The ancestry of platypus and echidnas , jointly known as egg-laying mammal , can be traced to diametrical realm live calendar month without sunlight , fossil point . This is just one of the findings emerging from an effort to put some purchase order into the egg-laying mammal mob Sir Herbert Beerbohm Tree .
Although they have pelt and grow milk , monotremes are so unlike other mammals . British naturalist excellently believed platypus specimenswere hoaxes : how else could feature resembling such take issue tool be compound in one animate being ? Today , egg-laying mammal are play purely by the platypus and four echidna species , but during the Cretaceous , they were more diverse , despite the competition from dinosaur .
Just how various remains a mystery , however , because the regions egg-laying mammal inhabit were either not great for fogy conservation , or lie beneath so much frappe today . However , some of Australia ’s leading palaeontologist have mix to make sense of the fossil we do have in a study published inAlcheringa : An Australasian Journal of Palaeontology .
The oldest known monotreme fogey , Teinolophos trusleri , is also the small . Having been found in 120 million - twelvemonth - old Strzelecki Group sedimentation in south - eastern Australia , it is estimated to have weighed just 40 grams ( 1.4 ounces ) – around the sizing of a shiner . Back then , Australia was attach to Antarctica and the Strzeleckis were near the Antarctic rotary .
First authorProfessor Tim Flanneryof the University of Melbourne told IFLScience thatTeinolophosis “ very much what you would expect of a prototypical egg-laying mammal . It had no right snoot , but a patch of electrosensitive skin . ” This patch acquire into the bill the platypus uses to hunt for insect prey in often muddy current and the beak echidnas practice to sense ant and termites . The capacity to detect electrical signals has remained as much a feature differentiate monotremes from other mammals as their egg place .
“ Doubtless there was a fossil record before [ Teinolophos ] but possibly not much before , ” Flannery added .
Despite the polar “ dinosaurs of darkness ” come across by two of this paper ’s co - author , the poles in the other Cretaceous may have been one of the more welcoming places for mammal at the time . During the late Cretaceous , at least four genera of monotremes evolved in the same region , one of which include some of the largest mammals of their day . However , it seems only one made it through thedeeper darknessafter the asteroid impact .
The extinction of the non - avian dinosaurs create an opening for mammals , but it seems monotreme paws were ill - suited to dig it . Although one monotreme fossilAsfaltomylos patagonicushas been find in South America from 63 million years ago , they have otherwise been restricted to Australia and sometime - connected islands like New Guinea , and have always been far outnumber , even there , by marsupial .
As Australia drifted north the monotreme may have been slower to adapt to non - polar precondition , although today the echidna ’s habitat cover more of the continent than any other native mammalian .
Flannery and carbon monoxide - authors place all have a go at it monotremes , living and nonextant , into five families , one of which , the Teinolophidae , has not been scientifically describe before . They rationality echidnas evolved from platypus in New Guinea during a time when it was isolated from Australia , before spreading to the south when water degree were low enough to get together the two .
Despite sticking fairly tightly to the echidna and platypus strain , some diversification did take position in the post - asteroid man , highlighted byMurrayglossus hacketti , at a meter long and an approximate 20 - 30 kilograms ( 44 - 66 pound ) the big egg-laying mammal that ever go . Flannery told IFLScience it probably wax tree diagram to fertilise off southwest Australia ’s arboreal termites .
