Archelosauria

Archelosaurs
Temporal range: 260–0 Ma Possible Capitanian records.
Proganochelys quenstedti
Scientific classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Sauria
Clade: Archelosauria
Crawford et al., 2015
Subgroups

Archelosauria is a clade grouping turtles and archosaurs (birds and crocodilians) and their fossil relatives, to the exclusion of lepidosaurs (the clade containing lizards, snakes and the tuatara). The majority of phylogenetic analyses based on molecular data (e.g. DNA and proteins) have supported a sister-group relationship between turtles and archosaurs. On the other hand, Archelosauria had not been historically supported by most morphological analyses, which have instead found turtles to either be descendants of parareptiles, early-diverging diapsids outside of Sauria, or close relatives of lepidosaurs within the clade Ankylopoda. Some recent morphological analyses have also found support for Archelosauria.

Classification

Multiple sequence alignments of DNA and protein sequences and phylogenetic inferences have shown that turtles are the closest living relatives to birds and crocodilians. There are about 1000 ultra-conserved elements in the genome that are unique to turtles and archosaurs, but which are not found in lepidosaurs. Other genome-wide analyses also support this grouping.

Archelosauria was named in a 2015 article by Crawford et al. The name is meant to evoke the archosaurs and chelonians (turtles), the two living subgroups of the clade. Crawford et al. defined Archelosauria as the clade formed by the descendants of the most recent common ancestor of Crocodylus niloticus (the Nile crocodile) and Testudo graeca (the Greek tortoise). A 2021 article by Joyce et al. modified the definition to specifically exclude the lizard Lacerta agilis from the group.

Below is the phylogeny from Crawford et al., showing interrelationships of Testudines at family level down to Durocryptodira. Archelosauria was grouped within Sauria (the clade formed by archosaurs and lepidosaurs), as the sister branch to Lepidosauria, the clade containing lizards, snakes and the tuatara.

Sauria
Lepidosauria

Sphenodon

Squamata

Anolis

Python

Archelosauria
Testudines
Pleurodira

Chelidae

Pelomedusoides

Pelomedusidae

Podocnemididae

Cryptodira
Trionychia

Carettochelys

Trionychidae

Durocryptodira

Archosauria

Crocodylus

Gallus

Analyses based on morphological data have generally recovered turtles either as non-diapsid reptiles nested within Parareptilia (a group of basal reptiles that lived from the Carboniferous to the Triassic), as early-diverging diapsids outside of Sauria, or as close relatives of Lepidosauria. The hypothetical clade formed by turtles and lepidosaurs to the exclusion of archosaurs is known as Ankylopoda. A 2022 analysis by Simões et al. found a monophyletic Archelosauria using only morphological data for the first time, thus agreeing with most molecular analyses. Archelosauria was diagnosed by two unambiguous synapomorphies (shared derived traits): a sagittal crest on the supraoccipital bone, and the lack of an entepicondylar foramen on the humerus. A cladogram adapted from their analysis is shown below:

Neodiapsida

Younginiformes

Eunotosaurus

Coelurosauravus

Sauria
Lepidosauromorpha

Sphenodontia

Squamata

Archelosauria
Testudines

Pappochelys

Odontochelys

Kayentachelys

Proganochelys

Archosauromorpha

Ichthyosauromorpha

Sauropterygia

Thalattosauria

Protorosauria

Allokotosauria

Rhynchosauria

Prolacerta

Archosauriformes

Wolniewicz et al (2023) also found evidence for an expanded Archelosauria containing the three Mesozoic marine reptile clades of uncertain placement:

Neodiapsida

Lepidosauromorpha

Coelurosauravus

Choristodera

Archelosauria

Testudines

Thalattosauria

Sauropterygia

Ichthyosauromorpha

Archosauromorpha


This page was last updated at 2024-03-06 01:04 UTC. Update now. View original page.

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