As only weighted mammals with surviving eggs in the world, the Australasia platforms and four species of echidna are among the most extraordinary animals of the earth.
They are also very different from each other.
The stake is well suited for a semi-aquatic lifestyle, passing up to 20 hours a day by swimming in the Australian sailors to feed on freshwater invertebrates. Echidnas, on the other hand, live entirely on earth. They are widely distributed through Australia and New Guinea, and adapted to feed on termites, ants and earthworms.
How did these differences emerged? Some researchers think that echidnes have evolved from a swimming ancestor and ornithorynque type. This assumption is based on evidence of aspects of their genes and anatomy, and hypotheses on their evolutionary history.
However, this idea is controversial because the fossil evidence of such a deep evolutionary transformation have been disadvantaged – so far.
Natalia Golovina / Shutterstock
A bone from 108 million years ago
In our study published today in PNAWe gleaned new data from a humenus mammal of 108 million (Bra Bone), found 30 years ago in Dinosaur Cove, Victoria, by a team from Victoria museums.
This arm bone, of a species called Kryoryctes Cadburyibelongs to an ancestral monotrem – a semi -aquatic burrow like the ornithorynque. Our results support the hypothesis that the echidnes of life of the earth have evolved from an swimming ancestor.
Kryoryctes Lived at the time of dinosaurs (the mesozoic), when the monotrimes and the monotremaic parents were more common than they are today. Overviews of this past diversity are found in the fossil file in Southern Victoria And Lightning Ridge, New South Wales.
However, the Australian mesozoic mammal fossils are extremely rare and mainly consist of teeth and jaws. Kryoryctes is the only known of a bone of members, which provides important information on its identity, relationships and lifestyle.
Peter Schouten
Tiny clues inside the bones
In order to test the evolutionary relationships of KryoryctesWe have added it to a wider data set of 70 fossil and modern mammals. From there, we have calculated an evolving tree. It showed Kryoryctes is an ancestral monotrem.
We have also compared the external shape of Kryroryctes Humerus bone with living monotremes. These analyzes have indicated that bone is more like those of echidnes rather than ornithordies.
But that was another story inside. When we looked at the internal structure of Kryoryctes Humerus with several 3D scanning techniques, we have discovered microscopic characteristics of this arm bone that looked more like those of the ornithorynque.
These tiny characteristics inside the bones give crucial clues to the lifestyle of an animal. Many previous studies Connect the bone microstructure in mammals and other tetrapods (animals with four members) with their ecology.
Using the wealth of data available for living mammals, we have compared the characteristics of the Kryoryctes Humerus microstructure with those of the Onithor Terms, Echidnes and 74 other species of mammals.
These analyzes have confirmed that the Kryoryctes The humerus has characteristics of the internal bones found in mammals of semi-aquatic burrows (such as the ornithorynque, the Muskrat and the Eurasian otter), rather than mammals burgled in the earth such as Echidna.
Victoria museums
Water to earth
This discovery suggests that a semi-aquatic lifestyle is ancestral for all living monotrimes. He also suggests that the amphibious lifestyle of the modern plastering had its origins at least 100 million years ago, at the time of dinosaurs.
In this scenario, the modern line of ornipositive has preserved the ancestral semi-aquatic lifestyle for more than 100 million years. Echidnas would have returned more recently to a terrestrial lifestyle.
For the Echidnas, a return to the earth seems to have led to adaptations such as their long bones becoming lighter, as shown by our study.
They may also have lost several other more useful characteristics for spending time in water rather than on earth, including the loss of a long tail, reducing the strap between the fingers and toes, the reduction in the duck bill to a narrow beak and a reduced number of electroreceptors on this beak.
However, precisely when this evolutionary transformation has occurred is not yet known. The answer must wait until the first Echidna fossils are – so far, nothing final has proven to be nowhere.
Modern habitats of monotrimes are increasingly threatened by environmental degradation, interactions with humans and wild predators and climate change. This is particularly true for storm oral. To ensure the survival of this old line, we must better understand how their unique characteristics have evolved and adapted.