Xenoposeidon is the earliest known rebbachisaurid sauropod dinosaur

Abstract

Xenoposeidon proneneukos is a sauropod dinosaur represented by a single partial dorsal vertebra, NHMUK R2095, which consists of the centrum and the base of a tall neural arch.Despite its fragmentary nature, it is recognisably distinct from all other sauropods, and is here diagnosed with five unique characters. One character previously considered unique is here recognised as shared with Rebbachisaurus garasbae: an "M"-shaped arrangement of laminae on the lateral face of the neural arch. Following the more complete Rebbachisaurus garasbae, these laminae are now interpreted as ACPL and lateral CPRL, which intersect anteriorly; and PCDL and CPOL, which intersect posteriorly. Similar arrangements are also seen in some other rebbachisaurid specimens (though not all, possibly due to serial variation), but never in non-rebbachisaurid sauropods. Xenoposeidon is therefore referred to Rebbachisauridae. Due to its elevated parapophysis, the holotype vertebra is considered a posterior dorsal despite its elongate centrum. Since Xenoposeidon is from the from the Berriasian-Valanginian (earliest Cretaceous) Ashdown Beds Formation of the Wealden Supergroup of southern England, it is the earliest known rebbachisaurid by some 10 million years. Electronic 3D models were invaluable in determining X e n o p o s e i d o n i s t h e e a r l i e s t k n o wn r e b b a c h i s a u r i d s a u r o p o d d i n o s a u rMichael P. Taylor. Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, England. dino@miketaylor.org.uk Ab s t r a c tXenoposeidon proneneukos is a sauropod dinosaur represented by a single partial dorsal vertebra, NHMUK R2095, which consists of the centrum and the base of a tall neural arch. Despite its fragmentary nature, it is recognisably distinct from all other sauropods, and is here diagnosed with five unique characters. One character previously considered unique is here recognised as shared with Rebbacdisaurus garasbae: an "M"-shaped arrangement of laminae on the lateral face of the neural arch. Following the more complete Rebbacdisaurus garasbae, these laminae are now interpreted as ACPL and lateral CPRL, which intersect anteriorly; and PCDL and CPOL, which intersect posteriorly. Similar arrangements are also seen in some other rebbachisaurid specimens (though not all, possibly due to serial variation), but never in non-rebbachisaurid sauropods. Xenoposeidon is therefore referred to Rebbachisauridae. Due to its elevated parapophysis, the holotype vertebra is considered a posterior dorsal despite its elongate centrum. Since Xenoposeidon is from the from the Berriasian-Valanginian (earliest Cretaceous) Ashdown Beds Formation of the Wealden Supergroup of southern England, it is the earliest known rebbachisaurid by some 10 million years. Electronic 3D models were invaluable in determining Xenoposeidon's true affinities: descriptions of complex bones such as sauropod vertebrae should always provide them where possible.

Sauropod dinosaur teeth from the lower Upper Cretaceous Winton Formation of Queensland, Australia and the global record of early titanosauriforms

“…Berriasian deposits in the United Kingdom and Denmark have yielded sauropod teeth that are indeterminate, albeit not referable to either Diplodocoidea or Lithostrotia [293,294], whereas coeval deposits in France have produced indeterminate embryonic sauropod teeth [295] and remains of both turiasaurians and macronarians [296]. Slightly younger (upper Berriasian–lower Valanginian) deposits in the United Kingdom have yielded evidence of turiasaurians ([96]; although the exact provenance and age of this material is uncertain), the possible non-neosauropod eusauropod Haestasaurus [211,297–299], rebbachisaurids [300–302] and probable titanosauriforms [303–305]. Most Valanginian–Hauterivian sauropods from Europe (e.g.…”

The Late Jurassic sauropod dinosaur ‘Morosaurus’ agilisMarsh, 1889 reexamined and reinterpreted as a dicraeosaurid

“…The South American origin of the clade becomes less certain when we consider more fragmentary but nonetheless definitive rebbachisaurid specimens from the Early Cretaceous of England, including Xenoposeidon (Taylor, 2018) and unnamed, isolated specimens that come from younger horizons within the Wealden Supergroup (Mannion, 2009;Mannion et al, 2011). The lower-level phylogenetic affinities of these fragmentary species are uncertain, although the Wealden material has been suggested to have rebbachisaurine affinities (Mannion et al, 2011(Mannion et al, , 2019.…”

Nuevos Restos De Rebaquisáuridos Desde La Formación Huincul (Cenomaniano Medio–turoniano Temprano) Del Centro De La Cuenca Neuquina, Patagonia, Argentina

“…Indeed, the recent description of Lingwulong from the Yanan Formation (upper Toarcian-Bajocian; late Lower-early Middle Jurassic) represents not only the earliest dicraeosaurid but also the oldest flagellicaudatan record, suggesting the presence of a ghost-lineage at least from the late Toarcian. Therefore, the putative Rebbachisauridae-Flagellicaudata divergence time-lapse would have happened during the Hauterivian, when the first rebbachisaurid occurrence was recorded (i.e., Histriasaurus; Dalla Vecchia, 1998, 2005, or even earlier if we consider the recent reassessment of Xenoposeidon from the Berriasian of England as a rebbachisaurid sauropod (Taylor, 2018). On the other hand, the incomplete dorsal neural arch AMNH-FR-5777 from the Morrison Formation (late Kimmeridgian-early Tithonian) that Cope (1878) described as the holotype of "Amphicoelias fragillimus", was recently considered as a basal rebbachisaurid by Carpenter origin and evolution, the validity of the taxon is still debated (Whitlock & Wilson Mantilla, 2020), especially considering the impossibility to access and review the holotype.…”

“…Lyddeker (1893); Taylor & Naish (2007); Taylor (2018) The specimens are listed following their chronostratigraphic provenances, from most modern to earliest. The numbers and symbols refer to the landmarks of Figure 8.…”