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.
In another example of slow-cooked science, this paper was the culmination of over three years worth of work collecting data on tegus. For the study, the authors looked at adult black and white tegus (Salvatore merianae). Tegus are an interesting group of lizards. They are the largest members of the family Teiidae and are often referred to as the monitor lizards of the new world, due to their convergent lifestyles (highly predaceous, active foragers). Besides their varanid-like demeanor, tegus are also known for their enormous jowls, especially in the males. The jowls hold the pterygoideus muscles, the big jaw snappers, which have been shown to increase in size for males during the breeding season (Naretto et al. 2014). As reptiles, tegus have been assumed to follow the standard ectothermic lifestyle of requiring external sources of heat to warm their bodies and maintain stable body temperatures. Looking at the natural history of the animals, tegus appear to fit the mold pretty well. They have distinctive winter and summer activity levels. In the summer, the animals regularly maintained body temperatures of 32–35°C, and in the winter they let their body temperatures drop to the temperature of their burrows (15–20°C). This is all fine and good for a bradymetabolic, ectothermic lizard, but when the researchers tracked body temperatures over time they discovered something completely unexpected.
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
Dr. Paul Sereno stands with others at a meeting for the American Association for the Advancement of Science in Chicago. Note the wheelbarrow like retroarticular processes on the "boar croc."
After spending? a few years collecting and looking at the weirdness that is Gondwanan crocodyliformes, Dr. Paul Sereno has finally started to unveil stuff. With the help of National Geographic comes When Crocs Ate Dinosaurs. It appears to be a special that focuses on the remarkable – and often underrated – diversity seen within this group of animals. The highlight of the program (at least in my opinion) is the focus on all the very un-crocodile like crocodyliformes.
The National Geographic website has a special section that shows off the various, apparently unnamed, taxa. For now, there are just placeholder names that will likely hurt the eyes and ears of anyone who had to deal with the aftermath of The Land Before Time.
The artwork is by artist Todd Marshall. I’ve always enjoyed his portrayals of prehistoric reptiles (he tends to get almost too fanciful with dewlaps and spikes though). Sadly the accompanying animations do not do Marshall’s incredible artwork justice.? It will be interesting to see how it all gets integrated into the television show.
Also airing tonight is a special on NOVA entitled: Lizard Kings. It features the work of Dr. Eric Pianka; a well known and respected lizard ecologist who has focused on monitors for much of his career.? The special looks to be very interesting. Especially given that it appears to have taken years for the film crew to get the footage they needed. As you read this the special has already aired. However, PBS does make their shows avaialable to watch online for free, on their website. The show should also be viewable on Hulu by tomorrow.
A perentie monitor (_Varanus giganteus_) poses for the camera.
I realize that both of these options are only available in the states. To date there seems to be no international options. At best there are some workarounds.
Still, for those that can get them, both shows should prove to be entertaining.
The old "cold blooded or warm blooded" argument once again rears its ugly head.
[Editor’s note: A response from the authors can be found here. It answers many of the questions I had about the paper, though I feel the biggest question remains open for debate. I appreciate the authors taking their time to answer my questions, and PLoS ONE for allowing this type of open communication.]
This post has taken an inordinate amount of time to write up. Mostly because it required finding enough free time to sit down and just type it out. So I apologize ahead of time for bringing up what is obviously old news, but I felt this paper was an important one to talk about, as it relied on a old, erroneous, but very pervasive, popular and rarely questioned hypothesis for how automatic endothermy (mammal and bird-style “warm-bloodedness”) evolved.
Back in November, a paper was published in the online journal: PLoS ONE. That paper was:
Using muscle force data for the hindlimbs of theropods, and applying it to a model based on Pontzer (2005, 2007), the authors were able to ascertain the approximate aerobic requirements needed for large bipedal theropods to move around. Their conclusion was that all but the smallest taxa had to have been automatic endotherms (i.e. warm-blooded).
Time to stop the ride and take a closer look at what is going on here.
In 2004, John Hutchinson – of the Royal Veterinary College, London UK – performed a mathematical study of bipedal running in extant taxa. He used inverse dynamics methods to estimate the amount of muscle that would be required for an animal to run bipedally. He then tested his models on extant animals (Basiliscus, Iguana, Alligator, Homo, Macropus, Eudromia, Gallus, Dromaius, Meleagris, and Struthio). The predictive capacity of his model proved to be remarkably substantial and stable (Hutchinson 2004a). A follow up paper in the same issue (Hutchinson 2004b) used this model to predict bipedal running ability in extinct taxa (Compsognathus, Coelophysis, Velociraptor, Dilophosaurus, Allosaurus, Tyrannosaurus and Dinornis). Results from this study echoed previous studies on the running ability of Tyrannosaurus rex (Hutchinson & Garcia 2002), as well as provided data on the speed and agility of other theropod taxa.
The difference between effective limb length and total limb length in the leg of Tyrannosaurus rex
Meanwhile in 2005, Herman Pontzer – of Washington University in St. Louis, Missouri – did a series of experiments to determine what was ultimately responsible for the cost of transport in animals. To put it another way: Pontzer was searching for the most expensive thing animals have to pay for in order to move around. One might intuitively assume that mass is the ultimate cost of transport. The bigger one gets, the more energy it requires to move a given unit of mass, a certain distance. However experiments on animals found the opposite to be the case. It actually turns out that being bigger makes one “cheaper” to move. So then what is going on here?
Pontzer tested a variety of options for what could be happening; from extra mass, to longer strides. In the end Pontzer found that the effective limb length of animals, was ultimately the limiting factor in their locomotion. Effective limb length differs from the entirety of the limb. Humans are unique in that our graviportal stance has us using almost our entire hindlimbs. Most animals, however, use a more crouched posture that shrinks the overall excursion distance of the hindlimb (or the forelimb). By taking this into account Pontzer was able to find the one trait that seemed to track the best with cost of transport in animals over a wide taxonomic range (essentially: arthropods – birds).
This latest study combines these two technique in order to ascertain the minimum (or approx minimum) oxygen requirements bipedal dinosaurs would need in order to walk, or run.
As with the previous papers, the biomechanical modeling and mathematics are elegant and robust. However, this paper is not without its flaws. For instance in the paper the authors mention:
We focused on bipedal species, because issues of weight distribution between fore and hindlimbs make biomechanical analysis of extinct quadrupeds more difficult and speculative.
Yet this did not stop the authors from applying their work on bipeds, to predicting the maximum oxygen consumption of quadrupedal iguanas and alligators. No justification is ever really given for why the authors chose to do this. Making things even more confusing, just a few sentences later, it is mentioned (ref #s removed to avoid confusion):
Additionally, predicting total muscle volumes solely from hindlimb data for the extant quadrupeds simply assumes that the fore and hindlimbs are acting with similar mechanical advantage, activating similar volumes of muscle to produce one Newton of GRF. This assumption is supported by force-plate studies in other quadrupeds (dogs and quadrupedal chimpanzees)
The force plate work cited is for quadrupedal mammals. However, mammals are not reptiles. As Nicholas Hotton III once mentioned (1994), what works for mammals, does not necessarily work for reptiles. This is especially so for locomotion.
In many reptiles (including the taxa used in this study) the fore and hindlimbs are subequal in length; with the hindlimbs being noticeably longer and larger. Most of the propulsive power in these reptiles comes from the hindlimbs (which have the advantage of having a large tail with which to lay their powerful leg retractor on). The result is that – unlike mammals – many reptiles are “rear wheel drive.”
The last problem is by far the largest, and ultimately proves fatal to the overall conclusions of the paper. The authors operated under the assumptions of the aerobic capacity model for the evolution of automatic endothermy.
It is here that we come to the crux of the problem, and the main subject of this post.
It’s a long (for the internet) read, so I’ll only do a few verbatim copies here. The gist of the study, by French scientist Stanislas Dehaene, is that the concept of integers (1,2,3 etc) is something that is hard wired in our brains. We have a natural ability to do rudimentary addition, and we can tell when one number is larger than another. Well, as long as the gap is large enough.
According to the article:
If you are asked to choose which of a pair of Arabic numerals?4 and 7, say?stands for the bigger number, you respond ?seven? in a split second, and one might think that any two digits could be compared in the same very brief period of time. Yet in Dehaene?s experiments, while subjects answered quickly and accurately when the digits were far apart, like 2 and 9, they slowed down when the digits were closer together, like 5 and 6. Performance also got worse as the digits grew larger: 2 and 3 were much easier to compare than 7 and 8. When Dehaene tested some of the best mathematics students at the ?cole Normale, the students were amazed to find themselves slowing down and making errors when asked whether 8 or 9 was the larger number.
…
Dehaene conjectured that, when we see numerals or hear number words, our brains automatically map them onto a number line that grows increasingly fuzzy above 3 or 4. He found that no amount of training can change this. ?It is a basic structural property of how our brains represent number, not just a lack of facility,? he told me.
This is fascinating. Especially the discovery of a “hard wired” number line (which goes right to left, apparently. See the article), which works really well up to about 4. The fascination comes not from the discovery of this in humans, but the fact that this degree of rudimentary math has been found in a wide variety of animals. The most recent being fish.
In that study, scientist found mosquito fish (Gambusia affinis) females were able to count up to four (right at the end of the number line). Also, like in human studies, the fish were able to tell which group of fish was larger, as long as the discrepancy was big enough (approximately 2:1).
Keeping with the theme of my site, the most famous example of reptilian counting would be that of varanids. Studies on the white throated monitor (Varanus albigularis), found that they can reliably count to six (King & Greene, 1999).
So it seems that the concept of math is so important that it has been hard wired in our genes for at least 400 million years.
Think about that the next time you ignore a mathematical equation.
Also, give the article a read through. It is very intriguing. It’s the closest that psychology has ever come to being a hard science, and the ramifications for education cannot be understated.
~Jura
King, D. & Green, B. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X, p. 43.
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.
Leatherbacks are already viewed as unique, but you might be surprised at just how strange this species really is. Picture from: amigosdomarnaescola.com
Continuing the series, let us now take a look at one weird turtle species in particular: Dermochelys coriacea, the leatherback sea turtle.
While the utter weirdness of D.coriacea is ultimately the main reason for why it wound up in this series, there is an ulterior motive. Having searched the internet for general information on the species I found myself rather disappointed with the amount of utterly generic / wrong info regarding leatherbacks. Its Wikipedia entry is particularly disappointing. So here’s hoping this influx of information can help alleviate that.
A turtle without a shell?
Yes, it’s true, leatherback turtles have lost their shells. Shell reduction is relatively common in turtles. It seems a little funny. After going through all the trouble of evolving impregnable armour, many taxa then went out and removed large chunks of it. We see shell reduction in snapping turtles (Chelydra and Macrochelys), soft-shelled turtles, and even other sea turtles. None of them, however, reduced their shells to the point of actually removing them.
In leatherbacks the “shell” is nothing more than a loose collection of osteoderms spread over the back and belly. There is no longer a definitive carapace, or plastron. In fact leatherbacks don’t even produce Beta-keratin (the hard component of reptile scales). Instead this has all been replaced by thick, leathery skin.
![Photo by: Jeff Werner [Fauna vol.1 number 3 Mar 98]](https://reptilis.net/index4/komodo2.jpg)
