Search Results : ankylosaurs

  • The “Dawn Shark” and “Hidden Face”

    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.

    Eocarcharia and Kryptops
    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:

    1. Theropoda
    2. Sauropoda
    3. 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:

    Evolution Explains Why Lolcats Control Your Mind

    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.


  • Jurassic World Review

    It's here!
    It’s here!

    I figured if I was going to do a Jurassic World-related post on Stegosaurus I might as well follow it up with a review for the film. I grossly underestimated the draw of dinosaurs to the cinema. Despite 22 years of Jurassic Park, Walking with Dinosaurs (BBC version, not the Disney thing), and so on, people never seem to be burnt out on dinosaurs. That’s good news for paleontology (yay!), and also for movies seeing as how Jurassic World just raked in a record-breaking $208.8 million domestic in its opening weekend.

    So what did I think?  In short: I liked it and found it to be a worthy successor to the franchise.

    If you’d like the longer, spoiler-ridden version click on the jump.
    Continue reading  Post ID 46


  • Get in on the deal: Indiana University Press one day sale.

    I apologize ahead of time for what will likely sound like spam, but:

    Just a quick post to remind folks that today, and only today, Indiana University Press is offering a 60% off sale on all their books. That includes their famed Life of the Past series.

    So if you have yet to get your copy of The Complete Dinosaur, or have been itching to snag the most comprehensive book ever written on Deinosuchus, ankylosaurs, or mosasaurs, but didn’t have the necessary funds; now is your chance to get them for cheap.

    Just remember, the sale ends today.

    ~Jura


  • T-U-R-T-L-E Power! Part 2: The weird and wacky origin of turtles.

    A Galapagos tortoise struts about, secure in the knowledge that no one will ever know where the hell it came from. Photo from petcaregt.com

    This is a long overdue follow up to my original Turtle Power article back in…yeah never mind the date.

    As established previously, turtles are a strange, and highly diverse group of animals, but how did they come to be this way?

    The turtle bauplan has been a phylogenetic double edged sword. On the one hand, the unique shell design, and the necessary body contortions associated with it, make chelonians a very easy group to classify. However, it is these same peculiarities that keep us from finding the ancestor to turtles. To date, there are no “half-turtles.” No good transitionals between one reptile group to that  of turtles. As such, the list of turtle ancestors runs all over Reptilia. Some paleontologists believe the origin lies at the base with reptiles like procolophonoids, and pareiasaurs. Others believe turtles are a bit more closely related to extant reptiles, and belong in, or alongside the sauropterygians (plesiosaurs, nothosaurs, and placodonts). There is even some evidence to suggest turtles are actually in the same reptile group as dinosaurs and crocodylians (Archosauria).

    Curse that shell! - Photo by tompain

    How can the list be this extensive? Read on to find out.

    Continue reading  Post ID 46


  • T-U-R-T-L-E Power! Part 1: Turtles are Weird.


    As the meme goes: I like turtles!

    They are such a unique group of animals, that one can’t help but be drawn to them. Yet despite their uniqueness, turtles tend to get thrown into the wastebin of “living fossils”. It’s not uncommon to hear documentaries, or books refer to turtles as having been static since their first appearance 200+ million years ago. It’s unfortunate because statements like these tend to downplay just how weird and wonderful turtles really are.

    So why are turtles so weird? Well, as one might expect, it’s all about the shell. The turtle shell is an iconic image. Everyone knows what a turtle basically looks like. Even strange turtles like the mata mata (Chelus fimbriatus) are still recognizable as turtles. Contrary to popular belief, turtles can neither come out of their shells, nor does the shell act as their home. One cannot pull a turtle from its shell. The shell is the result of a phenomenal transformation of the backbone, ribcage, sternum, clavicles and gastralia.

    Turtle shells are different from the armoured “shells” seen on dinosaurs like the ankylosaurs. It is also fundamentally different from the armour seen on armadillos, crocodylians and every other vertebrate out there. In all these other animals, the armour is composed of bony plates that are formed from bone which is made intramembranously in the dermal portions of the body. Turtles are the only animals we know of that develop their armour by using this dermal bone in conjunction with endochondral bones (i.e.. the vertebrae and rib cage).

    turtle_side_view1
    A turtle “coming out of its shell.” Image from the Encarta website.

    It is at this point that turtles go from simply being unique, to just being weird. In order for the shell to protect the exposed limbs and head, the shell had to engulf the limb girdles. The rib cage had to actually grow over the pectoral and pelvic girdles. Think about that for a minute. Take a look in the mirror sometime and see how your arms are placed. Our arms, and the arms of every other tetrapod alive today, are set outside the rib cage. In fact, we actually can (and do) rest our arms along the outside of our ribs. Turtles can’t do that. Having one’s ribs on the outside can really hamper the ability to move the arms. The arms can extend, but they cannot bend without banging into the ribs. In order to fix this, turtles had to reverse the way their arms bend. Turtle arms bend towards one another, rather than away as they do in all other tetrapods. Imagine if your arms bent like your legs do, and you get the idea. Protection of the head required another unique innovation. Namely, turtles had to become double jointed. Turtle neck articulation follows a standard “ball and socket” arrangement that is widespread among various extant reptiles. However, within each species there is between one and two vertebrae that feature a “ball” on both sides (Romer, 1956). This biconcavity creates a hinge joint that can bend a full 90°. It is this special joint, more than anything else, that allows turtles to contort their necks in such a manner. For pleurodires, as the name implies, this articulation allows the neck to be tucked to the side of the body under a lip of the carapace. For cryptodires, these double joints allow the head and neck to literally go inside the body cavity; something no other tetrapod can do, and something that is decidedly weird. 🙂 Another issue with having a shell composed of fused ribs and vertebrae, is that flexibility is reduced to zero. This has a huge effect on speed. Turtles cannot extend their stride by bending their spine; a behaviour that all other tetrapods are capable of . The only way to increase stride length is to increase the lengths of the limbs. This puts an immediate limit on turtle speed. While longer limbs could be evolved, they would not be able to fit inside the shell. The only way for a turtle to go faster is to speed up the stride frequency. Turtles were thus forced to give up on ever being speedy. Though there are some chelonian members (e.g. my Terrapene ornata luteola) which put that statement to the test.

    Yet another weird characteristic of turtles is how they have circumvented the issue of breathing while encased in armour.

    Normally, in tetrapods, breathing is achieved through the bellow like pumping of the lungs. This is accomplished by muscles connected to the ribs. These muscles expand the ribcage, allowing air to enter. As turtles no longer had the joints that allow the ribs to move, they lost the muscles that moved them. This creates a problem unique to turtles. How does one get air both in, and out of the body cavity. This is a problem that seems to have been solved multiple times in turtle evolution. Tortoises can “rock” their pectoral girdles back and forth in order to pump the lungs. Many semi-aquatic turtles can use the buoyancy of water to push air out of their lungs, while others can use the weight of their viscera to pull down on the lungs and allow air in. Many, though, have evolved sheets of muscle connected to the lungs, which will either expand, or contract the lungs and allow for respiration. Some, such as box turtles (Terrapene) require a sheets of muscle that will both expand and contract the lungs. In these animals, both inhalation and exhalation, are an energetic process. The upshot to this, is that by having independent muscles for respiration, box turtles are able to breathe even when fully sealed inside their shells (Landberg et al, 2003).

    One strange aspect of chelonians that is rarely brought up, is how incredibly diversified they are. If turtles had died out at the end of the Mesozoic, and all we had to go on were fossils, I doubt we would ever have realized just how “flexible” the turtle bodyplan actually is.

    Despite being encased in a shell both above and below, turtles are capable of chasing down prey (e.g. Trionyx and Apalone). Some are adept excavators; making extensive burrows that can run as long as 9 meters (30ft) and be 3.6m (12ft) deep (Gopherus agassizii). Still others like pancake tortoises (Malacochersis tornieri) are proficient rock climbers. Probably most surprising are musk turtles (Sternotherus). These normally waterbound turtles are quite adept tree climbers. Sternotherus minor has been observed scaling cypress trees up to 2 meters (Orenstein, 2001). Both of these species have relatively small plastrons which give them added flexibility. Still, even stiffened tanks like Leopard tortoises (Geochelone pardalis ) have been observed scaling fences that were blocking their way. The animals would climb up one side and then just topple over the other (Orenstein, 2001).


    Some, such as the big-headed turtle (Platysternon megacephalum) have evolved huge heads with strong jaws for crushing shellfish. Others are efficient filter feeders (Podocnemis unifilis); sieving the water of small food particles.

    Many freshwater turtle species have re-evolved ?gills.? These are areas of thin, permeable skin usually around their cloaca. This allows these species to take in oxygen through the water.

    Lastly, turtles don’t grow old (Congdon, 1992). Unlike most other animals, turtles show little to no signs of age related deterioration. 74 year old three toed box turtles (Terrapene carolina triunguis) were found to be just as reproductively active as turtles some 40 years younger than them. (Miller, 2001).

    So chelonians are weird, but how did they come to be this way? For that, you’ll have to stay tuned.

    ~Jura

    Extra geek points to folks who got the reference to the Partners in Kryme song from the first TMNT movie. Id est: the original turtle rap. None of that Vanilla Ice crap.


    References

    Congdon, J. 1992. Senescence in Turtles: Evidence from Three Decades of Study on the E. S. George Reserve. Senescence in Organisms in Natural Populations. American Association of Gerontologists. Washington, D.C.

    Landberg, T., Mailhot, J.D., Brainerd, E.L. 2003. Lung Ventilation During Treadmill Locomotion in a Terrestrial Turtle, Terrapene carolina. J.Exp.Biol. Vol. 206: 3391-3404.

    Miller, J.K. 2001. Escaping Senescence: Demographic Data from the Three-Toed Box Turtle (Terrapene carolina triunguis).

    Orenstein, R. 2001. Turtles, Tortoises and Terrapins: Survivors in Armor. Firefly Books. 304 pps. ISBN 1-55209-605-X

    Romer, A.S. 1956. Osteology of the Reptiles. U.Chicago Press. ISBN: 0-89464-985-x 772pps


  • A critical evalution of Tianyulong confiusci – part 3: Plucking at the idea of feathered dinosaurs

    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. 🙂

    Tianyulong

    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

    Scale impressions from the stegosaur Gigantspinosaurus sichuanensis, from Xing Lida's Dinosaur Channel

     

    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.
    “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.
    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.
    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.
    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.
    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.

    Test caption

    gekkoninae_rhacodactylus_ciliatus_orange

    atheris_hispida

    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.
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