Carboniferous tetrapod biostratigraphy, biochronology and evolutionary events

Abstract

Tetrapod (amphibian and amniote) fossils of Carboniferous age are known almost exclusively from the southern part of a paleoequatorial Euramerican province. The stratigraphic distribution of Carboniferous tetrapod fossils is used to identify five land-vertebrate faunachrons: (1) Hortonbluffian (Givetian-early Visean), the time between the FAD of tetrapods to the beginning of the Doran; (2) Doran (late Visean-early Bashkirian), the time between the FAD of the baphetid Loxomma and the beginning of the Nyranyan; (3) Nyranyan (late Bashkirian-Moscovian), the time between the FAD of the eureptile Hylonomus and the beginning of the Cobrean; (4) Cobrean (Kasimovian-late Gzhelian), the time between the FAD of the eupelycosaur Ianthasaurus and the beginning of the Coyotean; and (5) Coyotean (late Gzhelian-early Permian), the time between the FAD of the eupelycosaur Sphenacodon and the beginning of the Seymouran. This biochronology provides insight into some important evolutionary events in Carboniferous tetrapod evolution.

The Four Principal Megabiases in the Known Fossil Record: Taphonomy, Rock Preservation, Fossil Discovery and Fossil Study

“…The history of the discovery of fossils has been heavily influenced by the prospecting for, and extraction of, mineral resources. For example, the major difference between Moscovian and older/younger Carboniferous tetrapod records has its primary basis in coal mining [22,23]. Thus, the larger Middle Pennsylvanian tetrapod record is biased because almost all of the Moscovian tetrapod assemblages are associated with coal beds [23,25,26].…”

“…For example, the major difference between Moscovian and older/younger Carboniferous tetrapod records has its primary basis in coal mining [22,23]. Thus, the larger Middle Pennsylvanian tetrapod record is biased because almost all of the Moscovian tetrapod assemblages are associated with coal beds [23,25,26]. There is an abrupt decrease in mineable coals across the Middle-Late Pennsylvanian boundary, due to climate change driven by sea-level drop, the drifting northward of Euramerica and changing topography and drainage patterns due to Variscan tectonism [e.g., [27][28][29].…”

Halgaitosaurus gregarius, a New Upper Carboniferous Araeoscelidian (Reptilia: Diapsida) from the Halgaito Formation, Bears Ears National Monument, Utah, USA

“…The vertebrate fauna from the Halgaito Formation has been reported as Carboniferous (Sumida et al 1999a, b, c), Permian (Vaughn 1962), or spanning the boundary (Scott 2013). Huttenlocker et al (2018) determined that the Birthday bonebed vertebrate fauna is correlative with the Cobrean and Coyotean faunas in the El Cobre Canyon Formation in New Mexico and thus latest Carboniferous, Virgilian (Lucas 2005(Lucas , 2021. This age assignment is supported by a recent study (Huttenlocker et al 2020) of conodonts from marine carbonate marker units in the Rico and Halgaito formations in Valley of the Gods, including the Mc-Kim and 'A' limestones.…”

“…The fossil record of North American araeoscelidians is better represented and studied. Araeoscelis Williston, 1910, is known by two species from the Wolfcampian-Leonardian of Texas (correlative to Artinskian-Kungarian global stages), Araeoscelis gracilis Williston, 1910 (Arroyo Formation, Clear Fork Group, Leonardian based on Lucas 2018) and Araeoscelis casei Broom, 1913 (Nocona Formation, Wichita Group, Wolfcampian based on Lucas 2018). Other specimens from the Petrolia (former Belle Plains) Formation, Wichita Group, have not been assigned to either species (Vaughn 1955;Reisz et al 1984), which appear to differ only by their geologic age (Vaughn 1955).…”

“…Zarcasaurus tandyderus Brinkman, Berman, and Eberth, 1984, is known by a partial, incomplete skeleton from the upper portion of the El Cobre Canyon Formation, Cutler Group, Arroyo del Agua, New Mexico. It is confined biostratigraphically to the Coyotean Land Vertebrate Faunachron, which likely spans the Virgilian-Wolfcampian stages (correlative with Gzhelian-Sakmarian global stages) and, therefore, straddles the Carboniferous-Permian boundary (Lucas 2005). The most recently described araeoscelidian is Spinoaequalis schultzei deBraga and Reisz, 1995, which is based on a single immature specimen from the Calhoun Shale, Shawnee Group, Upper Pennsylvanian, Virgilian (correlative with the Gzhelian global stage) Hamilton Quarry, Kansas.…”