Kelmayisaurus petrolicus Dong, 1973

Brusatte, Stephen L., Benson, Roger B. J. & Xu, Xing, 2012, A reassessment of Kelmayisaurus petrolicus, a large theropod dinosaur from the Early Cretaceous of China, Acta Palaeontologica Polonica 57 (1), pp. 65-72 : 66-69

Kelmayisaurus petrolicus Dong, 1973

Figs. 1 , 2.

1973 Kelmayisaurus petrolicus Dong, 1973 : fig 2: 4.

2008 Kelmayisaurus petrolicus ; Zhao et al. 2008: fig. 323.

Holotype: IVPP V 4022, a complete left dentary and partial left maxilla.

Type locality: Near Wuerho (Urdo), Junggar Basin, Xinjiang, China (Shen and Mateer 1992; Rauhut and Xu 2005; Zhao et al. 2008).

Type horizon: Lianmugin Formation, Tugulu Group (Early Cretaceous:?Valanginian–Albian).

Emended diagnosis.—Carcharodontosaurid with a single autapomorphy: the presence of a deeply inset and dorsally concave groove located anteriorly on the lateral surface of the dentary ( Fig. 1B 1 ). Additionally, Kelmayisaurus shows a unique combination of characters not currently known in any other allosauroid: maxillary interdental plates more than twice as tall dorsoventrally as they are broad anteroposteriorly, prominent maxillary anterior process (the combination of these two characters results in a narrowing of the gap between the plates and the anteromedial process), and absence of an anteroventral “chin−like” process of the dentary.

Description

Maxilla.—Only a small fragment of the left maxilla is present, comprising the region anterior to the base of the ascending process. A distinct anterior ramus is present, which is separated from the base of the ascending process by a concave step in lateral view. The shape of the ramus may have been slightly modified by breakage of the dorsal surface. However, neither cancellous bone texture nor alveolar crypts are exposed, suggesting that such breakage is minimal and the presence and general shape of the process are real. The anterior ramus is present in many basal theropods and its shape is often used as a phylogenetic character (e.g., Holtz et al. 2004). In Kelmayisaurus the process is slightly shorter anteroposteriorly (70 mm) than it is high dorsoventrally (100 mm), similar to the condition in Allosaurus ( Madsen 1976) , Neovenator (Brusatte et al. 2008) , and Monolophosaurus (Brusatte et al. 2010; Zhao and Currie 1993). In contrast, carcharodontosaurids such as Carcharodontosaurus and Mapusaurus have an anterior process that is much taller than long anteroposteriorly, and thus is nearly indistinct as a discrete process (Sereno et al. 1996; Coria and Currie 2006).

The maxilla is heavily abraded but several regions of original bone surface are preserved. On the lateral surface, the best preserved patch of original surface texture is smooth, and lacks the rugose surface texture of abelisaurids (Sampson and Witmer 2007; Sereno and Brusatte 2008) and derived carcharodontosaurids such as Carcharodontosaurus (Sereno et al. 1996; Brusatte and Sereno 2007). Additionally, there is a row of primary neurovascular foramina approximately 15 mm above the ventral margin on the lateral surface. Where well preserved, the foramina are 4–5 mm in diameter and open ventrally into deep grooves that terminate at the alveolar margin. These grooves, along with other grooves on more abraded regions of the lateral surface, are marked by tightly packed and elongate internal bone grains. There are several larger foramina located dorsal to the primary row, but these do not appear to form a pattern.

The medial surface of the maxilla is poorly preserved, suggesting that it was exposed to subaerial weathering. However, important details of the interdental plates are apparent. Although the plates are damaged in many regions, it is clear that they were fused into a single lamina. Additionally, the first plate is preserved in its entirety; it extends dorsally to nearly the level of the anteromedial process and the two are only separated by a slight concave margin. This is also the case in Sinraptor ( Currie and Zhao 1993) . However, in Sinraptor this results from the more ventral position of the anteromedial process, whereas in Kelmayisaurus the process is located close to the dorsal margin of the maxilla as in most theropods. Thus, the close position of the first interdental plate and the anteromedial process in Kelmayisaurus is due to the increased depth of the plate itself. It is approximately twice as deep dorsoventrally as broad anteroposteriorly, as in derived carcharodontosaurids such as Acrocanthosaurus ( NCSM 14345), Carcharodontosaurus (Brusatte and Sereno 2007) , Giganotosaurus (MUCPv−Ch 1), and Mapusaurus (Coria and Currie 2006) , as well as the megalosaurids Megalosaurus (Benson 2010) and Torvosaurus (Britt 1991) and specimens of unnamed related taxa such as DCM G10603 ( Powell 1987; Benson and Barrett 2009). In contrast, other theropods, including the basal carcharodontosaurian Neovenator (Brusatte et al. 2008) , more basal allosauroids ( Allosaurus : Madsen 1976; Sinraptor : Currie and Zhao 1993), and ceratosaurids ( Madsen and Welles 2000; Rauhut 2004) possess shallower plates. Because derived carcharodontosaurids lack a distinct maxillary anterior process, the anteromedial process in these taxa is located further dorsally relative to the interdental plates than in Kelmayisaurus . Therefore the combination of tall interdental plates and an anteromedial process that is close to the dorsal margin of the plates is known only in Kelmayisaurus .

Parts of six alveoli are preserved; the anterior four are essentially complete and the posterior two are heavily weathered. Complete alveoli have oval outlines, which are wider mesiodistally than labiolingually. A replacement tooth is present in the crypt for alveolus 4. This tooth is 70 mm long apicobasally, its mesial margin is strongly curved, and its distal margin is nearly straight ventrally, similar to the replacement teeth of many theropods. Unfortunately, surface details, such as the presence of enamel wrinkles (Brusatte et al. 2007), are difficult to discern due to erosion. The labial parapet of the alveoli, comprised of the lateral surface of the maxilla, extends much further ventrally than the lingual parapet, formed from the interdental plates. However, this may be an artefact of poor preservation.

Dentary.—The left dentary is well preserved, and only the anterior tip and the fragile, sheet−like portion immediately posterior to the tooth row are missing. The dentary is 523 mm in length and keeps a relatively constant dorsoventral depth along most of the tooth row, but expands in depth posterior to alveolus 13. The anterior end is expanded only slightly relative to the remainder of the tooth row, unlike the condition in derived carcharodontosaurids in which the anterior dentary is expanded and squared−off, primarily by the presence of a distinct “chin−like” anteroventral process (Fig. 2C; e.g., Novas et al. 2005; Coria and Currie 2006; Brusatte and Sereno 2007). An unexpanded anterior dentary is also seen in the basal neovenatorid carcharodontosaurian Neovenator (Fig. 2A; Brusatte et al. 2008). The dorsal margin of the tooth row is concave when seen in lateral view, whereas the ventral margin is convex anteriorly and concave posteriorly. The

http://dx.doi.org/10.4202/app.2010.0125

Fig. 2. Dentaries of allosauroid theropod dinosaurs. A. Neovenator salerii Hutt, Martill, and Barker, 1996 , England, Wessex Formation, Lower Cretaceous ( BMNH R10001). B. Allosaurus fragilis Marsh, 1877 , United States, Morrison Formation, Upper Jurassic ( UMNH VP 6475). C. Giganotosaurus carolinii Coria and Salgado, 1995 , Argentina, Candeleros Formation, Upper Cretaceous (MUCPv−95). Photographs in lateral (A 1, B, C), medial (A 2), and dorsal (A 3) views. Scale bars 10 cm. dorsal section of the posterior margin of the dentary, which a dorsoventrally deep and strongly inset groove. The groove would have been overlapped by the surangular, is nearly ver− curves dorsally as it extends posteriorly, giving it a concave tical for a short distance before sloping posteroventrally. dorsal margin when seen in lateral view. However, as this cur− This is also the case in other allosauroids (e.g., Madsen vature occurs in concert with the posterior expansion of the 1976), whereas abelisaurids (e.g., Sampson and Witmer dentary, the groove is still located 25 mm ventral to the tooth 2007) and many coelurosaurs (e.g., Currie 1995) have poste− row where it terminates. The primary groove is especially rior margins that are essentially straight dorsoventrally. Al− deep and well defined in Kelmayisaurus , similar to the condithough the posterior part of the dentary is well preserved, tion in some megalosauroids (e.g., Rauhut 2003) and some there is no obvious concave margin for the external mandibu− carcharodontosaurids (Fig. 2C) but contrasting with the lar fenestra. Thus, if the dentary did border the fenestra, this weaker grooves of most other theropods (Rauhut 2003). In contribution must have been small. Allosaurus and Neovenator a discrete groove is absent, and fo−

In dorsal view, the dentary is straight across its entire ramina are simply arrayed in a series (Fig. 2A 1, B). length, as in the carcharodontosaurians Acrocanthosaurus Two additional neurovascular features are present on the ( NCSM 14345) and Neovenator (Fig. 2A 3; Brusatte et al. lateral surface. A ventral row of foramina, which are more 2008), as well as Sinraptor ( Currie and Zhao 1993) and most ovoid than the primary foramina, is located along the ventral other basal tetanurans. However, in derived carcharodonto− margin of the anterior dentary. These are present below the saurids ( Carcharodontosaurus : Brusatte and Sereno 2007; first four alveoli, and there is one foramen per alveolus. Addi− Giganotosaurus : Calvo and Coria 2000; Mapusaurus : Coria tionally, there is a pronounced groove anteriorly, anterior to and Currie 2006), Allosaurus ( Madsen 1976) , Piatnitzky− alveolus 5. This groove is 74 mm in length and curves dorsally saurus ( PVL 4073), and abelisaurids (e.g., Sampson and as it continues posteriorly, eventually becoming confluent Witmer 2007) the dentary curves anteromedially along its with the primary groove at the level of alveolus 6. Within this length to form a broad, U−shaped snout. groove are four deep foramina, which decrease in size posteri−

Original bone surface is present across most of the dentary, orly. This groove is not present in other basal tetanurans (Fig. and the smooth lateral surface is especially well preserved. 2; e.g., Madsen 1976; Currie and Zhao 1993; Allain 2002), The primary neurovascular row is distinct. Anteriorly, the row and is thus considered an autapomorphy of Kelmayisaurus . is comprised of deep, circular foramina. There is approxi− The medial surface of the dentary is well preserved. The mately one foramen per alveolus, and these are located only symphysis is nearly flat and poorly−defined, not bulbous and 15 mm ventral to the alveolar margin. Posterior to the fourth rugose as in derived carcharodontosaurids (Brusatte and Sealveolus the row curves ventrally, such that it is 25 mm ventral reno 2007). However, an anterodorsally−inclined longitudito the alveolar margin at the level of alveolus 6. Additionally, nal ridge traverses the symphysis immediately ventral to posterior to alveolus 8 the individual foramina are replaced by midheight. This feature has been noted in megalosauroids (Benson 2008) and may be widespread among theropods. Ventral to the third alveolus are two Meckelian foramina; both are ovoid, equal in size, and one is located anterodorsal to the other. The Meckelian groove is shallowly inset where it meets the foramina, but becomes more deeply inset and taller dorsoventrally as it continues posteriorly. Ventral to alveolus 13 the groove is marked by a distinct step where it meets the adductor fossa; ventral to this step is a rectangular notch for the splenial articulation. The groove extends anteroventrally and its dorsal margin is better defined than its ventral margin. It is bordered dorsally by the lingual bar, which is deepest anteriorly above the Meckelian foramina. The bar tapers in depth posteriorly until the level of alveolus 9, from which point it maintains a constant depth. It also becomes more robust posteriorly, in concert with the progressively more inset Meckelian groove. The bar is bordered dorsally by the paradental groove, above which the interdental plates are fused into a single lamina across the first 11 alveoli. The posterior−most three alveoli are small, triangular, and unfused. No tooth replacement foramina are clearly visible.

Fifteen alveoli are clearly visible, and there was likely a 16 th alveolus that is missing at the broken anterodorsal corner of the dentary. All alveoli are suboval in dorsal view and much longer mesiodistally than labiolingually. Even the second and third alveoli are suboval, unlike the situation in many megalosauroids (e.g., Charig and Milner 1997; Allain 2002; Sadleir et al. 2008) and Acrocanthosaurus ( NCSM 14345), in which the anterior three alveoli are subcircular and the third is relatively enlarged compared to the other alveoli. The third dentary alveolus of Neovenator is also relatively enlarged (Fig. 2A 3). In Neovenator the alveoli are subrectangular, similar to the condition in abelisaurids (e.g., Sereno et al. 2004) but unlike all other basal tetanurans. No erupted or replacement teeth are clearly preserved in Kelmayisaurus , but the labiolingually thin alveoli may suggest that the teeth were transversely compressed, as in some derived carcharodontosaurids (Sereno et al. 1996).

Figures

Fig. 1. Left maxilla (A) and left dentary (B) of carcharodontosaurid theropod Kelmayisaurus petrolicus Dong, 1973 (IVPP V 4022, China, Lianmugin Formation, Lower Cretaceous). Photographs in lateral (A1, B1), medial (A2, B2), ventral (A3), and dorsal (B3) views. Scale bars 5 cm. Designation “d” refers to dentary tooth, designation “m” refers to maxillary tooth position. Dorsal view of dentary shows tooth row only.