Echidnas look like a quirky blend of hedgehog and anteater. But they’re not related to these creatures at all. They’re even more mysterious and unusual than commonly assumed.
Australia has just one species, the short-beaked echidna (Tachyglossus aculeatus), which roams virtually the entire continent. But it has five subspecies, which are often markedly different. Tasmanian echidnas are much hairier and Kangaroo Island echidnas join long mating trains.
Here are four things that make echidnas remarkable.
1: They’re ancient egg-laying mammals
Short-beaked echidnas are one of just five species of monotreme surviving in the world, alongside the platypus and three worm-eating long-beaked echidna species found on the island of New Guinea.
These ancient mammals lay eggs through their cloacas (monotreme means one opening) and incubate them in a pouch-like skin fold, nurturing their tiny, jellybean-sized young after hatching.
2: From deserts to snow, echidnas are remarkably adaptable
There are few other creatures able to tolerate climate ranges as broad. You can find echidnas on northern tropical savannah amid intense humidity, on coastal heaths and forests, in arid deserts and even on snowy mountains.
3: Mating trains and hibernation games
Remarkably, the subspecies have very different approaches to mating. You might have seen videos of Kangaroo Island mating trains, a spectacle where up to 11 males fervently pursue a single female during the breeding season. Other subspecies do this, but it’s most common on Kangaroo Island. Scientists believe this is due to population density.
Pregnancy usually lasts about three weeks after mating for Kangaroo Island echidnas, followed by a long lactation period of 30 weeks for the baby puggle.
But Tasmanian echidnas behave very differently. During the winter mating season, males seek out hibernating females and wake them up to mate. Intriguingly, females can put their pregnancy on hold and go back into hibernation. They also have a shorter lactation period, of only 21 weeks.
4: What do marsupials and monotremes have in common?
Marsupials bear live young when they’re very small and let them complete their development in a pouch. Despite this key difference with monotremes, there’s a fascinating similarity between Australia’s two most famous mammal families.
At 17 days after conception, the embryo of the tammar wallaby (Macropus eugenii) hits almost exactly the same developmental milestone as echidna embryos. Both are in the somite stage, where paired blocks of tissue form along the notochord, the temporary precursor to the spinal cord, and each have around 20 somites.
What’s remarkable about this? Monotremes branched off from other mammals early on, between 160 and 217 million years ago. Marsupials branched off later, at around 143–178 million years ago.
Yet despite millions of years of evolutionary pressure and change, these very different animals still hit a key embryo milestone at the same time. This striking parallel suggests the intricate process has been conserved for over 184 million years.
Read the whole story at the Conversation.