Ancient croc was mammal mimic

By Marlowe Hood/AAP + AG staff 5 August 2010
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New fossils reveal a mammal-like crocodile that lived on land and chewed rather than chomped its prey.

MODERN CROCODILES CHOMP THEIR prey, tearing it with their large teeth and swallowing whole, but a newly-discovered ancient species of croc had more mammal-like teeth, which it used to chew its food.

Scientists from Australia and the US have unearthed fossil bones of  a 100-million-year-old creature in Tanzania, which was about the size of a domestic cat and more at home on land than in water. ‘Pakasuchus kapilimai’ had an unusually lean profile, a flexible backbone and relatively little scaly armour around its midriff, the better to leap in the air to grab giant dragonflies and other airborne prey. But the most bitingly distinctive feature of Pakasuchus, the researchers say, was its choppers.

It shared the overhanging, fang-like canines that today’s alligators and crocodiles use to rip into their victims’ flesh before swallowing them more-or-less whole. But it also had specialised teeth that looked suspiciously like the molars once thought to be unique to our distant warm-blooded ancestors. Unlike modern crocodiles, the researchers say, this creature’s molar teeth possessed shearing edges for processing food, similar in form to the teeth of some mammalian carnivores.

Wannabe mammal

“At first glance, this croc is trying very hard to be a mammal,” says Patrick O’Connor, a professor at Ohio University in Athens, US, and lead author of the study, published in Nature today. “A number of characteristics of this new species are very similar to features that were critical during the course of mammalian evolution from the Mesozoic into the Cenozoic,” which began 65 million years ago.

Aside from possessing molar teeth, this ancient croc had more forward facing nostrils and longer limbs, compared to modern crocs’ upward-facing nostrils and comparatively shorter limbs.

The discovery adds to a growing body of evidence suggesting that crocodiles were once far more diverse that they are today in body type, habitat and appetites. The small croc would have co-existed with carnivorous dinosaurs such as Australovenator, as well as the huge, plant-eating sauropods and survived long after the big dinosaur extinction. Though it was a crocodilian, it is not a close relative of today’s crocs, belonging instead to an offshoot group of modern crocodile ancestors that died out.

O’Connor and colleagues found a complete skeleton of Pakasuchus in Tanzania’s Rukwa Rift Basin in 2008, and have also recovered portions of seven individuals. They suggest that the land-living animal was abundant between 110 and 80 million years ago on what was then the super-continent of Gondwana, the land mass that eventually broke up into Africa, the Arabian peninsula, Australia, Madagascar, India, Antarctica and South America.


Eric Roberts from James Cook University’s School of Earth and Environmental Sciences collaborated on the research while at Southern Utah University. He says that few mammal fossils had been found in the landmasses that once made up Gondwana. The ones that have turned up don’t appear to be related to modern mammalia. “It could be that 100 million years ago this species of crocodile, which was land-based, filled the niche normally occupied by mammals,” he says.

This sheds more light on the evolution of crocodiles, he says, pointing to their “incredible success” at inhabiting different environments and diversifying the species.

Little is known about the vegetation during that period, he says, but clues from the sediment suggest the landscape was dominated by a large, long-lived river system and floodplains rich in vertebrate animal life.

The new crocodile’s name comes from “paka”, the Swahili word for cat, and “souchos,” Greek for crocodile. “Kapilimai” is a nod to Tanzania’s pioneering palaeontologist Saidi Kapilima.



Detailed digital representation of the skull of an ancient mammal-like crocodile (Credit: Ryan Ridgely and Patrick M. O’Connor, Ohio University)