Data from: A new phylogenetic hypothesis of turtles with implications for the timing and number of evolutionary transitions to marine lifestyles in the group

Evolutionary transitions to marine habitats occurred frequently among
Mesozoic reptiles. Only one such clade survives to the present: sea
turtles (Chelonioidea). Other marine turtles originated during the
Mesozoic, but uncertain affinities of key fossils have obscured the number
of transitions to marine life, and the timing of the origin of marine
adaptation in chelonioids. Phylogenetic studies support either a
highly‐inclusive chelonioid total‐group including fossil marine clades
from the Jurassic and Cretaceous (e.g. protostegids, thalassochelydians,
sandownids) or a less inclusive chelonioid total‐group excluding those
clades. Under this paradigm, these clades belong outside Cryptodira, and
represent at least one additional evolutionary transition to marine life
in turtles. We present a new phylogenetic hypothesis informed by high
resolution computed tomographic data of living and fossil taxa. Besides a
well‐supported Chelonioidea, which includes protostegids, we recover a
previously unknown clade of stem‐group turtles, Angolachelonia, which
includes the Late Jurassic thalassochelydians, and the
Cretaceous–Palaeogene sandownids. Accounting for the Triassic
Odontochelys, our results indicate three independent evolutionary
transitions to marine life in non‐pleurodiran turtles (plus an additional
two‐three in pleurodires). Among all independent origins of marine habits,
a pelagic ecology only evolved once, among chelonioids. All turtle groups
that independently invaded marine habitats in the Jurassic–Cretaceous
(chelonioids, angolachelonians, bothremydid pleurodires) survived the
Cretaceous–Palaeogene mass extinction event. This highlights extensive
survival of marine turtles compared to other marine reptiles. Furthermore,
deeply‐nested clades such as chelonioids are found by the middle Early
Cretaceous, suggesting a rapid diversification of crown‐group turtles
during the Early Cretaceous.