The Anatomy and Phylogenetic Relationships of “Pelorosaurus“ becklesii (Neosauropoda, Macronaria) from the Early Cretaceous of England

Abstract

The sauropod dinosaur “Pelorosaurus” becklesii was named in 1852 on the basis of an associated left humerus, ulna, radius and skin impression from the Early Cretaceous (Berriasian-Valanginian) Hastings Beds Group, near Hastings, East Sussex, southeast England, United Kingdom. The taxonomy and nomenclature of this specimen have a complex history, but most recent workers have agreed that “P.” becklesii represents a distinct somphospondylan (or at least a titanosauriform) and is potentially the earliest titanosaur body fossil from Europe or even globally. The Hastings specimen is distinct from the approximately contemporaneous Pelorosaurus conybeari from Tilgate Forest, West Sussex. “P.” becklesii can be diagnosed on the basis of five autapomorphies, such as: a prominent anteriorly directed process projecting from the anteromedial corner of the distal humerus; the proximal end of the radius is widest anteroposteriorly along its lateral margin; and the unique combination of a robust ulna and slender radius. The new generic name Haestasaurus is therefore erected for “P.” becklesii. Three revised and six new fore limb characters (e.g. the presence/absence of condyle-like projections on the posterodistal margin of the radius) are discussed and added to three cladistic data sets for Sauropoda. Phylogenetic analysis confirms that Haestasaurus becklesii is a macronarian, but different data sets place this species either as a non-titanosauriform macronarian, or within a derived clade of titanosaurs that includes Malawisaurus and Saltasauridae. This uncertainty is probably caused by several factors, including the incompleteness of the Haestasaurus holotype and rampant homoplasy in fore limb characters. Haestasaurus most probably represents a basal macronarian that independently acquired the robust ulna, enlarged olecranon, and other states that have previously been regarded as synapomorphies of clades within Titanosauria. There is growing evidence that basal macronarian taxa survived into the Early Cretaceous of Europe and North America.

The earliest known titanosauriform sauropod dinosaur and the evolution of Brachiosauridae

“…The anteromedial proximal process is longer than the anterolateral process (ratio =1.35). This value is similar to many sauropods, but is considerably lower than in the brachiosaurids Cedarosaurus and Venenosaurus (Mannion et al, 2013; Upchurch, Mannion & Taylor, 2015). In anterior view, the articular surface of the anteromedial proximal process is not concave, differing from the morphology seen in most titanosaurs (Upchurch, 1995; Upchurch, 1998), as well as some non-titanosaurian taxa, e.g., Giraffatitan (D’Emic, 2012).…”

“…In anterior view, the articular surface of the anteromedial proximal process is not concave, differing from the morphology seen in most titanosaurs (Upchurch, 1995; Upchurch, 1998), as well as some non-titanosaurian taxa, e.g., Giraffatitan (D’Emic, 2012). The posterior proximal process is much smaller than the other proximal processes, lacking the ‘T’ shaped proximal end outline that characterizes many titanosaurs (Upchurch, Mannion & Taylor, 2015). …”

Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover

“…In sauropods, this extinction is focused on broad-toothed non-neosauropod eusauropods and narrow-toothed diplodocids , with just two occurrences known from the Cretaceous (Gallina et al, 2014;McPhee et al, 2016), and is followed by the diversification of rebbachisaurids and titanosauriforms . The earliest Cretaceous therefore represented a 'transitional' phase in sauropod evolution (Upchurch et al, 2015b), a pattern also found in Asia, with the replacement of non-neosauropods by titanosauriforms across the J/K boundary (Wilson & Upchurch, 2009;Mannion et al, 2013).…”

“…This pattern is geographically focused in taxa from Europe and North and South America, with Africa and Asia relatively unaffected . However, the precise details and magnitude of this diversity reduction are obfuscated by relatively poor preservation, sampling, and dating of earliest Cretaceous dinosaur-bearing terrestrial exposures, particularly in Gondwana, North America, and Asia Upchurch, Mannion & Taylor, 2015b; Fig. 5A).…”

“…Late Jurassic representatives of Neosauropoda, comprising Macronaria and Diplodocoidea, were present on all sampled continents except Asia, and this diverse clade crossed the J/K boundary Mannion et al, 2011). Basal macronarians are only known to have survived into the earliest Cretaceous at least in Europe Upchurch et al, 2015b) and North America (D'Emic & Foster, in press), although overall titanosauriform diversity was seemingly unaffected across the J/K boundary Mannion et al, 2013). Cretaceous brachiosaurid diversity appears to have plummeted (or even reduced to zero) outside of North America (D'Emic, 2012; Mannion et al, 2013) and Africa (McPhee et al, 2016), although the clade possibly expanded into the northern tip of South America (Carballido et al, 2015), whilst Somphospondyli experienced a global radiation (D'Emic, 2012;Mannion et al, 2013).…”