Turtles. Modern Anapsids. General Characters. Evolved at least 200 MYA. All are anapsids. None have teeth - they have a keratinous sheath which grows continuously, just as in birds.
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10 genera and 35+ species.
Occur in Australia and S. America.
All are carnivorous.
Matamata may stalk prey, uses a sudden thrust of neck and rapid opening of mouth to create negative presure and capture prey.
They are highly aquatic & good swimmers.
Generally, lack mesoplastral elements.
Have cervical scute on carapace.
Reduction/loss of neural bone.
Nasals & vomers usually present.
Premax & dentaries unfused.
Pseudemydura: <15cm CL
Snake necks - Chelodina: neck length often exceeds length of carapace.
Shortnecks - Elseya, Emydura, Rheodytes
South American Subgroups.
Hydromedusa - extremely long necks.
Phrynops, Acanthochelys, Platemys.
Caretta: Loggerhead turtles. Most temperate form. Eats moluscs and crabs.
Chelonia: Green sea turtles: herbivorous - all other genera are carnivorous.
Eretmochelys: eats sponges and other sedentary invertebrates.
Africa and India.
Femoral flaps on the plastron.
3 genera and 4 species.
Lack femoral flaps.
11 genera and 17 species.
strictly terrestrial, columnar elephantine hindlimbs, high domed carapaces, large plastrons, primarily arid.
Shell shape and size prevents predation.
primarily semiaquatic and aquatic, but some terrestrial forms.
angular bone of lower jaw touches meckel’s cartilage.
Pareiasaurs have long lateral extending ribs. Fossils which are found with undisturbed ribs, are always lying belly down, indicating that this is the position of a body at rest … just as in modern turtles.
This suggests that the bodies of Pareiasuars are broader and flatter than originally thought.
The pectoral girdle of pareisaurs is narrower than the rib cage because the clavicles and coracoids do not form broad ventral plates. Also, it tends to be anterior to a wide flat carapace.
Most basal amniotes, including nyctiphruretians and procolophonoids have 5 cervical vertebrae and 20 dorsal vertebrae.
Sclerosaurus and Pareiasaurs have 5 cervical vertebrae and 14 or 15 dorsal vertebrae.
All turtles have 8 cervicals and 10 dorsals.
5 or 6 dorsals were lost in the lineage leading to sclerosaurus, pareiasaurs, and turtles.
In the transition to turtles, there was an increase in the number of cervicals and a reduction in the number of dorsals.
This suggests that the pectoral girdle shifted posteriorly about 3 vertebrae in turtles, and that cervicals 6 to 8 in turtles are modified dorsals.
the major line of neck flexion in pleurodires and cryptodiran turtles is between cervical 5 and 6 (perhaps the old cervical/dorsal boundary).
Cervicals 6, 7, and 8 usually work as a single rigid unit.
In pareiasaurs, the transverse processes on the 5 cervical centra are ventral, on the first 3 dorsals they gradually assume a more dorsal position.
In the earliest turtle, proganochelys, this change occurs at cervicals 6, 7, and 8.
The dorsal tip of the scapula liesadjacent to cervial 7 in proganochelys, but behind cervical 8 in later turtles. This change might represent the final stage in the posterior migration of the scapulocoracoid.
A similar pattern is seen with the pelvic girdle in pleurodires.