This leaves open the question whether the eutherian XY evolved 310 million years ago, shortly after the common ancestor of mammals and birds/reptiles, or less than 166 million years ago, at the time of the common ancestor of monotremes
and eutherians (Figure 5).
Answers: ACROSS: 1) gum 5) kangaroo 6) pouch 7) claws DOWN: 2) monotreme
3) marsupial 4) joey.
The cards containing the terms to be defined (like monotreme
, platypus, marsupial, etc.
The adaptation is clearly important: with the exception of the platypus and its fellow monotreme
, the echidna, the reproductive successes of mammals sporting external testes (and, conceivably, happier sperm) eventually allowed them to crowd out every other mammal on Earth.
Platypus are one of three monotreme
(egg-laying mammal) species remaining in the world and exist only along the east coast of Australia and in Tasmania.
While Geering (1983:table 5) recorded a single monotreme
bone (platypus, Ornithorhynchus anatinus) from between spits A10NW to A14, neither this nor the echidna (Tachyglossus aculeatus) was identified during this study.
It also implies that today's monotreme
descendants of T.
At the same time, the American Zoo and Aquarium Association's Marsupial and Monotreme
Taxon Advisory Group (AZA M & M TAG) recommended in its Regional Collection Plan (RCP) that the YFRW become a Species Survival Plan (SSP) species (AZA M & M TAG 2000).
Wacky Fact: The small monotreme
, when threatened, can dig a hole in soft soil with all fours at the same time while remaining completely horizontal
Australians call this egg-laying mammal, or monotreme
, the "Bits and Pieces Animal.
Webb is correct, however, to emphasize the possibility that the early inhabitants suffered from zoonotic diseases present in the remnant marsupial and monotreme
populations, particularly since these animals would have been isolated from placental mammals, including hominids, from the Cretaceous Period, some 136 million years ago, prior to the breaking up of Gondwanaland.
Studies of the only other two monotreme
species had suggested that the animals don't have REM sleep, implying that it evolved after monotremes
diverged from the other two mammalian branches, marsupials and placentals.
At another site, researchers have discovered the oldest known monotreme
in 110-million-year-old rocks (monotremes
, the earliest mammals, lay eggs and display both reptilian and mammalian characteristics).
We know the common ancestor would have been more platypus than echidna because fossils dating back to 60 million years reveal a monotreme
that was slightly larger than the modern-day platypus, but very anatomically similar," said Phillips.
Known as monotremes
, these mammals were more common tens of millions of years ago.