Xingxiulong
Skull and jaw
### Skull and jaw

[thumb\|left\|Detail of the skull and jaw of *Xingxiulong*](/wiki/File:Xingxiulong-3.jpg "Xingxiulong-3.jpg")
Unlike the contemporary *[Lufengosaurus](/wiki/Lufengosaurus "Lufengosaurus")*, *Xingxiulong* does not have a ridge on the side of its [maxilla](/wiki/Maxilla "Maxilla"). Eleven tooth sockets are preserved along the length of the maxilla. Further back, in front of the eye socket, the [lacrimal](/wiki/Lacrimal_bone "Lacrimal bone") bears a prominent projection near the top of its front end, which is also seen in *Lufengosaurus*, *[Adeopapposaurus](/wiki/Adeopapposaurus "Adeopapposaurus")*, *[Massospondylus](/wiki/Massospondylus "Massospondylus")*, and *[Riojasaurus](/wiki/Riojasaurus "Riojasaurus")*, but not *[Yunnanosaurus](/wiki/Yunnanosaurus "Yunnanosaurus")*, *[Jingshanosaurus](/wiki/Jingshanosaurus "Jingshanosaurus")*, or subsequent sauropodiforms. The contact surface between the [jugal bone](/wiki/Jugal_bone "Jugal bone") and [postorbital bone](/wiki/Postorbital_bone "Postorbital bone") is fairly long, like *Lufengosaurus* but not *Yunnanosaurus*. Among the three branches of the jugal, the backwards\-directed branch forms an angle of 80° with the upwards\-projecting branch, which is similar to *[Plateosaurus](/wiki/Plateosaurus "Plateosaurus")* and *[Thecodontosaurus](/wiki/Thecodontosaurus "Thecodontosaurus")* but much larger than other [sauropodomorphs](/wiki/Sauropodomorpha "Sauropodomorpha").

At the base of the skull, the [quadratojugal](/wiki/Quadratojugal_bone "Quadratojugal bone") bears two branches, one pointing forwards and one upwards; they are roughly perpendicular to each other, unlike *Lufengosaurus* (angle of 45°), *Yunnanosaurus* (angle of 60°), and *Jingshanosaurus* (angle of 110°). Above the quadratojugal, the [quadrate](/wiki/Quadrate_bone "Quadrate bone") has two [articulating condyles](/wiki/Condyle_%28anatomy%29 "Condyle (anatomy)"), a subtriangular one facing outward and a more rounded one facing inwards; the latter condyle is placed closer to the bottom, like *Lufengosaurus* and *Yunnanosaurus* but not *Plateosaurus*. At the back of the skull, between the [parietals](/wiki/Parietal_bone "Parietal bone") and [supraoccipitals](/wiki/Occipital_bone "Occipital bone"), there is a prominently developed postparietal fenestra; the supraoccipital itself slopes forwards at its bottom end so as to round off the base of the skull. The basipterygoid processes are long, slender, and project downwards and outwards like *Plateosaurus* and unlike *Lufengosaurus* and *Jingshanosaurus*, forming an angle of 80° with each other.

Compared to *Lufengosaurus*, *Yunnanosaurus*, and *Jingshanosaurus*, the [angular](/wiki/Angular_bone "Angular bone") and [surangular](/wiki/Surangular "Surangular") extend much further in front of the mandibular fenestra in *Xingxiulong*, which is closer to *Adeopapposaurus* and *Plateosaurus*. The articular bears an inward\-projecting and pyramidal process as an extension of the jaw joint; at its back end, it also possesses an upward\-directed and tab\-like process, which is also seen in *[Coloradisaurus](/wiki/Coloradisaurus "Coloradisaurus")*, *Jingshanosaurus*, and an as\-of\-yet unnamed sauropodomorph.


Where does the angular and surangular extend in front of the mandibular fenestra in Xingxiulong?