An unusual new fossil shark (Pisces: Chondrichthyes> from the Late Devonian of South Africa
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Abstract:
A new stem-group chondrichthyan fish, PlesioselacJllIs macracanthlls gen. et sp. nov., is described from the Late Devonian Witpoort Formation, representing an estuarine lagoon site, near Grahamstown, South Africa. Based on a single, fairly complete specimen, it is distinctive in its a single dorsal fin braced by a large, stout spine with numerous ribs and posterior denticles, apparently no second dorsal or anal fin, an amphistylic jaw suspension, and a distinctive triangular palatoquadrate. It is suggested that the species may represent a high-latitude, Late Devonian relict taxon.Keywords:
Devonian
Chondrichthyes
Dorsal fin
Late Devonian extinction
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Devonian
Chondrichthyes
Late Devonian extinction
Assemblage (archaeology)
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The ornament on a small external cast in pink chert shows considerable similarity with that of various Middle Palaeozoic and Triassic fish genera. It comes from the Permian–Triassic Oruatemanu Formation of Arrow Rocks, Whangaroa area, eastern Northland. Conodont faunas from a few metres above and below the sample allow correlation with the Neospathodus pakistanensis zone of the Early Triassic, which is assigned to the late Dienerian (late Induan), with adjacent conodont zone faunas in their correct stratigraphic association. The cast is assumed to be that of a small fragment of fin spine, most likely from the junction area of the crown and root on the right-hand side of a dorsal fin spine, possibly anterior, of a marine ctenacanthoid shark, a basal shark order not previously recorded from New Zealand.
Conodont
Early Triassic
Dorsal fin
Sequence (biology)
Ladinian
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Abstract: A new, third, specimen of Onychoselache traquairi from the Viséan (Holkerian) of Scotland allows a significant revision of the anatomy of this stem‐group elasmobranch. This first report of material from the Mumbie Quarry exposure of the Glencartholm fish beds presents a new reconstruction of Onychoselache showing broad‐based cephalic and nuchal spines, and exceptionally large pectoral fins. Details of the jaws, braincase and postcranial skeleton demonstrate that Onychoselache is a well‐characterized member of the Hybodontiformes. Comparisons of the pectoral skeleton with other early chondrichthyan examples, including new material of Tristychius arcuatus and Plesioselachus macracanthus , highlight a range of early chondrichthyan conditions that are incorporated into a revised hybodontiform phylogeny. Close resemblance between Onychoselache and Mesozoic and late Palaeozoic hybodonts implies that these clades diverged within the Carboniferous and Permian. Major differences between Onychoselache and the coeval Tristychius (a modified reconstruction of which is included) indicate that the Neoselachii‐Hybodontiformes split is probably Late Devonian, consistent with records of isolated teeth. The pectoral fins of Onychoselache , while unique among Palaeozoic forms, resemble those of Recent bamboo and epaulette sharks (Orectolobiformes). The functional corollary of this convergence is that Onychoselache represents an instance of a non‐tetrapod early vertebrate with a near‐walking gait.
Postcrania
Tetrapod (structure)
Devonian
Chondrichthyes
Late Devonian extinction
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ABSTRACT Polazzodus coronatus, gen. et sp. nov., is a pycnodontiform fish from two proximate Late Cretaceous fossil sites near Polazzo, in northeastern Italy, where it is relatively abundant. Its autapomorphic characters are the presence of a distinctively shaped second dorsal ridge scale with an anterior projection; the presence of an olfactory fenestra on the premaxilla; an axe blade-like morphology of the maxilla; and the presence of a conspicuous posterodorsal process on the cleithrum. Polazzodus coronatus, gen. et sp. nov., is closely related to the pycnodontids Oropycnodus, Pycnodus, and probably 'Coelodus' gridelli and Tergestinia. Although their phylogenetic interrelationships will be tested when the last two forms are revised, Polazzodus coronatus is assigned to the subfamily Pycnodontinae within the Family Pycnodontidae, because it possesses the autapomorphies of both latter groups; for instance, the presence of an exposed part of the endocranium, without overlying dermal bones, which is an autapomorphy of the Pycnodontinae. The shape and large size of the supraoccipital bone in Polazzodus, together with the arrangement of the other occipital bones, indicates that this exposed portion of the endocranium is most likely formed by the endochondral supraoccipital bone.
Autapomorphy
Premaxilla
Phyletic gradualism
Galea
Laurasia
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Late Devonian extinction
Western hemisphere
Devonian
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Although known from Mesozoic marine, fresh and brackish water deposits from North America, Europe, Africa and Asia, hybodont shark remains have been rarely reported from the Cretaceous formations of Kansas. Remains of hybodonts reported from outside Kansas consist of small teeth, distinctive cephalic hooks, dorsal fin spines, and occasionally even complete fish. Collections of micro-vertebrate remains in Kansas since 1999 have confirmed the presence of hybodontiformes in the Kiowa (Albian), Dakota (Cenomanian) and Carlile (Turonian) formations in three different counties in the state. These specimens have been assigned to the genus Meristodonoides Underwood and Cumbaa 2010, and add an important element to the known marine faunas of the Western Interior Sea during late Early Cretaceous and early Late Cretaceous time.
Chondrichthyes
Cenomanian
Dorsal fin
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A partial skeleton of a hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of Dorset, England, is described and designated as a new genus and species, Durnonovariaodus maiseyi gen. et sp. nov. The holotype and only known specimen, which is represented by disarticulated splanchnocranial elements with associated teeth, a single dorsal fin spine, the pelvic girdle, as well as unidentifiable cartilage fragments, plus countless dermal denticles, exhibits a puzzling combination of dental and skeletal features, providing important new insights into the morphological and ecological diversity of hybodontiforms. Durnonovariaodus gen. nov. displays a unique set of dental characters, showing close morphological resemblance to Secarodus from the Middle Jurassic of England, which was erected for distinctive, strongly labio-lingually compressed multicuspid cutting teeth originally described as Hybodus polyprion . Skeletally, Durnonovariaodus gen. nov. resembles Hybodus and Egertonodus in having a palatoquadrate with a palatobasal process and an ethmoidal articular surface, combined with the possession of dorsal fin spines ornamented with costae. Therefore, and given the absence of any conclusive phylogenetic framework, Durnonovariaodus maiseyi gen. et sp. nov. is here tentatively referred to Hybodontidae until more complete material becomes available in order to enable a more reliable suprageneric identification. The holotype of Durnonovariaodus maiseyi gen. et sp. nov. contains two separate pelvic half-girdles, a feature previously considered as evolutionarily primitive among hybodontiforms. However, unfused pelvic half-girdles also occur in the supposedly closely related species Hybodus hauffianus and may in fact have been more widely distributed among hybodontiforms than previously thought, thus rendering the phylogenetic utility of separated pelvic half-girdles for inferring hybodontiform interrelationships difficult and unresolved.
Pectoral girdle
Paratype
Pelvic girdle
Chondrichthyes
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A new ginglymodian fish, Khoratichthys gibbus, gen. et sp. nov., is described based on the impression of a single articulated fish preserved on a sandstone slab from the Late Jurassic–Early Cretaceous Phu Kradung Formation, northeastern Thailand. Khoratichthys gibbus is characterized by a distinct humpbacked body with elongate posterior spines on the dorsal ridge scales; the cheek is completely covered by bone; it has few infraorbitals, the elongate anterior-most one shows a tiny contact with the orbit, and six suborbitals arranged in one row; the opercule is rectancular in shape; the preopercule is narrow and regularly curved; and the interopercule large. A cladistic analysis including the type species of 25 ginglymodian genera indicates that Khoratichthys is the basal-most Lepisosteiformes, in an unresolved position with Neosemionotus and Lophionotus. This taxon provides a new evidence of the high diversity of ginglymodian fishes in the Phu Kradung Formation. A high taxic diversity of ginglymodians in Middle Jurassic–Early Cretaceous of southern Asian (excluding India) freshwater environments is observed, indicating that this clade occupied a major position in freshwater fish assemblages.http://zoobank.org/urn:lsid:zoobank.org:pub:AE3056BF-0C4A-421F-B517-3A4BC777A3E1SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Deesri, U., P. Jintasakul, and L. Cavin. 2016. A new Ginglymodi (Actinopterygii, Holostei) from the Late Jurassic–Early Cretaceous of Thailand, with comments on the early diversification of Lepisosteiformes in Southeast Asia. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1225747.
Actinopterygii
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Dorsal fin
Teleostei
Type locality
Cenomanian
Incertae sedis
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