Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 1998 Nov 24;95(24):14226-31.
doi: 10.1073/pnas.95.24.14226.

Complete Mitochondrial Genome Suggests Diapsid Affinities of Turtles

Affiliations
Free PMC article

Complete Mitochondrial Genome Suggests Diapsid Affinities of Turtles

R Zardoya et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Despite more than a century of debate, the evolutionary position of turtles (Testudines) relative to other amniotes (reptiles, birds, and mammals) remains uncertain. One of the major impediments to resolving this important evolutionary problem is the highly distinctive and enigmatic morphology of turtles that led to their traditional placement apart from diapsid reptiles as sole descendants of presumably primitive anapsid reptiles. To address this question, the complete (16,787-bp) mitochondrial genome sequence of the African side-necked turtle (Pelomedusa subrufa) was determined. This molecule contains several unusual features: a (TA)n microsatellite in the control region, the absence of an origin of replication for the light strand in the WANCY region of five tRNA genes, an unusually long noncoding region separating the ND5 and ND6 genes, an overlap between ATPase 6 and COIII genes, and the existence of extra nucleotides in ND3 and ND4L putative ORFs. Phylogenetic analyses of the complete mitochondrial genome sequences supported the placement of turtles as the sister group of an alligator and chicken (Archosauria) clade. This result clearly rejects the Haematothermia hypothesis (a sister-group relationship between mammals and birds), as well as rejecting the placement of turtles as the most basal living amniotes. Moreover, evidence from both complete mitochondrial rRNA genes supports a sister-group relationship of turtles to Archosauria to the exclusion of Lepidosauria (tuatara, snakes, and lizards). These results challenge the classic view of turtles as the only survivors of primary anapsid reptiles and imply that turtles might have secondarily lost their skull fenestration.

Figures

Figure 1
Figure 1
Proposed hypotheses explaining the phylogenetic relationships among living amniotes. (A) Mammals represent the sister group of all other extant amniotes. Turtles are the only living representatives of the Anapsida and are the sister group of diapsid reptiles (Lepidosauria and Archosauria; refs. , , –20). (B) Turtles have diapsid affinities and are the sister group of Lepidosauria (tuatara, lizards, and snakes; ref 4). (C) Turtles are diapsids as the sister group of Archosauria (birds and crocodiles) to the exclusion of Lepidosauria (–7). (D) Mammals and diapsids as sister groups to the exclusion of turtles, the Parareptilia hypothesis (10). (E) The Haematothermia hypothesis: birds are the sister group of mammals (, –13).
Figure 2
Figure 2
Bootstrap consensus trees (which used the 50% majority rule) of amniotes based on 100 pseudoreplications. The three data sets were subjected to MP, NJ, and ML analyses (bootstrap values are listed as upper, middle, and lower numbers above branches, respectively). (A) The first data set included mitochondrial protein-coding genes combined at the amino acid level. (B) The second data set combined all mitochondrial rRNA genes (C). The third data set combined all 22 tRNA genes. Teleosts (carp, loach, and rainbow trout) were used as outgroup taxa.
Figure 3
Figure 3
Phylogenetic position of the turtle. A data set combining the two rRNA mitochondrial genes (12S and 16S) was analyzed with MP, NJ, and ML phylogenetic methods (upper, middle, and lower numbers above branches, respectively). Numbers shown above branches represent bootstrap values from 100 pseudoreplicates. Rainbow trout, carp, and loach were used as outgroup taxa.

Similar articles

See all similar articles

Cited by 42 articles

See all "Cited by" articles

Publication types

Substances

Associated data

LinkOut - more resources

Feedback