Tyrannosaurus Research Articles

Fossil biomolecules suggest which dinosaurs were warm or cold blooded

People once assumed that dinosaurs were cold-blooded reptiles. That understanding has morphed over the last 50 years or so, and we now think that many dinosaurs were warm blooded and birdlike . New research offers some nuance. Using fossilized biomolecules, researchers have determined that some dinosaurs were warm and others cold blooded ( Nature 2022 , DOI: 10.1038/s41586-022-04770-6 ). The scientists’ estimates of the metabolic rates of dinosaurs also provide insights into the likely lifestyles of certain ones. Finding metabolic rates for living animals is easy. For example, we can put a hamster on a treadmill and measure how much oxygen it breathes relative to its body mass for a given period, says Jasmina Wiemann , a molecular paleobiologist at the California Institute of Technology. “We can’t do this with a Tyrannosaurus rex .” The solution, she says, was to look for metabolic markers in fossils. The oxidation reactions that

With what precision can the population size of Tyrannosaurus rex be estimated? A reply to Meiri

Interested in the absolute preservation rate of one of the best understood dinosaurs, Tyrannosaurus rex, Marshall et al. (2021) estimated the total number that ever lived.  This required estimating its geographic range, longevity, and population density, which required estimating its body mass and physiology.  Meiri (2021) questions the precision of our estimates, emphasizing the difficulties in estimating population densities and geographic ranges for living species, and in error propagation.  He posits that estimating population sizes of extinct species is ‘extremely unlikely’.  While we agree that we did not quantify some sources of uncertainty (for example, in the physiology of T. rex), our calculations do not depend on short-term changes in population density and geographic range, but rather on their long-term averages, rendering many of Meiri’s (2021) concerns moot.  We also note that Monte Carlo Simulation propagates uncertainties robustly.  That is, we feel we have, in fact, developed a general method for estimating population sizes for extinct species, regardless of any shortfalls in implementation.

Population sizes of T. rex cannot be precisely estimated

Marshall et al. recently estimated population densities, range sizes, instant and cumulative total population sizes for Tyrannosaurus rex with narrow ranges of uncertainly. I revisit the assumptions that led them to these conclusions and show that many of these parameters are associated with much wider margins of error than they estimated. Biogeographic estimates seem to have been especially unrealistic, seriously hampering the effort to calculate population level parameters. I posit that biogeographic and ecological uncertainties make it extremely unlikely to be able to estimate population sizes of long-extinct species.

Bite Force and Feeding Traces of Tyrannosaurusthroughout Ontogeny: A Review

Bite marks attributed to adult Tyrannosaurus rexare common in the fossil record and have been subject to numerous studies, though relatively few bite marks attributed to T. rexhave been traced to juveniles. However, a series of recent studies have contributed new information on bite force, behavior, and ecological interactions of juvenile Tyrannosaurus rex, providing insight into ontogenetic changes in lifestyle and ecological roles of juvenile tyrannosaurs in the late Cretaceous of North America. Recent bite force estimates for a juvenile Tyrannosaurus rexwere based on mechanical tests designed to replicate bite marks previously attributed to a T. rex of approximately 13 years old in the centrum of a caudal vertebra of Edmontosaurus(BMR P2007.4.1) and the left maxilla and nasal of a juvenile Tyrannosaurus (BMR P2002.4.1). Results indicate an estimated bite force of 5,641.19 N, and suggest that bite forces were increasing parallel to growth and were utilizing the same prey as adults. Additionally, evidence of intraspecific aggression in the form of lesions resulting from face biting are present in over 50% of juvenile and adult tyrannosaurs. The high frequency of facial scars positively correlates with the inferred onset of sexual maturity. Furthermore, lesions attributed to a Trichomonas gallinae‐like parasite are present on the dentaries and surangulars of adult tyrannosaurs. Presented here is the first evidence of similar pathologies on a juvenile Tyrannosaurus rex that also possesses facial scars from intraspecific aggression, supporting a cause‐and‐effect relationship between the two groups of facial pathologies. Collectively, these findings suggest tyrannosaurs increased interactions, aggressive bouts, and potential transmission of parasites at the onset of sexual maturity as they were moving into different ecological niches. Furthermore, the frequency and category of pathologies in late Cretaceous tyrannosaurs and late Jurassic theropods of North America are compared with the unique guild structures of tyrannosaurs in the late Cretaceous of North America, suggesting a possible relationship between theropod diversity, behavior, and parasitism.

2D and 3D visualizations of archosaur jaw muscle mechanics, ontogeny and phylogeny using ternary diagrams and 3D modeling.

Comparing patterns of performance and kinematics across behavior, development and phylogeny is crucial to understand the evolution of complex musculoskeletal systems such as the feeding apparatus. However, conveying 3D spatial data of muscle orientation throughout a feeding cycle, ontogenetic pathway or phylogenetic lineage is essential to understanding the function and evolution of the skull in vertebrates. Here, we detail the use of ternary plots for displaying and comparing the 3D orientation of muscle data. First, we illustrate changes in 3D jaw muscle resultants during jaw closing taxa the American alligator (Alligator mississippiensis). Second, we show changes in 3D muscle resultants of jaw muscles across an ontogenetic series of alligators. Third, we compare 3D resultants of jaw muscles of avian-line dinosaurs, including extant (Struthio camelus, Gallus gallus, Psittacus erithacus) and extinct (Tyrannosaurus rex) species to outline the reorganization of jaw muscles that occurred along the line to modern birds. Finally, we compare 3D resultants of jaw muscles of the hard-biting species in our sample (A. mississippiensis, T. rex, P. erithacus) to illustrate how disparate jaw muscle resultants are employed in convergent behaviors in archosaurs. Our findings show that these visualizations of 3D components of jaw muscles are immensely helpful towards identifying patterns of cranial performance, growth and diversity. These tools will prove useful for testing other hypotheses in functional morphology, comparative biomechanics, ecomorphology and organismal evolution.

21st Century Rex: maximising access to a privately owned Tyrannosaurus rex skeleton in the digital age

A ~60-70% complete Tyrannosaurus rex skeleton known as Stan recently sold for 31.8 million US dollars to an unknown buyer (announced in March 2022 as the Natural History Museum Abu Dhabi), pushing up the price of all such skeletons way beyond the budget of most museums. Wealthy private individuals who purchase expensive fossil specimens sometimes put them on public display but leave them in an intellectual limbo, unable to be studied and published. However, a partial T. rex skeleton known as Titus was excavated in Montana in 2018, shipped to the UK in 2020, and had casts of Stan's bones added to complete the skeleton during mounting. It was loaned to the Nottingham Natural History Museum, Wollaton Hall, as the centrepiece to a temporary exhibition called Titus: T. rex is King. This was the first time a mounted T. rex skeleton containing fossil bones had been on display in England for many decades. Importantly, before the mounting process began, all the real bones were 3D scanned in detail using photogrammetry. The resulting digital 3D models were sent to palaeontologists in America who studied them and produced a paper describing the palaeopathology before the mounting process was even complete. Replicas of all the identifiable bones were 3D printed for display in the exhibition and were accessioned into the museum collections, along with the 3D digital models and all associated data. This ensured that physical as well as digital replicas of the bones would remain accessible, and in theory publishable, forevermore.

Deep Time Paleoproteomics: Looking Forward

The goal of paleoproteomics is to characterize proteins from specimens that have been subjected to the degrading and obscuring effects of time, thus obtaining biological information about tissues or organisms both unobservable in the present and unobtainable through morphological study. Although the description of sequences from Tyrannosaurus rex and Brachylophosaurus canadensis suggested that proteins may persist over tens of millions of years, the majority of paleoproteomic analyses have focused on historical, archeological, or relatively young paleontological samples that rarely exceed 1 million years in age. However, recent advances in methodology and analyses of diverse tissues types (e.g., fossil eggshell, dental enamel) have begun closing the large window of time that remains unexplored in the fossil history of the Cenozoic. In this perspective, we discuss the history and current state of deep time paleoproteomics (DTPp), here defined as paleoproteomic study of samples ∼1 million years (1 Ma) or more in age. We then discuss the future of DTPp research, including what we see as critical ways the field can expand, advancements in technology that can be utilized, and the types of questions DTPp can address if such a future is realized.

Taphonomic and Diagenetic Pathways to Protein Preservation, Part I: The Case of Tyrannosaurus rex Specimen MOR 1125.

Simple SummaryContrary to traditional views, fossil bones have been shown to occasionally retain original cells, blood vessels, and structural tissues that are still comprised, in part, by their original proteins. To help clarify how such remarkable preservation occurs, we explored the fossilization history of a famous Tyrannosaurus rex specimen previously shown to yield original cells, vessels, and collagen protein sequences. By analyzing the trace element composition of the femur of this tyrannosaur, we show that after death its carcass decayed underwater in a brackish, oxic, estuarine channel and then became buried by sands that quickly cemented around the bones, largely protecting them from further chemical alteration. Other bones yielding original proteins have also been found to have fossilized within rapidly-cementing sediments in oxidizing environments, which strongly suggests that such settings are conducive to molecular preservation.Many recent reports have demonstrated remarkable preservation of proteins in fossil bones dating back to the Permian. However, preservation mechanisms that foster the long-term stability of biomolecules and the taphonomic circumstances facilitating them remain largely unexplored. To address this, we examined the taphonomic and geochemical history of Tyrannosaurus rex specimen Museum of the Rockies (MOR) 1125, whose right femur and tibiae were previously shown to retain still-soft tissues and endogenous proteins. By combining taphonomic insights with trace element compositional data, we reconstruct the postmortem history of this famous specimen. Our data show that following prolonged, subaqueous decay in an estuarine channel, MOR 1125 was buried in a coarse sandstone wherein its bones fossilized while interacting with oxic and potentially brackish early-diagenetic groundwaters. Once its bones became stable fossils, they experienced minimal further chemical alteration. Comparisons with other recent studies reveal that oxidizing early-diagenetic microenvironments and diagenetic circumstances which restrict exposure to percolating pore fluids elevate biomolecular preservation potential by promoting molecular condensation reactions and hindering chemical alteration, respectively. Avoiding protracted interactions with late-diagenetic pore fluids is also likely crucial. Similar studies must be conducted on fossil bones preserved under diverse paleoenvironmental and diagenetic contexts to fully elucidate molecular preservation pathways.

FRONTAL BONE ANATOMY OF TERATOPHONEUS CURRIEI (THEROPODA: TYRANNOSAURIDAE) FROM THE UPPER CRETACEOUS KAIPAROWITS FORMATION OF UTAH

A right frontal bone belonging to the tyrannosaurid theropod Teratophoneus curriei from the Campanian Kaiparowits Formation of Utah provides important anatomical information that is useful in understanding tyrannosaurid taxonomy and relationships. Many aspects of its anatomy indicate a subadult ontogenetic status of this individual, as they compare favorably with subadults of other tyrannosaurids such as Daspletosaurus torosus and Tyrannosaurus rex. This is consistent with the previous interpretation that this individual was subadult, based on different cranial bones such as lacrimal or maxilla. It is likely that a previous assessment of the body mass of this individual was underestimated, and it is presumed here that it was most likely around 1000 kg. This description of the frontal anatomy has several implications for previous works on tyrannosaurid cranial anatomy, and information that corrects aspects of our understanding on tyrannosaurid frontal anatomy is provided. Reanalysis of Nanuqsaurus hoglundi, a tyrannosaurid theropod that has similar frontal morphology with Teratophoneus curriei, implies that parts of its diagnosis are problematic and the proposed evidence for the supposed diminutive body size of this taxon is weak.

Two exceptionally preserved juvenile specimens of Gorgosaurus libratus (Tyrannosauridae, Albertosaurinae) provide new insight into the timing of ontogenetic changes in tyrannosaurids

ABSTRACT Known from dozens of specimens discovered since the early 20th century, Gorgosaurus libratus has arguably contributed more than any other taxon to our understanding of the life history of tyrannosaurids. However, juvenile material for this taxon is rare. Here, we describe two small, articulated Gorgosaurus specimens (skull lengths of ca. 500 mm) that help advance our knowledge of the anatomy and ontogeny of this taxon and of tyrannosaurids in general. The new specimens exhibit hallmark juvenile tyrannosaurid features, including long, low, and narrow skulls, large circular orbits, absent or incipient cranial ornamentation, ziphodont dentition, and an overall gracile skull frame. Comparison with other Gorgosaurus specimens of various ontogenetic stages allows for an examination of the timing of morphological changes that occurred through ontogeny in this taxon relative to other tyrannosaurids. Of particular note, Gorgosaurus and the larger Tyrannosaurus rex are found to have experienced similar ontogenetic transformations at similar percent skull length relative to the large known individuals for each respective taxon but at different absolute body sizes and biological ages, occurring at a larger size and older age in Tyrannosaurus than in Gorgosaurus. These results suggest a dissociation between the timing of cranial development and body size in tyrannosaurids. Finally, the recognition of ontogenetically invariant characters in Gorgosaurus makes it possible to determine the taxonomic identity of previously misidentified specimens.

Dinosaurian survivorship schedules revisited: new insights from an age‐structured population model

AbstractLittle is known of dinosaur population biology due to insufficient information on age‐dependent fecundities and mortalities. So far, survivorship curves (SC) of only six dinosaurs (four tyrannosaurs, one ceratopsian, one hadrosaur) have been erected from bone assemblages of aged specimens. They indicate high survival throughout most of their life with presumably higher mortalities after hatching and increasing mortalities towards its end. However, none of these studies recognized that to infer a reliable SC for a taxon, the assemblage must preserve a stationary age distribution (i.e. one which is stable, with constant population size over time as overall fecundities match mortalities, hereafter SAD population). To assess SCs of these dinosaurs, I built a simple population model with age‐dependent fecundities and survival rates. Its three input parameters are maximum longevity, age at sexual maturation and maximum annual offspring number, for which information exists on these dinosaurs. As bone histological studies and scaling relationships provide estimates on these parameters, my model is also applicable to other extinct taxa. Modelling suggests that bone assemblages did not preserve SAD populations. SCs determined for SAD populations of Albertosaurus sarcophagus, Gorgosaurus libratus, Dasplatosaurus torosus and Tyrannosaurus rex indicated that low mortalities followed high mortalities in early life or that mortality rates were rather constant throughout their life. In Psittacosaurus lujiatuensis, modelling suggests low mortalities throughout most of its life that increase towards its end. Due to its simplicity, my model was unable to render composite SCs, specifically the sigmoidal shape previously predicted for Maiasaura peeblesorum.

Complex neurovascular system in the dentary of Tyrannosaurus

ABSTRACT The morphology of the neurovascular canal in the jaw has been analysed in several fossil reptiles, including theropod dinosaurs. However, the details of the neurovascular canal in the dentary of theropods have not been fully elucidated. In this study, we described the well-preserved dentary of Tyrannosaurus rex, analysed the morphology of the neurovascular canal in the dentary using computed tomography techniques, and compared its distribution pattern with other dinosaurs and extant crocodiles. The results show that the neurovascular canal in the dentary of Tyrannosaurus exhibits a rather complex branching amongst the sampled dinosaurs, and that the complexity is comparable to that of extant crocodilians. The complexity of the canal branching is likely related to the high tactile sensitivity of the dentary, suggesting that the jaw tip of Tyrannosaurus may have played an essential role as a sensitive tactile sensor.

Applied linguistics as a smorgasbord of ontologies: A rejoinder to Lanvers’ ‘Spare a thought for the language learner!’

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The cranial anatomy of the long-snouted tyrannosaurid dinosaur Qianzhousaurus sinensis from the Upper Cretaceous of China

ABSTRACT Tyrannosaurid theropods topped the terrestrial food chain in North America and Asia during the latest Cretaceous. Most tyrannosaurids, exemplified by Tyrannosaurus rex, had deep snouts, thick teeth, and large jaw muscles that could generate high bite forces. They coexisted in Asia with a morphologically divergent group of long-snouted relatives, called alioramins. Qianzhousaurus sinensis, from the Maastrichtian of Ganzhou, China, is the largest alioramin yet discovered, but has only been briefly described. Here we present a detailed osteological description of the holotype cranium and mandible of Qianzhousaurus. We identify several new autapomorphic features of the genus, and new synapomorphies that unite alioramins (Qianzhousaurus, Alioramus altai, Alioramus remotus) as a clade, including a laterally projecting rugosity on the jugal. We clarify that the elongate skull of alioramins involves lengthening of the anterior palate but not the premaxilla, and is reflected by lengthening of the posterior bones of the lower jaw, even though the posterior cranium (orbit and lateral temporal fenestra) are proportionally similar to deep-skulled tyrannosaurids. We show that much of the variation among the alioramin species is consistent with growth trends in other tyrannosaurids, and that A. altai, A. remotus, and Qianzhousaurus represent different ontogenetic stages of progressive maturity, across which the signature nasal rugosites of alioramins became less prominent. We predict that the holotype skull of Qianzhousaurus represents the adult level of maturity for alioramins, and propose that the skull morphology of Qianzhousaurus indicates a much weaker bite than deep-skulled tyrannosaurids, suggestive of differences in prey choice and feeding style.

Bite force estimates in juvenile Tyrannosaurus rex based on simulated puncture marks.

BackgroundBite marks attributed to adult Tyrannosaurus rex have been subject to numerous studies. However, few bite marks attributed to T. rex have been traced to juveniles, leaving considerable gaps in understanding ontogenetic changes in bite mechanics and force, and the paleoecological role of juvenile tyrannosaurs in the late Cretaceous.MethodsHere we present bite force estimates for a juvenile Tyrannosaurus rex based on mechanical tests designed to replicate bite marks previously attributed to a T. rex of approximately 13 years old. A maxillary tooth of the juvenile Tyrannosaurus specimen BMR P2002.4.1 was digitized, replicated in dental grade cobalt chromium alloy, and mounted to an electromechanical testing system. The tooth was then pressed into bovine long bones in various locations with differing cortical bone thicknesses at varying speeds for a total of 17 trials. Forces required to replicate punctures were recorded and puncture dimensions were measured.ResultsOur experimentally derived linear models suggest bite forces up to 5,641.19 N from cortical bone thickness estimated from puncture marks on an Edmontosaurus and a juvenile Tyrannosaurus. These findings are slightly higher than previously estimated bite forces for a juvenile Tyrannosaurus rex of approximately the same size as BMR P2002.4.1 but fall within the expected range when compared to estimates of adult T. rex.DiscussionThe results of this study offer further insight into the role of juvenile tyrannosaurs in late Cretaceous ecosystems. Furthermore, we discuss the implications for feeding mechanisms, feeding behaviors, and ontogenetic niche partitioning.

The Role of the Intramandibular Joint, Symphyseal Tissues, and Wrapping Muscles on Theropod Dinosaur Mandibular Function

Sauropsids, unlike mammals, possess an intramandibular joint (IMJ) separating the dentary and postdentary bones, with different lineages either rigidifying (turtles & crocodilians) or maintaining compliance (lepidosaurs & birds) about the joint. IMJ construction and its role on mandibular performance is unclear, impeding our understanding of its function in extinct animals with extreme feeding behaviors like Tyrannosaurus rex. Sauropsids like T. rex pose a particular biomechanical paradox; feeding traces, coprolites, and their robust crania and teeth indicate that they regularly bit through and ingested bone, but their dorsoventrally-tall and mediolaterally-thin hemimandibles, IMJ, and patent mandibular symphyses suggest their mandibles were ill-suited for bone-crushing bites. Extant sauropsids also exhibit wrapping intramandibularis (mIRA) and pterygoideus ventralis (mPTv) muscles, whose effect on mandibular performance and interaction with the IMJ are unknown. Here we model the effect of the IMJ, symphyseal tissue properties, and wrapping muscle orientation on T. rex mandible biomechanical performance in order to give insight into the biomechanical constraints faced by sauropsids, and the link between their mandibular form and function. Joint tissue histology, gross dissection, and iodine contrast data of extant sauropsids were performed to inform model tissue properties, IMJ construction and muscle orientation. We imported a 3D STL model of the T. rex “STAN” and modeled the IMJ by differing material properties of modeled joint tissues to test the influence of linkage materials on mandibular performance. Muscles were mapped onto the model, and their corresponding muscle moments calculated from area centroids, muscle architecture, and volumes. Wrapping mIRA and mPTv muscles were simulated by directing their force vectors to appropriately positioned dummy points using extant sauropsids as a guide. The mandible was then constrained at the jaw joint and in a series of points along the tooth row from rostral to caudal, simulating both unilateral and bilateral bites. We find that while strains are quite high (>6000 µstrains) about the intramandibular joint, mediolateral bending stresses and strain are markedly reduced by the prearticular, which exhibits greater strain than the surrounding bone. Our results suggest the prearticular of T. rex acted as a strain sink to counteract bending about the IMJ and thereby rigidifying the mandible during feeding. We hypothesize that differences in IMJ articulation and prearticular construction may differentially facilitate or impede prearticular streptognathy, and thus intramandibular kinesis about the IMJ, in sauropsids. Forthcoming models will simulate other theropods within and without Tyrannosauridae to test this hypothesis.

Amber from a Tyrannosaurus rex bonebed (Saskatchewan, Canada) with implications for paleoenvironment and paleoecology

The Frenchman Formation (Maastrichtian) exposed within Chambery Coulee in southwestern Saskatchewan, Canada, has yielded exceptional vertebrate fauna specimens, including one of the largest known Tyrannosaurus rex individuals. The site has excellent preservation of a rich and diverse paleobotanical assemblage containing amber, which is analyzed in detail and compared to other sources of paleoecological data herein. Fourier-Transform Infrared (FTIR) spectroscopy of the fossil resin suggests a botanical source among the Cupressaceae (cypress trees). The ecological requirements of the crocodilians imply a mean annual temperature of 16 °C, which is slightly higher than previous estimates based on paleobotanical analyses. Stable isotope analyses of amber in the deposit provided insight into the environment and the ecological conditions at the time of resin secretion. The δD values showed a marine enrichment that suggests proximity to oceanic waters, and by extension, strong influence of the Western Interior Seaway in the region during the latest Cretaceous. The carbon isotope composition might also indicate that a potential ecological stress affected the trees such as a drought. These results highlight the interest of including amber in bonebed studies: even in the absence of identifiable inclusions, valuable paleoenvironmental, paleoecological, and even paleogeographic clues can be derived from chemical analyses of fossil resins.

Absolute abundance and preservation rate of Tyrannosaurus rex

Although much can be deduced from fossils alone, estimating abundance and preservation rates of extinct species requires data from living species. Here, we use the relationship between population density and body mass among living species combined with our substantial knowledge of Tyrannosaurus rex to calculate population variables and preservation rates for postjuvenile T. rex We estimate that its abundance at any one time was ~20,000 individuals, that it persisted for ~127,000 generations, and that the total number of T. rex that ever lived was ~2.5 billion individuals, with a fossil recovery rate of 1 per ~80 million individuals or 1 per 16,000 individuals where its fossils are most abundant. The uncertainties in these values span more than two orders of magnitude, largely because of the variance in the density-body mass relationship rather than variance in the paleobiological input variables.

Estimating dinosaur abundance

Paleontology Estimating the abundance of a species is a common practice for extant species and can reveal many aspects of its ecology, evolution, and threat level. Estimating abundance for species that are extinct, especially those long extinct, is a much trickier endeavor. Marshall et al. used a relationship established between body size and population density in extant species to estimate traits such as density, distribution, total biomass, and species persistence for one of the best-known dinosaurs, Tyrannosaurus rex , revealing previously hidden aspects of its population ecology. Science , this issue p. [284][1] [1]: /lookup/doi/10.1126/science.abc8300

Biomechanics of juvenile tyrannosaurid mandibles and their implications for bite force: Evolutionary biology.

The tyrannosaurids are among the most well-studied dinosaurs described by science, and analysis of their feeding biomechanics allows for comparison between established tyrannosaurid genera and across ontogeny. 3D finite element analysis (FEA) was used to model and quantify the mechanical properties of the mandibles (lower jaws) of three tyrannosaurine tyrannosaurids of different sizes. To increase evolutionary scope and context for 3D tyrannosaurine results, a broader sample of validated 2D mandible FEA enabled comparisons between ontogenetic stages of Tyrannosaurus rex and other large theropods. It was found that mandibles of small juvenile and large subadult tyrannosaurs experienced lower stress overall because muscle forces were relatively lower, but experienced greater simulated stresses at decreasing sizes when specimen muscle force is normalized. The strain on post-dentary ligaments decreases stress and strain in the posterior region of the dentary and where teeth impacted food. Tension from the lateral insertion of the looping m. ventral pterygoid muscle increases compressive stress on the angular but may decrease anterior bending stress on the mandible. Low mid-mandible bending stresses are congruent with ultra-robust teeth and high anterior bite force in adult T. rex. Mandible strength increases with size through ontogeny in T. rex and phylogenetically among other tyrannosaurids, in addition to that tyrannosaurid mandibles exceed the mandible strength of other theropods at equivalent ramus length. These results may indicate separate predatory strategies used by juvenile and mature tyrannosaurids; juvenile tyrannosaurids lacked the bone-crunching bite of adult specimens and hunted smaller prey, while adult tyrannosaurids fed on larger prey.