First adequately-known quadrupedal sirenian from Eurasia (Eocene, Bay of Biscay, Huesca, northeastern Spain)

Abstract

Sirenians are the only extant herbivorous mammals fully adapted to an aquatic lifestyle. They originated in Africa during the Paleocene from an undetermined clade of afrotherian mammals, and by the end of the Eocene they were widely distributed across the tropical latitudes. Here we introduce Sobrarbesiren cardieli gen. et sp. nov. It is the first adequately-known quadrupedal sirenian from Eurasia and the oldest record of this clade from western Europe. Fossils have been recovered from the middle Lutetian (SBZ15) site of Castejón de Sobrarbe-41 (Huesca, Spain), and comprise many cranial and postcranial remains, including pelvic girdle and hind limb bones, from at least six sirenian individuals of different ontogenetic stages. Sobrarbesiren shows a suite of characters previously considered synapomorphies of different clades of derived sirenians, such as the presence of the processus retroversus of the squamosal and the pterygoid fossa, combined with ancestral characters such as the presence of an alisphenoid canal, a permanent P5, at least two sacral vertebrae, a primitive pelvis and functional femora and fibulae. Sobrarbesiren is recovered as the sister taxon of Dugongidae and represents a transitional stage of adaptation to aquatic life between the amphibious quadrupedal prorastomids and the aquatic quadrupedal protosirenids.

The most representative vertebrate fossil record and palaeontological heritage from the western Pyrenees

“…The remains recovered in the Pamplona Basin and in the Urbasa-Andia Plateau (Basque-Cantabrian Region), range from the late Lutetian to the early Bartonian (middle Eocene, SBZ 16 and 17 biozones). These remains, together with those found in the Ainsa Basin, in the Castejón de Sobrarbe site (Huesca; middle Lutetian, SBZ 15 biozone; Díaz-Berenguer et al, 2018a), correspond to the oldest sirenian specimens of the northeastern Atlantic coast (Bay of Biscay). Both the fossil collections of Navarre and Huesca are important fi nds and essential to study the fi rst stages of the evolutionary history of the sirenian mammals.…”

“…The most abundant sirenian material comes from Arrasate and consists of axial elements and one appendicular bone. The sirenian remains of these localities correspond to the oldest sirenian fossils from Eurasia, together with the remains from the Castejón de Sobrarbe site in Huesca (Díaz-Berenguer et al, 2018a). Both the Arrasate and Lezaun sites contain a great amount of geological (see Payros et al, 2010 for an interpretation of shallow-marine carbonate sedimentary environments developed under greenhouse conditions) and palaeontological information (rich invertebrate fossil assemblages).…”

The Hind Limbs of Sobrarbesiren cardieli (Eocene, Northeastern Spain) and New Insights into the Locomotion Capabilities of the Quadrupedal Sirenians

“…This stem sirenian from the northeastern Atlantic coast (Bay of Biscay) is represented by a very complete skeleton including the skull, ribs, vertebrae, pectoral and pelvic girdle bones, and fore and hindlimb elements. To date, Sobrarbesiren is the first adequately known quadrupedal sirenian from Eurasia, and has been hypothesized to represent a transitional stage of adaptation to aquatic life between the amphibious prorastomid Pezosiren and the aquatic quadrupedal protosirenid Protosiren (Díaz-Berenguer et al 2018). This paper presents a microanatomical and morphofunctional analysis of the hindlimbs of Sobrarbesiren in order to test this hypothesis.…”

“…Sirenians originated in Africa during the Paleogene from an indeterminate clade of afrotherian mammals (Domning et al 1982;Hautier et al 2012;Benoit et al 2013, among others), and as early as the middle Eocene were widely distributed across the western and eastern Atlantic coasts and across the Tethyan Realm (e.g., Gingerich et al 1995a;Domning 2001a;Bajpai et al 2009;Astibia et al 2010;Domning et al 2010;Díaz-Berenguer et al 2018). Domning (2000) proposed three different stages of adaptation to aquatic life, represented by the families Prorastomidae, Protosirenidae and Dugongidae.…”

“…In the Pyrenean region, Eocene sirenian remains are scarce and fragmentary, and the most complete fossils are assigned to the genus Prototherium (e.g., Pilleri et al 1989;Balaguer and Alba 2016). The exception is the sirenian fossil remains found in the middle Lutetian site of Castejón de Sobrarbe-41 (Huesca, Spain), which were described as Sobrarbesiren cardieli (Díaz-Berenguer et al 2018) (Fig. 1).…”