Mammal fossils found on the Jurassic Coast have made the national news. The fossils are the tiny teeth of a primitive mammal that was scurrying around this part of the world around 145 million years ago. They might not sound like the most exciting fossils but their significance is huge.
This fabulous image was drawn by Mark Witton. It shows eutherian mammals on the shores of a lagoon that would have existed here 145 million years ago. Mark will be exhibiting some of his artwork at the Dorset County Museum as part of Dippy on Tour.
The mammal fossils were collected from Durlston Bay, near Swanage. If you’re wondering why you haven’t seen us promote Durlston Bay as a place to find fossils it’s because the cliffs there are very fragile and dangerous and the fossils tend to be hard to collect. In short it is a specialist site and not for the faint-hearted. These mammal teeth, only a few millimetres in size, are a good example of a ‘specialist’ find. The researchers found them in bulk samples of clay that were washed, sieved then searched under a microscope. The fossil-hunting part of this discovery happened in a lab.
This isn’t the first time mammal fossils have been found at Durlston Bay. Back in the 1850’s a man named Samuel Beckles directed a large excavation and recovered many specimens. This put the locality on the palaeontological map, adding to notoriety of a coastline already famous for its fossils. But it’s not just mammals. Durlston Bay is known to be a rich source of fossil fish, reptiles and insects. In 2007 a new species of primitive crocodile was recovered from a landside there. You can see it on display at the Dorset County Museum and online in the Jurassic Coast Fossil Finder database.
The fossil-rich rocks exposed in Durlston Bay belong to the Purbeck Limestone Group. A mixture of limestone, sandstone, marl, clay, and evaporate minerals tell us that these layers were laid down in a changeable environment. Imagine a coastline with sprawling swamps, lagoons, forests and lakes that shift and spread over time. Within these habitats dwelt fresh water and marine life, dinosaurs, pterosaurs, crocodiles, turtles and mammals all living side-by-side. This lasted for about five million years, between 145 and 140 million years ago, running through from the late Jurassic and into the early Cretaceous.
The reason these new mammal fossils are so important is that they come from a very special class of mammals called Theria. As Therians evolved two important ‘infraclasses’ emerged – the Metatherians, which includes marsupials, and Eutherians, which includes all placental mammals. Humans are Eutherians. Most mammals today belong to one of these infraclasses. The mammal fossils collected previously at Durlston belonged to extinct groups only distantly related to Therians. However, these newly discovered specimens show features that suggest they might have come from animals in the Eutherian infraclass. Fossils of Eutherian mammals aren’t unusual… in much younger deposits. The fact that they have been found in rocks 145 million years old is astounding! In fact they are the oldest fossil evidence of the type of mammals from which humans are directly descended. How amazing is that!
The scientific paper detailing the discovery is available for free online and can be downloaded here: https://www.app.pan.pl/article/item/app004082017.html
Sam Scriven, Programme Manager – Conservation & Heritage, Jurassic Coast Trust