The site has been pretty slow for the past couple of months as academic life has eaten up a lot of my free time. That should change in a few weeks (and I do have a doozy of a post I have been working on).
Whether, or not the crocodile meant to try this, or if this was an accidental predation attempt remains unknown. While this might be the first time this was caught on film, it is not the only account of this. Nile crocs have been known to attempt to take down large elephants by grabbing onto their trunks. The initial attack is almost always unsuccessful, but if the croc winds up doing enough damage it can result in the elephant dying days later (as a broken trunk pretty much limits all access to food). Not sure if the crocs ever benefit from this, but the fact that they can kill large adults is enough to make them a formidable threat to any thirsty elephant.
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.
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.
Two new papers have recently hit the journal circuit. Both of them involve using living crocodylians to gain a better understanding of paleo-life.
The first one comes from Denver Museum of Natural History paleontologist, Dr. Kenneth Carpenter:
Carpenter, K. 2009. Role of Lateral Body Bending in Crocodylian Track Making. Ichnos. Vol.16:202-207. doi:10.1080/10420940802686137.
The study used an adult Caiman sclerops (first use of a large adult reptile for a locomotion study; at least as far as I know) placed in a small room with two 30cm walls placed on either side of it. This restricted any lateral movement, and “funneled” the animal out the singular opening. At this opening, a camera was placed. It would photograph the animal as it left the room. The room itself, had a smoothed mud covering. This muddy floor would record the tracks of the C.sclerops as it walked by.? Several runs were done, and photographs were taken for each run.
This is the first study I have seen that gave a front view shot of an adult crocodylian as it walked along. As Carpenter mentioned in the paper:
This front view is in contrast to most photographic studies which only capture pro?le and top views….
Carpenter also mentioned the potential of there being an ontogenetic change in limb stance as animals move from hatchling to adult. This is something that I have hinted at previously Hatchling crocodylians seem to have weaker femoral adductors than adults. This is understandable given the greater weight that adult femora need to bear. This can result in a skewed view of crocodylian erect stance; with most authors tending to underestimate the degree of “parasagittality.”
That said, I was surprised to read that Carpenter had found the adult Caiman sclerops to have a hip adduction angle of approximately 65? from the horizontal. Judging from figure1B, the hindlimb appears to be much closer to the midline than the forelimb. Fig1D seems even closer to, if not 90?. It is important to point out that much of the hindlimb is blocked by the body in this shot, as the animal is fully laterally extended. A concurrent shot from behind would have been very useful here; as would an x-ray series of shots throughout the walk phase (for instance: see this long video of a Crocodylus acutus walk cycle. Pay special attention to the position of the femur).
Alas, that is not what the paper is about.
The paper is about how lateral movements during locomotion, have substantial effect on trackways. Dr. Carpenter points out how, despite the semi-erect stance of the forelimbs, the track evidence would suggest an animal with a much narrower (parasagittal?) stance. This has bearing on how prehistoric reptiles, in particular: quadrupedal dinosaurs, may have stood.
One might rightfully ask if we should expect dinosaurs to have had any lateral movement to their walking cycle at all. Carpenter points out that lateral body bending, though not quite as exaggerated as that of crocs, is present in most tetrapods. Birds seem to be the sole exception, with their extremely stiff thorax. However birds are also obligate bipeds, and the avian thorax is much shorter and stiffer than that of dinosaurs.
So it would seem to be a likely bet that quadrupedal dinosaurs likely exhibited some degree of lateral body bending.
Carpenter’s work rightfully asks us to caution reconstructions of stance based largely off of trackway evidence. A fine case study that the paper brings up, is ceratopians. This group, more than any other, has received considerable attention for how the forelimbs were oriented. Early work on ceratopians, favoured a hefty sprawl to the forelimbs (e.g.? Gilmore 1905, or Lull 1933). This was critically evaluated during the heyday of the dinosaur renaissance. Authors such as Bakker (1986), Paul and Christiansen (2000), instead favoured a fully erect stance. A large portion of the data supporting this assertion, was trackway based. The results of this study call into question that view. However this was not the first paper to have done so. Thompson and Holmes (2007) also questioned the “erect ceratopid” view, using a half scale model of a Chasmosaurus irvinensis forelimb. Their results come closer to the results from this paper. Though Thompson and Holmes felt that there was no real modern analogue to ceratopian forelimb mechanics.
In the end, Dr. Carpenter reminds future researchers of the importance in incorporating the entire animal when analyzing trackways.
The second paper comes from the Journal of Experimental Biology.
Owerkowicz, T., elsey, R.M. and Hicks, J.W. 2009. Atmopsheric Oxygen Level Affects Growth Trajectory, Cardiopulmonary Allometery and Metabolic Rate in the American Alligator (Alligator mississippiensis). J.Exp.Biol. Vol.212:1237-1247. doi:10.1242jeb.023945.
The authors embarked on a study of how previous paleo-atmospheric oxygen levels might have affected the lives of animals that would have been alive through these times. According to Owerkowicz et al, crocodylians were chosen because:
Given their phylogenetic position and highly conserved morphology throughout their evolutionary history, crocodilians are often thought to retain many characteristics of basal archosaurs.
I do take some issue with this, as prior reviews on crocodylomorph diversity (Naish 2001) coupled with many new discoveries ( Buckley et al 2000,? Clark et al 2004, Nobre & Carvalho 2006)? continually cast doubt on the old view that crocodylians have survived “unchanged” for some 200 million years. Nevertheless, the results of the study are both interesting, and relevant to reconstructions of how paleo-life would have adapted to these wildly different paleo-atmospheres.
Owerkowicz et al raised groups of hatchling American alligators (Alligator mississippiensis) under three different atmospheric conditions. A hypoxic (12% O2) condition reminiscent of paleo-atmospheric models for the late Triassic/Early Jurassic periods. Current atmospheric conditions (21% O2), and a hyperoxic (30% O2) condition reminiscent of paleo-atmospheric models for the Carboniferous and Permian periods.
The results were interesting, though not too surprising. As expected, hypoxic alligator hatchlings were smaller than their normal and hyperoxic counterparts. However, the degree of growth stunting is pretty surprising. Hypoxic hatchlings were about 12% shorter and 17% smaller than normal hatchlings.
Surprisingly, hatching time did not change under any conditions. This suggests a degree of “hard wired” embryological development inside the egg. In the case of the hypoxic hatchlings, they came out “almost done.” While all three groups had remnants of a yolk sac upon hatching, the hypoxic hatchlings actually had the yolk sac still protruding (normal and hyperoxic hatchlings just showed distended bellies). In some cases, the yolk sac was larger around than the hind legs, thus making movement clumsy and cumbersome.
Other interesting results from this study, included notable changes to the cardiopulmonary system. Hypoxic hatchling lungs were actually smaller than the lungs of normal hatchlings; which appears counterintuitive. The heart, meanwhile, showed distinct hypertrophy in hypoxic animals. The authors believe that lack of lung growth in hatchlings may have been due to the fact that lung function does not start until after hatchlings have hatched.? The heart, on the other hand, is hard at work circulating blood just as soon as it is formed; so it would have experienced the challenges of hypoxia at a very early stage.? Bolstering this hypothesis from the authors was the fact that three months after hatching, hypoxic alligators showed a distinct increase in lung growth rate (the lungs appeared to be “catching up” to the heart).? Hypoxic alligators showed shrunk livers as well. No real explanation for this was given, but it was mentioned that reduced liver mass seems to be a common trait in animals raised in hypoxic conditions. It appears to have some bearing on overall metabolic rate.
Hyperoxic hatchlings exhibited “typical” organ growth rates.? Where hyperoxic animals excelled was in breathing and metabolic rate.
Breathing rates were smaller in this group, while metabolism and growth rate were all larger. The explanation by the authors was that these hyperoxic animals were receiving such high amounts of oxygen in each breath, that they were actually hitting saturation at much shallower breaths; hence the shallow breathing. The higher metabolic rate is believed? due to a lack of right-left shunting in the crocodylian heart. This shunting is usually caused by low oxygen levels (like that experienced in diving), and tends to result in metabolic depression to conserve available oxygen stores.? Since these alligators lungs were constantly saturated with oxygen, right-left shunting never occurred, resulting in an elevated metabolism.
Incidentally, Owerkowicz et el give mention of a cardiac shunt known in embryological birds (via the ductus arteriosis). Though only analogous, one can’t help but wonder what this might have meant for all those dinosaurs that lie between these two groups.
Interestingly, hypoxic alligator hatchlings also showed a higher standard metabolic rate. Though these animals would voluntarily eat less than their normal and hyperoxic counterparts, their metabolism was more like hyperoxic hatchlings than they were normal hatchlings.? Owerkowicz et al believe the reason for the increased metabolism was due to the higher cost of breathing in these animals. Despite taking “normal” breaths, hypoxic hatchlings were taking in a larger tidal volume than their normal and hyperoxic siblings. The heart was also working harder to deliver enough oxygen to tissues.
Finally the authors give mention of growth rates in hyperoxic animals. Basically, it is faster. The authors mention that this might be caused by the persistently elevated metabolic rate, or perhaps from channeling saved energy from breathing (which is one of the main energetic costs in reptiles) into biomass.? It could be a mix of both, but I’m more inclined to think that it comes more from channeling energy reserves into other parts of the body. A high metabolism means nothing, if there is not enough free energy to go around. Just look at the hypoxic gators from this study. Despite their high metabolism, they grew slower than their peers.
The results of this study showed how modern animals can acclimate to different atmospheric conditions. They don’t show how animals would adapt and evolve in these conditions, but they do hint at the general directions, and help give us a clearer picture of what life was like millions of years ago.
Bakker, R. 1986. The Dinosaur Heresies. William Morrow. New York. ISBN: 0821756087, 978-0821756089 pps: 209-212.Buckley, G.A., Brochus, C.A., Krause, D.W., Pol.D. 2000. A Pug-Nosed Crocodyliform from the late Cretaceous of Madagascar. Nature. vol.405:941-944.
Clark.J.M., Xu, X., Forster, C.A., Wang, Y. 2004. A Middle Jurassic ‘Sphenosuchian’ from china and the Origin fo the Crocodylian Skull. Nature. Vol.430:1021-1024.
Gilmore, C.W. 1905. The Mounted Skeleton of Triceratops porosus.? Proceedings United States National Museum. Vol.29:433-435.
Lull, R.S. 1933. A Revision of the Ceratopsia, or Horned Dinosaurs. Memoirs of the Peabody Museum of Natural History. Vol.3:1-175.
Naish, D. 2001. Fossils Explained 34: Crocodilians. Geology Today. Vol.17(2):71-77.
Nobre, P.N. and Carvalho, I.S. 2006. Adamantinasuchus navae: A New Gondwanan Crocodylomorpha (Mesoeucrocodylia) from the Late cretaceous of Brazil. Gondwana Research. Vol.10:370-378.
Paul, G.S., and Christiansen, P. 2000. Forelimb Posture in Neoceratopsian Dinosaurs: Implications for Gait and Locomotion. Paleobiology, 26(3):450-465.
The Telegraph had a report today on a unique event in Africa. Hal Brindley, an American Wildlife photographer, happened to be in the right place in the right time for this to happen. The shots come from Kruger national park.
Photo taken by Hal Brindley and destributed by Solo Syndication
The photos show a leopard (Panther pardus) taking out a Nile crocodile (Crocodylus niloticus). The croc is smaller than the leopard, but the results are no less shocking.
Leopards, and most big cats in general, don’t go after crocodiles as a normal routine. Not only do the felines run the risk of becoming the hunted, but even if they do win (like this leopard did), there is really not a lot of meat to go around. Much of it is locked away by the bony osteoderms.
The only time I have seen a leopard take out a crocodile, was in a case where both animals were slowly starving and dehydrating. The crocodile died first, and the leopard took advantage of the free meal.
As one can see in the photo, this leopard wasn’t exactly starving, so it is hard to imagine desperation being the cause of this attack. The article also mentioned that the leopard attacked the croc on its own turf. Both situations are very unique, and make the fact that the leopard won, all the more amazing.
There was no run time given for the battle, so I’m not sure how long it lasted. Judging from some of the shots though, it must have been intense.
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.
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. >:)
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 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.
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.