Panguraptor lufengensis

You, Hai-Lu, Azuma, Yoichi, Wang, Tao, Wang, Ya-Ming & Dong, Zhi-Ming, 2014, The first well-preserved coelophysoid theropod dinosaur from Asia, Zootaxa 3873 (3), pp. 233-249 : 234-242

Panguraptor lufengensis gen. et sp. nov.

Holotype: Bureau of Land and Resources of Lufeng County LFGT-0103, an articulated partial skeleton that includes the skull and lower jaw, the presacral vertebral column, part of the ribs, the right scapula and partial right forelimb, part of the pelvic girdle and parts of both hind limbs, the right hind limb being almost complete.

Type locality and horizon. Lufeng County, Yunnan Province, China. Shawan Member of the Lufeng Formation ( Fang et al. 2000). This is equivalent to the Dull Purplish Beds of the Lower Lufeng Formation (Series) as defined by Bien (1940). In the Lufeng area, the Lufeng Formation overlies the Lower Jurassic Yubacun Formation and is disconformably overlain by the Middle Jurassic Chuanjie Formation ( Cheng et al. 2004). The age of the Lufeng Formation is probably early - middle Early Jurassic (Hettangian - Pliensbachian), based on biostratigraphic correlations ( Luo & Wu 1995). Magnetostratigraphic analysis has indicated late Sinemurian –?Toarcian for the age of the Lufeng Formation ( Huang et al. 2005).

Etymology. The genus name is from “Pangu” (Chinese), well known in Chinese mythology as the first living being and the creator of all reality, and “raptor” (Latin), meaning “thief” or “robber”. The specific name refers to “Lufeng County”, one of the world’s richest sources of Early Jurassic terrestrial vertebrate fossils.

Differential diagnosis (for genus and species by monotypy). A coelophysid theropod with the unique combination of the following three character states (autapomorphies marked with *): 1*) diagonal (rostrodorsalcaudoventral) ridge on lateral surface of maxilla, within antorbital fossa; 2) elliptical, laterally facing fenestra caudodorsal to diagonal ridge mentioned in previous character state, also present in Zupaysaurus rougieri ( Ezcurra 2006); 3*) distal tarsal IV with hooked craniomedial corner.

Description and comparisons. LFGT-0103 is an articulated partial skeleton, exposed mainly in right lateral view ( Fig. 1 ). The specimen is small, with a preserved skull length (taken from the rostral end of the maxilla to the ventral end of the quadrate because the premaxilla is missing) of 11.1 cm, presacral vertebral column length of ~ 58 cm (trunk/neck length ratio about 1.3), scapula length of 8.6 cm, femur length of 16.4 cm, and tibia length of 18.2 cm ( Table 1). Early theropods normally had a long tail contributing more than half of the total body length, implying that this dinosaur may have measured around two metres long at the time of death. Height at the hip was probably about half a metre.

LFGT-0103 probably represents a sub-adult individual, as indicated by the relatively small body size of the specimen, the large orbit, the lack of fusion between the scapula and coracoid, the lack of ossification of distal tips of the ischia, and the separation of the astragalus and calcaneum. However, the neurocentral sutures are fused, cervical ribs are fused to their respective centra, the ilium is fused to the ischium, and distal tarsal 3 is probably fused to metatarsal III, indicating that the specimen may be close to an adult individual. Growth curves of femur length vs. age for C. rhodesiensis ( Chinsamy 1994) and C. bauri ( Rinehart et al. 2009) suggest, respectively, that this dinosaur died at a sub-adult age of around four years or around two years.

skull length (from preserved rostral end to ventral end of quadrate) 111 preorbital length (preserved) 60 length of internal antorbital fenestra 37 height of antorbital fossa along at caudal margin along lacrimal 20 orbit length 30 orbit height 35 maximum height of skull across orbit midpoint 48 length of infratemporal fenestra 23 height of infratemporal fenestra 31 width of skull above middle antorbital fossa 12 narrist width of skull above orbit 10 length of low jaw (preserved) 111 Cervicals centrum length total height axis 18.5 22 C3 24 14.5 C 4 28 16 C 5 29 15 C 6 31 23 C7 30.5 22 C8 28.5 -

C9 28 -

C10 23 -

Dorsals centrum length total height D 9 24 32 D 10 26 36 D 11 26 35 D 12 25 34 D13 23 23+ sacral 1 length 22+ scapula length 86 maximum width of scapular blade 20 minimum width of scapular blade 11

humerus length 58+ metacarpal I length 10+ metacarpal II length 36 metacarpal II width at midportion 5

metacarpal III length 34 metacarpal III width at midportion 3.5 metacarpal IV length 22 metacarpal IV width at midportion 3

......continued on the next page Skull and lower jaw. The skull is almost complete, and exposed mainly in right lateral view ( Fig. 2 ). Assuming that the missing premaxillary body contributed ~10% of the total skull length (based on skull reconstruction of the “ Syntarsus ”c kayentakatae holotype of Tykoski 1998, figure 6), the intact skull of Panguraptor would have measured 12.4 cm, about half as long as adult skulls of C. bauri (AMNH 7224: 20.7 cm) ( Rinehart et al. 2001), C. rhodesiensis (QG 193: 22.0 cm) ( Raath 1977), and “S.” kayentakatae (MNA V2623: 23.0 cm) ( Rowe 1989). The preorbital length without the premaxilla (6.0 cm) is slightly more than half the preserved skull length (54%), and the maximum rostrocaudal length of the large triangular internal antorbital fenestra is about two thirds of the preserved preorbital length. In contrast, the internal antorbital fenestra is relatively small (about half as high as the orbit and half as long as the maxilla) in a similar-sized (skull length 12.3 cm) juvenile specimen of C. bauri NMMNH P-42200 ( Rinehart et al. 2009). The orbit is subcircular, though with a relatively straight rostral edge, and has a maximum length of 3.0 cm and maximum height of 3.5 cm. The maximum height of the skull at the mid-orbital level is 4.8 cm, or 39% of the estimated skull length. The postorbital portion of the lateral side of the skull is almost completely occupied by the rectangular infratemporal fenestra, which is 2.3 cm long and 3.1 cm high.

Most of the lateral surface of the right maxilla is exposed. The rostral process of the maxilla and the rostrodorsal edge of the maxillary body proper (the portion between the rostral process of the maxilla and the rostral rim of the internal antorbital fenestra, but not including the ascending process) have been lost, and the preserved rostrodorsal margin appears to represent the caudoventral rim of the external naris. The maxillary body proper is rostrocaudally longer than dorsoventrally high as in C. rhodesiensis (QG 193), but the opposite is true in “S.” kayentakatae (MNA V2623). The lateral surface of the maxillary body proper bears a diagonally aligned (rostrodorsal-caudoventral) ridge between the rims of the internal and external antorbital fenestrae. Caudodorsal to this ridge an elliptical fenestra opens laterally, while rostroventral to it are two small fenestrae separated by another short vertical ridge: a rostrally positioned fenestra that is more or less round in lateral view, and a caudally positioned one that is triangular. We interpret the rostral one as the promaxillary fenestra, which occupies a similar position in “S.” kayentakatae . However, the part of the antorbital fossa that lies just caudal to the promaxillary fenestra is smooth in “S.” kayentakatae , rather than interrupted by additional fenestrae. The longitudinal and very prominent alveolar ridge runs along the entire ventral border of the external antorbital fenestra and extends onto the rostral process of the jugal under the orbit. In “S.” kayentakatae the alveolar ridge extends further caudally, continuing onto the caudal process of the jugal. The ascending process of the maxilla is broken away from the rest of the bone, and judging from the orientation of the nasal and the shape of the antorbital fenestra, it would have been elevated about 30 degrees above the horizontal in the intact skull. The orientation of the ascending process is similar in C. rhodesiensis , but steeper in “S.” kayentakatae .

A large portion of the right nasal is visible, exposed in dorsal view. A large and subcircular hole penetrates the rostral half of the bone, probably not a true feature of the animal in life. The dorsal surface of the nasal is smooth, and lacks any evidence of a parasagittal vertical crest. The transverse width of the nasal above the antorbital fenestra exceeds the width of the frontal above the orbit. The transverse width of the prefrontal exceeds its rostrocaudal length. A depression is visible rostrodorsal to the orbit, at the junction between the nasal, prefrontal and frontal.

The robust and almost vertical ventral ramus of the lacrimal separates the caudal border of the antorbital fossa from the rostral border of the orbit. The caudodorsal corner of the lateral surface of the lacrimal bears a rostrodorsal-caudoventrally running groove, the caudal edge of which leads to a small foramen, which should be the exit of the naso-lacrimal duct. The lateral lamina seems to be restricted to the caudal margin of the ventral half of the ventral ramus of the lacrimal, and lacks an expansion at the dorsal end. The rostral process seems to contribute at least one third to the dorsal border of the antorbital fenestra because its rostral end appears to be broken off and incomplete.

The jugal borders the orbit ventrally, and seems to contact the maxilla ventral to the lacrimal as in C. rhodesiensis (QG 165) ( Bristowe & Raath 2004). The caudal edge of the postorbital process of the jugal forms an angle of approximately 70 0 with the dorsal edge of the caudal process, rather than a right angle as in “S.” kayentakatae . The ventral branch of the short and forked caudal process is slightly longer than the dorsal branch, and the slot for the quadratojugal formed by the two branches extends rostrally to a point located ventral to the base of the postorbital process.

The quadratojugal forms the ventral half of the caudal border of the infratemporal fenestra, and contacts the ventral process of the squamosal. This squamosal-quadratojugal contact excludes the quadrate from the border of the infratemporal fenestra, as in “S.” kayentakatae ( Tykoski 1998) but in contrast to the condition in C. rhodesiensis ( Raath 1977) . The frontal-parietal contact region is damaged. The dorsal surface of the frontals bulges along the midline at the level of the caudodorsal corners of the orbits. The rostral portion of the well-developed supratemporal fossa is bounded ventrolaterally by a sharp rimmed edge on the rostral process of the postorbital.

As preserved, the lower jaw is oriented almost perpendicular to the long axis of the skull, and the mandibular glenoid fossa is preserved close to the quadrate head and considerably displaced from the distal condyles of the quadrate. Judging from the position of the external mandibular fenestra, which is normally located underneath the orbit, the rostral end of the lower jaw comparable to the premaxilla is missing; in actuality the preserved lengths of the skull and the lower jaw are same. The caudal end of the lower jaw is overlapped by the atlas and axis. It is difficult to discern the sutures among the bones of the lower jaw. A longitudinal groove is visible on the lateral surface of the middle portion of the dentary, and a longitudinal ridge is present on the lateral surface of the surangular.

Six maxillary teeth are visible, four in the rostral one-third of the maxilla and two at the caudal end of the bone under the caudal part of the orbit. Ten dentary teeth are preserved. All maxillary and dentary teeth are slightly recurved, and bear few or no serrations.

Vertebral column and ribs. Ten cervicals, 13 dorsals and the first sacral vertebra are preserved ( Fig. 1 ). The atlas is disarticulated in such a way that its individual components are hard to identify ( Fig. 2 ). The axis is the shortest of all the cervicals, except for the atlas. The exposed right lateral side of the axial centrum does not bear any clearly visible pneumatic excavations (pleurocoels), although a shallow longitudinal groove is present ( Fig. 3 ). Although the neural spine is not complete, it is clearly tall and craniocaudally long.

The centrum of the third cervical is about 130% longer than that of the axis. Centrum lengths continue increasing steadily until cervical 7, then decrease gradually so that the last cervical is about equal in centrum length to the third one. All postaxial cervicals are elongate, with mid-central constrictions and stout prezygapophyses. The lateral surfaces of the centra of cervicals 4-5 bear deep, elongate pneumatic foramina (“pleurocoels) ( Fig. 3 ). In cervical 4, the rostral part of the pleurocoel is larger and deeper than the caudal part, but in cervical 5 the opposite is the case. Only weak pleurocoels are present on cervicals 6-7, and the condition in the rest of the cervicals is unknown due to poor preservation.

The shafts of the axial ribs are preserved ventral to cervical 3, and one of them extends far enough to lie partly ventral to cervical 4 ( Fig. 3 ). Although it is hard to trace individual ribs in the remainder of the cervical series, the existence of bundles of elongated ribs is evident. The third cervical rib has a small capitulum and tuberculum. In contrast, the remaining cervical ribs have well-developed capitula and tubercula, and are fused to their corresponding vertebrae.

The centra of the well-preserved caudal dorsals are less than twice as long as they are high, whereas the corresponding centra are about twice as long as high in C. bauri and C. rhodesiensis . The neural arches of the cranialmost seven dorsal vertebrae have sheet-like transverse processes that are strongly backswept and triangular when viewed from above. In contrast, the transverse processes of the eighth and ninth dorsals are rostrocaudally narrow and taper laterally ( Fig. 1 ). The parapophysis is short, and situated cranioventral to the transverse process. The neural spines are longer than high and so close together that they almost form a thin, continuous wall along the dorsal midline of the axial column. Only the first sacral is exposed, while the others are covered by the right ilium. This vertebra is slightly shorter than the caudal dorsals, and has a round, flat cranial articular surface.

Appendicular skeleton. An almost complete right scapula is exposed in lateral view, and is broken only near the articulation with the coracoid ( Fig. 1 ). The scapula is long. Its blade is expanded distally, and constricted proximally. The caudal edge of the blade is straight, while the cranial edge is concave. The coracoid is not preserved, indicating that it is not fused with the scapula.

In describing the forelimb, we orient it so that it is held vertically with the radius positioned cranial to the ulna and the flexor surface of the manus facing medially. The distal portion of the right humerus, including what seems to be the part of the deltopectoral crest that lies distal to the apex, is preserved ( Fig. 4 ). The distal end of the humerus curves slightly cranially. In distal view, the medial condyle is slightly mediolaterally wider than the lateral one.

The right radius and ulna are preserved, and are exposed mainly in caudal view ( Fig. 4 ). The well-preserved proximal end of the radius is well preserved, and can be seen in proximal view. The proximal surface is subrectangular in shape, being craniocaudally elongated, and protrudes slightly caudally, unlike the strongly caudally protruded condition in the Lufeng specimen FMNH CUP 2089 ( Irmis 2004). The distal end of the radius is not exposed. The ulna is broken into four pieces, the distalmost of which is detached from the others ( Fig. 1 ).

The right manus is represented by four digits, exposed mainly in medial and caudal views ( Fig. 4 ). Metacarpals I and II are more than twice as wide as metacarpals III and IV. Metacarpal I is less than half the length of metacarpal II, which is about the same length as metacarpal III. The slender metacarpal IV is preserved between metacarpals II and III, and measures about two thirds the length of metacarpal III. Phalanx 1 of digit 1 is not completely exposed, but seems to be as long as phalanx 2 of digit 2, one of the longest phalanges in the manus. The claw of digit 1 is almost the same length as phalanx 2 of digit 2, and is transversely compressed, strongly recurved, and equipped with a large flexor tubercle. The claw of digit 2 is not completely exposed, but seems less well developed than that of digit 1. Three slender phalanges of digit 3 are visible, but there is no trace of a claw. Only one small phalanx appears to be present in digit 4, although an additional small terminal nub may also exist as in “S.” kayentakatae ( Tykoski 1998) . Therefore, the manual phalangeal formula is 2-3-3-1/ 2-X.

Part of the right ilium is preserved ( Fig. 1 ). Most of the pre- and postacetabular processes are missing, but the portion surrounding the acetabulum is well preserved. The pubic peduncle is much stouter than the ischial peduncle, and bears an approximately triangular articular surface for the pubis in distal view. The acetabulum is bordered by a prominent supracetabular crest craniodorsally. The bone surface that forms the caudal and caudodorsal parts of the wall of the acetabulum is relatively narrow transversely and faces slightly laterally. The ischial peduncle is fused to the ischium, although a suture can be vaguely discerned.

The distal portions of the ischia are preserved ( Fig. 5 ). They are straight and mutually appressed, with moderately enlarged ends that are about two times broader craniocaudally than the shaft.

The right femur is broken into two portions. The proximal portion is exposed in cranial and lateral views, and the distal portion in lateral view ( Fig. 1 ). The femoral head is enlarged, well offset from the shaft, and directed craniomedially, with its end turned slightly downward. In proximal view, no clear constriction is apparent, and the proximal surface tapers caudolaterally. A longitudinal bulge is present near the proximal end of the caudolateral surface of the shaft. The anterior trochanter begins at the level of the ventral edge of this bulge, centered transversely on the craniolateral surface of the femur, as a prominent boss that extends ventrally. A tubercle lying caudal to the ventral end of the anterior trochanter may be homologous to the trochanteric shelf. The area proximal to the anterior trochanter is shallowly depressed.

The right tibia and fibula are preserved, and exposed mainly in proximal and lateral views ( Fig. 1 ). In proximal view, they combine to form a flat and roughly square articular surface for the femur. The cnemial crest forms the craniolateral corner of this surface, while the craniomedial corner consists of two small tubercles of the tibia that protrude slightly above the surface. The shafts of both the tibia and fibula are straight, and the fibula is closely appressed to the lateral surface of the tibia. The distal ends of both bones are enlarged.

The astragalus and calcaneum are clearly not fused to each other, or to the tibia and the fibula ( Fig. 5 ). The astragalus is visible in caudodistal view, and the calcaneum is slightly displaced from its original position. The articular surfaces between the astragalus and calcaneum are flat. In lateral view, the calcaneum acquires a semilunate shape.

One distal tarsal is visible, and is very likely to be distal tarsal IV based on its position and shape ( Fig. 5 ). Its proximal surface is slightly depressed, and it has an irregular outline with an expanded cranial portion. The craniomedial corner of the bone is hooked, rather than a simple right angle as in “S.” kayentakatae ( Tykoski 1998) . Right metatarsals III, IV and V are partially exposed ( Fig. 5 ). The proximal end of metatarsal IV is positioned slightly distal and dorsal to that of metatarsal III, indicating that the latter incorporates a fused distal tarsal III. The proximal end of metatarsal III extends ventrally well beyond the metatarsal shaft, and bears a clear ventrolateral process. The proximal surface of metatarsal IV has a triangular shape matching that of distal tarsal IV, with an expanded dorsal portion and a tapering ventral end. The fifth metatarsal is splint-like, with a proximal end at the same level as that of metatarsal III and a distal end that tapers abruptly to a point. The four phalanges of pedal digit III are preserved, as are the proximal three phalanges of pedal digit IV ( Fig. 1 ).

Figures

FIGURE 1. Skeleton of Panguraptor lufengensis gen. et sp. nov. (LFGT- 0103). a, photo; b, interpretive line drawing. Abbreviations: as, astragalus; ax, axis; ca, calcaneum; cer 3 – 10, cervical 3 - 10; dor 7, dorsal 7; dt IV, distal tarsal IV; fdt III, fused distal tarsal III; fi, fibula; hu, humerus; il, ilium; lfe, left femur; lj, lower jaw; is, ischia; ma, manus; mt IV, metatarsal IV; mt V, metatarsal V; pd III, pedal digit III; ph IV- 1, phalanx 1 of pedal digit IV; ra, radius; rfe, right femur; sac 1, sacral 1; sc, scapula; sk, skull; ti, tibia; ul, ulna.

FIGURE 2. Skull and lower jaw of Panguraptor lufengensis gen. et sp. nov. (LFGT- 0103) in right lateral view. a, photo; b, interpretive line drawing. Abbreviations: af, additional fenestra; ar, alveolar ridge; at, atlas; ax, axis; dr, diagonal ridge; emf, external mandibular fenestra; f, frontal; gd, groove on dentary; iaf, internal antorbital fenestra; itf, infratemporal fenestra; j, jugal; l, lacrimal; m, maxilla; n, nasal; or, orbit; pa, parietal; pf, promaxillary fenestra; po, postorbital; pr, prefrontal; q, quadrate; qj, quadratojugal; rsur, ridge on surangular; sq, squamosal; stf, supratemporal fossa.

FIGURE 3. Cervical vertebrae 2 - 6 of Panguraptor lufengensis gen. et sp. nov. (LFGT- 0103) in right lateral view. Abbreviations: a rib, axial rib; C 4 - C 6, cervicals 4 – 6; cp, caudal pleurocoel; rib of cer 3, rib of cervical 3; rp, rostral pleurocoel; sg, shallow groove on axis.

FIGURE 4. Forelimb of Panguraptor lufengensis gen. et sp. nov. LFGT- 0103. Abbreviations: dhu, distal end of humerus; dpc, deltopectoral crest; mtc I, metacarpal I; mtc IV, metacarpal IV; ph I- 1, phalanx 1 of digit I; ph III- 3, phalanx 3 of digit III; ph IV- 1, phalanx 1 of digit IV; pra, proximal end of radius.

FIGURE 5. Distal portions of ischia and right hind limb of Panguraptor lufengensis gen. et sp. nov. LFGT- 0103. Abbreviations: as, astragalus; ca, calcaneum; dt IV, distal tarsal IV; fdt III, fused distal tarsus III; fi, fibula; lis, left ischium; mt IV, metatarsal IV; mt V, metatarsal V; ris, right ischium; ti, tibia.