Lusorex taishanensis, Storch & Qiu, 2004

Storch, Gerhard & Qiu, Zhuding, 2004, First complete heterosoricine shrew: A new genus and species from the Miocene of China, Acta Palaeontologica Polonica 49 (3), pp. 357-363 : 358-361

Lusorex taishanensis sp. nov.

Holotype: A virtually complete skeleton with preserved soft body outline. Dentition of right side completely preserved. Collection of the Institute of Vertebrate Paleontology and Paleoanthropology ( IVPP), Chinese Academy of Sciences , Beijing, V 13915 .

Type locality and horizon: Shanwang (Diatomite quarry), Linqu County, Shandong Province, China. Early –midddle Miocene (Late Shanwangian, MN 5 equivalent) .

Etymology: Taishanensis , in allusion to the Taishan Mountain, one of the five celebrated mountains of China, which is located close to the fossil site.

Diagnosis.—As for genus.

Measurements

Tooth measurements in mm (P4–M3 greatest length × greatest width, other positions greatest length only; A = antemolars between 1st incisor and 4th premolar):

Upper teeth.— A1 1.24; A2 0.40; A3 0.60; A4 0.28; A5 0.80; P4 1.96×1.68; M1 1.68×1.92; M2 1.44×1.68; M3 0.84×1.28. Lower teeth.—i1 3.36; a1 0.88; a2 0.52; a3 0.64; a4 0.44; a5 0.88; m1 1.84; m2 1.60; m3 1.28.

Skeletal measurements in mm (greatest length); in parentheses measurements of an adult specimen of extant Sorex araneus :

Skull and body (premaxilla to pubis) 63.0 (62.4); skull 19.2 (19.7); tail ~24.5 (47.7); humerus 8.0 (7.4); ulna 10.5 (10.5); radius 7.5 (7.8); hand 6.9 (7.3); pelvis 11.5 (11.8); ilium 6.0 (5.5); femur 8.5 (7.8); tibia 11.3 (13.3); fibula 9.7 (fused to tibia over most of its length); hind foot 10.0 (11.8).

Indices of limb segments; in parentheses Sorex araneus : crural index (tibia:femur × 100) 133 (170); intermembral index (humerus + radius: femur + tibia × 100) 78 (72).

Description

Dentition.—The teeth are heavily pigmented. The dental formula is 1−6−3/1−5−3.

The first upper incisor is rather small. The medial tine is broken off yet there is not much doubt that the tooth was fissident. The broad apex is strongly curved ventrally.

There are five crowded, single−rooted upper antemolars between the first incisor and P4. The roots incline progressively toward the vertical from A1 to A5. A1 is distinctly larger than A2–5. It has a pointed and high anterolabial cusp. A sharp ridge runs from its apex transversely to a lingual cingular cuspule and subdivides the occlusal surface into a shallow anterior ledge and an expanded posterior basin. The laterally compressed posterior wall of the main cusp delimits the labial tooth margin. A2, A3, and A5 exhibit an anterolabial cusp and a flat distolingual heel. A5 has a sloping distolabial ridge. The minute peg−like A4 is squeezed between A3 and A5.

P4 is sub−triangular, with the labial side being much longer than the lingual one. The paracone is high and pointed, and has two weak sloping anterior crests extending to the precingulum. The posterior wing of the paracone is sharp and separated by a small notch from the postcingulum. The protocone is small and crest−like; its anterior and posterior arms are continuous with the pre− and postcingulum, respectively. The parastyle is small. The posterior basin is deep. A thin ridge connects the protocone to the base of the paracone. A hypocone is absent.

The upper molars decrease in size from M1 to M3. M1 and M2 are sub−rectangular in outline. The width of the ectoloph is subequal to the inner half of the teeth transversely. The cusps are high and sharp; the inner cusps are anteroposteriorly compressed into a wide V−shape. Protocone, paracone, and metacone are of subequal height; the hypocone is lower. The mesostyle is undivided, para− and metastyle are ridge−like, and the preparacrista of M1 is shorter than the postmetacrista. The hypocone is isolated anteriorly from the postprotocrista by a deep valley. The paraconule is small and its anterior and posterior arms are short. The metaconule is ridge−like; the premetaconule crista terminates at the base of the metacone, and the shorter postmetaconule crista is directed posteriorly. Thus, the two metaconule wings and the postprotocrista create a crest−like Y−shaped pattern. The prominent postcingulum closes the deep transverse posterior basin. The M2 is similar to M1, except for the subequal lengths of prepara− and postmetacrista. The M3 is reduced distally. The premetacrista is continuous with the postcingulum; distinct metacone, hypocone, and conules are lacking. The postprotocrista terminates posteriorly in the trigon basin.

The first lower incisor, like the upper, is rather small for a heterosoricine shrew. Its spatulate apex is gently curved upwards, the cutting edge is smoothly bicuspate, and the enamel is not wrinkled. The strong root exhibits a deep longitudinal groove along the lingual side.

The five antemolars between the first incisor and m1 are very crowded. They are inclined anteriorly and single−rooted; the roots incline progressively toward the horizontal from a5 to a1. The crowns overlap each other widely. The a1 and a5 (interpreted as p4) predominate in size, a1 being slightly larger than p4. The a1 has a high and sharp main cusp on the anterolabial corner and a broad, flat and posterolingually expanded heel. Weak lingual and posterior cingulids are visible. The a2 is small; its asymmetric chevron−shaped crown is composed of a low main cusp anteriorly and a slightly posterolingually expanded heel. The a3 resembles a1 but is distinctly smaller and lower. The very small a4 is squeezed between a3 and p4; it is morphologically similar to a2. The p4 is longer than wide and has an ovate occlusal outline. The high main cusp has a flat posterior face with a distinct posterolingual sloping ridge; its apex is antero−posteriorly compressed. The tooth shows a flat and slightly sloping heel and a weak continuous cingulid along the lingual and distal margins. The root of p4 is very strong.

The lower molars are graded in size. All cusps are very slender and piercing. The entoconid is sharp and laterally compressed. The metaconid and entoconid are of the same height and somewhat lower than the protoconid; the paraconid is lower than metaconid and entoconid, and the hypoconid is lowest. The oblique cristid terminates anteriorly beneath the protocristid notch. The postcristid joins the posterior wall of the entoconid directly, it is fused with the entoconid and there is no postentoconid valley. There is a deep V−shaped talonid notch between metaconid and entoconid.

The cingulids are weak and discontinuous at the bases of the protoconid and hypoconid. The trigonid basin is open lingually, and the deep hypoflexid opens at the level of the ectocingulid. The talonid of m1 is wider than the trigonid. The m2 closely resembles m1 except for the subequal width of trigonid and talonid. The m3 is basically similar to m2, but its talonid is narrower than the trigonid.

Skeleton.—No skull details are accessible. The horizontal ramus of the lower jaw is deep and robust. The coronoid process is strong and apically rather wide. X−ray photos reveal a long styliform angular process that is characteristic of shrews in general. The temporal fossa is deeply excavated but not pocketed. The masseteric fossa is well−excavated and subdivided by a horizontal crest. The condylar process exhibits two articular facets separated by a rather long and thin interarticular bridge. The mandibular foramen is wide and located in a depression below the crest−like ventral border of the temporal fossa.

The vertebral column includes 7 cervical (most likely), 13 thoracic, 6 lumbar, probably 3 sacral, and probably 13 caudal vertebrae. The caudals are simple and slender. The clavicles are well−developed. The scapula shows a narrow outline, a high spine, and a long acromion, which is apparently bifurcated. The pelvis has a straight ilium, a wide obturator foramen, and a narrow process of the pubis, which originates from the ventro−caudal edge of the pelvis. We cannot totally dissmiss the possibility that the pubic spines formed a symphysis. It seems, however, more likely that a true pubic symphysis is absent. The pubic condition may compare to that of soricomorphs such as the American shrew mole, Neurotrichus gibbsi , where there is no true symphysis but a small tendinous band between the pubic spines (see Reed 1951).

The humerus is gently bowed in anterior view. The well−developed teres tubercle and part of the pectoral ridge are discernible on the right humerus. Both terminate almost halfway down the bone. The extension of the distal end of the humerus compares with that of extant shrews in general. Ulna and radius are somewhat stronger than in Blarina . The olecranon is relatively long and slightly inclined anteriorly. The posterior crest (see Reed 1951, for definition) of the ulna is well−developed, particularly opposite the semilunar notch and the coronoid process. The presence of a proximal ridge on the olecranon cannot be substantiated since that area is damaged on both ulnae. The radius is almost straight. Only the distal carpal row is exposed on the right hand. The trapezium is largest, followed in size by the hamatum. The distal phalanges of the hands are relatively robust, their dorsopalmar thickness being greater than in Blarina . They are rather straight.

The femur is straight and shows a well−developed third trochanter distal to the greater trochanter. The shank departs morphologically from that of other soricids by its unfused tibia and fibula. However, the fibula is tightly pressed against the tibia along the distal half of the bones, and proximally they diverge like in other shrews. Thus, the fused and unfused condition are functionally most likely about the same. The falciform process of the tibia is well−developed and extends along the proximal third of the bone. Few details of the hind foot can be substantiated. The tuber calcanei is well−developed, and the distal phalanges appear to be rather straight.