Li et al.—New Triassic diapsid from China
Table 6. Measurements (mm) of the individual right hindlimb elements in the holotype specimen of Pectodens zhenyuensis n. gen. n. sp., IVPP V18578. L = Length; PW = width of proximal head; DW = width of distal head.
Element Femur
Tibia Fibula L
32.4 33.7 33.3
DW 4.0
- -
PW 3.9
- -
1311
calcite vein), which gives the impression of an articulation. In this case then there are just three phalanges—a condition that is widespread within protorosaurs. Somewhat unusually, metatarsal V is long and slender and
exhibits no indication of an offset head (or “hooked” shape) as seen in Tanystropheus (e.g., Wild, 1973; Nosotti, 2007).
Conclusions
Table 7. Measurements (mm) of the individual metatarsals in the holotype specimen of Pectodens zhenyuensis n. gen. n. sp., IVPP V18578.
I
Left tarsus Right tarsus
4.5 4.5
II
8.5 9.0
III
11.0 10.5
IV
12.0 12.0
V
10.0 10.0
Table 8. Lengths of each digit (mm), including the metacarpals and meta- tarsals, in each foot of the holotype specimen of Pectodens zhenyuensis n. gen. n sp., IVPP V18578.
Left manus Right pes Left pes
Digit 1 6.0
10.2 10.0
Digit 2 10.0
17.0 16.8
Digit 3 14.0
23.7 23.2
Digit 4 16.8
27.0 27.0
Digit 5 7.8
22.0 21.6
vertebra is considered to be the first dorsal and is mostly exposed, although the posterior end is covered by the coracoids (Fig. 1). If, as seems likely, the skeleton is still in complete articulation, then there is one dorsal vertebra entirely hidden. Furthermore, it is also difficult to determine whether the anterior edge of a centrum positioned adjacent to the crack running through the puboischiadic plate represents the last dorsal or the first sacral. On balance, it
The number of dorsal vertebrae is unclear. The inferred 12th
would appearmost likely that this is the last dorsal rather than the first sacral and that the first sacral is completely obscured. Unlike Tanystropheus, there is no evidence of dichocepha-
lous ribs in the anterior-most dorsals. Unfortunately there are no dorsal vertebrae showing the nature of the neural spine and whether it was relatively tall and elongate as in tanystropheids generally. The shape of the scapula is apparently not dissimilar to the
condition seen in Macrocnemus or Tanystropheus (e.g., Peyer, 1937; Wild, 1973; Nosotti, 2007). On first inspection it appears that there are only two
phalanges in digit V of the left manus, but a combination of a potentially very short second phalanx together with a thin calcite vein running through the more distally preserved part of the digit, introduces considerable uncertainty. Firstly, there is a distinct swelling on the section of bone distal to the fifth metacarpal. This is best explained by assuming that the swelling represents an articulation, and that the bone actually represents two phalanges partially overlapping each other, with the second one being relatively short in comparison with the other digits. In this case, the apparent ungual phalanx would be unusually long by comparison with the unguals of the other four digits. It is therefore possible that the narrow calcite vein actually obscures an articulation between separate phalanges. If both of these interpretations are correct, then Pectodens possessed four phalanges on the fifth digit. An alternative view is that there is a matrix-filled break in the second phalanx (just adjacent to the
A new, small terrestrial tetrapod is described from the Middle Triassic of Yunnan, China. Pectodens zhenyuensis n. gen. n. sp. bears very characteristic elongate teeth forming a comb-like marginal dentition. The elongate cervicals of Pectodens zhenyuensis n. gen. n. sp. with low neural spines together with the morphology of the cervical ribs are features consistent with protorosaurs, such as Macrocnemus. However, the imperforate puboischiadic plate, simple rounded proximal tarsals, and a straight 5th metatarsal are primitive characteristics. A key protorosaurian character is the long neck with elongated cervical ribs that typically extend across intervertebral articulations. It was mostly on the basis of these characters that Dinocephalosaurus from the Middle Triassic of China was referred to the protorosaurs (Li, 2003). Another long-necked form, Fuyuansaurus, also exhibits certain affinities with protorosaurs, in particular the tanystropheids (Fraser et al., 2013). Yet both taxa also display characters that are inconsistent with at least the tanystropheids. Unlike tanystropheids, but in common with Protorosaurus (personal observation, N.C. Fraser, 2013), both lack a thyroid fenestra in the pelvis. The Middle Triassic vertebrate faunas of southern
China are largely dominated by marine reptiles and fishes, but occasional terrestrial components (e.g., Macrocnemus fuyuanensis) are recovered from localities in the Zhuganpo Member of the Falang Formation (Li et al., 2007; Jiang et al. 2011). Likewise, Pectodens zhenyuensis n. gen. n. sp. exhibits no adaptations for an aquatic lifestyle; instead the long, slender limbs with pronounced articular ends, and elongate digits together with the claw-like distal phalanges speak to an entirely terrestrial existence. No fully terrestrial vertebrates have been documented previously from the Panxian-Luoping Fauna, although the archosaur Qianosuchus mixtus exhibits a combination of terrestrial and aquatic characteristics (Li et al., 2006). Pectodens is therefore the first fully terrestrial reptile reported from the Guanling Formation. The occurrence of terrestrial reptiles such as Macrocnemus and Pectodens are indicative of the proximity of the ancient coastline at the localities where they occur.
Acknowledgments
This work was supported from a special grant for fossil excavation and preparation by the Chinese Academy of Sciences. We especially thank Z. Li for his assistance in collecting the new specimen. We are grateful to H. Zhou for preparation of the specimen, W. Gao for photography, and W. Yu for the drawings. NCF acknowledges the European Union SYNTHESYS fund for travel support. He also thanks U. Göhlich (Natural History Museum Vienna), D. Schwarz- Wings (Museum für Naturkunde Berlin), and M. Farrell and
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