Читать книгу Hadrosaurs - David A. Eberth - Страница 82

DINOSAURIA Owen, 1842

ORNITHISCHIA Seeley, 1887

ORNITHOPODA Marsh, 1881

IGUANODONTIA Dollo, 1888

(sensu Sereno, 2005)

ANKYLOPOLLEXIA Sereno, 1986

(sensu Sereno, 2005)

STYRACOSTERNA Sereno, 1986

(sensu Sereno, 2005)

HADROSAURIFORMES Sereno, 1997

(sensu Sereno, 1998)

HADROSAUROIDEA Cope, 1870

(sensu Sereno, 2005)

GONGPOQUANSAURUS gen. nov.

Gongpoquansaurus mazongshanensis (Lü, 1997) comb. nov. Probactrosaurus mazongshanensis Lü, 1997 (original description). ?Probactrosaurus mazongshanensis (Norman, 2002, 2004). “Probactrosaurus” mazongshanensis (You and Li, 2009). “Probactrosaurus” mazongshanensis (McDonald et al., 2010). “Probactrosaurus” mazongshanensis (Carpenter and Ishida, 2010). “Probactrosaurus” mazongshanensis (Buffetaut and Suteethorn, 2011).

Type Species Gongpoquansaurus mazongshanensis (Lü, 1997) comb. nov.

Etymology Gongpoquan is the name of the basin where the material of the type species was recovered.

Diagnosis As for the type and only known species.

Holotype IVPP V. 11333 (Field Number 9208–21): Caudal part of an incomplete skull.

Referred Material IVPP V. 11334–16: part of the left quadrate; IVPP V. 11334–10, 11: two nearly complete maxillary teeth; IVPP V. 11334–12, 13, 14, 15: four isolated dentary teeth; IVPP V. 11334–1: four cervical vertebrae (including one nearly complete tenth cervical vertebra); IVPP V. 11334–2: second dorsal vertebra; IVPP V. 11334–3: nearly complete sacrum; IVPP V. 11334–4: two series of caudal vertebrae (some with neural spines and chevrons); IVPP V. 11334–17: complete left scapula; IVPP V. 11334–18: part of the left humerus; IVPP V. 11334–8: part of the preacetabular process of the left ilium; IVPP V. 11334–9: part of the postacetabular process of the right ilium; IVPP V. 11334–6, 7: parts of the right and left pubes; IVPP V. 11334–5: right femur missing the proximal part.

Locality and Horizon Gongpoquan Basin, Town of Mazongshan, Subei Mongol Autonomous County, Jiuquan City, Gansu Province. middle gray unit of Zhonggou Formation, Xinminpu Group, Lower Cretaceous (Albian). This fossil locality is now included in the Subei Gongpoquan Dinosaur Geopark of Gansu Province established in 2006, which covers an area of 2288 km².

Amended Diagnosis Gongpoquansaurus mazongshanensis is a basal hadrosauroid distinguishable from other taxa by the following unique combination of features: transversely elongated supratemporal fenestra, broad and flat dorsal surface of the parietals with a deep median groove, and large and straight nuchal crest (Fig. 4.2).

4.2. Holotype (IVPP V. 11333) of Gongpoquansaurus mazongshanensis comb. nov. Caudal part of the skull in dorsal view, showing its unique combination of features: (1) transversely elongated supratemporal fenestra; (2) a deep median groove on the broad and flat dorsal surface of the parietals; and (3) large and straight nuchal crest.

Comments and Comparisons All the specimens were collected from the southeastern part of the Gongpoquan Basin in the summer of 1992 during the Sino-Japanese Silk Road Dinosaur Expedition (Dong, 1997). The locality of the holotype is shown in figure 1 (Dong, 1997:7). All the referred specimens were probably recovered from the same quarry as the holotype (Dong, Z.-M., pers. comm.). Because it is common for more than one iguanodontian taxon to occur in the same horizon and locality, and another iguanodontian (Equijubus normani) has already been recovered from this horizon in the same (southeastern) part of the Gongpoquan Basin, there is a possibility that not all the referred specimens belong to Gongpoquansaurus mazongshanensis. Therefore, we prefer to restrict the diagnosis of this taxon, basing it on the holotype only.

Based on dentary crowns, Norman (2002) considered “Probactrosaurus” mazongshanensis to be more closely related to Altirhinus than to Probactrosaurus gobiensis. Buffetaut and Suteethorn (2011) found that the maxillary teeth of Siamodon nimngami are very similar to those of “Probactrosaurus” mazongshanensis, with a prominent median primary ridge, and strongly denticulate margins. As suggested above, the association between the referred teeth and the holotype needs to be confirmed.

4.3. Cladogram showing the phylogenetic relationships of Gongpoquansaurus mazongshanensis comb. nov. This is based on the results of cladistic analyses of McDonald et al. (2010) and McDonald (2011), with the addition of Xuwulong yueluni based on You et al. (2011).

In McDonald et al. (2010)’s cladistic analysis, which included “Probactrosaurus” mazongshanensis, Equijubus normani and Jintasaurus meniscus, “Probactrosaurus” mazongshanensis is more derived than Equijubus and less derived than Jintasaurus, with several intermediate taxa in between (Fig. 4.3). This supports the elevation of “Probactrosaurus” mazongshanensis as a new genus.

Carpenter and Ishida (2010) noticed that “Probactrosaurus” mazongshanensis is an immature individual as evidenced by the incomplete fusion of the neural arch with the centrum, and found substantial differences between it and Probactrosaurus gobiensis. In addition to the diagnostic cranial and cervical features identified here, they also noted the following differences: teeth with large marginal crenulations (small, less developed in P. gobiensis); dentary teeth significantly larger than maxillary teeth (nearly same size in P. gobiensis); sacrum rounded ventrally (keeled in P. gobiensis); and scapula expanded distally (nearly parallel-sided in P. gobiensis).

Jintasaurus, a slightly more derived hadrosauroid from the nearby Yujingzi Basin, shows clear differences with Gongpoquansaurus: the supratemporal fenestra is rostrolateral-caudomedially directed in Jintasaurus but transversely elongated in Gongpoquansaurus, and the parietals of Jintasaurus do not possess a median deep groove.