Crocodiles vs. elephants

November 18, 2014

I’ve been reading The Guinness Book of Animal Facts and Feats (Wood 1982) again. Here’s what he says on pages 98-99 about the strength of crocodiles, and what happens when they bite off more than they can chew.

The strength of the crocodile is quite appalling. Deraniyalga (1939) mentions a crocodile in N. Australia which seized and dragged into the river a magnificent 1 tonne Suffolk stallion which had recently been imported from England, despite the fact that this breed of horse can exert a pull of more than 2 tonnes, and there is at least one record of a full-grown black rhinoceros losing a tug-of-war with a big crocodile. Sometimes, however, even crocodiles over-estimate their strength. One day in the 1860s a hunted named Lesley was a witness when a saurian seized the hind-leg of a large bull African elephant while it was bathing in a river in Natal. The crocodile was promptly dragged up the bank by the enraged tusker and then squashed flat by one of its companions who had hurried to the rescue. The victorious elephant then picked up the bloody carcase with its trunk and lodged it in the fork of a nearby tree (Stokes, 1953). Oswell (1894) says he twice found the skeletons of crocodiles 15 ft 4.6 m up in trees by the river’s bank where they had been thrown by angry elephants. On another occasion a surprised crocodile suddenly found itself dangling 15 ft 4.6 m in mid-air when it foolishly seized a drinking giraffe by the head.

The idea of elephants lodging crocodile corpses up in trees seems too bizarre to be true, but seeing it independently attested by two witnesses makes me more ready to accept it. There’s plenty of Internet chatter about this happening, but I’ve not been able to find photos — or better yet, video — proving that it happens.

References

  • Deraniyalga, P. 1939. The tetrapod reptiles of Ceylon, vol. 1: Testudinates and crocodilians. Colombo Nat. Mus., Ceylon.
  • Oswell, W. Cotton. 1894. South Africa fifty years ago. Badminton Library of Sports and Pastimes (Big Game Shooting), London.
  • Stokes, C. W. 1953. Sanctuary. Cape Town.
  • Wood, Gerald L. 1982. The Guinness Book of Animals Facts & Feats (3rd edition). Guinness Superlatives Ltd., Enfield, Middlesex. 252 pp.

Just a quick post to link to all five (so far) installments of the “necks lie” series. I need this because I want to cite all the “necks lie” posts in a paper that I’ll shortly submit, and it seems better to cite a single page than four of them.

I’ll update this post as and when we write more about lying necks.

X-ray of the neck of a seal, from Irish Seal Sanctuary. Note that the vertebral column becomes much more vertical than the fleshy envelope suggests.

X-ray of the neck of a seal, from Irish Seal Sanctuary. Note that the vertebral column becomes much more vertical than the fleshy envelope suggests.

 

Folks,

You may know that the inaugral TetZooCon is set to take place next Saturday (12 July) at the London Wetland Centre. It’s an informal convention that’s condensed around occasional SV-POW!sketeer Darren Naish’s absurdly informative blog Tetrapod Zoology, and features a day of talks, a palaeoart workshop and a quiz. At £40 for the day, it’s a bit of a bargain.

Among the speakers is my own good self, and I will be talking about why giraffes are rubbish.

Taylor and Wedel 2013a: Figure 3. Necks of long-necked sauropods, to scale. Diplodocus, modified from elements in Hatcher (1901, plate 3), represents a “typical” long-necked sauropod, familiar from many mounted skeletons in museums. Puertasaurus, Sauroposeidon, Mamenchisaurus and Supersaurus modified from Scott Hartman’s reconstructions of Futalognkosaurus, Cedarosaurus, Mamenchisaurus and Supersaurus respectively. Alternating pink and blue bars are one meter in width. Inset shows Fig. 1 to the same scale.

Taylor and Wedel 2013a: Figure 3. Necks of long-necked sauropods, to scale. Diplodocus, modified from elements in Hatcher (1901, plate 3), represents a “typical” long-necked sauropod, familiar from many mounted skeletons in museums. Puertasaurus, Sauroposeidon, Mamenchisaurus and Supersaurus modified from Scott Hartman’s reconstructions of Futalognkosaurus, Cedarosaurus, Mamenchisaurus and Supersaurus respectively. Alternating pink and blue bars are one meter in width. Inset shows Fig. 1 to the same scale.

If that sounds like your idea of a good time, then you need to move fast! Booking closes at 4pm this evening. Better get on it now!

 

Order up!

Sauroposeidon OMNH 53062 articulated right lateral composite with giraffe

Sauroposeidon is stitched together from orthographic views of the 3D photogrammetric models rendered in MeshLab. Greyed out bits of the vertebrae are actually missing–I used C8 to patch C7, C7 to patch C6, and so on forward. The cervical ribs as reconstructed here were all recovered and they are in collections, but they’re in several jackets and boxes and therefore not easily photographed.

The meter bars are both one meter as advertised. The giraffe neck is FMNH 34426 (from this post), which is actually 1.7 meters long, but I scaled it up to 2.4 meters to match that of the tallest known giraffe. I think it’s cool that a world-record giraffe neck is roughly as long as two vertebrae from the middle of the neck of Sauroposeidon.

There are loads of little morphological details in the Sauroposeidon vertebrae that are clearer now than they were in our old photographs, but those will be stories for other posts.

Giraffe neck FMNH 34426 articulatedThe cervical series of Giraffa camelopardalis angolensis FMNH 34426, articulated by Mike and me and photographed by Mike back in the summer of 2005, cropped and composited by me recently, not previously posted because there’s just too much cool stuff, man. But we’re working on it.

By the way, if you want the details on this critter:

FMNH 34426 specimen tag

UPDATE April 23, 2014: What a maroon–I completely forgot to report the size of this thing! When we articulated all the centra and measured them (without cartilage, obviously), we got a length of 171 cm. When we measured the centra individually, leaving off the anterior condyles, we got a length of 164 cm. I think the discrepancy can be explained by the relative shallowness of the posterior cotyles of the vertebrae–as you can see in the big image above, the condyles do not nest completely within the cotyles, so each one does contribute a little bit to the length of the neck.

The measurements of each vertebra, as recorded by Mike in my notebook in the FMNH mammalogy collections in 2005, are here:

Giraffa FMNH 34426 cervical and dorsal measurements

Just for completeness, I should note that in our neck cartilage paper (Taylor and Wedel 2013b), we found that cartilage added considerably to the length of the articulated neck in many amniotes. Based on the intervertebral spacing in horses, 1-2 cm of cartilage between these giraffe vertebrae doesn’t seem unreasonable, which would bring the length of the neck to perhaps 1.8 meters. Amazingly, this is only 75% of the longest giraffe necks on record, which are up to 2.4 meters (Toon and Toon 2003).

References

supersaurus-vs-giraffe

At the top: our old friend BYU 9024 — the cervical vertebra that’s part of the Supersaurus vivianae holotype. At the bottom, C2 (the longest cervical) of Giraffa camelopardalis angolensis FMNH 34426.

The Supersaurus vertebra is 138 cm long. We don’t know which cervical it is, but there’s no reason to think it’s the longest. The giraffe vertebra is 31 cm long. Not only is the Supersaurus vertebra four times as long as that of the giraffe, it’s one of more than twice as many cervicals as the giraffe has.

Did we cheat by using an unusually small giraffe? Not really. When we articulated all seven cervicals as best we could, the sequence measured 171 cm, which is a fairly healthy 71% of the 2.4 m neck of the world-record giraffe. It’s not a monster, but it’s a decent-sized adult.

Bottom line, giraffes are just lame.

Having taken time to discuss at length why we posted our neck-anatomy paper on arXiv, let’s now return to the actual content of the paper. You may remember from the initial post, or indeed from the paper itself, that Table 3 of the paper summarises its conclusions:

Table 3. Neck-elongation features by taxon.

Needless to say, we puny humans lack all seven of the features that were discussed as contributing to long necks, while sauropods have them all. But it’s interesting to look at the giraffe and Paraceratherium, the two longest-necked mammals, and see what they have in common. They share quadrupedal stance; the giraffe has elongated cervical vertebrae; and Paraceratherium has absolutely large body size. But they both lack all four of the other features:

  • Small, light head
  • Numerous cervical vertebrae
  • Air-sac system
  • Vertebral pneumaticity

And they lack them for the same reason: because they are mammals. The same is true of all mammals, and the individual reasons for those four missing long-neck features are all the same: because mammals have hit local maxima, and can’t evolve away from them.

Mammals’ heads, for example, are all set up for extensive oral processing of food — certainly among large herbivores. (I think pretty much all the toothless mammals are insectivores.) They’ve got very good at it, and there’s no evolutionary pathway that can take a giraffe from its current lifestyle to a sauropod-like crop-and-swallow strategy without passing through an adaptive valley on the way. That means they are stuck with big, solid teeth and heavily engineered jaws, which means they can’t have light heads.

In the same way, mammals have much more efficient lungs than those of their reptile-like forebears, the common ancestors that they share with birds. They have evolved to a point where their lungs are too complex and effective to easily evolve into a different shape — yet by doing so, they have cut themselves off from the yet more efficient avian lung (shared by sauropods) that is capable of extracting twice as much oxygen as our lungs.

And of course in the absence of an avian-style lung, there can be no soft-tissue diverticula or air-sacs, and so no pneumatic invasion of the vertebrae.

A final nail in the coffin of mammal neck length is that we seem to be strongly wired to have exactly seven cervical vertebrae — no more, no less. The exceptions are very few and far between: sloths and sirenians, and even then they don’t vary from the seven-cervical pattern by more than one or two vertebrae.

Skull and cervical skeleton of the three-toed sloth, Bradypus tridactylus, taken at the University Museum of Zoology, Cambridge (UK). Note the nine cervical vertebrae — the most of any mammal.

As for why we can’t get past seven, or at most nine, cervicals — that’s harder to answer. There’s no reason why seven should be an adaptive maximum, so it seems that the reason is genetic: the instructions to produce seven cervicals are part of the same gene complex that gives us an advantage in some other way. I have vague memories of an excellent talk at the Bristol SVP suggesting that cervical-count is linked to cancer resistance, but I can’t remember any of the details.

Anyone able to elaborate?

Anyway: this is how evolution works, and why it doesn’t make organisms (including us) as perfect as we might wish. It has no goal in mind — such as a long neck — and blindly follows the path that at that moment gives the organism the best chance of reproducing successfully. That means an animal like a giraffe, even though it is clearly selecting for neck length, is trapped on an adaptive hill and can’t get down across the valley to a higher peak.

Follow

Get every new post delivered to your Inbox.

Join 412 other followers