Scientists Reveal a Surprising New Theory on Where Echidnas Came From

New research of a 100-million-year-old fossil embedded in a rocky cove in Australia suggests echidnas could have advanced from swimming ancestors.

That’s principally remarkable: While there are many examples of land-dwelling mammals evolving right into a extra aquatic way of life, it sort of feels that sooner or later, echidnas went in the other way.

Since its discovery within the early ’90s, paleontologists had been debating what sort of animal left in the back of the fossilized arm bone. They comprehend it was once a member of the monotreme order, mammals that lay eggs as an alternative of giving beginning to are living younger.

Based at the bone’s outward look, some suppose it belonged to a land-bound ancestor of recent echidnas. Others say it could had been a swimming monotreme that pre-dates either one of its residing family, echidnas and platypus.

New research at the tiny humerus bone, which belonged to the prehistoric species Kryoryctes cadburyi, helps an aquatic beginning tale.

“While the external structure of a bone allows you to directly compare it with similar animals to help work out the animal’s relationships, the internal structure tends to reveal clues about its lifestyle and ecology,” says paleontologist Suzanne Hand from the University of New South Wales, who led the find out about.

“The internal structure doesn’t necessarily give you information about what that animal actually is, but it can tell you about its environment and how it lived.”

Peeking within the fossil with microCT scans, Hand and her group came upon the bone has a thick, heavy wall and a tiny medullary hollow space (the hole house within bones the place pink and white blood cells are shaped).

Bones like this are noticed in semi or totally aquatic mammals, like sea otters, dugongs, and platypus. Like the burden belt scuba divers use to stick underwater, those characteristics cut back the animal’s buoyancy so it could actually stay underwater with little effort.

“The microstructure of the fossil Kryoryctes humerus is more like the internal bone structure seen in platypuses, in which their heavy bones act like ballast allowing them to easily dive to forage for food,” says Hand.

On land, such dense and heavy bones are a drawback, now not best as it takes extra effort to lug them round, but in addition as a result of they’re extra liable to fractures. This is why such characteristics aren’t noticed in echidnas, that have very skinny bone partitions.

The group additionally carried out phylogenetic research, piecing in combination the place Ok. cadburyi sits within the mammalian and monotreme circle of relatives bushes. This printed the species is certainly a stem monotreme, sharing a not unusual ancestor with platypus and echidnas.

It’s very bizarre information with regards to echidna evolution. It suggests their ancestor was once a swimming, burrowing monotreme that at last hung up the towel for an overly other existence on land. There are a couple of different clues that this may well be the case.

“The bill of the platypus is well known to have lots of highly sensitive receptors that detect tiny electrical currents generated by prey,” Hand issues out.

“And while the beak of the echidnas has fewer receptors, people have suggested that these receptors are a leftover of their platypus heritage, as are remnants of the platypus bill that can be found in the beak of echidna embryos.”

Echidnas even have hind toes grew to become backwards, which is helping them with digging, in the similar method platypus use their backwards toes like rudders to propel them thru water. Perhaps because of this echidnas had been recognized to island hop. This foot orientation is not noticed in every other mammals.

Perhaps echidnas were not left on shore via the intrepid, water-faring platypus. Maybe echidnas have been those that determined to project out into the unknown.

“We’re talking about a semiaquatic mammal that gave up the water for a terrestrial existence, and while that would be an extremely rare event, we think that’s what happened with echidnas,” says Hand.

This analysis was once printed in PNAS.