Late Jurassic-earliest Cretaceous belemnites (Cephalopoda: Coleoidea) from northeastern Mexico and their palaeobiogeographic implications

Abstract

In northeastern Mexico, the Upper Jurassic to lowermost Cretaceous La Caja and La Casita formations are well-known for their abundant and well-preserved marine vertebrates and invertebrates. The latter include conspicuous belemnites not formally described previously. They were identified as Cylindroteuthis spicularis modica SachS & NalNjaeva, 1964, Cylindroteuthis lenaensis SachS & NalNjaeva, 1964, Cylindroteuthis sp. ind. and a new species of the genus Rhaphibelus, R. aciculiformis. They are present in distinctive stratigraphic levels of the La Caja and La Casita formations (Early Kimmeridgian to earliest Berriasian). Cylindroteuthis spicularis modica was previously known from the Upper Jurassic of northern Siberia, European Russia and Spitsbergen, while C. lenaensis is common in the Upper Jurassic of Siberia. Both taxa thus indicate a Boreal distribution. The sporadic presence in northeastern Mexico of belemnite taxa of Boreal origin in distinct and welldefined intervals of the Kimmeridgian and the Tithonian appears to be linked to recurring ingression of cold-water into the Gulf of Mexico. Rhaphibelus, on the other hand, is only known from the Late Kimmeridgian and earliest Tithonian of southern Germany and Rhaphibelus aciculiformis n. sp. in the earliest Berriasian of northeastern Mexico and is therefore considered to be of Tethyan origin. Our new data expand both the palaeogeographical distribution as well as the stratigraphic range of these belemnites. Furthermore it substantiates faunal exchange between the Boreal Pacific and the Gulf of Mexico in the Late Jurassic. However, the presence of the genus Rhaphibelus in the earliest Berriasian could be an additional proof that a new connection opened in the earliest Cretaceous between the northeastern Gulf of Mexico and the European Tethys (Hispanic Corridor).