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RE: Phylogenetic position of Chelonia
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Derek Gatherer
>
> Hi
>
> I'd be grateful if anybody could summarise current thinking on
> the position
> of Chelonia relative to other reptiles (both extinct and extant), and if
> possible, provide a reference to an up-to-date review article or somthing
> similar. I'm working on some turtle viruses and have read the recent
> molecular evolutionary papers eg.
> http://mbe.oupjournals.org/cgi/reprint/16/6/784, but I'd like to
> know what
> the latest evidence of the fossil record is.
>
>From the Tree of Life webpage on Amniota
(http://tolweb.org/tree?group=Amniota&contgroup=Terrestrial_Vertebrates):
The position of turtles (Testudines) is uncertain; some authors place them
approximately in the position shown above (Laurin & Reisz, 1995; Lee, 1993,
1995), while others place them among Diapsida (deBraga & Rieppel, 1996,
1997; Rieppel & Reisz, 1999; Hedges & Poling, 1999; Mannen & Li, 1999).
deBraga M. & O. Rieppel. 1997. Reptile phylogeny and the interrelationships
of turtles. Zoological Journal of the Linnean Society 120: 281-354.
Hedges S. B. & L. L. Poling. 1999. A molecular phylogeny of reptiles.
Science 283: 998-1001.
Laurin, M. & R. R. Reisz. 1995. A reevaluation of early amniote phylogeny.
Zoological Journal of the Linnean Society 113: 165-223.
Lee, M., S. Y. 1993. The origin of the turtle body plan: bridging a famous
morphological gap. Science 261: 1716-1720.
Lee, M. S. Y. 1995. Historical burden in systematics and the
interrelationships of ''Parareptiles''. Biological Reviews of the Cambridge
Philosophical Society 70: 459-547.
Mannen H. & S. S.-L. Li. 1999. Molecular evidence for a clade of turtles.
Molecular Phylogenetics and Evolution 13: 144-148.
Rieppel O. 1995. Studies on skeleton formation in reptiles: implications for
turtle relationships. Zoology-Analysis of Complex Systems 98: 298-308.
Rieppel O. & M. deBraga. 1996. Turtles as diapsid reptiles. Nature 384:
453-455.
Rieppel O. & R. R. Reisz. 1999. The origin and early evolution of turtles.
Annual Review of Ecology and Systematics 30: 1-22.
Additionally, a good review can be found in:
Brochu, C.A. 2001. Progress and future directions in archosaur
phylogenetics. Journal of Paleontology 75:1185-1201.
(available online, if you have Bioone access, at:
http://www.bioone.org/bioone/?request=get-pdf&file=i0022-3360-075-06-1185.pd
f).
I would go so far as to say that the placement of turtles is the single
biggest problem in amniote systematics. This is not the case of the
molecules saying one thing and the morphology saying another. This is a
case of some molecules saying that they are lepidosauromorphs, some saying
that they are archosauromorphs, and some saying that they are archosaurs;
and the morphology saying that they might be parareptiles closer to
procolophonids, or to pareiasaurs, or WITHIN pareiasaurs, or the sister
group to sauropterygians (or just placodonts) within Lepidosauromorpha, or
the sister group to sauropterygians (or just placodonts) within
Archosauromorpha... Urk!!
Morphologically the problem is that even basal turtles like Proganochelys is
still very much a turtle, with many of the bizarre adaptations of the skull
and skeleton that make turtles distinctive. There isn't yet a turtle
"Archaeopteryx" with just a couple of synapomorphies with Chelonia but still
retaining most of the morphology of the outgroups. Whatever they were.
P.S. Back as a grad student in the 1980s, our vert. paleo. seminar solved
this problem by deciding that turtles were from Space, and therefore not
part of Amniota or any other terrestrial clade... ;-).
Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
College Park, MD 20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone: 301-405-4084 Email: tholtz@geol.umd.edu
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-405-0796