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 PORACANTHODIDAE GEN. ET SP. INDET. ( FIG. 3Q, R ; TABLE 1 ; SUPPL. 1, FIGS. 2 ) Referred specimens —A few sensory line scales were recovered from levels 395′–492.3′ ( 120.4–150.1 m ) in the BC II section, including UCR 10750-9 (level 456.5’= 139.1 m ) and UCR 930-3 (level 395’= 120.4 m ), AMF 97928 (level 503’= 153.3 m ), AMF 97929 (level 446.5’= 136.1 m ) figured by Parkes (1995 , fig. 29.9–29.12: captioned Chondrichthyan 1, 2), AMF 97949, 97952–97954 (all level 402’= 122.5 m ), AMF 97955 (level 395’= 120.4 m ) figured by Parkes (1995 , fig. 32.5, 32.6, 32.11–32.16: captioned Poracanthodes punctatus ); fragments of dentigerous jaw bone are from levels 424.9’ ( 129.5 m ), M48B=491.8’ ( 149.9 m ), and M48C=492.3’ ( 150.1 m ): Roberts Mountains Formation. Description —Short, wide scales are identified as ones that edged the sensory lines on the head, by comparison with squamation of articulated poracanthodid Zemlyacanthus menneri ( Valiukevičius 1992 , pl. 9.6a, 6b). These scales have a similar structure in all known poracanthodids, with multiple short sharp ridges and tubercles along the straight anterior margin overlapping similar ridges which cover the crown, or at least the anterior half of the crown with the posterior half showing rows or lines of pores. The posterior edge has often fractured off, revealing the posteriorly directed canals of the pore system. Pores open out on the crown between the ridges and tubercles. The neck is short and concave, and the base is low and slightly convex. Other elements include jaw fragments that are probably poracanthodid, because no other ischnacanthiform elements are found at the same levels.