• Category Archives Extant Reptiles
  • Articles about extant, or living reptiles

  • So, why go bipedal?

    As human beings this might come off as somewhat of a “duh” question.

    “To free our hands up, of course.”

    Ah, but like most things in life, the common sense answer is not the right one.

    Consider all the bipedal animals alive today. We have humans, obviously; kangaroos, birds, a few lemurs, and a whole swath of lizards. Of these, the “free up the forelimbs” argument really only holds true for humans, lemurs and birds. What of kangaroos and all those lizards? Exactly what does one benefit from when going bipedal?

    Do you go faster, run longer, or gain a better vantage point?

     

    C.kingii during a typical foraging run.

    All these questions were asked, and somewhat answered in a recent paper by Clemente et al.

    Clemente, C.J., Withers, P.C., Thompson, G., Lloyd, D. 2008. Why Go Bipedal? Locomotion and Morphology in Australian Agamid Lizards.J. Exp. Bio. 211: 2058-2065

    Abstract:

    Bipedal locomotion by lizards has previously been considered to provide a locomotory advantage. We examined this premise for a group of quadrupedal Australian agamid lizards, which vary in the extent to which they will become bipedal. The percentage of strides that each species ran bipedally, recorded using high speed video cameras, was positively related to body size and the proximity of the body centre of mass to the hip, and negatively related to running endurance. Speed was not higher for bipedal strides, compared with quadrupedal strides, in any of the four species, but acceleration during bipedal strides was significantly higher in three of four species. Furthermore, a distinct threshold between quadrupedal and bipedal strides, was more evident for acceleration than speed, with a threshold in acceleration above which strides became bipedal. We calculated these thresholds using probit analysis, and compared these to the predicted threshold based on the model of Aerts et al. Although there was a general agreement in order, the acceleration thresholds for lizards were often lower than that predicted by the model. We suggest that bipedalism, in Australian agamid lizards, may have evolved as a simple consequence of acceleration, and does not confer any locomotory advantage for increasing speed or endurance. However, both behavioural and threshold data suggest that some lizards actively attempt to run bipedally, implying some unknown advantage to bipedal locomotion.

    The conclusions reached, were interesting and quite unexpected.

    I’d say the most surprising part would have to be the discovery that both endurance and speed were found to be inconsequential. Those were the two forces that I figured would have driven the push towards bipedalism. Apparently this is not the case.

    In fact, the only correlate that the authors found was that a switch to bipedalism resulted in an increase in acceleration. Short of that, the authors viewed bipedalism as more of a side effect of speedy locomotion, rather than anything else.

    As one authour put it: “The lizards were pulling a wheelie.”

    There are some gripes (niggles if you will) with the paper. For one, the authors assert that a switch to bipedalism allowed birds to incorporate their forelimbs into wing design. While being bipedal certainly allowed for this, it could not have been the cause. Birds descended from dinosaurs, and very, very very few dinosaurs had wings. Theropods were sporting freed forelimbs for some 80 million years, or so (probably longer given the proposed ancestors of dinosaurs). Wings were not the cause, simply a benefit. Something else had to have spurred the evolution of bipedality.

    Side note: What the heck were theropods doing with those forelimbs anyway? Most paleo artists tend to draw theropods with their arms tucked to the side, yet work by Carpenter (2002) has shown that there was some considerable range of motion in theropod forelimbs. They weren’t brachiating from tree to tree, or anything, but they could certainly do a heckuvalot more than just tuck their arms to the side. Even T.rex with its embarrassingly short forearms, had a surprisingly large range of motion to them. So what’s up paleo art guys? Let’s see some theropods putting their arms to use.

    The largest SNAFU in the paper comes from the cladogram that the authors chose. They chose to go with the broken molecular tree used by Townsend et al, which asserts that Iguanians are actually Scleroglossan lizards. This might sit all fine and well when looking at molecules, but it utterly falls apart upon a morphological assessment. In order for Iguanians to fit in the Scleroglossan family tree, they had to have undergone a tonne of morphological reversals, including the re-softening of the tongue and the re-evolution of both postorbital bars (surprisingly, the latter is actually not out of the realm of impossibility as tuataras have apparently done just that).

    Due to this tree choice, the authors erroneously concluded that bipedalism evolved only once in the lacertilian tree and was lost a multitude of times, with a putative re-acquirement in varanids.

    Another minor complaint comes from the very slight use of Chlamydosaurus kingii; the only lizard known to be a “true” biped (see: Shine & Lambeck 1989). Given that the authors were trying to spot differences between bipeds and quadrupeds, I can understand the use of lizards like Ctenophorus, with their greater spectrum of gaits. However, in doing so they should have qualified their conclusions better in regards to how lizards obtain a bipedal stance. In Chlamydosaurus, bipedal trotting is attained from a standing start. Quadrupedal stance is only seen when stopping to eat. Furthermore, foraging runs and escape runs use two different gaits, with the latter gait more akin to that of other facultatively bipedal lizards. Judging from the stats given in the paper, it seems apparent that the C.kingii used in this study were mostly running away.

    The final complaint comes from the supplementary movies given.

    Frankly the movies are just too short. I have to go super slow-mo just to see anything. So that’s a bummer.

    Overall the paper is rather good. The authors discovered that Lophognathus gilberti runs bipedally 85% of the time. This suggests that C.kingii is not the only truly bipedal lizard out there.

    The authors also observed that, despite any advantage in speed, or endurance, some lizards intentionally push their center of mass towards their hips early on in the running phase in order to more quickly obtain a bipedal gait. The reasons behind this are unclear, but do suggest that bipedalism confers some advantage not discovered during this experiment.

    One advantage alluded to, but never really elaborated on, was the faster acceleration noted in bipeds. Though maximum speed was no different than in a quadruped, this speed was obtained faster. Ecologically I could see this being very advantageous. When one is trying to avoid a predator, maximum top speed is probably less important than reaching that top speed as fast as possible.

    If one lizard has a top speed of 12km/hr and another has a top speed of 8km/hr, and the goal (burrow) is only 50 meters away, then that extra speed isn’t going to mean much. Especially if the slower lizard is able to hit its top speed faster.

    Apparently lizards “pull a wheelie” because in their ecosystem it pays to be a drag racer, rather than a Daytona 500 car.

    ~Jura

    References

    Carpenter, K. 2002. Forelimb Biomechanics of Nonavian Theropod Dinosaurs in Predation. Concepts of Functional Engineering and Constructional Morphology. Vol. 82(1): 59-76.

    Shine, R., & Lambeck, R. 1989. Ecology of Frillneck Lizards, Chlamydosaurus kingii (Agamidae), in Tropical Australia. Aust. Wildl. res. Vol. 16: 491-500.

    Townsend T, Larson A, Louis E, Macey JR. 2004. Molecular Phylogenetics of Squamata: The Position of Snakes, Amphisbaenians, and Dibamids, and the Root of the Squamate Tree. Syst Biol. Vol. 53(5):735-57.


  • Lizards prove evolution can happen rapidly.

    I’m a little behind on this now 3 day old story. It’s been hard to get back into the proverbial swing of things. I believe part of it has to do with the large dearth of nothing that occurred during my “vacation.” The other part probably has to do with being bloody busy. >:)

    Here’s the story.

    And here’s a brief excerpt:

    In 1971, scientists transplanted five adult pairs of the reptiles from their original island home in Pod Kopiste to the tiny neighboring island of Pod Mrcaru, both in the south Adriatic Sea.

    After scientists transplanted the reptiles, the Croatian War of Independence erupted, ending in the mid-1990s. The researchers couldn’t get back to island because of the war, Irschick said.

    The transplanted lizards adapted to their new environment in ways that expedited their evolution physically, Irschick explained.

    The big and most interesting part of this story is how these amazing little saurians evolved new behaviours, a majour change in diet and they evolved a new physical characteristic (cecal valves in the intestine).

    All of this happened in only 36 years!


    Italian wall lizard

    Podarcis sicula; a representative of the species used in the study. Also, a bit of a show-off.

    That’s not just amazing, it’s bloody phenomenal!

    Prior to this study, the only thing that even came close (in tetrapods) was an “earlier” study by Jonathan Losos on Caribbean Anolis. In one study, Losos found rapid evolution of longer hindlimbs in introduced species of Anolis in as little as 14 years. The results were interesting, but were more a case of an amazing case of Natural Selection changing the frequency of a naturally occurring variation. This latest study is a little different. The kind of changes noticed here are normally the ones talked about in insects, or bacteria (i.e. large phenotypic changes).

    It has been argued by some that this finding might be viewed as more fuel for the nutty creationist movement. Proving that evolution can occur quickly, means that creationists can argue better for a Young Earth. However, since the core tenet of creationism is that life does not evolve, this would do quite the opposite for them.

    What this does bolster evidence for is Gould and Eldredge’s theory of Punctuated Equilibria.

    The theory states that most of the time, populations of organisms remain fixed and stable, with very little evolution occurring. Then, when a portion of the population gets segregated and/or are forced to adapt to a different environment, evolution kicks into high gear. Change happens rapidly, and the new population becomes a new species.

    That was a bit simplified, but you get the point.

    Gould and Eldredge used fossil trilobites to support their case. Studies on plants and insects have also shown that this type of speedy evolution can happen. Now we have proof in a relatively large vertebrate as well.

    I think these kinds of observations are good for the biological and paleontological sciences. I think that there is a tendency for paleontologists to “ride the brake” with evolution. Always insisting on measuring evolutionary change in millions and tens of millions of years. I don’t have a problem with this type of thinking when one is looking at changes in whole families and genera, but it seems very unlikely that many of the species seen in the fossil record were evolving so slowly from species to species (e.g. Tyrannosaurs, or mosasaurs). Showing that speedy evolution does happen, helps to better support a more “punctuated” view of evolution. One in which whole genera can arise in as little as a few thousand (or hundred thousand) years.

    Geologically speaking; that’s pretty damned fast.

    ~Jura



    Herrel A, Huyghe K, Vanhooydonck B, Backeljau T, Breugelmans K, Grbac I, Van Damme R, Irschick DJ. (2008) Rapid large-scale evolutionary divergence in morphology and performance associated with exploitation of a different dietary resource. Proc Natl Acad Sci U S A. 105(12):4792-4795.


  • Amazing acrobatic geckos


    wall runner

    High speed pictures of Cosymbotus platyurus running up a vertical surface

    I don’t know why, but for some reason herp news stories always seem to come in twos.

    Announced today (or yesterday by the time I get this posted), scientists at UC Berkeley have found geckos to be one of the most agile climbing animals ever studied.

    Jusufi, A., Goldman, D.I., Revzen, S. and Full, R.J. 2008. Active tails enhance arboreal acrobatics in geckos. PNAS. Vol. 105: 4215-4219.

    Goldman et al studied geckos of the species Cosymbotus platyurus. Lizards were ran on vertical surfaces that had various degrees of traction. To induce slippage, some of the surfaces were equipped with a section of dry erase board which had been covered with dry erase ink.

    Apparently geckos can’t grab onto everything after all.

    By placing the lizards at various sections of these surfaces, the researchers were able to get them to either slightly slip, almost fall, or completely.

    The results were interesting.

    For starters, lizards ran up the surfaces with their tails off the “ground” the entire time. That is, unless they slipped. Immediately upon slipping, the tail would come down and act as a brace to keep the body from tilting back and falling off. The most dramatic case of this came from an experiment in which the researchers had dropped the lizards down straight on the dry erase board. The gecko in question fell backward, caught itself with its hindlegs, and tail. The body fell away from the wall about 60? before the tail fully caught the animal, and it was able to right itself again (see photo above).
    self righting gecko
    By far the neatest test performed involved getting the lizards and placing them in a supine (belly up) position on a light polyethylene foil held together with four fishing lines. Then by gently shaking the platform (or waiting for the lizards to slip), they were able to dislodge the geckos and send them plummeting to their doom.

    Doom, in this case, being an embellishment for safely padded landing area.

    The lizards fell 2 meters down. High speed cameras recorded the first 23cm of that trip. These little guys were able to go from fully upside down to rightside up in only 106 milliseconds.

    Let me make sure I’m getting the full effect of that result across:

    These geckos were able to reorient themselves in 106 THOUSANDTHS of a second, or .00106 seconds!!

    Geckos now hold the record for fasting righting time of a vertebrate without the aid of wings.

    This unique feat is accomplished by rotating the substantial tail on these animals. As they fall, the tail is rotated counterclockwise. Physics does the rest. Conservation of angular momentum takes over and the entire body winds up turning clockwise, thus reorienting the animal. This phenomenon is known as: air righting with zero angular momentum. It’s the same effect that cats are often lauded for.

    Cats, and other air righting mammals (e.g. rats) accomplish their air righting maneuvers by flexing and twisting their backs. Evolution removed the need/use for a large powerful tail in mammals, hundreds of millions of years ago.

    No so with lizards. Thanks to this “fifth appendage” all the geckos needed to do was use their tail like a little propeller. There is, however, a caveat.

    Cosymbotus platyurus, like most geckos, is capable of caudal autotomy (i.e. voluntary tail loss). Would lizards that have lost their tails still be able to right themselves?

    Jusufi et al tested this scenario too. They carefully elicited the loss of the tails in some of their experimental animals, and then subjected them to the same tests as before. The results were striking. Tailless lizards were unable to keep themselves from falling in the vertical slip tests. When they were dropped supine, they still righted themselves, but the rate at which they did it was much slower. Tailless geckos relied on the kind of back flexion and twisting seen in mammals.

    Taking things one step further, the authours decided to see how much of a role the tail plays during free fall. They placed the lizards in vertically oriented wind tunnels and “set them free.” The results were unequivocal; the tail acts as the main rudder in these guys. Geckos would rotate their tails counterclockwise to turn left, and clockwise to turn right, while the body remained a stationary airfoil.

    The overall results demonstrated the incredible importance of tails in geckos. This is interesting given that so many geckos are also willing to part with their tails when in danger.

    It seems that in the natural world it’s better to risk knocking oneself out from a fall, than to risk getting eaten by a bodypart that stubbornly stays on.
    It’s unfortunate that the researchers didn’t test the air-righting ability of these geckos after their tails had grown back. Judging from the videos it appears that all the work is being generated by the proximal tail muscles; which stay even after autotomy. Theoretically then, it should still work in a regrown tail.

    Oh yeah, did I forget to mention, Jusufi et al not only recorded everything, but they made them available for everyone to watch.

    They’re all worth watching. It’s cool to see just how fast these little geckos are.

    And so the “slow, sluggish reptile” stereotype, receives yet another nail in its coffin.

    ~Jura


  • Bow down to the warrior croc _Guarinisuchus munizi_

    Recently published in Proceedings of the Royal Society B, scientists in Brazil have found the remains of a prehistoric crocodyliforme that used to roam the oceans of the Paleocene.

    The critter has been given the name: Guarinisuchus munizi, which translates out to: Muniz’s warrior crocodile. Despite the “crocodile” in its name, G.munizi was not that closely related to true crocodylians. It was more closely related to the giant pholidosaur Sarcosuchus imperator.

    Guarinisuchus muniziSarcosuchus


    Close relative of Guarinisuchus munizi [left] was Sarcosuchus imperator [right]. Not true crocodiles.

    The neat thing about the paper, was not so much the crocodyliforme itself. At 3 meters, G.munizi was small for a dyrosaurid. Rather, it is the implications of this find that are intriguing.

    Dyrosaurids first appeared in the Late Cretaceous Period (Maastrichtian age) . During this time they were very scarce, and hard to find. They were shallow marine predators, and in the Cretaceous that niche was already filled by another group of animals: the mosasaurs.

    These ancient sea lizards had one of the fastest diversification rates of any vertebrate group studied. They went from nothing to dozens of species with a cosmopolitan distribution and domination of many ecological niches. All of this occurred in the space of only 25 million years! That’s faster than mammal diversification, and faster than dinosaur diversification.

    Mosasaurs were showing no signs of slowing down right up to the K/T asteroid event. After that, they disappeared.

    That’s when the dyrosaurids started taking over.

    Analysis of Guarinisuchus munizi material has found that it is more closely related to African taxa than its geographically closer relatives in North America. This suggests that dyrosaurids had crossed the Atlantic ocean from Africa sometime before the K/T event. After said event, the vacant niches left by the mosasaurs were quickly snatched up by these dyrosaurids, as they moved up North, and eventually, worldwide.

    It is interesting to see how this group of animals was apparently held back during their earlier evolution. Yet, if they hadn’t been held back; if they had out-competed mosasaurs for the top spot in the food chain, then they wouldn’t have survived the K/T event.

    It’s funny – and completely make believe – but it almost appears as if dyrosaurids were already setting themselves up to take over. It’s almost as if they knew…

    They didn’t of course, but it’s fun to pretend that they did. >:)

    ~Jura


  • Bloody slow.

    It has been a painfully slow week in terms of herpetology and paleo. I’ve noticed that when I tend to talk about things being slow, there is usually a sudden surge in topics. Here’s hoping that will happen this time too.

    Until then, let’s all congratulate Chrysemys picta bellii for becoming Colorado’s official state reptile.

    More soon (hopefully)

    ~Jura


  • Update on Gharial plight.

    Astute observers may remember the news story about the mysterious death of gharials in the Yamuna river.

    A recent report by the National Geographic Society suggests the the culprit is the food being fed to these animals.

    They suggested that as the fish moved from polluted rivers into the Chambal, they ingested chemicals in their tissues. When the gharials eat the fish, these harmful substances pass into their systems.

    One of the international vets who has been working on the case, Paolo Martelli, explained to the publication: “When cold temperatures came, the uric acid precipitated [separated into a fine suspension of solid particles] and began causing problems.

    “So winter coupled with excess food could have made the gharials more susceptible to the toxin.”

    One step closer, and none too soon either. 110 animals have died from this poisoning. Given that the wild population is estimated at 200, or less individuals this was a setback that these animals could not afford.


  • Alligators can shift their lungs and lizard ecology determines movement.

    There were two new papers released today in the Journal of Experimental Biology.

    The first one is the biggest, as it received a news story.


    Uriona, T.J., and Farmer, C.G. 2008. Recruitment of the diaphragmaticus, ischiopubis and other respiratory muscles to control pitch and roll in the American alligator (Alligator mississippiensis). J. Exp. Biol. Vol. 211: 1141-1147 doi: 10.1242/jeb.015339

    Abstract

    We used electromyography on juvenile American alligators to test the hypothesis that the following muscles, which are known to play a role in respiration, are recruited for aquatic locomotion: M. diaphragmaticus, M. ischiopubis, M. rectus abdominis, M. intercostalis internus, and the M. transversus abdominis. We found no activity with locomotion in the transversus. The diaphragmaticus, ischiopubis, rectus abdominis and internal intercostals were active when the animals executed a head-down dive from a horizontal posture. Weights attached to the base of the tail resulted in greater electrical activity of diaphragmaticus, ischiopubis and rectus muscles than when weights were attached to the head, supporting a role of this musculature in locomotion. The diaphragmaticus and rectus abdominis were active unilaterally with rolling maneuvers. Although the function of these muscles in locomotion has previously been unrecognized, these data raise the possibility that the locomotor function arose when Crocodylomorpha assumed a semi-aquatic existence and that the musculoskeletal complex was secondarily recruited to supplement ventilation.

    Scientists at the University of Utah have discovered the unique internal subtleties that allow crocodylians to sink, rise, pitch and roll; all without disturbing the water (much). It turns out that the main muscles used for breathing, are also used to actually shift the lungs within the body!

    That’s just crazy awesome. Uriona & Farmer’s work raises the question of how prevalent this ability is in other semi-aquatic animals (e.g. seals, terrapins, manatees). By shifting the lungs further back in the body, crocodylians are able to change their local density. This allows the front, or back of the animal to rise and sink separately from the rest of the body. So too does moving the lungs from side to side allow for rolling in the water. All of this can occur without the need to move any external body parts. This means no extra turbulence gets created in the water, thus allowing crocodylians to better sneak up on their fishy, or fleshy prey.




    Baby crocodiles exhibiting their unique pulmonary powers.

    If anything, it sure speaks to why crocodyliformes have held dominion over the semi-aquatic niche for over 200 million years. Uriona and Farmer do suggest that the ability of these respiratory muscles to do this might not be an exaptation. Rather, this might have been the initial impetus behind the evolution of these muscles. Only later would they have been exapted to help with breathing on land. Though the authours provide some good parsimonious reasons for why this may be (basically it would take less evolutionary steps to accomplish than the other way around), it doesn’t really jive with the fossil evidence. Part of the reason why the crocodylian diaphragm works, is because the pubis (the forepart of the hip bone in most animals, and the part that juts out so prominently in theropod dinosaurs), is mobile. This mobility occurred early on in crocodyliforme evolution, with the crocodylomorph Protosuchus having a pubis that was almost mobile. The problem arises when one looks at this early crocodylomorph. Protosuchus was obviously terrestrial. If Protosuchus was evolving a mobile pubis already, then it was doubtful that it was being used to allow lung shifting in the body (an ability that is helpful when underwater, but pretty pointless on land). Furthermore, Crocodylia proper is the umpteenth time that crocodyliformes have returned to a semi-aquatic existence. It is doubtful that all the numerous land outings that occurred during crocodyliforme evolution, would have retained the ability to move the lungs to and fro. It seems far more likely that this was an ability that evolved in Crocodylia, or somewhere close by on the evolutionary tree, in some taxa that was still semi-aquatic.


    Protosuchus

    Protosuchus richardsoni. An example of an early crocodylomorph.

    Of course it is also possible that crocodyliforme phylogeny is just all f-ed up. With the amount of convergence rampant in that lot, this remains a distinct possibility.

    Either way this is a cool discovery, and one worthy of adding to the crocodylian pages.

    The second paper also comes from the Journal of Experimental Biology. This one involves lizards.


    McElroy, E.J., Hickey, K.L., Reilly, S.M. 2008. The correlated evolution of biomechanics, gait and foraging mode in lizards. J. Exp. Biol. Vol. 211: 1029-1040. doi: 10.1242/jeb.015503

    Abstract

    Foraging mode has molded the evolution of many aspects of lizard biology. From a basic sit-and-wait sprinting feeding strategy, several lizard groups have evolved a wide foraging strategy, slowly moving through the environment using their highly developed chemosensory systems to locate prey. We studied locomotor performance, whole-body mechanics and gaits in a phylogenetic array of lizards that use sit-and-wait and wide-foraging strategies to contrast the functional differences associated with the need for speed vs slow continuous movement during foraging. Using multivariate and phylogenetic comparative analyses we tested for patterns of covariation in gaits and locomotor mechanics in relation to foraging mode. Sit-and-wait species used only fast speeds and trotting gaits coupled with running (bouncing) mechanics. Different wide-foraging species independently evolved slower locomotion with walking (vaulting) mechanics coupled with several different walking gaits, some of which have evolved several times. Most wide foragers retain the running mechanics with trotting gaits observed in sit-and-wait lizards, but some wide foragers have evolved very slow (high duty factor) running mechanics. In addition, three evolutionary reversals back to sit-and-wait foraging are coupled with the loss of walking mechanics. These findings provide strong evidence that foraging mode drives the evolution of biomechanics and gaits in lizards and that there are several ways to evolve slower locomotion. In addition, the different gaits used to walk slowly appear to match the ecological and behavioral challenges of the species that use them. Trotting appears to be a functionally stable strategy in lizards not necessarily related to whole-body mechanics or speed.

    I haven’t had a chance to read much more than what was written already. I do take a bit of offense to the authours referring to scleroglossan foraging technique as “slow,” but what are you going to do?

    I do find it interesting that lizards seem to have lost the ability to “walk” numerous times. That almost seems bizarre. The study points out that ecology produces heavy pressures on lizards in terms of their locomotion type. This is extremely pertinent given how often one hears the old (and wrong!) adage about “reptiles” being incapable of intense aerobic activity.

    According to the above study (among others), it all depends on the animals being tested.

    There we go. Two really cool papers on reptiles, being released in one day.

    ~Jura

    Yes, I know. I used jive. I’m sorry.


  • Tuataras do it faster than anyone else.

    Oh yeah, that’s right. You know what I mean.

    This is what we call: subtext

    They evolve…at the molecular level.

    From: Trends in Genetics


    Hay, J., Subramanian, S., Millar, C.D., Mohandesan, E., Lambert, D.M. Rapid molecular evolution in a living fossil. Trends in Genetics
    Vol. 24 (3): 106-109

    Abstract
    The tuatara of New Zealand is a unique reptile that coexisted with dinosaurs and has changed little morphologically from its Cretaceous relatives. Tuatara have very slow metabolic and growth rates, long generation times and slow rates of reproduction. This suggests that the species is likely to exhibit a very slow rate of molecular evolution. Our analysis of ancient and modern tuatara DNA shows that, surprisingly, tuatara have the highest rate of molecular change recorded in vertebrates. Our work also suggests that rates of neutral molecular and phenotypic evolution are decoupled.


    Okay, so what does all that mean? It’s been well established that creatures evolve at rates proportional to their generation times. Animals that have a higher generational turn over, show higher rates of evolution. It’s a simple numbers game. The more offspring one has, the more chances for there to be a beneficial mutation. The shorter the time from birth to reproduction, the faster natural selection can act on these mutations.

    Hence why elephants are not exactly evolutionary racehorses, while insects rule the world. 🙂

    It’s been thought that evolution at the molecular level should mirror what we see on the phenotypic, or morphological level. It makes sense logically. There has to be some connection between molecular evolution and phenotypic evolution. We know that the former gives rise to the latter.

    So if one has a creature that has a short fossil history, or a particularly diverse one, then it suggests it is a fast evolver. Therefore one would expect to see speedy evolution on the molecular level too. This is one of the latest lines of evidence for automatic endothermy (i.e. warm-bloodedness) in dinosaurs and other fossil critters (don’t ask how we have molecular evidence for extinct animals. I just don’t know).

    This latest discovery throws a whole wrench into that mode of thinking. Tuataras (Sphenodon) are one of the slowest animals on the planet. They take a long time to reach sexual maturity (11-13 years). They are commonly referred to as living fossils (though, that really isn’t right). They are the last critter that one would expect to be an evolutionary Speedy Gonzalez.

    Yet, according to the work by Hay et al, that is exactly what has been discovered. Tuataras edge out all other animals studied so far. The closest any other creature comes, is the Ad?lie penguin (Pygoscelis adeliae) of Antarctica. Yet as the graph below shows:

    Tuatara evolution rate

    Tuataras are still significantly faster at their molecular evolution. So then, what does this mean regarding molecular evolution rates vs. morphological ones?

    That’s a good question. The argument of molecular phylogeny vs. morphology, is already a heated one. Morphologists scoff at molecular systematists, while the molecular systematists think morphological phylogeny is pointless since it’s all DNA based anyway. It doesn’t help that molecular data has repeatedly come up with results that fly in the face of morphological based orthodoxy.

    For example:

    Morphologically, tuataras are the sister group to squamates.

    Molecularally, tuataras have been found to nest with crocodiles and birds, in at least one study.

    Molecular systematists have found the false gharial (Tomistoma schlegelli) to nest with the true gharial (Gavialis gangeticus), while morphologists have consistently found T.schlegelli) to be a convergent animal more closely related to true crocodiles. This has resulted in heated back and forth arguments

    Turtles, whose ancestry is still very nebulous, have been found to be anywhere from the base of the diapsid family tree (making them ancestral to all extant reptiles), to offshoots of pareiasaurs, which would place them as offshoots from the main reptile line (basically throwing another 30-50 million years on their divergence from other reptiles).

    Molecular systematics, on the other hand, has found turtles to nest with archosaurs (crocs and birds). A few times (beware: PDF bomb), despite the lack of morphological correlates.

    And then there was just weird stuff during the early days of molecular studies, that didn’t help with its validity problem.

    So both camps are already very skeptical of the other’s findings.

    Now this study suggests that rates of molecular evolution have no relation to morphological rates. Among other things, this seems to make the whole “molecular clock” idea even less tenuous.

    It should be interesting to see what repercussions come from this study.

    ~Jura


  • Life in Cold Blood causes sale surge.

    From UKPets.co.uk, we have this interesting bit of news:

    Life In Cold Blood Sells Reptiles
    According to the UK pet store chain, Pets at Home, more people than ever are interested in owning a reptile as a pet, thanks to BBC’s Life in Cold Blood series. The company reports that sales of Fire-bellied Newts and Albino Clawed Frogs have more than doubled in some stores.

    Following the debut of the Sir David Attenborough series on 3rd February, and its second instalment[sic] the following week, Pets at Home received a surge of enquiries from customers regarding keeping reptiles and amphibians as pets.

    Follow the link for more. I think that this is just awesome that a documentary can spark the public’s interest this much. it will be interesting to see if an effect similar to this will be seen when the series hits U.S. shores.

    Till then, I wait…and remind folks that while the interest in owning a reptile as a pet is great; do make sure that you have done your homework on the particular species that you are interested in maintaining. After all, we are talking about living beings here; not toys.

    ~Jura


  • Owen and Mzee

    Owen and Mzee

    Though their’s is an old story, it’s so unique that I felt it deserved mentioning on my site at least once.Plus it was recently dugg, so I felt a need to respond.

    For those who don’t know the story; back in 2004 during the infamous tsunami disaster, a baby hippo was found stranded on a little piece of land out from the coast of Kenya. The baby hippo, Owen (named after one of the rescuers), was brought to Haller Park near Mombasa. There, the frightened hippo ran from its caretakers and hid by an old, crotchety aldabra tortoise (Geochelone gigantea) named Mzee (MIZ-ZAY). At first, Mzee wanted nothing to do with Owen, but the little (relatively speaking) hippo wouldn’t leave him alone. Eventually he grew to tolerate Owen’s constant harassment.

    Then something wonderous happened. Mzee and Owen became friends. Owen would follow Mzee around everywhere. They would eat together, bathe together, and sleep together. Mzee (the tortoise) invented a way of speaking to Owen. When Mzee wanted to go somewhere, he would gently nibble the tail of Owen. Soon Owen caught on and would do the same, when he wanted to go somewhere. It was an awesome spectacle to behold. This was completely different from what we see with, say, humans and their pet dogs, or cats. It was also different from the agricultural relationship between humans and livestock, or ants and aphids. This was a case of a genuine friendship between two very different animals (separated by over 300 million years of evolution!).

    Owen and Mzee had even developed their own way of talking to each other. They were also very protective. Neither would passively allow a human keeper to get near the other. It was and is one of the most heartwarming, and amazing things to ever be observed in the natural world.

    In 2006, a children’s book was released, documenting the story. Owen and Mzee became world famous, with visitors wanting to see the dynamic duo in person.

    Back in 2007, it was decided that Owen needed to make friends with other hippos. His relationship with Mzee resulted in Owen acting more, and more like a giant tortoise (a hilarious sight to behold). Unfortunately, the friend that they chose for Owen (a female named: Cleo), was too much of a rough houser with the giant tortoises, so they had to separate Owen and Mzee. It’s hard to say if either animal suffered any heartbreak from this separation (I haven’t read any mention of it anywhere). I also don’t know if the two guys are sharing adjacent enclosures, so they might be able to still hang out.

    Nonetheless, the story of Owen and Mzee is one that will live in infamy. An amazing case of inter-special friendship between a mammal and a reptile that, prior to this, no one probably ever thought was possible.

    It’s amazing, and it’s all completely documented on their official site: OwenandMzee.com Make sure to watch the documentary. It’s a heartstring puller.

    ~Jura