Month of Mesozoic Mammals #13: Looking Sharp

Spinolestes

Spinolestes was another gobiconodontid eutriconodont, closely related to Repenomamus but not quite so large. About 25cm long (10″), it’s known from an incredibly well-preserved fossil that includes fine microscopic details of fur, skin, and internal organs. Notably even its external ears were preserved, the earliest known in the fossil record, showing a broad mouse-like shape.

Its coat was made up of both underfur and guard hairs, with a longer mane along its neck and back. There were around a dozen keratinous scales on its rump, under the fur, along with numerous “protospines” – stiff spiky hairs similar to those of modern spiny mice. Some hairs even show damage that matches symptoms of a fungal infection.

It also had strong forelimbs and a reinforced spine similar to both modern xenarthrans and hero shrews. It was likely an insectivore, and may have used its strong back much like hero shrews are thought to do, pushing under heavy logs and rocks and levering them up to find invertebrate prey underneath.

Month of Mesozoic Mammals #12: Dinosaur-Eaters

Repenomamus

Living during the Early Cretaceous of China (125-122 mya), Repenomamus was part of a branch of the eutriconodonts known as gobiconodontids. These relatively big mammals were specialized carnivores, with strong bone-crushing jaws and their incisor teeth modified into long fang-like shapes.

Gobiconodon’s weird front-fangs
(cropped from Skeleton of Gobiconodon by Ghedoghedo || CC-BY-SA-3.0)

Repenomamus giganticus was roughly the size of a modern wolverine, about 1m long (3′3″). A second species in the same genus, Repenomamus robustus, was about two-thirds that size but still among some of the largest known Mesozoic mammals.

Since it was larger than some of the dinosaurs it lived alongside, it’s likely to have eaten some of them – and one specimen of R. robustus was actually found with the bones of a juvenile Psittacosaurus in its stomach.