Headscratchers / After Man: A Zoology of the Future

• Why are there still marsupials in megafauna niches even though Australia has collided with Asia and the placentals have invaded the continent? Large marsupials have proven unable to compete with placentals in the past, so logically only small opossum-like forms should be the only surviving marsupials.
  • Possibly the original extermination of large mammals impacted Southeast Asia, with its very dense human population, more severely than Australia, most of which is only sparsely inhabited. If Australia's marsupials bounced back faster than the wider world's placentals, then large-bodied marsupial species may have only been confronted by small types of placentals when the land bridge emerged. The real question for Australia is why it didn't get taken over by the rats and rabbits that were already in residence before the continental collision.
  • While many marsupials have been outcompeted by placental mammals, kangaroos and wombats are both pretty resilient and have a fairly rabid reproductive rate for their size. Both of those groups are still doing pretty well in Australia even with all the invasive placental species.
  • Marsupials are actually superior to placentals in certain environments, that's why they dominated Australia and once did so in South America. The modes of reproduction have their advantages. The reason they seem like such pushovers right now is because the Pleistocene extinction and human activity absolutely gutted Australia's whole food web to the point the largest native mammal would only be medium size at biggest elsewhere. Given a few millions of years to adapt and change without humans nerfing the food web, and many of the invasives in Australia would have a much harder time.
  • The map at the beginning shows a large mountain range between Australia and SE Asia, and the book mentions that those mountains are higher than the Himalayas. That's a pretty effective barrier to placental colonization.
• The predator rats make no sense. How would they retain sharp stabbing points in their teeth, if their teeth wear down and grow continuously?
  • Why would they even need stabbing points, for that matter? Rodent incisors already have a razor-sharp front rim that concentrates their bite-force quite efficiently for both grip-strength and penetration.
  • The predator rat's dentition is actually plausible as something like it has actually evolved at least once before in the Thylacoleo, which were predatory marsupials that were descended from herbivorous marsupials with rodent-like incisiors. Their sharp front teeth were very close in shape to the predator rat and they even had an incredibly powerful bite-force for their size. As for the growth issue, more than likely when they transitioned to a meat based diet their teeth simply evolved to grow at a much slower rate. That or they could simply wear down their teeth on the bones of their kills.
• So apparently female bardelots are smilodon-analogues while males hunt aquatic prey similar to polar bears? Why would they occupy such different niches? And how come it's the female who grows the big sabers, when usually it's the male mammals who grow elaborate weaponry (only male Asian elephants have tusks, for example).
  • The idea of an animal having males and females that occupy different niches isn't unprecedented. There was once a species of bird in New Zealand, the huia, which had males and females with differently-shaped beaks.
    • There's a bird in this book with extreme sexual dimorphism, the common pine chuck.
  • Possibly occupying different niches, with the females being the more heavily-armed, also allows a female bardelot to avoid the female bear's perennial problem of males killing and eating her cubs.
  • I checked, and the book doesn't mention the male bardelot hunting different prey than the female.
  • When male mammals evolve elaborate weaponry that females lack, it's almost invariably for the purpose of contending with other males for mating opportunities. In the male bardelot's case, population density may be so low that rival males aren't enough of an issue to be worth investing resources in sparring equipment. Rather, their need to traverse vast distances to find females promotes the males being lighter and more mobile than their mates, who need the added weaponry to kill enough prey to sustain cubs.
• So the vortex and porpin retain their single egg internally until it hatches. Wouldn't the cracking of the shell inside injure the mother? (There is one documented case of a domestic chicken that allegedly gave "live birth" in this manner, but the hen died of internal trauma.)
  • Possibly the shell dissolves rather than cracks. Or the female ejects the egg immediately before it hatches.
  • Or they just stopped adding an outer calcium layer to their eggs at all.
• How does the Clatta's tail protect it from predators? If its main enemy are the brachiating strigers then the predator could just hang down from the branch and attack it.
  • Or just climb down the tail to get at the non-armored part of it.
  • The clatta's tail seems long enough to where the striger simply can't reach down to get at the body. As for climbing down, that's likely a bad idea as it's possible that the clatta's tail isn't strong enough to hold the weight of both animals or the fact that if the striger killed the clatta when clinging to it's body then it's tail would stop holding on and the striger would fall to it's death.
  • It doesn't have to kill it outright; the striger could inflict some deep gashes and then hop back up onto the branch to wait for the clatta to bleed to death. As for the weight issue, if the clatta's grasp on its perch is that fragile, the striger wouldn't even need to draw blood: it can jump onto its prey from above, leap back off it even as its grip gives way, and snag an adjacent branch from which to watch its lunch plummet helplessly to its death.
    • That seems like a remarkably convoluted hunting strategy. Also, if the striger knocks to clatta to the ground then it will have to make the effort to reach the forest floor to eat it, at that point it would have been stolen by another predator and a creature as specialized for arboreal life as striger wouldn't fair well on solid ground.

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