The picture you conjure up when you hear Middle Jurassic, is one dominated by Dinosaurs, particularly the Tyrannosaurus rex. This is a considerable misconception, since the “Tyrant Lizard King” lived at the end of the Cretaceous about 100 million years later than the Middle Jurassic.
Yes, Dinosaurs dominated the Triassic, Jurassic and Cretaceous Periods, but these were not the only organisms around throughout these periods.
While our friends were a dominant feature on the landscape, our own early progenitors were etching out a living too. One of these creatures was Megaconus mammaliaformis. The best way to describe it is to compare it to a Rock Hyrax (Procavia capensis), a cute furry creature that walked like a Hyrax or an armadillo. It would have weighted about 250g and would have had an omnivorous diet. The fur would have been absent on its underbelly, with a generous covering over the rest of its body.
All this information from one newly discovered fossil skeleton from Dauhugou, Inner Mongolia, northern China. Megaconus is closely related to a family of early mammals called Eleutherodontids, which includes the geni of Eleutherodon and Sineleutherus. All three geni make up the Haramiyidan family. Megaconus shares more features with the Triassic cynodonts than to the later Multituberculates.
The latter represent the longest lasting group of mammals in mammalian history, post-dating the Haramiyidans. Yanoconodon illini: Early Cretaceous Mammal, about 100 million years later than M.
Understanding the features of skeletal anatomy and the ability to compare one fossil species to another is crucial to understanding who is related to who. The teeth are a gold mine of information. The fused root of Megaconus and their hypsodonty (High-crowned teeth), are features also found in the Eleutherodontids, but the tooth crown flutings are a feature unique to Megaconus within the Haramiyidans.
Most of the time, palaeontologists argue over the most meagre of evidence such as isolated teeth, but M. Mammaliaformis is eye-wateringly well preserved. The format of the foot bones lacks the derived characteristics of the bone in the feet of the later Multituberculates.
In addition, M. Mammaliaformis had its middle ear bones embedded within the back of its jaw in the postdentary trough, while the Multituberculates lacked such a feature. M. Mammaliaformis therefore lived prior to the Multituberculates, but well after the Triassic cynodonts. The fossil itself provides the earliest evidence for the existence of furry mammals, dating to between 165 and 164 million years ago.
Header Image : The Rock Hyrax (Procavia capensis) : Wiki Commons