Читать книгу Hadrosaurs - David A. Eberth - Страница 93

Cervical Vertebrae The axis is relatively complete, with minor deformation to the neural spine. The centrum is longer than it is tall and shorter than the large neural spine; its maximum length is 96 mm and it is 92 mm tall. The centrum is strongly opisthocoelous with a pronounced odontoid process fused to the anterior articular surface and buttressed by a broad ventral lip (Fig. 5.4). This lip terminates in a subrectangular parapophysis on each side of the centrum. The odontoid process is similar in form to that of Zalmoxes, Camptosaurus, Bactrosaurus, and Telmatosaurus, although it is proportionally larger than in Camptosaurus and it lacks the dorsal deflection of Bactrosaurus (Weishampel et al., 1993, 2003; Godefroit et al., 1998; Dalla Vecchia, 2006; Carpenter and Wilson, 2008). The fused odontoid process and ventral buttress are features typical of iguanodontians, and are absent in most hadrosaurids (although present in Telmatosaurus [Weishampel et al., 1993; Horner et al., 2004]). The prezygapophyses are oblong structures that sit flush with the sides of the neural spine. Small, rounded transverse processes occur caudal to the prezygapophyses; each terminates in a diapophysis. The neural arch and spine are robust, extending dorsally 156 mm above the centrum. The vertebral canal is wider than it is tall. The craniodorsal margin of the neural spine is blade like in lateral view and narrows dorsally. It extends cranially over the centrum as a pointed process but does not extend beyond the odontoid process. In lateral view the neural spine has a gentle slope (~60°) that rises caudally. Caudally, the neural arch bifurcates into separate, broad postzygapophyses with ventrally flattened articular facets. A plate from each postzygapophysis extends dorsally and meet at the caudal apex of the neural spine, creating an arch surrounded by a deep, caudally oriented fossa. The caudal articular surface of the centrum is deeply concave and slightly reniform in shape. In caudal view, the outline of the axis is roughly hourglass-shaped. The overall morphology of the axis is similar to the iguanodontians Iguanodon bernissartensis, Camptosaurus, and Bactrosaurus with some affinities to the primitive hadrosaur Telmatosaurus (Norman, 1980; Weishampel et al., 1993; Godefroit et al., 1998; Dalla Vecchia, 2006; Carpenter and Wilson, 2008).

The postaxial cervical vertebrae are roughly equal in length with strongly opisthocoelous centra, a character typical of hadrosauroids (Horner et al., 2004). The centra are broad mediolaterally and elongate axially, with a slight constriction in the middle of the centrum. Both in cranial and caudal view, the centra appear reniform and possess a ventral keel (Fig. 5.5A–C). The neural arch is vertically short and gently slopes caudodorsally. The neural spine is weakly developed or absent on the more cranial cervicals (Fig. 5.5A–C, F). The neural arch and spine broadens caudally approaching the dorsals (although the most caudal cervicals are incomplete). The prezygapophysis is elongate laterally and extends cranially over the centrum with an ovoid articular facet (Fig. 5.5D). The diapophysis is a rounded process that is deflected ventrocaudally from the transverse process. The postzygapophyses are elongate, wedge-shaped, and sweep caudolaterally at a wide angle. The postzygapophyses possess broad, ellipsoidal articular surfaces that are flattened and extend sharply outward.

5.5. Postaxial cervical vertebrae of UTA-AASO-2003. (A) cranial cervical vertebra in anterior view; (B) right lateral view of same; (C) posterior view of same; (D) caudal cervical vertebra in anterior view; (E) isolated cervical neural arch in dorsal view; (F) left lateral view of same. Note the cranial cervical in (A–C) is deformed, with the neural arch deflecting laterally to the right.

Dorsal Vertebrae The dorsal vertebrae consist of at least eight relatively complete specimens – more if miscellaneous fragments are included. Due to the fragmentary and disarticulated nature of the vertebrae, the complete number of vertebrae in the dorsal series is unknown. The cervicodorsal transition is seen in the proximal most dorsals, as they are low with small centra and dorsolaterally directed transverse processes (Fig. 5.6A–C). The neural arch and spines thicken along the dorsal series, with the neural spines increasing in height and straightening dorsoventrally. In one well-preserved cranial dorsal vertebra, the centrum is slightly opisthocoelous and subrounded, broadening posteriorly in lateral view. Above the neurocentral suture, two thin ridges of bone form an arch rising dorsally to the transverse process; within this arch is the parapophysis, which is small and sits at mid-height laterally beneath the transverse process. The transverse process rises dorsolaterally from the neural arch at a sharp angle. It is rectangular in lateral view, ending in a thick, subrounded diapophysis. The vertically arched transverse process is typical of the cranial dorsal series in hadrosauroids. A partial vertebra from the middle dorsal series is composed of a complete centrum with neural arch, a partial neural spine and partial transverse processes (Fig. 5.6D–F). The centrum is amphiplatyan, rounded in cranial and caudal view, and broadens caudally. The transverse processes project laterally at a near 90° angle to the neural spines, a feature that is typical of the middle to sacral dorsal vertebrae. The exact lengths of the transverse processes are unknown as the specimen is incomplete. The neural spine is rectangular in lateral view and projects dorsally. The prezygapophyses are subrounded with lateroventrally facing ellipsoidal facets and project dorsomedially from the base of the neural arch, but do not extend far over the centra. The postzygapophyses are not preserved. The remainder of the dorsal vertebrae are represented by centra only. All specimens are amphiplatyan and relatively rounded in cranial and caudal view.

5.6. Dorsal vertebrae of UTA-AASO-2003. (A) cranial dorsal vertebra in anterior view; (B) right lateral view of same; (C) posterior view of same; (D) caudal dorsal vertebra in anterior view; (E) right lateral view of same; (F) posterior view of same. Arrow notes slickensides on surface of bone.

Dorsal Ribs The ribs are represented by partial, disarticulated elements from the middle to the caudal end of the series (Fig. 5.7). The ribs are similar to those of Tethyshadros and Iguanodon, with the most diagnostic characters residing in the tuberculum and capitulum (Norman, 1980; Dalla Vecchia, 2009). The tuberculum is shorter than the capitulum and the shaft of the most caudal ribs is long and ventrally, rather than caudolaterally, situated. The capitulum is rod like; however, the tuberculum is not preserved. The mid-dorsal ribs (Fig. 5.7D, E) are curved ventrolaterally and appear triangular in cross section. The capitulum and tuberculum are much larger and better defined in the mid-dorsal series. The tuberculum is a small, rounded process that projects vertically away from the surface of the rib. The capitulum is a thin, rectangular projection that extends away from the tuberculum at a 30° angle, ending in a flattened articular surface.

5.7. Dorsal ribs of UTA-AASO-2003. (A) cranial dorsal rib; (B) cranial dorsal rib; (C) caudal dorsal rib; (D) middle dorsal rib; (E) middle dorsal rib.

5.8. Caudal vertebrae of UTA-AASO-2003. (A) first or second caudal vertebra in anterior view; (B) left lateral view of same; (C) posterior view of same; (D) anterior view; (E) proximal caudal vertebra in left lateral view; (F) posterior view of same; (G) middle caudal vertebra in posterior view; (H) right lateral view of same; (I) middle to distal caudal vertebra in anterior view; (J) right lateral view of same.

Caudal Vertebrae There are six caudal vertebrae: two proximal caudals represent the first, and second or third caudals; several middle to distal caudals are present; there are multiple fragmentary centra. In the proximal caudals the centra are round, amphiplatyan, and longitudinally compressed (Fig. 5.8A, B, D, E). The dorsal surface is defined by broad, triangular neural arches. The prezygapophyses are small, ovoid facets that project obliquely while the postzygapophyses are ventrolaterally directed, oblong facets attached to the posterior edge of the neural spine. The neural spines are rectangular in lateral view, tall (>30 cm long), relatively narrow, and deflected distally by ~45° to 60° (Fig. 5.8B, E). The neural spine is three times the length of the centrum and unexpanded distally. Its cranial edge is relatively straight, except for a slight convexity, similar to Eolambia (McDonald et al., 2012). The transverse processes are broken, but are attached at the base of the neural arch. In the middle caudal series, the centrum is heart shaped and the ventral surface is rounded, with a pronounced ventrally deflected hemapophysis for a chevron (hemal arch; Fig. 5.8G, I). Prezygapophyses are prominent while the postzygapophyses project ventrolaterally from the neural arch, with ovoid articular facets visible in lateral view. The neural spine is deflected distally, but at a greater angle (~60°) than proximal caudals. The opening for the neural canal is small and circular. Transverse processes are present and extend laterally with an oval cross section. The remaining middle to distal caudals are incomplete; all have heart-shaped centra and lack neural spines and zygapophyses. Transverse processes become less prominent in more distal caudals. The distal-most caudals have more elongate centra in lateral view.

Ossified Tendons Ossified tendon fragments were recovered but found isolated away from the caudal vertebrae. None were recovered on or associated with the caudal series. They are thin, cylindrical elements, pencil like in appearance. They are thicker along the proximal surface and thin distally.

Scapula The left scapula is a broad, robust element 356 mm in length from the ventral margin to the mid-shaft (Fig. 5.9A–C). The blade of the specimen was damaged during excavation, and is incomplete. The partial blade is straight in lateral aspect and oval in cross section, with no proximal constriction and a mild medial curvature to accommodate the ribcage. The cranial edge of the blade rises gently into the pseudoacromion process, which is a convex, rounded ridge that thins cranially, similar to that of Eolambia (McDonald et al., 2012) and it is gently inclined laterally toward the coracoid suture, as in Probactrosaurus (Norman, 2002). The pseudoacromion process curves ventrally into the coracoid suture. A low deltoid ridge is present, extending caudally as a low prominence from the pseudoacromion process. The coracoid suture is convex and bi-faceted into two thick, prominent surfaces in cranioventral view, similar to Camptosaurus and Mantellisaurus (Paul, 2007; Carpenter and Wilson, 2008). The coracoid suture is thick (94 mm) and curves into the scapular part of the glenoid. The proximal blade expands ventrally to produce a deep, pronounced (60 mm wide × 150 mm long) arched depression that terminates in a broad laterally projected buttress. It is similar in form to the iguanodontians Camptosaurus and Iguanodon and the hadrosauroid Probactrosaurus (Norman, 1986, 2002, 2004; Carpenter and Wilson, 2008). The angle of ascent of the scapula labrum away from the shaft is steep and similar in form to Eolambia (McDonald et al., 2012).

Coracoid The left coracoid is 200 mm long, slightly convex in lateral view, and concave in medial view (Fig. 5.9C–E). A large, elliptical coracoid foramen occurs near the caudal margin at the scapular contact. The glenoid surface is found along the caudoventral margin and is roughly equal in size to its counterpart on the scapula. The scapular suture is elongate and rugose at the glenoid contact, and tapers into a thin and blade-like ridge dorsocranially. The coracoid ridge is present on the cranial margin, forming a low, rounded prominence. Along the cranioventral margin is the base of the sternal process, which is broken and thus its exact shape cannot be determined. Overall the morphology of the coracoid strongly resembles that of Eolambia and Probactrosaurus (Norman, 2002; McDonald et al., 2012).

Ilium The left ilium has a vertical height of 212 mm and a total length of 604 mm, as preserved. The preacetabular process is incomplete missing its distal end (Fig. 5.10). The preserved portion of the preacetabular process is stout and rounded dorsally with a thin ventral margin, giving the process a nearly triangular cross section. It is gently deflected ventrolaterally and contains a well-developed medial shelf, similar to Eolambia and Probactrosaurus, (Norman, 2002; McDonald et al., 2012). The preacetabular notch is open. The pubic peduncle is short (36 mm) and subrounded with a slight inclination cranially, similar to Bactrosaurus, Probactrosaurus, Tethyshadros, and Eolambia (Godefroit et al., 1998; Norman, 2002; Dalla Vecchia, 2009; McDonald et al., 2012). The broad ischial peduncle is 176 mm in length and rectangular. The acetabular margin is 93 mm in length and relatively shallow.

The dorsal edge of the ilium underwent some postburial distortion, displacing the suprailiac crest dorsally (Fig. 5.10A, C). Its dorsal margin caudal to the pubic peduncle was likely straight or slightly convex in lateral view, and sigmoidal in dorsal view. The suprailiac crest begins as a narrow ridge just caudal to the pubic peduncle and it widens caudally, producing a thick (20 mm) curved ridge that deflects caudoventrally, and ends just caudal to the ischial peduncle, where it grades into the postacetabular process. This more cranial position of the suprailiac crest (“antitrochanter”) is distinctive of early hadrosaurids (Brett-Surman and Wagner, 2007). The postacetabular process is broad and triangular in lateral view, as is typical of derived iguanodontids and basal hadrosauroids (Norman, 2004; Brett-Surman and Wagner, 2007). A medial brevis shelf is absent. The medial surface of the ilium is concave, with the deepest portion overlying the ischial peduncle. Multiple facets for sacral rib attachment are visible (Fig. 5.10B). The ilium fits well into the first iliac morphotype recognized by Chapman and Brett-Surman (1990) and bears a strong resemblance to the ilium of Claosaurus (Prieto-Márquez, 2011).

5.9. Pectoral girdle of UTA-AASO-2003. (A) left scapula in lateral view; (B) medial view of same; (C) anterior view of same; (D) left coracoid in lateral view; (E) medial view of same; (F) posterior view of same.

5.10. Left ilium of UTA-AASO-2003. (A) lateral view; (B) medial view; (C) dorsal view.

5.11. Pelvic elements of UTA-AASO-2003. (A) left pubis in lateral view; (B) left ischium in medial view; (C) lateral view of same.

Ischium The left ischium is nearly complete, demonstrating the typical triradiate ornithopod form, although it shows multiple fractures along the shaft (Fig. 5.11). The ischium is 720 mm long, 256 mm from the pubic peduncle to the iliac peduncle, and ranges in width from 76 to 52 mm from the obturator process to the boot. The acetabulum is denoted by a gentle sloping, shallow concavity. The pubic peduncle is smaller than the iliac peduncle, similar to the ratios seen in Probactrosaurus, Bactrosaurus, and Eolambia (Godefroit et al., 1998; Kirkland, 1998; Norman, 2002; McDonald et al., 2012). The iliac peduncle is a broad (98 mm cranial width) and subrectangular process. The pubic peduncle is small (50 mm cranial width), narrow and rectangular. The craniomedial part of the proximal blade is weathered and the shape of the obturator process cannot be determined. A ridge extends dorsolaterally away from the obturator process down the length of the shaft, flattening distally. This tapering ridge is similar to the ischial ridge noted in Probactrosaurus, although more sublime (Norman, 2002). The shaft is straight for most of its length, with a gentle ventral deflection distally, and terminating in an ischial knob, or boot. The ischium fits within the Type 1 Gilmoreosaurus classification used by Brett-Surman and Wagner (2007).

Pubis A partial left pubis, 420 mm long as preserved, is primarily represented by the cranial pubic process, with the remainder shattered along the caudal shaft and acetabular margin (Fig. 5.11). The cranial pubic process is shallowly convex along the ventral margin and concave along the dorsal margin. The cranial pubic process is 180 mm in vertical height, twice that of the minimum constriction of the neck. It is laterally compressed and thins cranially with an axe-like cranial margin, similar to Eolambia (Kirkland, 1998; McDonald et al., 2012), however the margin is not completely preserved. The prepubic neck is relatively long, 12 cm and thin, and similar in form to that of Tethyshadros (Dalla Vecchia, 2009). The dorsal margin of the neck is thick and rounded, while the ventral margin is thin. Both the iliac and ischial peduncles are broken and missing, as is the acetabular margin. The pubis is morphologically similar to that of Tethyshadros and Eolambia (Kirkland, 1998; Dalla Vecchia, 2009; McDonald et al., 2012).

5.12. Right femur UTA-AASO-125. (A) posterior view; (B) anterior view. Arrows denote crocodyliform bite marks (see Noto et al., 2012).

Femur The femur is represented by a partial right element, but its smaller size relative to the other pelvic elements suggests it likely belongs to a different individual (UTA-AASO-125). The femur preserves the proximal third of the bone, including a partial femoral neck, the greater and cranial trochanters, and a small dorsal section of the fourth trochanter (Fig. 5.12). The medial surface is gently bowed, while the lateral surface is straight. The femoral head is missing, with only a fragmentary base indicating the neck was narrow and formed a saddle-shaped depression between the head and greater trochanter. The greater trochanter is craniocaudally elongate and mediolaterally compressed, with a convex dorsal surface, forming the majority of the proximolateral end of the femur. The greater and cranial trochanters were separated by a narrow vertical cleft. The cranial trochanter is weathered but shows it was small and occupied a craniolateral position on the femur. The fourth trochanter is missing, and its ventral extent truncated by a break in the shaft, so its exact shape cannot be determined. What is preserved shows it was positioned along the caudomedial surface of the shaft about a third of the way down, as opposed to about half way down the shaft as is seen in many hadrosauroids. The fourth trochanter was proximally narrow, probably forming a ridge as in Eolambia, Telmatosaurus, and Bactrosaurus (Weishampel et al., 1993; Godefroit et al., 1998; McDonald et al., 2012). Of note, this element preserves evidence of predatory behavior via two pit marks along the caudal shaft (Fig. 5.12A). The pit marks are round impressions in the bone surface attributed to the feeding behavior of a large crocodyliform, discussed in detail in Noto et al. (2012).