Fossil of Carnivorous Dinosaur Reveals Evolutionary Clues

(CN) – A mysterious new species of small to medium-sized, feathered, carnivorous dinosaur that lived during the Cretaceous Period has been recently discovered in New Mexico.

In a study published Thursday in the journal Scientific Reports, scientists describe how this fossil further deepens our understanding of dinosaur evolution during the Late Cretaceous period from approximately 70 million years ago.

Skeletal reconstruction of Dineobellator notohesperus. (Drawing based off work by Scott Hartman / Scientific Reports)

The creature known as Dineobellator notohesperus belongs to the family dromaeosaurid, which comes from the Greek word dromeus (runner) and sauros (lizard), though they were the most bird-like of all the dinosaurs. In fact, scientists now believe that sometime in the Jurassic period they shared a common ancestor with birds.

Though smaller than its relative Velociraptor depicted in the hit film “Jurassic Park,” the Dineobellator was likely just as lethal. Ranging in height from 2 to 20 feet – the tallest ever discovered stood at 36 feet – they were extremely quick and agile and had excellent eyesight, sharp talons for slashing, muscular jaws with sharp teeth and large brains for their size. They walked on two feet and had a sickle-shaped claw on the second toe of each foot known as the killing claw, though unlike other theropods they lifted this toe off the ground while in motion and instead used it for climbing and killing prey.

The hunters’ tails had stiff bones that extended down from the vertebrate, which are thought to have allowed the tail to function as a stabilizer for balance during quick motion. “Think of when a cheetah pursues a gazelle and you may be able to imagine the cheetah’s tail whipping back and forth as it changes direction to catch the gazelle,” said study author Steven Jaskinski. “Dineobellator may have been able to do a similar thing as the base of its tail was highly mobile but the rest of its tail would have been stiffened. It would act as a rudder and counterbalance, making Dineobellator especially adept at pursuit hunting.”

They also had a unique wrist joint that allowed their hands to flex sideways which – like modern birds – allowed it to achieve the flight stroke. In 1999, scientists found one member of the dromaeosaurid family, the Sinornithosaurus, had feathered wings and evidence of a venom pouch. In short, they were some of the most effective predators of their time.

Study author Steven Jasinski, from the State Museum of Pennsylvania in Harrisburg, and his colleagues discovered 20 identifiable skeletal elements of the Dineobellator buried in the deposits of the Ojo Alamo Formation in the San Juan Basin, New Mexico. This formation is well known for its sandstone rich in dinosaur fossils.

In their study, the authors describe several of this dinosaur’s unique features including a vertebra near the base of the tail that curved inward which could signify the Dineobellator possessed increased agility and improved its predation success. Also, they report a gouge mark on the fossil’s sickle-shaped claw and speculate it could have been sustained during an altercation with another Dineobellator or other theropod such as Tyrannosaurus rex.

“A distinct mark on the claw suggests Dineobellator got into a fight with another member of its species. While two Dineobellator could fight for multiple reasons, the two most likely reasons would be fighting over resources, especially in a pack for things like food, or fighting over a mate,” Jasinksi said.

Fossils from this family group have been discovered on nearly every continent except Australia, but this is the first fossil documenting the Dineobellator. Its name comes from the Navajo word Diné, meaning Navajo people, and the Latin word bellator, meaning warrior.

The dromaeosaurid family consists of 35 different genera and spans across 5 subfamilies. Six of these genera have been found in North America with an abundance of them in what is now Alabama. Some of the most prominent finds have been a Velociraptor tooth in west-central Alabama, a near complete Bambiraptor in Montana, and an 11-foot tall predator named Deinonychus, or terrible claw, in Montana and Wyoming.

Ancestors of the Dineobellator are currently thought to have migrated from Asia to North America where multiple lineages may have evolved. The Acheroraptor, known to roam North America 66 million years ago, was discovered in Asia in 2013 closely resembling the native Velociraptorines. This explanation potentially accounts for the differences in morphology between Dineobellator and other dromaeosaurids.

These findings successfully contribute to the sparse fossil records of dromaeosaurids. They indicate that this family continued to diversify at the end of the Cretaceous period prior to the mass extinction that wiped out nonavian dinosaurs 65.5 million years ago.

“Previously we didn’t have any good fossil material from dromaeosaurids in the southern United States or southern North America at the end of the Cretaceous, and indeed material from this group just before the extinction is rare worldwide,” Jasinski said. “This helps show us that these dinosaurs were still diversifying, still trying out new features and evolutionary pathways, even up to their catastrophic end.”

Jasinski notes that as the days of the dinosaurs were cut short by a large-scale event from space, we are doing the same to many modern species.

“We fear that the same thing may be happening to animals today, only instead of a meteorite, or large-scale volcanism, people may be the cause of much of it,” Jasinski said. “If we understand what happened with extinctions in the past, including iconic groups like dinosaurs, we may gain a better understanding of what we may be changing our world into as well.”

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