10 crocodylians, scariest beasts around

Watching crocodylians, live or on TV, hits something deep in your gut (or maybe just my gut). Watching them move, stalk and pounce seems to activate some deep-seated flight instinct that says, "You'd better get out of here if you don't want to end up in someone's belly". I don't get this when I see a shark, but even a smallish gharial or caiman can induce alarm bells in my head (and gut, as it happens). But I can't stop watching - crocodylians have survived on Planet Earth for 220m years, since the Triassic period, and roughly as long as the dinosaurs, and as such, are inordinately interesting creatures. Why do they work so well?

That's not really a question I can answer in a post, or even a question that I'm actually qualified to answer. What's clear though, is that the basic crocodylian bodyplan has remained the same for a very long time, through a plethora of shapes and sizes - long snout, lots of teeth, long muscular tail, short legs, long body, semi-erect posture. Oh, and scales.

First, some phylogeny. In this post, I want to focus on members of the order Crocodylia (hence crocodylians - crocodilians include earlier species which placed in different orders). There are 3 extant lineages in this order, Gavialoidea, Alligatoroidea and Crocodyloidea. Each branch has the obvious candidates, and Alligatoroidea includes the caimans as well.

1. Rhamphosuchus

Rhamphosuchus ("beaked crocodile") lived from about 25m years ago in what is now the Indian sub-continent. It was a member of Gavialoidea, and was probably a relative of extant gharials, as can be seen from the beaked snout. The species is poorly known from fossils, but was probably between 15-18m long. The beak is indicative of a fish diet (although not exclusively). Adjacent image from Wikipedia.

Some recent work done has reinterpreted Rhamphosuchus as a member of Tomistoma, the taxon that includes false gharials. False gharials have the same thin beaked snouts as true gharials, but were thought to be members of the clade Crocodyloidea. This has now changed due to DNA analysis - false gharials are really members of Gavialoidea.

2. Gharial

Adjacent image from Laelaps, an excellent zoological blog well worth reading. Gharials are found on the Indian sub-continent, and are one of 2 extant species in Gavialoidea. The other is the false gharial (of course). The long thin snout is an evolutionary adaptation to facilitate a diet of small fish. They can be up to 6m in length. Gharials are currently endangered, and are being pushed to extinction as the sub-continent develops and grows in population. They are already extinct in Bhutan, Nepal and Myanmar, and are only found in very small numbers in Pakistan and in small numbers in India.

3. Pristichampsus

Pristichampsus belonged to a genus of entirely terrestrial crocodiles that preyed on land mammals. It was about 10m long, and lived about 6om years ago. It had long legs, and was well adapted to a running lifestyle, as it had hooves on its toes. Adjacent image from this University of Bristol website. Pristichampsus is thought to predate the split between Alligatoroidea and Crocodyloidea. It's not a member of Gavialoidea though.

4. Ceratosuchus

Ceratosuchus is thought to be a basal member of Alligatoroidea, and lived in the Palaeocene, maybe about 65m years ago. Adjacent image from Wikipedia. The main unusual feature of this creature is the 2 triangular plates on its skull, and indeed its name means "horned crocodile". Ceratosuchus lived in what is now North America.

5. Chinese alligator

There are 2 extant species of alligator, the Chinese alligator and the American alligator. The Chinese alligator is smaller, about 1.5m in length, and has an armoured belly, which is quite rare among crocodylians. What's left of their wild population can be found along the lower reaches of the Yangtze, and there are fewer than 200 wild individuals left. There are approximately 10,000 animals in captivity though. Adjacent image from danmex.org.

6. Purussaurus

Purussaurus was a giant caiman found in South America in the Miocene, about 20m years ago (caimans are members of Alligatoroidea). Adjacent image from Tetrapod Zoology, and shows the scale of this animal - it was more than 15m in length, making it a very large crocodylian indeed, one of the largest to have ever existed. Darren Naish at Tet Zoo states that it was probably aquatic at that size, and would most likely have preyed on large mammals as well as other prey. His post on Purussaurus is here.

7. Spectacled caiman

The spectacled caiman is one of 5 extant species. All are found in Latin America. The difference between a caiman and an alligator lies in the septum between the nostrils - caimans have a bony one, alligators don't. The spectacled caiman is further distinguished by a bony ridge around the eye, which makes it look as if it is wearing spectacles. They grow to 2.5m in length, and are found from southern Mexico to Argentina. Adjacent image from US Geological Survey website.

8. Mekosuchus

Mekosuchus is a genus of crocodylians (4 species) that inhabited Australasia until quite recently, with remains discovered that are less than 4,000 years old. They were entirely terrestrial, and may well have been hunted to extinction by humans. One species, mekosuchus inexpectatus, was around 2m long, and had specialised back teeth that indicated a diet of molluscs. Adjacent image from Tetrapod Zoology, which has more information.

9. Baru

Crocodyloids of the genus Baru are thought to be mekosuchines, part of the same Australasian radiation. Adjacent image from Paul Willis's site - he does reconstructions of extinct crocodilians. As can be seen from the image (of a species called baru darrowi), baru mekosuchines had short broad snouts with long curved teeth. The fossils were found in Australia, and indicate that b. darrowi reached about 5m in length. It lived about 8m years ago, and is thought to have had a mostly terrestrial predatory lifestyle. According to this site, the first baru skull to be found had part of a marsupial lion's skull in its jaws.

10. Salt water crocodile

The largest crocodyloids (as well as crocodylians) alive today, salt water crocodiles are found in Australia and throughout South East Asia. They are ocean-going, and are up to 5m long. I have a video of a salt water crocodile underwater which I'm told was taken off Sipadan Island in Borneo, so they certainly get around. It is an ambush predator, and drowns its prey rather than tear it apart (although the famous "death roll" will rip off some flesh). There are documented cases of attacks on humans.

There are 13 species of crocodyloids extant today, across 2 genuses. The dwarf crocodile sits in its own genus, all the others are more closely related.


There are more interesting species of crocodylians I haven't yet discussed, although this post gives a quick run-through of the 3 main lineages and one of the extinct out-groups. Many so-called supercrocodile fossils discovered recently actually belong to the crocodylomorphs, a more basal group. More later perhaps. In the meantime, enjoy these beasties.