
Stevens, K.A., and Parrish, J.M. 2005. neck Posture, Dentition, and Feeding Strategies in Jurassic Sauropod Dinosaurs. In In Thunder Lizards: The Sauropodomorph Dinosaurs. (Virginia Tidwell and Kenneth Carpenter eds). Indiana University Press. pp 212-232.
Tumarkin-Deratzian, A.R. 2007. Fibrolamellar bone in adult Alligator mississippiensis. Journal of Herpetology. Vol. 41. No.2:341-345.
As human beings this might come off as somewhat of a “duh” question.
“To free our hands up, of course.”
Ah, but like most things in life, the common sense answer is not the right one.
Consider all the bipedal animals alive today. We have humans, obviously; kangaroos, birds, a few lemurs, and a whole swath of lizards. Of these, the “free up the forelimbs” argument really only holds true for humans, lemurs and birds. What of kangaroos and all those lizards? Exactly what does one benefit from when going bipedal?
Do you go faster, run longer, or gain a better vantage point?
C.kingii during a typical foraging run.
All these questions were asked, and somewhat answered in a recent paper by Clemente et al.
Bipedal locomotion by lizards has previously been considered to provide a locomotory advantage. We examined this premise for a group of quadrupedal Australian agamid lizards, which vary in the extent to which they will become bipedal. The percentage of strides that each species ran bipedally, recorded using high speed video cameras, was positively related to body size and the proximity of the body centre of mass to the hip, and negatively related to running endurance. Speed was not higher for bipedal strides, compared with quadrupedal strides, in any of the four species, but acceleration during bipedal strides was significantly higher in three of four species. Furthermore, a distinct threshold between quadrupedal and bipedal strides, was more evident for acceleration than speed, with a threshold in acceleration above which strides became bipedal. We calculated these thresholds using probit analysis, and compared these to the predicted threshold based on the model of Aerts et al. Although there was a general agreement in order, the acceleration thresholds for lizards were often lower than that predicted by the model. We suggest that bipedalism, in Australian agamid lizards, may have evolved as a simple consequence of acceleration, and does not confer any locomotory advantage for increasing speed or endurance. However, both behavioural and threshold data suggest that some lizards actively attempt to run bipedally, implying some unknown advantage to bipedal locomotion.
The conclusions reached, were interesting and quite unexpected.
I’d say the most surprising part would have to be the discovery that both endurance and speed were found to be inconsequential. Those were the two forces that I figured would have driven the push towards bipedalism. Apparently this is not the case.
In fact, the only correlate that the authors found was that a switch to bipedalism resulted in an increase in acceleration. Short of that, the authors viewed bipedalism as more of a side effect of speedy locomotion, rather than anything else.
As one author put it: “The lizards were pulling a wheelie.”
There are some gripes (niggles if you will) with the paper. For one, the authors assert that a switch to bipedalism allowed birds to incorporate their forelimbs into wing design. While being bipedal certainly allowed for this, it could not have been the cause. Birds descended from dinosaurs, and very, very very few dinosaurs had wings. Theropods were sporting freed forelimbs for some 80 million years, or so (probably longer given the proposed ancestors of dinosaurs). Wings were not the cause, simply a benefit. Something else had to have spurred the evolution of bipedality.
Side note: What the heck were theropods doing with those forelimbs anyway? Most paleo artists tend to draw theropods with their arms tucked to the side, yet work by Carpenter (2002) has shown that there was some considerable range of motion in theropod forelimbs. They weren’t brachiating from tree to tree, or anything, but they could certainly do a heckuvalot more than just tuck their arms to the side. Even T.rex with its embarrassingly short forearms, had a surprisingly large range of motion to them. So what’s up paleo art guys? Let’s see some theropods putting their arms to use.
The largest SNAFU in the paper comes from the cladogram that the authors chose. They chose to go with the broken molecular tree used by Townsend et al, which asserts that Iguanians are actually Scleroglossan lizards. This might sit all fine and well when looking at molecules, but it utterly falls apart upon a morphological assessment. In order for Iguanians to fit in the Scleroglossan family tree, they had to have undergone a tonne of morphological reversals, including the re-softening of the tongue and the re-evolution of both postorbital bars (surprisingly, the latter is actually not out of the realm of impossibility as tuataras have apparently done just that).
Due to this tree choice, the authors erroneously concluded that bipedalism evolved only once in the lacertilian tree and was lost a multitude of times, with a putative re-acquirement in varanids.
Another minor complaint comes from the very slight use of Chlamydosaurus kingii; the only lizard known to be a “true” biped (see: Shine & Lambeck 1989). Given that the authors were trying to spot differences between bipeds and quadrupeds, I can understand the use of lizards like Ctenophorus, with their greater spectrum of gaits. However, in doing so they should have qualified their conclusions better in regards to how lizards obtain a bipedal stance. In Chlamydosaurus, bipedal trotting is attained from a standing start. Quadrupedal stance is only seen when stopping to eat. Furthermore, foraging runs and escape runs use two different gaits, with the latter gait more akin to that of other facultatively bipedal lizards. Judging from the stats given in the paper, it seems apparent that the C.kingii used in this study were mostly running away.
Frankly the movies are just too short. I have to go super slow-mo just to see anything. So that’s a bummer.
Overall the paper is rather good. The authors discovered that Lophognathus gilberti runs bipedally 85% of the time. This suggests that C.kingii is not the only truly bipedal lizard out there.
The authors also observed that, despite any advantage in speed, or endurance, some lizards intentionally push their center of mass towards their hips early on in the running phase in order to more quickly obtain a bipedal gait. The reasons behind this are unclear, but do suggest that bipedalism confers some advantage not discovered during this experiment.
One advantage alluded to, but never really elaborated on, was the faster acceleration noted in bipeds. Though maximum speed was no different than in a quadruped, this speed was obtained faster. Ecologically I could see this being very advantageous. When one is trying to avoid a predator, maximum top speed is probably less important than reaching that top speed as fast as possible.
If one lizard has a top speed of 12km/hr and another has a top speed of 8km/hr, and the goal (burrow) is only 50 meters away, then that extra speed isn’t going to mean much. Especially if the slower lizard is able to hit its top speed faster.
Apparently lizards “pull a wheelie” because in their ecosystem it pays to be a drag racer, rather than a Daytona 500 car.
~Jura
References
Carpenter, K. 2002. Forelimb Biomechanics of Nonavian Theropod Dinosaurs in Predation. Concepts of Functional Engineering and Constructional Morphology. Vol. 82(1): 59-76.
Shine, R., & Lambeck, R. 1989. Ecology of Frillneck Lizards, Chlamydosaurus kingii (Agamidae), in Tropical Australia. Aust. Wildl. res. Vol. 16: 491-500.
Townsend T, Larson A, Louis E, Macey JR. 2004. Molecular Phylogenetics of Squamata: The Position of Snakes, Amphisbaenians, and Dibamids, and the Root of the Squamate Tree. Syst Biol. Vol. 53(5):735-57.
Otherwise known as: “The Shielded Devil Frog,” is a recent discovery made in Madagascar, by scientists from University College in London, and Stony Brook University, in New York. This behemoth was about 4.5 kg (~10lbs) in mass, with a length of 40.6 cm (16 inches). It lived during the late Cretaceous, about 70 mya, and appears to be related to the living genus Ceratophrys; more commonly referred to as: Pac Man frogs*.According to researcher David Krause:
“It’s not outside the realm of possibility that Beelzebufo took down lizards and mammals and smaller frogs, and even — considering its size — possibly hatchling dinosaurs,”
I’m sure Dr. Krause either added this bit in for shock value, or because he was being prodded by the journalist interviewing him. It always seems that any creature from the Mesozoic has to always be compared to dinosaurs.
That said, given the relationship of Beelzebufo ampinga to Ceratophrys, I wouldn’t rule dinosaur eating out of the menu either. The living animals are voracious.
~Jura
* Of course, frogs of the genus: Pyxicephalus, are also referred to as Pac Man frogs, which can lead to confusion. One reason why taxonomic names are preferred over common names.
As I strolled along internet looking for something to blog about, the only thing that I could find was a report that was mentioned a few days ago.
As is typical, it features the world’s most popular reptiles: Dinosaurs.
From left to right: “Fierce eyed Dawn Shark” Eocarcharia dinops and “Old hidden face Kryptops palaios
In this case, it is two theropods that were described by paleontological superstar Paul Sereno, and somewhat paleo-newbie Steve Brusatte. For members of the Dinosaur Mailing List, Brusatte is well known for his previous work on the internet, as a paleo-journalist. This description is credit well deserved for Steve. So good on him for that.As for the report, what is there to really say. It’s the discovery of two new theropods. In the world of dinosaur diversity, dinosaurs are usually broken up into 3 categories:
Theropoda
Sauropoda
Ornithischia
In terms of diversity, the previous categories are essentially in reverse order. Easily the most diverse dinosaur group was the Ornithischia. They included “duck billed” hadrosaurs, crested lambeosaur…hadrosaurs, horned ceratopians like Triceratops horridus, armoured stegosaurs and super-armoured ankylosaurs. Two legged hypsilophodonts, and helmeted pachycephalosaurs. Ornithischians were all over the map in terms of diversity.
Next up we have the sauropoda (or to be more inclusive: the sauropodomorpha). On the outset one might think that these guys weren’t really that diverse. I mean if you’ve seen one long necked, long tailed behemoth, then you’ve seen them all right?
Er, no.
Sauropods ranged in size from the super tiny Mussaurus patagonicus*, which topped out at 37cm (15 inches), to titans like Argentinosaurus huinculensis, Sauroposeidon proteles, and Amphicoelias fragillimus; all of which grew to excesses of 39.6m (130ft), and had masses 1,000 times greater, with some estimates as high as 122 metric tonnes!
Besides this humongous size range, we also had sauropods that had sail-backs (Amargasaurus cazaui), sauropods that had tail clubs and armour like ankylosaurs (Shunosaurus lii, Saltasaurus loricatus). We even had sauropods with strange beaks and short necks (Bonitasaura salgadoi, Brachytrachelopan mesai).
Finally we come to the theropoda. All are bipedal carnivores (one possible exception in segnosaurs). They came in two size classes: Frickin huge, and medium sized. Some had long necks (Coelophysis bauri), some had display crests (Dilophosaurus wetherilli, Cryolophosaurus ellioti). Many show reduction in arm size, with Tyrannosaurus rex and Carnotaurus sastrei taking the cake for tiniest arms. There was also one weird group that had sail-backs and crocodile like heads (the spinosaurs). Still, in terms of overall diversity, a theropod was a theropod.
Oh, and one group spawned birds, if you’re into that angle.
It never ceases to amaze me at how often the Dinosaur Mailing list, or dinosaur related websites, devote so much time to theropods. Even news stories seem to put more focus on the big meat eaters rather than the numerous plant eaters. Heck just look at how often we watched theropods fight in the Jurassic Park movies (do you know there was never a scene in the JP movies where a theropod attacked a plant eater?).
One is forced to ask why that is. I believe the answer lies in the ecology alluded to above. Though sauropods and ornithischians were a highly diverse bunch, they were all herbivores. The only carnivorous dinosaurs were theropods.
To elucidate this hypothesis even further, check out this story on Digg.com:
Psychologists at Yale University found that the human brain is biased towards images of animals. We are more likely to notice a change in an image, if that change involves animals. I’m going to take this one step further and say that not only are we biased towards pictures of animals, but that bias is even stronger for predatory animals. Especially predators that are large enough to pose a threat to ourselves (e.g. lions, tigers, crocodiles, large sharks, and of course: big theropods).
So there you have it. Theropods might be the plane Jane group of the Dinosauria, but they will always hog the spotlight. Evolution would have it no other way.
~Jura
*Technically M.patagonicus wasn’t actually that small. The type specimen was a hatchling. Adults were closer to 5m (16ft) in total length. Still small for a sauropod though.
