Henrietta

I haven't been following this topic too closely lately so this may have already been mentioned. I have been wondering about this: if you go back through human ancestors what is the first ancestor you get to that was not a primate. In other words what is human's closest non-primate ancestor. You hear a lot about early humans and about primates but I never see this mentioned. Maybe no one knows?

tronvillain

You'd have to back a <a href="http://www.anth.ucsb.edu/faculty/walker/classes/anth121/121names.htm" target="_blank">long time</a>. Genetic studies would probably be a better bet than the fossil record.

kwigibo

i have a feeling lemurs are involved somewhere along the line, as they are the most (or should i say least ) primative primates <img src="confused.gif" border="0">

Oolon Colluphid

Well, humans are primates... so as tronvillain says, you’ve got to got a looong way back -- the earliest primate, Purgatorius unio, is found around 70mya, back into the Cretaceous. The trouble is that, going so far back, modern definitions of things like ‘primate’ become fairly meaningless: you can only really talk about primitive and derived characteristics. The ‘last non-primate ancestor’ would be something like a tree shrew -- but that ancestor could be (was? I’ll check) equally the ancestor of modern tree shrews, bats, etc, and any number of extinct forms too. It wouldn’t be much like a modern primate. Before that, you’re into the junction with rodents etc.

It’s the same problem with eg Hyracotherium. It’s a horse... but it’s equally a rhino.

Hope that helps?!

Cheers, Oolon

lpetrich

In the posting "Evolution News Flash!", I presented a summary of a recent paper:

Science 2001 Dec 14;294(5550):2348-51. Murphy WJ, Eizirik E, O'Brien SJ, Madsen O, Scally M, Douady CJ, Teeling E, Ryder OA, Stanhope MJ, de Jong WW, Springer MS.

The whole question of the groupings of the various eutherian (placental) mammalian orders has long been a very controversial one, with various groupings proposed and disputed over the decades.

Most closely related to our order, the Primates, is a group composed of the tree shrews and the flying lemurs. All three groups, part of the old group Archonta, share the important feature of preferring to live in trees, at least ancestrally; this suggests that their common ancestor had also lived in trees.

Related to this group is the old group Glires, which includes both rodents and lagomorphs (rabbits, pikas); both subgroups are monophyletic (have a single ancestor).

This group forms a group that the authors of this paper have called the Euarchontoglires, but I'm sure that someone will think of a better name.

Related to it is a big group that has been recently named Laurasiatheria, after the onetime northern continent. There are several groups in it, I'll give them in order of split-off:

Eulipotyphla, a renaming of part of the old Insectivora (moles, shrews, hedghehogs)

Bats; the diurnal megabats are an offshoot of the more diversified nocturnal microbats.

The remainder is part of the old group Ferungulata, which may be renamed Cetferungulata. The first to split off is the Artiodactyla, the even-toed ungulates, sometimes renamed Cetartiodactyla. Its subgroups, in split-off order, are:

Camelids (camel, llama)
Pigs and peccaries
Ruminants
Hippopotamus
Cetaceans (dolphins, whales)

The next is the Perissodactyla, the odd-toed ungulates; these include the equines (horse, donkey, zebra), tapir, and rhinoceros.

Pangolins

Carnivores, with an early split between dog-like and cat-like.

The authors of this paper create a group called Boreoeutheria, on account of their northern origins, for all these groups.

The closest relative of these is the Xenarthra or Edentata, which include the armadillos, sloths, and South American anteaters.

And the Xenarthra-Boreoeutheria group has the Afrotheria, another recently-named group, as its closest relative. It has two subgroups, the old group Paenungulata and one containing the aardvarks, elephant shrews, golden moles, and tenrecs.

The Paenungulata contain hyraxes (rock rabbits, rock badgers of Africa and nearby), sirenians (sea cows), and elephants.

The timescale for these early divergences? The later part of the Cretaceous. The Afrotheria-others split occurred as a result of the splitting of Africa and South America by continental drift. It is interesting that this divergence had occurred while the (non-avian) dinosaurs were still alive.

And most of the early mammals would have looked rather mouselike or ratlike or squirrel-like, though without the rodent front-tooth specialization.

The eutherian-marsupial divergence occurred earlier, in the middle of the Jurassic, shortly before Gondwana and Laurasia split; the marsupials had survived in South America and Australia, both pieces of Gondwana.

One interesting conclusion is that specialization for eating ants and termites has evolved four times in Mammalia:

Echidna (spiny anteater)
South American anteater
Aardvark
Pangolin

This convergent evolution is paralleled by that of their prey; ants are descended from wasps and termites from cockroach-like insects.

Finally, having solved the higher-level splits of one major warm-blooded group, it would be interesting to take on the other major warm-blooded group -- the birds.

Henrietta

Thank you. I knew you guys would have an answer for me.