Geological setting and material
This protocol is extracted from research article:
High-performance suction feeding in an early elasmobranch
Sci Adv, Sep 11, 2019; DOI: 10.1126/sciadv.aax2742

The Wardie Shales represent a Member of the Gullane Formation, part of the West Lothian, Viséan stage Strathclyde Group (3235, 46, 47). The minimum age constraint for the Wardie Shales Member is defined by the nodosa conodont zone at the base of the Brigantian substage: no less than 333.95 ± 0.39 Ma (48). This overlies the Asbian substage MacGregor Marine Band goniatites from zone B2 of the English succession (37, 38, 4952), which, in turn, overlie the Wardie Shales. The maximum age constraint for the Gullane Formation is provided by the underlying Arthur’s Seat Volcanic Formation, 40Ar/39Ar dating of which is 335.1 ± 0.6 Ma (53). It follows that the age of the Wardie Shales Member is restricted to between ~333.5 and 335.5 Ma (54).

The Oil Shales of the Midland Valley of Scotland, including the Wardie Shale Member, were deposited on the floor of a large and likely thermally stratified lagoon, stagnant parts of which permitted chondrichthyan skeletal preservation (15, 5558). Irrespective of evidence of occasional marine influence, the shark component of the fossil biota, which also includes brachiopods, bivalves, ostracods, actinopterygians, and sarcopterygians including the tetrapod Lethiscus (59), persists throughout six of seven fish-bearing beds at Wardie shore. Hence, it appears that these Oil Shale sharks (12, 15, 55), of which T. arcuatus is by far the most abundant (14), were either nonmarine or able to tolerate a wide range of salinities.

Concretions (nodules) (fig. S1A) are restricted to the fish-bearing beds. Skeletal remains embedded within siderite matrix are often surrounded by a halo of iron pyrite and calcite-filled radiating cracks (14, 15). Preserved shark cartilage is occasionally freed from the surrounding matrix, but these items often consist of the cartilage core, with calcified tesserae and surface detail remaining embedded in the concretion. For this reason, mechanical preparation of specimens is not recommended, and nondestructive methods, such as computed tomography, are preferred.

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