Nobilesquama, Valiukevičius & Burrow, 2005

Valiukevičius, Juozas & Burrow, Carole J., 2005, Diversity of tissues in acanthodians with Nostolepis-type histological structure, Acta Palaeontologica Polonica 50 (3), pp. 635-649 : 646-647

Genus Nobilesquama nov.

Comment.—The sixth histological group of “nostolepids” does not have Nostolepis − type histology, and the species listed herein probably belong in a group with several other taxa, including most species tentatively referred to Gomphonchus ?. Their higher level relationships are unclear, but histologically they appear intermediate between Nostolepis − type and Acanthodes − type. Nobilesquama and Peregrinosquama are both based on scales and erected for the former Nostolepis , and Watsonacanthus spp. in this group.

Derivation of the name: From nobilis (Latin) known, recognizable and squama (Latin) scale.

Type species: Nobilesquama longipostera ( Valiukevičius, 2003b) ; Timan−Pechora region , Varknavt−5 borehole, depth 4082–4089 m; Lower Devonian , Lochkovian, Khatayakha Formation .

Age and geographic distribution: Lower Devonian, Lochkovian to lower Emsian. Timan−Pechora region, Severnaya Zemlya Archipelago and Salair ( Russia).

Species included: Type species and Nobilesquama minilonga ( Valiukevičius, 2003b) , and N. watsoni ( Valiukevičius, 2003a) .

Diagnosis.—Acanthodian with rhomboid scales of moderate size, crowns carrying from two to eight short subparallel or subradial ridges of which the longest lateral symmetric pairs may point posteriorly; scale bases high and deepest centrally or more anteriorly; scale crowns composed of syncitial dentine (often orthodentine−like) with long and wide ascending and radial vascular canals, and durodentine usually developed as thick layers in each growth lamellae formed after the scale primordium; scale bases composed of bone with a very low density of osteocyte cavities, frequently almost acellular.

Discussion.—The crown ornamentation is also within the range of the revised genus Nostolepis , and the deep scale bases resemble those of scles of Eifellepis Vieth−Schreiner, 1983 and some Laliacanthus Karatajūtė− Talimaa, 1986, but the histology differs from these taxa, as detailed earlier. The crown tissue is similar to the Acanthodes − type structure, but scale bases of the latter are pierced by canals of Williamson and are completely acellular. The histological structure is closest to that of Gomphonchus Gross, 1971 and Poracanthodes Brotzen, 1934 , but these taxa differ morphologically and by the latter having a pore canal system in the crown.