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…
- Alligators vs melons: the final battle
- The small, recently extinct, island-dwelling crocodilians of the south Pacific
- Even more recently extinct, island dwelling crocodilians
- Do crocodilians (sometimes) feed their young?
- The world’s largest modern crocodilian skull
- Filming Migo, the monster of Lake Dakataua
- Alligators eat fruit
- Purussaurs: monster caimans of the Miocene
- Tet Zoo picture of the day # 14 (on giant Saltwater crocs)
- Move over Theropoda, Sebecosuchia rules
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.