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Crocs dispel 'living fossil' myth
By Ella Davies
Earth News reporter

Holotype skull and lower jaw of Simosuchus clarki in side view (c) Jeanne Neville
The unusual pug-nosed skull of an ancient crocodile

Crocodiles can no longer be referred to as "living fossils", according to scientists.

Members of the crocodilian family have previously been thought to have changed little since prehistoric times.

However, new fossil analyses suggests that modern crocodilians actually evolved from a very diverse group.

Recently discovered ancient ancestors include small cat-like specimens, giant "supercrocs" and a pug-nosed vegetarian species.

Body structure

Modern crocodilians are adapted to aquatic environments with long snouts, strong tails and powerful jaws.

Yet contrary to popular belief, scientists now suggest that the basic body structure of crocodiles, alligators and ghariels evolved from a diverse group of prehistoric reptiles with different body shapes.

Artists impression of Simosuchus clarki (c) Nobu Tamura
Artist's impression of Simosuchus clarki

Since first discovering the unusual crocodilian Simosuchus clarki ten years ago, palaeontologists have worked to recover its fossil from Madagascar.

A decade later, a near-complete skeleton has been achieved, and its analysis has reignited discussion on the evolution of modern crocodilians.

"The skull and lower jaw in particular are preserved almost completely," says Nathan J. Kley, co-editor of the recent study in the Society of Vertebrate Paleontology Memoir.

"This, combined with high-resolution CT scans of the most exquisitely preserved specimen, has allowed us to describe the structure of the head skeleton - both externally and internally - in exceptional detail, including even the pathways of the tiniest nerves and blood vessels," he says.

Tank-like

S. clarki differs greatly to other crocodilians with a blunt snout, short tail and "tank-like" body.

WATER EXPERTS
American crocodile (c) photolibrary.com
Crocodiles bask on land to warm up their cold blood
They are adapted to hunting in aquatic habitats
They wait submerged in the water, striking when prey come close

With its short jaw and weak, leaf-shaped teeth, scientists suggest that the reptile would have been unable to take prey from the water's edge in the same way modern crocodiles do.

Instead, researchers propose that the ancient crocodile lived inland, feeding on vegetation in its semi-arid grassland habitat.

Researchers describe S. clarki as the "most bizarre" of a group of fossilised crocodilians thought to live around 66 million years ago.

This year, palaeontologists working in Tanzania also unearthed fossils of a tiny crocodile-like creature with teeth resembling those of mammals.

The "cat-like" crocodilian's unusual teeth differ from the conical teeth of modern crocodiles, used for ripping and tearing.

At the larger end of the scale, the preserved remains of an eight-tonne giant crocodile further fuelled debate when they were recovered in 2001.



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