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Description
Yanbeilong ultimus is the first of three new stegosaurian genera described in 2024, preceding Thyreosaurus and Baiyinosaurus. This unprecedented diversity is reflected by the fact that two new genera have never been named in the same year, let alone three! While the other two are early or basal taxa, Yanbeilong is the exact opposite, representing one of the youngest (most recent) stegosaurs confidently known in the fossil record. The holotype is known from the Zuoyun Formation (Albian, Early Cretaceous) of China.
The Yanbeilong holotype comprises a nearly complete series of dorsal and sacral vertebrae, a caudal vertebra, and much of the pelvis, all of which are notably distinct from Wuerhosaurus (one of the only other Cretaceous stegosaurs) and Stegosaurus (which it likely was closely related to). The holotype belongs to a fairly large individual, at about 6.5 meters long.
Shortly before the description of Yanbeilong was published, another paper announced stegosaur remains from the similarly aged Hekou Group of China. Due to very limited similarities to Stegosaurus, the authors assigned the specimen (GSAU 201201) to this genus, despite the extreme age discrepancy (along with Wuerhosaurus). Although the overlapping material with the Yanbeilong holotype is limited, hindering thorough comparison, the dorsal vertebrae of GSAU 201201 exhibit important similarities. An autapomorphic character of Yanbeilong is the ratio of the neural arch to neural canal height in the dorsal vertebrae. Yanbeilong is the only stegosaur where this number exceeds 4 (4.16–5.64 in this taxon). In GSAU 201201, the ratio also exceeds 5. Both specimens also have a unique protuberance on the anterior face of the centrum above the neural canal, which appears to be unique among stegosaurs. As such, I am informally referring to GSAU 201201 as "cf. ?Yanbeilong sp."
Despite the anatomical similarities of Yanbeilong and GSAU 201201, the unnamed latter specimen is much smaller, and may belong to an immature individual.
The Yanbeilong description paper can be found here.
The GSAU 201201 description paper can be found here.