T-Rex Wasn’t The Top Dino. This Predator May Have Been ‘King’ of All Dinosaurs, New Study Says

Researchers found the species not recognised earlier to be about 8 metres in body length, and greater than 1,000 kg in body mass

Left maxilla of Ulughbegsaurus. (a) Lateral, (b) medial, (c) ventral, (d) anterior and (e) posterior views. (f) Reconstruction of skull (grey missing bones are based on Neovenator, modified from Naish et al.) | Photo: The Royal Society

New Delhi: Dinosaurs lived on Earth in the Cretaceous period, for about 165 million years, and became extinct at the end of this period about 65 million years ago. The iconic Tyrannosaurus rex is infamously known to hold the top spot among dinosaurs during the Late or Upper Cretaceous period.

However, the Tyrannosaurus did not always dominate the top of the food web, a new study has found. 

Researchers led by the University of Tsukuba have described a new genus and species belonging to the Carcharodontosauria, which is a group of medium to large-sized predatory theropods (carnivorous bipedal dinosaurs), distributed worldwide during the Cretaceous period. 

Before the rise of tyrannosauroids (large, bipedal, carnivorous dinosaurs that existed in the late Cretaceous period), the probable apex predators of Asiamerica in the early Late Cretaceous period were the Carcharodontosauria, the study says. 

The researchers have mentioned in the study a species named Ulughbegsaurus uzbekistanensis, from the early Late Cretaceous or Turonian period, the second age in the Late Cretaceous epoch, of Central Asia. The study says that this species was the apex predator before the rise of tyrannosauroids, and is the first recorded Late Cretaceous carcharodontosaurian from Central Asia. 

Tyrannosauroids gained dominance after the disappearance of carcharodontosaurians and other large-bodied theropods (ceratosaurids and spinosaurids), during the last 20 million years of the Cretaceous.

The study was recently published in Royal Society Open Science. 

8 metres in body length, greater than 1,000 kg in body mass

The Bissekty Formation of the Kyzylkum Desert, the Republic of Uzbekistan, is a geologic formation harbouring many fossils of dinosaurs and other vertebrates. In this formation, a large and isolated fossil of a left maxilla (upper jawbone) was found, and was compared with the maxilla of other allosaurids (large bipedal carnivorous dinosaurs of the late Jurassic period), the study states. 

Upon comparing the maxillae, the researchers found the new species to be about eight metres in body length, and greater than 1,000 kg in body mass. The researchers note that the presumed body length and mass were suggestive of the fact that Ulughbegsaurus uzbekistanensis was the apex predator of the Bissekty formation, but was not recognised earlier. 

Also, smaller known tyrannosauroids were probable mesopredators, or mid-ranking predators.

Assistant Professor Kohei Tanaka, the first author of the study, said a theropod dinosaur’s body size could be estimated from the size of the maxilla because there is a correlation between the femur length and maxilla size, according to a University of Tsukuba statement. He also said the new dinosaur was of the size of a full-grown elephant. The study also notes that femur length is an indication of body mass.

The study states that the estimated size of the newly named dinosaur was significantly greater than that of other carnivorous dinosaurs from the Bissekty formation, including Timurlengia, which was a small tyrannosauroids with a body length of three to four metres, and a body mass of about 170 kg. Therefore, this indicated the fact that Ulughbegsaurus uzbekistanensis was probably the ‘king’ of all dinosaurs in the early Late Cretaceous period, according to the study.

The study explains that the taxon is the latest known coexistence between a carcharodontosaurian and a tyrannosauroid. The study also states that this species represents one of the latest surviving carcharodontosaurians in Laurasia.

Why Ulughbegsaurus uzbekistanensis?

The genus name, Ulubhbegsaurus, has been taken from the name of the Timurid sultan Ulugh Beg, who was an astronomer and mathematician in 15th century Central Asia. And since the fossil was discovered in Central Asia region, which is present-day Uzbekistan, uzbekistanensis has been used as the species name, the study states. Also, ‘Sauros’ means reptiles in Latin.

Why did Ulughbegsaurus disappear?

Ulughbegsaurus, along with other carcharodontosaurians, disappeared from Central Asia before the Late Cretaceous period, probably because of the ascent of tyrannosauroids as top predators, the study states. The researchers note that due to the scarcity of theropod remains in the lower Upper Cretaceous or the early Late Cretaceous, the transition of the apex predators is poorly understood.

Why is this discovery important?

The researchers say the discovery of Ulughbegsaurus increases their understanding of the dinosaur-dominated ecosystems of early Late Cretaceous Laurasia. It represents the first definitive fossil evidence of carcharodontosaurians from Central Asia. Thus, its discovery shows that carcharodontosaurians were widespread across Asia, the study states. Professor Yoshitsugu Kobayashi, senior author of the study, said the transition of the apex predator niche during the Late Cretaceous period could be understood better due to the discovery of the co-occurrence of a large predator like Ulughbegsaurus and a smaller tyrannosauroid in Laurasia, according to a statement by the University of Tsukuba.