DESCRIPTION

Maxilla. The nearly complete left maxilla and nasal of P. jonesi belong to the same individual. The body of the maxilla is relatively short rostrocaudally compared to Diplodocus, Nemegtosaurus, and Brachiosaurus and more robust than the maxilla of Camarasaurus (see Upchurch et al. 2004, figure 13.2). A broad, steeply sloping nasal, or ascending, process projects caudodorsally from the mid-region of the maxilla body and presents a long articular surface for the lacrimal (Figure 4). The nasal process is nearly twice the width of the same feature in any other sauropod. Rostral and ventral to the base of the nasal process is a long and broad premaxillary process. The maxilla forms a significant portion of the border of the external naris. The position of the external naris is comparable to that of Camarasaurus and Brachiosaurus. A prominent, triangular lacrimal process projects dorsally from the caudal end of the maxilla. One complete tooth is preserved in the tooth row, along with fragments of at least four others. Two additional fragmentary teeth were found in close proximity to the skull bones. In contrast to the condition in diplodocids, teeth are not restricted to the rostral portion of the maxilla. The maxilla is estimated to have held nine or 10 teeth.

Nasal. The premaxillary process of the nasal is minimally arched, indicating a relatively horizontal dorsal surface of the skull for P. jonesi (Figure 5.1). The premaxillary process is also narrow transversely and has a relatively strong lateral curvature at its distal (rostral) end (Figure 5.2). The lateral, or lacrimal, process of the nasal curves gently ventrally and rostrally but is broken at its distal end. Measurements for the maxilla and nasal are provided in Table 1.

Teeth. In addition to the teeth preserved within and in association with the maxilla, several other isolated sauropod teeth have been recovered from Jones Ranch (Figure 6). Teeth of P. jonesi are Camarasaurus-like, though less spatulate, and differ from the cylindrical teeth of diplodocoids and most titanosaurians. The crown apices are angled lingually. Tooth crowns have sharp mesial and distal margins that lack denticles. Enamel exhibits a wrinkled texture at the base of the crown but is smoother apically. Teeth possess an oblique lingual surface that is angled mesiolingually. However, tooth crowns do not overlap in the jaw. Overlap of tooth crowns is a synapomorphy for most eusauropods (Wilson 2002), but is lost in Paluxysaurus, diplodocoids, Brachiosaurus, and titanosaurians. The labial surface is strongly convex and there is also a narrow region of raised enamel on the lingual surface with shallow depressions on each side. Teeth of P. jonesi generally exhibit V-shaped wear facets, which is in contrast to the high-angled wear facets observed in diplodocoids and titanosaurians. Tooth wear patterns, however, are somewhat variable depending on tooth position and degree of wear.

All of the vertebrae found at Jones Ranch appear to pertain to adult individuals, as neural arches (where preserved) are completely fused to their centra. Presacral vertebrae of P. jonesi are strongly opisthocoelous, lack bifid neural spines, and exhibit an extensive network of vertebral laminae. Herein, I refer to these laminae using the nomenclature of Wilson (1999).

Cervical Vertebrae. Portions of at least nine cervical vertebrae have been recovered from the Jones Ranch quarry thus far, four of which are almost complete. Bone associations in the quarry suggest that all but two of these cervical vertebrae, FWMSH 93B-10-8 and FWMSH 93B-10-19, pertain to a single individual. Cervical vertebrae FWMSH 93B-10-32, FWMSH 93B-10-28, FWMSH 93B-10-19, FWMSH 93B-10-29, and FWMSH 93B-10-30 most likely represent vertebrae C3-C9 of the cervical column, based on comparison of the centrum length ratio between the third and fourth cervical vertebrae with that of Brachiosaurus brancai, the position and height of neural spines, and position relative to one another in the quarry. Most of the Jones Ranch cervical vertebrae have experienced some deformation related to crushing. All of the cervical vertebrae have long centra, as exhibited by high length-to-caudal height ratios, expressed as an elongation index [EI] (sensu Wilson and Sereno 1998; Wedel et al. 2000b; contra Upchurch [1998], who uses length/caudal centrum width to represent the EI). EI values for Jones Ranch cervical vertebrae range from 4.7 in C3 to 7.3 in C4 of the same individual (Table 2).

The height-to-width ratio of cervical centra is slightly less than 1.0 in cranial cervical vertebrae but decreases caudally. Cervical centra are characterized by long, relatively shallow lateral depressions that are perforated by small, well-defined pleurocoels (typically two in number), separated from each other by laminae of bone (Figure 7). The larger, more superficial lateral depressions do not have well-defined margins and occupy more than 80 percent of the centrum length in some vertebrae. Posterior to the parapophyses, the ventrolateral margins of the cervical centra consist of long (and in some cases very thin) pseudo-laminae that in Brachiosaurus brancai have been interpreted as posterior centroparapophyseal laminae (Janensch 1929, 1950). Wilson (1999) argues that the morphology of this feature is inconsistent with the definition of a true parapophyseal lamina, because the landmarks bridged by the thin bone in these cervical vertebrae are not the same as in the dorsal series.

Neural arches span nearly the entire length of the centrum in the cervical series. The neural arch is tall in mid-cervical vertebrae. Prezygapophyses extend beyond the cranial condyle of the centrum. Postzygapophyses are weakly developed and are positioned cranial to the caudal margin of the centrum. Diapophyses are lightly built in cranial cervical vertebrae but become more expansive in the middle and caudal cervical vertebrae. Only cervical vertebrae six (FWMSH 93B-10-28) and eight (FWMSH 93B-10-29) preserve most of the neural spine (Figure 8, Figure 9.1). The spine on C6 is low. In C8 the spine is missing the caudal one-third approximately, but it is tall and broad. Thus, a noticeable increase in neural spine height occurs between vertebral positions six and eight in the cervical series. A similar transition in cervical neural spine height has been documented in Brachiosaurus brancai and Sauroposeidon proteles (Wedel et al. 2000a).

Long, paired spinoprezygapophyseal laminae (sprl) (already defined) originate on the dorsal surface of the prezygapophyses and terminate near the craniodorsal margin of the neural spine (Figure 9). The sprl increases in length and becomes more prominent along the column as the neural spine migrates caudally and increases in height. In addition to broad centroprezygapophyseal laminae (cprl), the prezygapophyses are linked by paired intraprezygapophyseal laminae (tprl)(already defined). The tprl's meet medially where they are joined by a vertical lamina that divides ventrally and connects to the top of the centrum, outlining the neural canal. This accessory lamina creates two bilaterally symmetrical fossae just above the neural canal (Figure 8.2). A similar arrangement of laminae and fossae can be seen in some cervical vertebrae of Brachiosaurus brancai. The spinopostzygapophyseal lamina (spol) is paired, connecting the postzygapophyses to the caudal aspect of the neural spine. Intrapostzygapophyseal laminae (tpol) (already defined) traverse between the medial surface of the postzygapophyses and the midline of vertebrae where they meet above the neural canal. The tpol's and spol's outline a deep fossa behind the neural spine. A median strut runs between the tpol and the base of the neurocentral junction. Two fossae on either side of this lamina, in conjunction with the neural canal, form a tri-radiate pattern, similar to that on the cranial surface of the vertebrae (Figure 8.3). These fossae are bounded laterally by short centropostzygapophyseal laminae (cpol).

In contrast to most somphospondylians, the diapophyseal laminae are reasonably well developed in cervical vertebrae of Paluxysaurus jonesi. Four laminae stem from the diapophyses. The posterior centrodiapophyseal (pcdl) and postzygodiapophyseal (podl) laminae branch at a shallow angle away from the diapophysis caudoventrally and caudodorsally, respectively. A dorsoventrally wide, long, and shallow depression opens caudal to the diapophysis between the pcdl and podl. The acdl is a thin strut of bone projecting cranioventrally, terminating near the neurocentral junction. The prezygodiapophyseal lamina (prdl) is not prominent in cranial cervical vertebrae, but in succeeding vertebrae, as the diapophysis migrates caudally and the transverse processes increase in breadth, the prdl expands and forms broad, flat wing-like extensions that connect the prezygapophysis to the diapophysis (Figure 9).

Differences in morphology among cervical vertebrae from Jones Ranch can be explained by individual variation, serial variation along the cervical column, taphonomic influences, or a combination of these factors. Variability in calculated elongation indices within a single individual has been documented in other sauropod taxa (e.g., Wedel et al. 2000a). Therefore, the large difference in EI values between cervical vertebrae from Jones Ranch can be expected. The specimen FWMSH 93B-10-8, a cranial cervical vertebra, probably C5, was found isolated in the quarry. The vertebra is missing the prezygapophysis, diapophysis, and parapophysis from the left side and the cranial condyle of the centrum (Figure 10). General similarities, as suggested by Wedel (2003), in the form of this vertebra with cervicals of an unnamed titanosaurian from Brazil described by Powell (1987) may be due to preservation. Other cervicals from Jones Ranch do not closely resemble the vertebrae of the Brazilian taxon.

Cervical Ribs. Cervical ribs run subparallel to the length of the vertebral centrum, angled slightly ventrally. The ribs are long; in cranial cervical vertebrae, the ribs overlap with at least two succeeding vertebrae. Cervical ribs are dorsoventrally flattened proximally, becoming more rod-shaped along their length distally (Figure 11). The tuberculum is broad at its base and narrows dorsally where it meets the diapophysis. In cranial cervicals the diapophysis and tuberculum fuse along a nearly vertical line, but with caudal migration of the diapophysis along the cervical column, they are offset from one another in caudal cervicals, and the tuberculum angles strongly caudodorsally. Capituli are either not well preserved or displaced by post-depositional deformation in most cervical vertebrae, therefore making description of its orientation and morphology difficult.

Dorsal Vertebrae. A total of 14 dorsal vertebrae are known from Jones Ranch. Five dorsal vertebrae have been completely prepared, including two nearly complete, articulated cranial dorsal vertebrae, FWMSH 93B-10-13, which were partially described by Gomani et al. (1999). The remaining three dorsal vertebrae were found in different parts of the quarry and represent different positions within the dorsal series, most likely from more than one individual. In addition, a series of the last six vertebrae of the presacral column preserved in articulation with dorsal ribs, a complete pelvis, and a portion of the hindlimb of a single individual have been partially prepared. However, only the cranial most vertebra in this series is informative, as the caudal five are less exposed and are extensively weathered. Measurable lengths of preserved limb elements from the quarry suggest that all sauropods individuals were comparable in size. Therefore, whereas representing different individuals, dorsal vertebrae from different regions of the presacral series are described based on the assumption that they are directly comparable.

The height-to-width ratio of dorsal vertebral centra is less than 1.0, except for the last dorsal centrum, which is approximately circular (Table 3). The ventral surfaces of the caudal half of the first dorsal centrum and some caudal dorsal vertebrae are strongly bevelled caudoventrally (Figure 12). The cranial articular ball is prominent in cranial and caudal dorsal vertebrae and the caudal articular surface of the centrum is strongly concave in all dorsals. Lateral pleurocoels in the dorsal vertebrae possess a distinct dorsal border. There is slight variation in the shape of pleurocoels, from clearly oval in the first dorsal vertebra to more eye-shaped in the third and more caudal dorsal vertebrae. Pleurocoels are elongated in dorsal vertebrae three and four, possessing sharply defined fossae occupying more than two-thirds of the centrum with the pneumatocoel at the cranial end. Pleurocoels become craniocaudally compressed near the end of the dorsal series and are positioned cranially on the centrum.

In dorsal vertebrae of P. jonesi the parapophysis consists of a short, curved protrusion of bone that is convex on the cranial surface and, at least in caudal dorsal vertebrae, concave caudally. In the first dorsal vertebra the parapophysis is positioned about midway up the centrum, just cranial to the pleurocoel. Parapophyses migrate dorsally passing caudally along the dorsal series. The parapophyses migrate from the centrum to the neural arch between dorsal vertebrae three and four. In one caudal dorsal vertebra from Jones Ranch, TMM 42488 JP 1.2, the parapophysis occurs dorsal to the prezygapophysis but remains below the level of the diapophysis (Figure 13). This has not been documented in any other sauropod. Only Haplocanthosaurus priscus and Brachiosaurus brancai approach this condition. In other taxa the parapophysis is level with or ventral to the prezygapophysis in caudal dorsal vertebrae. Other caudal dorsal vertebrae from Jones Ranch do not offer sufficient preservation to assess the pervasiveness of this morphology.

Transverse processes of cranial dorsal vertebrae are robust, expanded dorsoventrally as well as craniocaudally. They are less expanded in caudal dorsal vertebrae. Diapophyses are horizontal in cranial dorsal vertebrae but begin to incline dorsally in the middle of the series and become more strongly angled in caudal dorsal vertebrae, where they form approximately a 30° angle with the neural spine.

Neural spines are vertical in cranial dorsal vertebrae but are directed slightly caudally in caudal dorsal vertebrae. This upright orientation is the primitive condition exhibited by all sauropods except somphospondylians. In somphospondylians, dorsal neural spines are strongly angled caudally. In P. jonesi dorsal neural spines are broadly expanded transversely at their base and taper distally. Neural spines do not appear to flare at their distal ends as they do in Brachiosaurus; however, the terminal end of the neural spine is not completely preserved in any of the dorsal vertebrae from Jones Ranch. If dorsal neural spines did flare in P. jonesi, it was very minor.

Neural spines have a slightly greater craniocaudal breadth in dorsal vertebrae three and four, due to greater development of the prespinal lamina. There is no evidence of a hyposphene in the first dorsal vertebra. However, a strongly developed hyposphene is present on the caudal surface of the fourth dorsal vertebra. The hyposphene is much reduced on mid-dorsal neural arches, but the condition is presently unknown in caudal dorsal vertebrae. As in the cervical vertebrae, the cranial face of the neural arch in cranial dorsal vertebrae is excavated by symmetrical fossae that occur above the neural canal and below the prezygapophyses.

The neural arches of the dorsal vertebrae of P. jonesi are supported by a greater number of vertebral laminae than those in the cervical vertebrae. Prominent tprl's connect the prezygapophyses in the first dorsal vertebra. A shorter, more horizontal tprl can be seen in dorsal vertebra three, but the lamina is not clearly developed in more caudal dorsal vertebrae. A short, but distinct horizontal connection can be recognized between the postzygapophyses in dorsal vertebra four but is absent in the first dorsal vertebra and in the caudal dorsal vertebral region. The cprl is broad and less sharply defined than other laminae throughout the dorsal series. In cranial dorsal vertebrae the cpol's form broad, parallel vertical columns on either side of the neural canal. In the fourth dorsal vertebra the cpol connects the base of the hyposphene to the caudal aspect of the neurocentral junction, and thus never actually contacts the postzygapophyses (Figure 14). With reduction of the hyposphene in caudal dorsal vertebrae, the cpol is also reduced or disappears completely. Mid-dorsal neural arches possess a small, shallow depression on the caudal surface, lateral to the hyposphene on each side of the vertebra.

Several laminae support the diapophysis and parapophysis on the neural arches of the dorsal vertebrae. The first dorsal vertebra has prominent cranial and caudal centrodiapophyseal laminae. The acdl meets the cprl at the craniodorsal margin of the centrum, forming deep infraprezygapophyseal and infradiapophyseal fossae craniodorsal and caudoventral to the acdl, respectively. No second dorsal vertebra has been recognized. In the third dorsal vertebra, the acdl is absent. A pcdl is present at this position in the dorsal series, and a single, large fossa is formed on the lateral aspect of the neural arch. In the fourth dorsal vertebra, the parapophysis has migrated dorsally onto the neural arch, just cranial and ventral to the diapophysis. In this case the parapophysis bisects what was the acdl in the first dorsal vertebra and is supported above and below by thin paradiapophyseal (ppdl) and anterior centroparapophyseal (acpl) laminae, respectively. The acpl appears in the mid- and caudal dorsal vertebrae of all sauropods except Shunosaurus (Wilson 2002). It is slightly longer than the ppdl in the fourth dorsal vertebra of P. jonesi and is oriented almost vertically. In more caudal dorsal vertebrae the ppdl is longer than the acpl. The pcdl is less expansive in mid- and caudal dorsal vertebrae as it is in cranial dorsal vertebrae. A posterior centroparapophyseal lamina (pcpl) first appears in the fourth dorsal vertebra and persists into caudal dorsal vertebrae. The presence of this lamina is a derived character shared by most neosauropods plus Jobaria but has been lost several times in the evolutionary history of sauropods. In dorsal vertebra four the pcpl connects the caudoventral aspect of the parapophysis to the cranial surface of the pcdl near its junction with the top of the centrum. The pcpl essentially divides the large infradiapophyseal fossa in half. Consequently, caudal to the parapophysis, the infradiapophyseal fossa is long and narrow. Below the parapophysis the acpl, pcpl, and dorsal margin of the centrum define the borders of a deep, roughly triangular infraparapophyseal fossa. The acpl and pcpl are less well developed and occur higher on the neural arch in caudal dorsal vertebrae. The conspicuous fossae that occur on the lateral surface of the neural arch in cranial and middle dorsal vertebrae also exhibit a dramatic reduction in the last dorsal vertebrae.

In dorsal vertebra three and more caudal vertebrae a short prezygoparapophyseal lamina (prpl) connects the parapophysis to the lateral surface of the prezygapophysis. The podl is short in cranial dorsal vertebrae, terminating proximally on the transverse process. In middle and caudal dorsal vertebrae the podl extends farther onto the caudal surface of the transverse process. A prespinal lamina (prsl) is particularly well developed in the third and fourth dorsal vertebrae as a thin plate of bone spanning the entire length of the neural spine. The prsl is rudimentary in the first dorsal and in caudal dorsal vertebrae and does not extend to the distal end of the spine. A weak postspinal lamina (posl) is visible in dorsal vertebra one, but there is no evidence of a posl in the other dorsal vertebrae where the caudal aspect of the neural spine is observable. In cranial dorsal vertebrae the sprl terminates near the base of the neural spine. In caudal dorsal vertebrae the sprl ends high up on the craniolateral aspect of the neural spine (Figure 14.1). In all dorsal vertebrae the spol originates on the lateral surface of the postzygapophyses and projects dorsomedially on both sides toward the midline of the neural arch forming a broad, V-shaped concave surface behind the neural spine. Only in mid-dorsal vertebrae of P. jonesi is the spol divided. A divided spol is a derived character that is lost in titanosaurians and is unknown in Euhelopus, the most basal somphospondylian, but is present in all other eusauropods, excluding Shunosaurus.

All P. jonesi dorsal vertebrae have expanded spinodiapophyseal laminae (spdl), which are responsible for producing a webbed appearance in the space between the neural spine and the diapophysis. In caudal dorsal vertebrae the spol is expanded equal to or more than the spdl and therefore also results in a broadly expanded region at the base of the neural spine. The spdl parallels the spol proximally on mid-dorsal neural arches. It is not clear whether the two laminae meet distally on the spine. Dorsal vertebrae possess a narrow but deep fossa on the caudal half of the lateral aspect of the neural spine that is bounded by the spdl, spol, and podl. One mid-dorsal vertebra, FWMSH 93B-10-27, exhibits a short accessory lamina that extends cranioventrally from the postzygapophysis and connects to the caudal aspect of the pcdl. In FWMSH 93B-10-27 this lamina defines the dorsal margin of a large, triangular fossa. In dorsal vertebra four (FWMSH 93B-10-13), there is an accessory horizontal lamina connecting the hyposphene to the middle of the pcdl, which serves as the dorsal border to the infrapostzygapophyseal fossa below, bounded by the pcdl and cpol cranially and caudally, respectively. The accessory postzygodiapophyseal lamina observed in FWMSH 93B-10-27 occurs above the fossa in FWMSH 93B-10-13. An isolated centrum of a dorsal vertebra (FWMSH 93B-10-48) that has lost most of its exterior bone to erosion reveals a network of thin laminae of bone forming a honeycomb-like pattern. This picture of the internal pneumatic structure of presacral vertebrae in the Jones Ranch sauropod differs from the conclusions reached by Gomani et al. (1999) and Wedel (2003).

Dorsal Ribs. Dorsal ribs are broad, plank-like bones (Figure 15). Rib heads are somewhat triangular-shaped to almost L-shaped, with the capitulum oriented almost perpendicular to the proximal rib shaft. The capitulum is considerably longer than the tuberculum and narrows to a point at its distal end. The proximal third of the dorsal ribs has a convex caudal surface and concave cranial surface. The proximal portion of a dorsal rib from Jones Ranch (FWMSH 93B-10-13) is rotated about the axis of the shaft distal to the proximal end (Figure 15.1). This twisting of the shaft is absent in FWMSH 93B-10-23 (Figure 15.2), which presumably represents a more cranial rib of P. jonesi. Some dorsal ribs exhibit pneumatic cavities on their proximal ends. Two distinct pneumatic cavities are preserved in FWMSH 93B-10-13. The smaller of the two excavates the tuberculum, and the larger is centrally located on the rib head and opens toward the rib shaft (Figure 15.2). However, the cavity itself does not seem to extend into the shaft of the rib.

Sacral Vertebrae. A nearly complete sacrum (FWMSH 93B-10-27) is known for P. jonesi but is still undergoing preparation from a massive concretion. Only the ventral surface of the sacrum has been prepared. Four sacral vertebrae are preserved (S2-S5). A dorsosacral vertebra would have contributed a fifth vertebra (S1) to the sacral series but the centrum is missing, and all that is preserved are the transverse processes, which articulate with the ilia at the cranial end of the sacrum. The absence of a sixth sacral vertebra distinguishes P. jonesi from more derived somphospondylian sauropods. The centrum of the second sacral vertebra (S2) is partially exposed in three dimensions. It is small and appears compressed dorsoventrally. Relatively large sacral foramina occur between the transverse processes, or sacral ribs, of the vertebrae. Transverse processes are narrow craniocaudally at mid-length but expand distally and fuse to form the sacrocostal yoke. A more complete description of the sacrum awaits further preparation of the specimen.

Caudal Vertebrae. More than 37 caudal vertebrae have been collected from Jones Ranch. This number includes two associated series: five mid-caudal vertebrae (FWMSH 93B-10-21) and eight articulated distal caudals (FWMSH 93B-10-17). Pleurocoels are absent from the lateral surfaces of the centra, and the lateral depressions that are seen in caudal centra of some sauropod taxa have not been observed in P. jonesi except in one proximal centrum. All caudal vertebrae of P. jonesi are amphiplatyan. Centrum height is less than centrum width in proximal and mid-caudal vertebrae (Table 4). Distal caudal centra are spool-shaped and are typically slightly taller than they are wide. Some mid-caudal centra are rhombus-shaped in lateral view, with the articular surfaces angled craniodorsally (Figure 16.1). Chevron facets are weakly developed on the ventral surface of most caudal centra. A clearly defined hyposphene cannot be recognized in any caudal vertebra.

Transverse processes, or caudal ribs, are short and span the neurocentral junction in the first few caudal vertebrae. The processes are triangular in shape and curve slightly in the caudal direction. Transverse processes increase in length in mid-caudals and occur high on the centrum but do not extend onto the neural arch. In mid-caudal vertebrae transverse processes are dorsoventrally compressed and broad craniocaudally at their origin, tapering laterally with a stronger caudal curvature. The neural arch is positioned cranially on the centrum of caudal vertebrae. Neural spines are short in proximal and mid-caudal vertebrae and are slightly caudally inclined (Figure 16.1). Proximal and mid-caudal neural spines flare laterally at the distal end (Figure 16.2–3).

Prezygapophyses are short and expanded dorsoventrally in the proximal most caudal vertebra, but extend well beyond the anterior margin of the centrum to articulate with the preceding vertebra in other caudals (Figure 16 and Figure 17). Prezygapophyses are nearly horizontal in the majority of caudal vertebrae, but are angled craniodorsally in mid-caudals. Postzygapophyses are short throughout the caudal series.

Distinct spinoprezygapophyseal and spinopostzygapophyseal laminae are visible in proximal and mid-caudal vertebrae. Mid-caudal neural arches possess an intraprezygapophyseal lamina (tprl), which together with the sprl on each side of the arch encloses a prespinal fossa above the neural canal (Figure 16.2). Weakly developed prezygodiapophyseal laminae connect the transverse processes to the prezygapophyses in some mid-caudal vertebrae, but are not visible in proximal caudals. Weak pre- and post-spinal laminae are preserved on the distal half of proximal and mid-caudal neural spines. Some proximal to mid-caudal vertebrae have lost the posl. None of the aforementioned laminae persist in distal caudals (Figure 18), and no other laminae present in the presacral series can be traced into the caudal region.

Chevrons. Three chevrons and fragments of at least three others were recovered from the Jones Ranch quarry (Table 5). Chevrons are Y-shaped in craniocaudal view but the rami are weakly forked proximally resulting in a narrow haemal canal. Chevrons are not forked in lateral view, which is a feature common to all titanosauriforms (Wilson and Sereno 1998). Shaft length of chevrons is greater than the length of the haemal canal. Chevron facets migrate to a more medial position passing caudally along the tail, and the haemal canal gradually becomes more restricted and shallower. In caudal chevrons the haemal canal becomes closed (Figure 19). Shafts are broader craniocaudally than transversely. Cranial chevrons broaden distally into the shape of a paddle. Caudal chevrons, on the other hand, taper distally. The shafts of chevrons have a slight caudal curvature. Chevron articular surfaces are round and angled medially.

Pectoral Girdle

Scapula. Two almost complete scapulae were available for study, although according to the field notes of J. Pittman and D. Winkler, several other scapulae or scapulocoracoids have been collected from Jones Ranch but await preparation. The scapula of P. jonesi exhibits a strong medial concavity. The scapular blade is convex on the lateral surface and is roughly D-shaped in cross-section. The blade thins and flattens distally and is moderately to strongly expanded at the distal end on both the caudoventral (glenoid) and craniodorsal (acromial) margins, but to a greater degree along the latter (Figure 20). The scapular blade is concave along the acromial edge, but the degree of this curvature varies among individuals. The opposite margin is straight. The long axis of the scapular blade is oriented perpendicular to the coracoid articular surface. The coracoid articular surface of the scapula is longer than the glenoid surface. The scapular glenoid curves caudally and is slightly bevelled laterally. The acromion process is relatively short in P. jonesi scapulae and protrudes from the base of the shaft at a slightly acute angle. The supraspinous fossa occupying the area of the acromial notch, caudodorsal to the acromion process, is variable but generally weakly developed. The infraspinous fossa is broad and shallow.

Coracoid. Two right coracoids were found in close proximity to a right scapula and sternal plate (FWMSH 93B-10-24). A third coracoid is preserved in articulation with a left scapula (TMM 42488). The left coracoid (TMM 42488) strongly resembles the coracoid of Camarasaurus grandis (YPM 1901). The coracoid is rounded along its cranioventral margin, which is similar to all non-somphospondylian sauropods (Wilson 2002), and the medial surface of the bone is moderately concave (Figure 20 and Figure 21). Proximodistal length of the coracoid is less than the length of the scapular articulation, which is also primitive for sauropods (Wilson 2002, Table 6). The scapular articulation is straight. The glenoid end is thick and is bevelled laterally, similar to the scapula, whereas the bone thins considerably toward the cranial border. The caudal edge of the glenoid protrudes from the body of the coracoid as a distinct caudoventral process. The coracoid foramen is located near the middle of the bone very close to the margin of the scapular articulation.

Sternal Plate. The sternal plate of P. jonesi is a thin, flat bone and approximates a half-moon in outline (Figure 22). The medial margin is rounded, and the lateral border is straight. The sternal plate is elongated craniocaudally; its greatest length (measured from the craniodorsal margin to the caudoventral margin) is about twice that of the greatest transverse breadth (Table 6).

Forelimb

Almost every bone from the forelimb is known for Paluxysaurus jonesi with the exception of some manual elements. P. jonesi has a shorter forelimb than hindlimb, which is typical of most sauropods except for Brachiosaurus brancai, B. altithorax, and Cedarosaurus weiskopfae. The forelimb bones of P. jonesi are slender relative to their overall length. Limb ratio measurements for P. jonesi and comparable values for other sauropod taxa are provided in Appendix 1.

Humerus. Of four humeri from Jones Ranch, three are nearly complete. An adult humerus of P. jonesi measures approximately 120-130 cm in length (Table 7). The humerus is hourglassed shaped. It is relatively gracile, and the transverse diameter at mid-shaft is slightly greater than the craniocaudal breadth (Figure 23). The proximal end of the humerus is relatively flat along the dorsal surface, with rounded lateral and medial corners, and little manifestation of a humeral head caudally, which occurs as a low, rounded bulge near the dorsomedial border. The proximal end is expanded medially, resulting in a concave medial edge of the shaft. The lateral margin exhibits minimal curvature. The deltopectoral crest is long and relatively narrow transversely.

The distal end of the humerus is expanded transversely. Distal breadth is approximately twice the minimum breadth of the shaft. On the caudal surface of the distal end, a well-defined olecranon fossa is bounded on both sides by distinct supracondylar ridges that extend from the lateral and medial epicondyles nearly to mid-shaft in some individuals. The distal articular surface is flat but with rugose texture, and in distal view the condyles angle caudolaterally.

Ulna. The forearm bones are slightly greater than 60% the length of the humerus (Appendix 1). One complete left ulna (FWMSH 93B-10-7) is known from the Jones Ranch assemblage. The distal end is bent proximomedially and caudally relative to the axis of the shaft as a result of taphonomic processes (Figure 24.1-4). The ulna is relatively slender, having a length that is over three times the greatest breadth at the proximal end (Table 7). Near mid-length the shaft is compressed craniocaudally. The distal end is considerably narrower than the proximal end and is approximately round in cross-section, but could be missing some bone on the caudomedial side (Figure 24.5–6). The proximal articular surface is nearly flat with a slightly elevated olecranon region. The proximal end of the ulna is approximately L-shaped with a deep radial fossa, which extends past mid-shaft of the bone, gradually shallowing and disappearing towards the distal end. A prominent caudal ridge extends from the proximal surface distally two-thirds of the length of the shaft. The craniomedial condylar process at the proximal end is longer and narrower than the craniolateral process (Figure 24.6).

Radius. A complete left radius (FWMSH 93B-10-7) of P. jonesi is preserved, found associated with the ulna described above (Figure 24.7–12). Similar to the ulna, the distal third of the radius is bent proximocaudally relative to the long axis of the shaft. The radius is somewhat shorter than the ulna (Table 7). The radius is compressed craniocaudally along the length of the shaft (Figure 24.9–10). Both ends are expanded transversely, the distal end being slightly more expanded than the proximal end. Distal breadth is close to twice the breadth at mid-shaft. The proximal end is triangular in proximal view, and in distal view the condyle is sub-rectangular, the long axis running mediolaterally (Figure 24.11–12). A prominent ridge begins on the lateral margin of the shaft approximately one-third the length of the bone from the distal end, extends onto the caudal surface about halfway, and terminates at the caudal edge of the proximal condyle (Figure 24.8). This ridge fits into the radial fossa of the ulna.

Manus. A nearly complete set of metacarpals was found together along with a distal radius (FWMSH 93B-10-36). In addition to those, two complete, isolated metacarpals are known along with a third that is missing its distal portion. Comparisons of the isolated metacarpals with the articulated hand suggest that the third metacarpal was the longest in the forefoot (Table 7). The longest metacarpal-to-radius ratio could not be determined for a single individual. FWMSH 93B-10-10, identified as a metacarpal IV, was found near the ulna and radius described above (FWMSH 93B-10-7) and may belong to the same individual. A minimum ratio of the longest-metacarpal-to-radius-length using the latter element was calculated to be 0.47 (Appendix 1). Metacarpals of P. jonesi are relatively long and slender compared to diplodocids. Assuming metacarpals of FWMSH 93B-10-36 are identified to the correct position in the manus, metacarpal I is shorter than metacarpal III, which is a primitive condition among sauropods (Upchurch 1998).

All of the metacarpals are expanded at their proximal end (Figure 25). Distal ends are only slightly expanded relative to the shaft. Two metacarpals exhibit a dorsolateral curvature of the distal shaft. In one other metacarpal, the shaft is contorted so that the proximal and distal ends are oriented obliquely to one another. FWMSH 93B-10-22, identified as metacarpal II, has a triangular-shaped proximal condyle and a well-developed, rounded distal condyle (Figure 25.1). The proximal end is bevelled cranially and is expanded caudomedially. The proximal third of the medial surface of the bone is flat. At mid-shaft, a low ridge runs a short distance parallel to the length of the bone at the craniomedial edge. A probable metacarpal III (FWMSH 93B-10-1) is wedge-shaped in proximal view (Figure 25.2). The bone is broken at the distal end, but the preserved portion of the shaft is straight. Metacarpal IV (FWMSH 93B-10-10) is triangular to L-shaped in proximal view (Figure 25.3). The distal condyle is weathered but is generally rounded in outline.

Pelvic Girdle

A large sandstone concretion (FWMSH 93B-10-27), containing a sacrum with associated pelvic girdle elements, other hindlimb bones, and dorsal vertebrae was removed from the Jones Ranch locality in 1997 and is currently being prepared in Fort Worth. The following description of the pelvic girdle is based on partially prepared elements of FWMSH 93B-10-27 plus additional material (pubes and ischia) found in the quarry.

Ilium. The cranial half of the ilium curves strongly laterally. The medial surface of the cranial half of the ilium faces cranioventrally but is not quite perpendicular to the axis of the sacrum. Its preacetabular process projects craniolaterally and is somewhat tapered. The distance separating the preacetabular processes of the ilia is significantly greater than the craniocaudal length of the ilium (Table 8). The pubic peduncle of the ilium is relatively short, and the ischial peduncle is significantly reduced, as is typical in all sauropods. Cranial to the pubic peduncle the ventral surface of the ilium is roughly straight, as opposed to concave.

Pubis. In addition to FWMSH 93B-10-27, an associated pubis and ischium (TMM 42488 JP 1.47, figures 26.1 and 26.2) were collected by J. Pittman in the early years of excavation at Jones Ranch, opposite pubes are associated with an ischium from another individual (FWMSH 93B-10-35, figure 26.3), and an articulated pubis and ischium were recently removed from the field and prepared (FWMSH 93B-10-51, figure 26.4). The pubis is a long, robust bone. The proximal end is moderately expanded craniocaudally and is thickened transversely at the iliac peduncle and acetabular surface. Development of the ambiens process is minor. The shaft of the pubis is uniformly broad craniocaudally and the distal end is slightly expanded transversely relative to mid-shaft. The proximal one-half of the pubis is slightly laterally deflected beginning at the pubic apron, creating an S-shaped pubic symphysis similar to other eusauropods (Wilson 2002). The shaft of the pubis is long relative to the length of the puboischial articular surface, which is a primitive sauropod feature (Wilson and Sereno 1998).

Ischium. Five ischia have been collected (four prepared), with an additional specimen still in the field. Most of these are associated with other pelvic girdle elements. The ischium is a slender bone with an expanded pubic peduncle that is rectangular and forms a long articular surface for the pubis (Figure 26.2 and 26.4). The iliac peduncle is long and thickened transversely. A deep but not expansive acetabular surface is apparent cranioventral to the iliac peduncle. Distal to the pubic peduncle, the ischial blade abruptly narrows. The junction of the proximal shaft of the ischium and the pubic peduncle forms an angle of about 150 degrees, the shaft of the ischium projecting as much ventrally as caudally. In cross-section the distal shaft is thin and flat. The shaft is rotated about its long axis with respect to the proximal end so that in distal view the broader aspect of the shaft is angled ventromedially. The distal ends of opposing ischial shafts meet medially, forming a broad angle greater than 90 degrees in cross-section. The greatest length of the ischium is significantly shorter than that of the pubis (Table 8), but the length of the ischial shaft is nearly as long as the shaft of the pubis, which is plesiomorphic for this taxon. In articulation, at the ventral end of the puboischial contact, the pubis and ischium form nearly a right angle.

Hindlimb

Complete examples of upper and lower hindlimb bones are known for P. jonesi but few of the bones of the hindfoot have been identified. As in the forelimb, hindlimb bones are long and slender. Limb ratio measurements for the femur are compared across some sauropod taxa in Appendix 1. Similar comparisons were not made for the tibia and fibula due to the inconsistency in orientation of the tibia and direction of measurement chosen by different researchers for these bones.

Femur. The femur is the best-represented sauropod limb element from the quarry. Six complete or partial femora were available for study. Two of the better-preserved femora are depicted in Figure 27. Three additional femora were confidently identified in the field but have yet to be prepared. According to Pittman's field notes, a tenth femur was found in the late 1980s, but this bone cannot be located. The estimated minimum number of five sauropod individuals from the quarry is based on the number of preserved femora.

At mid-shaft the transverse breadth is nearly twice the craniocaudal width in most individuals (Appendix 1). The proximal one-third of the shaft exhibits the prominent lateral bulge and medial deflection that has been interpreted as a synapomorphy of Titanosauriformes. As in other sauropods, the fourth trochanter is preserved as a broad, low ridge on the caudomedial surface of the shaft.

At the proximolateral border of the femur the greater trochanter is not prominent. The proximal surface of the femoral head is notably higher than the proximolateral border. The distal end of the femur is oriented perpendicular to the shaft and distal condyles are well developed. In distal view the condyles trend slightly craniolaterally-caudomedially and are separated by deep intercondylar fossae on both the cranial and caudal surfaces. A lateral epicondyle also appears to be moderately developed at the distal end. Based on closely associated but not articulated humeri and femora, humero-femoral length ratios for P. jonesi fall between 0.85 and 0.88.

Tibia. Four tibiae have been identified. One is completely prepared (FWMSH 93B-10-15), and the other three are only partially prepared (TMM 42488, FWMSH 93B-10-45, and FWMSH 93B-10-46). FWMSH 93B-10-15 is a left tibia found with its corresponding fibula (Figure 28.1–6). Another left tibia (TMM 42488) was collected prior to the involvement of SMU at Jones Ranch, and its provenance in the quarry is unknown.

The shaft of the tibia is strongly compressed craniomedially-caudolaterally and is more than twice as broad in the opposite direction, craniolaterally-caudomedially. The tibia is expanded at both ends relative to mid-shaft, but to a much lesser extent at the distal end (Table 9). The distal end is slightly wider transversely than craniocaudally, the articular surface for the ascending process extending out craniolaterally. The craniolateral margin of the shaft is concave, whereas the caudomedial aspect is straight. The proximal condyle is flat and diamond-shaped in proximal view. At the lateral margin, the proximal surface is strongly expanded, forming a broad tubercle that continues a short distance distally along the shaft as a low ridge. The proximal condylar surface, however, is more elongate fore to aft than transversely (Table 9). Paluxysaurus jonesi tibiae possess a pronounced cnemial crest. It is long, projecting craniolaterally, curving laterally at its distal extreme, and angling ventrally from the proximal condylar surface. A faint ridge extends the length of the shaft connecting the cnemial crest proximally with the articular surface for the ascending process at the distal end. Both the tibia and fibula of FWMSH 93B-10-15 were found near a right femur and right fibula (FWMSH 93B-10-25). On average, it is estimated that P. jonesi tibiae reach close to 60% of femur length (Appendix 1).

Fibula. Two fibulae from Jones Ranch are in the collections (FWMSH 93B-10-15 and FWMSH 93B-10-25). Both are heavily weathered. As noted above, FWMSH 93B-10-15 was found with a left tibia and FWMSH 93B-10-25 was associated with a right femur. The fibula is a slender bone (Figure 28.8–13) that is slightly longer than the tibia and close to two-thirds the length of the femur (Appendix 1). The proximal and distal ends are moderately expanded relative to mid-shaft, particularly in the craniocaudal direction, as in the tibia. Craniocaudal breadth at mid-shaft is slightly greater than the transverse breadth (Table 9). The distal end of FWMSH 93B-10-25 is expanded transversely to approximately 1.6 times the mid-shaft breadth and in FWMSH 93B-10-15 distal breadth is more than twice mid-shaft breadth. The lateral trochanter is well developed on the lateral surface approximately one-third the distance from the proximal end and is connected to the distal condyle by a low ridge. The proximal end is concave medially and convex laterally. The fibula thins at the proximocranial border and has a small cranial prominence. The tibial articular surface, or tibial scar, is plainly visible. The fibula/femur length ratio is 0.67.

Pes. Only metatarsals I, II, and IV are known for Paluxysaurus jonesi. Excluding fragmentary metapodials that could not be assigned confidently to the fore or hindfoot, no other pedal elements, including phalanges, tarsals, astragali, or calcanei, have been discovered so far. Metatarsals I and II (FWMSH 93B-10-16) are from the right side and were found together in the quarry, while metatarsal IV (FWMSH 93B-10-26) is probably a left and was found as an isolated bone. The shorter metatarsal of FWMSH 93B-10-16 is identified here as metatarsal I but might in fact be metatarsal V. Due to uncertainty in the identification, characters in the phylogenetic analysis describing morphology of either metatarsal I or V were not scored and left as unknowns for P. jonesi.

Metatarsal II is longer than metatarsal I (Table 9). Both are robust bones and are particularly expanded at the proximal end (Figure 29). Proximal condyles of the first two metatarsals are compressed dorsoventrally, and the shaft of metatarsal II is also compressed. The transverse breadth of the distal end of metatarsal II is subequal to mid-shaft breadth. The distal end of metatarsal I is rotated medially with respect to the axis of the shaft. In metatarsal II, the distal end is rotated medially and bevelled proximoventrally with respect to the shaft. A well-developed proximomedial process is present on the ventral surface of metatarsals I and II. In metatarsal I this process extends onto the shaft and nearly reaches the distal end. Metatarsal IV is relatively slender compared to metatarsals I and II. The fourth metatarsal is expanded dorsoventrally at the proximal end. All three preserved metatarsals have well-developed, rounded distal condyles.