Geological/paleoenvironmental information
Branchiosaurids mostly inhabited Permo-Carboniferous freshwater mountain-lake habitats of Middle Europe at an altitude of up to 2000 meters. Large quantities of specimens have been collected from the grey shales and limestones of Rotliegend localities of the Variscan orogen. The branchiosaurid fossil record is exceptional due to Lagerstatten conditions of these localities and the preservation of specimens representing various ontogenetic stages.Frobisch, N.B. and Schoch, R.R. 2009. The largest specimen of Apateon and the life history pathway of neoteny in theHistorical information/discovery
Branchiosaurids were recognized as a distinct group and given the family name by Fritsch (1879). In 1939 Romer hypothesized that branchiosaurids were, instead, larval morphotypes of largerClassification
Branchiosaurids form a clade within dissorophoid temnospondyls (one of the hypothesized origins of Lissamphibia). Dissorophoidea encompasses Micromelerpetidae and Xerodromes (all other taxa). Xerodromes includes the Olsoniformes and salamander-like Amphibamiformes. The latter includes four clades: Micropholidae, Amphibamidae, Branchiosauridae and Lissamphibia.R.R. Schoch. 2019. The putative lissamphibian stem-group: phylogeny and evolution of the dissorophoid temnospondyls. Journal of Paleontology 93(1):137-156 The amphibamids ''Amphibamus'' and ''Platyrhinops'' are the closest relatives of branchiosaurids and despite sharing homoplasies with amphibamids, Branchiosauridae forms a monophyletic group.Family description
The synapomorphies of Branchiosauridae include a palatine with a prominent process which extends from the center of the bone to contact the maxilla; six rows of isolated, slender and multi-ended branchials; 21-22 presacral vertebrae (reversed in some forms). One skeleton of the branchiosaurid ''Melanerpton tenerum'' has been discovered with preserved skin pattern. The preservation shows a regular pattern of bright spots blurred by dark pigments on the dorsal skin. This is the first record of this mosaic-type pattern in an extinct amphibian.Werneburg, R. 2007. Timeless Design: colored pattern of skin in early Permian branchiosaurids (temnospondyli:Dissorophoidea). Journal of Vertebrate Paleontology. 27(4):1047-1050Genera descriptions
The family Branchiosauridae includes the genera ''Branchiosaurus'', ''Apateon'', ''Melanerpeton'', ''Leptorophus'' and ''Schoenfelderpeton''. The stratigraphically oldest genus is ''Branchiosaurus'', with its only well-known species being ''B. salamandroides'', and forms the most basal node of Branchiosauridae. The post-''Branchiosaurus'' branchiosaurids fall into either the ''Melanerpeton''-clade or the ''Apateon'' clade. Within the morphogenically more diverse ''Melanerpeton''-clade, the genera ''Schoenfelderpeton'' and ''Leptorophus'' are sister groups. Within the ''Apateon''-clade, ''A. kontheri'' forms the basal-most taxon followed by ''A. gracilis'', ''A. pedestris'', ''A. dracyiensis'' and the sister-taxa ''A. caducus'' and ''A. flagrifer''. The genus ''Branchiosaurus'' is plesiomorphic with no autapomorphies. ''Branchiosaurus'' retains the prefrontal-postfrontal contact, the anteriorly extended jugal and ventral osteoderms. In the post-''Branchiosaurus'' clade the prefrontal-postfrontal contact is lost (although reversed in ''A. dracyiensis''), the maxilla sutures with quadratojugal in late development, the jugal is anteriorly shortened and ventral ossified osteoderms are lost. The diagnostic features of the genus ''Apateon'' are tabular horns separated from the skull table by a groove; tooth-bearing region of maxilla is broad and the dorsal osteoderms are smooth or with radiating striations. The diagnostic features of the ''Melanerpeton'' group are the palatine, the ectopterygoid and palatine ramus of pterygoid are extremely delicate, poorly ossified and have few or no denticles. The ''Melanerpeton'' genus has no autapomorphies and is paraphyletic with respect to the ''Leptorophus''-''Schoenfelderpeton'' group. The ''Leptorophus''-''Schoenfelderpeton'' group is characterized by a postorbital separated from supratemporal, a carotid foramina and grooves situated on sides of the cultriform process. The diagnostic features of the genus ''Leptorophus'' are a long triangular skull, anterior parts of nasal and vomer elongated, a very close prefrontal and postfrontal, elongated narial openings, a maxilla extended posteriorly, quadrate condyles posterior to occipital condyles, and a vomer with long posteromedial process. The autopamorphic features of the genus ''Schoenfelderpeton'' are an overall broad skull with an enlargedPaleobiology
The specialized pharyngeal denticles with brush-like branches of Branchiosauridae are indicative of gill clefts and suggest a filter-feeding mechanism focusing on plankton. In well preserved specimens of ''Branchiosaurus'', six rows of tooth-bearing ossicles are present on each side of the hyobranchial skeleton in a 1-2-2-1 configuration. This is consistent with the denticles being attached to the epithelium surrounding four cartilaginous ceratobranchials bordering three external gill-slits.Milner, A.R. 1982. Small Temnospondyl Amphibians From the Middle Pennsylvanian of Illinois. Paleontology 25(3):635-664 The jaw-like apparatus may have served to hold back prey items leaving the pharyngeal cavity with the water current or to form a tight closure of gill cleft during feeding. Branchiosauridae diversified partly through adaptations that included the co-evolution of delayed development of the upper jaw and cheek which resulted in a kinetic maxilla and allowed for more efficient suction feeding. This mechanism would have been adaptive for suspension feeding and feeding on single prey. In the ''Apateon''-clade different morphotypes evolved due to heterochronic changes. In some species (''A. caducus'' and ''A. flagrifer''), the maxilla consolidated early in development and the gape size and irregular dentition indicate an early transition in diet from suspension to carnivory. In other species (''A. dracyiensis'') the maxilla was never consolidated indicating a reinforced suction mechanism. Diagnostics of the ''Melanerpeton''-clade indicate a combination of filter-feeding and occasional capture of larger prey. Although the ''Melanerpeton''-''Apateon'' dichotomy is not correlated with any significant adaptations, the ''Melanerpeton''-clade generally had a larger body size which likely allowed them to occupy new niches in lake ecosystems. Most ''Apateon'' species did not appear to have competitors and thus were successful invaders.Ontogeny
Both neoteny (retention of larval somatic features into adulthood) and metamorphosis have been reported ontogenic pathways in branchiosaurids. Certain terrestrial branchiosaurid adaptations, such as the short trunk and long limbs, suggest that it was an initially terrestrial clade and thus reversals to aquatic life and metamorphosing trajectories occurred within the clade. The metamorphosis trajectory into terrestrial adults has been reported only in ''A. gracilis''. Changes that distinguish the adult ''A. gracilis'' from its larval counterpart occurred during a rapid phase of development and include ossification of the braincase, palatoquadrate, intercentra and girdles, muscle attachment scars, and polygonal ridges and grooves decorating the dermal skull roof. The larval somatic features including ossified branchial denticles and larval-type sculpturing of the skull roof are lost. Postcranial features of transformed ''A. gracilis'' indicate that it was terrestrial and biting force had become a more important factor than suction. Despite this instance of metamorphosis, neoteny is nearly ubiquitous throughout branchiosaurids and most species remained in an aquatic environment throughout their life (however we should not rule out the possibility that this is a relic of terrestrial metamorphosed specimens not being well preserved). Neoteny is one of the major modes of heterochrony in which there is a modification in the timing or rate of development of certain features that is inherited. Neotenic branchiosaurids experienced isometric growth of cranial bones while retaining juvenile features noted above. Adult branchiosaurid neotenes are distinguished from larval neotenes by accentuated larval-type skull roof ornamentation, increased ossification (although not as extensively as in metamorphosed specimens), and development of uncinate process on the anterior trunk ribs. Such phenotypic plasticity in the form of facultative neoteny has been reported in modern lissamphibians and has been suggested to also be highly advantageous in the high altitude habitats of branchiosaurids where the harsh, continually changing conditions would have made aquatic life favorable.Schoch, R.R. 2004. Skeleton Formation in the Branchiosauridae: A Case Study in Comparing Ontogenetic Trajectories. Journal of Vertebrate Paleontology 24(2):309-319Histology
Histological observations confirm anatomical evidence of neoteny in branchiosaurids. Skeletochronological analysis allows for the identification of sexual maturity (i.e. when the distance between lines of arrested growth (LAGs) suddenly decreases). In ''Apateon'' specimens determined to be sexually mature, the cartilaginous Katschenko's line can be observed when perichondral ossification is complete. The diaphyseal and epiphyseal ossification patterns of ''Apateon'' specimens (i.e. persistence of histological larval features into adulthood) are suggestive of paedomorphy and similar to those of urodeles (extant neotenic amphibians).Sanchez, S. et al. 2010. Developmental plasticity of limb bone microstructureal organization in Apateon: histological evidence of paedomorphic conditions in branchiosaurs. Evolution & Development. 12(3): 315-328References
{{Taxonbar, from=Q897687 Prehistoric amphibian families Carboniferous temnospondyls of Europe Permian temnospondyls of Europe Triassic temnospondyls of Europe Pennsylvanian first appearances Early Triassic extinctions Fossils of Germany Fossils of France Taxa named by Antonin Fritsch