Old African fossils provide new evidence for the origin of the American crocodiles

Abstract

Molecular and morphological phylogenies concur in indicating that the African lineages formerly referred to Crocodylus niloticus are the sister taxon the four Neotropical crocodiles (Crocodylus intermedius, C. moreleti, C. acutus and C. rhombifer), implying a transoceanic dispersal from Africa to America. So far the fossil record did not contribute to identify a possible African forerunner of the Neotropical species but, curiously, the oldest remains referred to the African C. niloticus are Quaternary in age, whereas the oldest American fossils of Crocodylus are older, being dated to the early Pliocene, suggesting that another species could be involved. We re-described, also thanks to CT imaging, the only well-preserved topotipic skull of Crocodylus checchiai Maccagno, 1947 from the late Miocene (Messinian) African site of As Sahabi in Libya. As previously suggested on the basis of late Miocene material from Tanzania, C. checchiai is a valid, diagnosable species. According to our phylogenetic analyses, C. checchiai is related to the Neotropical taxa and could be even located at the base of their radiation, therefore representing the missing link between the African and the American lineages. Extant crocodylians are represented by 25 species grouped into 9 genera 1. The most speciose and widespread genus is Crocodylus Laurenti, 1768 that hosts 12 species inhabiting a longitudinally very broad intertropical belt ranging from Australia to South Asia, to Africa and then America. The origin of Crocodylus was placed in the late Miocene (about 13.6-8.3 Ma) of Asia by Oaks 2 , on the basis of a time-calibrated species tree stemming from a DNA analysis, and recently reconstructed as Asian by Nicolai and Mazke 3 on the basis of historical biogeography models. Both the molecular 2,4,5 and the morphological/palaeontological 6-9 approaches, as well as the shared presence of parasites 10 concur in indicating that the origin of the American clade of Crocodylus should be sought in Africa. The four American species Crocodylus intermedius, C. moreleti, C. acutus and C. rhombiferare grouped together with the African Crocodylus niloticus Laurenti, 1768, which is placed at the base of the American branch. According to Meredith et al. 5 , the most parsimonious explanation that takes into consideration both the phylogenetic results and the fossil record of Crocodylus supports a relatively recent transAtlantic crossing of "C. niloticus" from Africa to America. The reason of the inverted commas placed by these authors around the name of Nile crocodile is related to the fact that the eastern and western clades of this species do not cluster together, but are arranged in paraphyly at the base of the American clade, a result shared by different authors applying different molecular techniques 2,4,5,11,12. Hekkala et al. 5 eventually proposed the resurrection of the name Crocodylus suchus Geoffroy Saint-Hilaire, 1807 for the western populations, keeping the name C. niloticus for the (predominantly) eastern populations that is directly at the ...

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

“…Crocodylinae seems to have diversified in the Miocene (Densmore, 1983;Brochu, 2000;Oaks, 2011), with the first appearances of both the sub-Saharan African taxon Mecistops (Tchernov, 1986;Pickford, 1994;Storrs, 2003;Brochu, 2020) and species of the crown genus Crocodylus (Brochu, 2000;Brochu & Storrs, 2012), which corresponds well with molecular divergence estimates for the origins of these genera (Oaks, 2011;Pan et al, 2021). Late Miocene Crocodylus comprises C. palaeindicus in Indo-Pakistan (Lydekker, 1886;Mook, 1933), C. checchiai from north and east Africa (Maccagno, 1947;Delfino, 2008;Brochu & Storrs, 2012;Delfino et al, 2020), C. niloticus in sub-Saharan Africa (Storrs, 2003;Brochu & Storrs, 2012) and possibly in the northwest of the continent too (e.g. Zouhri et al, 2012), and indeterminate occurrences that extend the distribution of the genus into southern Europe (Kotsakis, Delfino & Piras, 2004;Delfino, Böhme & Rook, 2007;Delfino et al, 2021;Delfino & Rook, 2008;Delfino & Rossi, 2013) and possibly even Central America (Carbot-Chanona, 2017) (Fig.…”

“…Gatesy et al, 2003;Schmitz et al, 2003;Willis, 2009;Oaks, 2011;Man et al, 2011;Lee & Yates, 2018;Pan et al, 2021;Hekkala et al, 2021); and (5) the species interrelationships of the crown genus Crocodylus, as well as the resulting biogeographic implications (e.g. Meganathan et al, 2010;Meredith et al, 2011;Oaks, 2011;Nicolaï & Matzke, 2019;Delfino et al, 2020Delfino et al, , 2021.…”

A Pliocene–Pleistocene continental biota from Venezuela

“…from the Pliocene Ware Formation of Colombia (Moreno-Bernal et al 2016), C. falconensis is still considered the oldest well-known record of true crocodylids in South America (Cidade et al 2019a). A recent phylogenetic analysis refined the position of Crocodylus falconensis to within the extant New World crocodiles and Crocodylus intermedius being the sister taxon to the remaining species (Delfino et al 2020).…”

Late Miocene remains from Venta del Moro (Iberian Peninsula) provide further insights on the dispersal of crocodiles across the late Miocene Tethys

“…Further remains of C. checchiai from As Sahabi were later described by Delfino (2008), but it is thanks to the new material from the Turkana Basin (Kenya) recently described by Brochu and Storrs (2012) that the phylogenetic relationships of this taxon have been further clarified, confirming its referral to Crocodylus . New evidence (Delfino et al, 2020) based on the revision of material originally described by Maccagno strengthens the referral of C. checchiai to Crocodylus by placing it at the base of the American extinct and extant species and, supporting and African American dispersal, testify for the dispersal abilities of the late Miocene crocodylids that inhabited the Mediterranean area. Other late Miocene crocodylians from Northern Africa have not been described and identified in detail, but worth mentioning are the materials from Tizi N'Tadderht (Morocco; Zouhri et al, 2012) and Djebel Krechem el Artsouma (Tunisia; Geraads, 1989).…”

“…C. niloticus Laurenti, 1768 whereas the Tunisian material has been referred to Crocodylus cf. C. checchiai but should be revised now that the morphology of the topotypic remains is better known than before (Delfino et al, 2020). The African C. checchiai is characterized by a set of features (among others, the mid-rostral boss) that are not accessible among the material from VM.…”