What do echidnas and platypuses have in common

But only the lineage leading to platypuses and echidnas survived the marsupial invasion, he says. He says monotremes would have only been able to survive by occupying ecological niches where they would have faced the least competition.

Phillips and his colleagues, Thomas Bennett, also from ANU, and Dr Michael Lee from the South Australian Museum, suggest the echidna and platypus found territory in which marsupials were restricted by their reproductive system. This both compromises the ability of the mother to forage in aquatic environments and provides an early development al constraint on the evolution of an anteater-style 'beak'," they write. Although it is no longer amphibious, the echidna can "swim very well and uses its bill like a snorkel", says Phillips.

Its hind feet are also reversed, and it retains the ankle spurs that are venomous in platypuses, but non-functional in the echidna. Tags: animals , evolution , palaeontology , marsupials. Email the editor. Use these social-bookmarking links to share Echidna ancestors swam with platypuses. By clicking 'Send to a friend' you agree ABC Online is not responsible for the content contained in your email message.

Once the young begins to be too big for the pouch and start to grow spines they are left in the burrow for about another days and continue to suck milk. They have copies of all the most abundant milk protein genes similar to the cow, including two novel proteins that may provide immunoprotection, indicative of their switch to lactation as the main method to support their young.

Monotremes also have a number of other unique characteristics. Firstly, it is very difficult to determine the sex in an echidna. Both males and females are very similar in size and all their reproductive organs are internal, they have no scrotum and their distinctive penis only emerges at copulation. Males have a venom gland that secretes novel compounds with currently unknown function into the venom. Adult monotremes also have no teeth, instead they have hard bony plates that they use to grind their food down.

As a result, both species have lost many of the key genes needed for the formation of teeth. Juvenile echidnas, but not platypus, have also lost even their juvenile teeth and with them the genes needed to form tooth enamel. The only tooth that both the echidna and platypus do have is their egg tooth, which helps them tear their way out of the egg at hatching.

A number of aspects of echidna biology are consistent with an amphibious platypus-like ancestor — a streamlined body, rearward-jutting hind limbs that could act as rudders, and the contours of a duck-like bill during embryonic development. It was thought that the much shorter fossil record for echidnas, from about 13 million years ago, was just due to the patchy nature of the fossil record," Phillips said.

Their new findings suggest "the lack of early echidna fossils was in fact because they simply had not evolved yet. The researchers conjecture that marsupials could not afford a substantial invasion of aquatic environments because when they are born, they need to suckle milk constantly for weeks; newborn marsupials could drown if their mothers ever had to venture into the water.

Not only that, but paper suggests that the change from a platypus-like body form to an echidna-like body form appears to have happened surprisingly quickly, in less than 15 to 25 million years. That such a major change in overall morphology could happen so quickly is intriguing. The hint that echidnas may have evolved after marsupials arrived in Australia "contradicts the common assumption that monotremes are living fossils just treading water in an evolutionary sense, and waiting to go extinct in the face of competition with 'superior' mammals, like marsupials," Phillips added.

The fossil record of monotremes remains very incomplete, particularly between about and 25 million years ago, Beck said, noting that fossils that fill this 75 million year gap "might be found in Australia, South America or even Antarctica.

However, there are a number of fossil sites in Australia that are 20 to 25 million years old, and the results of the current paper suggest that echidnas evolved during this period. With luck, future expeditions to these sites will discover fossil echidnas that demonstrate the change from a platypus-like to an echidna-like body form. Since a trait often considered primitive — egg-laying — might actually have helped monotremes survive to the present day, future research could investigate whether the same holds for other characteristics of theirs.