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Although morphological data have historically favored a basal position for
the Indian gharial (Gavialis gangeticus) within Crocodylia and a Mesozoic
divergence between Gavialis and all other crocodylians, several recent
molecular data sets have argued for a sister-group relationship between
Gavialis and the Indonesian false gharial (Tomistoma schlegelii) and a
divergence between them no earlier than the Late Tertiary. Fossils were
added to a matrix of 164 discrete morphological characters and subjected
to parsimony analysis. When morphology was analyzed alone, Gavialis was
the sister taxon of all other extant crocodylians whether or not fossil
ingroup taxa were included, and a sister-group relationship between
Gavialis and Tomistoma was significantly less parsimonious. In combination
with published sequence and restriction site fragment data, Gavialis was
the sister taxon of all other living crocodylians, but the position of
Tomistoma depended on the inclusion of fossil ingroup taxa; with or
without fossils, preferred morphological and molecular topologies were not
significantly different. Fossils closer to Gavialis than to Tomistoma can
be recognized in the Late Cretaceous, and fossil relatives of Tomistoma
are known from the basal Eocene, strongly indicating a divergence long
before the Late Tertiary. Comparison of minimum divergence time from the
fossil record with different measures of molecular distance indicates
evolutionary rate heterogeneity within Crocodylia. Fossils strongly
contradict a post-Oligocene divergence between Gavialis and any other
living crocodylian, but the phylogenetic placement of Gavialis is best
viewed as unresolved.
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