Taxonomical diversity and palaeobiogeographical affinity of belemnites from the Pliensbachian–ToarcianGSSP(Lusitanian Basin, Portugal)

Abstract

High-resolution analysis of the late Pliensbachianearly Toarcian belemnite assemblages from the Peniche section (Lusitanian Basin) has enabled, for the first time, recognition of eight taxa of the suborder Belemnitina, previously reported from contemporaneous north-west Tethyan and Arctic sections. The presence of Bairstowius amaliae sp. nov. in the late Pliensbachian (emaciatum Zone) represents a novelty given that hitherto the genus Bairstowius was known only from late Sinemurian and early Pliensbachian deposits. Additionally, the replacement of Bairstowius amaliae by Catateuthis longiforma, during the latest Pliensbachian, suggests an evolutionary relationship between the two taxa. This relationship suggests a new scenario for the subsequent development of endemic Toarcian Boreal-Arctic faunas, characterized by the occurrence of Catateuthis. Comparison of the Peniche belemnite fauna with coeval faunas from the Mediterranean/Submediterranean and Euro-Boreal domains indicates taxonomic uniformity during the late Pliensbachian and early Toarcian (emaciatum and polymorphum Zones), in the north-west Tethys. Despite the lack of a marked taxonomic turnover, the Pliensbachian-Toarcian boundary corresponds to a slight decrease in diversity observed not only in the Lusitanian Basin but also in coeval north-western European basins. Ordination and cluster analyses indicate that the largest changes in belemnite diversity and palaeogeographical distribution occurred rather during the Toarcian Oceanic Anoxic Event (base of the levisoni Zone). This event is marked by the extinction of taxa, affecting more severely the Mediterranean/Submediterranean domain and resulting in a more pronounced provincial differentiation among north-western European and Arctic belemnite faunas.

Ups and downs of belemnite diversity in the Early Jurassic of Western Tethys

“…This so-called 'belemnite gap' remains mysterious as it may be due to sedimentological hiatuses (Bardin et al 2015) poor sampling, taphonomic megabiases or real ecological rarity in the Toarcian palaeoenvironments of Maghreb. A similar pattern is reported from central and southern Italy, where passaloteuthid and hastitid belemnites are abundant in uppermost Sinemurian to lowermost Toarcian sediments (Mariotti 1994) but virtually absent above the Tenuicostatum-Serpentinum boundary (Weis et al 2015), as in Portugal (Rita et al 2019a, 2020. The apparent absence of belemnites in Toarcian and possibly also in lower Aalenian rocks of the Mediterranean domain has been interpreted by Dera et al (2016) as a delayed post-crisis recovery of southern faunas, linked to the Toarcian Oceanic Anoxic Event.…”

“…15) and Portugal (Rita et al . 2019a, 2020) suggest that the Tenuicostatum chronozone represents an intermediate peak in richness in these areas, that is bracketed by two low richness levels in the Spinatum and Serpentinum chronozones.…”

“…2015), as in Portugal (Rita et al . 2019a, 2020). The apparent absence of belemnites in Toarcian and possibly also in lower Aalenian rocks of the Mediterranean domain has been interpreted by Dera et al .…”

“…Recent local data obtained from Normandy (Weis et al 2018, fig. 15) and Portugal (Rita et al 2019a, 2020 suggest that the Tenuicostatum chronozone represents an intermediate peak in richness in these areas, that is bracketed by two low richness levels in the Spinatum and Serpentinum chronozones. Overall, the temporal pattern of belemnite species richness is marked by three high-level episodes in the Ibex, Bifrons and Dispansum chronozones and two low levels (the Spinatum-Serpentinum interval and the Aalenian stage).…”

Fossilized leftover falls as sources of palaeoecological data: a ‘pabulite’ comprising a crustacean, a belemnite and a vertebrate from the Early Jurassic Posidonia Shale

“…The specimen portrayed here is a belemnite associated with crustacean remains from the German Toarcian. Belemnites played a key role in the marine basins of Europe during the Jurassic (Dera et al, 2016;Neige et al, 2021;Rita et al, 2020). There is a growing body of evidence that belemnoids and their relatives preyed upon fish nearly as long as their mantle (Hart et al, 2020;Jenny et al, 2019;Keupp et al, 2010).…”