This blatant case of slander has raised the question of what one should do in this situation. It has also brought up the broader question of how scientists should handle the media. Should we just sit back, hoping that the interviewers will present the facts as best they can, and then deal with any possible blowback if/when that fails? Should scientists demand tighter editorial control over what is shown in videos like these? We are their scientific consultants after all. Theoretically they need us for legitimacy; which gives us a bargaining chip.
I don’t know what the right answer is. The least I can do is help Matt pass this info along so future researchers who are asked for an interview, can ask the production crew for assurances that they won’t be slandered in the final product.
Continuing my trend of “catching up,” an article in the November issue of Natural History magazine, talks about a new study in the Quarterly Review of Biology, that finds group nesting to be very common place among extant reptiles.
That study would be:
Doody, J.S., Freedberg, S., Keogh, J.S.? 2009. Communal Egg-Laying in Reptiles and Amphibians: Evolutionary Patterns and Hypotheses. Quart. Rev. Biol. Vol.84(3):229-252.
In the paper, Doody et al (no laughing) did a massive search through the herpetological literature (both technical journals, and hobbyist magazines) to look at instances of communal egg laying in reptiles and amphibians (herps). I’m not being hyperbolic here either, as the paper states:
In total, our assembled database was gathered from 290 different sources, including 176 different scientific journals, 72 books or book chapters, 29 unpublished reports, and 13 unpublished theses. We also have included a number of reliable personal communications from herpetologists.
What the authors found was that group gatherings of herps are vastly more common than previously believed. Group egg laying was found to be present in 345 reptile species. Now you might be thinking 345 really isn’t all that much for a group composed of some 8700 species.
Well then aren’t you a Debbie Downer?
Ophisaurus attentuatus brooding her eggs.
Seriously though, the authors address this by mentioning:
Although the difficulty in locating nests hampers our ability to determine the actual frequency of communal egg-laying among species, we can better estimate this proportion by dividing the number of known communally egg-laying species by the total number of species, excluding those for which eggs have not been found. We conducted such a calculation for the three families of Australian lizards known to include multiple communally egg-laying species—Gekkonidae, Pygopodidae, and Scincidae—as gleaned from the Encyclopedia of Australian Reptiles database (Greer 2004). Proportions of these lizard families known to lay communally were 4–9%, but, when we exclude species for which nests are not known, these values rise dramatically to 73–100%
The biggest take home message to get from Doody et al’s review, is just how much we don’t know about extant reptiles.
…the present review highlights our inadequate knowledge of the nests and/or eggs of reptiles. For instance, the eggs or nests are known in only 7% of Australian lizards of the three families that commonly lay communally (N = 411 oviparous spp.) (Greer 2004).The extent of this knowledge for Australian lizards is probably similar to that for reptile eggs on other continents, particularly South America, Africa, and Asia, where the reproductive habits of reptiles are poorly known. This is in stark contrast to other vertebrates such as birds, for which complete field guides to the eggs and nests are available for several continents
Indeed, just by doing the brief research run needed to compile this blog post, it was apparent that communalism is much more common in reptiles than anyone ever thought. However, because so many of these reports are either anecdotal, or buried in obscure journals, it is easy to miss all the many cases where it is known.
This discovery lead the authors to the inevitable follow up question of: “why?” What benefit do mothers gain by nesting communally?
Numerous hypotheses for why animals nest communally, have been proposed.
Saturated habitat (only so many suitable nest sites)
Sexual selection (choice of males that live in a particular area)
Artifact of grouping for other reasons
Attack abatement (easier to hide a bunch of eggs in one site, than in multiple sites. Less chance that your eggs will be the ones that are eaten).
Maternal Benefits (save time and energy finding a suitable nest site by “freeloading”)
Reproductive success (if the nest site worked once before…)
Egg insulation
The authors reviewed all of these possible reasons for communal egg laying in herps. In the end, they found evidence for both the maternal benefits hypothesis, and the reproductive success hypothesis, though they felt a mixed model better explained things.
Python brooding her eggs.
Sadly, though the authors mentioned how a lack of information on the natural history of most reptiles is largely responsible for this sudden revelation about their nesting behavior, they nevertheless make repeated mentions of how “social interactions are generally less complex in reptiles and amphibians than in other tetrapods” or how herp sociality forms “relatively simple systems“.
The reality is that the old view of simplistic “loner” reptiles that only come together to mate, is not accurate. This is especially true for parental care in reptiles.
The popular view (among the public, and the scientific community) is that reptiles are “lay’em and leave’em” types when it comes to reproduction. Despite all the herpetological knowledge to the contrary that has been acquired in the past 50 years, it is still popular to spout the party line about reptiles being “uncaring parents.”
Zoologist Louis Somma took issue with this view of reptilian (in particular, chelonian and lepidosaurian) parenting. He conducted a literature search to see how often mentions of parental care in reptiles are recorded. In the end he wound up finding 1400 references to parental care in reptiles (Somma 2003)!
Somma’s survey covered various aspects of parental care. He found reported evidence of nest building and / or guarding in tortoises like Manouria emys (McKeown 1999), Gopherus agassizii (Barrett & Humphreys 1986) and 4 other species of chelonian.
Turning to lepidosaurs, Somma found parental behaviour to be present in 133 species of lizards and 102 species of snakes. Even a species of tuatara (Sphenodon punctatus) is known to guard its nests (Refsnider et al. 2009). Though these numbers appear small compared to the total amount of species that have been described; much like the Doody et al. paper, this is just based off of species whose nesting behaviours we do know. That these taxa all span a wide phylogenetic range, suggests that parental care is more commonplace than initially thought.
Nest guarding is usually a maternal trait, but some squamates exhibit nest guarding behaviour in both parents, such as some cobra and crotaline snakes (Manthey and Grossman 1997) , as well as tokay geckos (Zaworski 1987).
Not only active guarding of the nest, but actual brooding of the eggs is also commonly reported in squamates such as various python species (Harlow & Grigg 1984, Lourdais et al. 2007), and skinks (Hasegawa 1985, Somma & Fawcett 1989). Some species are even known to groom their newly hatched young (Somma 1987).
More interesting still are various reports and observations of parental feeding in some reptile species, such as the skink Eumeces obsoletus (Evans 1959), and the cordylid lizard Cordylus cataphractus (Branch 1998). Not to mention recent evidence of parental feeding in captive crocodylians.
This leads me to the only reptile group where parental care is well publicized: that of the 23 extant crocodylian species. I could, at this point, list references for parental care in crocodylians. However because this behaviour is so well documented for this group, it would seem unnecessary. It is better to shed light on the many (MANY) examples of parental care in other reptile species. I also didn’t include related examples like placental evolution in the skink genus Mabuya, or instances of egg binding in captive reptile mothers; due to a lack of appropriate substrate to lay their eggs.
In the end, the paper by Doody et al. adds to a growing body of evidence which suggests that the “lay’em and leave’em” reptile species of the world, are the exceptions? and not the rule.
~ Jura
Next time: Biomechanics of running suggest “warm-blooded” dinosaurs. Or: why the aerobic capacity model needs to die already.
References
Barrett, S.L. & Humphrey, J.A. 1986. Agonistic Interactions Between Gopherus agassizii (Testudinidae)
and Heloderma suspectum (Helodermatidae). Southwestern Naturalist, 31: 261-263.
Branch, B.. 1998. Field Guide to Snakes and Other Reptiles of Southern Africa. Third revised edition. Sanibel Island: Ralph Curtis Books Publishing.
Doody, J.S., Freedberg, S., Keogh, J.S.? 2009. Communal Egg-Laying in Reptiles and Amphibians: Evolutionary Patterns and Hypotheses. Quart. Rev. Biol. Vol.84(3):229-252.
Evans, L.T. 1959. A Motion Picture Study of Maternal Behavior of the Lizard, Eumeces obsoletus Baird and Girard. Copeia, 1959: 103-110.
Harlow, P and Grigg, G. 1984. Shivering Thermogenesis in a Brooding Python, Python spilotes spilotes. Copeia. Vol.4:959?965.
Hasegawa, M. 1985. Effect of Brooding on Egg Mortality in the Lizard Eumeces okadae on Miyake-jima, Izu Islands, Japan. Copeia, 1985: 497-500.
Lourdais, O., Hoffman, T.C.M., DeNardo, D.F. 2007. Maternal Brooding in the Children’s Python (Antaresia childreni) Promotes Egg Water Balance. J. Comp. Physiol. B. Vol.177:560-577.
Manthey, U. and W. Grossman. 1997. Amphibein & Reptilien S?dostasiens. Natur und Tier Verlag, M?nster.
Mckeown, S. 1999. Nest Mounding and Egg Guarding of the Asian Forest Tortoise (Manouria emys). Reptiles, 7(9): 70-83.
Refsnider, J.M., Keall, S.N., Daugherty, C.H., & Nelson, N.J. 2009. Does nest-guarding in Female Tuatara (Sphenodon punctatus) Reduce Nest Destruction by Conspecific Females? Journal of Herpetology. vol.43(2):294-299.
Somma, L.A. 1987. Maternal Care of Neonates in the Prairie Skink, Eumeces septentrionalis. Great Basin Naturalist, 47: 536-537.
Somma, L.A. & Fawcett, J.D. 1989. Brooding Behaviour of the Prairie Skink, Eumeces septentrionalis, and its Relationship to the Hydric Environment of the Nest. Zoological Journal of the Linnean Society. Vol.95: 245-256.
Somma, L. 2003. parental Behavior in Lepidosaurian and Testudinian Reptiles: A Literature Survey. Krieger Publishing Company. 174pgs. ISBN: 157524201X
Zaworksi, J.P. 1987. Egg Guarding Behavior by Male Gekko gecko. Bulletin of the Chicago Herpetological Society, 22: 193.
Once again the blog has taken a backseat to my real life work. It’s unfortunate too as there have been at least three really interesting news stories / technical papers that I feel the need to tackle. The first story I want to talk about is the news of the ancient Mediterranean goat: Myotragus balearicus, and its alleged “reptilian” physiology.
Myotragus balearicus reconstruction.
On the outset M.balearicus appears like your standard goat; complete with horns, hooves and (likely) a penchant for eating practically anything. The part that makes M.balearicus stick out the most? is that it was a native inhabitant of small islands in the Mediterranean.? Modern goats reach islands through human intervention. There, they become invasive elements that often damage the native flora and fauna. Without human intervention, it is hard for goats – and indeed? most mammals – to become established on islands. Both getting to the islands, and surviving on them tend to require animals that are more metabolically adaptable. Despite their catholic diets, goats are still limited by the “always on” nature of mammalian metabolism.
At least, that’s what we thought.
Researchers at the Institute of Paleontology at the Autonomous University of Barcelona, looked at microslices of the bones in this goat. What they found was a pattern of bone deposition that is unusual for ungulates. Rather than have layers of bone strewn about in an interwoven pattern, the bone of M.balearicus was laid down evenly in concentric layers. The latter formation is often assumed to be a hallmark of reptiles and other “slow growing” animals. With this in mind, the authors suggest that M.balearicus had evolved a more plastic metabolism.
These findings lend support to the model that posits a shift in life history strategies to a lower end of the growth rate spectrum, in areas where mortality remains low.
The results, while interesting, bother me a bit, as they rely on certain views on reptile growth strategies that are known to be false.
For instance:
Ectotherm vertebrates have slow and flexible growth rates…
Ectotherms are characterized by lamellar-zonal bone throughout the cortex.
True zonal bone with growth marks deposited seasonally throughout ontogeny is a general ectotherm characteristic. In ectotherms, the bone matrix consists of slow growing lamellar bone.
While it is true that there are ectotherms that grow in a cyclical manner like this (especially animals from temperate regions), this is not a given for all ectotherms. In fact, it has since been well documented that fibrolamellar bone deposition occurs normally in crocodylians, as well as turtles (Reid, 1997).
It is a tad strange, as the authors do cite the Turmarkin-Deratzian gator paper, but they erroneously use it as an example of slow growth and contrast it with the fast fibrolamellar growth seen in most ungulates.? There is even a figure in the paper that shows, and even labels fibrolamellar growth in a crocodile, yet appears to get completely glossed over when it comes time to talk physiology.
Which brings me to my next point. The authors argue that the presence of lamellar zone bone in M.balearicus is suggestive of an ectotherm-like growth strategy. But does lamellar zone bone really indicate slow growth?
Work by Tomasz Owerkowicz on varanids (Owerkowicz 1997),? found that even the sedentary animals in his control group, could lay down bone at the same rate as his sedentary mammals (Morell 1996). Presumably this bone was lamellar zonal, though without the figures on hand, I can’t say for sure.
A more prominent example comes from Lieberman and Crompton (1998), who did a stress study on goats and opossums. The authors were looking at the remodeling response of bone to stress, and accidentally came across an interesting growth difference between these two taxa. They found that their opossums grew at a significantly faster rate than their goats, despite both taxa being of a developmentally equivalent stage. The interesting part is that the goat’s were depositing fibrolamellar bone, while the opossums were producing lamellar bone.
So no, lamellar bone need not be a hallmark of slow growth. Rather, it might be a response of the bones to specific stresses. Lamellar zonal bone is structurally stronger than fibrolamellar bone, so there might have been a more functional need for this type of bone.
Lastly, I have some issues with the final conclusions asserted by the authors in their closing comments:
The reptile-like physiological and life history traits found in Myotragus were certainly crucial to their survival on a small island for the amazing period of 5.2 million years, more than twice the average persistence of continental species. Therefore, we expect similar physiological and life history traits to be present in other large insular mammals such as dwarf elephants, hippos, and deer. However, precisely because of these traits (very tiny and immature neonates,low growth rate, decreased aerobic capacities, and reduced behavioral traits), Myotragus did not survive the arrival of a major predator, Homo sapiens, some 3,000 years ago.
Now I’m sure that there was a need to inject some melodrama at the end (as is typical for many papers), but the assertion that a “reptile-like physiological life history” must also incorporate a small aerobic scope, small neonates and reduced behavioural repertoire, is just uncalled for. All of these are frustratingly common misconceptions about reptiles, and bradymetabolic animals in general. Further, none of these assertions are based on any facts for M.balearicus. The only assertion that could really be tested is the small neonate one, and that appears to be falsified, as data on newborn M.balearicus show that newborns were large and precocial animals; pretty standard fare for an ungulate.
Overall the results of this study are interesting, and I look forward to seeing if pygmy elephants and hippos also display this apparent “slow growing” bone type. Comparing M.balearicus to reptiles based off this one similarity appears unjustified, and only goes to further perpetuate some common reptile misconceptions.
Needless to say, Myotragus balearicus was probably not “cold-blooded,” despite what the news headlines would have one believe.
Next up: Destroying the “uncaring parent” myth.
~Jura
References
Lieberman, D.E., & Crompton, A.W. 1998. “Responses of Bone to Stress: Constraints on Symmorphosis.” Principles of Animals design: The Optimization and Symmorphosis Debate. Weibel, E.R., Taylor, R.C., and Bolis, L. (eds). Cambridge U. Press. Pgs: 78-86. ISBN: 0521586674
Morell, V. 1996. A Cold, Hard Look at Dinosaurs. Discover. December. Available online.
Owerkowicz, T. 1997. Effects of Exercise and Diet on Bone-Building: A Monitor Case. Journal of Morphology. V. 232(3): 306
Reid, R.? 1997. ?Dinosaurian Physiology: The Case for ?Intermediate? Dinosaurs.?? The Complete
Dinosaur. Farlow, J.O. and Brett-Surman, M.K. (eds.)? Indiana U. Press. Pgs: 449 – 473. ISBN: 0253333490
This might have been a common image for early human settlers of Australasia. Image from Baxterking.com
A new study on Komodo dragon phylogeny has found that the mighty ora was, in fact, one of many.
The paper in question is:
Hocknull, S.A., Piper, P.J., van den Bergh, G.D., Due, R.A., Morwood, M.J., Kurniawan, I. 2009. Dragon’s Paradise Lost: Palaeobiogeography, Evolution and Extinction of the Largest-Ever Terrestrial Lizards (Varanidae). PLoS ONE 4(9):1-15 doi:10.1371/journal.pone.0007241
Since this is in PLoS ONE, that means it is freely available. Hooray!
The authors looked at the skeleton of Varanus komodoensis, V.salvator, and V.priscus (Megalania).? By carefully examining the various bones of the skeleton, the authors were able to determine the taxonomic placement of various large Varanus fossils found in Australia, Indonesia, and Asia.
In the end their results showed that contrary to popular belief, Komodo dragons are not examples of island giantism, but rather were already large migrants from Australia during periods of low sea level.
So much for the pygmy elephants scenario.
Along with finding strong support for the close association of V.komodoensis with V.priscus, the authors also showed that Australia was actually home to many large varanids during the Pliocene/Pleistocene. So while Meglania was certainly the biggest, it wasn’t unique. The authors showed that giantism evolved at least twice in varanids. Once in Asia, and again in Australia.
The paper also gives support to the statements of Molnar (2004), that the old belief that Komodo dragons (and reptiles in general) only got big because they were isolated from mammalian competitors, is completely false.? The authors point out that both data for the ora, and for another large (though now extinct) varanid – V.silvalensis – show that they existed contemporaneously with large mammalian competitors (hyaenas and tigers). Not only that, but it was on the mainland that they appear to have gotten large in the first place. So not only could large lizards hold their own against “sophisticated” mammalian predators, but they even appeared able to grow to competitive size despite the pressures.
Finally, the authors also discovered yet another large varanid that lived in Australia before making its way towards Timor. This one was intermediate in size between Komodo dragons and Megalania.
So it would appear that Australia was not unique in having reptilian megafauna during the Pliocene/Pleistocene.? It seems? that much of Australasia was rife with large, voracious varanids.
Must have sucked to be an Aborigine back then. >: )
~Jura
References
Hocknull, S.A., Piper, P.J., van den Bergh, G.D., Due, R.A., Morwood, M.J., Kurniawan, I. 2009. Dragon’s Paradise Lost: Palaeobiogeography, Evolution and Extinction of the Largest-Ever Terrestrial Lizards (Varanidae). PLoS ONE 4(9):1-15 doi:10.1371/journal.pone.0007241
Molnar, R.E. 2004. Dragons in the Dust: The Paleobiology of the Giant Monitor Lizard Megalania. Indiana University Press. 210pgs. ISBN: 0253343747/978-0253343741
If one has noticed a slight change to the blog, it has to do with an upgrade to WordPress. I had been trying get the auto-update to go through, but it was being very stubborn. I have since learned that it was a 1and1 problem (my host), and that I needed to switch to php5.
Needless to say, the problem has now been solved. If anyone else out there has been having the same problem, or just general issues getting the dashboard to work, consider the php version you are using. It might be what is causing the weirdness.
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.
Megalania chasing down Genyornis newtoni. Illustration by Peter Trusler for Wildlife of Gondwana
Just announced today in the journal: PNAS, is a new comprehensive study on Komodo dragon feeding ecology. The comprehensive nature of the paper is the result of the contributions from around 28 individuals from all over Australia, as well as the Netherlands, and Switzerland.
The paper in question is:
Fry, B., Wroe, S., Teeuwissed, W., van Osch, M.J.P., Moreno, K., Ingle, J., McHenry, C., Ferrara, T., Clausen, P., Scheib, H., Winter, K.L., Greisman, L., Roelants, K., van der Weerd, L., Clemente, C.J., Giannakis, E., Hodgson, W.C., Luz, S., Martelli, P., Krishnasamy, K., Kochva, E., Kwok, H.F., Scanlon, D., Karas, J., Citron, D.M., Goldstein, E.J.C., Mcnaughtan, J.E., and Norman, J. 2009. A Central role for Venom in Predation by Varanus komodoensis (Komodo Dragon) and the Extinct Giant Varanus (Megalania) prisca. PNAS Early Release. doi:10.1073/pnas.0810883106
*catches breath*
The paper is only six pages long, which downplays just how much work must have gone into this project. The authors used Finite Element Analysis, MRIs, and traditional biochemical and dissectional techniques to look deep into the venom apparatus of the living Komodo dragon (V. komodensis).
For those who may have missed it on the first go around, it has recently been discovered that venom is more widespread among squamates than previously thought (Fry et al 2005). The authors of that paper (a few of whom are on this paper) found the presence of specific glands at the base of the mandible in numerous lizard species. These glands were found to release salivary proteins that were, in fact, venom.
It was a “primitive” venom for the most part, with little denaturing, or tissue destroying properties, but enough that it seemed to warrant the construction of a new clade of squamates named: Toxicofera (Fry et al 2005, Vidal & Hedges 2009). Though the discovery of incipient venom production in many squamates, was an intriguing surprise, the resultant cladogram has proven problematic, and controversial. The authors found iguanians (iguanas, chameleons, most pet lizards) to be deeply nested within scleroglossa (skinks, snakes, varanids); a view that flies in the face of every morphological study ever done on this group (e.g. Romer 1956, Pianka and Vitt 2003). In order for Toxicofera’s current associations to be valid, iguanians would have to have re-evolved both their temporal bars, as well as a fleshy tongue. While possible (few things in evolution are impossible), it is extremely unlikely; kind of like expecting snakes to re-evolve limbs.
Despite this contentious relationship, the discovery of venom glands in animals like monitor lizards, was a surprise. This new study by Fry et al is the first to really look at the venom secreting abilities of this gland, and what it means to Komodo dragon ecology.
Photo by: Jeff Werner Fauna vol. 1 (3). March 1998.
It turns out that the mandibular venom gland in V.komodoensishas six different compartments that open between the teeth of the lower jaw. Unlike venomous snakes and helodermatid lizards, the venom does not travel through any grooves in the teeth. Rather, it appears to pool at their base; bathing the teeth of the lower jaw prior to biting a prey animal. It’s a crude method of venom delivery, but one that might explain why Komodo dragons have such thick gums (which the teeth erupt through during a bite).
According to the authors, the mandibular venom gland of a 1.6m (5.25ft) Komodo dragon has enough fluid to produce 150mg of venom; 30mg of which would be available for delivery. That’s a fair amount of venom, but how does that translate to toxicity?
Though the delivery method is crude, the venom is fairly potent. According to the authors it only takes 0.1mg/kg of venom in the blood stream to cause pronounced hypotension, and only 0.4mg/kg to cause hypotensive collapse (fainting).
To put this into perspective, I weigh approximately 76kg (168lbs). It would take approximately 7.6mg of Komodo dragon venom to make me light headed, and 30mg to knock my arse out.
Hmm, maybe I should reconsider that Komodo island trip?
Fry et al go on to discuss how V.komodoensis goes about using this venom delivery system during predation. It was at this point that I became a bit hesitant.
Komodo dragon feeding ecology has been the subject of much misconception. Much like dinosaurs, earlier work on these beasts was more accurate than the work that soon followed. When Komodo dragons were first discovered, they were thought to be scary top predators of their respective habitat. This was quickly downgraded to obligate scavenger; possibly due to the animal’s willingness to eat prekilled meat, but more likely from general incredulity that a large reptile can actively hunt mammals (see table 10-2 of Auffenberg 1981 for examples). It really wasn’t until Dr. Walter Auffenberg spent some 13 months in the wild with Komodo dragons, that this myth was officially dispelled, and some 20 years after for it to become common knowledge. However, once it was discovered that animals lucky enough to escape from an initial V.komodoensis attack were found to die hours/days later, the view of Komodo dragons as “bite and release” predators was born (e.g. Bakker 1986).
Auffenberg’s work did show that there is something septic about the bite of oras. This was originally attributed to bacterial flora living in the fairly dirty mouths of these predators. Indeed one study (Gillespie et al 2002) found 54 potentially pathogenic bacteria living in the mouths of oras!
However, and this is the part that always seems to get glossed over: there has never been a reported case of a komodo monitor using this “bite and release” killing strategy. Despite spending over a year living with these animals, Auffenberg never once found an animal bitten, released and then later tracked down after it died. Komodo dragon attacks were quite the opposite in fact. Small, to relatively large prey (goats, boar) were often killed on the spot using violent side to side shaking to snap the neck, while large prey like water buffalo were hamstringed (Achilles tendon severed), followed by abdominal evisceration of the now paralyzed (and often still alive) animal.
Despite the gruesome detail in which Auffenberg described ora attacks, as well as the sheer lack of evidence for a viper style feeding strategy; one can still read about how Komodo dragons “avoid confrontation with their prey” by allegedly employing this method of killing (for instance).
So one can forgive my trepidation over what was to be written about next in the Fry et al paper.
The authors do discuss the alleged “bite and release” hunting style posited for V.komodoensis, but are quick to point out (as I just did) that there has never been a documented case of this hunting strategy being used on dragon prey.Dr. Fry went went one step further in an interview for Science News:
What’s more, rare sightings of the lizards hunting didn’t fit with this method. Victims typically died quickly and quietly after going into shock, the authors say. “No one’s actually seen a Komodo dragon track a prey for three days until it dies of septicemia,” Fry says. “It’s an absolute fairy tale.”
This was very comforting to see. One can only hope that the other news outlets don’t miss this point when doing their write ups (Edit: so muchfor hope).
Fry et al then went on to dispel the myth that the mouth of dragons contain toxic microflora. Though there have been studies that have shown the presence of potentially pathogenic bacteria in wild oras, none of these studies found a consistent microflora between individuals. In fact, the authors point out that some of the bacteria found in Komodo dragon mouths, were the same bacteria found in the guts of most lizards.
That venom must be playing an important role in predation was determined by looking at the evolution of venom in squamates. The authors point out that:
We have shown that in the species that have developed secondary forms of prey capture (e.g., constricting) or have
switched to feeding on eggs, the reptile venom system undergoes rapid degeneration characterized by significant atrophying of the
glands, reduction in fang length, and accumulated deleterious mutations in the genes encoding for the venom proteins (9, 26,
27). This is a consequence of selection pressure against the bioenergetic cost of protein production (28). The robust glands
and high venom yield in V. komodoensis thus argue for continued active use of the venom system in V. komodoensis.
So, while the venom of Komodo dragons is not the primary means by which dragons dispatch their prey, it still must play a pretty important role in prey acquisition. Since envenomated prey tend to become docile and quiet (Auffenberg, 1981, and this paper), it may just play a role in initiating shock, and reducing retaliatory actions by prey. It may also serve as a good “failsafe” in the event of a missed kill. Bitten prey that are “lucky” enough to escape an initial attack, tend to find themselves easily preyed upon shortly thereafter. This is similar to hunting tactics seen in Canadian lynx (the only mammalian carnivores known to have a septic bite) when hunting caribou (Auffenberg 1981).
Komodo dragon FE skull made by the Computation Biomechanics Research Group. UNSW, Sydney Australia.
Using Finite Element Analysis, the authors compared the bite and skull strength of V.komodoensis with that of a similar sized saltwater crocodile (Crocodylus porosus). The results they obtained agreed with previous FE work on Komodo dragons (Moreno et al 2008), which found the bite of oras to be remarkably weak on its own, thus requiring the aid of the postcranial musculature in delivering much of the force. Ora skull strength is at its greatest during bite and pull behaviour. This data agrees well with field observations showing oras biting and pulling back on their prey. Coupled with their recurved and serrated teeth, this results in the creation of large, gaping wounds, which would aid in venom delivery as the ora’s venom would be spread throughout; quickly entering the bloodstream and speeding up shock.
Finally the authors extrapolated their work to the monstrous lacertilian behemoth Varanus (Megalania) prisca. Using the extant phylogenetic bracketing method (Witmer 1995, 1998), they were able to determine the likelihood of venom being present in Megalania. If true, this would make Megalania the largest venomous carnivore to have ever lived.
I’m not sure I buy this part. As Fry et al mentioned in the paper, the venom apparatus tends to degrade quickly when not used. Megalania was a big animal (over 2,000 kg according to the authors, though Molnar 2004 places it as just under 2,000kg for the largest individuals). Any hole that V(M)prisca would create when attacking its prey, would have been devastating enough without the need for anticoagulating venom.
Also:
Like the other members of this unique varanid lizard clade, the jawbones of V. prisca are also relatively gracile compared with the robust skull and the proportionally larger teeth similarly serrated (Fig. 3).
I’d be careful about this assumption, as there is only one fairly complete maxilla (upper jaw bone), and portions of the dentary (tooth bearing lower jaw bone), known for Megalania. This makes comparison with extant monitors, rather hard to do. What little skull bones do exist, show that the skull of Megalania was stronger (or at least, less flexible) than that of other monitor lizards (Molnar, 2004).
As it stands right now, there are frustratingly too few fossils of Megalania (especially the skull) to accurately say one way, or the other in regards to venom delivery.
Of course that doesn’t make it any less interesting to speculate about. 🙂
~Jura
References
Auffenberg, Walter, 1981, The Behavioral Ecology of the Komodo Monitor, Florida University press, pgs: 406.
Bakker, R. 1986. The Dinosaur Heresies. William Morrow. New York. ISBN: 0821756087, 978-0821756089 pgs: 481.
Fry, B.G., Vidal, N., Norman, J.A., Vonk, F.J., Scheib, H., Ryan Ramjan, S.F., Kuruppu, S., Fung, K., Hedges, S.B., Richardson, M.K., Hodgson, W.C., Ignjatovic, V., Summerhayes, R., Kochva, E. 2005. Early Evolution of the Venom System in Lizards and Snakes. Nature. Vol.439:584-588.
Gillespie, D., Fredekin, T., Montgomery, J.M. 2002. “Microbial Biology and Immunology” in: Komodo Dragons: Biology and Conservation. James Murphy, Claudio Ciofi, Colomba de La Panouse and Trooper Walsh (eds). pgs: 118-126. ISBN: 1588340732/978-1588340733
Molnar, R.E. 2004. Dragons in the Dust: The Paleobiology of the Giant Monitor Lizard Megalania. Indiana University Press. 210pgs. ISBN: 0253343747/978-0253343741
Moreno, K., Wroe, S., Clausen, P., McHenry, C., D’Amore, D.C., Rayfield, E.J., Cunningham, E. 2008. Cranial Performance in the Komodo Dragon (Varanus komodoensis) as Revealed by High-Resolution 3-D Finite Element Analysis. J.Anat. Vol.212:736-746.
Pianka, E.R., and Vitt, L.J. 2003. Lizards Windows to the Evolution of Diversity. U.Cal.Press. 333pgs. ISBN: 0520234014/9780520234017
Romer, A.S. 1956. The Osteology of the Reptiles. Krieger Publishing 800pgs. ISBN: 089464985X/978-0894649851
Vidal, N. and Hedges, S.B. 2009 The Molecular Evolutionary Tree of Lizards, Snakes, and Amphisbaenians. Biologies. Vol.332(2-3):129-139.
Witmer, L. 1995. “The Extant Phylogenetic Bracket and the Importance of Reconstructing Soft Tissues in Fossils” in: Functional Morphology in Vertebrate Paleontology. Jeff Thomason (ed). Cambridge Univ. Press. Cambridge, UK. pgs 19-33. ISBN 0521629217/978-0521629218
Witmer, L. M. 1998. Application of the Extant Phylogenetic Bracket (EPB) Approach to the Problem of Anatomical Novelty in the Fossil Record. J.Vert.Paleo. Vol.18(3:Suppl.): 87A.
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.
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Continuing from yesterday, the following is what I garnered from the Tianyulong confiusci specimen announced last week.
When looking at the fossil, a couple preliminary questions came to mind.
Is the fossil real?
Is the integument real feathers/protofeathers?
Is the fossil real?
Main slab for Tianyulong with highlights showing the breakage in the slab. Click the image to enlarge.
The initial paper gives no mention of how the fossil was collected (i.e. if it was collected by local farmers – as most of these fossils are – or if it was found in the field), so it is hard to tell how many hands this fossil has passed through before it was described. The specimen is broken into at least 3 different slabs (as shown in the first pic. Highlights [mine] show where breaks occur). The first, and most obvious, is across the top of the body, separating the dorsal vertebrae from the rest of the fossil. The second break, is a little less obvious. It appears to neatly separate the anterior part of the body, from the posterior part (pretty much right before the hip). It’s hard to tell from the photos, but this section might have been glued together. Whether this was before it reached the scientists, or after is left unclear. So there is room for suspicion there. The characters used to determine heterodontosaurid affinities come exclusively from the skull. The preservation of the hip makes it very hard to tell what one is looking at. The ischium appears quite a bit thicker than in Heterodontosaurus tucki. This could be chalked up to generic difference, or even an ontogenetic one. The authors mention the presence of extensive ossified tendons on both dorsal and ventral sides of the caudal vertebrae. This is actually unusual for an ornithopod. Ossified tendons tend to be arranged in a lattice-like geometry throughout the dorsal portions of the caudal verts, but not the ventral side. Tianyulong not only has ossified tendons on both dorsal and ventral sides of the caudals, but they are arranged in a parallel fashion rather than the more typical lattice work. This sounds much more like what one would expect to see in a dromaeosaur, not a heterodontosaurid. Especially since the eponymous Heterodontosaurus lacked ossified tendons. This would make this tendon arrangement both unique for heterodontosaurs, and unique for ornithopods.
Incidentally, there is yet another crack that separates this section of the tail from that of the proximal (and apparently tendonless) portion of the tail. It doesn’t look like the crack goes all the way through the slab, but this can’t be verified from the photos. Nonetheless, this is yet another cause for skepticism.
Another bit of strangeness is the presence of an apparent stain along most of the skeleton. It appears as a lighter, white colour, and is found within the body cavity, and along the back and tail. This might have been caused by the dissolving of the soft tissue. Whatever it is, this stain cuts off all the apparent filaments from the rest of the skeleton (save one small section that will be described later). In fact, there is one part where the stain appears to cut ? rather sharply ? right through the tail filaments. This cut is at an angle to the tail, thus not following the body contour at all. In fact, it almost looks like a deep gouge like that caused by a shovel, or (in this case) a trowel. Perhaps this was a casualty of the preparation/excavation.
After looking the fossil pictures over, I have to say that Tianyulong more than any other “feathered dinosaur” before it, has the potential to be a chimera.
Is the integument protofeathers/feathers?
Well, the answer is an emphatic no to the latter. These are definitely not feathers.
So then are they protofeathers?
In the paper, Zheng et al mentioned that the filaments bear a similarity to both the “quills” on Psittacosaurus , and the protofeathers of Sinosauropteryx. Curious; I decided to compare the three.
Comparison of the Psittacosaurus “quills” (top), Sinosauropteryx protofeathers (left) and Tianyulong “filaments” (right). Click the image to enlarge.
Right off the bat, I’d say one can dismiss any real relationship to the protofeathers of Sinosauropteryx. The filaments on Tianyulong are similar only in the sense that they don’t branch at all. Short of that, the size, and density of Tianyulong‘s filaments are quite different from those of S.prima (being wider, longer and more loosely packed).
When compared to the “quilled” Psittacosaurus, a much greater similarity can be seen as both filaments are rather long. The Psittacosaurus “quills” however, are quite a bit thicker, and seem to show up within the skin, while Tianyulong‘s filaments don’t touch the skeleton at all, save for the same spot where the strange (possible) groove is found.
Some folks have stated that the large filaments are focused on the caudal portion of the body, just like in the “quilled” Psittacosaurus specimen. I would caution against this. Most of Tianyulong‘s body is not preserved. Unlike the Psittacosaurus specimen, where one could tell that these “quills” appeared only on the tail, there is very little evidence for the same arrangement in Tianyulong. I would extend this caution to statements about Tianyulong being completely fuzzy too. There are some filaments found by the dorsal vertebrae and under the cervicals. However, these filaments are much removed from the body. The dorsal patch does not follow the arch of the vertebrae; instead lying more anterior to the bones. As for the ventral patch, unless one wants to posit a double chin on Tianyulong, they also don’t actually associate with the bones, nor do they follow the body contour.
The caudal filaments are strange in their own right. Like all the rest of these filaments they don’t follow the body contour (compare, for instance how the protofeathers of Sinosauropteryx follow the body rather tightly). In fact many of these filaments seem to be tangled amongst each other.
Note there is yet another apparent break in the slab, between the filaments.
If everything is arranged correctly, then these filaments seem to be tangling up with filaments that would have emerged much further up the back. Also unlike the singular “quills” on the Psittacosaurus, these thinner filaments all appear to protrude from the same narrow area. Instead of being more evenly spaced along the caudal vertebrae, they all bunch up by the proximal caudals. If these filaments did belong to the living animal, then it would appear that Tianyulong was brandishing a “smokestack haircut” long before Kid from Kid and Play ever did.
Final verdict:
Readers will no doubt have noted my extensive use of quotes around certain instances of protofeathers, as well as the mention of quills in the infamous Psittacosaurus specimen. I do so because of the questionable assignment of these filaments to those particular structures. In doing so, I am following in the steps of David Hone, who also suggested that one be cautious with one’s interpretation of some of these Yixian fossils (though my view is a little more extreme). Many of them have been described briefly, with little follow up work. The Psittacosaurus with the “quills” is a particularly nasty case. It received a quick right up in Nature, before it was discovered that the specimen was illegally collected. Now there is a veritable “shit storm” surrounding the fossil. This has resulted in it becoming a pariah that no journal dare touch. A result that has essentially put a halt to any further research for now. It’s unfortunate, as the identity of the Psittacosaurus filaments remains in limbo (not everyone is “happy” with the diagnoses of quills).
As for Tianyulong, there appears to be a fair amount of evidence to suggest the animal might have died on a plant, or was possibly being devoured by nematode like parasites prior to death. As for being protofeathers, they appear as unlikely in Tianyulong, as they do in Psittacosaurus. The relationship to the protofeathers of Sinosauropteryx prima, appear to be at the most basal geometric level (i.e. they are both straight and unbranching).
Still, what if everything is genuine? What kind of implications would that hold for dinosaurs?
![Photo by: Jeff Werner [Fauna vol.1 number 3 Mar 98]](https://reptilis.net/index4/komodo2.jpg)
