A morphological revision of Keraterpeton, the earliest horned nectridean from the Pennsylvanian of England and Ireland

Abstract

The aquatic diplocaulid nectridean Keraterpeton galvani is the commonest taxon represented in the Jarrow Coal assemblage from Kilkenny, Ireland. The Jarrow locality has yielded the earliest known Carboniferous coal-swamp fauna in the fossil record and is, therefore, of importance in understanding the history and diversity of the diplocaulid clade. The morphology of Keraterpeton is described in detail with emphasis on newly observed anatomical features. A reconstruction of the palate includes the presence of interpterygoid vacuities and new morphological details of the pterygoid, parasphenoid and basicranial region. The hyoid apparatus comprising an ossified basibranchial element has not been reported previously in nectrideans. The structure of the scapulocoracoid and primitive nature of the humerus is described and the presence of a five-digit manus confirmed. Previously unrecognised accessory dermal ossifications are present in the pectoral girdle. Keraterpeton longtoni from the Bolsovian in Staffordshire, England, is also described and newly figured. The primitive condition in diplocaulids is defined on the basis of the earliest occurrence at Jarrow and discussed in relation to functional morphology and mode of life. The evolution of the diplocaulid clade is assessed in relation to the revised diagnoses that define the primitive condition in Keraterpeton.

Microcomputed tomography of the holotype of the early tetrapodIchthyerpeton bradleyae(Huxley in Wright and Huxley, 1866) from the Pennsylvanian of Ireland

“…If the identification of the putative ilium in TCD.T87 is correct, then I. bradleyae had a unipartite dorsal iliac process, which is also seen in colosteids (Godfrey, 1989), nectrideans (Milner, 2019), and Aytonerpeton (Clack et al, 2016). However, in these three taxa, the dorsal process curves more posteriorly and is square-ended at its apex.…”

“…Clack et al (2019) identified a clade of stem tetrapods consisting of taxa with long bodies and reduced limbs (colosteids and nectrideans) or lacking limbs (aïstopods, adelospondyls, and Acherontiscus ). Vertebral arrangement is diverse within this clade, which includes rhachitomous vertebrae (colosteids: Hook, 1983; Godfrey, 1989), diplospondylous amphicoelous vertebrae ( Acherontiscus : Carroll, 1969; Clack et al, 2019), monospondylous vertebrae with sutured neural arches (adelospondyls: Andrews and Carroll, 1991), and holospondylous vertebrae (aïstopods and nectrideans [Anderson, 2002, 2003; Milner, 2019]). When present, the iliac process is unipartite in this clade, seen in colosteids (Godfrey, 1989), nectrideans (Milner, 2019), and Aytonerpeton (Clack et al, 2016).…”

“…1) to equate to the later part of the Bashkirian International Stage. Huxley in Huxley and Wright (1867) gave the first formal taxonomic account of tetrapods from Jarrow and described seven new species: the aïstopods Dolichosoma emersoni (Huxley in Huxley and Wright, 1867), now Dolichosomatites emersoni (Kuhn, 1961) and Ophiderpeton brownriggii (Huxley in Wright and Huxley, 1866); the temnospondyl Erpetocephalus rugosus (Huxley in Huxley and Wright, 1867), renamed Dendrepeton rugosum (Milner, 1980); the nectrideans Keraterpeton galvani (Huxley in Wright and Huxley, 1866), redescribed by Milner (2019), Lepterpeton dobbsii (Huxley in Wright and Huxley, 1866) and Urocordylus wandesfordii (Huxley in Wright and Huxley, 1866), reviewed in Bossy and Milner (1998); and Ichthyerpeton bradleyae (Huxley in Wright and Huxley, 1866), the subject of this paper.…”

The Making of Calibration Sausage Exemplified by Recalibrating the Transcriptomic Timetree of Jawed Vertebrates

“…Among Paleozoic tetrapods, tetradactyly is only known among “microsaurs” (including lysorophians), scincosaurids, some urocordylids, temnospondyls, and Colosteus (but not its close pentadactyl relative Greererpeton ). (Reports of tetradactyl limbs in diplocaulids have been erroneous: Marjanović and Laurin, 2019 ; Milner, 2019 , and references therein.) Colosteus and probably ( Clack et al, 2019 ) the urocordylids are stem-stegocephalians, but both were fully aquatic, thus unlikely to leave trackways; “microsaurs” and probably scincosaurids were tetrapods, and most were amphibious to terrestrial; temnospondyls spanned the full range of lifestyles, but see above for their phylogenetic position.…”

The making of calibration sausage exemplified by recalibrating the transcriptomic timetree of jawed vertebrates

“…Among Paleozoic tetrapods, tetradactyly is only known among “microsaurs” (including lysorophians), scincosaurids, some urocordylids, temnospondyls and Colosteus (but not its close pentadactyl relative Greererpeton ). (Reports of tetradactyl limbs in diplocaulids have been erroneous: Milner, 2019; Marjanović and Laurin, 2019, and references therein.) Colosteus and probably (Clack et al, 2019) the urocordylids are stem-stegocephalians, but both were fully aquatic, thus unlikely to leave trackways; “microsaurs” and probably scincosaurids were tetrapods, and most were amphibious to terrestrial; temnospondyls spanned the full range of lifestyles, but see above for their phylogenetic position.…”