The large, round head and shortened vertebral column are features Gerobatrachus shares in common with frogs and the early salamander Karaurus.
[1][2] Gerobatrachus also has a large embayment at the back of the skull called an optic notch, which is seen other amphibolids and in frogs and supports the tympanum, an eardrum-like structure used in hearing.
Gerobatrachus possesses another modern amphibian characteristic at the back of the skull, a widened bone called the parasphenoid basal plate.
[2] The nearly complete holotype skeleton USNM 489135 was collected from a fossil locality known as Don's Dump Fish Quarry in Baylor County, Texas in 1995.
As was the case in some previous analyses, caecilians were found to be the descendants of a group of small amphibious Paleozoic tetrapods called Lepospondyli while frogs and salamanders had an independent origin within Temnospondyli.
Their phylogenetic analyses confirmed that Gerobatrachus was an amphibamid temnospondyl, and since all modern amphibians nested within Lepospondyli, it was positioned far from the ancestry of frogs and salamanders.
[6] Below is a cladogram from the original 2008 phylogenetic analysis (left) and a cladogram from the 2012 analysis (right): Acanthostega Proterogyrinus Seymouria baylorensis Limnoscelis Lepospondyli (including caecilians) Greererpeton Eryops Balanerpeton Dendrerpeton Tambachia Ecolsonia Acheloma Branchiosauridae Micromelerpetontidae Tersomius Micropholis Eoscopus Platyrhinops Amphibamus Doleserpeton Gerobatrachus Triadobatrachus Anura (frogs) Albanerpetontidae Caudata (salamanders) Acanthostega Proterogyrinus Seymouria baylorensis Limnoscelis Lepospondyli Greererpeton Eryops Balanerpeton Dendrerpeton Tambachia Ecolsonia Acheloma Branchiosauridae Micromelerpetontidae Tersomius Micropholis Eoscopus Platyrhinops Amphibamus Doleserpeton Gerobatrachus Batrachia Eocaecilia Apoda (caecilians)