page_title: Jianianhualong
section_title: Skull
hierarchical_section_title: Jianianhualong / Description / Skull
caption_attribution_description: en.wikipedia.org/wiki/Mei_(dinosaur) www.tynhm.com/china/
context_page_description: Jianianhualong is a genus of troodontid theropod dinosaur from the Early Cretaceous of China. It contains a single species, Jianianhualong tengi, named in 2017 by Xu Xing and colleagues based on an articulated skeleton preserving feathers. The feathers at the middle of the tail of Jianianhualong are asymmetric, being the first record of asymmetrical feathers among the troodontids. Despite aerodynamic differences from the flight feathers of modern birds, the feathers in the tail vane of Jianianhualong could have functioned in drag reduction whilst the animal was moving. The discovery of Jianianhualong supports the notion that asymmetrical feathers appeared early in the evolutionary history of the Paraves.
  Jianianhualong possesses a combination of traits seen in basal as well as traits seen in derived troodontids. This is consistent with its phylogenetically intermediate position among the troodontids. This mixture of traits shows a distinct spatial organization, with basal traits being present in the forelimbs and pelvis, and derived traits being present in the skull and hindlimbs.
context_section_description: The skull of Jianianhualong is small and sub-triangular, with a short snout and a wide skull roof like Mei.The frontmost-preserved bone of the snout is the maxilla, the main body of which is taller than long. This contrasts Jianianhualong from all other members of the Troodontidae, along with the top margin of the bone forming a large angle of 45° with the bottom margin. The rear branch of the bone is also deep, like derived troodontids but unlike Sinovenator.
  Behind the maxilla, the indentation known as the antorbital fossa bears two large openings (the antorbital fenestra and the elongated, enlarged maxillary fenestra) that stretch from the top margin to the bottom margin of the fossa; Sinovenator, Sinornithoides, and Sinusonasus have one additional opening known as the promaxillary opening. The bar of bone separating the fenestrae is narrow, like in Sinovenator.
  The lacrimal bone, encircling the fossa from above and behind, has a long forward-projecting branch much like other troodontids. However, the descending branch of the bone is also nearly the same length, and the descending branch also bears a unique ridge on its front portion. The nasal bone is short and broad like Mei. The inner surface of the frontal suggests details about the braincase, including the widened olfactory tract and back of the cerebrum. Compared to Sinovenator, the forward branch of the postorbital bone is not as long.
  Overall, the lower jaw is subtriangular when viewed from the side, with a straight top margin and a curved bottom margin; it is not downturned, unlike Sinovenator. The dentary bone is long (occupying half of the jaw's length), shallow, and triangular, and it bears a groove that widens towards the back of the bone. A distinct fossa on the top surface of the surangular bone separates Jianianhualong from other troodontids. The angular bone projects upwards behind the dentary, like Sinovenator and various other members of the Deinonychosauria.
  The maxilla of Jianianhualong bore 21 teeth on each side, while the dentary bore 25 on each side. Like other troodontids, the teeth are short-crowned, strongly recurved, and unevenly distributed. The teeth at the front of the jaws are more closely packed than the rear teeth, which also have fine serrations on their rear edges. These serrations are fine, as in Sinovenator, instead of robust as in derived troodontids. Unusually, the first several teeth in the dentary appear to be angled forwards, or procumbent. This condition is present in several contemporary dromaeosaurids.
caption: Fossilized skeleton of Mei long, showing the subtriangular skull
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