Content uploaded by Christopher Brochu
Author content
All content in this area was uploaded by Christopher Brochu on Feb 24, 2017
Content may be subject to copyright.
A preview of the PDF is not available
Osteology of Tyrannosaurus rex: Insights from a Nearly Complete Skeleton and High-Resolution Computed Tomographic Analysis of the Skull
Abstract
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.
... II. The inner structures of the maxilla restricting the main nasal passage to the upper part of the internal skull [25,51]: the maxillary antrum wall [54] and preantral and postantral struts [55,56] are the inner structures that are profoundly correlated with the maxillary antrum, which would have held a part of the paranasal air sinuses [51,55]. III. ...
... Since there was no large maxillary fenestra on the maxilla in non-tetanuran theropod dinosaurs [5], it is unlikely that they possessed a developed maxillary sinus (figure 7) [51]. By contrast, the presence of a prominent maxillary fenestra in tetanurans suggests that they had a well-developed sinus in the maxillary antrum (figures 5-7) [54,55]. On the lineage toward modern birds, the maxilla was compressed downward and eventually reduced into a flat, predominantly palatal element [53,79]. ...
It has long been discussed whether non-avian dinosaurs were physiologically closer to ectotherms or endotherms, with the internal nasal structure called the respiratory turbinate present in extant endotherms having been regarded as an important clue for this conundrum. However, the physiological function and relevance of this structure for dinosaur physiology are still controversial. Here, we found that the size of the nasal cavity relative to the head size of extant endotherms is larger than those of extant ectotherms, with that of the dromaeosaurid Velociraptor being below the extant endotherms level. The result suggests that a large nasal cavity accommodating a well-developed respiratory turbinate is primarily important as a thermoregulation apparatus for large brains characteristic of endothermic birds and mammals, and the nasal cavity of Velociraptor was apparently not large enough to carry out this role required for an endothermic-sized brain. In addition, a hypothesis that the enlargement of the nasal cavity for brain cooling has been associated with the skull modification in the theropod lineage toward modern birds is proposed herein. In particular, the reduction of the maxilla in derived avialans may have coincided with acquisition of the avian-like cephalic thermoregulation system.
... The Fairpoint phalanx shares similarities with those reported from various tyrannosaurid taxa. These include a slightly sloping long axis; ventral rugosities near the proximal articular facet; and an arched ventral surface in medial and lateral views (Brochu, 2003); a shallowly concave proximal facet (evident in proximal phalanges; Lambe, 1917); deep and asymmetric collateral ligament fossae, a trait shared by all phalanges apart from those belonging to digit III, which are equal in size (Lambe, 1917;Brochu, 2003, Figs. 107 and 108;Brusatte, Carr & Norell, 2012); and a relatively shallow extensor pit (Brusatte, Carr & Norell, 2012, Fig. 80;Brochu, 2003, Fig. 105). ...
... 107 and 108;Brusatte, Carr & Norell, 2012); and a relatively shallow extensor pit (Brusatte, Carr & Norell, 2012, Fig. 80;Brochu, 2003, Fig. 105). However, there are also dissimilarities, some of which could be due to ontogenetic differences: DMNH EPV.138575 lacks the expanded distal and proximal articular regions relative to the shaft in dorsal and ventral views apparent in the adult Tyrannosaurus rex (Brochu, 2003; FMNH PR2081) but also, albeit less pronounced, in the subadult tyrannosaurid Albertosaurus sarcophagus from the Maastrichtian age Horseshoe Canyon Formation of Alberta, Canada (Mallon et al., 2019;CMN 11315); and the ratio of proximodistal length to mediolateral midshaft width is larger than three, if the abraded distal condyle is taken into account, a value greater than that identified for Tyrannosauridae (Brusatte et al., 2010, SOM). ...
We report here the first dinosaur skeletal material described from the marine Fox Hills Formation (Maastrichtian) of western South Dakota. The find consists of two theropod pedal phalanges: one recovered from the middle part of the Fairpoint Member in Meade County, South Dakota; and the other from the Iron Lightning Member in Ziebach County, South Dakota. Comparison with pedal phalanges of other theropods suggests strongly that the Fairpoint specimen is a right pedal phalanx, possibly III-2, from a large ornithomimid. The Iron Lightning specimen we cautiously identify as an ornithomimid left pedal phalanx II-2. The Fairpoint bone comes from thinly bedded and cross-bedded marine sandstones containing large hematitic concretions and concretionary horizons. Associated fossils include osteichthyan teeth, fin spines and otoliths, and abundant teeth of common Cretaceous nearshore and pelagic chondrichthyans. Leaf impressions and other plant debris, blocks of fossilized wood, and Ophiomorpha burrows are also common. The Iron Lightning bone comes from a channel deposit composed of fine to coarse sandstone beds, some of which contain bivalves, and a disseminated assemblage of mammal teeth, chondrichthyan teeth, and fragmentary dinosaur teeth and claws. We interpret the depositional environment of the two specimens as marginal marine. The Fairpoint bone derives from a nearshore foreset setting, above wave base subject to tidal flux and storm activity. The Iron Lightning specimen comes from a topset channel infill probably related to deposition on a tidal flat or associated coastal setting. The taphonomic history and ages of the two bones differ. Orthogonal cracks in the cortical bone of the Fairpoint specimen suggest post-mortem desiccation in a dryland coastal setting prior to transport and preservation in the nearby nearshore setting described above. The pristine surface of the Iron Lightning specimen indicates little transport before incorporation into the channel deposit in which it was found. The Fairpoint bone bed most probably lies within the Hoploscaphites nicolletii Ammonite Zone of the early late Maastrichtian, and would therefore have an approximate age of 69 Ma. The Iron Lightning bone is from the overlying H. nebrascensis Ammonite Zone, and is thus about one million years younger.
... Given the wealth of detailed osteologies describing tyrannosaurine specimens (e.g., Carr (1999);Brochu (2003) and Hurum & Sabath (2003)), our description of the holotype of D. wilsoni places heavy emphasis on characteristics (or combinations of characteristics) unique to this specimen, as well as those that are otherwise taxonomically or phylogenetically informative within Tyrannosaurinae, so as to avoid the reiteration of plesiomorphic tyrannosaurine morphologies (or synapomorphies of Daspletosaurus) already described by previous authors (e.g., Carr et al. (2017); Voris et al. (2019) and Voris et al. (2020)). ...
... As in all tyrannosaurids, the spinous processes of the cervical vertebrae are subequal in dorsoventral height to their corresponding centra. Both the spinous processes and the centra are craniocaudally short, similar to and most exaggerated in the cervical vertebrae of Tyrannosaurus (see Brochu, 2003, and figures therein). As in Tyrannosaurus (and other large tyrannosaurids), the cranial and caudal faces of the cervical centra in BDM 107 are dorsoventrally displaced from one another in order to create the characteristic 'S-curve' of the neck, and the cranial cervical centra are extremely foreshortened craniocaudally (i.e., much taller than long). ...
Here we describe a new derived tyrannosaurine, Daspletosaurus wilsoni sp. nov., from Judithian strata (~76.5 Ma) intermediate in age between either of the previously described species of this genus. D. wilsoni displays a unique combination of ancestral and derived characteristics, including a cornual process of the lacrimal reduced in height relative to D. torosus and more basal tyrannosaurines, and a prefrontal with a long axis oriented more rostrally than in D. horneri and more derived tyrannosaurines. The description of this taxon provides insight into evolutionary mode in Tyrannosaurinae, lending strength to previous hypotheses of anagenesis within Daspletosaurus and increasing the resolution with which the evolution of this lineage can be reconstructed. Cladistic phylogenetic methods, stratigraphy, and qualitative analysis of the morphology of relevant taxa supports an anagenetic model for the origin of morphological novelty in this genus, highlighting the predominance of anagenetic evolution among contemporary dinosaur lineages.
... There is a prominent and lateroventrally oriented flange at the posterior side of this alar crest posteriorly (noticeable in lateral view), which projects anteriorly to reach the base of the basipterygoid processes, delimiting a deep recess ventral to the pituitary fossa. Due to its location in the basisphenoid and its relation to the pituitary fossa, this crest is identified here as the "basisphenoidal flange" present in Heterodontosaurus (Norman et al., 2011) and part of the preotic pendant of saurischians (ala basisphenoidalis: Chure & Madsen, 1998;Rauhut, 2007;crista prootica: Chure & Madsen, 1998;Madsen & Welles, 2000;Brochu, 2003). The prominent flanges at the sides of the basisphenoid in lateral view were previously misinterpreted as the basipterygoid process (Pol et al., 2011), and are now considered the posterior portion of the preotic pendant, which becomes ventrolaterally prominent forming a triangular-shaped alar crest. ...
Heterodontosauridae is a clade that appears early in the ornithischian fossil record, and includes small-bodied, highly specialized species characterized by an unusual heterodont dentition. Although known from relatively few taxa, the early representation of the clade and unsolved phylogenetic relationships within heterodontosaurids and among early ornithischians implies that novel information has a marked effect on broader phylogenetic hypotheses and our understanding of early diversification patterns within Ornithischia. This paper describes the cranial osteology of the heterodontosaurid Manidens condorensis based on computed micro-tomographic scans of MPEF-PV 3211 and MPEF-PV 3809. This enabled more detailed descriptions of previously recognized bones, corrections to the literature, and the identification of undescribed elements. We present a new skull reconstruction and propose an emended diagnosis in light of novel anatomical information. Areas of jaw muscle attachment were identified and compared with Heterodontosaurus and Lesothosaurus, and mandibular function among heterodontosaurids is discussed. Our results indicate that diverse skull morphologies and functions existed among Early Jurassic ornithischians, with Manidens being intermediate between the plesiomorphic cranial shape and function associated with a generalist diet in ornithischians such as Tianyulong and Lesothosaurus, and the more derived cranial construction specialized for herbivory identified in heterodontosaurids from South Africa such as Heterodontosaurus.
... S2) (4,5). Among the arguments in favor of this interpretation are the relatively large sizes of some theropod teeth and evidence from the dinosaur phylogenetic bracket, where crocodylians, the closest extant dentigerous relatives of dinosaurs, lack extensive extraoral tissues (6)(7)(8). Some recent research on theropod rostral neurovasculature has argued that direct data and evidence are lacking for extraoral tissue reconstructions (9), but rigorous reconstructions of these tissues are important for biological inferences for dinosaurs. ...
Large theropod dinosaurs are often reconstructed with their marginal dentition exposed because of the enormous size of their teeth and their phylogenetic association to crocodylians. We tested this hypothesis using a multiproxy approach. Regressions of skull length and tooth size for a range of theropods and extant varanid lizards confirm that complete coverage of theropod dinosaur teeth with extraoral tissues (gingiva and labial scales) is both plausible and consistent with patterns observed in living ziphodont amniotes. Analyses of dental histology from crocodylians and theropod dinosaurs, including Tyrannosaurus rex, further indicate that the most likely condition was complete coverage of the marginal dentition with extraoral tissue when the mouth was closed. This changes our perceptions about the appearance and oral configuration of these iconic predators and has broad implications for our interpretations of other terrestrial animals with large teeth.
... Dental pathologies in theropods (see Table 2), although rare include split or diverging carinae (Bohlin, 1953;Erickson, 1995;Maisch and Matzke, 2003;Lanser and Heimhofer, 2015;Hendrickx et al., 2019), double cusped crowns (Anon, 1991); crowns with multiple rows of supernumerary serrations/denticles (Abler, 1997) and grotesque distortions of root and crown (Brochu, 2003 fig. 11C,D). ...
Trauma is the most common cause of lesions in the fossil record. Not only linked to bones themselves, traumatic injuries can be identified in footprints and teeth, although these seem to be less common. Scars, scratches, embedded teeth, pierced holes, and amputations are all event that can point to past injuries, but the physiological reaction of the injured body can also lead to formation of bone spicules or exostoses, suggesting some form of avulsions represent the attempt by the muscles and/or tendons to counterbalance the effect of the injury. Bony modifications due to external injuries can lead to diagnostic confusion. Exostoses should not be misdiagnosed as osteochondroma and osteochondritis that have a traumatic origin separate from that of osteochondrosis. The causes and rates of forming and healing are well characterized in human medicine, and their understanding in other animals (e.g., reptiles and birds) is continuously growing. This knowledge can be incorporated in paleopathology to decipher healing modes and tempo in extinct taxa, as well as the diversity of fractures and their impact on the lifestyle of the animals. Enthesiophytes are alteration of attachment site of tendons and ligaments. While exostoses can have a traumatic origin, they can also be found in non-pathological conditions (e.g., DISH) and perhaps aging (Long et al. 2021). Finally, osteoarthritis can have complicated injuries, but it is not associated with enthesophytes. The bony spicules characterizing osteoarthritis are osteophytes (van der Kraan 2007). Their location on diarthrodial joint is pathognomonic, whereas other features (eburnation, pitting joint deformation) lack specificity.
Despite nearly 200 years of scientific collecting and study, none of the extinct, bipedal, predatory, theropod dinosaurs have been reliably shown to exceed 12 m in length. Using digital 3D models of theropods with lengths spanning 80 cm to 12 m, their body masses were found to scale to the 3.5 power of body lengths. The lateral area of the pelvis and the cross-sectional area of the tail base of these animals corresponds to the cross-sectional areas of key muscle groups important for balance and locomotion, and both scale to the 2.4 power of body length. Body accelerations in the lateral and forward directions are, using F = ma, given by dividing muscle area (force proxy) by body mass. Plotting these acceleration estimates against body length shows them to decrease exponentially. The largest theropods with body lengths of 10–12 m have less than 10% of the acceleration capacity of the smaller forms. The distinct lack of fossil remains of theropods demonstrably longer than 12 m suggests that the theropod body plan had an upper size limit based on a minimum acceleration threshold. Rotational inertia of the theropod body was found to be proportional to body length raised to the 5.5 power, and with increasing length, the capacity for agility would rapidly diminish. The tight relationship between theropod pelvic area and body length allows for the estimation of body lengths of specimens lacking complete axial skeletons, and this is done for four, large, well-preserved pelves.
Megaraptora is a group of enigmatic, carnivorous non‐avian theropod dinosaurs from the Cretaceous of Asia, Australia, and especially South America. Perhaps the most striking aspect of megaraptoran morphology is the large, robustly constructed forelimb that, in derived members of the clade, terminates in a greatly enlarged manus with hypertrophied, raptorial unguals on the medialmost two digits and a substantially smaller ungual on digit III. The unique forelimb anatomy of megaraptorans was presumably associated with distinctive functional specializations; nevertheless, its paleobiological significance has not been extensively explored. Here we draw from observations of the pectoral girdle and forelimb skeletons of Megaraptora and myological assessments of other archosaurian taxa to provide a comprehensive reconstruction of the musculature of this anatomical region in these singular theropods. Many muscle attachment sites on megaraptoran forelimb bones are remarkably well developed, which in turn suggests that the muscles themselves were functionally significant and important to the paleobiology of these theropods. Furthermore, many of these attachments became increasingly pronounced through megaraptoran evolutionary history, being substantially better developed in derived taxa such as Australovenator wintonensis and especially Megaraptor namunhuaiquii than in early branching forms such as Fukuiraptor kitadaniensis. When considered alongside previous range of motion hypotheses for Australovenator, our results indicate that megaraptorans possessed a morphologically and functionally specialized forelimb that was capable of complex movements. Notable among these were extensive extension and flexion, particularly in the highly derived manus, as well as enhanced humeral protraction, attributes that very probably aided in prey capture.
Theropod dinosaurs have captured the imagination of the public and paleontologists alike. Histology of the bones of theropods has revealed much about dinosaur physiology, behavior, and growth. Histology and ultraviolet fluorescence (UVFL) microscopy of one controversial dinosaur, Nanotyrannus lancensis, reveals the presence of blood clots in post-fixed vessel canals of claw, vertebra, and other isolated post-cranial elements collected at Hell Creek, MT. These clots are thicker, more closely adherent to canal walls, and more reactive to 347 nm UVFL incident light than unfixed specimens. Theropod histology images in the literature display similar clots, and those should be subjected to UVFL for confirmation. In addition, nematodes are evidently preserved in vessel canals of dinosaurs.
A fragmentary tyrannosaurid skull and postcranial skeleton from the Kirtland Shale of northwestern New Mexico is the most complete specimen of a carnivorous dinosaur known from these strata. The specimen is identified as Aublysodon cf. A. mirandus on the basis of its narrow frontals, V-shaped frontal-parietal suture, and nondenticulate incisiform premaxillary tooth. The D-shaped cross section of the premaxillary tooth, rugose postorbital, well-developed footed pubis, and proximally constricted third metatarsal confirm the assignment of Aublysodon to the Tyrannosauridae. The limb bones are gracile and similar in proportions to those of Albertosaurus; however, the tibia and metatarsals are shorter relative to the femur. The distal end of the tibia exhibits a unique medial emargination not reported in other tyrannosaurids. -Authors
Individual variation for the large theropod Tyrannosaurus rex may be seen in the maxilla, dentary and ischium. The maxilla is variable in its depth, the size and shape of the maxillary and antorbital fenestrae, and the size and shape of the lacrimal and jugal processes. Even the left and right maxillae of the same skull show variation. Sexual dimorphism is suggested by the presence of two morphs, one more robust than the other. The angle between the ischia and caudals of the robust morph is greater than in the slender morph, and would provide ample space for the passage of eggs. On this basis, the robust morph is considered the female.
Introduction
The large theropod, Tyrannosaurus rex, was named by Osborn in 1905 on the basis of a partial skull and skeleton from the Hell Creek Formation of eastern Montana. The holotype (AMNH 973) was later transferred to the Carnegie Museum of Natural History (CM 9380) where it is presently on display. A second specimen (AMNH 5866) from the Lance Formation of eastern Wyoming, was named Dynamosaurus imperiosus by Osborn (1905) but later synonymized with T. rex (Osborn, 1906). This specimen [BM(NH) R7994 and R7995] is now mounted at the British Museum (Natural History). Numerous additional specimens have since been recovered from the Scollard and Willow Creek formations of Alberta, the Hell Creek Formation of North Dakota, South Dakota, and Montana, and the Laramie Formation of Colorado. These specimens are presently under study by Robert Bakker, Philip Currie, Ralph Molnar, Greg Paul, and myself.
The discovery in recent years of several well preserved and partially articulated skeletons of Tyrannosaurus rex has provided the impetus for a study of sexual dimorphism in dinosaurs. The fifteen significant specimens of Tyrannosaurus rex discovered to date may be divided into “robust” and “gracile” morphotypes. Examinations of extant crocodiles and birds show a link between musculature of sexual organs and sexual dimorphism of osteoskeletons. Analogous differences in articulated dinosaur remains point to a method of determining the gender of individual dinosaur skeletons and the presence of an intromittent organ in at least some species. For theropods, and particularly for Tyrannosaurus rex , the larger and more robust individuals are almost certainly female.