Fossils of a small animal that roamed what is now southern Brazil have turned out to be more than we thought. Brasilodon quadrangularis is an extinct species known to science and dated to 225 million years ago, but until recently it was thought to have been a small reptile. The oldest mammal was considered to be the 205 million-year-old Morganucodon. But a new study has determined that B. quadrangularis was actually a mammal, making it the oldest mammal species we know of.
How does one recognize a mammal fossil without soft tissue, like mammary glands? By the teeth. Reptiles lose teeth and grow replacement teeth throughout their lives, while mammals have two sets, the milk teeth and the permanent adult teeth. B. quadrangularis, a shrew-like creature about eight inches long, has the skull features that signal two sets of teeth over its lifetime.
We don't know whether B. quadrangularis is an ancestor of any of today's mammals, but its age is only five million years newer than the earliest dinosaurs we've found. Its existence shows us that mammals and dinosaurs co-existed for many millions of years. Read more about this discovery at CNN. -via reddit
(Image credit: 2022 Anatomical Society/Wiley)
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