• Tag Archives reptiles
  • Reptiles digest just as well as the rest

    Graphical Abstract from Wehrle and German 2023.

    Digestive efficiency is one of those reptile misconceptions that makes the rounds every now and again. It’s not as pervasive as the “lack of aerobic capacity” or “inability to maintain body temperature” arguments, but there is still a general view in many scientific circles (*cough* paleontology *cough*) that reptiles are less efficient at digesting food than similar sized mammals and birds. Much of this boils down to the old endothermocentric fallacy that the high costs associated with obligate endothermy should somehow translate to greater benefits everywhere else (Greenberg 1980).

    Well that, and the fact that reptile chewing is very different from mammalian chewing.

    Continue reading  Post ID 14905


  • Review: The Secret Social Lives of Reptiles

    The following is a quick review for the new book by J. Sean Doody, Vladimir Dinets, and Gordon M. Burghardt. The book came out last year and I feel like it received relatively little fanfare in the paleo and herpetological circles (though I did come across one review from the British Herpetological Society, as well as this podcast interview with Sean Doody).

    The TL;DR version of this post is as follows: The Secret Social Lives of Reptiles is a landmark piece of literature that should become a foundational reference for any future study looking at reptile behaviour. The authors firmly describes where we currently are in reptile social behaviour studies, and just how much further we can still go. It’s a must read for any budding herpetologist, and a highly recommended read for herpetoculturalists / reptile fans. The best part of the book is its extensive bibliography, which offers a strong launching point for anyone interested in studying reptile behaviour. If you study any aspect of reptiles as organisms, then this book deserves a spot on your shelf.

    So, go out and get it.

    For more specifics about the book, feel free to read on from here.

    Continue reading  Post ID 14905


  • It’s over 9,000!

    Last year was a busy year for me. As such the site had to go into dormancy yet again. This year doesn’t look to be any less hectic, but I couldn’t bear to have the site continue to stagnate. So in an attempt to jump-start things again I am going to try and push out some smaller updates.

    Which brings us to our topic.

    The Reptile-Database recently released the current known/generally accepted species count for reptiles. It is now at a whopping 9,952 species! For comparison, when I was growing up the standard species count for reptiles hovered around 6500–6700 species. In fact one can still probably find this widely cited figure in books today. Even when I started the Reptipage some 16 years ago, the total species count was approximately 7,500 species. So in the span of those 16 years, our knowledge of extant reptile diversity has grown by 33%. That’s pretty impressive. Especially when compared to other amniotes. For instance birds are routinely cited as having 10,000 species. The most recent species count for Aves is: 10,530 (IOC World Bird List), an increase of just 5.3%. Mammals were cited as having 5000 species when I was growing up. The most recent (2008) count I could find shows that this class now contains 5,488 species (IUCN Red List); an increase of only 9.8%.

    Part of the reason for the larger spike in reptile species counts vs. mammals and birds is due to a new interest in reptiles themselves. Much of the history of Reptilia is one of revulsion, lumping, and overall wastebinning. However, now with the rise of herpetoculture and the acknowlegement that reptiles represent more than just a “stepping-stone” towards mammals and birds, herpetology has seen a bit of a renaissance in taxonomy. Another reason for this spike in species counts for reptiles can be attributed to the use of molecular techniques to ascertain differences in populations, along with better morphological data (such as those used to help determine that Crocodylus suchus was a real species and not just a variant of the C. niloticus) as well as better ecological data. This spike in species count has come about largely through the elevation of subspecies rather than the discovery of new species (though that is still happening). Herpetology has had a long history of lumping taxa that seem similar enough. This reluctance to split populations into distinct species rather than populations variations had artificially limited the actual species counts. Along with the elevation of subspecies to full species, there has also been a trend to elevate many subgenera to full genus status. This move is somewhat more controversial as the question always pops up of what the ever moving criteria for a genus are. Of course the criteria for species are hardly set in stone either. Ultimately taxonomy is a largely arbitrary affair of biological bookkeeping. Despite this, the need to have these criteria is paramount. The human brain doesn’t work well without categories, even if they are largely self-imposed ones. The appeal of splitting up Reptilia like this is that it reflects a changing attitude about reptiles in general. Though it has been long known that reptiles outnumber mammals, there always seems to be an undercurrent of “but they’re all just the same lizard.” A view that reptiles may be speciose, but are still limited in their body shapes compared to mammals and birds, still pervades today. Hence one reason why there are 29 orders of mammals, some 23 orders of birds, but only 4 orders of reptiles. A move to upgrade subspecies to species and subgenera to genera adds greatly to dispelling the myth that reptiles are the forgettable “intermediate forms” on the tree of life.

    Example of the different “genericometers” of taxonomists. Top left–right: Different members of the Anolis genus: A. proboscis and A. sagrei. Bottom left–right: Different genera of wild cats: Leopardus pardalis and Leptailurus serval. Anolis photos from: Lucas Bustamante and lanare (wikipedia). Serval photo from Giuseppe Mazza. Ocelot photos is unattributed but widely found on the internet

    Regardless of these higher order relationships it looks like Reptilia will officially comprise over 10,000 species by the end of the year [Note: See the comments].

    That is pretty awesome.

    ~Jura


  • 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


  • New study suggests that group nesting should be the norm – not the exception – in reptiles.

    A colony of _Eumeces fasciatus_ brood their eggs.
    A colony of Eumeces fasciatus brood their eggs.

    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.
    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.
    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.
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  • Bone histology says ectothermic goats, but does it?

    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.
    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

  • New paper says dinosaurs were endomorphs.

    From left to right: Endomorphic Jay Cutler, Mesomorphic Arnold Schwarzenegger, and Ectomorphic poster-child Frank Zane
    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.

    So what am I rambling on about?

    Grab a calculator and come along for the ride.

    Continue reading  Post ID 14905


  • 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.

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    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.
    Coria, R.A. and Chiappe, L.M. 2007. Embryonic skin from Late Cretaceous Sauropods (Dinosauria) of Auca Mahuevo, Patagonia, Argentina. J. Paleo. Vol.81(6):1528-1532.
    Currie, P.J., Badamgarav, D., Koppelhu, E.B. 2003. The First Late Cretaceous Footprints from the Nemegt Locality in the Gobi of Mongolia. Ichnos. Vol.10:1-12.
    Czerkas, S. A., and S. J. Czerkas. 1997. The integument and life restoration of Carnotaurus. In D. L. Wolberg and G. D. Rosenberg (eds.), Dinofest International, Proceedings of the Symposium at Arizona State University, pp. 155?158. Philadelphia Academy of Natural Sciences, Philadelphia.
    Gregg, K., Wilton, S.D., Parry, D.A., and Rogers, G.E. 1984. A Comparison of Genomic Coding Sequences for Feather and Scale Keratins: Structural and Evolutionary Implications. Embo J. Vol.3(1): 175-178.
    Lavers, C. 2000. Why Elephants Have Big Ears: Understanding Pattersn of Life on Earth. St. Martins Press. NY. ISBN: 0312269022. pg 104.
    Parks, WA. (1924). Dyoplosaurus acutosquameus, a new genus and species of armoured dinosaur; and notes on a skeleton of Prosaurolophus maximus. University of Toronto Studies, Geological Series 18, pp. 1-35
    Pinegar, R.T., Loewen, M.A., Cloward, K.C., Hunter, R.J., Weege, C.J. 2003. A Juvenile Allosaur with Preserved Integument from the Basal Morrison Formation of Central Wyoming. JVP. vol.23(3):87A-88A.
    Sawyer, R.H. and Knapp, L.W. 2003. Avian skin Development and the Evolutionary Origins of Feathers. J. Exp. Zool. (Mol Dev Evol). Vol.298B:57-72.
    Schmidt-Nielson, K. 1975. Animal Physiology Adaptation and Environment. Cambridge University Press. Cambridge. ISBN: 0521570980, 978-0521570985. pg 669.
    Shine, R., 2005. Life-History Evolution in Reptiles. Annu. Rev. Ecol. Evol. Syst. Vol.36:23-46.
    Sternberg, C.H., 1909, A new Trachodon from the Laramie beds of Converse County, Wyoming. Science, v. 29, p. 753-754.
    Sternberg, CM., 1925, Integument of Chasmosaurus belli: Canadian Field Naturalist, v.39, p. 108-110.
    Withers, P.C. 1992. Comparative Animal Physiology. Brooks Cole. ISBN: 0030128471, 978-0030128479. pg 949.

  • Two new paleo-herps illustrate the problems of a persistent reptile myth.


    v

    Titanoboa picture by the paper’s co-author: Jason Bourque

    I was trying to wait until I could nab the papers for these guys, but since Geology does not feel like updating their site, I’m going to have to move without them.

    Reported on 1st February, John Tarduno of the University of Rochester, and his team have discovered an alleged freshwater turtle fossil in the Canadian Arctic. The animal – given the gorgeous name of Aurorachelys (“Dawn turtle” or “Arctic turtle” as the case may be) – was found in strata dating back to the late Cretaceous. According to the press release (which is all I have to go on at the moment), the presence of the turtle has lead Tarduno and his colleagues to suggest the presence of an immense halocline in the paleo-arctic ocean.? According to Tarduno:

    …the Arctic Ocean was more separated from the rest of the world’s oceans at that time, reducing circulation. Numerous rivers from the adjacent continents would have poured fresh water into the sea. Since fresh water is lighter than saltwater, Tarduno thinks it may have rested on top, allowing a freshwater animal such as the aurora turtle to migrate with relative ease.

    The other major discovery came out today in Nature.? Researcher John Jason Head, and colleagues have discovered the world’s largest snake. The new snake has been dubbed: Titanoboa cerrejonensis, and it has been estimated to grow to a whopping 13 meters in length (43ft) and could have weighed as much as 1,135kg (2,500lbs).? The fact that this immense animal even existed, is amazing enough, but the researchers took their find a little further.

    Since snakes are poikilotherms that, unlike humans, need heat from their environment to power their metabolism, the researchers suggest that at the time the region would have had to be 30 to 34 degrees Celsius for the snake to have survived. Most large snakes alive today live in the South American and southeast Asian tropics, where the high temperatures allow them to grow to impressive sizes.

    This is where I have my problems. First for Aurorachelys; how are the researchers determining that this animal was a freshwater turtle? As I mentioned prior, I have not had a chance to read either of these papers yet, but just off the top of my head, I can’t think of any specific osteological trait that can be used to determine whether an animal is capable of salt-excretion (i.e. marine). Edit: See Nick’s comment for a list of papers on osteological correlates to salt excretion. This is what I get for posting something right before bed. 🙂? Are the researchers, instead, using the extant phylogenetic bracketing method (EPB), and figuring that Aurorachelys was a freshwater inhabitant, based of critters it was most closely related to?

    If it’s the latter, then I have reason to pause. Uniformitarianism, or the assumption that present day processes are likely the same now as they were in the past, is a very useful tool.? It’s especially useful in the realm of geology, where rock cycles are unlikely to have changed.? In biology, too, uniformitarianism can be helpful for studying processes like evolution and ecological partitioning. However a uniformitarian view of life is much less sturdy when dealing with more labile things like behaviour, or the evolution of a specific trait. If the researchers are assuming that Aurorachelys was a freshwater animal based off of EPB, then I would have to assume that salt excreting glands must be a hard thing to evolve. But are they? I’m not sure we have an answer there.

    Another issue this raises is, if Aurorachelys was a freshwater turtle that was cast adrift, then what are the chances that it would have been fossilized in the first place. Fossilization is a one in a million process as it is. In general, parsimony tells us that unique individuals / behaviours, are unlikely to be preserved. When we find a giant representative of a species, it probably was not unique, but rather a high end average animal. So too, it would seem, with Aurorachelys.? It is highly unlikely that this turtle was caught out of its element.? This may mean that this large halocline was present and that freshwater turtles were undertaking this migration rather often, or it means that the ability to remove excess salt from the body, was present in this species. Interestingly, a similar situation exists for the giant alligatoroid Deinosuchus. Salt excreting glands appear to be a unique adaptation of crocodyloids,? and not their alligatorish kin. Yet Deinosuchus founds some way to cross the saltwater filled Western Interior Seaway. Again, how hard is it to evolve salt removing glands?

    The case of Titanoboa cerrejonensis is much the same. In this case, it appears to be a clear case of the erroneous belief that reptiles make good ecological thermometers; despite the presence of leatherbacks (Dermochelys coriacea) in the freezing Northern Atlantic, or the small Chinese alligator (Alligator sinensis) living in a part of China that readily freeze, or even the relatively tiny Andean lizards ((Liolaemus multiformis), who live in parts of the Andes mountain range that experience an average daytime temperature of 10°C (50°F) , all while maintaining body temperatures of 35°C (95°F). Both the Aurorachelys and Titanoboa cerrejonensis papers appear to make assumptions that seem questionable given the evidence.? However I will reserve final judgement until I’ve had a chance to read the respective papers. Hopefully there is some hard evidence to back up the assertions that have been proposed.


    Photo by Ray Carson

    Photo by Ray Carson

    Until then, check out the comparison on the vertebrae of a large Eunectes murinus (green anaconda) and Titanoboa cerrejonensis. This beast was huge.

    Papers

    Head, J.J.,Bloch, J.I., Hastings, A.K., Bourque, J.R., Cadena, E.A., Herrera, F.A., Polly, D.P., Jaramillo, C.A. 2009.
         Giant Boid Snake from the Palaeocene Neotropics Reveals Hotter Past Equatorial Temperatures. Nature. Vol 457 :715-717
         doi:10.1038/nature07671
    
    Vandermark, D., Tarduno, J.A., Brinkman, D.B., Cottrell, R.D., Mason, S. 2009. New Late Cretaceous Macrobaenid Turtle with Asian
        ?Affinities from the High Canadian Arctic: Dispersal via Ice-Free Polar Routes.Stephanie Mason. Geology, Vol 37.

  • One more reason why David Attenborough is cool.

    David Attenborough doing what he does best.
    David Attenborough doing what he does best.

    For anyone who enjoys nature documentaries, Sir David Attenborough is a household name.? His team is easily responsible for some of the best nature docs ever created (e.g. Planet Earth, Blue Planet, Life in the Undergrowth and of course: Life in Cold Blood).? A stranger to retirement, the? 82 year old documentarian extraordinaire is showing no signs of slowing down.

    His latest doc is on the bicentennial anniversary of Charles Darwin’s birth.

    As I have alluded to before,? I find Attenborough and his team’s work on nature docs to be of the highest calibre partly because they don’t hide the science from the viewer. Often, Attenborough’s team works hand in hand with scientists,? which has lead to the filmmaker’s capturing information that has never before been documented by science (e.g. new species, or new behaviours). Well now there is one more neat thing to add to the list. Sir David takes no shit from creationists.

    In an article from the U.K.’s Daily Telegraph,? Attenborough talks about the hate mail that he receives from creationists,? and how he deals with it. Rather than go the brash Richard Dawkins route,? Attenborough seems to prefer a more matter of fact approach.? It’s hard to argue with the results.

    http://www.telegraph.co.uk/culture/tvandradio/4345830/Sir-David-Attenborough-I-get-hate-mail-telling-me-to-burn-in-hell-for-not-crediting-God.html

    I would be curious to see what – if any – the rebuttals to the eye-boring worm would be.

    ~ Jura – who just checked his arm for devine bot flies.