Longirostrine crocodylians from the Bartonian of Morocco and Paleogene climatic and sea level oscillations in the Peri-Tethys area

Abstract

The Eocene-Oligocene transition was a period of high faunal and floral turnover, often correlated with climatic deterioration. Crocodyliforms are climate sensitive, and they have been often used for reconstruction of paleoclimates. The description of crocodylian material from the Bartonian of Aaiun-Tarfaya Basin (Morocco) allows the recognition of at least two longirostrine crocodylians, including a gavialoid. This identification is important, because the migration of gavialoids to South America probably occurred during the late Eocene. Close relationships between late Eocene-early Oligocene Eogavialis africanum from Egypt, Argochampsa krebsi from the Paleocene of Morocco, and the South American gavialoid clade suggests that Morocco could have had a particular place in the gavialoid dispersal route to South America. The resemblance between Moroccan material described herein and E. africanum is thus important in this context. Analysis of the distribution of longirostrine crocodylians in the Peri-Tethys area through the Eocene-Oligocene shows a strong difference in the evolution of the distribution between longirostrine crocodylians and Diplocynodon. Whereas the freshwater Diplocynodon has a continuous distribution in western Europe, the mainly marine longirostrine crocodylians have a northern maximal expansion that moves southward during the middle Eocene, being restricted to North Africa during late Eocene-early Oligocene. European freshwater Asiatosuchus-like taxa also disappear during the late Eocene. Climatic deterioration, helped by sea level oscillations, may have strongly impacted the diversity and latitudinal distribution of the crocodylians, but we highlight a possible differential tolerance in range of climatic conditions between crocodylians. This could help to refine the use of crocodylians as paleoclimatic proxies.

Phylogenetic analysis of a new morphological dataset elucidates the evolutionary history of Crocodylia and resolves the long-standing gharial problem

“…In our topology, these taxa are successively nested, with Argochampsa in a more crownward position than Aktiogavialis. Either scenario results in long ghost lineages and supports the hypothesis of a trans-Atlantic dispersal of gavialoids in the Paleogene (Buffetaut, 1982;Langston & Gasparini, 1997;Brochu & Rincón, 2004;Delfino, Piras & Smith, 2005;Salas-Gismondi et al, 2016;Jouve, Khalloufi & Zouhri, 2019) or latest Cretaceous (e.g. Jouve et al, 2021).…”

“…This dearth of Oligocene occurrences characterises much of the global record of Crocodylia in general (Markwick, 1998;Mannion et al, 2019;De Celis, Narváez & Ortega, 2020;Solórzano et al, 2020). Although sampling bias almost certainly plays a role in this apparent decline, it also likely reflects genuine latitudinal range retraction during the Eocene-Oligocene transition (Markwick, 1998;Martin, 2010a;Mannion et al, 2015;Whiting & Hastings, 2015;Jouve, Khalloufi & Zouhri, 2019;Macaluso et al, 2019;Stocker, Brochu & Kirk, 2021), which was characterised by global cooling and increased aridity (e.g. Zachos et al, 2001;Zanazzi et al, 2007;Hren et al, 2013;Li et al, 2016).…”

Miocene fossils from the southeastern Pacific shed light on the last radiation of marine crocodylians

“…Marine crocodylians were essentially shallow marine inhabitants. These environments have been proposed for several taxa of gavialoids by taphonomic, geologic, and isotopic data [12–19,22,54] and are consistent with their locomotion-related anatomy. Because marine crocodylians show no significant differences in the axial skeleton and the hindlimbs relative to living forms, they are inferred to have swum by using axial undulatory movements and terrestrial-adapted limbs (plesiopedal) [55].…”

“…Fossils suggest that several extinct gavialids had marine habits since they have been recovered from contexts depicting a wide range of salinities, including marginal to fully marine areas (e.g. [12][13][14][15][16][17][18][19]). These fossils are documented from most landmasses and such broad distribution requires crossing sea barriers to be explained [20][21][22].…”

Paleocene resurrection of a crocodylomorph taxon: Biotic crises, climatic and sea level fluctuations

“…This diversity rise despite the fall of the temperature, is surprising as the crocodyliforms are considered as a climate sensitive group (Markwick, 1998a(Markwick, , 1998bCarvalho et al, 2010;Martin et al, 2014;Mannion et al, 2015). Was there a differential tolerance between both tethysuchian lineages as suggested between some eusuchians lineages (Martin, 2010;Lance, 2003;Jouve et al, 2019)?…”