Early Jurassic (middle Hettangian) marine gastropods from the Pogibshi Formation (Alaska) and their paleobiogeographical significance

Abstract

A middle Hettangian marine gastropod assemblage is reported from the Kenai Peninsula of south-central Alaska supplying new paleontological evidence of this group in Lower Jurassic rocks of North America. Pleurotomaria pogibshiensis sp. nov. is described from the middle Hettangian marine succession informally known as Pogibshi formation, being the first occurrence of the genus in the Kenai Peninsula and the oldest occurrence of the genus in present-day Alaska and North America. One species of the genus Lithotrochus, namely Lithotrochus humboldtii (von Buch), is also reported for the first time from the Kenai Peninsula. Lithotrochus has been considered as endemic to South America for a time range from the early Sinemurian to the late Pliensbachian. The newest occurrence of Lithotrochus in rocks of the Pogibshi formation extends the paleobiogeographical and chronostratigraphical distribution of the genus into the present-day Northern Hemisphere. However, the Southern Hemisphere affinities are consistent with the hypothetical interpretations (although supported both by paleobiogeographical and paleomagnetic data) that the Peninsular terrane of south-central Alaska is far-traveled and may have originated at much more southerly paleolatitudes than its present-day position. Two other Early Jurassic caenogastropods typical of the Andean region of South America and of the Tethyan epicontinental seas are described for the first time in the Pogibshi formation, and these are Pseudomelania sp. and Pictavia sp. The new gastropod assemblage reported here shows close affinities with coeval South American and European gastropod faunas, supplying new evidence to interpret their distribution during the Early Jurassic.

First report of Euthyneura (Heterobranchia: Gastropoda) in the Early Jurassic of Southern Patagonia, Argentina

“…3), although it had been previously reported in the Late Triassic of the Pucará Group (Central Peru) (Has, 1953). The Early Jurassic Cylindrobullina species recorded in the Neuquén and Chubut basins might represent survivors from the end-Triassic marine mass extinction event in South America, as was previously suggested by Ferrari (2015b). The author supported the idea that the ancient Paleo-Pacific seaway from Peru to Argentina was the most plausible explanation for biotic exchange of benthic gastropod faunas across the Late Triassic/ Early Jurassic boundary (Ferrari, 2015b).…”

“…and Cossmannina australis nov. sp. The new report extends the palaeobiogeographical distribution of Euthyneura into the southern Patagonian region during the earliest Pliensbachian, suggesting the existence of a shallow marine connection between the Neuquén and Chubut basins during the earliest Jurassic, as had been previously hypothesized by Ferrari (2015b). The occurrence of the species Eoamaltheus sp.…”

“…The Early Jurassic Cylindrobullina species recorded in the Neuquén and Chubut basins might represent survivors from the end-Triassic marine mass extinction event in South America, as was previously suggested by Ferrari (2015b). The author supported the idea that the ancient Paleo-Pacific seaway from Peru to Argentina was the most plausible explanation for biotic exchange of benthic gastropod faunas across the Late Triassic/ Early Jurassic boundary (Ferrari, 2015b). The Late Triassic Cylindrobullina species from Peru showed the smallest size for the genus at that time, whereas the Pliensbachian Cylindrobullina of southern Patagonia showed the largest size.…”

Macroflora from Lower Jurassic (Pliensbachian) of Hicks Creek, southern Talkeetna Mountains, south‐central Alaska

“…2021) and other bivalve genera, gastropods (Ferrari et al . 2020), brachiopods (Sandy & Blodgett 2000), and both solitary and colonial scleractinian corals. Weyla is typical of warm‐water, low‐latitude faunas of western North America and South America.…”