for National Geographic News
Platypuses and their closest evolutionary relatives, the four echidna species, were thought to have split from a common ancestor sometime in the past 17 million to 65 million years.
But remains of what was believed to be a distant forebear of both the platypus and the echidna—the fossil species Teinolophos—actually belong to an early platypus, according to scientists who performed an x-ray analysis of a Teinolophos jawbone.
The finding means the two animals must have separated sometime earlier than the age of the fossil—at least 112 million years ago.
Outlived the Dinos
The international team, led by Timothy Rowe, of the University of Texas in Austin, used a specially modified CT scanner to capture high-resolution images of the internal structure of a 112.5- to 122-million-year-old Teinolophos jawbone found in southeastern Australia.
The scientists found that the Teinolophos had already developed features thought to be unique to modern platypuses, including an electro-sensitive "bill" for finding aquatic prey.
"This pushes the platypus back across the K-T boundary," Rowe said, referring to the mass extinction event that wiped out the dinosaurs about 65 million years ago.
"Now it looks like [platypuses] crossed the boundary without any problem."
The study appears in today's edition of the journal Proceedings of the National Academy of Sciences.
Platypus bills are complex sensory organs loaded with electrical receptors. In murky waters the animals hunt by tracking the weak electrical fields generated by muscle activity in fish and other prey.
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