On the “Prehistoric Predators” episode “Terror Bird,” which aired recently, they showed some footage of a terror bird running down and pecking to death a South American hoofed mammal which sounded, to my ears, anyway, like “homalottatherium.” Whatever it was, it has no living descendants, and no close living relatives, and I was just trying to find some further info, but apparently my spelling is a bit too far off to get a close Google hit.
Anyone? It looked sorta like a tapir, in the quick scenes it could be seen.
Googling “prehistoric South American hoofed mammal” resulted, among other things, in Gondwanatherium. More detailed information here, but I couldn’t find pictures. Could this be what you’re looking for?
Did the animal look like a little horse? If so then it was probably: Thoatherium - Wikipedia
South America was an island continent for tens of millions of years and hosted several orders of hoofed animals that were completely unrelated to our familiar artiodactyls and perrisodactyls. (Litopterna - Wikipedia, and Notoungulata - Wikipedia) Many of these creatures evolved to appear superficially similar to horses, hippos, rabbits, camels, and so on. There were also lots of large marsupials and other unique animals, such as armadillos and sloths and anteaters. Over time rodents and primates filtered in, perhaps through island hopping.
But then the Isthmus of Panama formed, and North America was connected by land bridge to the former isolated continent of South America. Some South American animals made it north (opossums, armadillos and porcupines are surviving examples) while many North American mammals made it south–jaguars, llamas, and so on. Great American Interchange - Wikipedia
I’ll bite. What is the latest idea on the divergence timelines of the various ungulates, like perissodactyls, artiodactyls, notoungulates, and throw in the xenarthrans and afrotheres and a uintatherium just for kicks (although I realize that any relationship with the afrotheres would have to predate the Africa/South America split). I’m assuming that these have a single common ancestor at some point, but that’s just an assumption. I have no formal background on the subject. I just like documentaries.
The problem is that all these conjectures about high-level relationships between mammal groups are pretty tentative, and they are very dependent on genetic analysis.
And since there are no surviving members of the South American ungulates, we’re pretty much restricted to morphological analysis. Which means that, for instance, we now think cetaceans and artiodactyls are closely related, we don’t have any definitive way to tell if notungulates belonged in that group or not.
Essentially, all of these groups were probably already distinct back in the Cretaceous, but gross morphologically they weren’t that different from each other–they were all little mousy-shrewy thingies. Some of those mousy-shrewies were the ancestors of artiodactyls, but the artiodactyl ancestors didn’t particularly look artiodactyly. And it’s also probable that most of our cretaceous mammal fossil species weren’t direct ancestors of any extant mammal species. That also means that we haven’t found actual fossils for the ancestors of today’s species–even if we have a fossil that can be positively identified as a very early artiodactyl that early artiodactyl is probably not directly ancestral to any extant artiodactyls.
So my answer is that there is no definitive answer to your question that would be supported by just about every scientist. Note that I’m not any kind of scientist, just another enthusiast.
And the frustrating thing is that since the cladogram is done by genetic analysis, we can’t place extinct groups in it. So no chalicotheres, no brothotheres, no uintotheres, no notungulates, no litopterns, no pyrotheres, no astrapotheres, and so on.
Yeah. I feel a similar frustration with the “whale ancestry” bit – do you know the story on that?
Roughly, contemporry whales evolved from archaeocetes, which bear a strinking likeness to the legendary sea serpents, but appear to have gone extinct at least 45 million years before man. They in turn evolved from protocetes which had fore and hind llimbs varyingly adapted from normal quadruped feet through sea lion-type flippers to modern whale flippers.
Skeletally, the closest relatives to the protocetes appear to have been the mesonychids, a group of primitive fairly large enormous-headed hooved carnivorous land mammals that died out in the Eocene.
By genetic analysis, clossest living relative to the cetaceans generally appears to have been the hippopotamuses (and their probable ancestors the anthracotheres) – to the point that whales are genetically closer to hippos and ruminants than either is to camels or pigs.
People who play cladistics and depend on genetic analysis are claiming this refutes the mesonychid relationship – which it does not. The key is closest living relative – and since mesonychids left no living descendants (other than maybe the whales, which begs the question), we don’t know where they would tie in on genetic-based cladistics. I could easily believe they were a primitive family of aberrant cetioartiodactyls – the entelodonts certainly were, and they have similar adaptations.
On the other hand, it’s possible to do cladistics using skeletal morphology – and I’m wondering if anyone has taken the defining features of a notoungulate or a litoptern and done comparison shopping with the primitive characters of other extant orders. Finch, you around with anything that might be useful there?
Whale phylogeny is still a bit controversial. Paleontologists traditionally preferred the mesonychid origin hypothesis, while molecular biologists felt that hippos were more closely related to cetaceans. The discovery of Pakicetids (currently Pakicetus, Nalacetus and Ichthyolestes) in 2001 sort of threw a wrench into both hypotheses.
Including these species in the skeletal-feature cladograms indicated that mesonychids were no longer the most-likely immediate ancestors. Further, they also sort of rule against a direct link between hippos and whales, instead demonstrating more of a link between whales in general and artiodactyls in general (that is, Cetacea and Artiodactyla become sister groups, rather than Cetacea being nested within Artiodactyla as a sister group to hippos). So, things are still a bit up in the air as to which of the three competing hypotheses is most accurate. Only time, additional fossils, and/or additional analyses incorporating all of the known data will resolve the issue. My (very) cursory readings on the topic indicate that there hasn’t been much done to incorporate both paleontological and molecular data into a single cladogram.
The coolest thing about the weird clawed Homoladotherium is that it’s an example of convergent evolution with a group of clawed perrisodactyls, the chalicotheres. Just like Thylacosmilus was convergent with the extinct sabertooth cats.
Actually, we just have a vacant econiche for “large-clawed browsing herbivore, generally with a capability of rearing to a tripodal feeding/defensive posture.” But there have been tons of them throughout the last quarter billion years: the therazinosaurs (FKA segnosaurs), the chalicotheres, the three families of ground sloth, the homoladotheres…
It’s just that South American mammals are such a striking example of convergency. They’ve got convergent evolution for everything, even for stuff we don’t have anymore. Australia’s marsupials are a very distant second place.
I never hear anything about weird Indian fossils, yet India was also an island continent for something like 40 million years.
[ul][li]Macraucheniids – camels and llamas[/li][li]Proterotheriids – horses and other equids[/li][li]Hegetotheres – hares[/li][li]Notohippids – hippopotamuses[/li][li]Toxodontids – rhinos[/li][li]Pyrotheres – elephantids[/li][li]Astrapotheres – mastodons[/li][li]Homalodotheres – chalicotheres[/li][li]Mesotheriids – sheep and similar forms[/li][li]Borhyaenids – caniform carnivores[/li][li]Thylacosmilids – sabertooth cats[/ul][/li]
Aside from the fact that stegosaurs survived in India well into the Cretaceous while going extinct everywhere else, I don’t know of any unique Indian forms.
