Manchurochelys manchoukuoensis Endo & Shikama 1942
Creators: name: Zhou, Chang-Fu
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Testudines
Macrobaenidae
Manchurochelys
Manchurochelys manchoukuoensis

description: Manchurochelys manchoukuoensis Endo & Shikama, 1942
(Figs 1–4)
Holotype: Registration No. 3898 (former Central National Museum of Manchoukuo) from Tsaotzushan, approximately 21km southwest of Yixian, western Liaoning, China. The whereabouts of the holotype are currently unknown, and it was probably lost during World War II.
Referred specimen: LPM-R00008 (Figs 1–4), an incomplete skeleton including the skull, shell, isolated cervicals, articulated caudal series, partial left forelimb, and the hind limbs. The specimen is from close to the type locality in Yixian County, western Liaoning (41° 32.142´N; 121°01.614´E).
Type locality and horizon: Tsaotzushan, approximately 21km southwest of Yixian, western Liaoning Province; Jingangshan beds of the Early Cretaceous Yixian Formation (Barremian-Early Aptian: Chang et al. 2009).
Revised diagnosis: A sinemydid turtle that is distinguished from Sinemys lens and S. gamera in having reduced frontals that are nearly excluded from the orbit, a cervical scute, a pygal, and eight neurals, and lacking a seventh peripheral process or spine. Distinguished from Dracochelys bicuspis by having separated prefrontals, a shallow nuchal emargination, a cervical scute, eight neurals, and a closed central plastral fontanelle.
Description. Skull. The skull is compressed dorsoventrally as a result of post-mortem crushing (Figs 1– 3). The snout is poorly preserved, while the postorbital part of the skull is well preserved and in articulation. Dorsally, the skull has a length of 41 mm from the tip of the frontal to the posterior end of the crista supraoccipitalis and a width of 32 mm across the quadrates. The upper temporal emargination is well developed, resulting in complete exposure in dorsal view of the ‘processus trochlearis oticum’. This differs from the condition in the co-existing Ordosemys liaoxiensis, in which the temporal emargination is much shallower (Tong et al. 2004). The crista supraoccipitalis is strongly elongated posteriorly beyond the main body of the occiput. The postorbital appears to be isolated from the quadrate/squamosal, similar to the condition in Sinemys lens and S. gamera, but differing from the contact seen in O. liaoxiensis. Ventrally, the skull is partially exposed with the palatoquadrate and braincase floor visible (Fig. 3 C, D). Near the anterior portion of the basisphenoid, a small foramen is present in the ptergoid, possibly representing the foramen basisphenoidale (= foramen carotico-pharyngeale), as in Judithemys sukhanovi (Parham & Hutchison 2003). In the posterolateral corner of the basisphenoid, there is a small opening for the foramen posterior canalis caroticus internus, which is partially enclosed by the pterygoid.
The anterior end of the snout is damaged. A pair of premaxillae is partially exposed in palatal view. The maxilla medially contacts the palatine. An isolated element possibly represents a small nasal. The prefrontals are missing, but the articular facets on the frontals indicate that the prefrontals were completely separated along the midline. The frontals are about 11 mm long, and firmly contact one another along the dorsal midline. Posteriorly, the frontals contact the parietals along an anteriorly concave suture. The parietal is subtriangular, and represents the largest element of the skull roof. Posteriorly, the parietal forms a notable crest that is confluent with the crista supraoccipitalis. Laterally, the postorbital is well developed, and together with the prefrontal strongly limits the contribution of the frontal to the orbital rim. Posteriorly, the postorbital is separated from the squamosal, as in Sinemys spp. A crescentic element is well preserved at the anterior corner of the quadrate, and is interpreted as a possible quadratojugal. Together with the prootic and the possible quadratojugal, the quadrate forms medially the ‘processus trochlearis oticum’, a thickening of the anterior wall of the otic capsule. Laterally, the quadrate is constricted to form the cavum typmpani and encloses completely the incisura columellae auris. The squamosal bears posteriorly a rounded crest that is curved laterally towards its end. The supraoccipital forms an elongate supraoccipital crest. The prootic, opisthotic, supraoccipital and exoccipital are dorsally well exposed within the upper temporal fossa (Fig. 3 A,B). A large foramen is situated between the prootic and the quadrate for the dorsal exit of the canalis stapedio-temporalis.
The palatoquadrate elements are exposed in ventral view. The quadrate forms the anterolateral wall of the middle ear, the condylus mandibularis, and the cavum tympani. The anterior portion of the large pterygoid firmly contacts the opposing pterygoid along the midline but the posterior portion is separated from the opposing element by the basisphenoid. Near the rostral tip of the basisphenoid, a cleft-like opening is present on the pterygoid-basisphenoid suture that is interpreted here as the foramen caroticum laterale, as in Dracochelys bicuspis. On each side, small foramina penetrate the pterygoid, possibly representing the foramen basisphenoidale (= foramen carotico-pharyngeale), as in Judithemys sukhanovi (Parham & Hutchison 2003). As in other eucryptodirans, the pterygoid forms posteriorly the floor of the middle ear, and more laterally contacts the quadrate.
The braincase is well exposed in ventral view, except for where it is partially overlapped by the hyoid on the left side. The basisphenoid is triangular and as long as wide, in contrast to the elongated basisphenoid of Sinemys gamera (Brinkman & Peng 1993a). A pair of blind pits is present on the middle portion of the basisphenoid. Posteriorly, the basisphenoid has a nearly straight suture with the basioccipital. More laterally, there is a small opening, the foramen posterior canalis caroticus internus, which is enclosed by the pterygoid and basisphenoid. As in Dracochelys bicuspis, Sinemys spp., and Ordosemys spp., the canal seems not to be completely enclosed between the foramen posterior canalis caroticus internus and the foramen basisphenoidal. The basioccipital is a massive element and forms the occipital condyle posteriorly.
Shell: The elongate oval shell of Manchurochelys manchoukuoensis (LPM-R00008) is well exposed in dorsal view (Figs 1–2), with a length of 170 mm and a width of 140 mm, slightly larger than the holotype, which has a width of 125 mm. The carapace is low and slightly sculptured by small and numerous pits and grooves. A shallow midline depression is present along the neural region on the carapace, as in Ordosemys liaoxiensis. Costal-peripheral fenestrae are absent, as in the holotype specimen.
The cervical scute is small and trapezoid. Its maximum width of 22 mm is approximately 3.7 times its minimum length of 6 mm. The vertebral scutes are sub-hexagonal and oriented along the midline of the shell. The first and fifth scutes are distinctly wider than long, while the second to fourth scutes are much longer than wide. This differs from the co-existing Ordosemys liaoxiensis, in which the vertebral scutes are much wider than long (Ji 1995; Li & Liu 1999; Tong et al. 2004).
Twelve pairs of marginal scutes are present. The first pair is small and subtriangular and the second is enlarged and strongly convex medially. By contrast, the remaining peripherals are subrectangular and slightly elongated posteriorly along the shell margin. The last pair of peripherals meet one another along the midline, and are the largest in size with a marginal length of 25 mm. In contrast, the last pair of peripherals is strongly reduced in the holotype of M. manchoukuoensis.
The nuchal plate is large and rectangular, covered dorsally by the cervical scute, the first marginal scute, and the first vertebral scute. There are eight neural plates present along the midline. They are slender and long and have an irregular, sub-rectangular shape. The eighth neural is greatly reduced, less than half of the size of the other neurals. The suture of the eighth neural and the first suprapygal is almost overlapped by the fourth intervertebral sulcus. Two suprapygals are present. The first suprapygal is much smaller than the second one, as in Sinemys lens, but different from Ordosemys spp., in which two suprapygals are comparable to each other in size (Brinkman & Peng 1993b; Tong et al. 2004). The pygal is rectangular. Eleven pairs of peripheral plates are present in LPM-R00008. The first pair is small and roughly triangular. The next five pairs of peripherals appear to be rectangular and longer than wide, with exception of the fifth peripherals, which have a small medial process. The medial process is accentuated in the last five pairs of peripherals. These peripherals are much larger than the first six pairs of peripherals.
Vertebral column: Six cervical vertebrae are preserved, but are displaced from their original position, representing most of the cervical series of eight vertebrae. They are subrectangular in dorsal view, and comparable to each other in size (Fig. 4). The neural spine is strongly reduced. The centra are keeled ventrally. The development and orientation of the articular surfaces of the centra cannot be determined in most cases because of poor preservation, but some nevertheless appear to be opisthocoelous. The undivided transverse processes are positioned anteriorly near the proximal end of the centrum. The dorsal vertebrae are not exposed. In contrast, the caudal vertebrae are well preserved. The proximal five caudals are exposed in ventral view and in articulation with remaining column, while a distal caudal series is exposed in lateral view, comprising 14 articulated caudals and two slightly displaced caudals. The transverse processes are slender and long in the proximal caudals, but strongly decrease in length posteriorly. The transverse processes disappear in the distal caudal series. Chevrons appear to be present on nearly all caudals.
Appendicular skeleton: The hind limbs are well preserved in articulation, but the forelimbs are only partially preserved on the left side with a humerus, ulna, and several isolated phalanges. The humerus is remarkable with two well expanded ends. The humeral head is dorsally positioned on the proximal end.
The hindlimbs are exposed in dorsal view and consist of both tibiae and fibulae and pedes. The tibia and fibula are subequal in length. Of these, the fibula is more slender. The tarsus is somewhat displaced from its original position. The largest tarsal is the astragalocalcaneum, and is situated adjacent to the distal ends of the tibia and fibula. The fifth metatarsal is large and subcircular. The phalanges are well preserved on the left side, with a phalangeal formula of 2-3-3-3-3. The unguals are slightly shorter than the penultimate phalanx.
description: Published as part of Zhou, Chang-Fu, 2010, A second specimen of Manchurochelys manchoukuoensis Endo & Shikama, 1942 (Testudines: Eucryptodira) from the Early Cretaceous Yixian Formation of western Liaoning, China, pp. 57-66 in Zootaxa 2534 on pages 58-64, DOI: 10.5281/zenodo.196603