The intrarelationships and evolutionary history of the temnospondyl family branchiosauridae

Synopsis

The larval or paedomorphic branchiosaurid temnospondyls, inhabitants of many Permo‐Carboniferous freshwater lakes across Europe, have never been analysed cladistically. In the present work, we have analysed the relationships between all the well‐defined species of the clade, with the following results: (1) despite homoplasies shared with amphibamids, the family Branchiosauridae forms a well‐supported monophylum; (2) if Micropholis is considered to be an amphibamid, then Branchiosauridae have arisen within the Amphibamidae and could be considered to be a clade of paedomorphic amphibamids; (3) the closest relatives of branchiosaurids are the amphibamids Amphibamus and Platyrhinops; (4) the stratigraphically oldest genus Branchiosaurus, here represented by its only well‐known species B. salamandroides, forms the most basal offshoot of the Branchiosauridae; (5) the remainder of the branchiosaurids fall into two clades referred to as the Melanerpeton‐clade and Apateon‐clade, respectively; (6) the Melanerpeton‐clade is morphologically more diverse than the Apateon‐clade; (7) within the Melanerpeton‐clade, Schoenfelderpeton and Leptorophus are sister groups; (8) within Apateon, A. kontheri forms the basal‐most taxon, followed by A. gracilis, A. pedestris, A. dracyiensis and the sister‐taxa A. caducus and A. flagrifer.

An evolutionary scenario suggests that branchiosaurids originated by invention of a key innovation: specialized pharyngeal denticles, housed in gill clefts, served as a filter‐feeding device focussing on plankton. The group diversified in part, by patterns of delayed development of the upper jaw and cheek resulting in a kinetic maxilla, thereby permitting manipulation of the oral margin during suction feeding. It can be shown that within the Apateon‐clade, the second component evolved along different lines into rather different adaptational directions, producing a range of morphotypes controlled by minor heterochronic changes.

Keywords:

• Temnospondyli
• Dissorophoidea
• Branchiosauridae
• ontogeny
• phylogeny
• evolutionary scenario