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Abstract
The mitochondrial genomes of the dwarf crocodile, Osteolaemus tetraspis, and two species
of dwarf caimans, the smooth-fronted caiman, Paleosuchus trigonatus, and Cuvier's
dwarf caiman, Paleosuchus palpebrosus, were sequenced and included in a mitogenomic
phylogenetic study. The phylogenetic analyses, which included a total of ten crocodylian
species, yielded strong support to a basal split between Crocodylidae and Alligatoridae.
Osteolaemus fell within the Crocodylidae as the sister group to Crocodylus. Gavialis
and Tomistoma, which joined on a common branch, constituted a sister group to Crocodylus/Osteolaemus.
This suggests that extant crocodylians are organized in two families: Alligatoridae
and Crocodylidae. Within the Alligatoridae there was a basal split between Alligator
and a branch that contained Paleosuchus and Caiman. The analyses also provided molecular
estimates of various divergences applying recently established crocodylian and outgroup
fossil calibration points. Molecular estimates based on amino acid data placed the
divergence between Crocodylidae and Alligatoridae at 97-103 million years ago and
that between Alligator and Caiman/Paleosuchus at 65-72 million years ago. Other crocodilian
divergences were placed after the Cretaceous-Tertiary boundary. Thus, according to
the molecular estimates, three extant crocodylian lineages have their roots in the
Cretaceous. Considering the crocodylian diversification in the Cretaceous the molecular
datings suggest that the extinction of the dinosaurs was also to some extent paralleled
in the crocodylian evolution. However, for whatever reason, some crocodylian lineages
survived into the Tertiary.