Evaluating the ecology of Spinosaurus: shoreline generalist or aquatic pursuit specialist?

Abstract

The giant theropod Spinosaurus was an unusual animal and highly derived in many ways, and interpretations of its ecology remain controversial. Recent papers have added considerable knowledge of the anatomy of the genus with the discovery of a new and much more complete specimen, but this has also brought new and dramatic interpretations of its ecology as a highly specialised semi-aquatic animal that actively pursued aquatic prey. Here we assess the arguments about the functional morphology of this animal and the available data on its ecology and possible habits in the light of these new finds. We conclude that based on the available data, the degree of adaptations for aquatic life are questionable, other interpretations for the tail fin and other features are supported (e.g., socio-sexual signalling), and the pursuit predation hypothesis for Spinosaurus as a "highly specialized aquatic predator" is not supported. In contrast, a 'wading' model for an animal that predominantly fished from shorelines or within shallow waters is not contradicted by any line of evidence and is well supported. Spinosaurus almost certainly fed primarily from the water and may have swum, but there is no evidence that it was a specialised aquatic pursuit predator.

Population modelling insights of extinct environments: the case of the Kem Kem palaeocommunity

“…There is also evidences indicating that this species was mainly piscivorous [6]. Despite these adaptations for active pursuing, Spinosaurus probably was a shoreline generalist [26]. This is in line with some observations that spinosaurids were not strictly piscivorous [20,25].…”

New spinosaurids from the Wessex Formation (Early Cretaceous, UK) and the European origins of Spinosauridae

“…It has been suggested that spinosaurids became increasingly aquatic during their evolution 15 and that highly modified taxa like Spinosaurus engaged in specialised underwater pursuit predation 7,8 . However, the sequence by which semiaquatic adaptations were acquired, and the degree of specialisation to aquatic life in Spinosaurus and other spinosaurids, remain debatable and the topic of ongoing research [16][17][18][19] .The majority of spinosaurid material comes from Early and "mid" Cretaceous strata, although isolated dental remains suggest persistence of the group into the Late Cretaceous (Santonian) 20 . Views on how spinosaurids relate to other theropods, and on the relationships within Spinosauridae itself, are controversial.…”

“…It has been suggested that spinosaurids became increasingly aquatic during their evolution 15 and that highly modified taxa like Spinosaurus engaged in specialised underwater pursuit predation 7,8 . However, the sequence by which semiaquatic adaptations were acquired, and the degree of specialisation to aquatic life in Spinosaurus and other spinosaurids, remain debatable and the topic of ongoing research [16][17][18][19] .…”

Contributions to a Discussion of Spinosaurus aegyptiacus as a Capable Swimmer and Deep-Water Predator

“…During propulsion, it facilitates lateral flexion of the trunk and sail in concert with tail undulations, similar to flexion of the body and dorsal fin in unison with undulations of the caudal fin in carangiform fish with their strong dorsal musculature. Despite the recent discovery of the swim tail, Hone and Holtz [ 40 ] question the lifestyle of Spinosaurus as an aquatic predator. In their elaborate discussion of the pros and cons of Spinosaurus’ adaptations, they use a more massive skeletal model than that published by Ibrahim et al [ 5 , 7 ].…”