Paleontologists working in northern Italy have announced the oldest large-size predatory dinosaur known to the fossil record. Saltriovenator zanellaiweighed about a ton and, at nearly 200 million years old, predates more famous megapredators by at least 25 million years.
Saltriovenator’s bones are also the first dinosaur remains to preserve evidence of marine animals that gnawed on its carcass. The biggest thing about S. zanellai, however, may be its hands: The animal’s fingers could solve a long-running debate about how bird wings evolved.
Saltriovenator would be a source of significant national pride at any size: It’s the first Jurassic dinosaur ever found in Italy. But the animal’s robust build and estimated length of more than 24 feet make it especially noteworthy, because other predatory dinosaurs of the period were typically less stocky and much smaller. Even bigger news: Researchers believe the Saltriovenator speciman was a sub-adult, with plenty of growing left to do.
Dined-Upon After Death
The first pieces of the new dinosaur were found in a quarry in 1996 by amateur fossil enthusiast Angelo Zanella. Alas, quarrying explosives had blown apart the fossiliferous layers of rock, splintering many of the bones. Painstaking excavation, preparation and analysis of the material took decades, which is why the find is only being formally named and described now.
Eventually, the team recovered 132 fragments, enough to piece together 64 complete or partial bones and confirm nearly all the material was from a single individual. A single tooth and a jaw fragment found with Saltriovenator turned out to be from a bony fish, which hints at the dinosaur’s watery resting place — and a fascinating aspect of the find.
Researchers confirmed at least 30 bore marks on the bones from a variety of marine invertebrates that had nibbled on the carcass. It’s the first time this kind of marine bioerosion has been found on a dinosaur. It suggests that Saltriovenator’s carcass sank to the bottom of a shallow marine basin or similar body of water, and remained partially exposed to scavengers for some time.
Jurassic Spark
Finding a large-body predatory dinosaur from the Early Jurassic could help explain a curious trend in the fossil record from this period. Saltriovenator belongs to one of the major dinosaur lineages: Theropoda. Theropods were almost exclusively meat-eaters, and preyed on another major lineage, the herbivorous sauropodomorphs. The most famous of the sauropodomorphs were also among the last of their line to evolve, and include the aptly-named titanosaurs.
But let’s back up to the Late Triassic, which predates the Jurassic Period. At this time, well over 200 million years ago, most sauropodomorphs were significantly smaller than the giants that evolved much later. (There are a couple exceptions, such as Argentina’s Ingentia prima, described earlier this year.) Then, suddenly, in the Early Jurassic — when Saltriovenator was around — the sauropodomorphs start getting bigger and bigger.
A number of explanations for this trend toward gigantism have been proposed, but the discovery of Saltriovenator suggests that predator and prey may have been engaged in a size-based arms race during the Early Jurassic.
Winging It
While its size in life (and the evidence of what ate it after death) are intriguing, the most scientifically significant thing about Saltriovenator may be the story told in its fingers. Birds are the lone surviving dinosaur lineage; more specifically, they’re the last theropod dinosaurs around. How the earliest birds evolved wings is one of the most contentious hot spots in the field, right up there with the evolution of feathers.
Some researchers believe that bird wings are the result of the first, second and third digits of the theropod hand becoming fused; others think the fusion was of the second, third and fourth digits. According to the authors of today’s study, Saltriovenator, which had a stubby fourth digit, provides supporting evidence for the hypothesis that modern bird wings evolved from the first, second and third digits of a distant theropod ancestor.
This digit debate may sound like a minor issue to casual dinosaur fans, but supporting evidence for either hypothesis can be found in both the fossil record and developmental research into modern bird embryos. Figuring out how bird wings evolved could provide us with a better idea of how specific traits emerge in a species.
Simplified evolutionary tree of predatory dinosaurs (theropods). Saltriovenator predates the massive meat eating dinosaurs by over 25 million years. It is the oldest known ceratosaurian, and the world largest predatory dinosaur from the Lower Jurassic. During the Jurassic, the three-fingered tetanuran theropods appeared, which gave rise to birds.