Branchiosauridae
Branchiosauridae Temporal range:
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Fossil of Branchiosaurus salamandroides in the Museo di Storia Naturale di Venezia
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Order: | †Temnospondyli |
Clade: | †Amphibamiformes |
Family: | †Branchiosauridae Fritsch, 1879.[1]
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Genera | |
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Branchiosauridae is an extinct family of small
Geological/paleoenvironmental information
Branchiosaurids mostly inhabited Permo-Carboniferous freshwater mountain-lake habitats of Middle Europe at an altitude of up to 2000 meters.
Although the absolute ages of certain Rotliegend
Branchiosaurid gene flow enhanced by periods of wet climate led to successful colonization of roughly 15 basins (known so far). It has been hypothesized that Branchiosaurids originated in the Central Bohemian basin of Czech Republic (WestphalianD), from which they migrated to basins of the Massif Central in France (Stephanian B) and subsequently to several Central German basins including Thuringian Forest, Ilfeld and Saale (Stephanian C).[5]
Historical 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,
Classification
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.
Family description
The
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.[8]
Genera descriptions
The family Branchiosauridae includes the genera Branchiosaurus, Apateon, Melanerpeton, Leptorophus and Schoenfelderpeton.[2]
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
There are several potential branchiosaurids that are as of yet too inadequately characterized to classify. However, in recent work one such species, Tungussogyriinus bergi has been further analyzed and shown to share clear synapomorphies with branchiosaurids including the Y-shaped palatine resulting in a gap between ectopterygoid and maxilla as well as brush-like branchial denticles. T. bergi differs from all other branchiosaurids in two autapomorphies: elongated process of ilium and tricuspid dentition. Thus, Tungussgyrinus is thought to represent a clade that is the closest relative to all other branchiosaurids and two new subfamilies, Tungussogyrininae and Branchiosaurinae fall under Branchiosauridae.[9]
Paleobiology
The specialized pharyngeal denticles with brush-like branches of Branchiosauridae are indicative of gill clefts and suggest a filter-feeding mechanism focusing on plankton.[2] 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.[10] 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.[2]
Branchiosauridae diversified partly through adaptations that included the
Although the Melanerpeton-Apateon dichotomy is not correlated with any significant
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.[4] The metamorphosis trajectory into terrestrial adults has been reported only in A. gracilis.[4] 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.[4] 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).[3] 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.[11]
Histology
References
- ^ Fritsch. 1879. Fauna der Gaskohle und der Kalksteine der Permformation Böhmens. Vol. 1, part 1. Selbstverlag: Prague.
- ^ a b c d e f g h i j k l Schoch, R.R. 2008. The intrarelationships and evolutionary history of the temnospondyl family branchiosauridae. Journal of Systematic Palaeontology. 6(4):409-431.
- ^ a b Schoch, R.R. and Frobisch, N.B. 2006. Alternative Pathways in an Extinct Amphibian Clade. Evolution. 60(7):1467-1475
- ^ a b c d e f Frobisch, N.B. and Schoch, R.R. 2009. The largest specimen of Apateon and the life history pathway of neoteny in the Paleozoic temnospondyl family Branchiosauridae. Fossil Record.12(1):83-90.
- ^ a b c Ronchi, A. and Schneider, J.W. 2007. The Early Permian Branchiosaurids (Amphibia) of Sardinia (Italy): systematic palaeontology, palaeoecology, biostratigraphy and palaeobiogeographic Problems. Palaeo geography, Palaeoclimatology, Palaeoecology. 252:383-404
- ISSN 1631-0683.
- ^ R.R. Schoch. 2019. The putative lissamphibian stem-group: phylogeny and evolution of the dissorophoid temnospondyls. Journal of Paleontology 93(1):137-156
- ^ Werneburg, R. 2007. Timeless Design: colored pattern of skin in early Permian branchiosaurids (temnospondyli:Dissorophoidea). Journal of Vertebrate Paleontology. 27(4):1047-1050
- ^ Werneburg, R. 2009. The Permotriassic branchiosaurid Tungussogyrinus Efremov, 1939 (Temnospondyli, Dissorophoidea) from Siberia restudied. Fossil Record. 12(2):105-120
- ^ Milner, A.R. 1982. Small Temnospondyl Amphibians From the Middle Pennsylvanian of Illinois. Paleontology 25(3):635-664
- ^ Schoch, R.R. 2004. Skeleton Formation in the Branchiosauridae: A Case Study in Comparing Ontogenetic Trajectories. Journal of Vertebrate Paleontology 24(2):309-319
- ^ 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): 315-328