Cranial anatomy of Shunosaurus, a basal sauropod dinosaur from the Middle Jurassic of China

Abstract

Shunosaurus, from the Middle Jurassic of China, is probably the best‐known basal sauropod and is represented by several complete skeletons. It is unique among sauropods in having a small, bony club at the end of its tail. New skull material provides critical information about its anatomy, brain morphology, tooth replacement pattern, feeding habits and phylogenetic relationships. The skull is akinetic and monimostylic. The brain is relatively small, narrow and primitively designed. The tooth replacement pattern exhibits back to front replacement waves in alternating tooth position. The teeth are spatulate, stout and show well‐developed wear facets indicative of coarser plant food. Upper and lower tooth rows interdigitate and shear past each other. Tooth morphology, skull architecture, and neck posture indicate that Shunosaurus was adapted to ground feeding or low browsing. Shunosaurus exhibits the following cranial autapomorphies: emargination of the ventral margin of the jugal/quadratojugal bar behind the tooth row; postorbital contains a lateral pit; vomers do not participate in the formation of the choanae; pterygoid is extremely slender and small with a dorsal fossa; quadrate ramus of the pterygoid is forked; quadratojugal participates in the jaw articulation; tooth morphology is a combination of cylindrical and spatulate form; basipterygoid process is not wrapped by the caudal process of the pterygoid; trochlear nerve has two exits; occlusal level of the maxillary tooth row is convex downward, whereas that of the dentary is concave upward, acting like a pair of garden shears; dentary tooth count is 25 or more; and the replacing teeth invade the labial side of the functional teeth. Cranial characters among the basal sauropods are reviewed. As Shunosaurus is the earliest sauropod for which cranial remains are known, it occupies an important position phylogenetically, showing the modification of skull morphology from the prosauropod condition. Although the skull synapomorphies of Sauropoda are unknown at present, 27 cranial synapomorphies are known for the clade Eusauropoda. © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society, 2002, 136, 145−169.

Titanosauriform teeth from the Cretaceous of Japan

“…Except for the most distal teeth of some taxa, the V-shaped wear is developed on the teeth of basal Eusauropoda and basal Macronaria such as Camarasaurus (Calvo 1994, Salgado and Calvo 1997, Wilson and Sereno 1998, Upchurch and Barrett 2000, Chatterjee and Zheng 2002. Although the V-shaped wear is supposed to be formed by the occlusion of the upper and lower teeth (Fig.…”

The Braincase of Apatosaurus (Dinosauria: Sauropoda) Based on Computed Tomography of a New Specimen with Comments on Variation and Evolution in Sauropod Neuroanatomy

“…Many of the more recent descriptions are based on synthetic endocasts. These include Plateosaurus (Galton, 1985), Shunosaurus (Chatterjee and Zheng, 2002), an early Cretaceous titanosauriform (TMM 40435;Tidwell and Carpenter, 2003), and Camarasaurus (Chatterjee and Zheng, 2005;Sereno et al, 2007). A digital endocast was extracted from HMS 175 and described as Diplodocus hayi (Franzosa, 2004), although the allocation of this specimen to Diplodocus is questionable (see Harris, 2006).…”

An Early Jurassic Sauropod Tooth From Patagonia (Cañadón Asfalto Formation): Implications for Sauropod Diversity

“…This is significant because different tooth morphologies and wear patterns have been interpreted as indicating different jaw mechanics (Calvo, 1994), and thus, probably, differences in diet. The broad overlapping crowns with extensive v-shaped wear facets of basal eusauropods indicate that the lower and upper tooth row have an interlocking type of occlusion (Chatterjee and Zheng, 2002). In contrast, the narrow and non-overlapping crowns with planar apical wear facets of derived neosauropods indicate that the upper and lower teeth met in a one-to-one fashion (Chure et al, 2010).…”

“…1.2-3). Labial wear facets are commonly found in the teeth of the dentaries of other eusauropods (Shunosaurus, Giraffatitan Janensch, 1914;Chatterjee and Zheng, 2002;Janensch, 1935Janensch, -1936. Most of the dentine is poorly preserved and it is not possible to observe the presence of scratches or pits on its worn surface.…”

“…The narrow profile of the crown differs from the broad-crowned condition of most non-neosauropod sauropods (Amygdalodon, Tazoudasaurus Allain et al, 2004, Patagosaurus Bonaparte, 1979, Mamenchisaurus Young, 1954Carballido and Pol, 2010;Allain and Aquesbi, 2008;Bonaparte, 1986;Ouyang and Ye, 2002) and basal macronarians (Camarasaurus Cope, 1878;Madsen et al, 1995). Among basal sauropods, mesiodistally unexpanded tooth crowns are found in some taxa, such as Shunosaurus Dong et al, 1983 (Chatterjee andZheng, 2002).…”