Teeth or fangs? When we think of tusks, the first animal that comes to mind is an elephant or a mammoth. Now, a new study from Harvard University (USA) has confirmed that the fossil remains discovered 176 years ago and belonging to dicynodonts that existed between 201 and 270 million years ago (before the dinosaurs) are tusks and not teeth, making them the first known animal with fangs.
“We were able to show that the first tusks belonged to animals that came before modern mammals, called dicynodons,” said Kenneth Angielczyk, co-author and curator of the Field Museum in Chicago. “They are very rare animals.”
At the time of their discovery, scientists observed that they had protruding teeth in the upper jaw, but scientists were not sure if they were officially the oldest known example of a mammal with fangs. It has already been officially confirmed, thanks to new research that traced the earliest tusks back to dicynodons and shed light on the evolution of protruding teeth by first defining what it is that makes a tusk actually a tusk.
They determined that a tusk must extend from the mouth, consist solely of a substance called dentin, and continue to grow throughout the animal’s life, even if it is damaged.
“Fangs have a very famous anatomy, but until I started working on this study, I never thought about how fangs are restricted to mammals, ” said Megan Whitney, a researcher in evolutionary biology at Harvard University.
In fact, those protruding teeth have attracted a lot of attention since the first dicynodont fossils were scrutinized more than 150 years ago. The famous paleontologist Richard Owen claimed in 1845 that they were made primarily of dentin, with thin layers of enamel, and a fairly open pulp cavity.
“For this article, we had to define a tusk, because it ‘s a surprisingly ambiguous term ,” says Whitney.
Dicynodonts are not mammals but they are distant relatives. They had a beak at the front of their mouth that was made of keratin and resembled the beak of a turtle.
A convergent evolution
The researchers analyzed thin sections of 19 fossilized dicynodont tusks, representing 10 different species from South Africa, Antarctica, Zambia and Tanzania. They also used microcomputed tomography scanners to examine how the fossils were attached to the skull and whether their roots showed evidence of continued growth. They found that while some of the dicynodonts studied had true fangs, without enamel, the rest had large teeth. The scientists also found that different members of the dicynodont family developed tusks independently at different times, and some never developed true tusks.
“I was hoping there was only one moment in the evolutionary history of the dicynodon where the tusks evolved because that is the simplest explanation. However, we found a convergent evolution of the tusks in the evolution of the dicynodon ,” Whitney said. (When similar characteristics evolve independently in different species or in different time periods.)
“Everything is raised to give us a better understanding of the tusks that we see in mammals today,” the researchers conclude.
Referencia: The evolution of the synapsid tusk: insights from dicynodont therapsid tusk histology, Proceedings of the Royal Society B: Biological Sciences (2021). DOI: 10.1098/rspb.2021.1670. rspb.royalsocietypublishing.or … .1098/rspb.2021.1670
