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Aberdeen, United Kingdom

Newman M.J.,Vine Lodge | Burrow C.J.,Ancient Environments | den-Blaauwen J.L.,University of Amsterdam | Davidson R.G.,35 Millside Road

The five species of genus Euthacanthus Powrie, 1864 are reduced to two species on morphological and stratigraphical evidence. Euthacanthus macnicoli Powrie, 1864 and Euthacanthus grandis Powrie, 1870 are here synonymised in the type species E. macnicoli Powrie, 1864. In a previous article, Euthacanthus gracilis Powrie, 1870 and Euthacanthus elegans Powrie, 1870 were combined in the species E. gracilis, and the fifth species, Euthacanthus curtus Powrie, 1870, was reassigned to Uraniacanthus curtus (Powrie, 1870). In this work, we give an in-depth study of the full range of morphological and histological structure of scales over the body of E. macnicoli, as well as of fin spine structure. Our study reveals new features of E. macnicoli, including a large ornamented dorsal sclerotic bone, ornament on the branchiostegal plates, a separate series of gular rays, calcified cartilage forming the jaws, and a postbranchial protruding spinose plate rather than the flat prepectoral plate previously described. © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. Source

The acanthodian originally described as Euthacanthus curtus Powrie, 1870 from the Early Devonian (Lochkovian) of Scotland was tentatively reassigned to Diplacanthus Agassiz, 1844 later in the nineteenth century, although doubt was cast on this revision. In 1976 Paton suggested that specimens comparable with the single type could belong to Uraniacanthus Miles, 1973, based on similarities with the type species U. spinosus Miles, 1973 from the Lochkovian of England. Hanke et al. (2001) noted that the Canadian Lochkovian species Gladiobranchus probaton Bernacsek & Dineley, 1977 was also very similar to U. spinosus. Our investigations indicate that all three species belong to the genus Uraniacanthus (which has priority over Gladiobranchus Bernacsek & Dineley, 1977) in the family Gladiobranchidae Bernacsek & Dineley, 1977, order Diplacanthiformes Berg, 1940 (revised). This identification supports a biogeographical connection between the Canadian, Scottish and English Early Devonian based on the common presence of the genus Uraniacanthus, as well as other acanthodian genera, including Ischnacanthus Powrie, 1864. Uraniacanthus could also be represented by isolated scales in coeval deposits in the Baltic. © Publications Scientifiques du Muséum national d'Histoire naturelle, Paris. Source

Burrow C.J.,Queensland Museum | Davidson R.G.,35 Millside Road | Den Blaauwen J.L.,University of Amsterdam | Newman M.J.,Vine Lodge
Journal of Vertebrate Paleontology

Disarticulated elements in a large, uncompressed regurgitate from Tillywhandland Quarry (Lochkovian), as well as serial sections of an articulated specimen, reveal the three-dimensional shape and structure of fin spines, scapulocoracoid and dermal plates, and the histological structure of dermal and endoskeletal hard tissues of the climatiid acanthodian Climatius reticulatus. Globular calcified cartilage is the only form of mineralization of the head endoskeleton, with the jaws preserved as double-layered globular calcified cartilage. Tooth whorls are borne on both the upper and lower jaws and comprise a vascularized bone base and tooth cusps composed of a vascular network and mesodentine, without a central pulp cavity. The short admedian spine is the only strongly laterally compressed spine; the anterior dorsal fin spine has a wide, splayed base. No evidence was found of large dermal plates between the pectoral fin spine and the median lorical plates, with the prepectoral pinnal plates with spines being the only large paired dermal components of the shoulder girdle. The anterior lorical plate, pinnal plates, and tesserae on the scapulocoracoid bear ornament comparable to the postbranchial apronic ornament in acanthothoracid placoderms. Branchiostegal plates have a thin, dense inner bone layer and an outer dentinous ornament layer but lack a middle osteodentine layer; other postcranial plates and fin spines have a smooth-surfaced inner layer of bone and a thick middle osteodentine layer. Body scales have a crown with areal growth zones formed of Stranggewebe and syncitial mesodentine on a cellular bone base. © 2015 by the Society of Vertebrate Paleontology. Source

Burrow C.,Geosciences | den Blaauwen J.,University of Amsterdam | Newman M.,Vine Lodge | Davidson R.,35 Millside Road
Palaeontologia Electronica

The Diplacanthiformes are a clade of acanthodian fishes which were widespread during the Middle and early Late Devonian. They are best represented in the Middle Devonian, by articulated fossils, fin spines, and abundant scales, the latter particularly from northern Europe. Three species of diplacanthid diplacanthiforms, Diplacanthus crassisimus, Diplacanthus tenuistriatus, and Rhadinacanthus longispinus, are found in Middle Devonian (Eifelian–Givetian) assemblages of articulated fish in northern Scotland. Our detailed study of the dermal structures and endoskeletal shoulder girdles in these fish supports the validity of Rhadinacanthus as a separate genus from Diplacanthus, with the two being differentiated by spine morphology, scale morphology, and histology, and shape and form of the pectoral girdle. In Orkney and Caithness, D. crassisimus first occurs in the Thursius macrolepidotus vertebrate biozone and disappears by the Millerosteus minor + Thursius pholidotus vertebrate biozone. Diplacanthus tenuistriatus and R. longispinus range from the Coccosteus cuspidatus biozone to the end of the Millerosteus minor + Thursius pholidotus biozone. Through comparing the results of our detailed work on the morphology and histology of fin spines and scales from the articulated fish with diplacanthid taxa based on isolated scales and fin spines from the Baltic region, Belarus, and Severnaya Zemlya, we recognize many of the latter taxa from contemporary deposits as junior synonyms of the Scottish species. Phylogenetic analysis of selected gnathostome genera shows the diplacanthiforms Diplacanthus, Rhadinacanthus, Uraniacanthus, and Culmacanthus form a well-supported clade within a larger clade comprising all acanthodian taxa plus a monophyletic Chondrichthyes. © March 2016 Palaeontological Association. Source

Burrow C.J.,Ancient Environments | Newman M.J.,Vine Lodge | Davidson R.G.,35 Millside Road | den Blaauwen J.L.,University of Amsterdam

Parexus Agassiz was one of the first Early Devonian 'spiny sharks' to be described. The genus is readily recognized by the large size and ornament of its anterior dorsal fin spine. Although two species were erected, reappraisal of all known specimens indicate they should be synonymized in the type species Parexus recurvus. Farnellia tuberculata Traquair, originally described as a vertebral column, is actually tooth rows of jaw dentition, and is also now considered to be a junior synonym of P. recurvus. Parexus has a perichondrally ossified scapulocoracoid of typical acanthodian shape, and diagnostic features of the family Climatiidae, but has distinctive scales comprising appositional growth zones that closely resemble those of the putative stem chondrichthyan Seretolepis elegans Karatajute-Talimaa. © 2013 Copyright Taylor and Francis Limited. Source

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