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Platyhystrix
Platyhystrix (from Greek: πλατύς platús, 'flat' and Greek: ῠ̔́στρῐξ hústrix, 'porcupine') is an extinct temnospondyl amphibian with a distinctive sail along its back, similar to the unrelated synapsids, Dimetrodon and Edaphosaurus. It lived during the boundary between the latest Carboniferous and earliest Permian periods throughout what is now known as the Four Corners, Texas, and Kansas about 300 million years ago.
Not much is known about Platyhystrix, with a majority of the fossils found composed of the distinct neural spines, and fractured skull fragments. There is only one species within the genus, Platyhystrix rugosus. Its phylogenetic relationships to other members of the family Dissorophidae have been debated in recent years, due to its unique cranial features, and recent discoveries as to the origins of modern day lissamphibians. Synonyms and alternate spellings include: Zatrachys apicalis, Ctenosaurus rugosus, Platyhystryx, Platyhistryx.
The holotype of Platyhystrix (AMNH FARB 4785) was first discovered in the Early Permian Cutler formation in Rio Arribas Co, New Mexico in 1881 by American paleontologist, E.D. Cope. The holotype consisted of a few fragmented neural spines, and was initially listed under the species name, Zatrachys apicalis. In 1910, American paleontologist E.C. Case reclassified the neural spines as belonging to a new species of the pelycosaurian reptile Ctenosaurus, Ctenosaurus rugosus (the specific name means "wrinkled, shriveled"), since they resembled spines from Texas belonging to C. koeneni, described by Friedrich von Huene.
In Case's description of the Platyhystrix holotype, he initially classified it as part of a new reptile specimen, but still noted tubercles along the neural spines which were similar to the projections found on amphibian skulls. It was S.W. Williston who created the genus in 1911, and placed it within the Temnospondyli order once fractured skull elements were described in 1916.
Compared to other dissorophid temnospondyls, Platyhystrix's skull is rather large (over 19 cm long along midline), as well as long and narrow when analyzed in dorsal view. There is a wide variety in dermal sculpturing which occurs along the dorsal and lateral portions of the skull. Large ridges and tubercle-like processes are present along the dorsal half of the orbital rim, edges of the skull table, and areas which adjoin the cheek. Nodular-like processes are most pronounced on the posterior portion of the skull roof, on the postorbital, squamosal, supratemporal, and tabular. The central dorsal portion of the skull is characterized by a reticulated pitting pattern, which becomes finer as it extends towards the nasals. These kinds of dermal ornamentation are what diagnose Platyhystrix from other members of Dissorophidae. Based on marginal dentition and preserved portions of the premaxilla, Platyhystrix may have had upwards of 65 teeth on either side of the upper jaw, in the form of simple, pointed pegs.
Other diagnostic features of the skull include: long and narrow nasals, whose length is equivalent to approximately one third of the midline length of the skull; posteriorly closed otic notch; parietal is large and extends anteriorly beyond margin of orbit; parietals are longer than the frontals; postfrontal length is greater than twice its width and equal to the length of the supratemporal; cheek is steeply inclined and meets the skull table at nearly right angle.
The most notable characteristic of Platyhystrix is its elongated neural spines. Initially, these "spines" were thought to be an extension of the neural arch above the transverse process. However, the reassignment of Platyhystrix to the armored Dissorophidae clade and the blade's extensive ornamentation led Vaughn in 1971 to reinterpret this feature as an osteoderm that was fused to the true neural spine instead. This reclassification suggested a superficial convergence with the neural spines present in synapsids. Histological analysis revealed that the dorsal blades of Platyhystrix do indeed share histological features and were likely homologous with the internal osteoderm series present in other dissorophids. This evidence points to the blades being of dermal origin, and are a novel example of dermal-endochondral co-ossification in a Paleozoic tetrapod.
It is estimated that the notable sail was made up of a range of 11-15 laterally compressed and distally expanded blades. Most of the distal length of these dorsal blades is covered with ridges and pustules, similar to the dermal ornamentation seen on the skull. Similar to Edaphosaurus, a paired set of lateral tubercles can be found proximally on the blade, and while some spines curve anteriorly, the rest exhibit severe curving toward the pelvis.
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Platyhystrix
Platyhystrix (from Greek: πλατύς platús, 'flat' and Greek: ῠ̔́στρῐξ hústrix, 'porcupine') is an extinct temnospondyl amphibian with a distinctive sail along its back, similar to the unrelated synapsids, Dimetrodon and Edaphosaurus. It lived during the boundary between the latest Carboniferous and earliest Permian periods throughout what is now known as the Four Corners, Texas, and Kansas about 300 million years ago.
Not much is known about Platyhystrix, with a majority of the fossils found composed of the distinct neural spines, and fractured skull fragments. There is only one species within the genus, Platyhystrix rugosus. Its phylogenetic relationships to other members of the family Dissorophidae have been debated in recent years, due to its unique cranial features, and recent discoveries as to the origins of modern day lissamphibians. Synonyms and alternate spellings include: Zatrachys apicalis, Ctenosaurus rugosus, Platyhystryx, Platyhistryx.
The holotype of Platyhystrix (AMNH FARB 4785) was first discovered in the Early Permian Cutler formation in Rio Arribas Co, New Mexico in 1881 by American paleontologist, E.D. Cope. The holotype consisted of a few fragmented neural spines, and was initially listed under the species name, Zatrachys apicalis. In 1910, American paleontologist E.C. Case reclassified the neural spines as belonging to a new species of the pelycosaurian reptile Ctenosaurus, Ctenosaurus rugosus (the specific name means "wrinkled, shriveled"), since they resembled spines from Texas belonging to C. koeneni, described by Friedrich von Huene.
In Case's description of the Platyhystrix holotype, he initially classified it as part of a new reptile specimen, but still noted tubercles along the neural spines which were similar to the projections found on amphibian skulls. It was S.W. Williston who created the genus in 1911, and placed it within the Temnospondyli order once fractured skull elements were described in 1916.
Compared to other dissorophid temnospondyls, Platyhystrix's skull is rather large (over 19 cm long along midline), as well as long and narrow when analyzed in dorsal view. There is a wide variety in dermal sculpturing which occurs along the dorsal and lateral portions of the skull. Large ridges and tubercle-like processes are present along the dorsal half of the orbital rim, edges of the skull table, and areas which adjoin the cheek. Nodular-like processes are most pronounced on the posterior portion of the skull roof, on the postorbital, squamosal, supratemporal, and tabular. The central dorsal portion of the skull is characterized by a reticulated pitting pattern, which becomes finer as it extends towards the nasals. These kinds of dermal ornamentation are what diagnose Platyhystrix from other members of Dissorophidae. Based on marginal dentition and preserved portions of the premaxilla, Platyhystrix may have had upwards of 65 teeth on either side of the upper jaw, in the form of simple, pointed pegs.
Other diagnostic features of the skull include: long and narrow nasals, whose length is equivalent to approximately one third of the midline length of the skull; posteriorly closed otic notch; parietal is large and extends anteriorly beyond margin of orbit; parietals are longer than the frontals; postfrontal length is greater than twice its width and equal to the length of the supratemporal; cheek is steeply inclined and meets the skull table at nearly right angle.
The most notable characteristic of Platyhystrix is its elongated neural spines. Initially, these "spines" were thought to be an extension of the neural arch above the transverse process. However, the reassignment of Platyhystrix to the armored Dissorophidae clade and the blade's extensive ornamentation led Vaughn in 1971 to reinterpret this feature as an osteoderm that was fused to the true neural spine instead. This reclassification suggested a superficial convergence with the neural spines present in synapsids. Histological analysis revealed that the dorsal blades of Platyhystrix do indeed share histological features and were likely homologous with the internal osteoderm series present in other dissorophids. This evidence points to the blades being of dermal origin, and are a novel example of dermal-endochondral co-ossification in a Paleozoic tetrapod.
It is estimated that the notable sail was made up of a range of 11-15 laterally compressed and distally expanded blades. Most of the distal length of these dorsal blades is covered with ridges and pustules, similar to the dermal ornamentation seen on the skull. Similar to Edaphosaurus, a paired set of lateral tubercles can be found proximally on the blade, and while some spines curve anteriorly, the rest exhibit severe curving toward the pelvis.
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