British scientists have discovered two fossilised teeth and described them as “the earliest undisputed fossils of mammals belonging to the line that led to human beings”. The 145-million-year-old teeth, found by a University of Portsmouth student, belonged to two separate species, both of them furry and ratlike, researchers from the university write in a study published Tuesday in Acta Palaeontologica Polonica.
The adjective “undisputed” has a context, for there has been another claimant to being the earliest fossil of a mammalian ancestor of humans. Juramaia sinensis, found in China, was described in 2011 from a fossil that was 160 million years old. The new study, however, disputes the claim that Juramaia was a eutherian, or placental mammal, a grouping that includes humans.
“Various molecular studies have come up with a much later date for the origin of Eutheria, thus eliminating Juramaia from Eutheria, but these are all theoretical,” Steve Sweetman, lead author of the new study, told The Indian Express by email. “In contrast, fossils provide physical evidence and Averianov 2015 [a study] does not accept Juramaia as a eutherian based on dental characters, and in this we agree,” Sweetman added. “Our teeth are unequivocally eutherian and so, at least for now (!), are the earliest examples.”
The newly published paper cites the 2015 study, by Alexander Averianov of the Russian Academy of Scientists. Neither Averianov nor Zhe-Xi Luo, the paleontologist who had described Juramaia in 2011, had responded to emails from The Indian Express at the time this report was being written.
The two newly described species have been named Durlstodon ensomi and Durlstotherium newmani. The University of Portsmouth team credits Grant Smith, an undergraduate student, with finding the two teeth among earliest Cretaceous rocks collected on the coast of Dorset in Southern England. Smith is now reading for his Master’s degree at the university.
“I was asked to look at them and give an opinion and even at first glance my jaw dropped!” Sweetman said in a statement released by the university.
One of the ratlike mammals fed on insects, while the other may have also eaten plants. Both were likely nocturnal creatures. Sweetman explained how a study of the teeth led to those conclusions. “One of the species (Durlstotherium) had teeth that very closely resemble teeth of modern insectivores; the other had more robust teeth that indicate it may have eaten plant material as well as insects,” Sweetman wrote to The Indian Express, in response to a question. “Some early mammals are represented by skeletons including skulls, and study of the brain shape and nerves indicates that many of these animals had eyesight adapted to nocturnal activity.”
After Smith, the university student, had found the teeth, his supervisor, palaeobiology professor Dave Martill, confirmed that they were mammalian. “We looked at them with a microscope but despite over 30 years’ experience these teeth looked very different and we decided we needed to bring in a third pair of eyes and more expertise in the field in the form of our colleague, Dr Sweetman,” Martill said in the university statement. “Steve made the connection immediately, but what I’m most pleased about is that a student who is a complete beginner was able to make a remarkable scientific discovery in palaeontology and see his discovery and his name published in a scientific paper. The Jurassic Coast is always unveiling fresh secrets and I’d like to think that similar discoveries will continue to be made right on our doorstep.”
Of the two new species, Durlstotherium newmani has been named after Charlie Newman, the landlord of the Square and Compass pub in Worth Matravers, close to where the fossils were discovered.