John Pojeta

A synoptical classification of the Bivalvia (Mollusca)

Preface This classification summarizes the suprageneric taxonomy of the Bivalvia for the upcoming revision of the Bivalvia volumes of the Treatise on Invertebrate Paleontology, Part N.

ECHINOCHITON DUFOEI: A NEW SPINY ORDOVICIAN CHITON

Abstract Echinochiton dufoei new genus and species is described from the Ordovician age Forreston Member, Grand Detour Formation (Blackriveran) near Beloit, Wisconsin. For a variety of reasons, we regard E. dufoei as a chiton; the species is known from four articulated or partially articulated specimens, one of which has eight plates and two of which have a mucro on the tail plate. Echinochiton dufoei differs from other chitons in having large hollow spines that project from each of the known plates. In plate shape and position, E. dufoei is much like the Upper Cambrian species Matthevia variabilis Walcott, 1885, and the Lower Ordovician species Chelodes whitehousei Runnegar, Pojeta, Taylor, and Collins (1979).

EARLY AND MIDDLE(?) CAMBRIAN METAZOAN AND PROTISTAN FOSSILS FROM WEST AFRICA

ABsTRACr-Supposed Upper Proterozoic strata in the southwest Taoudeni Basin, Guinea and Senegal, and from the Mauritanide fold belt, Mauritania, have yielded mostly poorly preserved small skeletal fossils of metazoan and protistan origin. Problematic, but possible echinoderm material and spicules of the heteractinid sponge Eiffelia dominate the Taoudeni Basin assemblage. The age of the material is not certain but the paleontologic data suggest an Early Cambrian age for the stratigraphically lowest faunas, and a Middle Cambrian age is possible for the stratigraphically highest collections.

A Bohemian-type Silurian (Wenlockian) pelecypod faunule from Arctic Canada.

The pelecypod genera Slava and Rhombopteria are reported for the first time from Canada, where they occur in a limestone concretion within the Cape Phillips Formation, Cornwallis Island, Arctic Archipelago. These genera are characteristic of Silurian rocks in Bohemia, Czechoslovakia. Graptolites from the same concretion indicate the Monograptus ludensis Zone (uppermost Wenlockian); this age is substantiated by associated conodonts, trilobites, vertebrates, and pelecypods but with less precision. It is difficult to explain the occurrence of Slava and Rhombopteria in the middle of Laurentia on the basis of some map reconstructions of the Wenlockian world. The Canadian material of Slava novaterra n. sp. and Rhombopteria cf. R. mira (Barrande) is described. Leptodesma ( Leptodesma ) sp. A and an indeterminate grammysiid pelecypod from the same concretion are illustrated. Information is provided to show that Newsomella Foerste, from Wenlockian–Ludlovian rocks of Illinois, Wisconsin, and Tennessee, is not a subgenus of Rhombopteria Jackson.

PSEUDOMULCEODENS: A MISSISSIPPIAN ROSTROCONCH FROM MEXICO

This finding of Pseudomulceodens in Mississippian-age rocks of the Santiago Formation provides the first evidence of the molluscan class Rostroconchia in Mexico. Elsewhere in North American Mississippian rocks the class occurs in Arkansas (Hoare et al., 1982, 1988); Illinois (Weller, 1916); Indiana (Beede, 1906); Iowa (White and Whitfield, 1862); Michigan (Winchell, 1870); Montana and Nevada (Pojeta and Runnegar, 1976); Ohio (Hyde, 1953; Hoare, 1990); and Oklahoma (Branson, 1958). Pseudomulceodens cancellatus (Hyde, 1953) confirms the Osagean age (Early Mississippian) of the Santiago Formation, and reinforces the conclusion that there is paleobiogeographic similarity between faunas of the Nochixtlan region of Oaxaca, Mexico and the midcontinent of the USA during Early Carboniferous time. It seems likely that there was a close connection between southwestern Mexico and the Mid-Continent Paleoprovince, located in the east and central regions of the United States. Prior to this study the rostroconch genera Aphelakardia and Pseudomulceodens were placed in the family Hippocardiidae; they are here transferred to the family Conocardiidae. The rostroconchs figured here were collected 18 m above the base of the Santiago Formation, in the stream bed of Arroyo Las Pulgas. This locality is 600 m north of Santiago Ixtaltepec town, 17°29′–17°34′N, 97°05′–97°08′W, in the Nochixtlan Region, State of Oaxaca, Mexico. The Santiago Formation was first described by Pantoja-Alor (1970); we use the term Santiago Formation as redefined by Sour-Tovar et al. (1997), who considered only the first 67 m of the …

THE “CURSE OF RAFINESQUINA:” NEGATIVE TAPHONOMIC FEEDBACK EXERTED BY STROPHOMENID SHELLS ON STORM-BURIED LINGULIDS IN THE CINCINNATIAN SERIES (KATIAN, ORDOVICIAN) OF OHIO

ABSTRACT Thousands of lingulid brachiopods were found clustered beneath hundreds of individual valves of the strophomenid brachiopod Rafinesquina in the Upper Ordovician of Ohio. This association suggested a relationship between the two brachiopods, but the nature of this relationship was unclear. We utilized serial thin sectioning to examine these brachiopods and to determine the origin of the bed in which they were found. Sedimentary structures, mixed taphonomies, and stratigraphic and paleogeographic setting suggest that the lingulids occupied a hiatal concentration that had previously been reworked, but not significantly transported, by tropical storms. The final burial event was a storm that exhumed living lingulids along with disarticulated Rafinesquina shells from the same sediments. Neither living nor dead shells were transported, but were reworked locally, then reburied together. The lingulids then burrowed upward to escape, but most were trapped by the concave-downward Rafinesquina shells that had been redeposited above them. This finding offers the first documented example of negative ecosystem engineering and taphonomic feedback in the fossil record, as well as the oldest documented lingulid escape traces. It also suggests that taphonomic feedback can be subdivided into live-dead interactions that occur under normal background depositional conditions and those that occur during periodic short-lived sediment-reworking events, such as storms and tsunamis.

Matthevia (Polyplacophora) invades the Ordovician: The first reported post-Cambrian occurrence

The polyplacophoran Matthevia Walcott, 1885 has been reported previously only from Cambrian rocks. Recovery of specimens of two different species of Matthevia from the top of the cherty lower Gasconade Dolomite in Missouri extends the known range of the genus into the Ordovician. The presence of the Lower Ordovician trilobite Praepatokephalus Lochman, 1964 in one collection provides the biostratigraphic evidence that the new specimens of Matthevia are Ordovician in age. Matthevia erecta n. sp. is described. An emended diagnosis for the trilobite Praepatokephalus is provided; two species of the genus are briefly described but are left in open nomenclature as P . sp. A and P . sp. B. Collections were made from 10 localities. The 10 specimens of Matthevia described here are from localities 4 and 6 in the upper part of the cherty lower Gasconade Dolomite of eastern Missouri, south of St. Louis (Figs. 1, 2). Locality 4 is at Spring Branch in Meramec State Park. Locality 6, which is just west of the settlement of Old Mines, Missouri, is owned by Guy and Doris Darrough. The species of Matthevia described here are the first undoubted representatives of the genus reported from rocks of Ordovician age. Figure 1 —Stylized stratigraphic section of the Cambrian–Ordovician boundary beds in eastern Missouri. The disconformity between the Eminence and Gasconade marks the traditional Cambrian–Ordovician boundary. The work herein and the definition of the boundary by Cooper et al. (2001) indicate that the boundary in eastern Missouri is at the top of the Gunter Sandstone Figure 2 —Generalized locality map of study area Stinchcomb and Darrough (1995, p. 54) noted the occurrence of Matthevia in the Gasconade Dolomite; however, they did not describe or illustrate any specimens from this formation. The single specimen they figured is from some unspecified level …

Claudeonychia babini nov. gen. et nov. sp. of Ordovician Ambonychiid pelecypods from Cincinnati, Ohio, USA

Abstract A new genus of anteriorly-posteriorly elongate, posterodorsally alate, simplicicostate, strongly prosocline Ordovician ambonychiids is described. To honor Claude Babin and his extensive work with Ordovician pelecypods, the genus is named Claudeonychia . The type species is Claudeonychia babini nov. sp. In addition to the type species, the Ordovician species Byssonychia? byrnesi Ulrich , (1895), Opisthoptera notabilis Ulrich , (1895), and O. laticostata Ulrich , (1895) also are placed in Claudeonychia .