This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Crocodiles, alligators and gharials are the modern members of a far grander, far more diverse clade of archosaurian reptiles termed Crocodylomorpha. It's gradually becoming better known that, in additional to including amphibious, long-skulled taxa like the living ones, the group encompasses an incredible array of terrestrial and semi-terrestrial omnivores, herbivores, carnivores and insectivores. Some had short, deep skulls and complex, heterodont teeth (various notosuchians), or leaf-shaped teeth (some sphenosuchians); others had deep, narrow skulls and laterally compressed blade-like teeth (various sebecosuchians); others had ridiculous, enormously long jaws and snouts and are termed 'duck-faced' crocodylomorphs (stomatosuchids and nettosuchine caimans). There were marine, flippered crocodylomorphs that had tail flukes (some thalattosuchians), and gigantic aquatic or amphibious kinds that must have looked like souped-up, super-sized versions of the gharials, alligators and crocodiles we're familiar with (some tethysuchians and extinct gavialoids and alligatoroids). [Images below by Smokeybjb and Dmitry Bogdanov.]
An issue that needs to be covered just about every time crocodylomorph diversity gets discussed is the terminology we use for the various relevant clades; it’s confusing, and it’s made all the more so by the fact that some workers are currently arguing that we should give up on the current consensus and change it again! No, BAD idea!
Ok... the clade that includes crocodiles, alligators and gharials and all of their extinct relatives is termed Crocodylomorpha. Crocodylomorpha is itself part of a more inclusive archosaur clade that includes the largely Triassic aetosaurs, rauisuchians and so on, variously termed Pseudosuchia or Crurotarsi depending on who you ask. Crocodylomorpha includes the archaic, long-legged sphenosuchians of the Triassic and Jurassic as well as the more ‘classically crocodilian’ lineages grouped together as the Crocodyliformes (sphenosuchians are crocodyliform-like, but differ conspicuously from them in possessing a typical archosaurian pelvis where the pubis contributes to the border of the acetabulum). This latter group – Crocodyliformes – includes virtually all the famous extinct lineages, all the protosuchians, sebecosuchians, notosuchians, tethysuchians, archaic neosuchians and so on as well as the crown-clade: the group that includes living gavialoids, crocodyloids and alligatoroids (all of which debuted in the Late Cretaceous).
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There are indications that thalattosuchians – the famous and awesome sea-going crocs of the Mesozoic – might be non-crocodyliform crocodylomorphs: we’re waiting for a key paper to appear on that subject (or is it already out?). Anyway, the crown-clade* within Crocodyliformes is termed Crocodylia (forget ‘Crocodilia’: it doesn’t have a formal meaning in the majority of current studies). Other schemes of nomenclature are out there, but what I’ve just described is the one that’s being used most widely.
* The ‘crown’ is the bit of a phylogenetic tree delimited by extant species only. ‘Crown’ does not just mean ‘that clade of most recently evolved species’ – it has to include extant species by definition. The rest of the lineage is termed the stem.
I'm still planning to produce a grand, group-by-group review of crocodylomorph diversity here some time. But, then, I plan a lot of things, and you might have to wait for the book I'm currently working on. Anyway, suppose you think crocodylomorphs are awesome, and suppose you think that this fact needs to become better appreciated by humanity at large. I would strongly recommend the wearing of the following t-shirt design...
Buy it now from the Tet Zoo redbubble shop, and show the love and look awesome by wearing it to TetZooCon (happening July 12th at the London Wetland Centre: full programme now online).
Tet Zoo has now covered crocodylomorphs living and extinct on quite a few occasions. Here, I've listed them all together, grouped according to their position on the cladogram...
Crocodylomorphs in general
Thalattosuchians
Notosuchians
Archaic neosuchians
Crocodylians
The Saltwater crocodile, and all that it implies (crocodiles part III)
Crocodiles of New Guinea, crocodiles of the Philippines (crocodiles part IV)
The Freshie: Australian crocodile, seemingly from the north (crocodiles part V)
Tool use in crocodylians: crocodiles and alligators use sticks as lures to attract waterbirds
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