Although first described more than 175 years ago and represented by many hundreds of specimens, t... more Although first described more than 175 years ago and represented by many hundreds of specimens, the small (less than 60 mm long) mesacanthid acanthodiform originally named Acanthodes pusillus is the most poorly known acanthodian-grade vertebrate from the Middle Devonian of Scotland. The classification of the species received some attention in the late nineteenth century, but it is only in the last decade that more substantive interest has been shown in this little fish. Here we re-evaluate the type material for the species, and assess the validity of its putative junior synonym Mesacanthus peachi based on morphological and histological study of mesacanthid specimens from all levels of the Eifelian and Givetian from the Orcadian Basin. New information on the taxon revealed by these studies includes the shape of the jaw cartilages, ornamentation of the sclerotic plates, structure and morphology of the different fin spines, variation in scale shape and size over the body, and histological structure of the dermal elements. Our study supports synonymizing M. pusillus and M. peachi and erecting a new genus Orcadacanthus, type species O. pusillus. The depositional environment appears to have influenced the mode of preservation of the new taxon at different localities. Variability in the degree of mineralization, particularly in the head region, is linked to ontogenetic changes.
Fossil Record 9. New Mexico Museum of Natural History and Science Bulletin 94., 2023
A new late Emsian (Devonian) phlyctaenioideid arthrodire species, Valentinaspis profundus gen. et... more A new late Emsian (Devonian) phlyctaenioideid arthrodire species, Valentinaspis profundus gen. et sp. nov., is described from Belarus and Estonia. This taxon, under the name Kartalaspis belarusica in various spellings, has been reported in literature since the 1980s, but until now had not been formally described or figured (and was known as a nomen nudum). This is unfortunate as various authors have used the species as a zone fossil for the Rēzekne Regional Stage of the Baltic area. This species was also used as a zonal index for the Vitebsk deposits in the territory of Belarus. The late palaeontologist Elga Mark-Kurik was in the process of preparing a manuscript to formally describe the species but died before much progress had been made. The specimens were recovered from two boreholes and consist mostly of disarticulated dermal plates. However, some plates are articulated to one another, and two cranial shields have also been recovered. This has allowed the species to be formally described and compared with similar forms from similar-aged deposits in Spitsbergen (Svalbard).
Lungfish (Dipnomorpha; Sarcopterygii) first evolved in the Early Devonian (Lochkovian-Emsian, 419... more Lungfish (Dipnomorpha; Sarcopterygii) first evolved in the Early Devonian (Lochkovian-Emsian, 419-393 My), and are characterized by a modified upper and lower jaw dentition, associated with the pterygoid and prearticular bones, respectively. Also possessing this modified dentition is Youngolepis praecursor Chang & Yu, 1981, sister taxon to the Dipnoi, recently described as having a tooth-plated dipnoan-like dentition in the upper jaw (Cui et al., 2022). Early Devonian taxa retaining this tooth-plated dentition include the basal taxon
Mesacanthus mitchelli is an important taxon in elucidating relationships amongst stem chondrichth... more Mesacanthus mitchelli is an important taxon in elucidating relationships amongst stem chondrichthyans, being the best known and most abundant of the oldest known acanthodiform acanthodians. Here we note some newly recognized morphological features and describe the histological structure of the endoskeleton and dermal elements. The jaws are preserved as a single layer of irregularly tessellate bone-like mineralizations. A mandibular bone is not present, contrary to previous descriptions. Fin spines have a wide central cavity that is more than half the width at mid-spine level. Prepelvic spines have a very narrow leading edge ridge and a wide open pulp cavity. Head sensory lines are enclosed by a pair of tesserae with a smooth crown, flat base and concave sides, bordering the sensory line canal. The tiny body scales have a relatively large pulp cavity in the embryonic zone. The large size of the eyes relative to the head and body size in Mesacanthus mitchelli , the structure and small size of the scales relative to those of other acanthodians of a similar size, and the wide central pulp cavity in the spines, all indicate that the species is likely to have undergone paedomorphism.
Serial sectioning of a nodule encapsulating an adult specimen of the arthrodire placoderm Watsono... more Serial sectioning of a nodule encapsulating an adult specimen of the arthrodire placoderm Watsonosteus fletti from the Eday Flagstone Formation (Givetian) in the Orcadian Basin of northern Scotland has revealed the presence of a number of embryos within the adult. This specimen represents the oldest known record of fossilized vertebrate embryos. Thin sections of two of the slices have revealed the detailed histological structure of embryonic plates in placoderms, showing that as previously deduced from visual examination, the outer and inner layers were the first to form. Gut contents preserved near the embryos show that the species had a varied diet, with dermal bone fragments from sarcopterygians and placoderms.
Vertebrate fossils are extremely rare below the Achanarras fish beds and equivalent strata in nor... more Vertebrate fossils are extremely rare below the Achanarras fish beds and equivalent strata in northern Scotland. Here we describe the cheiracanthid acanthodians from the lowest Middle Devonian of this region, comprising partial articulated specimens and squamation patches of two species Cheiracanthus flabellicostatus and C. brevicostatus. Both species were previously only known as isolated scales from the eastern Baltic and Russia. The stratigraphic range of the two species in Scotland extends up into the Achanarras equivalent fish beds in the Moray Firth.
Articulated cheiracanthid acanthodians are relatively rare above the Dickosteus thrieplandi biost... more Articulated cheiracanthid acanthodians are relatively rare above the Dickosteus thrieplandi biostratigraphic zone in the Orcadian Basin, with Cheiracanthus peachi den Blaauwen, Newman & Burrow the only species identified to date. Here we describe two other taxa Fallodentus davidsoni nov. gen. et sp. and Markacanthus costulatus Valiukevičius from the Mey Flagstone Formation. F. davidsoni occurs at the base of the formation, in the Osteolepis panderi biostratigraphic zone, and is readily identified by its robust fin spines which have a wide longitudinal ridge on each side below the groove separating the leading edge from the side of the spine. The taxon is most similar to Homalacanthus concinnus (Whiteaves) from the younger (Frasnian) Escuminac Formation in Quebec, Canada. The unique specimen of Markacanthus costulatus is from the top of the Mey Flagstone Formation. This taxon was previously only known from isolated scales from the upper Narva and Aruküla Regional Stages of the east B...
The cheiracanthid acanthodiforms were widespread during the Middle Devonian, often being the most... more The cheiracanthid acanthodiforms were widespread during the Middle Devonian, often being the most abundant acanthodians in northern European vertebrate macroand microfaunal assemblages. Three species of cheiracanthids, Cheiracanthus murchisoni, C. grandispinus, and C. latus, have been known from the Middle Devonian (Eifelian-Givetian) of northern Scotland since the nineteeth century. Here we review the anatomy of these species and show that the main distinguishing features for the three species are the scale ornamentation, general body shape, and relative robustness of their scapulocoracoids and fin spines. They also show different stratigraphic and geographic distributions in the Orcadian Basin. All three species appear at the base of the Coccosteus cuspidatus + Pterichthyodes milleri placoderm biostratigraphic zone; C. latus disappears towards the upper limit of this zone, C. murchisoni extends into the base of the overlying Dickosteus threiplandi zone, and C. grandispinus reaches up to the middle of this zone. Some cheiracanthid taxa based on isolated scales from the Baltic countries, Belarus, and Russia are considered junior synonyms of the Scottish species. The new data we provide should prove helpful in further elucidating the taxonomic position of cheiracanthids.
Two specimens of a new early actinopterygian Cheirolepis jonesi nov. gen. et sp. have been collec... more Two specimens of a new early actinopterygian Cheirolepis jonesi nov. gen. et sp. have been collected from the lagoonal Middle Devonian (Givetian) Fiskekløfta Member, the upper member of the Tordalen Formation in the Mimerdalen Subgroup of Spitsbergen. This is the second oldest Cheirolepis species known from articulated remains. The holotype consists of an articulated head and the anterior trunk. The other specimen is an articulated skull which was 3D scanned to determine the internal structure and general architecture. The new taxon differs from other Cheirolepis species in the relative dimensions of the bones of the head, including a narrow anterior end of the dentary, longer accessory operculum and correspondingly shorter dermohyal, as well as a longer premaxilla and proportionally larger quadratojugal, and the organisation and relative size of the teeth.
Spiracles are a general character of gnathostomes (jawed fishes), being present in antiarch placo... more Spiracles are a general character of gnathostomes (jawed fishes), being present in antiarch placoderms, commonly regarded as the most basal gnathostome group. The presence of spiracular tubes in acanthodians has been deduced from grooves on the neurocranium of the derived acanthodiform Acanthodes bronni from the Permian of Germany, but until now these tubes were presumed to lack an external opening, rendering them non‐functional. Here we describe the external spiracular elements in specimens of the Middle Devonian acanthodiforms Cheiracanthus murchisoni, Cheiracanthus latus and Mesacanthus pusillus from northern Scotland, and the internal structure of these elements in C. murchisoni, demonstrating that the spiracle in acanthodiforms differed from all known extant and extinct fishes in having paired cartilage‐pseudobranch structures. This arrangement represents a transitional state between the presumed basal gnathostome condition with an unconstricted first gill slit (as yet not identified in any fossil) and the derived condition with a spiracle and a single pseudobranch derived from the posterior hemibranch of the mandibular arch. We identify the main tissue forming the pseudobranch as elastic cartilage, a tissue previously unrecorded in fossils.
The Givetian (Middle Devonian) antiarch Asterolepis orcadensis was first described in 1932 based ... more The Givetian (Middle Devonian) antiarch Asterolepis orcadensis was first described in 1932 based on a limited amount of material. Newly collected material has allowed the head to be described in more detail, especially the premedian plate which has an embayment at the centre of the anterior edge. Also, the anterior section of supra-orbital sensory line has been identified on the premedian plate. Other elements newly described include the pectoral appendages which are shown to be quite broad at their proximal ends. The anterior ventro-lateral plate has been described in detail for the first time, particularly structures associated with the attachment of pectoral appendages. The posterior median dorsal plate has been shown not to have had a more pointed posterior edge as depicted in the 1932 description, but a flatter posterior edge reminiscent of Asterolepis saevesoederberghi which is shown to be closely related to A. orcadensis. The shortness of the posterior median dorsal plate has emphasised the broadness of the whole armour, making A. orcadensis one of the broadest species of Asterolepis. Whilst A. orcadensis is endemic to the Orcadian Basin of northern Scotland, it fits into a biostratigraphical column at the same level as A. saevesoederberghi so strengthening the evidence of a close relationship between these two forms.
A number of partial articulated specimens of Cheiracanthus peachi nov. sp. have been collected fr... more A number of partial articulated specimens of Cheiracanthus peachi nov. sp. have been collected from the Mey Flagstone Formation and Rousay Flagstone Formation within the Orcadian Basin of northern Scotland. The new, robust-bodied species is mainly distinguished by the scale ornament of radiating grooves rather than ridges. Compared to other Cheiracanthus species in the Orcadian Basin, C. peachi nov. sp. has quite a short range making it a useful zone fossil. As well as describing the general morphology of the specimens, we have also described and figured SEM images of scales and histological sections of all elements, enabling identification of other, isolated remains. Of particular biological interest is the identification of relatively robust, tooth-like gill rakers. Finally, the species has also been identified from isolated scales in Belarus, where it appears earlier and has a longer stratigraphical range, implying the species evolved in the marine deposits of the east and migrated west into the Orcadian Basin via the river systems.
Two body fossils of the Middle Devonian acanthodian Cheiracanthus intricatus Valiukevičius have b... more Two body fossils of the Middle Devonian acanthodian Cheiracanthus intricatus Valiukevičius have been collected from the Fiskekløfta Member, the upper member of the Tordalen Formation in the Mimerdalen Subgroup of Spitsbergen. One of the specimens is articulated, the first such known of this species. In the Baltic region the species is only known from scales, from the upper part of the Eifelian and the Givetian (Narva to Burtnieki regional stages). Previous workers investigating the Mimerdalen strata speculated that Givetian spores found in the Fiskekløfta Member have been reworked from older deposits, and have given the member a Frasnian age. However, the reworking of an articulated acanthodian from older deposits is a near impossibility, so we are confident in dating the Fiskekløfta Member as Middle rather than Late Devonian. Furthermore, other genera identified from this member include the sarcopterygians Laccognathus Gross, 1941 and Miguashaia Schultze, 1973 and the arthrodire Plourdosteus Ørvig, 1951, also supporting an upper Givetian age, and confirming recent dating based on analysis of the spores. Overall, the fish fauna indicates that the Fiskekløfta Member is most likely contemporary to the Gauja Regional Stage in the Baltic region.
Over recent years the authors have been co-authors on a number of papers re-describing acanthodia... more Over recent years the authors have been co-authors on a number of papers re-describing acanthodian species from classic localities in the Devonian strata of Scotland and Canada. In a number of works the noting of syntypes of particular species has been mentioned, but the authors have neglected to designate a lectotype for some of these species. In this article we remedy this oversight.
Abstract The Lower Old Red Sandstone terranes of the Midland Valley of Scotland and the Anglo-Wel... more Abstract The Lower Old Red Sandstone terranes of the Midland Valley of Scotland and the Anglo-Welsh Basin have been considered as separate realms due to the rarity of fish species common to both areas. Although in the first half of the 19th century the osteostracan Cephalaspis lyelli was thought to occur in both terranes this was shown in be incorrect in the latter part of that century. It was not until 1968 that it was demonstrated that the thelodont agnathan Turinia pagei occurred in both terranes. This species has a much wider distribution across the whole of the Old Red Sandstone continent, but its presence in both realms indicates they were connected either directly or indirectly. In 2012 it was suggested that the osteostracan Janaspis watsoni might be present in both basins and in 2013 the acanthodian Parexus recurvus was shown to definitely occur in both. Here we show that other acanthodian genera and species were present in both regions during the Lochkovian (earliest Devonian). Co-specific plants also occur in both terranes during the Lochkovian. As there is no evidence of a marine connection to the Midland Valley in the Lochkovian, the only logical conclusion is that the connection between the two terranes was fluvial.
ABSTRACT Disarticulated elements in a large, uncompressed regurgitate from Tillywhandland Quarry ... more ABSTRACT 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 smoothsurfaced 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.
The five species of genus Euthacanthus Powrie, 1864 are reduced to two species on morphological a... more 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, Eutha canthus 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.
Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 2004
The large Middle Devonian osteostracan Cephalaspis magnifica Traquair, 1893a, from the Late Eifel... more The large Middle Devonian osteostracan Cephalaspis magnifica Traquair, 1893a, from the Late Eifelian Upper Caithness Flagstone Group of Caithness, Scotland, is redescribed on the basis of the holotype and a second, hitherto undescribed specimen. This species is assigned to a new genus, Trewinia gen. nov. and, on account of its probable lack of lateral cephalic fields, is regarded as a possible member of the Escuminaspididae, which are hitherto only known from the Late Devonian of Quebec, Canada. Other characters of the head shield of T. magnifica also accord with the structure of the largest known escuminaspidid Escuminaspis. The morphology, relationships and biogeography of the few other Middle and Late Devonian osteostracans are discussed. North American osteostracans are generally quite distinctive from European ones throughout the Devonian, and only few taxa seem common to the two areas. The Escuminaspididae could be one of these, and this would agree with similar distributions ...
Although first described more than 175 years ago and represented by many hundreds of specimens, t... more Although first described more than 175 years ago and represented by many hundreds of specimens, the small (less than 60 mm long) mesacanthid acanthodiform originally named Acanthodes pusillus is the most poorly known acanthodian-grade vertebrate from the Middle Devonian of Scotland. The classification of the species received some attention in the late nineteenth century, but it is only in the last decade that more substantive interest has been shown in this little fish. Here we re-evaluate the type material for the species, and assess the validity of its putative junior synonym Mesacanthus peachi based on morphological and histological study of mesacanthid specimens from all levels of the Eifelian and Givetian from the Orcadian Basin. New information on the taxon revealed by these studies includes the shape of the jaw cartilages, ornamentation of the sclerotic plates, structure and morphology of the different fin spines, variation in scale shape and size over the body, and histological structure of the dermal elements. Our study supports synonymizing M. pusillus and M. peachi and erecting a new genus Orcadacanthus, type species O. pusillus. The depositional environment appears to have influenced the mode of preservation of the new taxon at different localities. Variability in the degree of mineralization, particularly in the head region, is linked to ontogenetic changes.
Fossil Record 9. New Mexico Museum of Natural History and Science Bulletin 94., 2023
A new late Emsian (Devonian) phlyctaenioideid arthrodire species, Valentinaspis profundus gen. et... more A new late Emsian (Devonian) phlyctaenioideid arthrodire species, Valentinaspis profundus gen. et sp. nov., is described from Belarus and Estonia. This taxon, under the name Kartalaspis belarusica in various spellings, has been reported in literature since the 1980s, but until now had not been formally described or figured (and was known as a nomen nudum). This is unfortunate as various authors have used the species as a zone fossil for the Rēzekne Regional Stage of the Baltic area. This species was also used as a zonal index for the Vitebsk deposits in the territory of Belarus. The late palaeontologist Elga Mark-Kurik was in the process of preparing a manuscript to formally describe the species but died before much progress had been made. The specimens were recovered from two boreholes and consist mostly of disarticulated dermal plates. However, some plates are articulated to one another, and two cranial shields have also been recovered. This has allowed the species to be formally described and compared with similar forms from similar-aged deposits in Spitsbergen (Svalbard).
Lungfish (Dipnomorpha; Sarcopterygii) first evolved in the Early Devonian (Lochkovian-Emsian, 419... more Lungfish (Dipnomorpha; Sarcopterygii) first evolved in the Early Devonian (Lochkovian-Emsian, 419-393 My), and are characterized by a modified upper and lower jaw dentition, associated with the pterygoid and prearticular bones, respectively. Also possessing this modified dentition is Youngolepis praecursor Chang & Yu, 1981, sister taxon to the Dipnoi, recently described as having a tooth-plated dipnoan-like dentition in the upper jaw (Cui et al., 2022). Early Devonian taxa retaining this tooth-plated dentition include the basal taxon
Mesacanthus mitchelli is an important taxon in elucidating relationships amongst stem chondrichth... more Mesacanthus mitchelli is an important taxon in elucidating relationships amongst stem chondrichthyans, being the best known and most abundant of the oldest known acanthodiform acanthodians. Here we note some newly recognized morphological features and describe the histological structure of the endoskeleton and dermal elements. The jaws are preserved as a single layer of irregularly tessellate bone-like mineralizations. A mandibular bone is not present, contrary to previous descriptions. Fin spines have a wide central cavity that is more than half the width at mid-spine level. Prepelvic spines have a very narrow leading edge ridge and a wide open pulp cavity. Head sensory lines are enclosed by a pair of tesserae with a smooth crown, flat base and concave sides, bordering the sensory line canal. The tiny body scales have a relatively large pulp cavity in the embryonic zone. The large size of the eyes relative to the head and body size in Mesacanthus mitchelli , the structure and small size of the scales relative to those of other acanthodians of a similar size, and the wide central pulp cavity in the spines, all indicate that the species is likely to have undergone paedomorphism.
Serial sectioning of a nodule encapsulating an adult specimen of the arthrodire placoderm Watsono... more Serial sectioning of a nodule encapsulating an adult specimen of the arthrodire placoderm Watsonosteus fletti from the Eday Flagstone Formation (Givetian) in the Orcadian Basin of northern Scotland has revealed the presence of a number of embryos within the adult. This specimen represents the oldest known record of fossilized vertebrate embryos. Thin sections of two of the slices have revealed the detailed histological structure of embryonic plates in placoderms, showing that as previously deduced from visual examination, the outer and inner layers were the first to form. Gut contents preserved near the embryos show that the species had a varied diet, with dermal bone fragments from sarcopterygians and placoderms.
Vertebrate fossils are extremely rare below the Achanarras fish beds and equivalent strata in nor... more Vertebrate fossils are extremely rare below the Achanarras fish beds and equivalent strata in northern Scotland. Here we describe the cheiracanthid acanthodians from the lowest Middle Devonian of this region, comprising partial articulated specimens and squamation patches of two species Cheiracanthus flabellicostatus and C. brevicostatus. Both species were previously only known as isolated scales from the eastern Baltic and Russia. The stratigraphic range of the two species in Scotland extends up into the Achanarras equivalent fish beds in the Moray Firth.
Articulated cheiracanthid acanthodians are relatively rare above the Dickosteus thrieplandi biost... more Articulated cheiracanthid acanthodians are relatively rare above the Dickosteus thrieplandi biostratigraphic zone in the Orcadian Basin, with Cheiracanthus peachi den Blaauwen, Newman & Burrow the only species identified to date. Here we describe two other taxa Fallodentus davidsoni nov. gen. et sp. and Markacanthus costulatus Valiukevičius from the Mey Flagstone Formation. F. davidsoni occurs at the base of the formation, in the Osteolepis panderi biostratigraphic zone, and is readily identified by its robust fin spines which have a wide longitudinal ridge on each side below the groove separating the leading edge from the side of the spine. The taxon is most similar to Homalacanthus concinnus (Whiteaves) from the younger (Frasnian) Escuminac Formation in Quebec, Canada. The unique specimen of Markacanthus costulatus is from the top of the Mey Flagstone Formation. This taxon was previously only known from isolated scales from the upper Narva and Aruküla Regional Stages of the east B...
The cheiracanthid acanthodiforms were widespread during the Middle Devonian, often being the most... more The cheiracanthid acanthodiforms were widespread during the Middle Devonian, often being the most abundant acanthodians in northern European vertebrate macroand microfaunal assemblages. Three species of cheiracanthids, Cheiracanthus murchisoni, C. grandispinus, and C. latus, have been known from the Middle Devonian (Eifelian-Givetian) of northern Scotland since the nineteeth century. Here we review the anatomy of these species and show that the main distinguishing features for the three species are the scale ornamentation, general body shape, and relative robustness of their scapulocoracoids and fin spines. They also show different stratigraphic and geographic distributions in the Orcadian Basin. All three species appear at the base of the Coccosteus cuspidatus + Pterichthyodes milleri placoderm biostratigraphic zone; C. latus disappears towards the upper limit of this zone, C. murchisoni extends into the base of the overlying Dickosteus threiplandi zone, and C. grandispinus reaches up to the middle of this zone. Some cheiracanthid taxa based on isolated scales from the Baltic countries, Belarus, and Russia are considered junior synonyms of the Scottish species. The new data we provide should prove helpful in further elucidating the taxonomic position of cheiracanthids.
Two specimens of a new early actinopterygian Cheirolepis jonesi nov. gen. et sp. have been collec... more Two specimens of a new early actinopterygian Cheirolepis jonesi nov. gen. et sp. have been collected from the lagoonal Middle Devonian (Givetian) Fiskekløfta Member, the upper member of the Tordalen Formation in the Mimerdalen Subgroup of Spitsbergen. This is the second oldest Cheirolepis species known from articulated remains. The holotype consists of an articulated head and the anterior trunk. The other specimen is an articulated skull which was 3D scanned to determine the internal structure and general architecture. The new taxon differs from other Cheirolepis species in the relative dimensions of the bones of the head, including a narrow anterior end of the dentary, longer accessory operculum and correspondingly shorter dermohyal, as well as a longer premaxilla and proportionally larger quadratojugal, and the organisation and relative size of the teeth.
Spiracles are a general character of gnathostomes (jawed fishes), being present in antiarch placo... more Spiracles are a general character of gnathostomes (jawed fishes), being present in antiarch placoderms, commonly regarded as the most basal gnathostome group. The presence of spiracular tubes in acanthodians has been deduced from grooves on the neurocranium of the derived acanthodiform Acanthodes bronni from the Permian of Germany, but until now these tubes were presumed to lack an external opening, rendering them non‐functional. Here we describe the external spiracular elements in specimens of the Middle Devonian acanthodiforms Cheiracanthus murchisoni, Cheiracanthus latus and Mesacanthus pusillus from northern Scotland, and the internal structure of these elements in C. murchisoni, demonstrating that the spiracle in acanthodiforms differed from all known extant and extinct fishes in having paired cartilage‐pseudobranch structures. This arrangement represents a transitional state between the presumed basal gnathostome condition with an unconstricted first gill slit (as yet not identified in any fossil) and the derived condition with a spiracle and a single pseudobranch derived from the posterior hemibranch of the mandibular arch. We identify the main tissue forming the pseudobranch as elastic cartilage, a tissue previously unrecorded in fossils.
The Givetian (Middle Devonian) antiarch Asterolepis orcadensis was first described in 1932 based ... more The Givetian (Middle Devonian) antiarch Asterolepis orcadensis was first described in 1932 based on a limited amount of material. Newly collected material has allowed the head to be described in more detail, especially the premedian plate which has an embayment at the centre of the anterior edge. Also, the anterior section of supra-orbital sensory line has been identified on the premedian plate. Other elements newly described include the pectoral appendages which are shown to be quite broad at their proximal ends. The anterior ventro-lateral plate has been described in detail for the first time, particularly structures associated with the attachment of pectoral appendages. The posterior median dorsal plate has been shown not to have had a more pointed posterior edge as depicted in the 1932 description, but a flatter posterior edge reminiscent of Asterolepis saevesoederberghi which is shown to be closely related to A. orcadensis. The shortness of the posterior median dorsal plate has emphasised the broadness of the whole armour, making A. orcadensis one of the broadest species of Asterolepis. Whilst A. orcadensis is endemic to the Orcadian Basin of northern Scotland, it fits into a biostratigraphical column at the same level as A. saevesoederberghi so strengthening the evidence of a close relationship between these two forms.
A number of partial articulated specimens of Cheiracanthus peachi nov. sp. have been collected fr... more A number of partial articulated specimens of Cheiracanthus peachi nov. sp. have been collected from the Mey Flagstone Formation and Rousay Flagstone Formation within the Orcadian Basin of northern Scotland. The new, robust-bodied species is mainly distinguished by the scale ornament of radiating grooves rather than ridges. Compared to other Cheiracanthus species in the Orcadian Basin, C. peachi nov. sp. has quite a short range making it a useful zone fossil. As well as describing the general morphology of the specimens, we have also described and figured SEM images of scales and histological sections of all elements, enabling identification of other, isolated remains. Of particular biological interest is the identification of relatively robust, tooth-like gill rakers. Finally, the species has also been identified from isolated scales in Belarus, where it appears earlier and has a longer stratigraphical range, implying the species evolved in the marine deposits of the east and migrated west into the Orcadian Basin via the river systems.
Two body fossils of the Middle Devonian acanthodian Cheiracanthus intricatus Valiukevičius have b... more Two body fossils of the Middle Devonian acanthodian Cheiracanthus intricatus Valiukevičius have been collected from the Fiskekløfta Member, the upper member of the Tordalen Formation in the Mimerdalen Subgroup of Spitsbergen. One of the specimens is articulated, the first such known of this species. In the Baltic region the species is only known from scales, from the upper part of the Eifelian and the Givetian (Narva to Burtnieki regional stages). Previous workers investigating the Mimerdalen strata speculated that Givetian spores found in the Fiskekløfta Member have been reworked from older deposits, and have given the member a Frasnian age. However, the reworking of an articulated acanthodian from older deposits is a near impossibility, so we are confident in dating the Fiskekløfta Member as Middle rather than Late Devonian. Furthermore, other genera identified from this member include the sarcopterygians Laccognathus Gross, 1941 and Miguashaia Schultze, 1973 and the arthrodire Plourdosteus Ørvig, 1951, also supporting an upper Givetian age, and confirming recent dating based on analysis of the spores. Overall, the fish fauna indicates that the Fiskekløfta Member is most likely contemporary to the Gauja Regional Stage in the Baltic region.
Over recent years the authors have been co-authors on a number of papers re-describing acanthodia... more Over recent years the authors have been co-authors on a number of papers re-describing acanthodian species from classic localities in the Devonian strata of Scotland and Canada. In a number of works the noting of syntypes of particular species has been mentioned, but the authors have neglected to designate a lectotype for some of these species. In this article we remedy this oversight.
Abstract The Lower Old Red Sandstone terranes of the Midland Valley of Scotland and the Anglo-Wel... more Abstract The Lower Old Red Sandstone terranes of the Midland Valley of Scotland and the Anglo-Welsh Basin have been considered as separate realms due to the rarity of fish species common to both areas. Although in the first half of the 19th century the osteostracan Cephalaspis lyelli was thought to occur in both terranes this was shown in be incorrect in the latter part of that century. It was not until 1968 that it was demonstrated that the thelodont agnathan Turinia pagei occurred in both terranes. This species has a much wider distribution across the whole of the Old Red Sandstone continent, but its presence in both realms indicates they were connected either directly or indirectly. In 2012 it was suggested that the osteostracan Janaspis watsoni might be present in both basins and in 2013 the acanthodian Parexus recurvus was shown to definitely occur in both. Here we show that other acanthodian genera and species were present in both regions during the Lochkovian (earliest Devonian). Co-specific plants also occur in both terranes during the Lochkovian. As there is no evidence of a marine connection to the Midland Valley in the Lochkovian, the only logical conclusion is that the connection between the two terranes was fluvial.
ABSTRACT Disarticulated elements in a large, uncompressed regurgitate from Tillywhandland Quarry ... more ABSTRACT 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 smoothsurfaced 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.
The five species of genus Euthacanthus Powrie, 1864 are reduced to two species on morphological a... more 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, Eutha canthus 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.
Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 2004
The large Middle Devonian osteostracan Cephalaspis magnifica Traquair, 1893a, from the Late Eifel... more The large Middle Devonian osteostracan Cephalaspis magnifica Traquair, 1893a, from the Late Eifelian Upper Caithness Flagstone Group of Caithness, Scotland, is redescribed on the basis of the holotype and a second, hitherto undescribed specimen. This species is assigned to a new genus, Trewinia gen. nov. and, on account of its probable lack of lateral cephalic fields, is regarded as a possible member of the Escuminaspididae, which are hitherto only known from the Late Devonian of Quebec, Canada. Other characters of the head shield of T. magnifica also accord with the structure of the largest known escuminaspidid Escuminaspis. The morphology, relationships and biogeography of the few other Middle and Late Devonian osteostracans are discussed. North American osteostracans are generally quite distinctive from European ones throughout the Devonian, and only few taxa seem common to the two areas. The Escuminaspididae could be one of these, and this would agree with similar distributions ...
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Papers by Michael Newman
that more substantive interest has been shown in this little fish. Here we re-evaluate the type material for the species, and assess the validity of its putative junior synonym Mesacanthus peachi based on morphological and histological study of mesacanthid specimens from all levels of the Eifelian and Givetian from the Orcadian Basin. New information on the taxon revealed by these studies includes the shape of the jaw cartilages,
ornamentation of the sclerotic plates, structure and morphology of the different fin spines, variation in scale shape and size over the body, and histological structure of the dermal elements. Our study supports synonymizing M. pusillus and M. peachi and erecting a new genus Orcadacanthus, type species O. pusillus. The depositional environment
appears to have influenced the mode of preservation of the new taxon at different localities. Variability in the degree of mineralization, particularly in the head region, is linked to ontogenetic changes.
that more substantive interest has been shown in this little fish. Here we re-evaluate the type material for the species, and assess the validity of its putative junior synonym Mesacanthus peachi based on morphological and histological study of mesacanthid specimens from all levels of the Eifelian and Givetian from the Orcadian Basin. New information on the taxon revealed by these studies includes the shape of the jaw cartilages,
ornamentation of the sclerotic plates, structure and morphology of the different fin spines, variation in scale shape and size over the body, and histological structure of the dermal elements. Our study supports synonymizing M. pusillus and M. peachi and erecting a new genus Orcadacanthus, type species O. pusillus. The depositional environment
appears to have influenced the mode of preservation of the new taxon at different localities. Variability in the degree of mineralization, particularly in the head region, is linked to ontogenetic changes.