Moros intrepidus
Early tyrannosauroid from the Late Cretaceous of Utah.
Moros is a genus of small, carnivorous tyrannosauroid dinosaur from the Late Cretaceous of what is now Utah. The only known species is *Moros intrepidus*. It is among the earliest definitive tyrannosauroid fossils found in North America.
The first remains were discovered in 2013 at the Stormy Theropod site in Emery County, Utah, after a decade of research in the area. Limb bones protruding from a hillside led to an excavation. The species was formally described in February 2019 by a team including Lindsay E. Zanno, Ryan T. Tucker, Aurore Canoville, Haviv M. Avrahami, Terry A. Gates, and Peter J. Makovicky. The genus name comes from the Greek *Moros*, a spirit of impending doom, referencing how this lineage would later dominate North America by the end of the Cretaceous. The species name *intrepidus* is Latin for "intrepid," alluding to the hypothesized dispersal of tyrannosauroids from Asia into North America after *Moros* arrived.
The holotype specimen (NCSM 33392) was collected from the lower Mussentuchit Member of the Cedar Mountain Formation, which dates to the Cenomanian age, with a maximum age of 96.4 million years. It consists of a right leg—the thighbone, shinbone, second and fourth metatarsals, and the third and fourth phalanges of the fourth toe. Growth lines in the bones show it was a subadult, six or seven years old, nearly full-grown. Two premaxillary teeth (specimens NCSM 33393 and NCSM 33276) have also been assigned to the species.
*Moros* was a small, fast-running tyrannosauroid, with an estimated leg length of 1.2 meters (3.9 feet) and a body mass of about 78 kilograms (172 pounds). Its foot bones were very slender, with metatarsal proportions closer to those of ornithomimids than to other Late Cretaceous tyrannosauroids.
Phylogenetic analysis by Zanno and colleagues in 2019 placed *Moros* as a basal pantyrannosaurian, closely related to mid-Cretaceous Asian taxa like *Xiongguanlong* and *Timurlengia*. This connection suggests *Moros* was part of a well-documented exchange of animals between Asia and North America during the mid-Cretaceous.
Quick Facts
- Genus
- Moros
- Species
- intrepidus
Facts from the source article.
Lore & Background
Moros was first discovered at the Stormy Theropod site in Emery County, Utah. Palaeontologists had been researching the area for ten years when, in 2013, limb bones were seen jutting out of a hillside, prompting the excavation. The bones were described as a new species in February 2019. The type species, Moros intrepidus, was named and described by Lindsay E. Zanno, Ryan T. Tucker, Aurore Canoville, Haviv M. Avrahami, Terry A. Gates, and Peter J. Makovicky. The generic name is derived from the Greek term Moros (an embodiment of impending doom), in reference to the establishment of the tyrannosauroid lineage in North America that would soon dominate the continent by the end of the Cretaceous. The specific name is the Latin word intrepidus ('intrepid'), referring to the hypothesized dispersal of tyrannosauroids from Asia throughout North America following the arrival of Moros.
The holotype specimen, NCSM 33392, was found in the lower Mussentuchit Member of the Cedar Mountain Formation dating from the Cenomanian age. The layer has a maximum age of 96.4 million years. The holotype consists of a right leg, specifically the thighbone, shinbone, second and fourth metatarsal, and the third and fourth phalanx of the fourth toe. Lines of arrested growth indicate that it represents a subadult individual of six or seven years old, nearing its maximum size. Additionally, two premaxillary teeth were referred to the species, specimens NCSM 33393 and NCSM 33276.
Reader's Guide
Moros intrepidus is significant as one of the earliest diagnostic tyrannosauroid fossils from North America, filling a critical gap in the evolutionary history of tyrannosauroids on the continent. Its small body size—estimated leg length of 1.2 m and body mass of 78 kg—contrasts with the later, larger tyrannosaurids that dominated the end of the Cretaceous. The foot bones of Moros were extremely slender, with metatarsal proportions more similar to ornithomimids than to other Late Cretaceous tyrannosauroids, suggesting a cursorial lifestyle. Phylogenetic analyses recovered Moros as a basal pantyrannosaurian alongside Asian taxa such as Xiongguanlong and Timurlengia, indicating a transcontinental exchange between Asia and North America during the mid-Cretaceous. This dispersal event, hypothesized in the specific name intrepidus, marks the arrival of the lineage that would eventually produce apex predators like Tyrannosaurus rex. The holotype's lines of arrested growth show it was a subadult of six or seven years, nearing its maximum size, providing insight into growth rates of early tyrannosauroids.
Did You Know?
- The generic name Moros comes from the Greek term for an embodiment of impending doom.
- The holotype specimen consists of a right leg, including the thighbone, shinbone, and parts of the foot.
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