[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Turtles and Crocodylians are not Reptiles - no? What are they?
Fossil DNA may be refering to DNA collected from fossils - which is normally
very degraded if present - although we do have some neanderthal and mamoth DNA,
and protein from a T-Rex from which we can infer possible DNA sequences, or it
could refer to "fossil genes"
Ones which have a mutation in the promoter function, and are no longer
functional coding DNA, but the sequence is unmistakable for a gene encoding
protein, and it was inferred to be functional in the past, but probably became
non-functional after a duplication event allowed another version of it to
evolve, eventually replacing the first gene's function.
I have heard of this referred to by the term "fossil" DNA- by non
paleontologists of course. Perhaps vestigial DNA is a better term.
But in the usage below, I'd guess they mean fragmentary DNA recovered from
I'm also not sure what you
> mean by "fossil DNA", which you mention below.
> > Probably the turtle position issue will be settled
> down - as occurred
> > in the Cetacea case - when a new informative fossil
> (or a collection
> > of informative fossils) was found and/or descripted
> (or eventually
> > fossil DNA).
> The most recent morphological/fossil data place whales near
> the base of the Artiodactyla. The analysis of Thewissen
> &c from late 2007 places Cetacea as the sister taxon to
> the Raoellidae, a group of aquatic basal artiodactyls.
> Thus, although the Cetacea come out as artiodactyls, they
> are not at all close to hippopotamids, and are in fact
> outside the crown Artiodactyla.
> Thewissen JGM, Cooper LN, Clementz MT, Bajpai S, and Tiwari
> BN (2007). Whales originated from aquatic artiodactyls in
> the Eocene epoch of India. Nature 450: 1190-1194.
> So, whereas the molecular phylogenetic analyses recovered
> whales as the sister group to hippos, and the morphological
> phylogenetic analyses previously found whales and
> mesonychians to be sister taxa, the most recent morpho
> analysis (including new fossil specimens) found the Cetacea
> to lie somewhere in between: basal Artiodactyla.
> I reckon a similar situation will emerge with turtles
> (Testudinata): the molecular analyses tend to place them
> inside or next to the Archosauria; older morpho/fossil
> analyses put them in an anapsid clade that is outside the
> Diapsida; but new fossil discoveries will consolidate a
> position for the turtles somewhere in between, i.e. inside
> the Diapsida as either basal lepidosauromorphs or as
> non-saurian neodiapsids.
> > But there is a lack of less derived turtle fossil that
> show this
> > affinity - i.e. fossil that is more similar to a
> putative common
> > exclusive ancestral between Testudines and
> Although there are no actual proto-turtles (yet) to back it
> up, Michael Lee outlines a possible scenario here:
> Lee MSY (1993). The origin of the turtle body plan:
> bridging a famous morphological gap. Science 261:
> Lee MSY (1997). Pareiasaur phylogeny and the origin of
> turtles. Zool. J. Linn. Soc. 120: 197â280.
> I'm not actually advocating the pareiasaur-turtle
> hypothesis; and other studies have found fault with these
> analyses (e.g., Rieppel & Reisz, 1999; Annu. Rev. Ecol.
> Syst. 30: 1â22). But the pareiasaur-turtle hypothesis
> does provide a series of intermediate stages, and can be
> tested against the fossil record (e.g., such as when
> proto-turtles are discovered or recognized).
> With Windows Live for mobile, your contacts travel with