65 million years ago, the impact of the Chicxulub asteroid led to a mass extinction that wiped out most life on Earth. The end of the dinosaurs enabled the rise of mammals, which occupied many vacant ecological niches and rapidly evolved into numerous new species. Among these was Militocodon lydae, whose fossil was discovered by Lucas Weaver of Kent State University and his team. Although Militocodon lydae outwardly resembles modern martens or red pandas, it is not closely related to them and belongs to a completely different evolutionary lineage.
The fossil comes from the Corral Bluffs site in Colorado and dates to a time shortly after the Chicxulub event. Rock analyses indicate that it was formed around 600,000 years after the impact, which is a relatively short period of time in geological terms. The remains of the animal offer valuable insights into the early phase of mammal evolution, as fossils from this epoch are rare. The partially preserved fossilised skull of Militocodon lydae is therefore particularly remarkable. Based on the skull, Weaver and his team estimate that the animal was about the size of a modern chinchilla and weighed less than 500 grams.
The skull has various features that enable researchers to categorise Militocodon lydae as belonging to the Condylarthra group – a predecessor group of today’s ungulates such as cows, antelopes and deer. The animal’s teeth also resemble those of herbivores or omnivores.
Although the Chicxulub impact enabled the rise of mammals, the first mammal species already lived during the time of the dinosaurs and had already achieved a remarkable diversity, albeit without a dominant position. Mammal-specific traits such as complex dentition, keen senses and the provisioning of fewer offspring through suckling had already evolved in the dinosaur era before mammals really took centre stage after the mass extinction.
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