Recent refs about reptile evolution

["bh480@scn.org" <bh480@scn.org>]

From: Ben Creisler bh480@scn.org
A couple of recent articles on reptile evolution may be of interest to the
mailing list. Apologies if they have already been mentioned. Note that both
papers provide support for turtles as diapsids.

Rest, J. S. , J. C. Ast, C. C. Austin, P. J. Waddell, E. A. Tibbetts, J. M.
Hay and D. P. Mindell, 2003. Molecular systematics of primary reptilian
lineages and the tuatara mitochondrial genome. Molecular Phylogenetics and
Evolution 29: 289-297 (2003)

Abstract
We provide phylogenetic analyses for primary Reptilia lineages including,
for the first time, Sphenodon punctatus (tuatara) using data from whole
mitochondrial genomes. Our analyses firmly support a sister relationship
between Sphenodon and Squamata, which includes lizards and snakes. Using
Sphenodon as an outgroup for select squamates, we found evidence indicating
a sister relationship, among our study taxa, between Serpentes (represented
by Dinodon) and Varanidae. Our analyses support monophyly of Archosauria,
and a sister relationship between turtles and archosaurs. This latter
relationship is congruent with a growing set of morphological and molecular
analyses placing turtles within crown Diapsida and recognizing them as
secondarily anapsid (lacking a skull fenestration). Inclusion of Sphenodon,
as the only surviving member of Sphenodontia (with fossils from the
mid-Triassic), helps to fill a sampling gap within previous analyses of
reptilian phylogeny. We also report a unique configuration for the
mitochondrial genome of Sphenodon, including two tRNALys copies and an
absence of ND5, tRNAHis, and tRNAThr genes. 

TEXT HIGHLIGHTS:
Phylogenetic placement of snakes has been controversial, with no consensus
at present. Some studies place snakes among lizards within Anguimorpha and
close to varanids (monitor lizards) ([Lee, 2000]; [Macey and Verma, 1997]),
whereas others place them as sister to a clade including all the lizards (
[Underwood, 1970]). Sequencing of the mt genome for Sphenodon and its
supported position as sister to other Lepidosaurs (Fig. 2 and Fig. 3)
allows us to focus further on the position of snakes using Sphenodon as an
outgroup and three additional anguimorph taxa for mt ND1, ND2, and eight
tRNA genes (see above). Addition of these three taxa may help reduce
potential bias due to the relatively long branch for the representative
snake (Fig. 3). BI and BPP analyses for seven taxa with Sphenodon as an
outgroup are congruent with analyses of the larger set of taxa in Fig. 3.
Dinodon is placed within Anguimorpha and well supported as sister to the
two varanids within our set of study taxa, and the sister relationship
between Eumeces and Iguana remains (Fig. 4). A sister relationship between
Scincomorpha (skinks and relatives) and Anguimorpha is not supported. A
tree placing Dinodon and Eumeces as sisters but with all other
relationships as in our optimal tree (Fig. 3) was rejected using the AU
test with the 14 taxa dataset ( Fig. 2, tree H). ....
Our estimates derived from these calibrations are 111 mya for the
divergence between Chrysemys and Chelonia, 72 mya for divergence of Caiman
and Alligator, 109 mya for the polytomy among three bird lineages, 285 mya
for divergence between Lepidosauria and other diapsids (including turtles),
220 mya for the divergence of snakes from the representative other lizards,
and 158 mya for the Eumeces and Iguana divergence (Fig. 3). The estimate of
109 mya for divergence among some extent avian lineages is roughly
consistent with other mid-late Cretaceous estimates based on molecular data
(e.g., [Waddell et al., 1999]) and with biogeographical analyses (
[Cracraft, 2001]), but not with studies based on fossils alone (e.g.,
[Feduccia, 1999]). The estimate for the divergence between the stem snake
lineage and lizards at about 220 mya is significantly older than the oldest
fossils clearly attributable to crown-clade snakes (Serpentes) which have
been dated to about 100 mya ([Benton, 1993]; [Tchernov et al., 2000]). Our
estimate of 111 mya for the divergence between Chrysemys and Chelonia is in
close agreement with the estimated range of 90?120 mya for these primary
cryptodire turtle lineages based on fossils alone ([Shaffer et al., 1997]). 
To summarize, our analyses firmly support a sister relationship between
Sphenodon and Squamata, represented by Eumeces, Iguana, and Dinodon. Using
Sphenodon as an outgroup for select squamates we found evidence indicating
a sister relationship among Dinodon (representing Serpentes) and Varanus
(Varanidae). Our analyses support monophyly of Archosauria, and a sister
relationship between turtles and archosaurs. Morphological analyses by
[Rieppel and Reisz, 1999], however, place turtles as sister to lepidosaurs
rather than to archosaurs. 


Müll, J. 2003. Early loss and multiple return of the lower temporal arcade
in diapsid reptiles. 
Naturwissenschaften 90(10): 473 - 476 October 2003

Abstract: The temporal arches of diapsid reptiles have received attention
for several decades. In particular, it has been observed that the lower
temporal bar at the ventral margin of the cheek is frequently reduced due
to the absence of a contact between jugal and quadratojugal. The loss of
the arcade was formerly considered to be of high systematic value, but is
now often interpreted as being autapomorphic for the respective taxon, and
the presence of both arcades is generally regarded as a plesiomorphic
feature. Here I show, based on a cladistic analysis as well as on further
anatomical evidence, that the lower temporal arcade was lost only once in
diapsid evolution, and that the presence of the arch in "higher" diapsids
is secondary, which is indicated by the different ratio between jugal and
quadratojugal as well as by ontogeny. This result also sheds new light on
the understanding of the cheek configuration of enigmatic taxa such as
ichthyosaurs and turtles. 
Electronic Supplementary Material Supplementary material is available for
this article if you access the article
http://dx.doi.org/10.1007/s00114-003-0461-0 
TEXT HIGHLIGHTS:
Additionally, the present model indicates that the poorly understood cheek
morphology of ichthyosaurs, for which a diapsid status is increasingly
accepted (Motani et al. 1998; Motani 2000), might have evolved from a
configuration that originally lacked the lower temporal bar. In basal
ichthyosaurs, such as Grippia or Utatsusaurus, the jugal is relatively low,
whereas the quadratojugal is anterodorsally expanded and forms a contact
with the postorbital, but not with the jugal (Fig. 2i, see also Maisch and
Matzke 2002 for further discussion). An ancestrally interrupted lower
temporal arcade would explain the missing contact between jugal and
quadratojugal, and suggest that the peculiar cheek configuration resulted
from an expansion of the more dorsally situated temporal bones, instead of
a ventral emargination of the cheek.
Assuming an open lower temporal bar in the ancestral condition might also
be helpful for the understanding of another putative diapsid clade,
Testudines. As exemplified in the Triassic taxon Proganochelys (Gaffney
1990), the quadratojugal is short but tall in early turtles, whereas the
jugal, by contrast, extends far posteriorly (Fig. 2j). This is different in
parareptilian pareiasaurs, which some authors suppose to be closely related
to turtles (Lee 1997, Fig. 2k). On the basis of the scenario proposed here,
the elongated jugal and the short quadratojugal would correspond to a
secondarily closed temporal bar, and the lower temporal fenestra would have
been obliterated afterwards, or in concert with this secondary closure. It
should be noted that Lakjer (1926) had already suggested diapsid affinities
of turtles due to the presence of a quadrato-maxillary ligament, as is
present in lizards (see above). Given that this ligament may represent the
remnant of a primary arcade, Lakjer's hypothesis would gain new support
from the present study.




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