Riojavenatrix

MEANING: La Rioja huntress

PERIOD: Early Cretaceous

CONTINENT: Europe

Riojavenatrix is one of the most recent baryonychines to have lived. Like other spinosaurids, it was a large bipedal theropod with specializations for feeding in aquatic habitats, and likely fed on fish, though it may have been a more versatile predator. Riojavenatrix is estimated to have grown up to 8 m in length, and weighed around 1.5 t in body mass.

Abstract from paper: A new member of Spinosauridae from the Enciso Group (uppermost Barremian–lower Aptian) from Igea (La Rioja, Spain) is here erected on the basis of axial, pelvic girdle, and hindlimb elements that exhibit a unique combination of characters. Riojavenatrix lacustris gen. et sp. nov. is one of the latest Iberian and European spinosaurid taxa. It retains a triangular pubic boot, like the megalosaurids, and a medial condyle of the femur that shows a transitional stage between the anteroposteriorly oriented long axis of non-spinosaurid theropods and the posteromedially oriented long axis of Spinosauridae. The spinosaurid record of Iberia ranges from the late Hauterivian–early Barremian to the latest Barremian–early Aptian so far, and both the oldest and the most recent evidence comes from the Cameros Basin, where spinosaurid remains are especially abundant in the Barremian deposits. A review of the spinosaurid record has allowed us to dismiss the presence of the genus Baryonyx from Iberia; hence, only Camarillasaurus, Iberospinus, Protathlitis, Riojavenatrix gen. nov., and Vallibonavenatrix are considered to be present in the Early Cretaceous of Iberia. According to this study, Riojavenatrix is one of the youngest baryonychines in the fossil record.

Riojavenatrix 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.

Riojavenatrix is a baryonychine spinosaurid. Baryonychinae is an early, distinctive branch of the Spinosauridae, a group of theropod dinosaurs best known for their crocodile-like skulls and semi-aquatic adaptations. Named after Baryonyx, baryonychines are typically characterized by their elongated, narrow jaws lined with numerous conical teeth, ideal for grasping slippery prey such as fish. Unlike more derived spinosaurines, baryonychines sometimes retain certain basal features, such as serrated teeth and more robust forelimbs with a large curved thumb claw, possibly used in fishing or manipulating prey. These dinosaurs walked on two legs and likely hunted both in water and on land, making them versatile predators in their ecosystems.

Baryonychines are primarily known from the Early Cretaceous of Europe and parts of Africa, with fragmentary remains also reported in South America and Asia. Their fossils are often found in environments that were once river systems or floodplains, supporting the interpretation of a semi-aquatic lifestyle. Baryonychines reveal the early evolutionary experimentation that led spinosaurids into niches rarely occupied by other large theropods.