Total evidence analysis and body size evolution of extant and extinct tortoises (Testudines: Cryptodira: Pan-Testudinidae).

Abstract

Testudinidae (tortoises) is an extant clade of terrestrial turtles of worldwide distribution and with a rich fossil record that provides an exceptional context for studying their evolutionary history. Because of the lack of global phylogenetic analyses integrating extinct taxa, our current knowledge of the relationships of the total clade of Testudinidae is rather poor. To resolve this issue, we performed the first total evidence analysis of Pan-Testudinidae. The total evidence trees are congruent with the molecular topology and agree on the dichotomy of derived Testudinidae (=Testudininae; Converted Clade Name) into two previously recognized major clades, Testudona and Geochelona (New Clade Name). The integration of extinct taxa into the analysis allowed the stratigraphic fit of the total evidence trees, indicating that crown Testudininae, Testudona and Geochelona all originated by the Late Eocene, in agreement with recent molecular estimates. Ghost lineage analysis indicates high diversification in the Late Eocene and in the Miocene. The age of crown Testudo is Late Miocene, again in accordance with some molecular dates. Phylogenetic placement of fossils demonstrates that giant body size independently evolved in multiple continental mainland taxa and confirms recent results deduced from living taxa-giantism in Testudinidae is not linked to the insular effect. An unexpected outcome is the recovery of miniaturization in Testudona (<30cm carapace length) that emerged sometime between the Oligocene and Early Miocene. No clear correlation between body size evolution and climate is apparent, but increased taxon sampling may nevertheless demonstrate the role of cooling and warming as one of many influential variables.