Around 250 million years ago, the Earth was an alien planet. All the continents we know today were joined into a supercontinent known as Pangaea, sitting snugly over the Equator. Much of this land was covered in desert, similar to modern-day North Africa. It is here in these unforgiving environments that the earliest dinosaurs began their rise to power, setting themselves up to dominate land for the next 190 million years.
Alongside the dinosaurs, their close evolutionary cousins – the crocodiles – also began to thrive. Together, crocodiles and dinosaurs (along with their living ancestors, the birds) make up a group known as Archosauria. Archosaurs, or ‘ruling reptiles’, dominated for tens of millions of years, so figuring out their origins and why they were so successful is key to our understanding of the history of life.
Unfortunately, the fossil record from around this period is quite meagre. The ravages of time, along with conditions that didn't favour the preservation of organisms, have meant that fossils from this era are rare, and present gaps in our knowledge of early crocodile and dinosaur evolution.
But now, a new study led by Dr Sterling Nesbitt, assistant professor of geological sciences at Virginia Tech, has identified a new animal that could be crucial in forging an evolutionary link between the earliest crocodiles and dinosaurs.
The animal's ancient remains (245-240 million years old) were unearthed in Tanzania and have been named Nundasuchus songeaensis – ‘Nunda’ is Swahili for predator, ‘suchus’ from the Greek ‘soukhos’ (meaning crocodile) and ‘songeaensis’ in a nod to the nearby provincial capital of Songea. Nundasuchus would have looked a lot like a modern-day crocodile, but with limbs positioned underneath the body, giving it a more upright stance. It probably spent much of its time on land hunting near lakes and rivers for prey a bit more satisfying than fish.
As far as fossils from this period go, Nundasuchus is fairly complete. Although only a single incomplete skeleton exists, its many skull elements, multiple parts of the vertebral column and limb bones (it even had body armour, similar to modern crocodiles) provided a wealth of information that Nesbitt and his team could use in comparing Nundasuchus to other primitive archosaurs. These include many similar and highly bizarre animals, such as the long-snouted and terrifyingly armoured phytosaurs, and the plant-eating but equally armoured aetosaurs.
Unfortunately, the team's investigations did not bring many definitive answers about the link between the earliest crocodiles and the dinosaurs. Was Nundasuchus one of the first archosaurs and a common ancestor of all dinosaurs and crocodiles? Or was it more evolutionarily advanced and part of the crocodile lineage? We still don't know. That's because there are aspects of its anatomy that are common in both early crocodiles and dinosaurs, particularly in the ankle bones.
Nevertheless, the Nundasuchus finding has pretty important implications and it's shaken up the archosaur family tree, raising questions about how well we really know the relationships between early crocodiles and the ancestors of dinosaurs. It also proves that this period in time was a crucial one in the early history of these groups, and something important was happening to their anatomy that enabled them to survive for hundreds of millions of years, while others faded into the realms of extinction.
Why did crocodiles and dinosaurs rise to infamy and dominate as kings of the reptiles? Only time, and more amazing fossil finds, will provide us with an answer.
Top header image: Spencer Wright, Flickr
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