Romano et al.—Early Triassic Fishes of Elko County (Nevada)


1035


Figure 6. Saurichthys sp. (PIMUZ A/I 4397) from the latest Smithian of Palomino Ridge, Elko County, Nevada, USA. (1) fossil in left, dorsal, and right view (from left to right); (2) interpretive drawings of 6.1; asterisks in 6.2 mark the positions of the ossification centers of the frontals and the dermopterotic; anterior is up. Scale bar = 50mm (total).


dermal bones, carrying the ornamentation, is mostly weathered and the suture lines are visible. Dermal skull roof.—The dermal cranial roof is mainly


formed by the large, paired frontals, and the large, paired dermopterotics. The medial boundaries between these bones are intermittently visible from near the caudal end of the skull fragment up to a short distance posterior to the tip of the rostrum. The frontals are oriented mostly horizontally, except for the part anterodorsal to the orbital opening, where the bone exhibits a small, laterally facing flange. The ossification centers of both frontals are well visible and located at about the level of the hind margin of the orbit. The supraorbital sensory canal runs from these ossification centers up until the level of the external narial openings, where the canal turns laterally. The ossification center of the dermopterotic is situated close to the posterolateral margin of the dermal skull roof


(Fig. 6). The boundary between the frontal and the dermoptero- tic is scarcely visible, but judging from the circumferences of the growth lines radiating from the ossification centers of both of these bones, their mutual boundary runs sinuously from anterolateral to posteromedial. Anteriorly, the dermopterotic forms the posterior part of the dorsal margin of the orbit. The dermopterotic forms an extended lateral flange posterodorsal to the orbital opening. The remains of a poorly preserved dermosphenotic may be visible along the anterior margin of this lateral flange. A sensory canal is traceable along the lateral border of the postorbital portion of the dermal skull roof, running through the dermopterotic in the rostrocaudal direction. Posterodorsal to the orbital opening, the canal turns ventrolat- erally. Some tubercles are visible along the sensory canal in the posterolateral part of the left dermopterotic. A pair of small parietals is developed medially to the dermopterotics and


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