1310
Journal of Paleontology 91(6):1306–1312
Table 3. Measurements (mm) of the individual caudal vertebrae in the holotype specimen of Pectodens zhenyuensis n. gen. n. sp., IVPP V18578. CL = centrum length; TPL = length of transverse process.
Vertebra 27
28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67
CL 4.3
4.4 4.7 4.7 5.8 5.0 5.0 5.5 5.8 - -
6.3 6.3 6.0 6.0 6.0 5.9 5.9 5.7 5.5 5.5 5.4 5.5 5.3 5.2 5.1 5.1 4.8 4.7 4.6 4.1 4.0 3.6 3.4 3.0 2.9 2.5 1.9 1.4 1.0 0.8
TPL 6.5
8.0 7.1 6.1 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
-
(Table 5) and phalanges of the left manus are in complete articulation. Nevertheless, in digit V, the complete phalangeal formula is difficult to determine and it is unclear whether it has three or four phalanges. The right manus overlies the anterior cervicals and is partly
obscured by the posterior part of the skull so that it provides even less clarity. The manual phalangeal formula is therefore 2:3:4:5:3 or 4. The pelvic girdle and hindlimb.—The pelvis is difficult to
interpret. Parts of all three elements that are visible on both sides do seem to be compressed together so that the ventral edges of both pubes appear to be exposed (Fig. 1). The fracture unfortunately passes directly through the puboischiadic plate. There is no clear indication of a thyroid fenestra, and while there is a slight emargination of the anterior edge of the ischium it appears to represent a broken edge. The femur is a relatively straight and slender element with
little expansion of the proximal and distal heads. The tibiae and fibulae are also very long, slender elements that are just a little
longer than the femur (Table 6). The tibia is the more robust element of the two epipodials. There are only two clear ossifications preserved in both tarsi,
Table 4. Measurements (mm) of the individual forelimb elements in the holotype specimen of Pectodens zhenyuensis n. gen. n. sp., IVPP V18578. L = Length; PW = width of proximal head.
Element
Left Humerus Left Radius Left Ulna
Right Humerus Right Radius Right Ulna
L
28.1 22.1 22.8 28.8 23.1 23.9
PW 5.5
5.5 - -
- -
however, it is impossible to determine whether they were expanded in ventral aspect. The humeri are somewhat longer than the epipodials, which are also relatively slender elements (Table 4). The ulna has a slightly more robust proximal head than the radius and it is also marginally longer. The left manus only preserves two ossifications (presumably
the ulnare and radiale), although there is a large gap between these ossifications and the metacarpals, and the metacarpals are in complete articulation with the phalangeal elements (Fig. 1). This suggests that there were other elements that had not ossified—a feature that is consistent with the specimen being a juvenile.
Metacarpals and phalanges are relatively slender elements with quite marked articular expansions. The metacarpals
which are assumed to represent the proximal tarsals. In the right tarsus there is an elongate fragment of bone in the approximate position of distal tarsal four, but it almost certainly represents part of the underlying caudal vertebra rather than any tarsal element. There is, nevertheless, perhaps the merest hint of a gap between the tarsals and metatarsals. However, on the left side there is not even the slightest gap in the tarsus that might have accommodated the distal tarsals. Instead the proximal tarsals appear to be in direct articulation with metatarsals III–V. The presumed astragalus and calcaneum are circular elements with no distinguishing features—there is no indication of a perforating foramen, for example. However they are in close articulation with each other in both ankles. The fifth metatarsal is completely straight just like the other
metatarsals, and is the third longest metatarsal after metatarsals III and IV, with metatarsal I being the shortest (Fig. 1; Table 7). The phalanges (Table 8) are all clearly preserved in complete
articulation in both feet with a pedal phalangeal formula of 2:3:4:5:4. Apart from the unguals, each phalanx has a “waisted” appearance with expanded proximal and distal ends.
Etymology.—In honor of Zhenyu Li, who contributed greatly to the collection of the specimen from the field.
Remarks.—The cervicals closely resemble those of Tanystropheus with an extremely low neural spine (Fig. 3). The centra of cervicals six, seven, and eight are eroded, presumably from poor preservation of the bone close to the surface, although it conceivably hints at hollow centra.
Table 5. Measurements (mm) of the individual metacarpals in the holotype specimen of Pectodens zhenyuensis n. gen. n. sp. IVPP V18578.
I
Left manus Right manus
0.2 0.2
II
0.5 0.5
III 0.7 0.65 IV
0.75 0.7
V
0.3 -
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