Ancient fossil remains discovered recently on the shores of Lake Kariba have excited dinosaur researchers from the UK's Natural History Museum. This is the first evidence from Southern Africa of the existence of crocodile-like phytosaurs from the Earth's Late Triassic Period (237-201 million years ago).
Image © Smokeybjb/Wikimedia Commons
The new discovery in the vicinity of the Matusadona National Park shows that this diverse group of animals that looked superficially a lot like crocodiles, but are even more ancient were far more widely distributed than previously thought.
A news item published by the Natural History Museum in January 2020, describes the importance of this find:-
"The Late Triassic Period was a time of great diversity. Dinosaurs were 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 documenting the Lake Kariba finds.
Steve Edwards, a local safari guide and owner of Musango Island Safari Camp brought the fossils to the attention of Prof Paul Barrett, a dinosaur researcher at the Museum of Natural History. Together with his South African, Zimbabwean and American colleagues, he launched two expeditions to the area (pictured below) in 2017 and 2018 to help document the fossils and the sites from which they were discovered.
Image ©dmitri_66/Flickr CC BY-NC 2.0
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 jaws show a striking similarity to those of modern-day crocodiles © Barrett et al. 2020
The study 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.
...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.
The teeth of the phytosaurs show that they were well adapted to catching fish © Barrett et al. 2020
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.
That theory has now been proven wrong.
Steve Edwards has been interested in fossils for some years after discovering a few sites near Lake Kariba. 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, he says
When checking out these sites, Paul Barratt 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 gleaned 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."
Related articles:-
Where dinosaurs roamed - the Matusadona reveals its fossil treasures - (Travel Blog April 2017)
Big Game: Hunting for dinosaurs in Zimbabwe's wilderness (Travel Blog November 2015)