When even a peer-reviewed scientific paper refers to a group of dinosaurs as “bizarre” you know these stand out even among the terrible lizards. Our knowledge of spinosaurids is lacking compared to other dinosaur lineages, not helped by the fact the bones with which the family was named were destroyed in World War II. However, a reassessment of one specimen could help us understand the evolution of these enormous semi-aquatic predators.
At around 15 meters (50 feet) long Spinosaurus was the largest terrestrial carnivore to ever live. Despite a starring role in Jurassic Park III, it never achieved the public recognition of Tyrannosaurs, perhaps because it lived in Africa and fewer fossils have been found. Spinosaurids are a family of around a dozen genera that shared with Spinosaurus crocodile-like skulls and retracted nostrils, indicating a semi-aquatic lifestyle — though that is far from confirmed. Many, although not all, had the enormous sails on their backs that gave the original species their name.
Spinosaurids’ evolution has been particularly obscure; for 50 million years the few fossils that might be from their ancestors also have alternative explanations, leading palaeontologists to refer to a “ghost lineage”. A new paper in PLOS ONE argues a debated specimen, known as ML1190, could partially fill the gap.
ML1190 was discovered in 1999 in 125 million-year-old Portuguese rocks, and was first described in 2011. Several efforts have been made since to establish where it fits on the dinosaur family tree. Where many specimens are nothing but a single bone or tooth, quite a lot of ML1190 has survived, but generally in bad condition, with almost as many fragments of teeth and ribs as intact bones.
Octåvio Mateus and Dario Estraviz-Lòpez of Portugal's NOVA School of Science and Technology argue ML1190 represents a new species, which they call Iberospinus Natarioi, and consider an early spinosaurid. Previous descriptions have mostly considered ML1190 a member of the Baryonyx genus, sometimes placing it in the familiar species B. walkeri.
Iberospinus was a fish-eater that waded through rivers and swampland in search of food, the authors conclude, although it probably also consumed other prey that died near riverbanks or foolishly ventured close. They do not estimate a total size, but it was probably similar in length to B. walkeri’s estimated 9 meters (30 feet).
Although many spinosaurids, including the largest, lived in Africa, the authors conclude the clade probably originated in Western Europe, and most likely from the Iberian peninsula, long before the period when high sea levels turned Iberia into an island. Nevertheless, even if Iberospinus fills in some of the missing chunks of time, 30 million years of spinosaurid evolution remains a mystery, and only the discovery of some Jurassic fossils will fill this in.
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