Description and Classification

Riojavenatrix was a medium-sized carnivorous dinosaur, walking on two legs. Scientists estimate it grew to be about 7 to 8 meters (23 to 26 feet) long and weighed around 1.5 metric tons. As a member of the Spinosauridae family, Riojavenatrix likely had an elongated, crocodile-like snout filled with conical teeth, which were well-suited for grasping slippery prey like fish. While a complete skull has not yet been found for Riojavenatrix, its classification suggests it would share many features with its relatives.

This dinosaur belongs to a group within the spinosaurids called Baryonychinae. This subfamily includes other well-known dinosaurs such as Baryonyx from England and Suchomimus from Niger. Baryonychines are characterized by their robust forelimbs, often with a large, hooked claw on the first finger (thumb), and relatively taller, less elongated snouts compared to some other spinosaurids. The discovery of Riojavenatrix is important because it is one of the youngest known baryonychines found in Europe, suggesting this group survived longer on the continent than previously thought.

Distinguishing Features

While fossils of Riojavenatrix are incomplete, scientists have identified features that help distinguish it from other dinosaurs, particularly other spinosaurids:

• It possessed unique characteristics in its vertebrae (backbones) and pelvic bones that set it apart as a new genus and species.
• As a baryonychine spinosaurid, it would likely have had strong forelimbs, possibly equipped with a large thumb claw used for hunting or defense, similar to its close relative Baryonyx.
• Its teeth were likely conical and not blade-like, ideal for gripping fish, a common trait among spinosaurids.
• The timing of its existence, late in the Early Cretaceous, makes it one of the last known members of the Baryonychinae subfamily in Europe.

Paleoenvironment and Diet

Riojavenatrix lived in an environment in ancient Spain that was characterized by extensive river systems, lakes, and floodplains. The Enciso Group, where its fossils were found, provides evidence of such a watery landscape. This type of habitat would have been rich in fish, which were likely the primary food source for Riojavenatrix. Its specialized snout and teeth were perfectly adapted for a piscivorous (fish-eating) diet. It may have waded into shallow waters or hunted from the banks, snatching fish with its long jaws.

In addition to fish, Riojavenatrix might have opportunistically preyed on other small animals, including small dinosaurs or pterosaurs, if the chance arose. It shared its world with other dinosaurs, including plant-eating iguanodontians and sauropods, as well as other theropods, creating a complex ecosystem.

Significance and Ongoing Research

The discovery of Riojavenatrix is significant for several reasons. It increases our knowledge of the diversity of spinosaurid dinosaurs in Europe during the Early Cretaceous. Its presence in rocks dating to the Barremian age extends the known time range of baryonychine spinosaurids in this region, indicating they thrived there for a considerable period. This finding helps paleontologists piece together the evolutionary history and geographic distribution of these fascinating predators.

Ongoing research on Riojavenatrix will involve further detailed study of its known fossils. Scientists will continue to compare its anatomy with that of other spinosaurids, like Vallibonavenatrix also from Spain, to better understand its relationships within the family. Future fossil discoveries in the La Rioja region could provide more complete remains of Riojavenatrix, offering clearer insights into its appearance, biology, and behavior. This “Rioja huntress” adds another important piece to the puzzle of dinosaur life in ancient Iberia.