A new cheiracanthid acanthodian from the Middle Devonian (Givetian) Orcadian Basin of Scotland and its biostratigraphic and biogeographical significance

Abstract

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.

Architectural and ultrastructural features of tessellated calcified cartilage in modern and extinct chondrichthyan fishes

“…Biomineralized tissue of the lower jaw in “acanthodian” Cheiracanthus peachi (Middle Devonian; Eifelian‐Givetian, ca . 395–390 bp ) also consists of calcified cartilage globules or blocks rather than perichondral bone (den Blaauwen et al ., 2019, Figure 5). Ørvig (1951) also described (but did not illustrate) GCC in Cheiracanthus murchisoni , associated with a superficial layer which he regarded as poorly differentiated bone tissue.…”

“…This TCC “character” is often listed as number 1 in published data sets, seemingly suggesting that it is an example of clear character state definition and “easy” coding; in those analyses, the “bony” acanthodian fishes (a grade of stem chondrichthyans) are distinguished from “conventionally defined” chondrichthyans in supposedly lacking TCC ( e.g ., Brazeau & Friedman, 2014; Zhu et al ., 2013). Nevertheless, there is mounting evidence (reviewed later) that at least some attributes of TCC are recognizable in certain acanthodian fishes (Burrow et al ., 2015, 2018; den Blaauwen et al ., 2019) and that previous usage of TCC as an unambiguous phylogenetic character of “conventionally defined” chondrichthyans is therefore suspect.…”

A new species of ischnacanthiform acanthodian from the Givetian of Mimerdalen, Svalbard

“…2J). The spiky denticles which line the outside of the jaw bones are presumed to have been in the skin originally, and can be compared with the extraoral structures identified in Lower Devonian ischnacanthiforms (Blais et al, 2011;Burrow et al, 2018). The small tooth whorls resemble the multicuspid buccal and extraoral elements of Ischnacanthus gracilis (Burrow et al, 2018).…”

A new Meckel’s cartilage from the Devonian Hangenberg black shale in Morocco and its position in chondrichthyan jaw morphospace

“…However, Maisey et al (2020) describes the presence of subtessellated calcified cartilage in some acanthodians, while actual tessellated calcified cartilage (showing the outer prismatic layer) is apparently absent ( Brazeau & Friedman, 2014 ). Acanthodians like Climatius ( Burrow et al, 2015 ), Ischnacanthus ( Burrow et al, 2018 ) or Cheiracanthus ( Den Blaauwen, Newman & Burrow, 2019 ) are mentioned to show this subtessellated calcified cartilage. When looking at Climatius, it appears granular and no actual polygons are visible on the surface as mentioned above ( Burrow et al, 2015 , Fig.…”

“…In Ischnacanthus ( Burrow et al, 2018 ), a subtessellated calcified cartilage is described using histology; we cannot compare the HBS specimen to that. In Cheiracanthus ( Den Blaauwen, Newman & Burrow, 2019 ), the surface appears “globular or randomly tessellated” . To sum this up, acanthodian fossils, or stem chondrichthyans, show a rather globular or irregular pattern ( Burrow et al, 2015 , Fig.…”