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Re: Sky Monsters - Nat. Geo. channel
David Peters wrote:
Also, I wonder why the preview stated that "we don't have a clue about how
they evolved." To my knowledge, we've known that for 5 years. Or if you
want to go the archosaur route, why not show Scleromochlus? That's been a
favorite for decades.
Irrespective of whether you go the prolacertiform route or the archosaur
route, the *exact* phylogenetic affinities of the Pterosauria remain hazy.
I think the evidence supporting archosaur affinities trumps the evidence
favoring prolacertiform affinities; but the _Scleromochlus_-Pterosauria link
is nevertheless quite weak. In other words, one can find support for
regarding pterosaurs as archosaurs without necessarily advocating
_Scleromochlus_ as the sister taxon to the Pterosauria.
There are new Triassic taxa that are said to be a non-pterosaurian
pterosauromorphs, and may shed light on pterosaur origins. Both taxa have
given names (in a dissertation), but as nomina nuda they can only cause
trouble until the day the names become official. (Both names are fairly
easy to find on the Internet; but it's probably good policy to avoid
propagating the names until they do become official. Not all nomina nuda
end up as official names.) Some of the material previously referred to
_Protoavis texensis_ may be referrable to one of these putative
Renato Santos wrote:
Of couse we have adaptational stories garnered from Cenozoic examples such
bats, which would suffer as severely from the same problem if it
weren't for colugos. But where is the pterosaurian colugo? Even bats,
with Icaronycteris and its ilk, seem pretty much finished in general
design by the time we find fossils of them.
The colugo ('flying lemur') might be a nice analog for what the immediate
ancestors of bats looked like. However, the usefulness of colugos might end
there. The idea that colugos represent the sort of aerial furball from
which bats evolved is intuitively attractive - but there is no support for
this from either molecular phylogenies nor from the fossil record.
Molecular phylogenies argue against it; the fossil record is keeping its
cards close to its vest.
Traditionally, bats were linked to colugos (as well as primates and
tree-shrews) in a group called the Archonta. Some classifications even
proposed a colugo-bat clade called Volitantia. But the idea of a close
relationship between bats and colugos doesn't have nearly as much support as
it used to. Molecular analyses fail to find any close relationship between
the two, and in fact remove bats (Chiroptera) completely from the Archonta.
Waddell et al. (1999)'s synthesis of placental molecular-based phylogeny
assigned bats to a group called the Scrotifera, which puts them closer to
the likes of horses, whales, ruminants, carnivorans, and pangolins.
As Renato said, the earliest-known fossil bats reveal nothing about what the
pre-flight chiropterans might have looked like. Also, there are no
identifiable chiropteran sister taxa in the fossil record. In other words,
we have no chiropteran equivalent for _Archaeopteryx_, nor a chiropteran
equivalent for the deinonychosaurs (or any other maniraptoran for that
matter). So fossil corroboration for this molecular-based grouping for bats
is so far lacking. (Unlike Afrotheria, which appears to be accreting some
support from the fossil record.) Long story short: bats might have evolved
from a colugo-like glider, but there is no evidence that this animal was
related to the modern colugos.