Acanthospina irregulare, Valiukevičius, 2003
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publication ID |
https://doi.org/ 10.5281/zenodo.4665088 |
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persistent identifier |
https://treatment.plazi.org/id/586B87E1-FFAD-FFA8-FF21-F47F6AE2C1FB |
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treatment provided by |
Felipe |
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scientific name |
Acanthospina irregulare |
| status |
sp. nov. |
Acanthospina irregulare n. sp. ( Figs 30 View FIG C-F; 46-51)
Nostolepis sp. no. 6 – Valiukevičius 1988a: 604, 605.
“An unusually squamose acanthodian” – Valiukevičius 1997: 25.
HOLOTYPE. — LIG 35-A-344. Incomplete specimen exposing only squamation ( Fig. 46G). Pod”emnaya River, outcrop 67, bed 12.
PARATYPES. — LIG 35-A-352: part of head with jawbone fragments, intact or poorly articulated teeth, one tooth whorl, isolated palatine teeth, denticles, scales and plates ( Fig. 46 A-F). Another small part of specimen LIG 35-A-345, exposing squamation (fully dissolved). Both specimens from the Pod”emnaya River, outcrop 67, bed 12.
ETYMOLOGY. — From irregularis (Latin): irregular, in reference to variable, inconstant crown ornamentation.
LOCALITY AND AGE. — October Revolution Island: Pod”emnaya River, outcrop 67, bed 12. Lower Devonian, lower Lochkovian, top of the Severnaya Zemlya Formation.
DIAGNOSIS. — Fish having large sub-rhombic to inconstantly shaped scales with high spiny denticles on crowns. Denticles rarely flattened, grown together areally. Scale necks and bases randomly porose. Crowns composed of Stranggewebe with a dense network of diversified vascular canals, partly down streamed and piercing the highly cellular bone of the scale base. Dentition of powerful sharp, high-pyramidal main cusps, smaller intercusps and rounded or flattened palatine teeth, composed of trabecular dentine with, in parabasal part, mono- or bi-branched multipulpar canals directed toward the apex. Tooth whorls also present.
DESCRIPTION
Squamation
Scales densely displayed in lines without overlaps. Their crowns vary in length from 0.4 to 1.7 mm, with a majority from 0.7-1.1 mm. In smaller examples the crowns are wider than long. The shape is inconstant in form varying from sub-rhombic ( Figs 30C View FIG ; 47C View FIG ) to oval or elongated ( Fig. 47J, K View FIG ). Crowns consist of one, some or numerous areas-denticles. Multidenticle scales distinctly dominate, with well defined denticle margins ( Fig. 30C View FIG ) each being additionally ornamented with short anterior ridgelets ( Figs 30C View FIG ; 47A, H View FIG ). Sometimes the denticles of medial area are flattened and fused together, resembling almost horizontal crown plate ( Fig. 47A, C View FIG ). This sort of crown has often well grown anterior denticles or essentially rounded starlets ( Fig. 47A, C View FIG ), slightly elevated and separated from the remaining crown part by larger grooves. The crowns overhang posteriorly the bases. A majority of scales have numerous, irregularly shaped denticles with longitudinal ridges
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( Fig. 47 View FIG F-H), growing on all sides of the central one and highering slightly posteriorly or rarely making a large angle with the base ( Fig. 47G View FIG ). Rare scales of smaller size bear an anterior fore- crown, which protrude from beneath posterior- and sideward, enlarged plates, thus pointing growth in one direction ( Fig. 47D View FIG ). The minority belong to tesserae-like scales with separate rounded and striated blunt denticles, joined with flat or slightly convex base plate ( Fig. 47J View FIG ). The scale neck is porose, low to mid-high. The highest crowns are distinguished by their almost absent neck, with denticles arising from the base. The base is massive, convex, rhombic, and sub-rhombic to oval or widened quadrangular, protruding the crown anteriorly and laterally. Its bottom surface exposes numerous randomly distributed large pore openings ( Fig. 47B, I View FIG ).
The scale histological structure is of the “ Nostolepis ”- type. Crowns are composed of areally grown lamellae with a modified meso- dentine tissue. All their space is pierced by a very diversified system of dense and large (wide and long), ascending, circular and radial vascular canals, of various shapes. There is almost no place left for dentine tubules of a typical mesodentine network ( Figs 48A, B View FIG ; 49A, B View FIG ). The largest radial canals are occurring over the base, but smaller branches are also met higher in the crowns, where they interconnect with ascendant canals and form the principal canal network. Several canals are directed baseward to open on its surface ( Fig. 48A View FIG ). A Stranggewebe with elongated lacunae of variable size and osteocyte spaces ( Figs 48D View FIG ; 49B View FIG ) composes all crown. The
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base is composed of superpositionally growing highly cellular bone ( Fig. 48C View FIG ) with polygonal large osteocytes; vascular canals pierce it. Thorn-like scales ( Fig. 49 View FIG C-E) show the same tissue composition.
Dentition
Teeth fused to dermal jawbones have oval, sub-circular or, rarely, a rounded triangular parabasal section. Their arrangement relative to lateral line is destroyed. The paratype ( Fig. 46A) has yielded slightly basally striated main cusps (up to 7 mm high) and smaller interspersed and lateral cusps. Teeth have a stretched highpyramidal longitudinal section. They are rarely recurved, with sharp apexes and side flanges. Palatine teeth ( Fig. 46 B-D), 0.2-0.7 mm high are, thin and elongated, rounded or longitudinally flattened, and also exhibit side flanges. They are always found with a bony base of inconstant deepness and sometimes bear small blunt fragile denticles, disposed all around the palatine cusp. Two-cuspidate palatine teeth ( Fig. 46C) are rarely encountered. The tooth whorl ( Fig. 46E), about 4.8 mm long and to 3.9 mm wide is, massive, grouping on a slightly curved bony base three rounded main cusps (very weathered), gradually thinning in one direction. One or two cusps of smaller size are present on each side of the main cusp.
In their histological structure, the main cusps ( Fig. 50 View FIG ) and palatine teeth ( Fig. 51B View FIG ) are rather identical. The basal cellular bone is highly vascularised. In parabasal part a trabecular dentine occur with multipulpar canals. Higher in crown their number reduces to one or two. Monotonous dentine weakly branched tubules arise and are directed at right angle upward and toward all sides. Sectioned blunt rounded denticles are composed of cellular bone and superficial dentine ( Fig. 51A View FIG ). A strip between them contains extremely enlarged vascular canals with numerous outerward ascending dentine tubules.
DISCUSSION
The systematic position of Acanthospina irregulare n. gen., n. sp. remains uncertain. The histological structure of scales (diversified system of principal canal net, Stranggewebe composing all crown space, highly cellular and also vascularised bone in base), which can be defined as modified “ Nostolepis ” - type, is closest to that of representatives of the Climatiidae . This basic character leads to place the taxon within acanthodians. Particularly, by several histological features (growth type, style of Stranggewebe, vasculars in bases), the new taxon resembles Nostolepis robusta (Brotzen, 1934) ( Gross 1971: text-figs 15, 16), but differs in its lack of superficial simple mesodentine strip, surrounding each growth lamella.
According to morphologic characters, especially to spiny denticles on crowns, it looks rather Chondrichthyes-like. Acanthospina n. gen. crowns resemble those known in certain hybodontiform chondrichthyans, e.g., Arauzia federicoi from the Early Devonian of Spain ( Mader 1986: pl. 6, figs 1-14) or Hybodontoid gen. et sp. indet. from the Early Carboniferous of Queensland, Australia ( Turner 1993: figs 12, 13). Several more essential differences occur in the shape and type of porosity of scale neck and base.
BIOSTRATIGRAPHIC SIGNIFICANCE
Key species of the Poracanthodes menneri Subzone , it is associated with other articulated acanthodians and occurs at the topmost part of
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the Severnaya Zemlya Formation. Age is early Lochkovian. Tentatively correlates to the woschmidti Zone of standard conodont scale.
| A |
Harvard University - Arnold Arboretum |
| B |
Botanischer Garten und Botanisches Museum Berlin-Dahlem, Zentraleinrichtung der Freien Universitaet |
| C |
University of Copenhagen |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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Kingdom |
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Phylum |
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Genus |
Acanthospina irregulare
| Valiukevičius, Juozas 2003 |
Nostolepis
| VALIUKEVICIUS J. 1988: 604 |