First fossils of crocodile-like phytosaurs from southern Africa

The Late Triassic Period (237-201 million years ago) was a time of great diversity. Dinosaurs we just coming into their own, archosaurs were vying for dominance, and the ancestors of mammals were scurrying around in the undergrowth.

Among them was a group of animals called phytosaurs. Looking a lot like modern crocodiles, their fossils are well known from North America and Europe, as well as Morocco, Brazil, Madagascar and India.  

But despite southern Africa containing ample rocks from the right age and plenty of Triassic fossil sites, the remains of phytosaurs have been conspicuously absent from this region. Now, a team of international palaeontologists have published a new paper showcasing phytosaur fossils from northern Zimbabwe.

Prof Paul Barret, a dinosaur researcher at the Museum, helped document the fossils and the sites from which they were discovered along with his South African, Zimbabwean and American colleagues.

'This is the first discovery of phytosaurs from southern Africa,' says Paul. 'It provides us with our first snapshot of an mostly aquatic environment from this part of the world, which was part of the ecological puzzle that was missing before.'

The study has also allowed the researchers to properly date the rocks in which the fossils were found, placing the entire site into much greater context with the other Triassic-age formations found across South Africa, Namibia, Botswana, Zambia and Tanzania.

Ancient aquatic ecosystems

Phytosaurs are a group of extinct semi-aquatic animals that thrived during the Late Triassic. While superficially they look similar to crocodiles as they played a similar role in the environment, they are far more ancient. It is thought that phytosaurs evolved before dinosaurs and crocodiles separated.

Some phytosaurs evolved into crocodile-like animals, with long slender snouts filled with sharp teeth perfect for catching slippery prey. The main difference between the two groups is the location of the nostrils, which are found at the tip of the snout in modern crocodiles but near the eyes in phytosaurs. 

But phytosaurs were diverse, with other forms seemingly more suited for grappling land-based prey and more still that were intermediate forms. They ranged in size from animals a few metres in length to others that were up to 12 metres long.   

Most importantly, phytosaurs are a good indicator of what the environment was like at a particular time and place.

'Phytosaurs usually need permanent bodies of water,' explains Paul. 'They're big animals that liked large lakes and rivers.'

These kinds of environments would not have been unusual during the Late Triassic, which is one of the reasons why the distinct lack of any phytosaurs from southern Africa is particularly curious.

It had been suggested that the animals were limited geographically to the subtropics as the majority of fossils found have been from places that were once much closer to the equator.  

A cosmopolitan group

That theory has been proven wrong. On the shores of Lake Kariba in northern Zimbabwe a local safari guide called Steve Edwards made a significant discovery. Bringing the fossils to the attention of Paul and his South African colleagues, they launched two expeditions to the region in 2017 and 2018. 

'I've been interested in fossils for some years now after discovering a few sites near Lake Kariba,' explains Steve. 'Of particular interest is the discovery of the phytosaur remains, and over the years I have found armoured plates from these animals as well as a variety of lungfish teeth, which may even belong to a new species.'

When checking out these sites, Paul and his colleagues found further bits of phytosaur, including jaws, teeth and armour plates, as well as plenty more lungfish teeth and the remains of ancient amphibians known as metoposaurids, confirming that this must have once been a freshwater environment.  

A bigger picture of what this region was like 210 million years ago can be gleamed from the copious amounts of fossil wood littering the site.  

'Most of that fossil wood comes from conifer-type trees,' says Paul. 'So it was probably a fairly densely wooded area, with some of those large trees reaching up to a metre in diameter, surrounding a permanent bodies of water or large river channels.'

This site is important, as there has been little evidence for aquatic habitats of this age in this region, and helps us to understand just how cosmopolitan phytosaurs were during the Late Triassic.