Month of Mesozoic Mammals #11: Getting Airborne


One of the earliest major branches of the theriiformes were the eutriconodonts. First appearing in the fossil record in the Early Jurassic, about 190 million years ago, these mammals were a highly successful group that adapted to a variety of different niches and lasted up until nearly the end of the Cretaceous.

Their exact relationships to other theriiformes are a little uncertain, with it being unclear whether they split off before or after the multituberculates (another major group featured later this month).

Volaticotherium is known from the Middle Jurassic of China (165-161 mya), and was the first gliding Mesozoic mammal to be discovered (although we now know about quite a few more). It was part of a branch of the eutriconodonts known as the volaticotherians, a widespread lineage which ranged through most of the Jurassic period and into the mid-Cretaceous.

Measuring about 26cm long (10″), or about 14cm (5.5″) excluding the tail, it’s known from a mostly complete skeleton with impressions of fur and skin. A gliding membrane extended from its hands to its hindlimbs and the base of its tail, its feet had grasping toes, and its tail was flattened to create an airfoil-like shape.

It had sharp slicing teeth, indicating a carnivorous or insectivorous diet – unusual since most other known gliding mammals are predominantly herbivores.

Unsolved Paleo Mysteries Month #19 – Mesozoic Maritime Mammal Molars

Icthyoconodon jaworowskorum was a member of the volaticotherians, a group of eutriconodonts most famous for featuring the earliest known gliding mammal. Living during the Early Cretaceous of Morocco (~145-140 mya), it’s known only from a few isolated teeth.

Based on the measurements of the teeth it was probably one of the larger eutriconodonts, close in size to Jugulator. I can’t find any body size estimates, but it may have have a total length of around 50-60cm (20-24″).

Plenty of fossil mammals are known solely from teeth, but what’s most interesting about this one is that its remains were found in coastal marine deposits without any signs of degradation or transport damage by water currents. This indicates the animal probably died at sea very close to the location where it was preserved.

A few other eutriconodonts are now known to have been semi-aquatic, so Ichthyocondon might have been adapted to a similar lifestyle, making it one of the earliest known marine mammals. Another potential explanation is that it was a Volaticotherium-like glider that got blown out to sea.

As with many of this month’s paleontological mysteries, we need some more substantial fossil remains to know for sure. I’ve reconstructed it here as both main possibilities, as an otter-like semi-aquatic animal and as a patagium-bearing glider.