Aviatyrannis: Portugal’s very own Tyrannosaur… Maybe

Aviatyrannis, an illustration by Johan Egerkrans

Found in rocks dating back to the Late Jurassic period, this small theropod dinosaur might be the grandmother of the famous T. rex. However, new research is putting its classification into question.

Aviatyrannis was discovered by German paleontologist Oliver Rauhut in the year 2000 in Guimarota, a lignite coal mine in the district of Leiria, Portugal.

It was described in a paper published in 2003, and given the name Aviatyrannis jurassica, which aptly translates to ‘the tyrant's grandmother from the Jurassic’. It was a small theropod dinosaur, a term used to describe mostly meat eating predators like T. rex, Allosaurus, or Velociraptor, but also some dinosaurs with a more generalist diet like Gallimimus, Ornithomimus, or Deinocheirus, and even a branch of herbivores with long sharp claws like Therizinosaurus, one of the most recent additions to the cast of the Jurassic World franchise.

With an estimated length of 1 meter (3.3 ft) and a body mass of 4 kg (8.8 lb) it wouldn’t be much larger than a medium size dog. However, Rauhut believes that the holotype specimen he described was only a juvenile, meaning Aviatyrannis could potentially reach a larger size.

A holotype is a single type specimen upon which the description and name of a new species is based. In this case, Aviatyrannis’ holotype is named IPFUB Gui Th 1 and consists of an ilium, the bone that makes up the upper portion of the hip bone and pelvis, only ninety millimeters long (3.54 inches).

Oliver Rauhut also referred two other bones to this species, a partial right ilium, and a right ischium, another hip bone, that belonged to slightly larger individuals, along with sixteen isolated teeth.

Found in the Alcobaça Formation, a geological formation that dates back to about 155 million years ago, this would put Aviatyrannis as one of the oldest tyrannosaurs ever found. Currently, the oldest known ancestor of the mighty T. rex is Proceratosaurus, a three meter (9.8 ft) long dinosaur found in the UK, that lived about 166 million years ago.

However, a 2023 paper by a group of Japanese researchers lead by Soki Hattori had a closer look at Aviatyrannis’ holotype and reclassified it as an ornithomimosaur.

This team of paleontologists noted that this dinosaur’s ilium was strikingly similar to that of the recently described Tyrannomimus, a deinocheirid. Even though a more detailed study is needed, the authors argue that Aviatyrannis could be the earliest known ornithomimosaur and even possibly the earliest known deinocheirid.

Although not close as famous as Tyrannosaurs, Deinocheirids were a particular family of theropod dinosaurs. The most well-known was Deinocheirus, an unusual looking dinosaur that could grow to be 11 meters (36 ft) long, and weighing 6.5 metric tons (7.2 short tons).

If you’re familiar with the documentary series Prehistoric Planet, Deinocheirus makes an appearance in one episode, bathing in a swamp and, well, relieving himself to put it kindly.

Deinocheirus as portrayed in Apple TV’s Prehistoric Planet Episode ‘Freshwater’

It might not be as glamorous, but being the earliest known deinocheirid is in and of itself an interesting feat for such a small dinosaur found in the most unlikely of places.

Living among Giants

155 million years ago, during the Late Jurassic period, the region now known as Portugal was a lot different than it is today. Portugal was part of the northern margin of the supercontinent Laurasia, near the Tethys Ocean that would later become the Atlantic.

It had a warm tropical to subtropical climate with lush forests and shallow seas covering coastal areas.

Aviatyrannis lived alongside large meat eating dinosaurs like Allosaurus, and Ceratosaurus, giant sauropods like Lusotitan, Dinheirosaurus, and Lourinhasaurus, and even the thagomizer wielding Stegosaurus.  

It shared its environment with various species of fish, amphibians, turtles, lizards, and mammals. In the skies it would not be uncommon to spot the occasional pterosaur, like Rhamphorhynchus.

Much is yet to be known about Aviatyrannis but regardless of where it fell in the dinosaur family tree it already earned its place as one of the most intriguing creatures of Jurassic Portugal.