Invictibellatrix

MEANING: Unconquered female warrior

PERIOD: Early Cretaceous

CONTINENT: Europe

Invictibellatrix is a megaraptoran theropod that lived during the Early Cretaceous period in what is now England. It is the first megaraptoran discovered in Europe, shedding light on how this group diversified and dispersed throughout the Cretaceous. Invictibellatrix is relatively small for a megaraptoran, at an estimated 3-4 m in total body length.

Abstract from paper: Theropod remains from the Lower Cretaceous Wessex Formation of the Isle of Wight, U.K., are rare and often fragmentary, making the phylogenetic placement of several species questionable. Based on first-hand observations and micro-CT scan data, we present a previously undescribed braincase from the Wessex Formation (NHMUK PV R6775). It represents the first braincase referrable to a non-avian coelurosaur from the U.K., and a phylogenetic analysis that included 88 taxa and 1760 characters recovered it as a megaraptoran. This makes it among the oldest known megaraptorans, and new megaraptoran synapomorphies found by this analysis, and present in this specimen, include a rounded, subrectangular occipital condyle, prominent subcondylar recesses and a unique foramen magnum to occipital condyle ratio (FOR). Theropod braincases are often described as morphologically and phylogenetically conservative, but the new braincase characters identified here potentially provide useful data that might help refine theropod phylogeny. For example, these features differ from those of other theropod groups, in which the occipital condyle is dorsoventrally depressed and kidney-shaped (early-branching theropods), sub-spherical (Abelisauroidea), spherical (Spinosauridae) or elliptical (Carcharodontosauridae and Maniraptora). The occipital condyle of the new specimen is slightly larger than the foramen magnum, differing from Abelisauroidea and Carcharodontosauridae (in which the occipital condyle is significantly smaller than the foramen magnum) and maniraptorans (in which it is significantly larger), but it is similar to those of the megaraptorans Murusraptor and Megaraptor. The specimen differs from tyrannosaurids, such as Daspletosaurus, due to a significantly different FOR and from other non-tyrannosaurid tyrannosauroids, such as Guanlong, due to the shape of the foramen magnum. The FOR has distinctive trends across different theropod clades. The new specimen can be distinguished from the two other known megaraptoran braincases (those of Megaraptor and Murusraptor) by its possession of the following autapomorphies: a small basipterygoid recess is present anterior to the -asisphenoid recess on each side of the parabasisphenoid, a slightly compressed hourglass shaped sagittal nuchal crest in posterior view and the presence of two large, deep, dorsoventrally elongate paracondylar recesses on the ventrolateral sides of the basioccipital. Globally, three-dimensionally preserved braincases of early-diverging coelurosaurs are rare and often incomplete, so this new specimen provides important information for understanding their evolution, and also supports the nesting of Megaraptora within Coelurosauria. This new specimen increases our knowledge of Early Cretaceous European tyrannosauroids, hints at a Laurasian origin of Megaraptora and might indicate a greater diversity of these taxa than previously suspected.

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Invictibellatrix is from the Early Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Early Cretaceous making up roughly the first half, lasting from about 143 to 100 million years ago. The poles were ice-free, due to the relatively warm climate, and forests extended into high latitudes. The continued breakup of the continents created new coastlines and isolated landmasses, influencing the evolution of distinct dinosaur faunas.

It was a time of transition, as many groups of animals and plants began to take on more modern forms while others declined or disappeared. Pterosaurs continued to thrive, though early birds were becoming more diverse and widespread. Mammals remained small but adapted to a variety of ecological niches. In the oceans, ichthyosaurs and plesiosaurs were common, and early mosasaurs began to appear.

Dinosaurs remained the dominant land animals, with groups like iguanodontians, spinosaurids, and carcharodontosaurids rising to prominence. While sauropods declined in some regions, they remained abundant in the Southern Hemisphere. The first true ceratopsians appeared, and ankylosaurs replaced stegosaurs in their niche. Dromaeosaurs and other small theropods diversified. During this time, the first flowering plants evolved, gradually changing global ecosystems by providing new food sources for herbivores.

Invictibellatrix is a megaraptoran. Megaraptora is a group of large predatory theropods that lived during the Cretaceous Period. They were most diverse in South America, but they had a widespread distribution. Despite their name, megaraptorans are not closely related to the smaller dromaeosaur “raptors”. Instead, they represent a distinct lineage of large-bodied predators that occupied apex roles in their ecosystems, though their exact phylogenetic affinities are not clear. Different studies place them among coelurosaurs, carnosaurs, or as a distinct branch within allosauroid theropods, reflecting ongoing uncertainty in their phylogenetic relationships.

The most distinctive feature of megaraptorans is the enlarged, recurved claws on their forelimbs, which in some species exceeded 30 centimeters in length. These claws, combined with long, powerful arms and lightly built skeletons, suggest they were agile hunters that relied heavily on grasping and slashing during predation. Their skulls were relatively lightly built compared to other large theropods, and they likely used their forelimbs as their primary weapons. Fossil evidence indicates they persisted into the Late Cretaceous, making them some of the last surviving large predatory dinosaurs in the Southern Hemisphere.