Late Silurian to earliest Devonian vertebrate biostratigraphy of the Birch Creek II section, Roberts Mountains, Nevada, U. S. A. Author Burrow, Carole Jan Author Murphy, Michael Author Turner, Susan text PaleoBios 2023 2023-06-06 40 1975 1 32 http://dx.doi.org/10.5070/p940454153 journal article 10.5070/P940454153 0031-0298 10913559 58312615-0833-432E-BF5D-3DFFBF361AAA FUNICRISTATA NEVADAENSIS N. GEN, N. SP. BURROW, 2023 ( FIG. 5 ; TABLE 1 ; SUPPL. 1, FIGS. 2 , 5–7 , 9 –11, 14) Zoobank LSID — urn:lsid:zoobank.org:act: 1BB5B9FC-3E9B-4F4B-B238-A25CA0E9A8D8 Diagnosis —Acanthodian with small scales up to 0.5 mm wide and 0.6 mm long; crown with strong branched ridges with a ‘twisted’ appearance leading back from anterior edge and converging towards posterior corner of crown, or at least extending past lateral corners of crown; neck low or absent anteriorly on most scales, with only small pore openings; base only slightly convex and deepest below anterior margin of crown; crown extends up to a base-length beyond posterior corner of base; four or five superposed crown growth zones with a thin enameloid top; wide-calibre canal extends from primordial crown growth zone to posterior corner of crown, its presence usually marked by longitudinal ridge on crown. Holotype — Holotype scale UCR 10750-3 ( Fig. 5A–C ); 456.5’ (= 139.1 m ) level, BC II section, Roberts Mountains , Eureka county , central Nevada , U.S.A. : Roberts Mountains Formation (Late Silurian, Přidolí) . Figure 5. Funicristata nevadaensis n. gen . n. sp. from the uppermost Silurian of the Birch Creek II section. A–C. UCR 10750-3 (level 456.5') in crown views and magnified view of the crown ridges; D, E. UCR 10750-2 (level 456.5') in crown and lateral views; F, G. UCR 10746-10 (level 430.5') in anterocrown and crown views; H, I. UCR 10746-8 (level 430.5') in anterocrown and laterocrown views; J, K. UCR 10750-10 (level 456.5') vertical longitudinal section; L. UCR 10750-12 (level 456.5') horizontal section through crown. Abbreviations: c=canal; en=enameloid; h=hyphal boring; po=pore openings. Scale bars=0.1 mm in A, B, D–L, 0.01 mm in C ; anterior is to left or down, otherwise arrows point to anterior. See Table 1 for meterage. Paratypes — Paratypes scales UCR 10750-2, UCR 10746-8, -10, thin sections UCR 10750-10, 12. Referred specimens —Forty-three scales including the type specimens. Occurrence —Only known from the type locality at levels 395–492.3’ ( 120.4–150.1 m ). Etymology — Nevada , for the U.S. state where the type material was found, and ensis, Latin suffix denoting place. Description —Scales are small, up to 0.5 mm wide, 0.6 mm long and 0.3 mm high. Most scales appear dorsoventrally compressed, with a low or absent neck anteriorly on most scales ( Fig. 5A–E ). The crowns have a distinctive ornament comprising branching ridges with a ‘twisted’ or rope-like appearance leading back from the anterior edge, extending towards the posterior corner of crown ( Fig. 5A–G ), or at least extending past the lateral corners of the crown ( Fig. 5H, I ). The crown extends up to a base-length beyond the posterior corner of the base, with most scales having a marked median ridge running back from the middle of the scale to the posterior tip ( Fig. 5A, E, I ). In many scales, particularly the more ‘flattened’ examples, the crown ornament resembles a branching tree, with the posterior median ridge being the trunk with the radiating, branching ridges extending out towards the anterior edges. The neck has only small pore openings ( Fig. 5I ). The base on all scales is only slightly convex and deepest below the anterior margin of the crown, with a marked rim between the base and neck. Histological preservation is poor at these levels, with extensive hyphal borings, so that only general features can be discerned. The crown has four or five growth zones with all except the embryonic zone being extremely thin under the crown surface, comprising only enameloid posterior to the apex of the base ( Fig. 5J, L ). A wide calibre canal runs from the embryonic zone up and back through the middle of the posterior crown, aligned with the median ridge on the crown surface, to the posterior corner ( Fig. 5J, K ). Fine branching dentine tubules rise up in the anterior parts of the crown. No bone cell lacunae are detectable in the base. Comparison —These scales differ from all known taxa, based on their distinctive crown ornament resembling a tree with successively branching ridges. The single large canal extending from the primordial zone back to the posterior corner could indicate that the taxon is a highly derived poracanthodid, but no poracanthodids resemble this species in morphology or position of pore canals.