Platypuses Emerged 120 Million Years Ago

Oct. 22, 2007 -- Close relatives of the platypus, a semi-aquatic mammal that is so unusual scientists at first thought it was a hoax, emerged much earlier than previously thought, scientists announced recently.

Instead of dating to long after the great extinction event that wiped out the dinosaurs, as researchers suspected, it is now believed that platypus descendents, including those of their echidna relatives, go back to at least the Early Cretaceous period, and possibly even earlier.

The Early Cretaceous is associated with the first appearance and prominence of numerous dinosaur groups.

The key to the platypus puzzle was an ancient egg-laying mammal relative called Teinolophos trusleri, whose fossils have been collected over the past decade.

"It suggests that both the platypus and echidna lineages were distinct by 120 million years ago, and that the platypus, at least, has occupied its stable niche as an electro-receptive aquatic predator ever since," explained Timothy Rowe, who announced the finding at the Society of Vertebrate Paleontology annual meeting in Austin, Texas.

Rowe, a vertebrate paleontologist at the University of Texas at Austin, and his team used a high-resolution X-ray CT scanner to examine the Teinolophos trusleri remains.

The scans revealed a large internal canal located in the animal's lower jaw. Platypuses today still have this canal, which is involved in electrical signal detection. Around 40,000 neurons, present in the platypus duckbill, pick up signals that prey, such as tadpoles, shellfish and bugs, emit as they swim. The neurons exist in thick, cable-like fibers that leave large canals in the platypus's lower and upper jawbones.