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Polysacos vickersianum
Taxonomy
Polysacos vickersianum was named by Vendrasco et al. (2004). Its type specimen is USNM 520742, a valve, and it is a 3D body fossil. Its type locality is Monroe Co. [Edwardsville Lmst], which is in a Mississippian marine limestone in the Edwardsville Limestone Formation of Indiana. It is the type species of Polysacos.
Synonymy list
| Year | Name and author |
|---|---|
| 2004 | Polysacos vickersianum Vendrasco et al. p. 290 |
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
†Polysacos vickersianum Vendrasco et al. 2004
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| M. J. Vendrasco et al. 2004 | As for genus. The holotype is an incompletely articulated individual, 25mm in total length, preserved in near-life orientation. In addition to head and tail valves, seven of the ten lateral intermediate valves are well preserved and the middle valve of each series is present on both sides (valve 4, Fig. 1a). The anterior lateral valve is missing from the right
side, the fifth lateral valve is missing from the left side, and the sixth lateral valve of the left side lies beneath valve 4 on the left side. Four of the five intermediate valves on each side are similar in shape; the fifth, which is the anterior-most one, is different and, remarkably, it overlaps both the head valve as well as the intermediate valve that follows it. Every other intermediate valve overlaps the one behind it. The apices of the head and tail valves are at the anterior and posterior ends of their respective valves, whereas the apices of the intermediate valves are centrally positioned and curve slightly forward. Four of the five central valves are in place along the dorsal midline but the anterior one is displaced so that it lies near the right margin of the head valve. Many marginal spines are missing, but it is clear from those that are present that there were approximately 60 spines in all. The spines have concave dorsal surfaces and prominent projections at their proximal ends that presumably served to anchor them in the body wall. |