The Venericardia planicosta group in the Gulf province

Abstract

Venericardia planicosta of authors is considered as a monophyletic group of species rather than as a single specific unit. This group is restricted stratigraphically to the Eocene, but it is world-wide in geographic distribution. Each of the included species is generally confined to a single formation or member, but within its zone each is widely distributed, abundant, and conspicuous by reason of its size and ornamentation. As guide fossils the members of the plan•icosta group are therefore among the most significant of the Mollusca. Although no ancestral types have been recognized in the Cretaceous of the Gulf region, two virile branches of the planicosta group were already established in the region at the beginning of the Eocene epoch, and the present study is an attempt to trace their progress and development through the Eocene. Both of the branches, represented in the Midway deposits by V. smithii and V. mediaplata, are abundantly represented in the Wilcox deposits, particularly in the eastern Gulf province, by descendants of the Midway species. During the deposition of the middle Wilcox Tuscahoma and Bashi formations the planicosta group probably attained its greatest prominence in the size and abundance of individuals and in the diversification of the species, but their development is provincial. The faunas of the lower Claiborne deposits, on the other hand, especially those from the upper part of the lower Claiborne, are the most cosmopolitan of all the Eocene venericard faunas. The transgressional seas were not confined to the Gulf province but invaded Mexico, the Isthmus of Panama, and northern South America. So far as the venericards are concerned, the marine upper Claiborne, best represented by the Gosport sand, contains nothing more than a greatly reduced lower Claiborne fauna. After the widespread emergence at the end of Claiborne time, the venericards failed to regain their former prominence. Several species are known in Jackson deposits, but none of them are abundant, and the decline in the number of individuals and species during the Jackson epoch heralded the extinction of the group at the end of the Jackson. The occurrences of the planicosta group in western North America, South America, and the Old World are briefly considered. For the Asia-European representatives of the planicosta group, the life cycle was essentially the same as in America. In this paper 44 species and subspecies are deffcribed and illustrated; of these, 24 are new.

Is Cyclocardia (Conrad) a wastebasket taxon? Exploring the phylogeny of the most diverse genus of the Carditidae (Archiheterodonta, Bivalvia)

“…The tribe Venericorini, defined by Pérez () and formerly known as planicostate carditids (Gardner & Bowles ; Pérez et al . ), falls into Cyclocardia s. l .…”

“…Phylogenetic relationships among carditids have not been extensively explored. Qualitative approaches are included in the works of Harris (), Stewart (), Gardner & Bowles () and Heaslip (), among others. Quantitative approaches were made by McClure & Lockwood (), González & Giribet () and Pérez ().…”

Systematics and palaeobiogeography ofMegacarditaSacco in the Neogene of Europe (Bivalvia, Carditidae)

“…There is a rather extensive literature on the Palaeogene carditids with flattish ribs, i.e. planicostate carditids sensu Stewart (), Verastegui () and others, mostly from the USA (Cossmann ; Stewart ; Gardner & Bowles ; Verastegui ; Moore ; Sakakura et al . ; McClure & Lockwood , etc.).…”

Late Paleocene examples of residual coloration and embryonic features in juvenile marine mollusks from Northwest Louisiana

“…Large taxonomic groups of mollusks occurring in the Wilcox of the Gulf Coastal Plain such as the Venericardia planicosta group (Gardner and Bowles, 1939) and the Turritellidae (Bowles, 1939) contain morphologically similar species. Some of these species may be chronospecies comparable to the taxa of the Oligocene Pecten perplanus stock from the southeastern United States studied by Glawe (1969).…”

“…umbillical view, diameter 1.10 mm, USNM 546641, drilling depth 1351 ft, Pendleton Fm., transparent, cinder cone volcano-shaped shell with very faint growth lines and a deep umbilicus; 23, gastropod Cerithiella sp. apertural view with bluish white coloration (GSA R-CC 5B 9/1), height 3.11 mm, USNM 546642, drilling depth 987 ft, Pendleton Fm., showing spiral and radial ornamentation and a protoconch with different axis of coiling than the conch; 24, gastropod Rudiscala harrisi Palmer, 1937; apertural view with yellowish gray coloration (GSA R-CC 5Y 8/1), height 0.83 mm, USNM 546643, drilling depth 1612 ft, Lower Wilcox, showing curved axial ribs and an apertural lip; 25, gastropod Melanella wheeleri Palmer, 1937; apertural view with yellowish gray coloration (GSA R-CC 5Y 8/1), height 0.55 mm, USNM 546644 drilling depth 1507 ft, Marthaville Fm., exhibiting a sutural collar; 26, bivalve Venericardia densata pendletonensis Gardner and Bowles, 1939; interior with grayish orange coloration (GSA R-CC 10YR 7/4), height 1.79 mm, USNM 546645,depth 668 ft, Pendleton Fm., showing internal ribbing along ventral margin; 27, RV exterior of previous specimen exhibiting denticulations on ribs; 28, gastropod Dorsanum scalatum (Heilprin, 1891); apertural view with light brown (GSA RCC 5YR 6/4) and grayish orange (GSA 10YR 7/4) coloration on shell, height 2.00 mm, USNM 546646, drilling depth 987 ft, Pendleton Fm., showing development of external ornamentation on the whorls from radial lines to spiral lines to nodes; small, internal nodes are visible on the outer lip of aperture; 29, gastropod Ringicula butleriana Aldrich, 1895; apertural view, height 1.52 mm, USNM 546647, drilling depth 2299 ft, Lower Wilcox, showing spiral grooves on shell exterior, prominent columellar folds; 30, gastropod Buccitriton sagenum (Conrad, 1833); apertural view with grayish orange coloration (GSA R-CC 10YR 7/R), height 2.90 mm, USNM 546648, drilling depth 666 ft, Pendleton Fm., showing a similar development of ornamentation as observed in Dorsanum scalatum except B. sagenum lacks the development of prominent nodes on whorls; 31, gastropod Atys cf. FIGURE 3 caption next page.…”