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Osteology of Tyrannosaurus rex: Insights from a Nearly Complete Skeleton and High-Resolution Computed Tomographic Analysis of the Skull

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A detailed osteological description of Tyrannosaurus rex Osborn, 1905 is presented, based primarily on the most complete specimen yet collected of this taxon (FMNH PR2081, popularly known as “Sue”) but also including observations from other specimens.Skull morphology of FMNH PR2081 is largely congruent with that described for previous specimens, but new details are added. Palatal morphology of FMNH PR2081 differs slightly from that of previously-described specimens—the internal choanae are slightly larger relative to skull size, and the anterior expansion of the fused vomers is elongate. Posteriorly, the vomers pass medially for nearly the entire length of the pterygoids.High-resolution x-ray computed tomographic (CT) analysis of the skull reveals internal details not previously observed. Complex recess systems can be traced in the jugal, lacrymal, ectopterygoid, quadrate, exoccipital, supraoccipital, prootic, and basioccipital. The exoccipital recess was perforated by a small foramen on the posterodorsal surface of the paroccipital process, and may have communicated with pneumatic chambers in the atlas-axis complex. The maxillary antra were bound medially by a thin bony wall; traces of these walls in earlier CT studies of tyrannosaurid skulls may have led to the impression that these animals had bony maxillonasal turbintes. A digital endocast was constructed from these images, confirming many previous observations based on natural endocasts, but also yielding new details, such as the presence of a large and presumably pneumatic sinus in the prootic adjacent to the pathway for the maxillary-mandibular branches of the trigeminal nerve. The olfactory bulbs were very large.The postcranium is also largely congruent with previously published descriptions. The precaudal vertebral column was heavily pneumatized, with pneumatopores penetrating the centra and neural arches of all presacral vertebrae, the cervical ribs, and the anteriormost four sacral centra. Unusual structures are tentatively identified as a proatlas arch and a rib on the last presacral vertebrae, structures previously thought absent from tyrannosaurids. The “missing chevron” partially responsible for claims that FMNH PR2081 is female was actually present.The gastralia are extensively fused anteriorly, and the morphology of the anteriormost gastral segments closely resembles the only published account of a tyrannosaurid sternum. This raises several possibilities, including the complete absence of a bony sternum in tyrannosaurids.The appendicular skeleton is congruent with those of other tyrannosaurids. A slender rodlike bone may represent a partial furcula, but this is not certain. The scapulocoracoids would probably not have met at the midline, but would nonetheless have closely approached each other in articulation.Several abnormalities in the skeleton have attracted popular attention. There is no defensible evidence for bite trauma on the skull, but the rib cage does show evidence for healed fractures. Lesions on the right scapulocoracoid and humerus coincide with fractured ribs on the right cervical-dorsal transition and may indicate a single trauma to the right side of the body. The left fibula is pathological, but may not have been fractured. Two fused tail vertebrae may preserve natural molds of the tail muscles.
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... The cervical rib 5 is represented by its proximal end. It is assigned to CR5 on the basis of the presence of a short and small tubercle, absence of an anterior process, and presence of a large capitulum, a combination of features present in CR5 of Allosaurus, Tyrannosaurus 43,44 and CR5 of Aerosteon and CR6 of Megaraptor. ...
... At mid-length, the shaft becomes abruptly thin and rod-like and curves ventrally. This morphology occurs in the [43][44][45] . The lateral surface of the rib shaft is flat and dorsoventrally tall anteriorly and becomes progressively shallower posteriorly. ...
... A probable first left dorsal rib is almost completely preserved, lacking only its distal end ( Fig. 11A-C). It is identified as a first dorsal rib, because of a strong proximal concavity, a slightly medially concave shaft and the presence of one flange on its posterior side and two flanges on its anterior side (as in Australovenator but also other theropods such as Allosaurus or Tyrannosaurus; 43,44 ). ...
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Megaraptora is a theropod clade known from former Gondwana landmasses and Asia. Most members of the clade are known from the Early to Late Cretaceous (Barremian–Santonian), with Maastrichtian megaraptorans known only from isolated and poorly informative remains. The aim of the present contribution is to describe a partial skeleton of a megaraptorid from Maastrichtian beds in Santa Cruz Province, Argentina. This new specimen is the most informative megaraptoran known from Maastrichtian age, and is herein described as a new taxon. Phylogenetic analysis nested the new taxon together with other South American megaraptorans in a monophyletic clade, whereas Australian and Asian members constitute successive stem groups. South American forms differ from more basal megaraptorans in several anatomical features and in being much larger and more robustly built.
... This fascination extends to many professional paleontologists. The great beast has been the focus of an outsized number of modern studies on its size, growth, locomotor performance, population dynamics, soft tissue preservation, and predatory capabilities (Paul, 1988(Paul, , 2008Carpenter, 1990;Molnar, 1991Molnar, , 2008Horner, 1994;Chin et al., 1998;Carpenter & Smith, 2001;Carrano & Hutchinson, 2002;Brochu, 2003;Carr & Williamson, 2004;Erickson et al., 2004;Sampson & Loewen, 2005;Schweitzer et al., 2007;Schweitzer et al., 2016;Happ, 2008;Holtz, 2008;Hutchinson et al., 2011;Currie 2011, 2016;DePalma et al., 2013;Myhrvold, 2013;Wick, 2014;Gignac & Erickson, 2017;Cost et al., 2019;Persons et al., 2019;Snively et al., 2019;Carr, 2020;Woodward et al., 2020;Bijiert et al., 2021;Marshall et al., 2021;Ullmann et al., 2021). In 2008, an entire multi-author technical book (Larson and Carpenter 2008) was dedicated to the one paleospecies T. rex, a rare event in the dinosaur literature. ...
... Despite the abundance of research directed towards this one genus, the assumption that all adult Tyrannosaurus specimens from the plains of Canada to the southwestern United States belong to the single species T. rex (Carpenter, 1990;Brochu, 2003;Carr & Williamson, 2004;Sampson & Loewen, 2005;Wick, 2014;Brusatte and Carr 2016;Persons et al., 2019;Carr, 2020;Woodward et al., 2020) has never been quantitatively and stratigraphically tested with a large sample. This includes studies on the status of small tyrannosaurid specimens as potential juvenile members of the genus Tyrannosaurus (Carr, 2020;Woodward et al., 2020) and studies that have sought to diagnose the distinction between Tyrannosaurus from other tyrannosaurid taxa at the generic level (Brochu, 2003;Carr & Williamson, 2004;Osborn, 1905;Paul, 1988;Sampson & Loewen, 2005;Wick, 2014). ...
... Despite the abundance of research directed towards this one genus, the assumption that all adult Tyrannosaurus specimens from the plains of Canada to the southwestern United States belong to the single species T. rex (Carpenter, 1990;Brochu, 2003;Carr & Williamson, 2004;Sampson & Loewen, 2005;Wick, 2014;Brusatte and Carr 2016;Persons et al., 2019;Carr, 2020;Woodward et al., 2020) has never been quantitatively and stratigraphically tested with a large sample. This includes studies on the status of small tyrannosaurid specimens as potential juvenile members of the genus Tyrannosaurus (Carr, 2020;Woodward et al., 2020) and studies that have sought to diagnose the distinction between Tyrannosaurus from other tyrannosaurid taxa at the generic level (Brochu, 2003;Carr & Williamson, 2004;Osborn, 1905;Paul, 1988;Sampson & Loewen, 2005;Wick, 2014). So widespread and ingrained is this assumption that footprints attributable to a Late Maastrichtian giant theropod have been assigned specifically to T. rex (Caneer et al., 2021), despite their location 1000 km from the nearest skeletal material adequate to be assigned to the genus. ...
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All skeletal specimens of the North American dinosaur Tyrannosaurus and a number of trace fossils have been attributed to the single species: T. rex. Although an unusual degree of variation in skeletal robustness among specimens and variability in anterior dentary tooth form have been noted, the possibility of sibling species within the genus Tyrannosaurus has never been tested in depth in both anatomical and stratigraphic terms. New analysis, based on a dataset of over three dozen specimens, finds that Tyrannosaurus specimens exhibit such a remarkable degree of proportional variations, distributed at different stratigraphic levels, that the pattern favors multiple species at least partly separated by time; ontogenetic and sexual causes being less consistent with the data. Variation in dentary incisiform counts correlate with skeletal robusticity and also appear to change over time. Based on the current evidence, three morphotypes are demonstrated, and two additional species of Tyrannosaurus are diagnosed and named. One robust species with two small incisors in each dentary appears to have been present initially, followed by two contemporaneous species (one robust and another gracile) both of which had one small incisor in each dentary, suggesting both anagenesis and cladogenesis occurred. The geological/geographic forces underlying the evolution of multiple Tyrannosaurus species are examined. A discussion of the issues involving the recognition and designation of multiple morphotypes/species within dinosaur genera is included.
... At mid-length, the shaft becomes abruptly thin and rod-like and curves ventrally. This morphology occurs in the posterior half of the neck in other theropods [42][43][44] . The lateral surface of the rib shaft is at and dorsoventrally tall anteriorly and becomes progressively shallow posteriorly. ...
... This results in that the medial end of the element is posterodorsally facing. This posterodorsal surface articulates with the anteroventral surface of the posterior gastralia, resulting in the typical theropod interwoven gastral arrangement 43,45 . ...
... Moreover, the morphology observed in Megaraptor resembles more to the condition of most theropods (such as Allosaurus or Sinraptor; 42,44 ) than with Maip. Within Theropoda, the proportions of the axis of Maip resembles more to tyrannosaurids (such as Tyrannosaurus; 43 ) and carcharodontosaurids (such as Acrocanthosaurus), which have anteroposteriorly short axis. The high/width ratio of the axis is 2.1 times in Maip and Tyrannosaurus, 1.8 in Acrocanthosaurus and 1.3 in Allosaurus. ...
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... The preotic pendant (crista prootica of Brochu, 2003; ala basisphenoidalis of Paulina-Carabajal et al., 2021) is a posteroventrolaterally-oriented projection located ventral to the trigeminalfacial nerve foramen (Holliday and Witmer, 2008;Bever et al., 2013). The preotic pendant is shallow and crest-like in juvenile Gorgosaurus (TMP 2009.12.14), extending more posterolaterally than ventrally. ...
... The Fukuiraptor, Murusraptor, Orkoraptor, Vayuraptor;Madsen, 1976;Britt, 1991;Currie & Zhao, 1993;Azuma & Currie, 2000;Novas et al., 2008;Coria & Currie, 2016;Samathi et al., 2019) (Fig. 3.1, 3 Tyrannosaurus; Madsen, 1976;Currie & Zhao, 1993;Brochu, 2003; MCF-PVPh-411) (Fig. 3.1, 3 Madsen, 1976;Britt, 1991;Brochu, 2003;Rauhut & Pol, 2019). The posterior intercondylar sulcus in MAU-PV-CM-653 as well as in Australovenator (White et al., 2013) and ...
... The Fukuiraptor, Murusraptor, Orkoraptor, Vayuraptor;Madsen, 1976;Britt, 1991;Currie & Zhao, 1993;Azuma & Currie, 2000;Novas et al., 2008;Coria & Currie, 2016;Samathi et al., 2019) (Fig. 3.1, 3 Tyrannosaurus; Madsen, 1976;Currie & Zhao, 1993;Brochu, 2003; MCF-PVPh-411) (Fig. 3.1, 3 Madsen, 1976;Britt, 1991;Brochu, 2003;Rauhut & Pol, 2019). The posterior intercondylar sulcus in MAU-PV-CM-653 as well as in Australovenator (White et al., 2013) and ...
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