A new genus and species of stegosaur from the Middle Jurassic have been identified from postcranial remains found in the Middle Atlas Mountains south of Fez, Morocco.
Thyreosaurus atlasicus lived in North Africa during the Middle Jurassic period, approximately 165 million years ago.
Life reconstruction of Dacentrurus armatus , a sister species of Thyreosaurus atlasicus . Image credit: Sci.News.
The species is closely related to Dacentrurus , a member of the clade Dacentrurinae within the thyreophoran dinosaur family Stegosauridae.
“Thyreophora is a diverse clade of herbivorous ornithischian dinosaurs composed of stegosaurs, ankylosaurs, and basal forms,” said Dr. Mostafa Oukassou of Hassan II University in Casablanca and colleagues.
The partially disarticulated skeleton of Thyreosaurus atlasicus was found in the grey marls of the El Mers III Formation at the northern locality of Boulahfa, near Boulemane, in the Middle Atlas of Morocco.
“In 2021, during a geological mapping mission south of Boulemane, we discovered a new site rich in dinosaur remains in the El Mers III Formation,” the paleontologists said.
“This site, called Boulahfa North, is located north of the Boulahfa quarry.”
“The material was collected during several consecutive field trips and consists of a partial postcranial skeleton of a stegosaur that includes dorsal vertebrae and ribs, a limb bone, and dermal armor.”
According to the team, Thyreosaurus atlasicus had asymmetrical dermal armor, typical among stegosaurs.
“The dermal armor of Thyreosaurus atlasicus is made up of thick, up to 4 cm (1.6 in), subo-ovate to subrectangular osteoderms,” the researchers said.
“The asymmetrical texture of its sides, one roughly decorated with small pits and fiber bundles, the other with a well-marked cross-hatch pattern, is clearly different from that observed to date in other stegosaurs and ankylosaurs.”
“The bone histology of these osteoderms is reminiscent of that of the tail spines of stegosaurs.”
“These osteoderms are interpreted to have been arranged in a recumbent position on the animal’s body, rather than in an upright position.”
Thyreosaurus atlasicus had an estimated body length of over 6 m (19.7 ft).
The findings appear in the journal Gondwana Research .
