Continuing our march through the Top 10 Open Access Fossil Taxa of 2017…
Today’s marsupials are almost entirely a southern hemisphere phenomenon–other than the Virginia opossum and a few other opossum-like species, the northern half of our globe is pretty depauperate in marsupials. Competition from placental mammals (the group including us humans, as well as most of the other mammals we know and love) is often cited as a major factor, and this situation has held for much of time since the big dinosaur extinction.
Still, some surprises remain in the fossil record. Anatoliadelphys maasae, described this past summer in PLOS ONE, was a marsupial-cousin from central Turkey. I say marsupial cousin because it it falls just outside of the “crown group” of modern marsupials and their relatives; it split off from the evolutionary tree a bit earlier than kangaroos and possums and kin, but is still part of the larger group called Metatheria. Anatoliadelphys falls out at Number 3 on our Top 10 list!
Anatoliadelphys lived around 44 million years ago, and is known from a partial skull and skeleton. The amount of skeletal material places Anatoliadelphys as a pretty well-known metatherian, providing plenty of information to reconstruct its diet and lifestyle.
Based on comparison with modern animals, Anatoliadelphys was probably about the size of a housecat, weighing in at 3 or 4 kg. Their teeth, jaw proportions, and jaw muscle attachments suggest something with a fairly strong bite force, feasting on meat as well as chowing down on hard-shelled invertebrates (e.g., snails). The limb bone anatomy shows that they were capable of climbing and moving through the trees, although weren’t as adept as many modern climbing animals (e.g., squirrels). In the eyes of the authors, perhaps the best modern analogy for Anatoliadelphys is the tiger quoll. These contemporary marsupials are adequate, but not great, climbers, versatile carnivores, and roughly the same size as Anatoliadelphys.
For its time and location in the northern hemisphere, Anatoliadelphys is an unusual critter. It’s comparatively large for an early-splitting metatherian, and its lifestyle and diet are also remarkable for a northern metatherian. The authors suggest that it might have benefited from comparative geographic isolation; other animals in the same fossil assemblage are perhaps consistent with an isolated ecosystem relative to the rest of the world, and geology suggests the area was an island. Furthermore, this ties in with a hypothesis of competitive exclusion for metatherian evolution–if modern-type carnivorous placental mammals had been around, metatherians such as Anatoliadelphys wouldn’t have stood stand a chance.
Anatoliadelphys is a neat animal–it has a decent amount of fossil material known, and is unusual for its time and place. As such, it has earned its spot on this year’s Top 10 list!
Maga AM, Beck RMD (2017) Skeleton of an unusual, cat-sized marsupial relative (Metatheria: Marsupialiformes) from the middle Eocene (Lutetian: 44-43 million years ago) of Turkey. PLoS ONE 12(8): e0181712. https://doi.org/10.1371/journal.pone.0181712