New technologies have the potential to shed light on old discoveries. Stephen Gatesy, a professor of ecology and evolutionary biology at Brown Univ., knows that firsthand.
Back in 1995, Gatesy and colleagues were digging in Greenland when they found a pair of jaw bones inside a small limestone slab. It marked the first instance of a haramiyid fossil being more than simply teeth. Haramiyids are precursors to mammals, and lived 210 million years ago.
According to the New York Times, the first haramiyid tooth, which boasted reptilian and mammalian features, was found in Germany in 1847.
Gatesy and colleagues in 1997 published a paper on the find, and determined the fossil was an example of proto-mammal diversification before the origin of “crown mammals.”
Now, the team revisited the fossil specimen, using high-resolution computer tomography and 3-D computer reconstruction. “Haramiyavia (clemmenseni) had a unique way of chewing,” the researchers write in Proceedings of the National Academy of Sciences. “Its teeth of multiple cusp-rows were adapted to omnivory or herbivory and are distinctive from the teeth of other early mammal relatives that are presumed to be insectivorous. On the mammal family tree Haramiyavia occupies a position crucial for dating the initial appearance of the major mammalian groups.”
“Micro-CT scanning allowed extremely detailed 3-D models to be created of each tooth and bone,” said Gatesy. “We then combined evidence from all the material into a composite jaw. I don’t think this would have been possible without digital tools. Out anatomical conclusions largely corroborate the findings of our earlier paper but also increase our confidence in key characters.”
Co-author Neil Shubin, who was part of the original 1995 team, and his lab at Univ. of Chicago led the research.
The new imaging techniques helped the team discover primitive jaw structures, including a postdentary trough connected to the primitive middle ear.
According to Shubin, the jaw’s primitive features clearly place it at the base of the mammalian family tree, and separate from multituberculates, a group of early mammals once thought to be related to haramiyids.
“The findings place Haramiyavia and all other members of the haramiyid lineage on a more ancestral position in the mammalian evolutionary tree, on a separate branch from mammals,” according to the Univ. of Chicago. “It also reaffirms previous arguments that the explosion of modern mammal diversification did not occur in the Triassic period, but many millions of years later in the Jurassic.”
