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The case for Nanotyrannus
Abstract
The genus Nanotyrannus was erected in 1988 by Bakker, Williams, and Currie, redescribing a skull (CMNH 7541) from the Maastrichtian (Lancian) Hell Creek Formation of Montana, first described as Gorgosaurus lancensis by Gilmore (1946). In part due to the absence of additional specimens, the validity of Nanotyrannus came under question by various researchers, culminating in 1999 when Carr assigned the specimen to Tyrannosaurus rex. Carr presented a compelling argument that CMNH 7541 was a juvenile and that characters separating Nanotyrannus from Tyrannosaurus were ontogenetic. In 2001 a second specimen was located that compared very well with the type of Nanotyrannus. This new specimen (BMR P2002.4.1), nicknamed “Jane,” consists of a beautifully preserved partial skull and skeleton. Although some researchers are convinced that BMR P2002.4.1 confi rms Carr's juvenile Tyrannosaurus rex hypothesis, this paper questions that conclusion. Fusion of the scapula-coracoid, fusion of the pelvis, and fusion and partial fusion of the centra to the dorsal spines throughout the represented vertebral column indicate cessation or near cessation of growth. A ninefold increase in size for BMR P2002.4.1 to reach the adult weight of FMNH PR 2081 (“Sue”) seems a “stretch.” BMR P2002.4.1 and the holotype have 15 or 16 tooth positions in their maxillae; all specimens unquestioningly ascribed to Tyrannosaurus rex have 11 or 12. BMR P2002.4.1's dentaries have 17 tooth positions; T. rex has 13 or 14. BMR P2002.4.1 and the type possess an incisiform and small first maxillary tooth, a character shared with Gorgosaurus and Albertosaurus but not with T. rex. A score of cranial and several post-cranial characters present in BMR P2002.4.1 and the type of Nanotyrannus lancensis are absent in T. rex. This leads to the conclusion that Nanotyrannus is a valid taxon. © 2013, The Burpee Museum of Natural History. All rights reserved. © 2013 by The Burpee Museum of Natural History. All rights reserved.
... cannot be used as its "adult" status since the feature is a individual variation rather than ontogenetic feature in dinosaurs. For example, even young Ceratosaurus specimens (Carrano et al., 2008) show completely fused pelvises (Marsh 1884) and extremely young tyrannosaurid specimen LH PV18("Raptorex kreigsteini") shows the similar pelvis fusion status (Fowler et al., 2011) with adult Tyrannosaurus rex (Larson 2013 (Fowler et al., 2011). This strongly suggests that vertebrae fusions are not related to growth in tyrannosaurids. ...
... This strongly suggests that vertebrae fusions are not related to growth in tyrannosaurids. BMR P2002.4.1.'s "completely fused" scapula-coracoid suture is also not appropriate for its ontogenetic status since the oviraptorosaur embryo preserved in the egg has fused scapulocoracoid (Norell et al., 2001) and even Larson stated Tyrannosaurus specimens had different fusions between both scapulocoracoids (Larson 2013). Therefore, this is not an ontogenetic feature, but rather an individual variation. ...
... One feature, pneumatopore on "Nanotyrannus" quadratojugal is stated by Larson as unusual among tyrannosaurids. However, as Gorgosaurus varies in similar feature (Currie 2003, Larson 2013, this could be an individual variation as well. ...
In this paper, I comment on Larson's 2013 paper "The case for Nanotyrannus". All the osteological differences proposed by Larson (2013) seem to be due to ontogeny and individual variation. Therefore, Larson's claim that "Nanotyrannus lancensis" is not a juvenile Tyrannosaurus rex is incorrect. And based on their striking anatomical similarities, it is more parsimonious to assume that "Nanotyrannus lancensis" is the junior synonym of Tyrannosaurus rex and represents a juvenile stage of the taxon.
... cannot be used as its "adult" status since the feature is a individual variation rather than ontogenetic feature in dinosaurs. For example, even young Ceratosaurus specimens (Carrano et al., 2008) show completely fused pelvises (Marsh 1884) and extremely young tyrannosaurid specimen LH PV18("Raptorex kreigsteini") shows the similar pelvis fusion status (Fowler et al., 2011) with adult Tyrannosaurus rex (Larson 2013 (Fowler et al., 2011). This strongly suggests that vertebrae fusions are not related to growth in tyrannosaurids. ...
... This strongly suggests that vertebrae fusions are not related to growth in tyrannosaurids. BMR P2002.4.1.'s "completely fused" scapula-coracoid suture is also not appropriate for its ontogenetic status since the oviraptorosaur embryo preserved in the egg has fused scapulocoracoid (Norell et al., 2001) and even Larson stated Tyrannosaurus specimens had different fusions between both scapulocoracoids (Larson 2013). Therefore, this is not an ontogenetic feature, but rather an individual variation. ...
... One feature, pneumatopore on "Nanotyrannus" quadratojugal is stated by Larson as unusual among tyrannosaurids. However, as Gorgosaurus varies in similar feature (Currie 2003, Larson 2013, this could be an individual variation as well. ...
In this paper, I comment on Larson's 2013 paper "The case for Nanotyrannus". All the osteological differences proposed by Larson (2013) seem to be due to ontogeny and individual variation. Therefore, Larson's claim that "Nanotyrannus lancensis" is not a juvenile Tyrannosaurus rex is incorrect. And based on their striking anatomical similarities, it is more parsimonious to assume that "Nanotyrannus lancensis" is the junior synonym of Tyrannosaurus rex and represents a juvenile stage of the taxon.
... Dorsal articulation of the quadrate abutting to the cotyle of the squamosal and contacting other bones of the braincase in some theropod taxa (Fig. 2D). The quadrate head, as it is called by Britt (1991), Charig & Milner (1997), Madsen & Welles (2000), Sampson & Witmer (2007), Sereno et al. (2008), Norell et al. (2009), Brusatte, Carr & Norell (2012, Choiniere et al. (2014a), Choiniere et al. (2014b) and Lautenschlager et al. (2014) among others, has also been termed 'quadrate cotylus' (Currie, 2003;Coria & Currie, 2006), 'quadrate cotyle' (Currie, 2003;Coria & Currie, 2006), 'squamosal condyle' (Coria & Salgado, 1998), 'squamosal articulation' (Turner, Pol & Norell, 2011), 'dorsal articular surface' (Larson, 2013), and 'otic process' (Maryańska & Osmólska, 1997;Burnham, 2004;Holliday & Witmer, 2008). In avian theropods, the quadrate head is homologous to the 'Caput quadrati' of Elzanowski, Paul & Stidham (2001) and Elzanowski & Stidham (2010), and roughly equivalent to the 'Processus oticus' (Baumel & Witmer, 1993). ...
... The large majority of non-avian theropods have a monostylic quadrate head (Rauhut, 2003;C Hendrickx, pers. obs., 2015); yet, oviraptorids (Maryańska & Osmólska, 1997: Fig. 3B), the alvarezsaurid Shuvuuia deserti (Chiappe, Norell & Clark, 1998), and some tyrannosaurids such as Tyrannosaurus and Gorgosaurus (Larson, 2013) have the apomorphic condition of possessing a bistylic quadrate head. In those theropods, the otic capitulum of the quadrate head always contacts the braincase. ...
... Indeed, one of the key centers of deformation during normal biting is the quadrate-squamosal contact, which would have experienced large shear stresses associated with torque and asymmetrical loading during biting (Rayfield, 2005), and the presence of a minimal amount of cartilage between the quadrate and squamosal would therefore suggest that the synovial zone was rather a growth zone than a mobile one. A streptostylic quadrate in Tyrannosaurus rex (Molnar, 1991;Molnar, 1998), Nanotyrannus lancensis (Larson, 2013), Oviraptor philoceratops (Smith, 1992), Heyuannia huangi (Lü, 2005) and Dromiceiomimus brevitertius (Russell, 1972) based on the saddle joint between the quadrate and squamosal only is therefore unlikely. ...
The quadrate of reptiles and most other tetrapods plays an important morphofunctional role by allowing the articulation of the mandible with the cranium. In Theropoda, the morphology of the quadrate is particularly complex and varies importantly among different clades of non-avian theropods, therefore conferring a strong taxonomic potential. Inconsistencies in the notation and terminology used in discussions of the theropod quadrate anatomy have been noticed, including at least one instance when no less than eight different terms were given to the same structure. A standardized list of terms and notations for each quadrate anatomical entity is proposed here, with the goal of facilitating future descriptions of this important cranial bone. In addition, an overview of the literature on quadrate function and pneumaticity in non-avian theropods is presented, along with a discussion of the inferences that could be made from this research. Specifically, the quadrate of the large majority of non-avian theropods is akinetic but the diagonally oriented intercondylar sulcus of the mandibular articulation allowed both rami of the mandible to move laterally when opening the mouth in many of theropods. Pneumaticity of the quadrate is also present in most averostran clades and the pneumatic chamber—invaded by the quadrate diverticulum of the mandibular arch pneumatic system—was connected to one or several pneumatic foramina on the medial, lateral, posterior, anterior or ventral sides of the quadrate.
... Over the next 15 years, excavation of the site yielded 50 additional bones from this specimen, including a right maxilla with teeth and a left dentary with teeth. Although not yet formally described, these remains have enabled us to clearly distinguish slender, blade-like shed teeth of Nanotyrannus [37] from the more robust crushing teeth of Tyrannosaurus, both of which are commonly found in the bonebed. ...
... HR Bonebed taxa represented. Nanotyrannus designation based on Larson[37]. ...
Over twenty years of work on the Hanson Ranch (HR) Bonebed in the Lance Formation of eastern Wyoming has yielded over 13,000 individual elements primarily of the hadrosaurid dinosaur Edmontosaurus annectens. The fossil bones are found normally-graded within a fine-grained (claystone to siltstone) bed that varies from one to two meters in thickness. Almost all specimens exhibit exquisite preservation (i.e., little to no abrasion, weathering, and breakage), but they are disarticulated which, combined with our sedimentological observations, suggests that the bones were remobilized and buried after a period of initial decay and disarticulation of Edmontosaurus carcasses. Because of the large number of recovered fossil elements, we have been able to gain deeper insight into Edmontosaurus biostratigraphy including disarticulation and transport of skeletal elements. The most common postcranial elements in the bonebed are pubes, ischia, scapulae, ribs, and limb bones. By contrast, vertebrae, ilia, and chevrons are rare. The most common craniomandibular bones include dentaries, nasals, quadrates, and jugals, whereas the premaxillae, predentaries, and braincase bones are underrepresented. Thus, overall, chondrocranial and axial elements, as well as distal elements of the limbs, are distinctly underrepresented. We hypothesize that following decay and disarticulation, hydraulic winnowing removed the articulated sections (e.g., vertebral columns) and the small, distal-most elements before, or at the same time, the remaining bones were swept up in a subaqueous debris flow that generated the deposit. Comparison of the HR Bonebed with other widely dispersed Upper Cretaceous hadrosaurid-dominated bonebeds reveals many shared attributes, which suggests similar processes at work in the formation of these bonebeds across space and time. This in turn reflects similar behavior by populations of these species around the world resulting in similar modes of death, becoming interred in similar depositional settings.
... The fossil faunas of the Lance Formation and similarly aged North American formations have been extensively worked, and the only know theropod genera large enough to be potential candidates for the trackmaker are the tyrannosaurids Nanotyrannus and Tyrannosaurus. The validity of the former genus is controversial and is thought by some to be an early ontogenetic stage of the latter (Carr, 1999;Larson, 2013). Putative skeletal material from both Nanotyrannus and Tyrannosaurus has been found in the Glenrock Section. ...
... BMR P2002.4.1 has an estimated hip height (here measured as the summed length of the femur, tibia, and metatarsal III) of 2120 mm. Proponents of the validity of Nanotyrannus have considered BMR P2002.4.1 to be assignable to that genus (Larson, 2013), and BMR P2002.4.1 is the only presently described potential Nanotyrannus specimen with nearly complete hindlimb elements. The hip height of Tyrannosaurus exceeds 2800 mm among adults. ...
... This effect coupled with its size and morphology, hints to the immature state of the G. scabrosus holotype, highlighted by its characters with ontogenetic influence. Indeed, as recently seen for other taxa (Carr, 2020;Horner & Goodwin, 2006;Horner & Goodwin, 2009;Larson, 2013;Woodward et al., 2020), more time should be devoted toward the placement of a given specimens in ontogenetic context whenever possible. ...
Baurusuchidae comprises a clade of top-tier terrestrial predators and are among the most abundant crocodyliforms found in the Adamantina Formation, Bauru Basin, Brazil (Campanian-Maastrichtian). Here, we provide a detailed description of the cranial and postcranial osteology and myology of the most complete juvenile baurusuchid found to date. Although the preservation of juvenile individuals is somewhat rare, previously reported occurrences of baurusuchid egg clutches, a yearling individual, and larger, but skeletally immature specimens, comprise a unique opportunity to track anatomical changes throughout their ontogenetic series. Its cranial anatomy was resolved with the aid of a three-dimensional model generated by the acquisition of computed tomography data, and its inferred adductor mandibular musculature was compared to that of mature specimens in order to assess possible ontogenetic shifts. A subsequent phylogenetic analysis included the scoring of Gondwanasuchus scabrosus, the smallest baurusuchid species known to date, to evaluate its phylogenetic relations relative to a known juvenile. We find considerable differences between juveniles and adults concerning skull ornamentation and
muscle development, which might indicate ontogenetic niche partitioning, and also anatomical and phylogenetic evidence that G. scabrosus corresponds to a young semaphoront lacking mature cranial features.
... 2.8). Similar differences are also observed between juvenile and adult individuals of Tyrannosaurus rex and Tarbosaurus bataar (Witmer and Ridgely, 2010;Tsuihiji et al., 2011;Larson, 2013), although the anterior process in adults is significantly wider than in adult Gorgosaurus. ...
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.
... The following study examines a possible growth series of tracks inferred to pertain to tyrannosaurid trackmakers in order to explore whether we can capture an ontogenetic trajectory in foot morphology. Tyrannosaurids are particularly suitable subjects for the exploration of size-dependent differences in track morphology, as their growth patterns are the subject of rigorous research and ongoing debate (e.g., Russell, 1970;Currie, 1998Currie, , 2003Carr, 1999;Horner and Padian, 2004;Erickson et al., 2004Erickson et al., , 2006Hutchinson et al., 2011;Larson, 2013;Woodward, 2020). Specifically, tyrannosaurids were hypothesized to undergo a relatively rapid growth phase during mid-life, possibly associated with shifts in locomotor performance (Currie, 1998(Currie, , 2003Erickson et al., 2004;Hutchinson et al., 2011). ...
Fossil tracks should theoretically capture differences in pedal anatomy between growth stages of the same taxon, particularly those related to the soft tissue of the foot, providing a more realistic view of pedal ontogeny than skeletal material alone. However, recognizing these ontogenetic trajectories is complicated by the influence of preservation and kinematics on track morphology, as well as the inherent difficulty of referring different tracks to a single taxon. Here, we explore differences in track morphology from a collection of tracks attributed to tyrannosaurids from Unit 4 of the Wapiti Formation (upper Campanian) in western Canada. Along with morphology, close geographic and stratigraphic associations suggest that the tracks pertain to similar tyrannosaurid trackmakers. A geometric morphometric analysis of the track outlines reveals size-dependent increase in relative track robusticity, driven primarily by an increase in 'heel' breadth and surface area. This relationship is lost when the dataset is expanded to include tyrannosaurid tracks globally, which we attribute to increased stratigraphic and taxonomic 'noise' within the global dataset that masks the tightly constrained patterns obtained from the Wapiti Formation tracks. Although there is some substrate and kinematic influence on certain aspects of track morphology, we hypothesize that the observed size-dependent relationship reflects genuine expansion in the breadth of the heel soft tissues and probably their overall surface area associated with growth. Increased pedal robusticity likely assisted with weight bearing and locomotor stability as body mass increased over ontogeny, supporting previous hypotheses that some tyrannosaurids underwent a growth-related reduction in relative agility and/or cursorial performance.
... This uncovered negative allometric growth of the humerus [76], as expected within our interpretation. Ontogenetic negative allometry has been argued for humerus length in Tyrannosauridae [77], although this analysis grouped specimens from different genera, and the juvenile status of some specimens has been questioned [78]. No other studies have provided any statistical assessment of negative forelimb allometry in the ontogeny of non-avian theropods. ...
Background:
The origin of birds is marked by a significant decrease in body size along with an increase in relative forelimb size. However, before the evolution of flight, both traits may have already been related: It has been proposed that an evolutionary trend of negative forelimb allometry existed in non-avian Theropoda, such that larger species often have relatively shorter forelimbs. Nevertheless, several exceptions exist, calling for rigorous phylogenetic statistical testing.
Results:
Here, we re-assessed allometric patterns in the evolution of non-avian theropods, for the first time taking into account the non-independence among related species due to shared evolutionary history.We confirmed a main evolutionary trend of negative forelimb allometry for non-avian Theropoda, but also found support that some specific subclades (Coelophysoidea, Ornithomimosauria, and Oviraptorosauria) exhibit allometric trends that are closer to isometry, losing the ancestral negative forelimb allometry present in Theropoda as a whole.
Conclusions:
Explanations for negative forelimb allometry in the evolution of non-avian theropods have not been discussed, yet evolutionary allometric trends often reflect ontogenetic allometries, which suggests negative allometry of the forelimb in the ontogeny of most non-avian theropods. In modern birds, allometric growth of the limbs is related to locomotor and behavioral changes along ontogeny. After reviewing the evidence for such changes during the ontogeny of non-avian dinosaurs, we propose that proportionally longer arms of juveniles became adult traits in the small-sized and paedomorphic Aves.
... Timurlengia (Averianov and Sues, 2012), Torvosaurus (Araújo et al., 2013) and Troodon (Varricchio et al., 2002). Unserrated teeth are also present in the premaxillary teeth of the "Jordan Theropod" LACM 28471 (Molnar, 1978), considered to be a specimen of Nanotyrannus (Larson, 2013) or a juvenile individual of Tyrannosaurus (Carr and Williamson, 2004). In mature individuals, unserrated teeth are restricted to the mesial dentition of some coelophysoids such as Megapnosaurus rhodesiensis (Raath, 1977) and 'Syntarsus' kayentakatae (Rowe, 1989), and the basal pantyrannosaurian Xiongguanlong Figure 11.4) and an indeterminate tyrannosauroid from the Cenomanian of Utah (Zanno et al., 2019). ...
Isolated theropod teeth are some of the most common fossils in the dinosaur fossil record and are continually reported in the literature. Recently developed quantitative methods have improved our ability to test the affinities of isolated teeth in a repeatable framework. But in most studies, teeth are diagnosed on qualitative characters. This can be problematic because the distribution of theropod dental characters is still poorly documented, and often restricted to one lineage. To help in the identification of isolated theropod teeth, and to more rigorously evaluate their taxonomic and phylogenetic potential, we evaluated dental features in two ways. We first analyzed the distribution of 34 qualitative dental characters in a broad sample of taxa. Functional properties for each dental feature were included to assess how functional similarity generates homoplasy. We then compiled a quantitative data matrix of 145 dental characters for 97 saurischian taxa. The latter was used to assess the degree of homoplasy of qualitative dental characters, address longstanding questions on the taxonomic and biostratigraphic value of theropod teeth, and explore the major evolutionary trends in the theropod dentition.
In smaller phylogenetic datasets for Theropoda, dental characters exhibit higher levels of homoplasy than non-dental characters, yet they still provide useful grouping information and optimize as local synapomorphies of smaller clades. In broader phylogenetic datasets, the degree of homoplasy displayed by dental and non-dental characters is not significantly different. Dental features on crown ornamentations, enamel texture, and tooth microstructure have significantly less homoplasy than other dental features and can be used to identify many theropod taxa to ‘family’ or ’sub-family’ level, and some taxa to genus or species. These features should, therefore, be a priority for investigations seeking to classify isolated teeth.
Our observations improve the taxonomic utility of theropod teeth and in some cases can help make isolated teeth useful as biostratigraphic markers. This proposed list of dental features in theropods should, therefore, facilitate future studies on the systematic paleontology of isolated teeth.
... TMP 1985absent: TMP 1998.063.0084). The foramen is distinct from the quadratojugal pneumatopore seen in Daspletosaurus horneri and Nanotyrannus lancensis, which occurs lower on the lateral surface of the dorsal process, beyond the bounds of the fossa (Larson, 2013;Carr et al., 2017). ...
Several published censuses have noted the presence of two tyrannosaurids, Daspletosaurus sp. and Albertosaurus sarcophagus, within the Upper Cretaceous Horseshoe Canyon Formation of Alberta. Although A. sarcophagus is known from more than a dozen major discoveries in these strata, Daspletosaurus sp. is known from just a single problematic skeleton (lacking most of the skull) of a young individual. Here we describe and figure this skeleton, and marshal a variety of osteohistologic, morphometric, and phylogenetic methods to accurately determine its taxonomic status. Although none of these methods individually provides convincing evidence regarding the affinities of the specimen, together (and including other historical and biostratigraphic considerations) they strongly imply that the skeleton instead pertains to a young A. sarcophagus. In this way, we show that only a single species of tyrannosaurid is definitively present in the Horseshoe Canyon Formation, greatly simplifying interpretations of tyrannosaurid evolution and ecology in this setting. Anat Rec, 303:673–690, 2020. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.
... Following this trend the low δ 44/42 Ca of N. lancensis would indicate a bone rich diet as well. This means T. rex and N. lancensis had very similar diets providing more insight in the debate whether they are separate species or not (Bakker et al., 1988;Carr, 1999;Larson, 2013aLarson, , 2013bYun, 2015). Heuser et al. (2011). ...
Stable isotopes can give key information on environment and behaviour of animals in both present and past ecosystems. This study firstly looks at trophic level and bone consumption and secondly migratory behaviour of Tyrannosaurus rex from the Hell Creek formation, Montana USA, using 44Ca/42Ca and 87Sr/86Sr ratios, respectively. Because these techniques are relatively new these data add significantly to the existing dataset and enhance understanding of these subjects.
The measured 44Ca/42Ca values in T. rex vary between -0.669‰ and -0.817‰. These low values suggest T. rex occupied a high trophic level and a high rate of bone consumption, confirming its position as apex predator in its environment.
The 87Sr/86Sr signal has values starting out high followed by two drops. These changes in 87Sr/86Sr indicate a change in local geology, suggesting migration. This can be either T. rex itself migrating, or herbivores are migrating through its territory
The results confirm hypotheses from earlier studies on trophic level and bone consumption of Tyrannosaurus rex and bring new and interesting data on migratory behaviour of T. rex on which many new studies concerning migratory behaviour during the Maastrichtian in the Hell Creek Formation can be based.
This study is done as part of a larger project focussing on a new specimen of Tyrannosaurus rex owned by Naturalis Biodiversity Center in Leiden, the Netherlands.
... Currie et al. (2003) found Tyrannosaurus rex as sister to Nanotyrannus, and this North American clade as sister to clade comprising Daspletosaurus, Tarbosaurus and Alioramus. However, this is problematic since Nanotyrannus is very likely a juvenile Tyrannosaurus rex Carr, 1999;Carr and Williamson, 2004;Yun, 2015; but see Larson, 2013). Many more recently named genera were missing in the Currie al (2003) analysis. ...
It is an undoubtable fact that Tyrannosaurus rex is the most iconic dinosaur species of all time. However, it is currently debatable whether this species has a North American origin or Asian origin. In this paper, I test these two hypotheses based on current fossil records and former phylogenetic analyses. Phylogenetic and fossil evidence, such as derived tyrannosaurine fossils of Asia, suggests that the hypothesis of an Asian origin of Tyrannosaurus rex is the most plausible one, but this is yet to be certain due to the scarcity of fossil records.
... 6A). It does not contact the anterior and posterior border of this fossa as seen in Tyrannosaurus and Tarbosaurus (Larson, 2013 (Carr & Williamsom, 2004) the maxillary fenestra of AMNH FARB 5477 is separated from the anterior edge by a narrow apron of bone. In Appalachiosaurs, Albertosaurus (Carr et al., 2005), juveniles Tyrannosaurus and Daspletosaurus (Carr & Williamsom, 2004), Bistahieversor, Alioramus altai (Brusatte et al., 2012), Lythronax and Teraphoneus (Loewen et al., 2013) all display a maxillary fenestra that is separated from the border by a proportionally wider apron of bone. ...
Daspletosaurus is a Campanian genus of Tyrannosauridae from North America. This genus
occupied the same geographic area of Albertosaurus, but remains of Albertosaurus are more
abundant than Daspletosaurus. Here is described a subadult maxilla (AMNH FARB 5477)
of Daspletosaurus sp. from Montana (USA) and possibly from the Two Medicine Formation.
The description is based on Carr (1999) that described cranial ontogenetic variations in
tyrannosaurids. The maxilla belongs to the ontogenetic Stage 3 sensu Carr (1999), in which
the maxilla is thick, the lateral surface of the bone well sculptured, and the maxillary fenestra
is subcircular and well separated from the anterior edge of antorbital fossa. Possibly there were
more than one species of Daspletosaurus and the locality of the here described subadult specimen
suggests that Daspletosaurus species occurred more southern than Albertosaurus.
... In USNM 10865, the rugose projections are hypothesized to be osteological modifications associated with a highly pathologic caudal series; thus, it is thought that the spinal projections are a response from the need to horizontally maintain the caudal series [43]. Additionally, several titanosauriform specimens have been documented which retain biomineralized and non-biomineralized remnants of their vertebral ligaments [42,44]. The most extensive of these documented are reported by Cerda et al. (2015), in which nine biomineralized supraspinal ligaments are reported in titanosauriform sacra. ...
Rugose projections on the anterior and posterior aspects of vertebral neural spines appear throughout Amniota and result from the mineralization of the supraspinous and interspinous ligaments via metaplasia, the process of permanent tissue-type transformation. In mammals , this metaplasia is generally pathological or stress induced, but is a normal part of development in some clades of birds. Such structures, though phylogenetically sporadic, appear throughout the fossil record of non-avian theropod dinosaurs, yet their physiological and adaptive significance has remained unexamined. Here we show novel histologic and phylogenetic evidence that neural spine projections were a physiological response to bio-mechanical stress in large-bodied theropod species. Metaplastic projections also appear to vary between immature and mature individuals of the same species, with immature animals either lacking them or exhibiting smaller projections, supporting the hypothesis that these structures develop through ontogeny as a result of increasing bending stress subjected to the spinal column. Metaplastic mineralization of spinal ligaments would likely affect the flexibility of the spinal column, increasing passive support for body weight. A stiff spinal column would also provide biomechanical support for the primary hip flexors and, therefore, may have played a role in locomotor efficiency and mobility in large-bodied species. This new association of interspinal ligament metaplasia in Theropoda with large body size contributes additional insight to our understanding of the diverse biomechanical coping mechanisms developed throughout Dinosauria, and stresses the significance of phylogenetic methods when testing for biological trends, evolutionary or not.
... We recognise that the specimens have undergone some deformation (as is the norm for fossil specimens); however, we disagree with Martin and colleagues conclusions and consider these differences true morphological traits-perhaps due to differing perception of morphological species. However, Machimosaurus species (sensu Young et al., 2014a) still differ from each other in stratigraphic occurrence, basioccipital apophysis cross-section, relative size and shape of the basioccipital tuberosities, relative size of the paroccipital processes and the expansion at their lateral ends, tooth morphology, tooth enamel surface morphology, and tooth count (exceeding modern crocodylian intra-specific variation Larson, 2013;Brown et al., 2015)). Perhaps more importantly, it should also be noted that the supposed synonymy of Ma. buffetauti and Ma. ...
Teleosaurids were a group of semi-aquatic crocodylomorphs with a fossil record that spanned the Jurassic Period. In the UK, abundant specimens are known from the Oxford Clay Formation (OCF, Callovian to lower Oxfordian), but are very rare in the Kimmeridge Clay Formation (KCF, Kimmeridgian to lower Tithonian), despite their abundance in some contemporaneous deposits in continental Europe. Unfortunately, due to the paucity of material from the intermediate ‘Corallian Gap’ (middle to upper Oxfordian), we lack an understanding of how and why teleosaurid taxic abundance and diversity declined from the OCF to the KCF. The recognition of an incomplete teleosaurid lower jaw from the Corallian of Weymouth (Dorset, UK) begins to rectify this. The vertically oriented dentition, blunt tooth apices, intense enamel ornamentation that shifts to an anastomosed pattern apically, and deep reception pits on the dentary unambiguously demonstrates the affinity of this specimen with an unnamed sub-clade of macrophagous/durophagous teleosaurids (‘
Steneosaurus
’
obtusidens
+
Machimosaurus
). The high symphyseal tooth count allows us to exclude the specimen from
M. hugii
and
M. mosae
, but in absence of more diagnostic material we cannot unambiguously assign DORCM G.3939 to a more specific level. Nevertheless, this specimen represents the first mandibular material referable to Teleosauridae from the poorly sampled middle-upper Oxfordian time-span in the UK.
... No other tyrannosaurid taxon has two reduced mesial dentary teeth, or such a size disparity between them and the more distal teeth in mature individuals as is seen in the holotype of Nanuqsaurus hoglundi ( Figure 3A, L, M). The first two dentary teeth are reduced in the controversial tyrannosaurid specimens CMNH (Cleveland Museum of Natural History, Cleveland, Ohio, USA) 7541 and BMR (Burpee Museum of Natural History, Rockford, Illinois, USA) P2002.4.1, both of which have been identified as either a separate tyrannosaurid taxon (Nannotyrannus lancensis), or as ontogenetically immature Tyrannosaurus rex [6,21,[25][26][27][28]. However, the mesiodistal length of the second dentary tooth or alveolus is still more than half the size of the third tooth/alveolus in these disputed specimens, versus approximately 45 percent in the holotype of Nanuqsaurus hoglundi. ...
Tyrannosaurid theropods were dominant terrestrial predators in Asia and western North America during the last of the Cretaceous. The known diversity of the group has dramatically increased in recent years with new finds, but overall understanding of tyrannosaurid ecology and evolution is based almost entirely on fossils from latitudes at or below southern Canada and central Asia. Remains of a new, relatively small tyrannosaurine were recovered from the earliest Late Maastrichtian (70-69Ma) of the Prince Creek Formation on Alaska's North Slope. Cladistic analyses show the material represents a new tyrannosaurine species closely related to the highly derived Tarbosaurus+Tyrannosaurus clade. The new taxon inhabited a seasonally extreme high-latitude continental environment on the northernmost edge of Cretaceous North America. The discovery of the new form provides new insights into tyrannosaurid adaptability, and evolution in an ancient greenhouse Arctic.
In Dr. Kenneth Carpenter's 1982 paper describing baby dinosaur dentaries and teeth, one tooth cataloged as UCMP 119853 seemed to have a morphology reminiscent of adult Tyrannosaurus rex specimens. After an extensive critique of the tooth, along with comments from other professional paleontologists (Professor Holtz, Jr., Sebastian Dalman, and Dr. Joshua B. Smith), this author believes that UCMP 119853 is a baby T. rex tooth that was situated in either the premaxillary (first or second), or the first maxillary, position. This author tends to lean more towards the premaxillary, but is still open to the possibility that the specimen is a first maxillary tooth. UCMP 119853 has a single carina that overlaps the tip of the tooth and is located in the labial and lingual positions of the crown, and the carina is denticulate. The morphology of UCMP 119853 differs from that of other young tyrannosauroid specimens that are categorized as either "Nanotyrannus," or "juvenile T. rex specimens" (which this author categorizes as cf. Dryptosaurus aquilinguis). A comparison between UCMP 119853 and the premaxillary, and first maxillary, teeth from other tyrannosauroid genera showed that T. rex's tooth morphology stayed consistent throughout the animal's lifetime, and was close to that of the genus' sister taxon Tyrannosaurus/Tarbosaurus bataar.
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.
Dryptosaurus aquilunguis is a tyrannosauroid from the late Maastrichtian of Eastern North America (Brusatte et al., 2011, pp. 2 and 5). This is also known as Appalachia (Brownstein, 2018, p. 1). So far, only one good specimen, the holotype ANSP 9995, has been found for the genus. A few teeth have been assigned to the genus (Brownstein, 2018, p. 5 Table 1), but no relatively complete specimens have been described yet. However, after an exhaustive examination of the controversial “Nanotyrannus”/juvenile Tyrannosaurus rex specimens, a new hypothesis is going to be brought forth: Dryptosaurus lived in Appalachia and Laramidia towards the end of the Maastrichtian. The tyrannosauroid specimens previously labeled as “Nanotyrannus” are actually Dryptosaurus.
Both Dryptosaurus and “Nanotyrannus” lived during the same time (Brusatte et al., 2011, p. 5) (Larson, 2013, p. 15). Numerous publications have suggested that Laramidia and Appalachia reconnected when the Western Interior Sea subsided around 70.8-67 Ma (Blakey, 2014) (Bell and Currie, 2014, Figure 4) (Brownstein and Bissel, 2021, Discussion, para. 3-4) (Druckenmiller et al., 2021, Figure 1). Both Laramidia and Appalachia seemed to have had similar fauna: lambeosaurs, ceratopsians, and mosasaurs (Gallagher et al., 2012, p. 147) (Van Vranken and Boyd, 2021, Abstract; p. 5) (Rolleri et al., 2020, pp. 284-285) (Sullivan et al., 2011) (Brownstein and Bissel, 2020, Abstract; Discussion, para. 3-4) (Serrano-Branas and Prieto-Marquez, 2022). Ceratopsids, in particular, were thought to have not existed in Appalachia. However, a ceratopsian tooth has been found in the Maastrichtian-aged Owl Creek Formation, which is in Appalachia (Farke and Phillips, 2017) (Brownstein and Bissel, 2021, Discussion, para. 4). If animals in Laramidia can be found in Appalachia, and vice versa, then hypothetically, Dryptosaurus could migrate into Laramidia.
Dryptosaurus and “Nanotyrannus” share many physical characteristics:
Both Dryptosaurus and “Nanotyrannus” have a first maxillary tooth that is incisiform (small and similar in morphology to the premaxillary teeth) (Cope, 1869, pp. 100-101) (Brusatte et al., 2011, p. 9) (Larson, 2013, pp. 33-35). This trait is not present in T. rex (Molnar, 1978, p. 77) (Bakker et al., 1988, p. 24) (Larson, 2013, pp. 33-35).
Both genera have about 25 or so caudal vertebrae (Cope, 1869, p. 102) (pers. obs. in Pantuso, 2019) (pers. obs. in Mapping, North Carolina Museum of Natural Sciences, North Carolina, United States). T. rex and Tarbosaurus/Tyrannosaurus bataar have 40 or more caudal vertebrae (Brochu, 2003, pp. 49 and 90). This is also seen in the young T. bataar specimen PIN 552-2, so the bone count didn’t increase or decrease during ontogeny (Maleev, 1955b, p. 4) (Maleev, 1974, pp. 13 and 29).
Morphology of the arms of both genera are identical ( Brusatte et al., 2011, p. 19) (Pantuso, 2019). The humeri are identical and differ in shape compared to T. rex’s (Brochu, 2003, p. 97 Figure 85) (pers. obs. in Holtz, 2021). The manual phalanx 1-1 of Dryptosaurus and “Nanotyrannus” are extremely elongated, and this is an autapomorphy of Dryptosaurus (Brusatte et al., 2011, pp. 5 and 47; Table 3) and Megaraptor (Novas et al., 2016, p. 53 Figure 3; p. 56). G./A. libratus’ manual phalanx 1-1 is somewhat longer than other tyrannosaurids (9.8 cm) (Brusatte et al., 2011, p. 47 Table 3), but it’s still only half as long as Dryptosaurus’ (16 cm) (Table 3) or “Nanotyrannus’” (Larson, 2020). T. rex’s, and T. bataar’s, manual phalanx 1-1 are shorter than Dryptosaurus’ and “Nanotyrannus’’’ (Maleev, 1974, p. 36 Table 5) (Larson, 2008, pp. 41-42) (Brusatte et al., 2011, p. 47 Table 3) (Larson, 2018) (Persons IV et al., 2019, p. 669 Table 1). The manual unguals of the two genera are large and comparable in morphology and size (Brusatte et al., 2011, p. 20 Table 2) (Pantuso, 2019) (Stein, 2021, p. 43 Figure 8 C) (Larson, 2016), contra to T. rex’s and T. bataar’s short manual unguals (Tsuihiji et al., 2011, p. 2 Figure 1 A) (Larson, 2018) (TD-13-047, PaleoAdventures, South Dakota, United States).
Both genera have tibiae that are either longer than their femora, or they are about the same size as each other (Carpenter et al., 1997, p. 568 Table 3) (Persons IV et al., 2016, Tables 1 and 4). This is a trait seen in basal tyrannosauroids. Brusatte et al., (2011) said that Dryptosaurus’ tibia is smaller than the femur (p. 20 Table 2; p. 30), but other sources say the tibia is longer (Carpenter et al., 1997, p. 568 Table 3) (Persons IV and Currie, 2016, Table 1). Brusatte et al., (2011) also stated that the tibia’s “proximal and distal ends are slightly eroded” (p. 30), so the tibia could have been longer. The Dryptosaurus holotype specimen is considered to be an adult, or close to maturity (p. 5). Other examples are Qiazhousaurus/Alioramus sinensis, Appalachiosaurus, Alectrosaurus, Dilong, Guanlong, and Yutyrannus (Lu et al., 2014, Supplementary Materials, p. 9 Table 5) (Persons IV and Currie, 2016, Table 1). These are all basal or derived tyrannosauroids, and most of these specimens are considered to be adults or subadults. As for the basal tyrannosaurids, both Gorgosaurus/Albertosaurus libratus and Albertosaurus sarcophagus have femora and tibiae lengths that fluctuate between the femur being longer than the tibia, or both bones are about the same length (Persons IV and Currie, 2016, Tables 1 and 2). As for the tyrannosaurinae, the 14-year old T. rex specimen LACM 23845 (Erickson et al., 2004, p. 774 Table 1), had a femur and tibia length of 82.5 cm, while the adult specimen CM 9380 has a longer femur (Table 2). Rozhdestvensky (1965) said that the young T. bataar specimen, PIN 552-2, had a femur and a tibia that are “almost the same length,” while an older specimen, PIN 551-2, has a longer femur (p. 10).
There are other traits that “Nanotyrannus” had that are seen in other basal and advanced tyrannosauroids, such as the lingual bar on the interior side of the dentary covering the first alveoli instead of the first two as in T. rex or T. bataar (Dalman and Lucas, 2017, pp. 23-24). All of the information listed above indicates that “Nanotyrannus” could be Dryptosaurus. This would also indicate that Dryptosaurus was present in Appalachia and Laramidia, creating a regional barrier that would help separate “Nanotyrannus” from being lumped into T. rex because, as of right now, no Tyrannosaurus specimens have been found in the Eastern United States. This technique helped to separate Torosaurus from Triceratops (Deak and McKenzie, 2016, slide 7).
An alternative hypothesis could be that Dryptosaurus was actually a juvenile T. rex. Brusatte et al., (2011) did not perform a histological test to see how many LAGs the Dryptosaurus holotype had in its femur or tibia, which could potentially go against their conclusion that the holotype was actually mature. They just used the closed neurocentral sutures to estimate the age of the specimen (p. 5). The “Nanotyrannus” specimen BMRP 2002.4.1 (“Jane”) had visible neurocentral sutures on caudals 1-11, but caudals 12 and others, along with one dorsal vertebra, show closed sutures and are fused. This was used to suggest an older age for the specimen (Larson, 2013, p. 19). However, a histological analysis on the specimen’s femur showed that “Jane” was just 13 years old, and was still growing when it died (Woodward et al., 2020, Results, para. 4). Since Dryptosaurus lived during the same time as T. rex, and has similar traits that the “Nanotyrannus”/juvenile T. rex specimens have, then perhaps it was a juvenile T. rex? The author of this paper does not believe this to be the case, especially since actual juvenile T. rex specimens are already known and have different traits that are not present in “Nanotyrannus” or Dryptosaurus (Dalman, pers. comm.). This will be elaborated on in the future.
In conclusion, the traits that are present in the “Nanotyrannus” specimens are also seen in the holotype specimen of Dryptosaurus. Both genera lived during the same time, and had coexisting taxa that were present in Appalachia and Laramidia. This suggests that the Western Interior Sea began to recede, or it had already. This could have allowed Dryptosaurus to migrate into Laramidia. More publications will be published in the future to explore this hypothesis further.
Tooth counts are commonly recorded in fossil diapsid reptiles and have been used for taxonomic and phylogenetic purposes under the assumption that differences in the number of teeth are largely explained by interspecific variation. Although phylogeny is almost certainly one of the greatest factors influencing tooth count, the relative role of intraspecific variation is difficult, and often impossible, to test in the fossil record given the sample sizes available to palaeontologists and, as such, is best investigated using extant models. Intraspecific variation (largely manifested as size-related or ontogenetic variation) in tooth counts has been examined in extant squamates (lizards and snakes) but is poorly understood in archosaurs (crocodylians and dinosaurs). Here, we document tooth count variation in two species of extant crocodylians (Alligator mississippiensis and Crocodylus porosus) as well as a large varanid lizard (Varanus komodoensis). We test the hypothesis that variation in tooth count is driven primarily by growth and thus predict significant correlations between tooth count and size, as well as differences in the frequency of deviation from the modal tooth count in the premaxilla, maxilla, and dentary. In addition to tooth counts, we also document tooth allometry in each species and compare these results with tooth count change through growth. Results reveal no correlation of tooth count with size in any element of any species examined here, with the exception of the premaxilla of C. porosus, which shows the loss of one tooth position. Based on the taxa examined here, we reject the hypothesis, as it is evident that variation in tooth count is not always significantly correlated with growth. However, growth trajectories of smaller reptilian taxa show increases in tooth counts and, although current samples are small, suggest potential correlates between tooth count trajectories and adult size. Nevertheless, interspecific variation in growth patterns underscores the importance of considering and understanding growth when constructing taxonomic and phylogenetic characters, in particular for fossil taxa where ontogenetic patterns are difficult to reconstruct.
© 2015 Anatomical Society.
Ceratosauria represents the first widespread and diverse radiation of theropod dinosaurs comprising two main sister clades, Neoceratosauria and Coelophysoidea. This chapter discusses the diagnostic features, phylogenetic placement, and paleobiology of ceratosaurians. The fossil record for Ceratosauria spans a minimum of 155 million years, from the late Carnian of the Late Triassic to the end of the Cretaceous. Ceratosaurs had an essentially global distribution, their remains being found on every continent except Australia and Antarctica. Ceratosaurs evolved into a broad range of sizes and body forms, from lightly built, diminutive taxa such as Segisaurus (1 to 1.5 m in length) to the large abelisaurids, such as Carnotaurus (10 to 11 m). Several coelophysoid taxa were collected from mass burials, where multiple individuals were preserved together. In particular, Syntarsus rhodesiensis is known from at least thirty individuals found at localities in Zimbabwe and South Africa.
The Jordan theropod skull is shown to belong to Aublysodon mirandus,, a theropod dinosaur previously known only from isolated teeth. Although the skull is incomplete, it retains numerous primitive characters that set it apart from all other known Late Cretaceous theropods. These features include a long, low muzzle, relatively large teeth, frontals longer than wide, smooth nasals, V-shaped anterior margin of antorbital fossa, premaxillary- maxillary suture acutely inclined, and low angle of symphysis. Aublysodon is characterized by premaxillary teeth D-shaped in cross section and with posteriorly directed carinae, a V-shaped frontoparietal suture, and a peculiar first dentary tooth. It probably possessed small premaxillaries. Aublysodon is an aberrant theropod which at this time is best retained in its own family, the Aublysodontidae.
The discovery of a new genus and species of tyrannosauroid from the Demopolis Formation (middle Campanian) of Alabama increasesthe known diversity of the clade, although it does not elucidate the place of initial dispersal. This subadult tyrannosauroid is the most complete non-avian theropod collected and described fromthe Cretaceous of eastern North America. In contrast to tyrannosaurids, the new taxon possesses several plesiomorphic characters, including lacrimals that lack a distinct peaked cornual process, and a dorsoventrally shallow horizontal ramus ofthe maxilla. Autapomorphies include a wide jugal process of the ectopterygoid, a caudal pneumatic foramen of the palatine thatpierces the rostral half of the vomeropterygoid process of the bone, an articular surface for the lacrimal on the palatine that is distally positioned on the dorsolateral process, and pedal unguals that have a distinct proximodorsal lip over the articular surface. Cladistic analysis indicates the new taxon is a basal tyrannosauroid and its presence in eastern North America suggeststhat the recent common ancestor of Tyrannosauridae probably evolved following the transgression of the Western Interior Seaway. Cladistic analysis indicates that Dryptosaurus aquilunguisis also a basal tyrannosauroid but is less derived than the new genus.
Tyrannosauridae can be subdivided into two distinct subfamilies-the Albertosaurinae and the Tyrannosaurinae. Previously recognized subdivisions Aublysodontinae and Shanshanosaurinae are rejected because they are based on insufficient material and juvenile specimens. Our results are based upon a phylogenetic analysis using PAUP program (Swofford 1999) of 77 skull characters and seven genera (Albertosaurus, Alioramus, Daspletosaurus, Gorgosaurus, Nanotyrannus, Tarbosaurus, and Tyrannosaurus); with Allosaurus as outgroup. Of the 77 characters used, more than half were parsimony informative. A single most parsimonious tree was obtained with the Tree Length being 88. The analysis of cranial characters and comparison of postcranial features reveal that Tarbosaurus bataar is not the sister taxon of Tyrannosaurus rex (contra Holtz 2001). Their similarities are partially due to the fact that both are extremely large animals. Thus, Tarbosaurus should be considered a genus distinct from Tyrannosaurus.
The following values have no corresponding Zotero field:
PB - Indiana University Press Bloomington, Indiana
The skull of a newly prepared Tarbosaurus bataar is described bone by bone and compared with a disarticulated skull of Tyrannosaurus rex. Both Tarbosaurus bataar and Tyrannosaurus rex skulls are deep in lateral view. In dorsal view, the skull of T. rex is extremely broad posteriorly but narrows towards the snout; in Ta. bataar the skull is narrower (especially in its ventral part: the premaxilla, maxilla, jugal, and the quadrate complex), and the expansion of the posterior half of the skull is less abrupt. The slender snout of Ta. bataar is reminiscent of more primitive North American tyrannosaurids. The most obvious difference between T. rex and Ta. bataar is the doming of the nasal in Ta. bataar which is high between the lacrimals and is less attached to the other bones of the skull, than in most tyrannosaurids. This is because of a shift in the handling of the crushing bite in Ta. bataar. We propose a paleogeographically based division of the Tyrannosaurinae into the Asiatic forms (Tarbosaurus and possibly Alioramus) and North American forms (Daspletosaurus and Tyrannosaurus). The division is supported by differences in anatomy of the two groups: in Asiatic forms the nasal is excluded from the major series of bones participating in deflecting the impact in the upper jaw and the dentary-angular interlocking makes a more rigid lower jaw.