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

Abstract

Although belemnites form a major clade of extinct cephalopods, the early stage of their diversification remains poorly known in time and space. Here we investigate the first diversification episodes of belemnites (order Belemnitida) using a new species‐level database encompassing the Hettangian–Aalenian interval (Early Jurassic – earliest Middle Jurassic) and covering the Western Tethys. Rarefied richness shows a four‐fold increase from the Planorbis chronozone to the Ibex chronozone, a strong decrease between the Margaritatus and Spinatum chronozones, followed by a drop in the Spinatum–Serpentinum interval that is coeval with the second‐order Toarcian biological crisis. The Bifrons chronozone records a high richness that departs significantly from those of the surrounding chronozones. A last richness peak in the Dispansum chronozone precedes a decrease towards the Aalenian. Biogeographical analyses do not reveal any clear large‐scale provincialism for belemnites, in sharp contrast with ammonoids. Such a long‐term homogeneous spatial distribution of belemnites is probably due to: (1) the relatively poorly‐documented fossil record of belemnites, especially in Mediterranean localities; and (2) contrasted dispersal abilities of belemnites compared to ammonoids over the studied time interval.

Refining the marine reptile turnover at the Early–Middle Jurassic transition

“…This reduces the uncertainty on the timing and duration of this turnover to 4 instead of 14 million years and packs a series of extinctions and diversifications within a short period of abrupt climate cooling and changes in oceanic currents (Korte et al, 2015). This Aalenian shift from a Toarcian Warm Mode to Aalenian-Bajocian Cool Mode (Korte et al, 2015) also appears associated with a marked faunal disruption in belemnites, where random (i.e., non-morphologicallyselective) extinctions lead to a distinct drop in belemnite biodiversity at least in the northwestern Peri-Tethys Ocean (Dera, Toumoulin & de Baets, 2016;Neige, Weis & Fara, 2021). This major disruption in the evolutionary history of Jurassic belemnites ended at the Aalenian-Bajocian boundary and resulted in a radiation of the suborder Belemnopseina that partially replaced the previously dominant Belemnitina in the Western Tethys (Weis, Mariotti & Riegraf, 2012;Weis, Sadki & Mariotti, 2017), furthermore entailing a distinct Boreal vs. Tethyan belemnite provincialism (Doyle, 1987;Mariotti, Santantonio & Weis, 2007;Mariotti et al, 2012;Dzyuba et al, 2019).…”

Morphological response accompanying size reduction of belemnites during an Early Jurassic hyperthermal event modulated by life history

“…1 ), additionally indicates harsh conditions during the T-OAE 48 . Belemnites are among the organisms that suffered considerably during this crisis 48 – 52 . Their abundance in the fossil record 48 , 53 – 55 , and rapid response to environmental changes, makes these predators suitable for studying responses to past climate changes.…”

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).…”