July 2024
·
16 Reads
This page lists works of an author who doesn't have a ResearchGate profile or hasn't added the works to their profile yet. It is automatically generated from public (personal) data to further our legitimate goal of comprehensive and accurate scientific recordkeeping. If you are this author and want this page removed, please let us know.
July 2024
·
16 Reads
January 2023
·
382 Reads
·
3 Citations
Palaeontologia Electronica
June 2022
·
34 Reads
·
1 Citation
Scottish Journal of Geology
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 recognised 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 mineralisations. 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.
June 2021
·
308 Reads
·
5 Citations
Papers in Palaeontology
The ‘acanthodian’ fishes provide key anatomical insights into the deepest branches of the chondrichthyan stem group. We review the anatomy of the acanthodian Vernicomacanthus uncinatus from the Lochkovian (Lower Devonian, 419.2–410.8 Ma) of Scotland based on eight articulated fossils, one of which is newly described. Broadly, the anatomy of V. uncinatus fits with that of contemporaneous acanthodians such as Climatius and Parexus, with a head covered by robust tesserae, an enlarged postorbital scale, an armoured shoulder girdle, and many pairs of ventrolateral spines. However, it departs from this anatomy in key respects. Its pectoral fin spines are obliquely ridged and posteriorly denticulated, similarly to Carboniferous gyracanth stem‐group chondrichthyans. Its scales consist of multiple anteroposteriorly aligned odontodes, similarly to many Palaeozoic ‘sharks’. And its endoskeletal shoulder girdle may have a posterolateral angle, previously observed only in shark‐like chondrichthyans. We propose that the differences between V. uncinatus and its congeneric, V. waynensis, which include potentially phylogenetically significant characters of the shoulder girdle and spines, are sufficient to erect a new genus for V. waynensis:Dobunnacanthus gen. nov. The scales of Vernicomacanthus are identical to those of the ‘shark’ scale genus Altholepis, suggesting that some such scales may instead belong to taxa with acanthodian‐like gross anatomies. Based on these scales we highlight potential patterns in chondrichthyan scale evolution, in particular the axial addition of odontodes. Anatomical similarities between Vernicomacanthus and gyracanths, highlighted by previous authors, may indicate the existence of a grade including these and similar acanthodian‐grade taxa placed relatively crownwards in the chondrichthyan stem‐group.
April 2021
·
288 Reads
·
8 Citations
Norwegian Journal of Geology
September 2020
·
60 Reads
·
2 Citations
Palaeontology
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.
September 2020
·
48 Reads
·
3 Citations
Scottish Journal of Geology
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 Baltic region. The dorsoventral preservation of the head region in the F. davidsoni specimens reveals clearly the position of the ceratohyal cartilages in a cheiracanthid, as well as showing for the first time that there is a basihyal cartilage anterior to the ceratohyals.
July 2020
·
61 Reads
·
3 Citations
Scottish Journal of Geology
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.
February 2020
·
95 Reads
·
9 Citations
Journal of Anatomy
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. In this study, we found the first evidence of a paired spiracular structure in the first gill arch position on ancient stem sharks, representing the only known example of a transitional state between the fully functional first gill postulated (but not yet identified) to have occurred in stem jawed fishes and the single, reduced pseudobranch present in more derived taxa. We have also identified the oldest record of elastic cartilage in the fossil record.
January 2020
·
49 Reads
·
8 Citations
Norwegian Journal of Geology
... In addition, Entelognathus shows a complement of fin spines that adds significant details to the evolution of these structures. Entelognathus 9 bears a pair of dermal pectoral girdles with spinal plates, as in other placoderms [72][73][74][75] , stem chondrichthyans [76][77][78][79] , and some early osteichthyans 53,80,81 (Supplementary Fig. 7). Entelognathus also has a dorsal fin spine, which is absent in most placoderms 39 but present in some ptyctodonts [82][83][84] . ...
January 2023
Palaeontologia Electronica
... Of the four families recognised within the Acanthodiformes, the Mesacanthidae are mostly distinguished by features that are considered 'primitive' because they are shared with 'Climatiiformes' sensu lato -having one pair of prepelvic spines, a shallowly inserted dorsal spine, an unmineralised endocranium, and a simple mandibular joint (Burrow, 2021). As noted by Burrow et al. (2022), recent cladistic analyses (e.g., Zhu et al. 2022, extended data figure 9b) retrieve mesacanthids as the sister group to most other acanthodiforms. ...
June 2022
Scottish Journal of Geology
... Our understanding of the relationships of early jawed vertebrates has changed markedly over the past decades (Brazeau, 2009;Brazeau & Friedman, 2014;Burrow & Rudkin, 2014;Li et al., 2021;Lu & Zhu, 2008;Miller et al., 2003;Zhu et al., 2001Zhu et al., , 2021Zhu et al., , 2022. Along with the discovery of new taxa has come restudy of long-known species, with acanthodians of particular interest (e.g., Brazeau, 2012;Burrow et al., 2008Burrow et al., , 2013Burrow et al., , 2015Dearden et al., 2019Dearden et al., , 2021Snyder et al., 2017;Turner et al., 2005;Warren et al., 2000). Although traditionally assigned to the Acanthodii (e.g., Denison, 1979), recent cladistic analyses (Andreev et al., 2022;Burrow et al., 2016;Coates et al., 2018;Giles et al., 2015) show the Gyracanthidae Woodward, 1906 amongst a cluster of basally branching stem chondrichthyan taxa, crownward of the Acanthodii sensu lato Coates et al., 2018). ...
June 2021
Papers in Palaeontology
... Type species and holotype: Cheirolepis trailli Agassiz, 1835 [31]. Included species: C. aleshkai, Plax, 2020 [4]; C. canadensis, Whiteaves, 1881 [33]; C. gaugeri, Gross, 1973 [32]; C. gracilis, Gross, 1973 [32]; C. jonesi, Newman et al., 2021 [34]; C. schultzei, Arratia and Cloutier, 2004 [35]; and C. bychovensis, Plax, 2022 [17]. Material: 21 scales (13 scales from Belarus and 8 scales from Lithuania). ...
April 2021
Norwegian Journal of Geology
... The best known of these is Coccosteus cuspidatus, a freshwater/brackish [13,14] coccosteomorph represented by several complete specimens [15]. Extensive postcranial material and/or body outlines are also known for the non-eubrachythoracid arthrodires Holonema westolii [16], Africanaspis doryssa, and A. edmountaini [17]; the coccosteomorphs Millerosteus minor, Dickosteus threiplandi, Watsonosteus fletti [18], Plourdosteus canadensis [19], and Incisoscutum ritchei [20]; the aspinothoracidan Amazichthys trinajsticae [21]; and Rhachiosteus pterygiatus, a eubrachythoracid of uncertain phylogenetic position (see [22][23][24]). Limited post-thoracic material has been reported for several other arthrodires, including Paramylostoma arcualis [25], Heintzichthys gouldii [26,27], and Dunkleosteus terrelli itself [28,29]. ...
September 2020
Palaeontology
... Into the 21 st century, more detailed work based on acanthodians had identified conspecific forms not only in the Baltic Region and the Orcadian Basin, but also Belarus, Spitsbergen, and Severnaya Zemlya (Burrow et al. 2016(Burrow et al. , 2020(Burrow et al. , 2021den Blaauwen et al. 2019;Newman et al. 2019Newman et al. , 2021b. The reason for acanthodian synonymy is discussed later in this article. ...
September 2020
Scottish Journal of Geology
... Into the 21 st century, more detailed work based on acanthodians had identified conspecific forms not only in the Baltic Region and the Orcadian Basin, but also Belarus, Spitsbergen, and Severnaya Zemlya (Burrow et al. 2016(Burrow et al. , 2020(Burrow et al. , 2021den Blaauwen et al. 2019;Newman et al. 2019Newman et al. , 2021b. The reason for acanthodian synonymy is discussed later in this article. ...
July 2020
Scottish Journal of Geology
... It has been demonstrated in many previous publications (e.g., Burrow et al., 2020b) that there are five fish-bearing faunal zones in the Middle Devonian Orcadian Basin. These zones equate well to the biostratigraphy of the Baltic region (Newman et al., 2017), Belarus and elsewhere in Laurussia (Plax and Newman, 2021). ...
January 2020
Palaeontologia Electronica
... Ischnacanthids more commonly occur in Lower to Middle Devonian strata at many sites globally but less commonly in Upper Devonian strata (Burrow, 2004(Burrow, , 2021Blais et al., 2015;Hairapetian & Burrow, 2016;Burrow et al., 2018;Voichyshyn & Szaniawski, 2018); none are known from Carboniferous or higher strata. Frasnian-age ischnacanthid taxa include those from marine deposits of North America, Europe, Spitsbergen, Russia, and Iran (e.g., Reed, 1986;Burrow, 2004;Newman et al., 2020), while previous to this study, Famennian ischnacanthid taxa were represented by two described species, Atopacanthus juvai (Hairapetian & Burrow, 2016) from marine deposits of Iran, and Grenfellacanthus zerinae (Long et al., 2004) from non-marine deposits of Australia (Fig. 1B) and a partial dentigerous jaw bone from Turkey described as an ischnacanthid (Janvier, 1983). The only Late Devonian ischnacanthid specimen known from articulated remains is from the lower Frasnian Oberer Plattenkalk, Bergisch-Gladbach, Germany. ...
January 2020
Norwegian Journal of Geology
... Baron (2015) showed that there were no proportional morphological differences between M. pusillus and M. peachi and synonymised the two species, supporting Trewin and Davidson's (1999) opinion, while also showing statistical differences between the older type species M. mitchelli and the Middle Devonian species. The most recent papers concerning M. pusillus are the description by Burrow et al. (2020a) of a putative dermal spiracle cover in a specimen from Cromarty, nomination of a lectotype by Baron and Seymour (2021), and description of the jaw cartilage structure by Burrow and den Blaauwen (2021). Up to date, no morphological description of the head or skeletal reconstruction of the species has been published. ...
February 2020
Journal of Anatomy