ANURA (FROGS, TOADS)

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 : 49-50

CROWN ANURA (FROGS, TOADS) (44)

Node Calibrated. Divergence between Leiopelmatidae / Ascaphidae and derived frogs and toads (Neobatrachia, plus stem forms), based recent phylogenies (Roelants et al., 2007; Pyron and Wiens, 2012).

Fossil Taxon and Specimen. Eodiscoglossus oxoniensis Evans et al. (1990) from the Forest Marble Formation , upper Bathonian of Oxfordshire, England (holotype, Natural History Museum, London, NHMUK R11700 , a right ilium).

Phylogenetic Justification. Eodiscoglossus is identified as a member of crown Discoglossidae on the basis of two apomorphies in combination, the possession of opisthocoelous vertebrae together with an ilium bearing a dorsal crest ( Evans et al., 1990; Ruta and Coates, 2007).

Minimum Age. 165.3 Ma

Soft Maximum Age. 201.5 Ma

Age Justification. The Forest Marble Formation has long been assigned to the Late Bathonian, dated as 166.5-166.1 Ma ± 1.2 Myr ( Gradstein et al., 2012, pp. 765, 777), so giving an age of 165.3 Ma as the minimum constraint.

The soft maximum constraint can be set as equivalent to the base of the Jurassic, allowing for finds of various stem anurans and other small tetrapods from several continents, but as yet no crown taxa, and so 201.3 Ma ± 0.2 Myr, so 201.5 Ma.

Discussion. There are several stem frogs in the Triassic and Jurassic, with Triadobatrachus the oldest (Triassic, Induan) through Jurassic forms such as Prosalirus, Vieraella , and Notobatrachus , but these do not belong to any modern anuran subclades, and so are not helpful in determining a minimum age for the crown-clade Anura (Roelants and Bossuyt, 2005) .

Among major anuran subclades, Discoglossoidea provides the oldest fossil, Eodiscoglossus . This predates the oldest members of other anuran subclades, namely Rhadinosteus parvus from the Kimmeridgian (Rhinophrynoidea), an indeterminate pelobatid from the Late Cretaceous (Pelobatoidea), Shomronella jordanica , Cordicephalus gracilis , and Thoraciliacus rostriceps from the Hauterivian of Israel ( Pipidae ), and Baurubatrachus pricei from the Late Cretaceous of Brazil (Neobatrachia). Roelants and Bossuyt (2005, p. 120) selected an age of 164 Ma for Eodiscoglossus .