Animals or antediluvian monstrosities?

The famous painting Duria Antiquior, by the Victorian geologist Henry De la Beche, is acknowledged as being the first piece of palaeoart, ie. depiction of prehistoric life based upon fossil evidence.  Because of this it’s palaeontologically important, but it’s also pretty awesome in itself as a picture, with various marine creatures eating one another as pterosaurs swoop overhead, and even a rare depiction of a pooing plesiosaur.  There is in fact so much awesomeness going on that you’d struggle to find room to swing a cat (or whatever the Mesozoic equivalent is-perhaps Pakasuchus?) anywhere in the crowded landscape.  While a great picture, it doesn’t actually do a very good job of illustrating what a Mesozoic seascape would have looked like, instead depicting various monsters doing battle.

Everything looks so happy

The smiley ichthyosaurs make it all look so jolly.

This brings us to the theme of this blog post: the temptation to ‘mythologise’ prehistoric animals and the world in which they lived.  Duria Antiquior was painted in 1830, and obviously palaeontological understanding has come a long way since then.  Equally, the depiction of overcrowded, overdramatised scenes in palaeoart is fair enough.  No-one would be interested in a Mesozoic seascape if it depicted an empty ocean with something that might or might not be the silhouette of an ichthyosaur in the murky distance.  But this popular view of the prehistoric world as a planet populated by antediluvian monstrosities does still sometimes colour the way that people try to understand it.

One of the fundamental tools available to palaeontologists to help them understand extinct animals is information from animals that are alive today.  To understand how a dinosaur’s moved they would look at the principles that govern movement in modern animals, rather than making up special rules for dinosaurs.  Sometimes, however, palaeontologists give in to the temptation to treat prehistoric life specially.

Azhdarchid pterosaurs were a group of large, long-necked pterosaurs from the Cretaceous, including the famous (for a pterosaur anyway) Quetzalcoatlus.  Their shape has led some to suggest that they fed like modern ground hornbills, hunting on the ground with their enormous beaks (see picture).  One argument (among a number) put forward against this hypothesis is that any azhdarchid that landed on the ground to feed during the Cretaceous would be immediately torn apart by voracious theropods.

Quetz

Admittedly hornbills don’t eat sauropods.

But would this actually be the case? Darren Naish (a proponent of the hornbill-esque feeding idea) points out in a recent blog post that it probably wouldn’t be.  Notwithstanding that the size of these pterosaurs offered protection in itself, there’s no reason to think that every inch of the Cretaceous landscape was being constantly monitored by hungry tyrannosaurs.  Taking the modern African savannah as an example; it’s not like every animal that summons up the courage to peek around the side of a baobab tree is instantly ripped to shreds by lions.  To suggest that azhdarchids could never have been safe seems a bit like mythologising the Cretaceous environment and its predators.

It’s not just predators that have been ascribed ‘special rules’.  Amongst ornithodirans (pterosaurs and dinosaurs) are found a amazing array of crests and weird head ornaments (eg. hadrosaurs in picture below), and a number of suggestions have been put forward for why these evolved.  One of the most prominent has been that of ‘interspecific recognition’, where they helped animals to identify mates of the same species.  This hasn’t been conclusively demonstrated to be the reason for ornaments in any animals alive today, but proponents of this idea claim that dinosaurs represent a special case.

hadrosaur_heads_small

I like to think that this is what the album cover for a hadrosaur boy band would look like.

A counter-explanation put forward has been that of mutual sexual selection, where the crests have been selected for (in both genders) to aid attracting a mate (a more in depth discussion of which is found here).  In modern taxa this often seems to be the explanation for such ornaments, and so seems to me to be the more likely hypothesis for those in dinosaurs:  there is no need to invoke ‘special rules’ for extinct animals.  To do so is just another example of (inadvertently) mythologising them and their ecology.

It is true that there are cases where we can’t treat extinct taxa by the same rules as living ones because we have no living analogues to tell us what the rules are.  Enormous bipedal carnivores and giant fully aquatic reptiles are examples.  However, this doesn’t mean we ought to believe that widely applicable principles that we know from modern ecology wouldn’t apply for no reason other than that the animals in question were extinct.  If palaeontologists were studying the function of these animals’ bones they would prefer modern analogues to ‘special rules’, there’s no reason why the same approach shouldn’t be taken to inferring their ecology.

In the two examples I’ve given here, accusing the palaeontologists in question of viewing extinct animals as ‘antediluvian monstrosities’ is an exaggeration.  I do think however that they serve as examples of people applying ‘special rules’ to the ecology of extinct groups just because they’re, well, extinct.  In depictions such as Duria Antiquior such mythologising is both harmless and useful, and sometimes aspects of prehistoric life appear to have no direct modern analogues.  But to view them as anything more than animals in a world governed by the same ‘natural laws’ as those today just gets in the way of understanding these fascinating creatures.

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