D’Emic et al.—Revision of the sauropod dinosaur Sonorasaurus
Smithsonian Institution. Anatomical measurements were made from the images using the programImageJ (Rasband, 1997) and following the recommendations of the IAWA for softwood identification (IAWA committee, 2004). The transverse sections revealed that the secondary xylem
consists of homoxylous pycnoxylic wood (Fig. 7.3). Although some hand specimens appear to have growth rings, when viewed under the microscope they are indistinct. Resin canals are absent, and axial parenchyma is rare or absent. The tracheids are medium to small, rectangular to polygonal, and arranged in radial files. They range from 24.3–51.8 μm in tangential dia- meter measured from middle lamella to middle lamella. The mean tangential diameter of the tracheids is 41.8 μm, standard deviation is 7.5 μm(n = 25). In TLS, uniserate (rarely locally biseriate) rays 1–14 cells high (n = 5) are separated by ~4 files of tracheids (Fig. 7.4). The ray cells are procumbent and elliptic in tangential section (15.1 μm across by 23.4 μm high). They have smooth and thin cell walls (Fig. 7.4). Ray density is ~5.0 raysmm−1. In RLS, uniseriate, closely spaced to con- tiguous circular bordered pits with circular apertures (abietinean pits) are visible on the radial walls of the tracheids (Fig. 7.5). Pit diameter is 19–20 μm, and aperture diameter is 3.7–10.1 μm; scalloped tori, torus extensions, and notched borders were not observed. Pits in the cross-field are poorly preserved oculipores
with either elliptic or oval apertures. 1–6 oculipores per cross field, usually in two rows (Fig. 7.6). The ratio of aperture length to pit border diameter is undetermined. Following the key to Mesozoic conifer wood types
provided by Philippe and Bamford, (2008) this wood should be classified as a Group C Mesozoic conifer wood, either Taxodioxylon Hartig or Cupressinoxylon Göppert. Species in these genera share pycnoxylic wood with abietinean pitting and primarily uniserate rays, but they can usually be distinguished by the cross-field pitting. Although there are some fossil woods that combine the characteristic features of these two genera (Falcon-Lang, 2003), Taxodioxylon is characterized by oculi- pores in the cross-field in which the pit aperture is oval to elliptic and larger than the pit border, whereas Cupressinoxylon is characterized by oculipores in which the pit aperture is elliptical and as long as or shorter than the diameter of the pit border (Philippe and Bamford, 2008). Based on the presence cross-field pits without a visible elongate aperture, we tentatively assign the specimens described here to
Cupressinoxylon.The fossil wood described here was most likely produced by trees in the family Cupressaceae or possiblyCheirolepidiaceae. The trees grew up to at least 32.0m tall based on Niklas’ (1994) allometric scaling relationship for woody trees (log10 H = 1.59+0.39 log10 D−0.18 (log10 D)2)whereDis stem diameter above the basal flare, andHis tree height.
Other dinosaur specimens from the Bisbee Group
The dinosaurs of the Bisbee Group were reviewed by Lucas and Heckert (2005) and McCord and Gillette (2005), who noted the presence of Sonorasaurus, fish, turtles, crocodilians, nodosaur- ids, a claw referred to cf. Deinonychus, a tooth referred to cf. Acrocanthosaurus, and ornithopod femora that closely resemble that of Tenontosaurus (see also Galton and Jensen, 1979). Previous to these reviews, Miller (1964:378) reported
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(via personal communication) the presence of a stegosaur “of probable Lower Cretaceous age” from southern Arizona, but no other details are known about this report. Only a few other taxonomically informative dinosaur specimens exist from the Bisbee Group; we describe these below and offer new information about the tooth referred to cf. Acrocanthosaurus (ASDM 300).
Sauropod dorsal ribs.—We re-opened the holotype quarry of Sonorasaurus in 2014, but no additional elements were found. However, two partial dorsal ribs were collected from a site 0.6km distant and ca. 125m stratigraphically above the Sonorasaurus quarry. One rib (ASDM 857, incorrectly given as ASDM 807 by Ratkevitch [1998]; Supplemental Data 2) was found before Sonorasaurus’ discovery (R. Thompson, personal communication, 2014) and was mentioned by Ratkevitch (1998:72, 80). It is 142cm long as preserved, but it is not complete proximally or distally. Its proximal end bearswhatmight be a pneumatic foramen or fossa (Supplemental Data 2), but this is difficult to assess due to damage. Its cross section near its mid-length is plank-like, measuring about 7.0cm by 2.2cm. This plank-like morphology indicates that this rib pertains to a titanosauriform (Wilson, 2002). At the same site, we collected a ca. 30-cm long fragment of a dorsal rib (ASDM 2070). It has essentially the same cross sectional measurement as ASDM 857 (8cm by 2.5cm), which tapers dis- tally such that it cannot be a broken distal fragment of that rib. Based on its cross section, ASDM 2070 also pertains to a titanosauriform. It is likely that these two ribs pertained to a single individual based on their proximity and similar size and preservation.
Sauropod maxilla.—Part of a sauropod maxilla (ASDM 2069; Supplemental Data 3) was discovered at the same site as the two dorsal ribs (ASDM 857, 2070). Unfortunately, only the ca. 1mm thick lateral skin of bone bounding six alveoli was present, and most of the bone could not be collected. A badly crushed, single tooth root measuring about 8mm in diameter was present in the maxilla.
Theropod femur.—Part of a proximal theropod femur shaft (ASDM 2111; Supplemental Data 4) was found approximately 300m from the Sonorasaurus quarry in a reddish sandstone layer just superjacent to one of the black pebble petrified wood–bearing conglomerate layers. The bone preserves the fourth trochanter, but lacks other processes including the femoral head. Its preserved length is 34cm and its circumference at its preserved distal end is approximately 25.5cm.
Theropod tooth.—In describing the bones of Sonorasaurus, Ratkevitch (1997a:215) reported the presence of a large ther- opod dinosaur tooth (ASDM 330; Fig. 8) that was stated to “match bite marks on the radius and ulna of our skeleton” and tentatively referred this tooth to Acrocanthosaurus (Ratkevitch, 1997a:fig. 7; see also Scarborough, 2000:fig. 5; McCord and Gillette, 2005: Table 2). This tooth was further prepared in 2013 by MDD, making its cross–sectional shape visible and clarifying the shape of its margin. The tooth is at least 5.9cm long as preserved (=‘crown height’ of Smith et al., 2005; versus the ‘apical length,’ which was greater than 5.6cm long), and
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