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| Invictibellatrix amberina with contemporary fauna in the lower part of the Wessex Formation. Morrison, Scherer, Mannion, Porro, Clark, Folkes & Barrett, 2026 Artwork by Sergey Krasovskiy and Pedro Salas |
Abstract
Theropod dinosaur remains from the Barremian (Lower Cretaceous) Wessex Formation of the Isle of Wight, UK, are rare and often fragmentary. Here, we present a previously undescribed braincase from this formation that represents a new coelurosaurian, Invictibellatrix amberina gen. et sp. nov. Phylogenetic analysis and comparative anatomy indicate that Invictibellatrix is distantly related to all previously named theropods from this stratigraphic unit. Theropod braincases are often regarded as morphologically and phylogenetically conservative, but we demonstrate that neurocranial characters provide essential data that can help clarify the phylogenetic relationships of theropods. The sub-circular occipital condyle, sub-oval foramen magnum and presence of a sagittal nuchal crest indicate that Invictibellatrix is referable to Megaraptora, with phylogenetic analyses recovering it as an early-diverging member of this clade, within a paraphyletic array of Eurasian taxa. Incorporation of Invictibellatrix into a biogeographical analysis suggests that non-megaraptorid megaraptorans likely had a cosmopolitan distribution in the Early Cretaceous, and that the absence of megaraptorans in the Late Cretaceous of Laurasia is best explained by regional extinction. The recognition of this new genus increases our knowledge of Early Cretaceous European coelurosaurian diversity, which now includes tyrannosauroids, maniraptoriforms and megaraptorans.
Keywords: megaraptora, endocast, Early Cretaceous, theropod, dinosaur, biogeography, Wessex Formation
Systematic palaeontology
Dinosauria Owen, 1842
Saurischia Seeley, 1888
Theropoda Marsh, 1881
Tetanurae Gauthier, 1986
Coelurosauria Huene, 1914
Megaraptora
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| Photographs of the holotype braincase (NHMUK PV R6775) of Invictibellatrix amberina gen. et sp. nov. in A: anterior, B: posterior; C: right lateral; D: left lateral; E: ventral; F: dorsal views. Abbreviations: atr, anterior tympanic recess; boc, basioccipital crest; bpr, basipterygoid recess; bsr, basisphenoid recess; bt, basal tubera; btw, basituberal web; CN, cranial nerves V, VII; cp, cultriform process; cvl, crista ventrolateralis of basisphenoid; fm, foramen magnum; oc, occipital condyle; ova, fenestra ovalis; pcr, paracondylar recess; pit, depression of the pituitary gland within the pituitary fossa; pp, paraoccipital process; prp, preotic pendant; psncr, parasagittal nuchal crest recess; scr, sub-condylar recess; snc, parasagittal nuchal crest; sok, supraoccipital knob; sta, sella turcica. Scale bar equals 50 mm. |
Invictibellatrix amberina gen. et sp. nov.
Etymology: the generic name Invictibellatrix is derived from the Latin ‘invictus’ (‘unconquered’) and ‘bellatrix’ (‘warrior’ in the feminine form) and honours the future role of Megaraptora as Gondwanan apex predators, while early on in their evolutionary history they were smaller, non-apex predators [55–57]. This name is to give hope and strength to all those who are bullied, discriminated, victimized and oppressed that tomorrow will be theirs and not to give up in the face of such odds. The species epithet amberina is derived from the amber present in the plant debris beds of the Wessex Formation [58].
Locality and horizon: Sudmoor Point, near Brook, southwestern coast of the Isle of Wight, UK; Wessex Formation, Barremian, Lower Cretaceous. Most likely from the lower plant debris beds (L1 to L5).
Holotype: NHMUK PV R6775, a partial braincase.
Diagnosis: Invictibellatrix amberina can be diagnosed by the following unique character combination (autapomorphies marked with an asterisk): (i) *presence of a small basipterygoid recess anterior to the anterior tympanic recess (ATR) on each side of the parabasisphenoid, (ii) *slightly transversely compressed, hourglass-shaped nuchal crest, (iii) the presence of two large, deep and dorsoventrally elongate paracondylar recesses on the ventrolateral sides of the basioccipital, and (iv) *parasagittal nuchal crest recesses that are slightly curved and pronounced.
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| An artist's illustration of the new theropod dinosaur, Invictibellatrix amberina (center of the image), in its ecosystem on the Isle of Wight, United Kingdom, in the Early Cretaceous (around 120 million years ago). It lived in what was likely a seasonally wet-to-dry floodplain environment and is surrounded by other dinosaurs including large long-necked rebbachisaurid sauropods (directly behind Invictibellatrix, center) and relatives of Iguanodon (right). A spinosaurid theropod, potentially the apex predator of the time, fishes (left). Invictibellatrix has just caught and is consuming two small mammals. Gymnosperms dominate the environment as flowering plants (angiosperms) were not common at this time. Other reptiles including relatives of modern lizards, crocodiles and turtles enjoy the warm Early Cretaceous weather of the U.K. Artwork by Sergey Krasovskiy and Pedro Salas |
Cassius Morrison; Charlie R. Scherer; Philip Mannion; Laura B. Porro; Brett Clark; Daniel D. Folkes; Paul M. Barrett. 2026. A new megaraptoran dinosaur from the Lower Cretaceous Wessex Formation, UK, and its implications for theropod evolution and biogeography. R. Soc. Open Sci. 13(10): 260937. DOI: doi.org/10.1098/rsos.260937 [14 Oct 2026]
