Enough mammals for the time being: crocodiles on Inside Nature's Giants (part III)


The third episode of Inside Nature's Giants (still available to watch, if you're in the UK) looked at a 17-year-old, 4 m long Nile crocodile Crocodylus niloticus that had died (very much prematurely) at a crocodile park in France (please read part I and part II unless you have already). RVC pathologist Alun Williams tried to work out the cause of death. Greg Erickson was the on-site crocodile expert, so (as expected) jaw anatomy and bite force were focused on to begin with (see Erickson et al. 2003a, b). The pterygoideus muscles - you can see some of them here, with Erickson in the background - are phenomenally large.


In addition to discussing the oesophagus and stomach, they showed how the trachea is highly mobile and often pushed to the side by the oesophagus, and then spent some time discussing the lungs and hepatic piston diaphragm (linked to the mobile pubic bones). They also discussed the role of the musculature in helping to control the animal's attitude in the water (see Uriona & Farmer 2008). They inflated the lungs artificially (crocodile lungs are pretty enormous), and one of the coolest bits was when Reidenberg blasted air from the trachea through the larynx, causing the corpse to vocalise loudly. They also looked in detail at the four-chambered heart, with its complicated vasculature and two aortic arches. Colleen Farmer's research on the role of the right aortic arch in shunting CO2-rich blood to the stomach, and hence in helping to produce especially high amounts of gastric acid (Farmer et al. 2008), was featured [crocodile heart shown here, from Pharyngula. Extra complexity, compared to what you might be used to].


The episode also looked briefly at crocodilian evolutionary history. They noted the genesis of the crocodilian body plan in small, terrestrial forms (like sphenosuchians), made passing mention of giant, aquatic crocs (Sarcosuchus was illustrated), and discussed the rise of modern crocodilians (eusuchians). It was stated several times in the programme that crocodiles have survived unchanged 'since the age of the dinosaurs'. Of course, this is the first thing that anyone ever says as soon as crocodilians are mentioned. I find it a bit irritating, as it implies that modern crocodilians are archaic, and perpetuates the stereotype that they're anachronistic vestiges. On the one hand, it's true that crocodilians generally similar to the modern ones have been around since the Jurassic. On the other hand, modern crocodilians in the strict sense are mostly a post-Mesozoic event, and in fact some modern taxa - Crocodylus in particular - are not particularly old. Inside Nature's Giants at least emphasised the fact that, whether ancient or not, crocodilians are not 'primitive', and if they've been conservative in their history, that's because they've stuck with a winning formula.


The heat-collecting and protective roles of the dorsal scutes were discussed. That's great, but what I'd really like to see being discussed by anatomists is the proposed 'self-carrying system' (this is where the musculature attached to the ventral surfaces of the scutes supposedly plays a role in supporting the axial skeleton and hence in carrying the animal's weight during high-walking). Palaeontologists tend to know a lot about this system because it was conceived of, and promoted by, palaeontologists, but neontologists tend not to talk about it. Having said that, I should add at this point that it's rather misleading to imply that there's a dichotomy between palaeontologists and neontologists, given that many anatomists - Erickson is a particularly good example - bridge the divide. Anyway, it was a shame that they didn't cover this sort of stuff, as I'd really like to know what they thought of it. In fact, palaeontologists have made quite a few claims about crocodilian anatomy that you never hear reported or discussed in the neontological literature: is this because neontologists don't know about these claims, or because they think they're problematical? One example: Frey (1988) proposed that some of the cervical ribs in the crocodilian neck prop up against each other and help keep the neck supported via a sort of ventral compressive bracing [crocodile neck shown here, photo courtesy Mathew Wedel]. If you work on crocodilians, please let us know what you think (I say 'us' because I'm not the only one interested in this).

Anyway, including crocodiles in the series was a clever move. Mammals are nice and all, but they do get a bit samey :) Give us something with scales and armour. Anyway, next: back to mammals, with giraffes...

For previous Tet Zoo stuff on crocodilians see...

Refs - -

Erickson, G. M, Lappin, A. K. & Vliet, K. A. 2003b. The ontogeny of bite-force performance in American alligator (Alligator mississippiensis). Journal of Zoology 260, 317-327.

- , Lappin, A. K., Parker, T. & Vliet, K. A. 2003a. Comparison of bite-force performance between long-term captive and wild captured American alligators (Alligator mississippiensis). Journal of Zoology 262, 21-28.

Farmer, C. G., Uriona, T. J., Steenblik, M., Olsen, D. & Sanders, K. 2008. The right-to-left shunt of crocodilians serves digestion. Physiological and Biochemical Zoology 81, 125-137

Frey, E. 1988. Anatomie des Korperstammes von Alligator mississippiensis Daudin. Stuttgarter Beiträge zur Naturkunde Serie A (Biologie) 424, 1-106.

Uriona, T. J. & Farmer, C. G. 2008. Recruitment of the diaphragmaticus, ischipubis, and other respiratory muscles to control pitch and roll in the American alligator (Alligator mississippiensis). Journal of Experimental Biology 211, 1141-1147.

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Sorry to post a comment off-topic Darren, but I posted a couple of questions on previous posts that didnt get answered.

Firstly, what is your opinion about the size of Megalainia?
(I'm really hoping you weren't sucked in by John Long's interpretation)

And secondly, what is the consensus, and your opinion, on plesiosaur bodyshape? Is the old, barrel-chested model still being used? I ask this question because Ben Kear of the South Australian Museum has apparently concluded that their bodies were not shaped like this at all.

Please, pretty please answer my questions.

By Tim Morris (not verified) on 28 Jul 2009 #permalink

Anyone happen to know the dental formula for a mammoth?

Seemed as likely a place as any to get an answer.

Greg Erickson is in this documentary too? I TA'd for Greg one semester several years ago, and even then it was remarkable how many TV programs he had been on. He was really great and arranged for the class to go watch necropsies of a juvenile manatee and a juvenile dolphin.

Anyway, I am looking forward to these videos becoming available in the USA.

correction: (I hope you hadn't been sucked in by Steve Wroe's interpretation)

By Tim Morris (not verified) on 29 Jul 2009 #permalink

It really is amazing how huge those jaw muscles are. It is tempting to look at a large crocodile, or alligator laying out in the sun with these huge jowels, and think that it is just a bunch of fatty deposits; when in fact, all that "fat" is jaw muscle that ran out of skull to lay on.

"Wait a second, isn't Isisfordia a basal representative of the crown group? And it's from the Cretaceous, isn't it?"

TMK, no. Isisfordia is outside of the crown group.

Is it true that this autopsy was done in Scotland? You know, Crocodile, Dundee?

That's pretty amazing stuff! Has there been any information on these programs so far that has surprised you Darren?

By Sebastian Marquez (not verified) on 29 Jul 2009 #permalink

This was indeed a great series , with phenomenal shots of the internal workings of the presented animals.

BUT.....I noticed several errors in the elephant episode, which was quite surprising given the Royal Veterinary College and so many experts were involved with this project.

1. The tusk was referred to as a canine tooth, when in fact elephants do not have canines, rather it is an incisor.

2. "if they lie down, they can suffocate" the program made it seem that if an elephant ever goes down, it would certainly die. That may be true in certain circumstances but it is also very misleading. It has been well documented both in the wild/captivity that elephants DO lie down to sleep quite frequently. They can stay down on their sides for even up to a few hours without any adverse health effects.
The problems arise when they fall in awkward positions, such as on their chest which interrupts proper breathing. Also, its potentially fatal when elephants are down for extended periods (longer than normal sleeping) and are unable to raise to their feet at will.

3. The 3D animation of the skeleton chewing was showing the incorrect motion. It demonstrated the mandible dropping, swinging forward then making contact with the top teeth and pulling back.
If you ever witnessed elephant mastication, the mandible drops, while moving backwards, then makes contact with the upper teeth as it grinds forward. This is readily visible in live elephants, and also clearly illustrated by Maglio (1973) and Kingdon (1979).

Despite those errors, I thoroughly enjoyed the episode.

This may sound a bit silly, but having watched a crocodile necropsy, does it give clues on how ancestral humans long ago might have killed and carved up crocs? Would a sharp obsidian blade penetrate the scutes or skin, or a chipped flint/basalt axe? Those thick jaw muscles would make for some stew meat perhaps?

I consulted on the series (all 4 shows; just pictured in 2 of them) and tried to get the facts right; however I was only one of many people involved. I didn't get to see the final scripts, drafts of the show, or any animations, and I could not see which of my corrections they took on board, although now that I've seen the shows I know they did take many. I recall that I debated the "crocs haven't changed" phraseology with them, and feel fine with how they did that; it is a semantic minefield. At least they did not use the phrase "living fossil," I think...

Inevitably some errors crept through, like the elephant incisor/canine (d'oh, I caught that too) and the simplified explanation of lying down and breathing in elephants, among other things... Many cooks were involved, and let's not forget the all-powerful TV execs. As usual with this kind of show there are some interesting behind-the-scenes stories that could be told but this ain't the place.

I was really impressed however with the researchers' (i.e. the documentary researchers/writers/directors) interest in the science, from day one of discussions of the show content. When I first spoke to them >1 yr ago it really hit me how they were aiming high in terms of factual content and talking to the right experts. That's a big reason the RVC got involved. We could tell that the Windfall Films guys had their hearts in the right place and it would be a respectful, rigorous, and original documentary.

The crocodylian bracing system was discussed at some point as something that could be shown but IIRC it was decided that it wouldn't show up as clearly in dissection as they'd like. The tissue under the scutes is a bit of a mess visually. Personally I don't find it a terribly convincing argument, or an overstated and undertested one anyway, but that's not why it was omitted.

There were a lot of cool things that were discussed for inclusion, and plenty ended up on the cutting room floor (including me on croc locomotion!), but time was tight and the producers were really trying to pack in lots of meaty (nudge, nudge) facts.

Anyway, glad ya liked it!

By John Hutchinson (not verified) on 29 Jul 2009 #permalink

Does anyone know (Dr. Hutchinson perhaps?) where they got the footage of the croc galloping on - what might have been - a treadmill? Could this be from some of the work that Sereno is supposed to be doing on croc galloping? It shows up for 2 seconds early in the show, and is never shown again. It looks really neat. Since there was only a glimpse, it was hard for me to see which species it was. It kind of looked like _C.rhombifer_. That would be pretty amazing if it was.

Glad I caught this blog post, as I spent a lot of time on the phone with Windfall in the development process for this episode including trying to get a big C. porosus over there. I'm curious to see how much of the detail we discussed ended up in the final cut, but try as I might I can't convince the Channel 4 website that I'm from the UK. We discussed all the detail you mentioned in the blog, but with these shows it's always a question of how much of the interesting detail gets whittled away. The various possible roles of the osteoderms were certainly there, but the question was how best to show it. Did they end up taking microtome samples to illustrate growth rings by any chance?

Jura, we filmed galloping with Paul Sereno only a few months ago for another project. I doubt this is what you're talking about though (it wasn't on a treadmill, and it wasn't C. rhombifer) although it did look spectacular at 1,000 fps. I would be keen to see C. rhombifer subjected to the same technology.

The occasional mistake is probably inevitable - indeed I noticed a few were corrected during the episodes.

But I admire the fact that C4 were willing to take the risks involved in putting together something as different as this. I have no idea how much the series cost to make, but I suspect it wasn't cheap, and so I applaud whoever conceived the idea, and the management who had the guts to put up the cash.

I also note the enthusiasm for their subject shown by the experts - these people clearly loved their subjects, and I found that infectious. I recall disections can be messy procedures (and that some times the smell can gut-wrenching), but that poor woman wallowing in whale guts (indeed almost falling in to the body she was dissecting) and apparently still loving it, was something else.

To those who haven't seen this series, when you get the chance don't miss it. It is a bit rough and ready in parts, but to me that just added to the feel and made me feel a part of it.

By Mark Lees (not verified) on 29 Jul 2009 #permalink

Yeah the croc footage was C. rhombifer (over a force platform), which you'll see more of in the near future... We've studied bounding (the fastest gait of crocs; galloping is slower) and other gaits in ~17 crocodylian species now.

By John Hutchinson (not verified) on 29 Jul 2009 #permalink

Thanks for the clarification Dr. Hutchinson, I guess with so many people of different disciplines involved there are bound to be a few errors.

By the way, your work on elephant locomotion is phenomenal, first heard about you a few years back on Discovery Channel Canada. Absolutely amazing research you do....keep it up!

The shows are available on YouTube, with the HQ option too.

With the 10 minute limit on video size each episode is chopped up into 5 pieces. If you will...

There is some controversy about the age of the crown group. According to Chris Brochu and, I believe, most other paleontologists, it it indeed Cretaceous. In fact, Brochu shows three extant lineages crossing the KT boundary: Gavialoidea, Alligatoroidea, and Crocodyloidea.

Now, aside from the controversy, which for some reason is still alive, regarding the relationships of Gavialis, molecular folks tend to be dubious about this age, since it requires crocodylians to have bizarrely slow rates of molecular evolution. Absent such rates, the basal divergence among crocs according to molecular data would seem to be somewhere around the early Neogene. There is very little pre-Neogene material assigned to extant genera, but there are lots of fossils assigned to extinct crown-group genera extending throughout the Paleogene. I don't know how to resolve that contradiction.

Here's a paper with a tree showing fossil ages: Brochu, C. A. 1997. Fossils, morphology, divergence timing, and the phylogenetic relationships of Gavialis. Systematic Biology 46:479-522.

By John Harshman (not verified) on 30 Jul 2009 #permalink

For Tim:

Okay, why does it seem like everyone is mentioning that Dragons of the Dust book recently? I mean I've heard the findings of the book mentioned three times in the last two weeks. And yet, the place I found my copy of the book was in a used book store.

As for the crocodilians, I find the neck posture of crocs in that one picture rather interesting. It looked almost mammal-like a bit (of course, crocs aren't ornithodirans in the slightest). Just another point of evidence which seems to suggest crocs are archosaurs trying very hard to be mammals (what with the heterodont dentition in Mesozoic forms, crurotarsial heel, and whatnot).

By Anonymous (not verified) on 31 Jul 2009 #permalink

DDeden: My understanding is that it's pretty straightforward to cut and carve *wood* with stone tools, so I assume that in general croc hide would be easier going than that.

Response to John Harshman:

1. The debate about Gavialis persists because it is unresolved. Yes, molecular data generally (though not universally) support a relationship with Tomistoma, and character sampling is massive. But morphological data do not, and taxon sampling is much greater. Both sources of data have compelling signals, and until we can figure out why one disagrees with the other, both must be considered.

2. It is not strictly true that crocodylian divergences are within the Neogene if Gavialis is related to Tomistoma. The alligatoroid-crocodyloid split is still within the Late Cretaceous regardless of what happens to Gavialis, and several other major divergences (Alligator-Caiman, Paleosuchus-Caiman, Tomistoma-Crocodylus with or without Gavialis) are in the Paleogene. In fact, the gator-caiman split might even be in the latest Cretaceous, though fossil evidence doesn't really support that.

Molecular data overwhelmingly support most of these divergences. Gavialis remains unresolved, and there's some widginess about the dates within caimans, but agreement otherwise is broad.

A more recent survey:

Brochu, C.A. 2009. Crocodylia. pp. 402-406 in S.B. Hedges and S. Kumar (eds.), The Timetree of Life, Oxford University Press, New York.

By chris brochu (not verified) on 04 Jan 2010 #permalink

molecular folks tend to be dubious about this age, since it requires crocodylians to have bizarrely slow rates of molecular evolution.

Just to not leave this uncontradicted...

That was another "controversy", the one about the age of the genus Crocodylus. Turns out that 1) the molecular biologists used the name Crocodylus for the crown-group, while the paleontologists used it for the total group or even a paraphyletic assemblage; and 2) lots of fossils of mediocre preservation had been wrongly assigned to the paleontological concept of Crocodylus. Therefore the molecular biologists said Crocodylus goes back to the Pliocene, while the paleontologists said it goes back to the Early Cretaceous. They just weren't talking about the same thing. This illustrates what can happen when you used rank-based nomenclature.

By David MarjanoviÄ (not verified) on 04 Jan 2010 #permalink

And not to leave THAT uncontradicted...

Although I agree with David that rank-based nomenclature can be misleading, I'm not sure it was the root of the problem surrounding Crocodylus. The names were being used in different ways, regardless of "rank." To one group, it was a biological entity with a discrete origin in time (common ancestor) and reasonably-well-constrained membership (living species). To another, it was a form-based category including anything that wasn't obviously something else. To one group, membership in Crocodylus was based on what an organism was; to another, it was based on what an organism was not.

Even now, not all "genera" as used by phylogenetically-oriented paleontologists are crown-genera. Alligator, for example, is applied to fossils as old as the Late Eocene, even though the last common ancestor of the two living species of Alligator was in the Early or Middle Miocene. The difference is that this more inclusive Alligator is monophyletic; pre-phylogenetic Crocodylus was not.

By chris brochu (not verified) on 05 Jan 2010 #permalink

the two living species of Alligator

So the Chinese one has survived the Three Gorges dam?

By David MarjanoviÄ (not verified) on 05 Jan 2010 #permalink

The difference is that this more inclusive Alligator is monophyletic; pre-phylogenetic Crocodylus was not.

That's part of what I meant by "what can happen when you used rank-based nomenclature": RN doesn't require valid names to apply only to monophyletic taxa. It also doesn't require that everyone uses the same valid name for the same definition; such a requirement would have prevented most of the Crocodylus confusion, if not all of it.

By David MarjanoviÄ (not verified) on 05 Jan 2010 #permalink


So the Chinese one has survived the Three Gorges dam?

Captive populations of Chinese alligators are, according to this source, 'healthy'. So yes, the species survives, although perhaps no longer in its natural habitat.


By David MarjanoviÄ (not verified) on 05 Jan 2010 #permalink