Cretaceous opine bivalves from the Pacific slope of North America and palaeobiogeography of subfamily Opinae Chavan, 1969

2010

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The Late Cretaceous to late Paleocene record of glycymeridid bivalves in the region extending from the Alaska Peninsula, southward to Baja California, Mexico is studied in detail for the first time. Glycymeris pacifica (Anderson, 1902), of late Cenomanian to late Turonian age, is the earliest known glycymeridid in the study area. Very locally, it is found with the middle to late Turonian Glycymeris yoloensis n. sp. The latter apparently represents some intermediate state between genus Glycymeris da Costa, 1778 and genus Glycymerita Finlay and Marwick, 1937. In the study area, Glycymerita is represented by Glycymerita veatchii (Gabb, 1864), middle to late Turonian to late Campanian; Glycymerita banosensis (Anderson, 1958) new combination, late Campanian to latest Maastrichtian; Glycymerita aleuta n. sp., known only from Alaska and of early Maastrichtian age; and Glycymerita major (Stanton, 1896) new combination, Selandian to Thanetian. All the studied species lived in warm-temperate, shallow-marine waters and were shallow burrowers in fine-grained siliciclastic sediments. Variability in morphology is common in sizeable populations of the various species, especially Glycymerita veatchii, which increased nearly fivefold in size during its 19.5 million-year-long range and culminated in shells up to 84 mm in length.

Section: Global Overview Of Cretaceous and Paleocene Glycymeridinesmentioning

confidence: 80%

Section: Paleobiogeography Of the Studied Glycymerididsmentioning

confidence: 96%

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Northeast Pacific Upper Cretaceous and Paleocene Glycymeridid Bivalves

2010

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“…Current summaries of the geological details of the formations and members containing study area Atira can be found in the following papers (listed in ascending chronostratigraphic order): Hornbrook Formation, Osburger Gulch Member (Squires and Saul, 2003a); Redding Formation, Frazier Siltstone Member (Squires and Saul, 2003b); Ladd Formation, upper Baker Canyon Member (Squires and Saul, 2003c); Ladd Formation, lower and middle Holz Member (Saul, 1982); Chico Formation at Granite Bay [= Texas Flat = Rock Corral] (Squires and Saul, 2009); Cedar District Formation and Chatsworth Formation (Squires and Saul, 2001); upper Tuna Canyon Formation (Squires and Saul, 2009); Chico Formation, Musty Buck Member (Squires and Saul, 2003c); Williams Formation, Pleasants Sandstone Member (Squires and Saul, 2001); El Piojo Formation (Squires and Saul, 2009); Moreno Formation, Tierra Loma Member (Squires and Saul, 2006); Deer Valley Formation (Squires and Saul, 2006); and Panoche Formation near Martinez, California (Squires and Saul, 2006).…”

Section: Methodsmentioning

confidence: 99%

Northeast Pacific record of the Cretaceous marine gastropodAtiraand a review of its paleobiogeography

2010

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The Cretaceous record of the shallow-marine margaritine gastropod genus Atira Stewart, 1927 in the region extending from Vancouver Island, to northern Baja California is studied in detail for the first time. It is represented by A. popenoei n. sp. (late Turonian to earliest Campanian), A. ornatissima (Gabb, 1864) (latest Santonian to late Campanian or possibly early Maastrichtian), and A. inornata (Gabb, 1864) (“mid” Maastrichtian), which is the youngest known species of Atira.Atira originated in the tropical waters of the Tethys Sea in western Europe as early as the Early Cretaceous, possibly during the Hauterivian but was present there by the late Aptian to early Albian. The genus subsequently immigrated to other regions and became adapted to warm-temperate waters. By the late Turonian it had migrated westward to northern California. During the Campanian it reached south Sakhalin and in the earliest Maastrichtian it was present in southwest Japan. Although Atira? nebrascensis (Meek and Hayden, 1856) has been questionably reported from Campanian to “mid” Maastrichtian deposits in the Wyoming area of the Western Interior Basin, this species does not belong in genus Atira.

“…Pyropsis grahami n. sp. is found in rocks of late early Campanian age in southern British Columbia but as discussed in Saul and Squires (2008) and Squires and Saul (2009), Late Cretaceous fossil localities in southern British Columbia were most likely tectonically transported from northern California. Future collecting might reveal that Pyropsis has a continuous geologic range from late Turonian to late early Campanian in the northeast Pacific.…”

Section: Paleobiogeography Of Pyropsismentioning

confidence: 97%

Northeast Pacific Cretaceous record ofPyropsis(Neogastropoda: Pyropsidae) and paleobiogeography of the genus

2011

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The neogastropod genusPyropsisConrad, 1860 (family Pyropsidae Stephenson, 1941) is recognized for the first time from Upper Cretaceous shallow-marine siliciclastic rocks in the region extending from Vancouver Island, British Columbia southward to southern California. Four new species were detected:Pyropsis aldersoni(earliest Coniacian, southern California),Pyropsis californica(early Coniacian, northern California),Pyropsis louellae(late Coniacian or early Santonian, northern California), andPyropsis grahami(late early Campanian, Vancouver Island).A critical review of the global reports ofPyropsis, a genus that has been commonly confused with other genera (especiallyTudiclaRöding, 1798), establishes thatPyropsishad an amphitropical distribution and lived in warm-temperate waters adjacent to a broad tropical realm. It is rare to uncommon wherever found, and its geologic range is middle Cenomanian to an age near the Cretaceous/Paleogene boundary (probably earliest Paleocene). It was moderately widespread before the Maastrichtian but was predominantly restricted to the New World during the Maastrichtian.