This paper provides а taxonomic list of the fossil Mesozoic and Cenozoic shark and bony fish teet... more This paper provides а taxonomic list of the fossil Mesozoic and Cenozoic shark and bony fish teeth from the collections of the National Museum of Natural History, Bulgarian Academy of Sciences (NMNHS). The material was collected mostly from Bulgaria, but specimens from Angola and France are also available. Elasmobranch taxa prevail in the collection (47 specimens), with the rest of the material consisting of actinopterygian teeth (8 specimens). The largest portion of specimens (35) is of Turonian age. Of particular systematic interest ...
ABSTRACT Based upon fragmentary remains of dermal armor, a new form of arandaspid fish, Ritchieic... more ABSTRACT Based upon fragmentary remains of dermal armor, a new form of arandaspid fish, Ritchieichthys nibili, gen et. sp. nov., is described from subsurface core material from the Katian (Late Ordovician) Nibil Formation of the Canning Basin, Western Australia. Ritchieichthys nibili represents the first documented record of a fish from the Ordovician of the Canning Basin. Allied to the previous descriptions of arandaspsids from the Amadeus and Warburton basins of the Northern Territory and New South Wales, respectively, this record extends the paleogeographic range of arandaspids across the hypothetical Ordovician Larapintine Seaway and increases the stratigraphic range of the Order Arandaspidiformes into the Katian. The hard tissue histology of Ritchieichthys nibili confirms the presence of a cellular dentine forming the bulk of the dermal armor ornament in arandaspids, a tissue that had not been directly observed previously, and confirms the presence of largely unconnected osteocytes within the dermal bone that forms the majority of the armor.
Microstructural scanning electron microscope investigation was performed on sectioned and surface... more Microstructural scanning electron microscope investigation was performed on sectioned and surface-etched isolated, prehensile teeth of the Late Triassic semionotiform species Sar-godon tomicus and Pycnodontidae incertae sedis from the Late Cretaceous. The teeth of both taxa display a system of vascular canals penetrating the dentine and the overlying hypermineralized acrodin cap; small tubules are radiating at an angle to the long axis of the canals, interpreted as residual spaces left by odontoblast cell processes. This is the first detailed account of vascular acrodin encountered in a pycnodont species. New information is revealed also about Sargodon dental his-tology in the shape of mineralized remnants of the basal lamina at the acrodin–dentine junction. This implies that deposition of the acrodin organic matrix proceeded centrifugally by the cells of the inner dental epithelium, probably with minor collagen contribution from odontoblasts. This is contrary to the more typical centripetal formation (beneath the basal lamina) of the acrodin layer implied for the studied pycnodontid teeth. The rare occurrences of vascular acrodin within Actino-pterygii, and the demonstrated differences in its histogenesis, do not suggest the usefulness of the tissue as systematic character but rather point to its adaptive significance. The superficial increase in the order of acrodin bundle orientation, observed in both species, is similarly regarded as conver-gently acquired mechanical adaptation. The observed uneven shape of crystallite rows and lesser degree of mineralization of the inner collariform ganoin, compared to its outer portion, is indicative of epithelial-ectomesenchymal interaction and qualifies the tissue as enameloid. Microsc. Res.
Journal of Vertebrate Paleontology Publication details, including instructions for authors and su... more Journal of Vertebrate Paleontology Publication details, including instructions for authors and subscription information:
Studies of Ordovician micromeric fish scales from the Sandbian of North America have identified a... more Studies of Ordovician micromeric fish scales from the Sandbian of North America have identified a number of scale-based taxa potentially referable to the chondrichthyans and therefore can be among the stratigraphically oldest representatives of the clade described to date. Two of these, Tezakia hardingensis gen. et sp. nov. and Canyonlepis smithae gen. et sp. nov., are formally described herein. Tezakia gen. nov. scales are composed exclusively of tubular dentine and possess poly-odontocomplex crowns with a characteristically large primor-dial odontode. Similar scale crown architecture has been reported only in the reputed chondrichthyan Altholepis compo-sita (Lower Devonian of Podolia, Ukraine), and on these grounds, the two are united within the newly erected Altho-lepidiformes ordo nov. Multiple odontocomplexes are also a feature of Canyonlepis gen. nov. scale crowns; however, the latter do not demonstrate prominent primordial odontodes and are supported by a base composed of acellular bone. Additional data suggest that both taxa possess a combination of characteristics (areal crown growth, scale symmetry, linear od-ontocomplex architecture and absence of enamel, osteons, cancellous bone and hard-tissue resorption) previously documented to occur only in chondrichthyan scales. This study contributes to a growing body of evidence that reveals the presence of diverse tissue types (bone, tubular and atubular dentine) and morphogenetic patterns (odontocomplex and non-odontocomplex type of scale crown growth) in the dermal skeleton of putative Ordovician chondrichthyans.
The triple-layered enameloid organization of neoselachian teeth has proven to be a reliable syste... more The triple-layered enameloid organization of neoselachian teeth has proven to be a reliable systematic character of the group. This study uses scanning electron microscopy to investigate the orientation of the parallel enameloid bundles in the area of the serrated cutting edges in certain fossil elasmobranchs. The examined teeth come from two Upper Cretaceous Squalicorax species and the Upper Miocene carcharhiniforms Galeocerdo sp., Carcharhinus sp., and Hemipris-tis serra. The parallel bundles are revealed by surface etching, which removes the superficial shiny-layered enameloid. In the teeth of Squalicorax, the bundles around the cutting edge bend once, before they reach the serrations. The studied carcharhiniform species show a more complicated pattern with a change of parallel bundle course inside the serrations. H. serra teeth do not display the first bending of the bundles, whereas it was present in the other two carcharhiniforms. The course of the crystalline bundles in both Squalicorax species is not affected by the presence of the serrations, regardless of the twofold difference in tooth size between them. In the carcharhini-form species, the bended bundles occur within the primary and secondary serrations and are always associated with them. This feature might have functional significance by strengthening the cutting edge or could simply develop as a consequence of the enameloid mineralization around the individual serrae. Microsc. Res. Tech. 73:704–713,
This paper provides а taxonomic list of the fossil Mesozoic and Cenozoic shark and bony fish teet... more This paper provides а taxonomic list of the fossil Mesozoic and Cenozoic shark and bony fish teeth from the collections of the National Museum of Natural History, Bulgarian Academy of Sciences (NMNHS). The material was collected mostly from Bulgaria, but specimens from Angola and France are also available. Elasmobranch taxa prevail in the collection (47 specimens), with the rest of the material consisting of actinopterygian teeth (8 specimens). The largest portion of specimens (35) is of Turonian age. Of particular systematic interest ...
ABSTRACT Based upon fragmentary remains of dermal armor, a new form of arandaspid fish, Ritchieic... more ABSTRACT Based upon fragmentary remains of dermal armor, a new form of arandaspid fish, Ritchieichthys nibili, gen et. sp. nov., is described from subsurface core material from the Katian (Late Ordovician) Nibil Formation of the Canning Basin, Western Australia. Ritchieichthys nibili represents the first documented record of a fish from the Ordovician of the Canning Basin. Allied to the previous descriptions of arandaspsids from the Amadeus and Warburton basins of the Northern Territory and New South Wales, respectively, this record extends the paleogeographic range of arandaspids across the hypothetical Ordovician Larapintine Seaway and increases the stratigraphic range of the Order Arandaspidiformes into the Katian. The hard tissue histology of Ritchieichthys nibili confirms the presence of a cellular dentine forming the bulk of the dermal armor ornament in arandaspids, a tissue that had not been directly observed previously, and confirms the presence of largely unconnected osteocytes within the dermal bone that forms the majority of the armor.
Microstructural scanning electron microscope investigation was performed on sectioned and surface... more Microstructural scanning electron microscope investigation was performed on sectioned and surface-etched isolated, prehensile teeth of the Late Triassic semionotiform species Sar-godon tomicus and Pycnodontidae incertae sedis from the Late Cretaceous. The teeth of both taxa display a system of vascular canals penetrating the dentine and the overlying hypermineralized acrodin cap; small tubules are radiating at an angle to the long axis of the canals, interpreted as residual spaces left by odontoblast cell processes. This is the first detailed account of vascular acrodin encountered in a pycnodont species. New information is revealed also about Sargodon dental his-tology in the shape of mineralized remnants of the basal lamina at the acrodin–dentine junction. This implies that deposition of the acrodin organic matrix proceeded centrifugally by the cells of the inner dental epithelium, probably with minor collagen contribution from odontoblasts. This is contrary to the more typical centripetal formation (beneath the basal lamina) of the acrodin layer implied for the studied pycnodontid teeth. The rare occurrences of vascular acrodin within Actino-pterygii, and the demonstrated differences in its histogenesis, do not suggest the usefulness of the tissue as systematic character but rather point to its adaptive significance. The superficial increase in the order of acrodin bundle orientation, observed in both species, is similarly regarded as conver-gently acquired mechanical adaptation. The observed uneven shape of crystallite rows and lesser degree of mineralization of the inner collariform ganoin, compared to its outer portion, is indicative of epithelial-ectomesenchymal interaction and qualifies the tissue as enameloid. Microsc. Res.
Journal of Vertebrate Paleontology Publication details, including instructions for authors and su... more Journal of Vertebrate Paleontology Publication details, including instructions for authors and subscription information:
Studies of Ordovician micromeric fish scales from the Sandbian of North America have identified a... more Studies of Ordovician micromeric fish scales from the Sandbian of North America have identified a number of scale-based taxa potentially referable to the chondrichthyans and therefore can be among the stratigraphically oldest representatives of the clade described to date. Two of these, Tezakia hardingensis gen. et sp. nov. and Canyonlepis smithae gen. et sp. nov., are formally described herein. Tezakia gen. nov. scales are composed exclusively of tubular dentine and possess poly-odontocomplex crowns with a characteristically large primor-dial odontode. Similar scale crown architecture has been reported only in the reputed chondrichthyan Altholepis compo-sita (Lower Devonian of Podolia, Ukraine), and on these grounds, the two are united within the newly erected Altho-lepidiformes ordo nov. Multiple odontocomplexes are also a feature of Canyonlepis gen. nov. scale crowns; however, the latter do not demonstrate prominent primordial odontodes and are supported by a base composed of acellular bone. Additional data suggest that both taxa possess a combination of characteristics (areal crown growth, scale symmetry, linear od-ontocomplex architecture and absence of enamel, osteons, cancellous bone and hard-tissue resorption) previously documented to occur only in chondrichthyan scales. This study contributes to a growing body of evidence that reveals the presence of diverse tissue types (bone, tubular and atubular dentine) and morphogenetic patterns (odontocomplex and non-odontocomplex type of scale crown growth) in the dermal skeleton of putative Ordovician chondrichthyans.
The triple-layered enameloid organization of neoselachian teeth has proven to be a reliable syste... more The triple-layered enameloid organization of neoselachian teeth has proven to be a reliable systematic character of the group. This study uses scanning electron microscopy to investigate the orientation of the parallel enameloid bundles in the area of the serrated cutting edges in certain fossil elasmobranchs. The examined teeth come from two Upper Cretaceous Squalicorax species and the Upper Miocene carcharhiniforms Galeocerdo sp., Carcharhinus sp., and Hemipris-tis serra. The parallel bundles are revealed by surface etching, which removes the superficial shiny-layered enameloid. In the teeth of Squalicorax, the bundles around the cutting edge bend once, before they reach the serrations. The studied carcharhiniform species show a more complicated pattern with a change of parallel bundle course inside the serrations. H. serra teeth do not display the first bending of the bundles, whereas it was present in the other two carcharhiniforms. The course of the crystalline bundles in both Squalicorax species is not affected by the presence of the serrations, regardless of the twofold difference in tooth size between them. In the carcharhini-form species, the bended bundles occur within the primary and secondary serrations and are always associated with them. This feature might have functional significance by strengthening the cutting edge or could simply develop as a consequence of the enameloid mineralization around the individual serrae. Microsc. Res. Tech. 73:704–713,
Uploads
Papers