CAUDATA (SALAMANDERS, NEWTS)

Benton, MJ, Donoghue, PCJ, Vinther, J, Asher, RJ, Friedman, M & Near, TJ, 2015, Constraints on the timescale of animal evolutionary history, Palaeontologia Electronica (Florence, Italy) 15 (1), pp. 1-107 : 50

CROWN CAUDATA (SALAMANDERS, NEWTS) (45)

Node Calibrated. Divergence between the Cryptobranchoidea (cryptobranchids and hynobiids) and the Salamandroidea (all other salamanders).

Fossil Taxon and Specimen. Iridotriton hechti Evans et al., 2005 , from the Brushy Basin Member of the Morrison Formation of the Dinosaur National Monument, Rainbow Park microsite, Utah.

Phylogenetic Justification. Iridotriton is identified as a member of Salamandroidea, and hence crown Caudata , by the possession of several apomorphies, including the presence of spinal nerve foramina in the tail.

Minimum Age. 146.8 Ma

Soft Maximum Age. 175.1 Ma

Age Justification. The Brushy Basin Member of the Morrison Formation is dated as Kimmeridgian or early Tithonian. The upper boundary of the Early Tithonian is 147.7 Ma ± 0.9 Myr ( Gradstein et al., 2012, pp. 764, 777), so 146.8 Ma.

The soft maximum constraint is based on the possibility that the Kirtlington ‘Salamander B’ might be a crown caudate, lowering the age estimate to Late Bathonian, and indeed, the range is extended to the base of the Middle Jurassic, dated as 174.1 Ma ± 1.0 Myr, so 175.1 Ma.

Discussion. There are various salamander taxa reported from the Middle and Late Jurassic of Eurasia, but these largely belong to the stem caudate family Karauridae : the Late Jurassic Karaurus from Kazakhstan, Kokartus from Kirghizia, Marmorerpeton from the Middle Jurassic of England and Portugal, and unnamed forms from the Middle Jurassic of England ( Evans et al., 2005). These authors note that an older salamandroid may be represented by postcranial elements referred to ‘Salamander B’ from the forest Marble Formation (late Bathonian) of the Kirtlington locality, Oxfordshire, UK.