[Papers in Palaeontology, 2020, pp. 1–29] TAXONOMICAL DIVERSITY AND PALAEOBIOGEOGRAPHICAL AFFINITY OF BELEMNITES FROM THE PLIENSBACHIAN– TOARCIAN GSSP (LUSITANIAN BASIN, PORTUGAL) by PATRICIA RITA1,2 , ROBERT WEIS3,LUIS V. DUARTE2,4 and KENNETH DE BAETS1 1Geozentrum Nordbayern, Friedrich–Alexander University Erlangen–Nurnberg,€ Erlangen, 91054, Germany; [email protected]; [email protected] 2MARE (Marine and Environmental Sciences Centre), 3004-517, Coimbra, Portugal; [email protected] 3Department of Palaeontology, National Museum of Natural History Luxembourg, L-2160, Luxembourg, Luxembourg; [email protected]; 4Department of Earth Sciences, University of Coimbra, 3070-790, Coimbra, Portugal Typescript received 25 May 2020; accepted in revised form 26 August 2020 Abstract: High-resolution analysis of the late Pliens- Pliensbachian and early Toarcian (emaciatum and polymor- bachian – early Toarcian belemnite assemblages from the phum Zones), in the north-west Tethys. Despite the lack of a Peniche section (Lusitanian Basin) has enabled, for the first marked taxonomic turnover, the Pliensbachian–Toarcian time, recognition of eight taxa of the suborder Belemnitina, boundary corresponds to a slight decrease in diversity previously reported from contemporaneous north-west Teth- observed not only in the Lusitanian Basin but also in coeval yan and Arctic sections. The presence of Bairstowius amaliae north-western European basins. Ordination and cluster anal- sp. nov. in the late Pliensbachian (emaciatum Zone) repre- yses indicate that the largest changes in belemnite diversity sents a novelty given that hitherto the genus Bairstowius was and palaeogeographical distribution occurred rather during known only from late Sinemurian and early Pliensbachian the Toarcian Oceanic Anoxic Event (base of the levisoni deposits. Additionally, the replacement of Bairstowius ama- Zone). This event is marked by the extinction of taxa, affect- liae by Catateuthis longiforma, during the latest Pliens- ing more severely the Mediterranean/Submediterranean bachian, suggests an evolutionary relationship between the domain and resulting in a more pronounced provincial dif- two taxa. This relationship suggests a new scenario for the ferentiation among north-western European and Arctic subsequent development of endemic Toarcian Boreal–Arctic belemnite faunas. faunas, characterized by the occurrence of Catateuthis. Com- parison of the Peniche belemnite fauna with coeval faunas Key words: belemnite, diversity, palaeobiogeography, from the Mediterranean/Submediterranean and Euro-Boreal Pliensbachian–Toarcian boundary, Toarcian Oceanic Anoxic domains indicates taxonomic uniformity during the late Event, Lusitanian Basin. B ELEMNITES are coleoid cephalopods that originated in et al. 2003; Pinard et al. 2014), and the lack of high-reso- the Late Triassic (Iba et al. 2012), rapidly radiated in the lution (ammonoid subzone) analysis of the belemnite Early Jurassic and subsequently played a key role in mar- assemblages in particular localities (Choffat 1880; Riegraf ine ecosystems (Weis & Delsate 2006; Dera et al. 2016; 1980; Mouterde et al. 1983; Schlegelmilch 1998). Addi- Hoffmann & Stevens 2019). The Pliensbachian–Toarcian tionally, many studies on Toarcian belemnites are focused interval (Early Jurassic) is considered a major bottleneck on the Euro-Boreal basins (Riegraf et al. 1984; Doyle in belemnite early evolutionary history (Dera et al. 2016), 1990, 1992; Little 1995; Schlegelmilch 1998; Morten & probably related to major palaeoenvironmental and Twitchett 2009; Caswell & Coe 2014; Xu et al. 2018), palaeogeographical changes during the Toarcian. However, whereas little is known from the Mediterranean/ the study of belemnite diversity during this time-interval Submediterranean domain (Lissajous 1927; Combemorel has been hampered by a variety of factors, including the in Rulleau et al. 1998; Sanders et al. 2015; Weis et al. poor stratigraphic representation of the Pliensbachian– 2015). Therefore, palaeobiogeographical patterns, diversifi- Toarcian boundary in many European sections (Morard cation patterns and evolutionary trends of Early Jurassic © 2020 The Authors. doi: 10.1002/spp2.1343 1 Papers in Palaeontology published by John Wiley & Sons Ltd on behalf of The Palaeontological Association This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 2 PAPERS IN PALAEONTOLOGY RITA ET AL.: DIVERSITY AND BIOGEOGRAPHY OF BELEMNITES 3 FIG. 1. Stratigraphic distribution and absolute abundance of belemnite species (per bed and per m2) in the Peniche section (Lusita- nian Basin, Portugal). Fewer than two occurrences per bed are not represented (see Rita et al. 2020, tables S1–S2 for the full dataset). The Pliensbachian–Toarcian boundary event and the Toarcian Oceanic Anoxic Event (T-OAE) are highlighted and were positioned based on Rocha et al. (2016) and Duarte et al. (2018). Sequence stratigraphy according to Duarte (2007). The bed numbers in square brackets correspond to merged beds due to sample size constraints, regarding the Peniche diversity analysis, and follow Rita et al. (2019). Stratigraphic log based on Rita et al. (2019). Ammonite zonation and subzonation from Mouterde (1955) and Rocha et al. (2016), respectively. Lithostratigraphy from Hesselbo et al. (2007). Bed numbers from Rita et al. (2019). Abbreviations: BG, belemnite gap; elisa, elisa/hawskerense Subzone; mir., mirabile/paltum Subzone; solare, solare/apyrenum Subzone. belemnites, in the north-west Tethys, remain poorly con- of the Iberian margin belemnite fauna allows, for the strained and some aspects of their provincialism remain first time, a comparison of diversity patterns at an speculative (Doyle 1994). ammonite zone and subzone scale across the Mediter- During the Pliensbachian, the north-west Tethys was ranean/Submediterranean and Euro-Boreal domains. This characterized by a homogeneous European belemnite comparative approach permits an assessment of the fauna (Doyle et al. 1994; Weis & Thuy 2015). However, impact of the Pliensbachian–Toarcian crisis on belemnite the early Toarcian, characterized by palaeoenvironmental diversity and a better understanding of the palaeobio- changes and the second-order mass extinction (Toarcian geographical belemnite dynamics during the Early Juras- Oceanic Anoxic Event, T-OAE), represents an important sic of the north-west Tethys. period of taxonomic and geographical changes in belem- nite assemblages, leading to a Boreal/Tethyan provincial- ism (Doyle 1994; Dera et al. 2016). In the Euro-Boreal GEOLOGICAL SETTING basins, belemnites recovered and experienced a radiation during the middle–late Toarcian (Dera et al. 2016), The Peniche section corresponds to the Toarcian GSSP despite the effects of the T-OAE during the early Toar- (Rocha et al. 2016) and it is well constrained in terms of cian, which caused a reduction in belemnite abundance ammonite zonation (Duarte & Soares 2002; Duarte et al. (Caswell & Coe 2014). The belemnite stratigraphic 2018). It is located in the Lusitanian Basin, a Mesozoic record in the Mediterranean/Submediterranean domain sedimentary basin developed in the Iberian Western Mar- basins (Italy, Portugal and Morocco) displays a severe gin during the North Atlantic Ocean and Occidental reduction in belemnite abundance, or total absence of Tethyan opening, as a consequence of the Pangea frag- belemnites, during the T-OAE (latest polymor- mentation (Thierry et al. 2000; Kullberg et al. 2013). The phum – early levisoni Zones; Sanders et al. 2015; Weis first sedimentary cycle (Wilson et al. 1989) corresponds et al. 2015; Ait-Itto et al. 2017; Rita et al. 2019). More- to extension and rifting episodes and occurred during the over, the Toarcian marks the beginning of the endemism Late Triassic – Middle Jurassic (Callovian). It led to the of Arctic faunas, probably related to northward migra- deposition, among others, of a marly limestone succession tions of north-west Tethyan groups (Doyle 1987; Doyle related to the large opening of the carbonate ramp to the et al. 1994), which survived regionally during the early marine environment (Duarte & Soares 2002; Azer^edo Toarcian crisis, and their rapid evolution into new ende- et al. 2003; Azer^edo et al. 2014). mic genera (Sachs & Nalnjaeva 1975; Meledina et al. The studied section corresponds to a marly limestone 2005; Dzyuba et al. 2015). succession, 45 m thick, assigned to the upper Pliens- In this study we present for the first time a detailed bachian – lower Toarcian interval, corresponding to an systematic description of the Lusitanian Basin belemnite outer ramp environment in an epicontinental sea (Duarte fauna from the late Pliensbachian to the early Toarcian, & Soares 2002; Duarte 2007; Duarte et al. 2018; Fig. 1). and a diversity analysis. This study is based on a high- The end of the Pliensbachian, represented by the Lemede resolution stratigraphic analysis of more than 900 speci- Formation, corresponds to an alternation of decimetric mens collected in the Toarcian GSSP Peniche section. marly limestones and centimetric marls, 11.2 m thick. The excellent outcrop conditions, and the abundant The next c. 11 m of the succession, belonging to the belemnite fauna of the Peniche section, enable, on Toarcian (polymorphum Zone), corresponds to the first the one hand, a detailed analysis of intraspecific and member of the Cabo Carvoeiro Formation (CC1)