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Re: Weird mammal cladograms, and dino implications



At 11:57 AM 5/11/99 -0700, Nick Pharris wrote:
>
>No mention of the studies that show rabbits to be archontans, close to
>tree shrews?
>
>Do Guinea pigs and relations fall out in this clade as well?

In the "summary cladogram" on the cover, they don't address these particular
problems.  However, many variations on these do show up in the particular
papers in that issue (just got back from reading them in more detail).

>> Euarchonta (old
>> Archonta minus the bats), and the new Laurasiatheria.  Atlantogenates are
>> the (ancestrally South American?) Xenarthra (sloths, anteaters, armadillos)
>> and the recently proposed Afrotheria, containing the golden mole-tenrec
>> clade Afrosoricida, elephant shrews, aardvarks, hyaxes, and tethytheres.
>
>Some of this stuff is really weird, but (if you'll excuse the unscientific
>sentiment) I've always had a good "feeling" about Afrotheria.

Unscientifically, I've begun to grow fond of them, too.  It would a great
extra example of convergence in isolation.  Instead of simply Aussie
marsupials versus South American marsupials and meridungulates versus the
rest of the world's placentals, the latter would be broken into African
afrotheres and Laurasian laurasiatheres.  Each group would have produced its
own anteater, for example.

That's why I mentioned I thought it would be great if the South American
"ungulates" wind up being the sister taxon to Xenarthra within
Atlantogenata: there would a highly diverse South American clade as the
sister taxon to a highly diverse African clade.

Too bad that the fossil record for terrestrial early Tertiary India isn't so
good.  It would be very, very interesting to see what the native mammalian
fauna was like prior to docking with Asia.

>Perissodactyls, carnivorans, and pangolins???!!!  Oy, vay!

I admit the first two are a bit of a weird grouping to me, but apparently
pangolin-carnivoran groupings have been suggested in the past.

>> Not addressed in these papers, and something I'd like to see new analyses of
>> in light of these topologies, are: the phylogenetic position of the South
>> American "ungulates": within Ungulata gone, where the heck do they go?
>> Sister group to Xenarthra would be too much to ask...;
>
>Or maybe sister group to Afrotheria, which contains a bunch of
>"paenungulate" stuff.

True.  (In fact, they use Paenungulata for the traditional hyraxes plus
tethytheres, and Pseudungulata for aardvarks plus paenungulates).

As John Bois mentioned, one of the paper far too briefly mentions the
possibility of competition between small dinosaurs and early placentals
(and, to be fair, between early placentals and lizards, too).  One of the
authors is said to be working on a paper toward that effect, so maybe we'll
see more in the future.

I do hope they remember, though, the important lesson my students have to
learn: Which dinosaurs are small?  ALL dinosaurs are small, at least when
they are born.  (A **MAJOR** difference between dinosaurs and placental
mammals: a baby elephant is still one of the bigger non-rodent mammals on
the Serengeti, whereas a baby sauropod is a fairly little tyke).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:tholtz@geol.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661