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Description of a partial Dromiceiomimus (Dinosauria: Theropoda) skeleton with comments on the validity of the genus
Abstract
Dromiceiomimus brevitertius is a North American ornithomimid diagnosed primarily by the ratio of tibia length to femur length. It has recently, and perhaps incorrectly, been considered synonymous with Ornithomimus edmontonicus, with several authors questioning the utility of limb ratios in diagnosing taxa. While isolated ornithomimosaur material is common, specimens with sufficient diagnostic material to explore the question of synonymy are comparatively rare. The putative Dromiceiomimus specimen UALVP 16182 represents one of the few specimens in which diagnostic elements are available. It is therefore an important specimen for assessing the validity of Dromiceiomimus and for examining the utility of using limb proportions to diagnose ornithomimid taxa. In this paper, UALVP 16182 is described, the tibia/femur ratio is examined in closely related ornithomimid taxa, and the ratio is found to distinguish Dromiceiomimus from Gallimimus, Ornithomimus, and Struthiomimus. A phylogenetic analysis recovered Anserimimus and Ornithomimus as sister taxa with Dromiceiomimus as an outgroup. Comparison of the manus revealed differences in the morphology of metacarpal I and the flexor tubercle of manual ungual II-3. Differences also appear in the surangular and scapula. An examination of stratigraphic positions of various specimens indicates that Dromiceiomimus is generally higher in section than Ornithomimus, although there are too few specimens to be statistically significant. This study agrees with other studies in concluding that limb proportions are roughly isometric in small theropods like ornithomimids and that the tibia/femur ratio may therefore be useful for diagnosing certain small taxa. These findings suggest that Dromiceiomimus may indeed be a valid taxon.
... The midshaft just distal to the proximal end is not affected by pathology, preserving the original morphology of the midshaft on gross inspection (Fig 4). The morphology of the proximal midshaft is typical of ornithomimosaurs, with a suboval cross-section (wider anteroposteriorly than mediolaterally), displaying flat lateral and posterior surfaces, and convex medial and anterior surfaces ( Fig 4B) like Dromiceiomimus brevitertius and Rativates evadens, which also exhibit a similar flat surface on the posterior surface of the second metatarsal [73,74]. But it differs from the late-diverging ornithomimosaur taxa, such as O. velox, G. bullatus, and Struthiomimus altus as well as those of early-diverging ornithomimosaurs A. fridayi, B. grandis and Harpymimus okladnikovi, which have a relatively convex posterior surface. ...
... In anterior view, the lateral margin of MSC 13139 is more laterally extensive than the medial margins, which would have only slightly overhung the second metatarsal. [73], and A. tugrikinensis, but it is much weaker in these taxa than the well-developed lateral tab of troodontid metatarsals (e.g., T. sampsoni, Troodon formosus, and S. inequalis [43,74,75]) (S4D Fig). A shallow, semicircular-shaped extensor ligament pit is present immediately proximal to the distal articular caput as in ornithomimosaurs (Fig 5A), which is differentiated from those of oviraptorosaurs, such as Anzu, G. erlianensis and Heyuannia huangi [64,65]. ...
... On the posterior surface, there are two distinct ridges along the lateral and medial borders of the proximal heel (Fig 7A5). These ridges are separated by a deep sulcus as in other theropods, such as ornithomimosaurs and tyrannosaurids [14,25,62,73,74,102], but unlike those of oviraptorosaurs and therizinosauroids, which typically exhibit a relatively flat surface at this region. The medial ridge is mediolaterally wide and stouter than the lateral ridge (Fig 7A5 and 7B5). ...
Reconstructing the evolution, diversity, and paleobiogeography of North America's Late Cretaceous dinosaur assemblages require spatiotemporally contiguous data; however, there remains a spatial and temporal disparity in dinosaur data on the continent. The rarity of vertebrate-bearing sedimentary deposits representing Turonian-Santonian ecosystems, and the relatively sparse record of dinosaurs from the eastern portion of the continent, present persistent challenges for studies of North American dinosaur evolution. Here we describe an assemblage of ornithomimosaurian materials from the Santonian Eutaw Formation of Mississippi. Morphological data coupled with osteohistological growth markers suggest the presence of two taxa of different body sizes, including one of the largest ornithomimosaurians known worldwide. The regression predicts a femoral circumference and a body mass of the Eutaw individuals similar to or greater than that of large-bodied ornithomimosaurs, Beishanlong grandis, and Gallimimus bullatus. The paleoosteohistology of MMNS VP-6332 demonstrates that the individual was at least ten years of age (similar to B. grandis [~375 kg, 13-14 years old at death]). Additional pedal elements share some intriguing features with ornithomimosaurs, yet suggest a larger-body size closer to Deino-cheirus mirificus. The presence of a large-bodied ornithomimosaur in this region during this time is consistent with the relatively recent discoveries of early-diverging, large-bodied ornithomimosaurs from mid-Cretaceous strata of Laurasia (Arkansaurus fridayi and B. grandis). The smaller Eutaw taxon is represented by a tibia preserving seven growth cycles, with osteohistological indicators of decreasing growth, yet belongs to an individual approaching somatic maturity, suggesting the coexistence of medium-and large-bodied ornithomimosaur taxa during the Late Cretaceous Santonian of North America. The Eutaw ornithomimosaur materials provide key information on the diversity and distribution of North American ornithomimosaurs and Appalachian dinosaurs and fit with broader evidence of PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.
... From around the turn of the century until now a number of academic studies have examined and sometimes named new sibling paleospecies within dinosaur genera, in all but one case with little immediate post publication criticism in the news media (Barrett et al. 2005;Evans and Reisz 2007;Sereno 2010;Scannella et al. 2014;Tschopp et al.;Campbell et al. 2016;MacDonald & Currie 2018;Fowler and Freedman 2020). Most of these and other papers on dinosaur species have not explicitly addressed at length the methods used within to determine fossil species, Paul (2006) and Carpenter (2010) being rare exceptions. ...
... indicate character bimodality is important if not critical to species designation and diagnosis. However, as noted in Paul et al. (2022), characters used to differentiate and diagnose species are often not bimodal and nonoverlapping in distribution (Maisch 2008;Maxwell 2012;Scannella et al. 2014;MacDonald & Currie 2018;Harvati & Ackermann 2022), and statistical, measurements based bimodality is often not even presented in defense of paleospecies (Mihlbacher 2008;Mader 2010;Sereno 2010;Knutsen 2012;Tschopp et al. 2015;Fowler and Freedman 2020;Johnson et al. 2020). ignore these numerous examples that contradict their view. ...
... Skeletal robusticity, especially that of the femur, has been used to help distinguish the tyrannosaurids Daspletosaurus torosus from Gorgosaurus libratus that share the same habitat (Russell 1970;Paul 1988;Currie 2003b;Snively et al. 2006). Currently Ornithomimus edmontonicus and Dromiceiomimus brevitertius are morphologically differentiated by their different femur tibia ratios (MacDonald & Currie 2018). ...
Intrageneric dinosaur species have been being named for decades without either significant examination of the methods and standards used to do so, or widely publicized controversy over the results. The long standing assumption that all large known specimens of the iconic North American Tyrannosaurus consisted of just the one popular species T. rex was recently challenged with the first comprehensive test of the question. The result was the diagnosing and naming of two additional taxa, T. imperator and T. regina, based on a number of species levels characters regarding robustness and tooth proportions in the context of their stratigraphic distribution. In association a rare in-depth look was taken at the current state of naming vertebrate paleospecies, which it turns out are not highly rigorous because of inherent problems with the species concept and other matters. The results of the paper were severely criticized in in a manner never seen before for new dinosaur species even when based on less evidence. This study takes another look as the determination of paleospecies, and shows that many of the claims made in the criticisms regarding the Tyrannosaurus species work were inaccurate. New data on the proportions of strength bars in Tyrannosaurus skulls reinforces the basing of the three species in part on robustness factors, and allows all but one skull to be assigned to one of the species. These results allow the first detailed systematic examination of the supraorbital display bosses of the genus. They sort out as visually distinctive species specific ornaments based on both stratigraphic and taxonomic factors, strongly affirm that Tyrannosaurus was multispecific, and the species probably dimorphic. New skulls of T. rex show that the species sported, males probably, striking display bosses not yet observed in other tyrannosaurids.
... The ischium is roughly 80% as long as the pubis (Table 1). Among ornithomimosaurs, the equivalent ratio is similar in Ornithomimus edmontonicus, Struthiomimus altus and Dromiceiomimus brevitertius (Nicholls and Russell, 1980;Macdonald and Currie, 2019), but only about 71% in Sinornithomimus dongi and Gallimimus bullatus (Osm olska et al., 1972;Kobayashi and Lü, 2003), and more than 90% in Shenzhousaurus orientalis, Deinocheirus mirificus and Archaeornithomimus asiaticus, although the relative lengths of the pubis and ischium may be subject to ontogenetic as well as taxonomic variation (Smith and Galton, 1990;Ji et al., 2003;Lee et al., 2014). In lateral view, the ischial shaft appears essentially straight, but its distal end curves slightly anteriorly as in most other ornithomimosaurs. ...
... No sacral material is known for the ornithomimosaurians Nqwebasaurus thwazi, Beishanlong grandis, Qiupalong henanensis, Dromiceiomimus brevitertius, Paraxenisaurus normalensis and Tototlmimus packardensis (Makovicky et al., 2010;Xu et al., 2011;Serrano-Brañas et al., 2016;Sereno, 2017;Macdonald and Currie, 2019;Serrano-Brañas et al., 2020;Cuesta et al., 2022). Furthermore, no pelvic material is known for Paraxenisaurus normalensis and Tototlmimus packardensis, taxa represented exclusively by fragmentary specimens (Serrano-Brañas et al., 2016. ...
... Furthermore, no pelvic material is known for Paraxenisaurus normalensis and Tototlmimus packardensis, taxa represented exclusively by fragmentary specimens (Serrano-Brañas et al., 2016. However, Beishanlong grandis differs from all other ornithomimosaurians in which the pelvis is known, including LH-02-01, in that the ischium has the sigmoid curvature typical of late-diverging taxa but lacks a strongly developed distal boot and obturator process (Makovicky et al., 2010); LH-02-01 differs from Qiupalong henanensis in that the right and left components of the pubic boot are fused anteriorly, and in that the ischial process of the pubis has a convex caudal margin and lacks a ventral tubercle (Xu et al., 2011); and LH-02-01 differs from Dromiceiomimus brevitertius in that the anteriormost caudal centrum is less than twice as long as wide, and in that the dorsal edge of the postacetabular process of the ilium, and the distal and the posterodorsal edges of the distal part of the ischium, are straight rather than convex (Macdonald and Currie, 2019). The only known specimen of Nqwebasaurus thwazi preserves partial pubes in which the distal boot is only incipiently developed, in marked contrast to the condition in LH-02-01 (de Klerk et al., 2000;Sereno, 2017). ...
A newly identified ornithomimosaurian pelvis and sacrum from the Upper Cretaceous Erlian Formation of Nei Mongol, China is described in detail in this paper. This specimen is distinguished from previously described taxa by the presence of a combination of features that is unique among Ornithomimosauria: sacrum comprising five vertebrae with neural spines fused into a continuous plate, iliac posterior end rectangular, pubic shaft distally straight, ischial boot not broadened transversely, and ischial shaft proximally straight, distally curved, and 80 percent as long as the pubis. This specimen differs from at least some material assigned to the sympatric Archaeornithomimus asiaticus, showing that two distinct ornithomimosaurian taxa are present in this Late Cretaceous fossiliferous rock unit. A phylogenetic analysis places LH-02-01 in a relatively early-diverging position within Ornithomimosauria, outside the two major clades Deinocheiridae and Ornithomimidae, but its relationships with other early-diverging ornithomimosaurs remain unresolved. The primitive nature of LH-02-01 adds to the evidence from fossil vertebrates that the Erlian Formation correlates with the Turonian Bissekty Formation of Uzebekistan, while the biostratigraphic evidence from non-vertebrates instead indicates a Campanian to Maastrichtian age for the Erlian Formation. This apparent contradiction remains unresolved, pending future research aimed at reconciling the seemingly incompatible lines of evidence.
... The curvature is weak in lateral views of all specimens and www.nature.com/scientificreports/ similar to those of the second and third digits of most ornithomimosaurs [26][27][28][29] ; nonetheless, it is straighter than those of Shenzhousaurus 30 and Sinornithomimus 31 . ...
... In addition, while some ornithomimosaurs lack the concavity on the anterior margin, many ornithomimosaurs do not have the corresponding portions preserved, so the conditions of these species remain unknown. In addition to the direct comparisons above, the phylogenetic analysis was conducted with Aviatyrannis being included and scored based on the published description of the holotype 29 . The resulting tree suggests that Aviatyrannis is a sister taxon of Tyrannomimus without any other changes on the shape of the consensus trees from other analyses. ...
Ornithomimosauria consists of the ostrich-mimic dinosaurs, most of which showing cursorial adaptations, that often exhibit features indicative of herbivory. Recent discoveries have greatly improved our knowledge of their evolutionary history, including the divergence into Ornithomimidae and Deinocheiridae in the Early Cretaceous, but the early part of their history remains obscured because their fossil remains are scarce in the Aptian–Albian sediments. In recent years, many isolated ornithomimosaur remains have been recovered from the Aptian Kitadani Formation of Fukui, central Japan. These remains represent multiple individuals that share some morphological features common to them but unknown in other ornithomimosaurs, suggesting a monospecific accumulation of a new taxon. As a result of the description and phylogenetic analysis, the Kitadani ornithomimosaur is recovered as a new genus and species Tyrannomimus fukuiensis, the earliest definitive deinocheirid that complements our knowledge to understand the early evolutionary history of Ornithomimosauria. Due to its osteological similarity to Tyrannomimus, a taxon previously considered an early tyrannosauroid based on fragmentary specimens, namely Aviatyrannis jurassica, may represent the earliest ornithomimosaur from the Upper Jurassic of Europe, significantly expanding the temporal and biogeographic range of Ornithomimosauria. This finding fills a 20-million-year ghost lineage of Ornithomimosauria implied by the presence of the oldest fossil record of Maniraptora from the Middle Jurassic and is consistent with the hypothesis that their biogeographic range was widespread before the Pangaean breakup in the Kimmeridgian.
... Data from Cullen et al. [33] were used to provide an example of growth zone thickness differences between bones of the same individual (CMN FV 12068, cf. Dromiceiomimus brevitertius (sensu [56])). Lastly, data from Cullen et al. [30,34], based on data originally published in Woodward et al. [51], from the tibia of a juvenile tyrannosaurid (BMRP 2006.4.4, ...
Osteohistological data are commonly used to study the life history of extant and extinct tetrapods. While recent advances have permitted detailed reconstructions of growth patterns, physiology and other features using these data, they are most commonly used in assessments of ontogenetic stage and relative growth in extinct animals. These methods have seen widespread adoption in recent years, rapidly becoming a common component of the taxonomic description of new fossil taxa, but are often applied without close consideration of the sources of variation present or the dimensional scaling relationships that exist among different osteohistological measurements. Here, we use a combination of theoretical models and empirical data from a range of extant and extinct tetrapods to review sources of variability in common osteohistological measurements, their dimensional scaling relationships and the resulting interpretations that can be made from those data. In particular, we provide recommendations on the usage and interpretation of growth mark spacing/zonal thickness data, when these are likely to be unreliable, and under what conditions they can provide useful inferences for studies of growth and life history.
... In any case, similar pedal morphology (Farlow et al., 2013) and growth rates (Erickson et al., 2004) indicate that tracks made by species of Gorgosaurus, Daspletosaurus, and Albertosaurus would likely be comparable in their growth trajectories. (Fig. 8C, D) The taxonomic affinity of small-to-medium tridactyl theropod footprints (such as Th.Tw1.4.6B) is complicated by the presence of at least one indeterminate ornithomimid within the Wapiti Formation (Ryan and Russell, 2001;Weishampel et al., 2004;Fanti and Miyashita, 2009) and at least three ornithomimid genera identified from the Horseshoe Canyon Formation (Ryan and Russell, 2001;Cullen et al., 2013;Claessens and Loewen, 2015;Macdonald and Currie, 2018). Based on North American ornithomimid pedes that are reasonably complete (e.g., Osborn, 1916;Cullen et al., 2013) and using these to scale more fragmentary, but larger specimens (see Longrich, 2008: fig. ...
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.
... On the other hand, the impact fractures located in the phalanges III-1 and IV-4, which supported the weight of Othnielosaurus on the ground, might had causing chronic pain and, consequently, a limp. Similar cases of pedal pathologies affecting an individual's mobility have been described in the fossil record of dinosaurs, crocodyliforms and mammals, including hominoids (Hanna 2002;Farke and O'Connor 2007;Cabral et al. 2011;Anné et al. 2014;Foth et al. 2015;McCrea et al. 2015;Macdonald and Currie 2018;Hunt et al. 2019). Survival of lesions of weight-bearing bone would have greater consequence for obligate bipeds and evidence of lesions healing in these bones is rare (Hearn and Williams 2019). ...
The study of palaeopathology provides valuable information about injury and behaviour in extinct organisms. Appendicular pathologies are interesting as they directly affect mobility and therefore the ability of an animal to survive. Here, the injuries recorded in the left pes of the neornithischian Othnielosaurus consors are described. The implications of these injuries in its behaviour are also discussed. Othnielosaurus shows pathological features in all its pes digits, with three types of pathologies have been identified: calcium pyrophosphate deposition disease (CPPD), and pilon and impact fractures. Calcium pyrophosphate deposition disease is visible on the articular surface of phalange II-3 as a small osseous plaque. A pilon fracture is evidenced by the growth of callus tissue on the shaft of the phalange I-1 and demonstrates healing before death. The impact fractures are identified as a focal subsidence on the articular surfaces of phalanges III-1 and IV-4, which are partially healed. Perhaps the suite of palaeopathologies encountered would generate pain and discomfort when walking, which probably resulted in a limp that would have impacted on its lifestyle. Finally, the fact that the fractures are in different stages of healing would suggest that impact fractures could have contributed to the death of the individual.
... Rounding out the controversial basal ornithomimosaurs is Pelecanimimus, recovered as the first branching alvarezsauroid based on characters such as an elongate anterior maxillary ramus (311:1), posterior tympanic recess in the otic recess (27:1), lateral teeth set in grooves (302:1), over 30 dentary teeth (90:3), and a proximally expanded metacarpal II (370:0). Constraining it as an ornithomimosaur only requires two additional steps, however, where it emerges just above Shenzhousaurus as in Macdonald & Currie (2018). As only two of their characters supporting an ornithomimosaurian identification were not used by us, and only one from Brusatte et al. (2014), its true position is unclear pending a detailed osteology such as Perez-Moreno's (2004) unreleased description. ...
The last two decades have seen a remarkable increase in the known diversity of basal avialans and their paravian relatives. The lack of resolution in the relationships of these groups combined with attributing the behavior of specialized taxa to the base of Paraves has clouded interpretations of the origin of avialan flight. Here, we describe Hesperornithoides miessleri gen. et sp. nov., a new paravian theropod from the Morrison Formation (Late Jurassic) of Wyoming, USA, represented by a single adult or subadult specimen comprising a partial, well-preserved skull and postcranial skeleton. Limb proportions firmly establish Hesperornithoides as occupying a terrestrial, non-volant lifestyle. Our phylogenetic analysis emphasizes extensive taxonomic sampling and robust character construction, recovering the new taxon most parsimoniously as a troodontid close to Daliansaurus, Xixiasaurus, and Sinusonasus. Multiple alternative paravian topologies have similar degrees of support, but proposals of basal paravian archaeopterygids, avialan microraptorians, and Rahonavis being closer to Pygostylia than archaeopterygids or unenlagiines are strongly rejected. All parsimonious results support the hypothesis that each early paravian clade was plesiomorphically flightless, raising the possibility that avian flight originated as late as the Late Jurassic or Early Cretaceous.
A fragmentary tibia of an actively growing sub-adult individual from the Upper Cretaceous (Maastrichtian) Udurchukan Formation at Kundur, Amur oblast, Far East, Russia, is similar to the tibia of Qiupalong henanensis from the Maastrichtian of Henan Province, China, in bearing a weak posteromedial ridge at the distal end and equally projecting distal malleoli. Qiupalong had a transcontinental distribution and likely originated in North America. Similarly, lambeosaurine hadrosaurids from the Udurchukan Formation have American affinities and their ancestors may had dispersed from North America to East Asia together with a Qiupalong-like ornithomimid. Q. henanensis and Ornithomimidae indet. from Kundur are the only records of the Maastrichtian Ornithomimidae in Asia outside Gobi Desert.
Tyrannosaurs are among the most intensively studied and best-known dinosaurs. Despite this, their relationships and systematics are highly controversial. An ongoing debate concerns the validity of Nanotyrannus lancensis, interpreted either as a distinct genus of small-bodied tyrannosaur or a juvenile of Tyrannosaurus rex. We examine multiple lines of evidence and show that the evidence strongly supports recognition of Nanotyrannus as a distinct species for the following reasons: 1. High diversity of tyrannosaurs and predatory dinosaurs supports the idea that multiple tyrannosaurids inhabited the late Maastrichtian of Laramidia; 2. Nanotyrannus lacks characters supporting referral to Tyrannosaurus or Tyrannosaurinae but differs from T. rex in >150 morphological characters, while intermediate forms combining the features of Nanotyrannus and T. rex are unknown; 3. Histology shows specimens of Nanotyrannus showing (i) skeletal fusions, (ii) mature skull bone textures, (iii) slow growth rates relative to T. rex, (iv) decelerating growth in their final years of life, and (v) growth curves predicting adult masses of~1500 kg or less, showing these animals are subadults and young adults, not juvenile Tyrannosaurus; 4. growth series of other tyrannosaurids, including Tarbosaurus and Gorgosaurus, do not show morphological changes proposed for a Nanotyrannus-Tyrannosaurus growth series, and deriving Tyrannosaurus from Nanotyrannus requires several changes inconsistent with known patterns of dinosaur development; 5. Juvenile T. rex exist, showing diagnostic features of Tyrannosaurus; 6. Phylogenetic analysis suggests that Nanotyrannus may lie outside Tyrannosauridae. Tyrannosaur diversity before the K-Pg extinction is higher than previously appreciated. The challenges inherent in diagnosing species based on fossils mean paleontologists may be systematically underestimating the diversity of ancient ecosystems.
Despite an abundance of ornithomimid fossils from the Late Cretaceous of Alberta, Canada, only isolated elements are known from the upper Maastrichtian Scollard Formation. Ornithomimus velox and Struthiomimus sedens are the two taxa recognized from penecontemporaneous formations in the U.S.A., but the incomplete nature of these specimens and the lack of contemporary material from Alberta creates a gap in our understanding of ornithomimid diversity during the late Maastrichtian of North America. Here, I describe the first diagnostic ornithomimid fossils from the upper Maastrichtian Scollard Formation of central Alberta, Canada, providing new information about the taxonomic composition of North American ornithomimids during the late Maastrichtian. The first fossil, an articulated forelimb, exhibits metacarpal ratios and features of the manual unguals that support its referral to the genus Ornithomimus. The second fossil, an associated hind limb, belongs to a large-bodied ornithomimid, and based on characteristics of the pedal unguals is assigned to the genus Struthiomimus. Based on these taxonomic designations, the stratigraphic ranges of both Ornithomimus and Struthiomimus are extended from the upper Campanian Dinosaur Park Formation through to the upper Maastrichtian Scollard Formation of Alberta, which constitutes more than 10 million years of time. These specimens offer new knowledge on the taxonomic composition of ornithomimids in Alberta, but the unusually long stratigraphic range coupled with the difficulty in diagnosing either specimen to species underscores the need for review of North American ornithomimid taxonomy.
Locomotion is a fundamental aspect of palaeobiology and often investigated by comparing osteological structures and proportions. Previous studies document a stepwise accumulation of avian-like features in theropod dinosaurs that accelerates in the clade Maniraptora. However, the soft tissues that influenced the skeleton offer another perspective on locomotory adaptations. Examination of the pelvis for osteological correlates of hind limb and tail musculature allowed reconstruction of primary locomotory muscles across theropods and their closest extant relatives. Additionally, the areas of pelvic muscle origins were quantified to measure relative differences within and between taxa, to compare morphological features associated with cursoriality, and offer insight into the evolution of locomotor modules. Locomotory inferences based on myology often corroborate those based on osteology, although they occasionally conflict and indicate greater complexity than previously appreciated. Maniraptoran pelvic musculature underscores previous studies noting the multifaceted nature of cursoriality and suggests that a more punctuated step in caudal decoupling occurred at or near the base of Maniraptora.
Abstract: Tyrannosaurids were the apex predators of Late Cretaceous Laurasia and their status as dominant carnivores has garnered considerable interest since their discovery, both in the popular and scientific realms. As a result, they are well studied and much is known of their anatomy, diversity, growth, and evolution. In contrast, little is known of the earliest stages of tyrannosaurid development. Tyrannosaurid eggs and embryos remain elusive, and juvenile specimens — although known — are rare. Perinatal tyrannosaurid bones and teeth from the Campanian–Maastrichtian of western North America provide the first window into this critical period of the life of a tyrannosaurid. An embryonic dentary (cf. Daspletosaurus) from the Two Medicine Formation of Montana, measuring just 3 cm long, already exhibits distinctive tyrannosaurine char- acters like a “chin” and a deep Meckelian groove, and reveals the earliest stages of tooth development. When considered to- gether with a remarkably large embryonic ungual from the Horseshoe Canyon Formation of Alberta, minimum hatchling size of tyrannosaurids can be roughly estimated. A perinatal premaxillary tooth from the Horseshoe Canyon Formation likely pertains to Albertosaurus sarcophagus and it shows small denticles on the carinae. This tooth shows that the hallmark characters that distinguish tyrannosaurids from other theropods were present early in life and raises questions about the ontogenetic variability of serrations in premaxillary teeth. Sedimentary and taphonomic similarities in the sites that pro- duced the embryonic bones provide clues to the nesting habits of tyrannosaurids and may help to refine the prospecting search image in the continued quest to discover baby tyrannosaurids.
The Upper Cretaceous Djadokhta Formation has been intensively surveyed for its fossil vertebrate fauna for nearly a century. Amongst other theropods, dromaeosaurids and parvicursorines are common in the formation, but ornithomimosaurs are extremely rare. A new ornithomimosaur material was discovered from the Djadokhta Formation, represented by eolian deposits, of the Tögrögiin Shiree locality, Mongolia. This is only the third ornithomimosaur specimen reported from this formation, and includes the astragalus, the calcaneum, the third distal tarsal, and a complete pes. The new material is clearly belonged to Ornithomimidae by its arctometatarsalian foot condition and has the following unique characters; unevenly developed pair of concavities of the third distal tarsal, curved contacts between the proximal ends of second and fourth metatarsals, the elongate fourth digit, and a laterally inclined medial condyle on phalanx IV-1. These diagnostic characters of the Djadokhtan ornithomimosaur indicate that this is a new taxon. Our phylogenetic analysis supports three clades within derived ornithomimosaurs, and the new taxon is placed a member of the derived ornithomimosaurs. The present specimen is the first ornithomimid record from eolian Tögrögiin Shiree locality, and is indicative of their capability to adapt to arid environments.
Ornithomimid material from the Belly River Group (Campanian) of Alberta, Canada is described as sharing characters with Qiupalong henanensis from the Qiupa Formation of Henan Province, China. Derived characters and character combinations of the pubis and astragalocalcaneum were previously used to diagnose Q. henanensis and support the referral of this material to Qiupalong sp., representing the first known occurrences of Qiupalong outside of China. Qiupalong is the sixth ornithomimid taxon to be reported from the Dinosaur Park Formation and the first ornithomimid genus with a transcontinental distribution. The Alberta material represents the oldest known occurrences of Qiupalong, and a reconsideration of character evidence suggests that this genus is phylogenetically nested within other North American ornithomimids. A North American origin for Qiupalong and subsequent dispersal to Asia is proposed.
Among extant vertebrates, pneumatization of postcranial bones is unique to birds, with few known exceptions in other groups. Through reduction in bone mass, this feature is thought to benefit flight capacity in modern birds, but its prevalence in non-avian dinosaurs of variable sizes has generated competing hypotheses on the initial adaptive significance of postcranial pneumaticity. To better understand the evolutionary history of postcranial pneumaticity, studies have surveyed its distribution among non-avian dinosaurs. Nevertheless, the degree of pneumaticity in the basal coelurosaurian group Ornithomimosauria remains poorly known, despite their potential to greatly enhance our understanding of the early evolution of pneumatic bones along the lineage leading to birds. Historically, the identification of postcranial pneumaticity in non-avian dinosaurs has been based on examination of external morphology, and few studies thus far have focused on the internal architecture of pneumatic structures inside the bones. Here, we describe the vertebral pneumaticity of the ornithomimosaur Archaeornithomimus with the aid of X-ray computed tomography (CT) imaging. Complementary examination of external and internal osteology reveals (1) highly pneumatized cervical vertebrae with an elaborate configuration of interconnected chambers within the neural arch and the centrum; (2) anterior dorsal vertebrae with pneumatic chambers inside the neural arch; (3) apneumatic sacral vertebrae; and (4) a subset of proximal caudal vertebrae with limited pneumatic invasion into the neural arch. Comparisons with other theropod dinosaurs suggest that ornithomimosaurs primitively exhibited a plesiomorphic theropod condition for axial pneumaticity that was extended among later taxa, such as Archaeornithomimus and large bodied Deinocheirus. This finding corroborates the notion that evolutionary increases in vertebral pneumaticity occurred in parallel among independent lineages of bird-line archosaurs. Beyond providing a comprehensive view of vertebral pneumaticity in a non-avian coelurosaur, this study demonstrates the utility and need of CT imaging for further clarifying the early evolutionary history of postcranial pneumaticity.
Coelurosauria is the most diverse clade of theropod dinosaurs. Much of this diversity is present in Paraves—the clade of dinosaurs containing dromaeosaurids, troodontids, and avialans. Paraves has over 160 million years of evolutionary history that continues to the present day. The clade represents the most diverse living tetrapod group (there are over 9000 extant species of Aves—a word used here as synonomous with “bird”), and it is at the root of the paravian radiation, when dromaeosaurids, troodontids, and avialans were diverging from one another, that we find the morphology and soft tissue changes associated with the origin of modern avian flight. Within the first 15 million years of known paravian evolutionary history members of this clade exhibited a difference of nearly four orders of magnitude in body size, a value that is similar to the extreme body size disparity present today in mammalian carnivorans, avians, and varanoid squamates. In this respect, Paraves is an important case study in characterizing the patterns, processes, and dynamics of evolutionary size change. This last point is of particular interest because of the historical significance placed on the role of body size reduction in the origin of powered avian flight.Our study reviews and revises the membership of Dromaeosauridae and provides an apomorphy-based diagnosis for all valid taxa. Of the currently 31 named dromaeosaurid species, we found 26 to be valid. We provide the most detailed and comprehensive phylogenetic analysis of paravians to date in order to explore the phylogenetic history of dromaeosaurid taxa. The general pattern of paravian relationships is explored within the broader context of Coelurosauria with an emphasis on sampling basal avialans, because of their importance for character optimizations at the base of Paraves.A large dataset was constructed by merging two datasets, one examining coelurosaur relationships broadly (based on previous TWiG datasets) and the other examining avialan relationships specifically (Clarke et al., 2006). This merged dataset was then significantly revised and supplemented with novel character analysis focusing on paravian taxa. During character analysis, particular attention was given to basal members of Dromaeosauridae, enigmatic basal paravians such as Jinfengopteryx elegans and Anchiornis huxleyi, and the incorporation of new morphological information from two undescribed troodontid species from the Late Cretaceous of Mongolia. A final dataset of 474 characters scored for 111 taxa was used to address paravian evolution. This dataset is important in that it bridges a phylogenetic gap that had persisted between studies on birds and studies on all other coelurosaurs. Most scorings in this matrix were based on the direct observation of specimens.All most parsimonious trees recovered in the cladistic analysis support the monophyly of Paraves, Troodontidae, Dromaeosauridae, and Deinonychosauria. A new clade of basal troodontids is discovered including two undescribed Mongolian troodontids and Jinfengopteryx elegans. Xiaotingia and Anchiornis form a clade at the base of Troodontidae. Recently proposed relationships within Dromaeosauridae are further supported and a succession of clades from Gondwana and Asia form sister taxa to a clade of Laurasian dromaeosaurids. Avialan monophyly is strongly supported with Archaeopteryx, Sapeornis, Jeholornis, and Jixiangornis forming the successive sister taxa to the Confuciusornis node. This topology supports a more basal position for Sapeornis than previous phylogenetic analyses and indicates a progressive acquisition of a fully “avian” shoulder morphology.
Quantitative morphometric analyses, particularly ontogenetic allometry, are common methods used in quantifying shape, and changes therein, in both extinct and extant organisms. Due to incompleteness and the potential for restricted sample sizes in the fossil record, palaeobiological analyses of allometry may encounter higher rates of error. Differences in sample size between fossil and extant studies and any resulting effects on allometric analyses have not been thoroughly investigated, and a logical lower threshold to sample size is not clear. Here we show that studies based on fossil datasets have smaller sample sizes than those based on extant taxa. A similar pattern between vertebrates and invertebrates indicates this is not a problem unique to either group, but common to both. We investigate the relationship between sample size, ontogenetic allometric relationship and statistical power using an empirical dataset of skull measurements of modern Alligator mississippiensis. Across a variety of subsampling techniques, used to simulate different taphonomic and/or sampling effects, smaller sample sizes gave less reliable and more variable results, often with the result that allometric relationships will go undetected due to Type II error (failure to reject the null hypothesis). This may result in a false impression of fewer instances of positive/negative allometric growth in fossils compared to living organisms. These limitations are not restricted to fossil data and are equally applicable to allometric analyses of rare extant taxa. No mathematically derived minimum sample size for ontogenetic allometric studies is found; rather results of isometry (but not necessarily allometry) should not be viewed with confidence at small sample sizes.
Background
Osteohistological examinations of fossil vertebrates have utilized a number of proxies, such as counts and spacing of lines of arrested growth (LAGs) and osteocyte lacunar densities (OLD), in order to make inferences related to skeletochronology and mass-specific growth rates. However, many of these studies rely on samplings of isolated bones from single individuals. These analyses do not take individual variation into account, and as a result may lead to misleading inferences of the physiology of extinct organisms. This study uses a multi-element, multi-individual sampling of ornithomimid dinosaurs to test the amount of individual variation in the aforementioned osteohistological indicators. Based on these results we also assess the conclusions of previous studies that tested paleohistological hypotheses using isolated elementsResultsLAG number was found to be consistent within the hind limb bones of each individual, with the exception of the fibula, which preserves one additional LAG. Considerable differences in LAG spacing were found between elements of the sampled individuals, with larger variation found in elements of the foot compared with the femur, fibula, and tibia. Osteocyte lacunar density ranged between 29000 and 42000 osteocyte lacunae per mm3, and was found to vary more between hind limb bones of an individual and within bones, than between the average values of individuals.Conclusions
The variation between hind limb elements in LAG number and LAG spacing suggests that direct comparisons of these elements may be misleading, and that LAG spacing is not a reliable proxy for mass-specific growth rates of an individual. Sampling of multiple bones should be performed as an internal check of model-based LAG retro-calculation and growth equations. The observation that osteocyte lacunar density varies more between individual bone elements than between average individual values suggests that the choice of sampled element can greatly influence the result, and care should be taken to not bias interpretations of the physiology of fossil tetrapods.
Polar dinosaurs provide unique insights for testing hypotheses regarding paleobiology, paleoecology, and pa-leobiogeography. Critical for such testing is a comprehensive understanding of the taxonomic diversity of contemporaneous polar and lower-latitude paleofaunas. Here we determine the taxonomic identity of a theropod metatarsal that was discovered in the Upper Cretaceous Prince Creek Formation on the North Slope of Alaska. Its morphology and size are most consis-tent with a metatarsal IV of an ornithomimosaurian or a juvenile tyrannosaurid. Long bone histological analysis reveals a bone tissue composed of fibrolamellar matrix with a mosaic of laminar, longitudinal, sub-plexiform, radiating, and reticular vascularization patterns. The spacing between two outer growth lines diminishes near the periosteal surface, suggesting that the individual was near somatic maturity at the time of death. This finding suggests that its adult body size was comparable to contemporaneous North American ornithomimids, such as Ornithomimus, and much smaller than those of known tyran-nosaurids. Thus, we ascribe the Alaskan specimen to Ornithomimosauria, providing new evidence on the known taxonomic diversity of the Prince Creek fauna. Interestingly, the Alaskan specimen primarily shows annuli, which is inconsistent with the pronounced lines of arrested growth (LAGs) reported in the purported southern high-latitude ornithomimosaurian Timimus and observed variably in contemporaneous lower-latitude ornithomimids. Due to this inconsistency, additional dinosaurian specimens are needed to comprehensively examine the relevance of particular histological features to polar climate habitation.
Microvertebrate remains are described from five formations (Pacoota Sandstone, Horn Valley Siltstone, Stairway Sandstone, Stokes Formation, Carmichael Sandstone) in the Ordovician sequence of the Amadeus Basin, central Australia. Two new genera and species are erected for scales and other elements with distinctive morphology and histology. Other material is referred to indeterminate species of the agnathan genera Arandaspis and Porophoraspis previously described from central Australia, and Sacabambaspis previously described from the Ordovician of Bolivia. The most common vertebrate from the Stokes Formation is referred to Areyonga oervigi, gen. et sp. nov., a form taxon provisionally assigned to the Chondrichthyes. Scales of this species apparently lack a base, and are made of an atubular laminar surface tissue of uncertain histology. Mode of scale growth was similar to that of the Early Devonian form Polymerolepis. If correctly interpreted, this taxon is the oldest chondrichthyan and/or gnathostome known from the fossil record. The form taxon Apedolepis tomlinsonae, gen. et sp. nov. contains scales with possible osteocyte spaces in the basal tissue, and a crown composed of dentine covered with an enamel-like surface layer which also lines chambers of a pore canal system. Affinity to arandaspidid pteraspidomorphs may be indicated by a similar system of pores opening to the surface. A pore-canal system, and bone rather than aspidin, may have been primitively present in agnathans. Indeterminate remains from the early Arenig and Caradoc (Horn Valley Siltstone, Stokes Formation) may include endoskeletal ossification. These new microvertebrate faunas are assigned to four assemblages ranging in age from early Arenigian to Caradocian (Bendigonian-Eastonian). They have biostratigraphic potential for age control in Ordovician marginal marine sediments, and are important in demonstrating new combinations of hard tissue types at the beginning of the vertebrate fossil record.
A unique dinosaur assemblage from the Cretaceous beds of western Inner Mongolia preserves geologic and paleontologic data that clearly delineate both the timing and mechanism of death. Over twenty individuals of the ornithomimid Sinornithomimus dongi perished while trapped in the mud of a drying lake or pond, the proximity and alignment of the mired skeletons indicating a catastrophic mass mortality of a social group. Histologic examination reveals the group to consist entirely of immature individuals between one and seven years of age, with no hatchlings or mature individuals. The Sinornithomimus locality supports the interpretation of other, more taphonomically ambiguous assemblages of immature dinosaurs as reflective of juvenile sociality. Adults of various nonavian dinosaurs are known to have engaged in prolonged nesting and post hatching parental care, a life history strategy that implies juveniles spent considerable time away from reproductively active adults. Herding of juveniles, here documented in a Cretaceous ornithomimid, may have been a common life history strategy among nonavian dinosaurs reflecting their oviparity, extensive parental care, and multi-year maturation.
Bonebeds can provide a wealth of anatomical, taphonomic, and ontogenetic information about the specimens preserved within them, and can provide evidence for inferred behavior. The material described here represents the first known bonebed of ornithomimids in North America, and the fourth record of an ornithomimosaur bonebed in the world. Partial skeletons representing three individuals are preserved in this assemblage, each comprising primarily portions of the posterior postcrania (pelvis, hind limbs and tail). All three individuals are morphologically similar, although one is larger in overall size. Given the stratigraphic position of the site, and the morphology of the postcrania, the preserved material represents a taxon from the clade containing Ornithomimus and Struthiomimus. Pedal ungual morphology is examined and found to be too variable to be useful in distinguishing these species taxonomically. This site provides additional evidence of gregarious behavior in ornithomimids and the first probable record of that behavior in North American forms.
A new ornithomimosaur from the Yixian Formation of Liaoning Province People's Republic of China is described. These beds are near the Jurassic-Cretaceous boundary. This specimen is interesting because it has several primitive characters for ornithomimosaurs such as teeth and a short first metacarpal. This taxon is placed in a phylogenetic analysis of Coelurosauria and shown to be near the base of the ornithomimosaur clade. Using this phylogeny we comment on the biogeographic history of this group.
THE Lower Cretaceous lithographic limestones from Las Hoyas (province of Cuenca, Spain) have yielded important vertebrate fossil remains. We report here a new specimen, the first ornithomimosaur theropod found in Europe. Pelecanimimus polyodon gen. et sp. nov., has some striking elements preserved, such as the hyoid, sternum and integumentary impressions. The fossil has revealed other unexpected features, including a derived hand in an ancient ornithomimosaur, and a large number of teeth (over 200) with a distinctive morphology. This specimen suggests an alternative evolutionary process towards the toothless condition in Ornithomi-mosauria, which could be explained by an exaptation. Pelecanimimus polyodon stresses the relationship between Troodontidae and Ornithomimosauria.
The holotype of Garudimimus brevipes, discovered from the Upper Cretaceous sediments of Mongolia and named by Barsbold in 1981, is redescribed in detail in this paper. Reexamination of the holotype reveals a great deal of anatomical information, which allows us to revise the original diagnosis of this taxon and make comparisons with other ornithomimosaur taxa to understand the evolution of ornithomimosaurs. This paper suggests that characters used to differentiate this taxon in the original paper (short ilia, short metatarsals, exposure of the proximal end of metatarsal III, presence of pedal digit I, and absence of pleurocoels) are not apomorphies but represent the primitive conditions in ornithomimosaurs and are symplesiomorphies. Revised diagnoses are assigned for G. brevipes (posteriorly positioned jaw articulation, fossae at base of dorsal process of supraoccipital, paired depressions on neural spines of proximal caudal vertebra, and deep groove on lateral surface of pedal phalanges III-1 and III-2). Metatarsals of Garudimimus display a non-arctometatarsalian condition as in an Early Cretaceous form, Harpymimus, but the constriction of metatarsal III in Garudimimus is intermediate between Harpymimus and the arctometatarsalian condition in Gallimimus and other derived ornithomimosaurs (ornithomimids). Garudimimus is the only non-ornithomimid ornithomimosaur with edentulous jaws, which were probably covered by rhamphothecae. The loss of teeth with evolution of rhamphothecae and development of a cutting edge in the dentary of Garudimimus suggest the acquisition of feeding habits that included plucking food at the anterior portion of the jaw and cutting at the middle portion, similar to ornithomimids.
Troodontid dinosaurs form one of the most avian-like dinosaur groups. Their phylogenetic position is hotly debated, and they have been allied with almost all principal coelurosaurian lineages. Here we report a basal troodontid dinosaur, Sinovenator changii gen. et sp. nov., from the lower Yixian Formation of China. This taxon has several features that are not found in more derived troodontids, but that occur in dromaeosaurids and avialans. The discovery of Sinovenator and the examination of character distributions along the maniraptoran lineage indicate that principal structural modifications toward avians were acquired in the early stages of maniraptoran evolution.
The Upper Cretaceous Nemegt Formation of Mongolia is rich in well-preserved dinosaurs and Ornithomimosauria is one of the most common taxa in the formation. Three ornithomimosaur taxa, Anserimimus planinychus, Deinocheirus mirificus, and Gallimimus bullatus, have been discovered from the formation so far. However, the recently discovered specimens suggest there is even greater morphological variation of ornithomimosaurs in the Nemegt Formation than are presently recognized. This study focuses on the structures of manual elements among Nemegt ornithomimosaurs and reveals their remarkable diversity. The manual structures of seven individuals, including aforementioned three known taxa and four new individuals, are morphologically distinct from each other. Numerical analyses on metacarpals, phalanges, and unguals also support high morphological diversity of the Nemegt ornithomimosaurs. The large diversity of manual morphology may be related to large variety of palaeoecological niches were prevailed in the Nemegt ecosystem.
Troodontids are known from Asia and North America, with the most complete specimens from the Jurassic of China and the Cretaceous of Mongolia. North American troodontids are poorly known, and specimens that have been described are isolated elements or partial skeletons with limited material. A new troodontid from the upper Dinosaur Park Formation (upper Campanian) is based on partial skulls, several vertebrae, ribs, gastralia, chevrons, a sacrum, partial pelvis, and partial fore and hind limbs. It is the largest troodontid known, with an estimated height of 180 cm and length of 350 cm. Like other troodontids, it possesses an elongated ambiens process and has a horizontal ventral margin of the postacetabular process. It differs from all other derived troodontids in that the slightly retroverted pubis has a shaft that curves anteroventrally. Some specimens from the Dinosaur Park Formation previously assigned to Troodon are reassigned to the new taxon, including multiple partial crania, an associated dentary and metatarsus, and a partial skeleton. Previously undescribed elements from the lower part of the Dinosaur Park Formation are assigned to the resurrected Stenonychosaurus inequalis. Distinct stratigraphic separation of Stenonychosaurus inequalis and the new taxon indicates a replacement in troodontid fauna, similar to the turnover of large ornithischians in the same formation. The new taxon is phylogenetically more closely related to Mongolian taxa, indicating the replacement of Stenonychosaurus may have been from an earlier Asian form immigrating into North America.
Evidence for sexual dimorphism is extremely limited in the non-avian dinosaurs despite their high diversity and disparity, and despite the fact that dimorphism is very common in vertebrate lineages of all kinds. Using body-size data from both Alligator mississippiensis and Rhea americana, which phylogenetically bracket the dinosaurs, we demonstrate that even when there is strong dimorphism in a species, random sampling of populations of individuals characterized by sustained periods of growth (as in the alligator and most dinosaurs) can result in the loss of this signal. Dimorphism may be common in fossil taxa but very hard to detect without ontogenetic age control and large sample sizes, both of which are hampered by the limitations of the fossil record. Signal detection may be further hindered by Type III survivorship, whereby increased mortality among the young favours the likelihood that they will be sampled (unless predation or taphonomic bias against small size acts against this). These, and other considerations relating to behaviour and ecology, provide powerful reasons to suggest that sexual dimorphism in dinosaurs may be very difficult to detect in almost all currently available samples. Similar issues are likely also to be applicable to many fossil reptiles, or animals more generally.
The demonstration of sexual dimorphism in the fossil record can provide vital information about the role that sexual selection has played in the evolution of life. However, statistically robust inferences of sexual dimorphism in fossil organisms are exceedingly difficult to establish, owing to issues of sample size, experimental control, and methodology. This is particularly so in the case of dinosaurs, for which sexual dimorphism has been posited in many species, yet quantifiable data are often lacking. This study presents the first statistical investigation of sexual dimorphism across Dinosauria. It revisits prior analyses that purport to find quantitative evidence for sexual dimorphism in nine dinosaur species. After the available morphological data were subjected to a suite of statistical tests (normality and unimodality tests and mixture modeling), no evidence for sexual dimorphism was found in any of the examined taxa, contrary to conventional wisdom. This is not to say that dinosaurs were not sexually dimorphic (phylogenetic inference suggests they may well have been), only that the available evidence precludes its detection. A priori knowledge of the sexes would greatly facilitate the assessment of sexual dimorphism in the fossil record, and it is suggested that unambiguous indicators of sex (e.g., presence of eggs, embryos, medullary bone) be used to this end.
A partial ornithomimid skeleton, ROM 1790, from the lower Dinosaur Park Formation (upper Campanian) of Alberta was previously referred to Struthiomimus altus, but lacks diagnostic characters of that species. It is here described as the holotype of a new species, Rativates evadens, gen. et sp. nov., diagnosed by the form of the maxilla-jugal contact, the reduction of the mid-caudal neural spines, the convex fusion of the left and right ischial shafts, the straight-edged distal end of the third metatarsal, and possibly the relatively enlarged medial condyle of the tibia. A histological section of the femur confirms that the type specimen is not a juvenile, despite its relatively small size (approximately 50% the size of large individuals of Struthiomimus altus). Phylogenetic analysis recovers Rativates as a member of a derived ornithomimid clade that includes Ornithomimus, Struthiomimus, and the Asian taxa Anserimimus and Qiupalong. Fusion of the proximal tarsals to the tibia in some ornithomimid specimens was observed to be more complete than previously recognized, increasing the suite of features that these non-avian dinosaurs share homoplastically with birds. http://zoobank.org/urn:lsid:zoobank.org:pub:E0163526-7C26-4E8C-90C9-C72A3E90ED2D SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: McFeeters, B., M. J. Ryan, C. Schröder-Adams, and T. M. Cullen. 2016. A new ornithomimid theropod from the Dinosaur Park Formation of Alberta, Canada. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1221415. 2016
The theropod genus and species Ornithomimus velox was erected based on a partial hind limb recovered from the late Maastrichtian Denver Formation. A partial manus, which likely belonged to the same individual, was also recovered and described in the same paper. Ornithomimus edmontonicus is the only other valid species currently recognized in the genus. The validity of Ornithomimus velox has been questioned due to its fragmentary nature and because the diagnostic features identified when the species was erected are now considered characteristic for the family. The pes and manus of Ornithomimus velox were never fully prepared. In the original description, reconstructed metatarsals were figured, but manual phalanges, although preserved, were not described. Here we describe and reevaluate Ornithomimus velox based upon a new preparation of the specimen. Metacarpal proportions are diagnostic for the genus, with metacarpal I longer than metacarpal II, which in turn is longer than metacarpal III. The pes and manus of Ornithomimus velox are smaller than in the type specimen of Ornithomimus edmontonicus. Ornithomimus velox can be distinguished from Ornithomimus edmontonicus based on the robusticity of the pes. Material previously referred to Ornithomimus velox from the Kaiparowits Formation of Utah is older and morphologically distinct and does not represent the same species. The morphological disparity and temporal separation observed in specimens referred to Ornithomimus edmontonicus suggest that it may represent a species complex. The redescription and diagnosis of Ornithomimus velox provides a new framework to investigate ornithomimid systematics.
New ornithomimid material discovered from the Upper Cretaceous Packard Shale Formation, (Cabullona Group) of Sonora, Mexico is described. The material includes a partial skeleton, which is assigned to a new genus and species, Tototlmimus packardensis. This new taxon differs from other ornithomimids in having five unique characteristics that separate it from other northamerican ornithomimids: (1) a distinctively articulation between metatarsals, where the distal ends of metatarsals II and IV contact directly with the distal facet of metatarsal III; (2) a metatarsal III with a weakly ginglymoid distal articular face; (3) the medial and lateral sides of metatarsal III are shaped into the form of metatarsals II and IV, so all distal ends fit together when they articulate; (4) an asymmetrical and narrow pedal ungual with shallow grooves in both medial and lateral sides; and finally, (5) the presence of a deep sulcus on the ventromedial edge, close to the articular end. Phylogenetic analysis suggests that Tototlmimus packardensis corresponds to a derived ornithomimid included in the Northamerican clade, forming a monophyly with Ornithomimus. Tototlmimus packardensis is the first definitive ornithomimid described for Mexico, and represents one of the southernmost occurrences in the Western Interior Basin of North America.
Sympatric populations of mule deer (Odocoileus hemionus) and white-tailed deer (O. virginianus) in the Cypress Hills, southern Alberta, were studied by comparing interspecific with intraspecific dispersion patterns and by observing interactions between the species to determine whether competitive interference on overlapping range existed. Groups of mule deer and white-tailed deer did not avoid each other or other species at distances above 50 yards; below 50 yards, concurrence of deer and other ungulates and deer-coyote (Canis latrans) concurrence is less common than the concurrence of deer groups; and below 25 yards, interspecific deer aggregations are less common than aggregations within each deer species. Several other conclusions are tentative: white tail groups are spaced more widely than mule deer groups; spacing between groups of different deer species resembles the mule deer pattern at longer distances but approaches the whitetail pattern at shorter distances; deer of each species concur more often with deer of the opposite species than with third species; of species other than deer, cattle are avoided the least and coyotes the most; and whitetails appear to be less tolerant than mule deer of cattle and coyotes. Indirect evidence suggests that with low population densities, optimum mule deer habitat is free of whitetails, and optimum white tail habitat is used by few if any mule deer. The observed segregation of the two species in winter is probably not caused by competitive exclusion. If competition occurs, it is apparently based on exploitation of common food resources rather than on direct competitive interference. Neither species dominates the other socially; rather, intraspecific class hierarchy is extended to relations between species. Mule deer, however, may be more aggressive, and mule deer bucks show an interest in whitetails during the rut. Hybridization appears to be prevented mainly by an early behavioral block in interspecific pair formation. This isolating mechanism has probably evolved in sympatry.
The following values have no corresponding Zotero field:
PB - Indiana University Press Bloomington, Indiana
A high-resolution biostratigraphic analysis of 287 dinosaurian macrofossils and 138 bonebeds in the Edmonton Group (Upper Cretaceous) of southern Alberta provides evidence for at least three dinosaurian assemblage zones in the Horseshoe Canyon Formation (HCFm). From bottom to top the zones comprise unique assemblages of ornithischians and are named as follows: (1) Edmontosaurus regalis – Pachyrhinosaurus canadensis (lower zone); (2) Hypacrosaurus altispinus – Saurolophus osborni (middle zone); and (3) Eotriceratops xerinsularis (upper zone). Whereas the lower and middle zones are well defined and based on abundant specimens, the validity of the uppermost zone (E. xerinsularis) is tentative because it is based on a single specimen and the absence of dinosaur taxa from lower in section. The transition from the lower to the middle zone coincides with the replacement of a warm-and-wet saturated deltaic setting by a cooler, coastal-plain landscape, characterized by seasonal rainfall and better-drained substrates. Whereas changes in rainfall and substrate drainage appear to have influenced the faunal change, changes in mean annual temperature and proximity to shoreline appear to have had little influence on faunal change. We speculate that the
faunal change between the middle and upper zones also resulted from a change in climate, with ornithischian dinosaurs responding to the re-establishment of wetter-and-warmer climates and poorly-drained substrates. Compared with the shorter duration and climatically-consistent dinosaurian assemblage zones in the older Dinosaur Park Formation of southern Alberta, HCFm assemblage zones record long-term morphological stasis in dinosaurs. Furthermore, the coincidence of faunal and paleoenvironmental changes in the HCFm suggest climate-change-driven dinosaur migrations into and out of the region.
The family Ornithomimidae is defined on the basis of the skeletal morphology of the three genera Ornithomimus, Struthiomimus, and Dromiceiomimus known in continental strata in Alberta, which are temporally equivalent to the Upper Campanian substage. At least two genera occur in Canadian Lance (Upper Maestrichtian) equivalent strata, but cannot be identified at present. A group of more primitive ornithomimoid theropods is represented else-where by the late Jurassic Elaphrosaurus and early Cretaceous Archaeornithomimus.Ornithomimid attributes include a general body form which parallels that of the ratites; elongate forelimbs, a kinetic skull, enormous eyes, a relatively highly evolved brain, and possibly a secondary palate and supertemporal fenestrae which were nearly encircled by alae of the squamosal. A reconstruction of the myology of the thigh indicates that ornithomimids were extremely fleet, but lacked the agility characteristic of modern large ground birds. They probably subsisted on small, soft-bodi...
A new specimen of Struthiomimus altus is described from the Oldman Formation of Alberta. Ossified xiphisternal structures are present, which are similar to the posterolateral processes of the sternum of some birds. The gastralia are found to consist of two, rather than three, overlapping segments. Four genera of Upper Cretaceous ornithomimids are recognized: Struthiomimus, Ornithomimus, Dromiceiomimus, and Gallimimus. The structure of the manus is found to be the most reliable character suite distinguishing them. Dromiceiomimus, however, can still be distinguished only on the basis of limb proportions, and its recognition remains tentative until further material is forthcoming. Refs.
New material of an ornithomimid from the Late Cretaceous deposits of Tsagan Khushu (Gobi Desert, Mongolia) is described. The material includes a partial axial skeleton, and hind and forelimb elements. The specimen is similar to Anserimimus planinychus from nearby Bugin Tsav locality in having ventrally flat, long, almost straight manual unguals. The new specimen differs from A. planinychus in the length of the penultimate manual phalanx II-2, which is only slightly shorter than Ph III-3, in a considerably lesser alae of the manual unguals, and in the height/width ratio of the proximal articular surfaces. The material suggests presence of third, hitherto unknown ornithomimid from the Nemegt Formation.
Sexual dimorphism, the condition whereby males and females differ from one another physically, is one of the most fundamental aspects of the biology of any animal. However, sexually dimorphic characters can be subtle and are mainly related to soft tissue anatomy. They are, therefore, difficult to identify reliably in the fossil record particularly when dealing with small sample sizes and osteology alone. The first geometric morphometric analysis of dimorphism in a thyreophoran (armored) dinosaur shows that the femora of the stegosaurian dinosaur Kentrosaurus aethiopicus (Upper Jurassic, Tanzania) bear a statistically significant shape difference of the proximal end, which is independent of size and is therefore proposed to be a sexual difference. Although the disarticulated nature of the material means that intraspecific variation in other skeletal elements, such as the enigmatic dermal armor, cannot be identified as sexual dimorphism at this time, this study provides a methodology for further work on articulated stegosaurian specimens and has the potential to reveal additional information regarding the palaeobiology and population dynamics of this poorly understood clade.
The main features of the phylogeny program TNT are discussed. Windows versions have a menu interface, while Macintosh and Linux versions are command-driven. The program can analyze data sets with discrete (additive, non-additive, step-matrix) as well as continuous characters (evaluated with Farris optimization). Effective analysis of large data sets can be carried out in reasonable times, and a number of methods to help identifying wildcard taxa in the case of ambiguous data sets are implemented. A variety of methods for diagnosing trees and exploring character evolution is available in TNT, and publication-quality tree-diagrams can be saved as metafiles. Through the use of a number of native commands and a simple but powerful scripting language, TNT allows the user an enormous flexibility in phylogenetic analyses or simulations.
© The Willi Hennig Society 2008.
We studied resource partitioning between sympatric populations of Columbian white-tailed (CWTD; Odocoileus virginianus leucurus) and black-tailed (BWTD) deer (O. odocoileus hemionus columbianus) in western Oregon to understand potential mechanisms of coexistence. We used horseback transects to describe spatial distributions, population overlap, and habitat use for both species, and we studied diets with microhistological analysis of fecal samples. Distribution patterns indicated that white-tailed and black-tailed deer maintained spatial separation during most seasons with spatial overlap ranging from 5%–40% seasonally. Coefficients of species association were negative, suggesting a pattern of mutual avoidance. White-tailed deer were more concentrated in the southern portions of the study area, which was characterized by lower elevations, more gradual slopes, and close proximity to streams. Black-tailed deer were more wide ranging and tended to occur in the northern portions of the study area, which had higher elevations and greater topographical variation. Habitat use of different vegetative assemblages was similar between white-tailed and black-tailed deer with overlap ranging from 89%–96% seasonally. White-tailed deer used nearly all habitats available on the study area except those associated with conifers. White-tailed deer used oak-hardwood savanna shrub, open grassland, oak-hardwood savanna, and riparian habitats the most. Black-tailed deer exhibited high use for open grassland and oak-hardwood savanna shrub habitats and lower use of all others. The 2 subspecies also exhibited strong seasonal similarities in diets with overlap ranging from 89% to 95%. White-tailed deer diets were dominated by forbs, shrubs, grasses, and other food sources (e.g., nuts and lichens). Columbian black-tailed deer diets were dominated mostly by forbs and other food sources. Seasonal diet diversity followed similar patterns for both species with the most diverse diets occurring in fall and the least diverse diets in spring. High overlap in habitat use and diets resulted in high trophic overlap (81–85%) between white-tailed and black-tailed deer; however, the low spatial overlap reduced the potential for exploitative competition but may have been indicative of inference competition between the species. Diverse habitat and forage opportunities were available on the study area due to heterogeneous landscape characteristics, which allowed ecological separation between white-tailed and black-tailed deer despite similarities in diets and habitat use. We make several recommendations for management of CWTD, a previously threatened species, based on the results of our study. © 2011 The Wildlife Society.
Only two ornithomimid genera, Ornithomimus and Struthiomimus, are currently known from the Upper Cretaceous of North America. However, a number of ornithomimid elements from Alberta’s Dinosaur Park Formation (Upper Campanian), cannot be assigned to either Ornithomimus or Struthiomimus. These bones, including a frontal, caudal vertebrae, and unguals of the manus and the pes, come from animals significantly larger than any previously known Judithian ornithomimid. The frontal exhibits several unusual features, including transverse expansion over the prefrontals, and extreme reduction of the supratemporal fossae. Caudal vertebrae are characterized by neural arches that are posteriorly shifted and transversely expanded. Manual unguals possess a highly concave articular surface, a flexor tubercle divided by a sulcus, and a broad claw. Pedal unguals display highly concave articular surfaces, and a ridge-like flexor tubercle dividing a deep ventral fossa. Although it is difficult to know whether these elements represent a single taxon, this is currently the most parsimonious hypothesis. This study demonstrates how isolated dinosaur bones can extend our knowledge of dinosaur faunas.
A partial skeleton of the ornithomimid dinosaur, discovered from the Late Cretaceous Qiupa Formation of Luanchuan County, Tantou Basin, Henan Province, China, is described here and assigned to a new genus and species, Qiupalong henanensis, with unique features (a notch on the lateral surface of the lateral posterior process of the proximal end of tibia and a small pit at the contact between astragalus and calcaneum). A phylogenetic analysis in this study suggests that it is a derived ornithomimid and form a monophyly with North American ornithomimids (Struthiomimus altus and Ornithomimus edmontonicus), sharing two characters (straight pubic shaft and large acute angle between pubic shaft and boot). Some characters (small anterior process of the pubic boot and curved pedal unguals) are seen in basal ornithomimosaurs as well, but these features in Q. henanensis are reversal. Qiupalong is the first definitive ornithomimid from outside of the Gobi Desert and is the southern-most occurrence of Late Cretaceous ornithomimid from eastern Asia, demonstrating southern extension of ornithomimid distribution in Asia.
Many tyrannosaurid skeletons have been collected in Canada, the United States, and Mongolia. These fossils tend to represent mature individuals, but juveniles are also known. Skeletons of five genera of tyrannosaurids representing two distinct clades (albertosaurines and tyrannosaurines) were measured, and bivariate analysis was done on 85 dimensions. Allometric differences among mature specimens of different species are shown to be trivial when compared with the allometric differences associated with growth. Nevertheless, albertosaurines tend to be more lightly built than tyrannosaurines. When compared with a tyrannosaurine of the same absolute size, albertosaurines had slightly shorter, lower skulls, shorter ilia, longer tibiae, longer metatarsals, and longer toes. The arms of albertosaurines and tyrannosaurines are the same size, with the exception of Tarbosaurus, which has shorter front limb elements. Tooth counts show individual and interspecific variation, but there is no evidence that tooth numbers are controlled by the size or age of an animal. Dinotyrannus, Jenghizkhan, Maleevosaurus, Shanshanosaurus, Stygivenator, and possibly Nanotyrannus have proportions that suggest they are ontogenetic stages of either Tarbosaurus or Tyrannosaurus.
Podarcis bocagei and P. carbonelli are two closely related lacertid species, very similar morphologically and ecologically. We investigated sexual dimorphism patterns presented by both species in allopatry and in sympatry. Sexual size and shape dimorphism patterns were analyzed using both multivariate and geometric morphometric techniques. Multivariate morphometrics revealed a marked sexual dimorphism in both species--males being larger with more robust habitus and females presenting a longer trunk. General patterns of sexual size dimorphism are not modified in sympatry, although there is evidence for some morphological change in male head size. The application of geometric morphometrics offered a more detailed image of head shape and revealed that males present a more developed tympanic area than do females, while females have a more rounded head. Differences in the degree of sexual shape dimorphism were detected in sympatry, but no consistent patterns were observed. From the results of the study, and based on previous knowledge on the populations studied, we conclude that the morphological differences observed are probably not caused by exploitative competition between the species, but rather appear attributable to the modification of the relative influence of sexual and natural selection on both sexes.
Harpymimus. The Carnivorous Dinosaurs. K. Carpenter
- Y Kobayashi
- R Barsbold