Contributions to Zoology 68 (1) 19-36 (1998)Shen Yan-bin; Rod S. Taylor; Frederick R. Schram: New spelaeogriphacean (Crustacea: Peracarida ) from the Upper Jurassic of China

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Liaoningogriphus quadripartitus Shen Yan-bin & Taylor, sp. nov.

(Fig. 2 and Fig. 3; pl. 1- 2)

Diagnosis.- As only one species is currently recognized for this genus, the species diagnosis is the same as that for the genus.

Material.- Holotype, NIGP 126269 (Pl. 1b): carapace, thorax, abdomen and almost complete tail fan, preserved in dorsal view, no appendages visible (see descriptions of paratypes); paratypes, NIGP 126270A/B: lateral view, thorax, abdomen and tail fan, with pleopods; NIGP 126275-1: dorsal view, carapace and thorax with antennae and antennules; NIGP 126278A/B-2: lateral view, (incomplete) head, thorax and (incomplete) abdomen, with partial thoracopods; NIGP 126286-1 and 2: ventral view, abdomens with incomplete tail fans and pleopods; and NIGP 126348: dorsal abdomen and tail fan, partial pleopods; NIGP 126352: ventral view of complete (juvenile?) animal. Also additional figured specimens 126269; 126271-1, 2; 126275-8; 126276-8; 126278A-1, 3, 4; 126282-1. All material is housed at the Nanjing Institute of Geology and Palaeontology (abbreviated here as NIGP), Academia Sinica, the People’s Republic of China.

Additional material.- NIGP 126271: 3-5, NIGP 126272-126274, NIGP 126275: 2-7, NIGP 126276: 1-7, NIGP 126277, NIGP 126278A/B: 5-12, NIGP 126279: 1-20, NIGP 126280-126281, NIGP 126282: 2, NIGP 126283-126285, NIGP 126286:3-6, NIGP 126287A/B, NIGP 126349.

Localities and stratigraphy.- Jianshangou sedimentary intercalation, Upper Jurassic Yixian Formation from Chaomidianzi (see slide 1) village, Jianshangou, Beipiao County, Liaoning Province; and Dakangpu sedimentary intercalation, Upper Jurassic Yixian Formation from Dakangpu village, Yixian County, Liaoning Province (see Figure 1).

Description.- The body is elongate and cylindrical and is approximately 3-4 times as long as it is wide, with a maximum observed length of >1.75 cm (see Table 1) (Plate 1b). The carapace makes up approximately one fifth of the total body length (see Table 1) and is undecorated, thinly sclerotized and covers the head and most of the first two thoracomeres (NIGP 126271-1). It possesses a very short (<0.5 mm) broadly rounded rostrum.

 

Table 1: Measurements of spelaeogriphacean morphology, from dorso-ventrally oriented specimens (in mm): Specimen Carapace width (max) carapace length (min/max) Thorax width (max) Cephalothorax length abdomen width (max) Abdomen length (max) Telson length 126269 5.8 2.9/3.4 4.5 7.5 3.8 8.0 2.0 126271 4.9 2.9/3.2 3.8 7.1 3.0 9.0 - 126274 - -/- - - 3.0 - 2.2 126275A - 2.7/3.3 - 7.0 3.1 - - 126276h-1 4.1 2.7/3.2 3.5 7.0 3.0 - - 126276k - -/- - - 3.1 6.1 - 126276h-2 4.0 2.5/3.5 2.8 5.9 2.5 6.2 1.7 126276g - - - - - 7.3 1.9 126275c - - 3.0 - 3.6 7.6 2.0 126281 - - 3.3 - - - - 126178Aa - - 3.6 6.8 3.6 7.8 1.9 126275x 4.4 2.5/2.8 3.2 6.8 - - -

The lateral carapace margins are smoothly rounded at both the antero-lateral and postero-lateral ends of the carapace, resulting in an almost ovoid appearance in lateral view. Shallow, smooth ‘optical‘ grooves are located between the rostrum and the antero-lateral margins (Plate 1b, Plate 2d). A 0.5 mm deep indentation occurs along the medial posterior margin, resulting in a small portion of the second thoracomere being exposed dorsally. The postero-lateral margins partially cover the anterior part of the third pereiomere (NIGP 126276-8) (see Figure 3).

The antennules possess two robust flagella and a peduncle of three segments, totalling 2 mm in length. The basal segment is approximately 0.8 mm long, while the second and third segments are each approximately 0.6 mm in length. The antennae are uniramous, with only three segments clearly visible in the peduncle. The first and second peduncular segments are equal in length and together are approximately the same length as the distal segment, with a total peduncular length of 2.5 mm (NIGP 126275-1, 8). No scaphocerite is evident (Figure 2a) . Neither antennal nor antennular flagella are complete, thus flagellar length is not known. The longest observed is ~1 mm long: a far cry from those of the recent Spelaeogriphacea, which are almost as long as the total body length.

The thorax makes up approximately one fourth of the body length of the animal (see Table 1) with the last six free thoracomeres exposed Plate 1b, Plate 2d). Thoracomere size is reduced anteriorly: thoracomeres 1-3 are smaller than the others and possess medially directed lateral margins, in contrast to the rectangular shape of segments 4-8. In adult individuals, thoracomeres 1, 2 and 3 have widths of 2.5, 3.0 and 3.5 mm and lengths of 0.5, 0.6 and 0.7 mm respectively (detailed measurements for the anteriormost thoracomeres are not provided in Table 1 due to the fact that these segments can be accurately measured in only two specimens). Thoracomeres 4-8 are subequal in size and measure approximately 4.0-4.5 mm in width and 0.75 mm in length (NIGP 126269; NIGP 126271-1). Specimens preserved in a skewed dorso- or ventro-lateral position show a slight width reduction in thoracomeres 7 and 8, which probably reflects the presence of shorter pleura in these segments(Plates 1a, 1b and Plate 2d). These pleura are smoothly rounded and are directed ventrally (NIGP 126282-1; NIGP 126271-2).

The following can be determined from the few preserved thoracopods (Plate 1a). Limbs 2-8 are well developed and approximately equal in size, with the endopods consisting of 1) a protopod, made up of a small (approximately 1 mm in length combined) coxa and basis (details of the attachment to the thorax are, unfortunately, not clear), 2) elongate subequal (1.0 mm) ischium and merus, and 3) slightly shorter carpus, propodus and dactylus. These are subequal in length (0.8 mm) but become progressively narrower distally. The dactylus is pointed distally. Thoracopod 1 is larger than all others and appears to be developed into a maxillipede (Plate 1a), possessing a broader ischium, merus and carpus than all other thoracopods (NIGP 126278A-1). Both the ischium and merus are subtriangular. Precise attachment to the thorax is not determinable, as no clear signs of the coxa or basis are visible. The propodus is not completely preserved, and no trace of the dactylus is evident. No exopods or epipodites are observed on any of the thoracopods preserved (Plates 1a, 1c).

The abdomen makes up almost one half of the total body length (see Table 1). Pleomeres 1-5 are equal in width (approximately 3.5 mm), with pleomere 6 being slightly narrower (approximately 3.0 mm). Pleomeres 1-4 are equal in length (approximately 1.25 mm), while 5 and 6 are slightly longer than the first four (approximately 1.5 - 1.75 mm) (NIGP 126269; NIGP 126348) (Plate 2b, c). Pleura are well developed Plate 2b): they are rounded and laterally oriented anteriorly but become progressively more posteriorly directed along the length of the abdomen (NIGP 126269; NIGP 126278A-3) (Plate 2c). Each of pleomeres 1-5 possess a posteriorly-pointed triangular apodeme, which is clearly visible but only in dorsally preserved specimens (Plate 2d) suggesting thinly sclerotized tergites (NIGP 126271-1; NIGP 126276-8).

Very well-developed, elongate, biramous pleopods are equally present on pleomeres 1-5 (Plates 2b,c; Figure 2b). The sub-rectangular protopod possesses a slight medio-lateral indentation to the right of center on the otherwise rounded proximal margin. The distal protopod margin is sigmoidally curved, with a grooved invagination near the lateral margin, and anchors a two-segmented exopod (Plate 2a) and an ovoid endopod. The proximal exopodal segment is subtriangular with a broad distal margin while the distal lobe is ovoid, creating an overall ovoid appearance for this ramus (Figure 2b, Plate 1c , Plate 2a ). Both the distal exopodal lobe and the endopod are quite setose, although setal length is undetermined. All three pleopodal segments are subequal in size. (NIGP 126269; NIGP 126286-1, 2; NIGP 126348) (Figure 2b).

The telson is subtriangular, is slightly longer than wide, possesses a pair of short, robust median terminal spines (NIGP 126348) and is subequal in length to the sixth pleomere (Plate 2b). The uropods are elongate and biramous and are approximately twice as long as the telson. Each uropod possesses a rectangular protopod that is setose along its distal lateral margin. The setose exopod has two articles, with the rectangular proximal segment equal in size and shape to the protopod. The distal segment is narrower but approximately the same length as the proximal article, somewhat pointed distally, and also setose. The endopod is approximately 1.5 times the size of the uropodal protopod, is ovoid in shape and heavily setose (NIGP 126278A-4; NIGP 126348).

See Figure 3 for complete dorsal and lateral reconstructions of Liaoningogriphus quadripartitus.

Species Etymology.- The species name quadripartitus (‘four-parted‘) is a reference to the two-segmented nature of the pleopodal exopod, resulting in pleopods with four ‘articles‘.

Remarks.- As mentioned previously, specimens of the new spelaeogriphacean taxon Liaoningogriphus quadripartitus have been collected from two separate localities representing the Upper Jurassic Yixian Formation from the Northern China tectonic platform. The Yixian Basin is a small, isolated fault basin formed as a result of volcanic activity initiated by the subduction of the Pacific plate under the eastern part of the Asian continent.

The exposure at Chaomidianzi village, Jianshangou, Beipiao County consists of intermediate-basaltic volcanic rocks thinly interbedded with very-fine grained grey paper shales (Chen et al. 1982), sometimes slightly calcareous. Associated with the spelaeogriphaceans in this strata are the conchostracan Eosestheria ovata and the fish Peipiaosteus panii. This ‘exposure‘ is actually the eroded banks of a river-bed, and extends several hundred meters vertically. Almost 3 metres of this unit are exposed at this locality.

The second locality represents the slightly younger Dakangpu sedimentary intercalation and is found in Dakangpu village, Yixian County (Figure 1). It is composed of thin-bedded fine-grained siltstones (Chen 1988; Chen et al. 1980) and slightly darker silty limestones, and is an intercalation of intermediate-basaltic volcanic rocks (Chen et al. 1982). The insect Ephemeropsis trisetalis and the conchostracan genus Diestheria are also found at this locality, each in amazingly abundant numbers (Zhang et al. 1976). Three specimens of previously undescribed terrestrial insects (tentatively identified thus far as a cicada, a necopteran and a hymenopteran) have also been found from this locality, which will be the focus of a later paper. This exposure is small, a lens of approximately 10 cm thickness that is exposed along the banks of a railroad track excavation.

This region contains a fresh water fauna known as the Jehol Fauna, which includes the previously mentioned insects, conchostracans and fish and extends through the Late Jurassic to the early Cretaceous in eastern Asia. Recent exploration throughout the area has uncovered numerous new taxa including dinosaurs, birds and angiosperms. The stratigraphy and lithology of this region, as well as the associated faunas, tell us these deposits were laid down in a lacustrine environment. These localities are located near the southern margin of what is interpreted as humid temperate zone bordering on a semiarid-arid subtropical zone (Wang 1985).

Preservation varies considerably between the two localities. Specimens from the siltstone locality at Dakangpu village are preserved as carbonaceous films with no relief evident in any specimens. Some details of internal anatomy are observable in dorso-ventrally oriented specimens, with both upper and lower preservational surfaces at least partially visible in most of these specimens.

Almost all of those collected from the paper shales at Chaomidianzi show some relief. Many of these Chaomidianzi specimens are preserved as molds, with no traces of the original organic material (or replacement material) evident. Others are partially phosphatized; these show considerably more information than the matrix-impression specimens, usually possessing greater relief as well. No internal anatomy is visible; however, in some specimens the outlines of structures (i.e., segment margins) on the lower preservational surface are visible through the upper preservational face of the specimens.

There is (and has been for some time) discussion and debate as to the actual age of the Yixian Formation. The traditional perspective, as used in this paper, is that it was deposited during the Upper Jurassic. However, recent age dating studies (i.e., the Smith et al., 1995 study using 40Ar-39Ar) for the Yixian Formation suggest that it is actually Early Cretaceous in age. An attempt will later be made to help clarify this issue through an examination of the palynomorphs present in material collected from the Yixian Formation. This information will be included in the previously mentioned paper dealing with several new insect taxa from the region.

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