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Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus
Abstract
The holotype of Deinocheirus mirificus was collected by the 1965 Polish-Mongolian Palaeontological Expedition at Altan Uul III in the southern Gobi of Mongolia. Because the holotype consists mostly of giant forelimbs (2.4 m in length) with scapulocoracoids, for almost 50 years Deinocheirus has remained one of the most mysterious dinosaurs. The mosaic of ornithomimosaur and non-ornithomimosaur characters in the holotype has made it difficult to resolve the phylogenetic status of Deinocheirus. Here we describe two new specimens of Deinocheirus that were discovered in the Nemegt Formation of Altan Uul IV in 2006 and Bugiin Tsav in 2009. The Bugiin Tsav specimen (MPC-D 100/127) includes a left forelimb clearly identifiable as Deinocheirus and is 6% longer than the holotype. The Altan Uul IV specimen (MPC-D 100/128) is approximately 74% the size of MPC-D 100/127. Cladistic analysis indicates that Deinocheirus is the largest member of the Ornithomimosauria; however, it has many unique skeletal features unknown in other ornithomimosaurs, indicating that Deinocheirus was a heavily built, non-cursorial animal with an elongate snout, a deep jaw, tall neural spines, a pygostyle, a U-shaped furcula, an expanded pelvis for strong muscle attachments, a relatively short hind limb and broad-tipped pedal unguals. Ecomorphological features in the skull, more than a thousand gastroliths, and stomach contents (fish remains) suggest that Deinocheirus was a megaomnivore that lived in mesic environments.
... In the case of Archaeornithomimus, we restrict the genus to its type species, A. asiaticus; the status of "Archaeornithomimus" affinis from the Lower Cretaceous Arundel Clay of Maryland remains uncertain (Brownstein, 2017). The phylogenetic analysis is based on the character-taxon matrix first presented by Choiniere et al. (2012) and subsequently modified by Lee et al. (2014), Sues and Averianov (2016a), Yao et al. (2022), andHattori et al. (2023). We added character states for Kinnareemimus from the Lower Cretaceous Sao Khua Formation of Thailand, using scores for this taxon provided by Samathi (2024). ...
... Cervical Vertebrae-The postzygapophyses curve slightly laterally on the posterior cervicals of Dzharacursor (Fig. 4C), Dromiceiomimus, Gallimimus, Sinornithomimus, and Ornithomimus (Kobayashi & Lü, 2003;Macdonald & Currie, 2019;Makovicky, 1995;Makovicky et al., 2004;Osmólska et al., 1972), whereas the posterior cervicals of Deinocheirus, Garudimimus, and Pelecanimimus have straight postzygapophyses (Cuesta et al., 2022;Kobayashi & Barsbold, 2005b;Lee et al., 2014). Dorsal Vertebrae-In Dzharacursor, the most anterior dorsal vertebrae have large hypapophyses, but this feature is absent on the more posterior dorsals. ...
... The hypapophysis is absent or poorly developed on the anterior dorsals of Archaeornithomimus, Gallimimus, Garudimimus, Harpymimus, Ornithomimus, Pelecanimimus, Sinornithomimus, and Struthiomimus (Cuesta et al., 2022;Kobayashi & Barsbold, 2005a, 2005bKobayashi & Lü, 2003;Osmólska et al., 1972;Smith & Galton, 1990;Watanabe et al., 2015). Aside from Dzharacursor, the hypapophysis is pronounced on the anterior dorsals of Deinocheirus and Nqwebasaurus (Choiniere et al., 2012;Lee et al., 2014). ...
... Deinocheirus is a bizarre and unique theropod dinosaur, characterized by its enlarged body, elongated snout, deep mandible, relatively short hindlimbs unsuitable for running, and massive forelimbs [Lee et al., 2014]. The holotype of Deinocheirus was discovered in 1976 and consists primarily of enlarged forelimbs, measuring 2.4 meters in length, along with scapulocoracoids [Roniewicz et al., 1970]. ...
... The more complete specimen, MPC-D 100/127, is exceptionally well-preserved, lacking only some middle dorsal vertebrae, caudal vertebrae and right forelimb. The other specimen, MPC-D 100/128, represents a younger, sub-adult individual and is about the 74% the size of the former [Lee et al., 2014]. This smaller specimen MPC-D 100/128 preserves a relatively complete dorsal vertebra with hyperelongated neural spines that reach up 8.5 times the height of the corresponding centra, suggesting the presence of a raised dorsal sail or hump-like structure [ Gallina et al., 2019]. ...
... However, the spine elongation of Spinosaurus (N/C height ratio of 11) is still considerably greater than that of both Deinocheirus and Ouranosaurus. Due to the limited number of specimens, the elongated neural spines are only preserved in the smaller individual, MPC-D 100/127 (Lee et al., 2014). This makes it difficult to determine whether the feature would change in proportion or morphology as the animal matured. ...
Deinocheirus is a bizarre and unique theropod dinosaur. The holotype of Deinocheirus was discovered in 1976, but its characteristics and phylogenetic position remained largely enigmatic due to the scarcity of fossil material. This changed in 2014 when Lee et al. described two additional specimens, providing a deeper insight into this mysterious creature. Notably, the smaller specimen MPC-D 100/128 preserved a relatively complete dorsal vertebra with hyperelongated neural spines, reaching up to 8.5 times the height of the corresponding centra. This suggests that Deinocheirus possessed a raised dorsal sail or hump-like structure. Elongated neural spines have evolved multiple times in dinosaurs, including in ornithopods of ornithischians as well as theropods and sauropods of saurischians, with various hypothesized functions such as thermoregulation, fat storage, or sexual display. However, previous research on the neural spines of Deinocheirus has been limited to brief description, lacking detailed analysis and leaving the morphology and function of these dorsal structures poorly understood. To better understand the possible dorsal structure of Deinocheirus and its ecological role, this study examines the dorsal neural spines of Deinocheirus and 26 other dinosaurs. Through measurement and comparative analyses, we categorize the height and width of neural spines into different categories. Our comparison reveal that the neural spines of Deinocheirus are most similar to those of Spinosaurus and Ouranosaurus, with a height ratios exceeding 7 and overall morphology closer to the latter. Additionally, the anteroposterior width of neural spines of Deinocheirus is slightly narrower than that of Spinosaurus and Ouranosaurus. Based on these data and previous studies, we infer that the hyperelongated neural spines of Deinocheirus may serve dual functions: supporting a sail related to aquatic habits and a hump associated with an intricate interspinous ligament system, potentially for fat storage to aid in surviving dry seasons. Finally, we discuss avenues for future research, such as bone histology and finite element analysis, which could provide further insights into the morphology and function of the neural spines of Deinocheirus.
... Data on other ornithomimosaurs were from published literature. I put the character states of Kinnareemimus into the data matrices of Choiniere et al. (2012) (plus Deinocheirus, Lee et al. (2014)) and McFeeters et al. (2016). ...
... Almost all cladistics analyses (Fig. 2) agreed that the clade Ornithomimosauria consists of Nqwebasaurus as the early-branching ornithomimosaur, the clade Ornithomimidae as the late-diverging ornithomimosaurs, and the phylogenetically intermediate forms between the oldest basal ornithomimosaur and the latest Cretaceous forms (Senter 2007;Xu et al. 2011;Choiniere et al. 2012;Lee et al. 2014;Sues & Averianov 2016;McFeeters et al. 2017). Sereno (2017) redefined the Ornithomimoidea as a branch-based clade encompassing all ornithomimosaurs more advanced than Nqwebasaurus thwazi. ...
... The ratio of length from the distal end of metatarsal III to the medial expansion of metatarsal III is 0.25 in Kinnareemimus, compared with 0.4 in Deinocheirus, 0.436 in Harpymimus, 0.354 in Garudimimus, and 0.288 in ornithomimids (i.e., Gallimimus) (see Lee et al. 2014). ...
A small-bodied ornithomimosaur, Kinnareemimus khonkaenensis Buffetaut, Suteethorn, and Tong 2009, from the Lower Cretaceous Sao Khua Formation of northeastern Thailand was first reported in 1995, then named in 2009. It is the only report of this group in Southeast Asia and was concluded to be a member of Ornithomimosauria, more derived than Harpymimus and Garudimimus but more basal than Archaeornithomimus. Since then, a few published studies have analyzed the phylogenetic position of Kinnareemimus but failed to find it within the clade Ornithomimosauria. Here, the phylogenetic analyses for assessing the relationships of Kinnareemimus within Ornithomimosauria were performed. The results suggested it might be a basal ornithomimosaur or belongs to the subclade Deinocheiridae. Kinnareemimus shares with deinocheirids the proximally projected cnemial crest and the shape of the fibula in proximal view. Its metatarsal III shows subarctometatarsalian condition with metatarsal III pinched between II and IV but visible in anterior view proximally, which might have evolved independently from other ornithomimids. However, the basal position of Kinnareemimus could also be due to the immaturity and the incomplete nature of this animal.
... Ornithomimosaurs repeatedly evolved gigantic body size during their evolutionary history [14,69,[112][113][114] (Fig 9), although evidence for directional mass evolution, as opposed to stochastic processes, is lacking [115]. Early-diverging ornithomimosaurs from the Early Cretaceous (pre-Albian), such as Nqwebasaurus thwazi [90] from Africa, Hexing qingyi [101], Shenzhousaurus orientalis [106], and Kinnareemimus khonkaenensis [103,116] from Asia, Pelecanimimus polyodon [104,117] from Europe, and Nedcolbertia justinhofmanni [15,118] from North America) were universally small bodied (>12 kg [115, S1 Table]). ...
... By the end of the Cretaceous (Campanian-Maastrichtian), multiple large-bodied species are known to have inhabited Laurasian landmasses, including the deinocheirid Paraxenisaurus normalensis, from the Campanian Cerro del Pueblo Formation of Mexico, indeterminate large-bodied ornithomimid materials from the Dinosaur Park Formation, Canada [25,27,114,121,122] and G. bullatus (MPC-D 100/11) from the Nemegt Formation of Mongolia [77]. Moreover, by this time ornithomimosaurs had achieved gigantism, as exemplified by D. mirificus (MPC-D 100/127), which is estimated to have weighed over 6,000 kg [113] (S1 Table). ...
... However, co-occurrences of both small/medium and large-bodied ornithomimosaur genera are rare. Few examples include the Late Cretaceous Nemegt Formation (early Maastrichtian) of Mongolia, which preserves the medium-bodied taxa Anserimimus planinychus and G. bullatus and large-bodied taxon D. mirificus [113,128,129], and the Dinosaur Park Formation (mid to late Campanian) of Canada, including the medium-bodied taxa O. edmontonicus, R. evadens, and S. altus, and potentially also an unnamed large ornithomimosaur [73,122]. ...
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 Deinocheirus 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 co-existence 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 multiple cohabiting species of ornithomimosaurian dinosaurs in Late Cretaceous ecosystems of Laurasia.
... The sacrum consists of five sacral vertebrae, which are sandwiched between the ilia. Among ornithomimosaurs in which the sacrum is known, only Shenzhousaurus orientalis, Archaeornithomimus asiaticus and Gallimimus bullatus possess five sacral vertebrae (Osm olska et al., 1972;Smith and Galton, 1990;Ji et al., 2003), rather than the typical number of six (Makovicky et al., 2004;Kobayashi and Barsbold, 2005a;Lee et al., 2014;McFeeters et al., 2016;Sues and Averianov, 2016a). The sacral centra are elongated and spool-shaped, having a constriction in the middle but expanding at their anterior and posterior ends. ...
... The well-preserved neural spines of the third and fourth sacrals are anteroposteriorly expanded and fused together, forming a continuous narrow plate. A similar condition occurs in the deinocheirids Harpymimus okladnikovi, Garudimimus brevipes and Deinocheirus mirificus (Kobayashi and Barsbold, 2005a, b;Lee et al., 2014), whereas in Gallimimus bullatus and Rativates evadens the sacral neural spines are separate (Osm olska et al., 1972;McFeeters et al., 2016), and in the Bissekty ornithomimid the neural spines are fused ventrally but separate near their dorsal ends (Sues and Averianov, 2016a). The neural spines are very high and likely projected above the dorsal margin of the ilium in the intact specimen, so that the dorsalmost parts of the spines were exposed in lateral view. ...
... If so, this feature is peculiar. The neural spines are fully concealed by the ilium in most ornithomimosaurs, and extend far enough dorsally to be visible in lateral view only in Harpymimus okladnikovi and Deinocheirus mirificus (Kobayashi and Barsbold, 2005b;Lee et al., 2014). ...
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.
... Ornithomimosaurs repeatedly evolved gigantic body size during their evolutionary history [14,69,[112][113][114] (Fig 9), although evidence for directional mass evolution, as opposed to stochastic processes, is lacking [115]. Early-diverging ornithomimosaurs from the Early Cretaceous (pre-Albian), such as Nqwebasaurus thwazi [90] from Africa, Hexing qingyi [101], Shenzhousaurus orientalis [106], and Kinnareemimus khonkaenensis [103,116] from Asia, Pelecanimimus polyodon [104,117] from Europe, and Nedcolbertia justinhofmanni [15,118] from North America) were universally small bodied (>12 kg [115, S1 Table]). ...
... By the end of the Cretaceous (Campanian-Maastrichtian), multiple large-bodied species are known to have inhabited Laurasian landmasses, including the deinocheirid Paraxenisaurus normalensis, from the Campanian Cerro del Pueblo Formation of Mexico, indeterminate large-bodied ornithomimid materials from the Dinosaur Park Formation, Canada [25,27,114,121,122] and G. bullatus (MPC-D 100/11) from the Nemegt Formation of Mongolia [77]. Moreover, by this time ornithomimosaurs had achieved gigantism, as exemplified by D. mirificus (MPC-D 100/127), which is estimated to have weighed over 6,000 kg [113] (S1 Table). ...
... However, co-occurrences of both small/medium and large-bodied ornithomimosaur genera are rare. Few examples include the Late Cretaceous Nemegt Formation (early Maastrichtian) of Mongolia, which preserves the medium-bodied taxa Anserimimus planinychus and G. bullatus and large-bodied taxon D. mirificus [113,128,129], and the Dinosaur Park Formation (mid to late Campanian) of Canada, including the medium-bodied taxa O. edmontonicus, R. evadens, and S. altus, and potentially also an unnamed large ornithomimosaur [73,122]. ...
Reconstructing the evolution, diversity, and paleobiogeography of North America’s Late Cretaceous dinosaur assemblages requires 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 paleohistology of MMNS VP-6332 demonstrates that the individual was at least 11 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 Deinocheirus 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 with near reaching somatic maturity of the larger taxon, suggesting the co-existence 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 multiple cohabiting species of ornithomimosaurian dinosaurs in Late Cretaceous ecosystems of Laurasia.
... This has sparked a heated debate regarding the degree of ecological specialization in Spinosaurus, which has been described as actively pursuing prey in waters 11 , with alternative proposals suggesting a more terrestrial or 'wader-heron' model on the basis of anatomical observations and 3D digital models 12,13,23 . Aquatic habits have also been suggested for a handful of other dinosaurs based on gut contents (other spinosaurids 24 and ornithomimosaurs 6,8 ) or anatomical proxies (halszkaraptorine dromaeosaurids 10 , compsognathids 5 and various ornithischians 3,4,7 ), but remain ambiguous and controversial. This illustrates the inherent challenges of reconstructing ecomorphological relationships in vertebrates 25 and the resulting difficulties in inferring ecological traits in extinct species. ...
... Phylogenetic optimization of bone density and the presence of osteosclerosis tentatively suggests that subaqueous foraging is ancestral for Spinosauridae (Fig. 2c, Extended Data Figs. 8,9) and that the absence of osteosclerosis in Suchomimus results from secondary loss rather than primitive absence. The absence of osteosclerosis does not rule out a dependency on aquatic habitats for predation in Suchomimus: anatomical traits are consistent with a largely piscivorous diet, including an elongate snout and conical dentition. ...
... To address the statistical non-independence of interspecific comparisons, we assembled two informal amniote-wide supertrees (Extended Data Figs. 8,9) using Mesquite v. 3.40 57 on the basis of Upham et al. 58 for Mammalia, Simoes et al. 59 for the backbone of Diapsida, Nesbitt et al. 60 for Archosauria, Langer et al. 61 for Dinosauria, this study for Tetanurae, Brusatte et al. 62 for Coelurosauria, and Prum et al. 63 for Neoaves. We calibrated the resulting tree using the function 'bin_timePaleoPhy' from the R package Paleotree 64 , scaling the branches on the basis of genus-level stratigraphic ranges sourced from the Paleobiology Database (www. ...
Secondary aquatic adaptations evolved independently more than 30 times from terrestrial vertebrate ancestors1,2. For decades, non-avian dinosaurs were believed to be an exception to this pattern. Only a few species have been hypothesized to be partly or predominantly aquatic3–11. However, these hypotheses remain controversial12,13, largely owing to the difficulty of identifying unambiguous anatomical adaptations for aquatic habits in extinct animals. Here we demonstrate that the relationship between bone density and aquatic ecologies across extant amniotes provides a reliable inference of aquatic habits in extinct species. We use this approach to evaluate the distribution of aquatic adaptations among non-avian dinosaurs. We find strong support for aquatic habits in spinosaurids, associated with a marked increase in bone density, which precedes the evolution of more conspicuous anatomical modifications, a pattern also observed in other aquatic reptiles and mammals14–16. Spinosaurids are revealed to be aquatic specialists with surprising ecological disparity, including subaqueous foraging behaviour in Spinosaurus and Baryonyx, and non-diving habits in Suchomimus. Adaptation to aquatic environments appeared in spinosaurids during the Early Cretaceous, following their divergence from other tetanuran theropods during the Early Jurassic17. In extinct species including non-avian dinosaurs, bone density is shown to be a reliable indicator of aquatic behavioural adaptations, which emerged in spinosaurids during the Early Cretaceous.
... In recent phylogenies, Ornithomimosauria is one of the most basal clades in Coelurosauria, more derived than Tyrannosauroidea, and the sister-group to Maniraptora (e.g. Choiniere et al., 2010Choiniere et al., , 2012Lee et al., 2014;Chinzorig et al., 2018). ...
... New detailed descriptions of historic material have also been provided (e.g. Kobayashi & Barsbold, 2005a, b;Lee et al., 2014;Claessens & Loewen, 2016). Among the vast ornithomimosaurian record, the axial and appendicular skeletons are altogether well represented. ...
... Among the vast ornithomimosaurian record, the axial and appendicular skeletons are altogether well represented. Taxa such as Archaeornithomimus Russel, 1972(Gilmore, 1933Smith & Galton, 1990), Deinocheirus Osmólska & Roniewicz, 1970(Lee et al., 2014, Gallimimus bullatus Osmόlska et al., 1972, Harpymimus Barsbold & Perle, 1984(Kobayashi & Barsbold, 2005a, Ornithomimus edmontonicus Sternberg, 1933, Sinornithomimus Kobayashi & Lü, 2003 or Struthiomimus Lambe, 1902(Nicholls & Russell, 1981, 1985 have an almost complete and well-preserved axial skeleton, pectoral girdles and forelimbs. On the other hand, the atlas-axis complex is poorly represented in the fossil record, as only Deinocheirus (Lee et al., 2014), Gallimimus bullatus Osmólska et al., 1972, Garudimimus Barsbold, 1981(Kobayashi & Barsbold, 2005b, Sinornithomimus (Kobayashi & Lü, 2003) and Struthiomimus (Lambe, 1902) preserve them complete or partially complete. ...
Pelecanimimus polyodon was discovered in 1993 in the Spanish Barremian fossil site of Las Hoyas, being the
first ornithomimosaur described from Europe. So far, there has been no detailed description of the holotype
of Pelecanimimus, which is composed of the anterior-half of an articulated skeleton. Here we report a new,
detailed, revised and more accurate osteological description of its postcranial skeleton, comparing this new
data to information about Ornithomimosauria from the last three decades. This osteological and phylogenetic
analysis of Pelecanimimus shows several ornithomimosaur synapomorphies and a unique combination of
characters that emend its original diagnosis. Pelecanimimus diverged early in Ornithomimosauria and reveals
an enlargement trend of the manus, shared with derived ornithomimosaurians, due to a long metacarpal I and
elongated distal phalanges. This evolutionary novelty, and other synapomorphies, has led to the definition of a
new clade, Macrocheiriformes, including Pelecanimimus and more derived ornithomimosaurs. Pelecanimimus has
the only ossified sternal plates among ornithomimosaurs and the first evidence of uncinate processes in a nonmaniraptoran theropod, indicating a convergent appearance of these structures in Coelurosauria. The character
combination in an early-diverging ornithomimosaur like Pelecanimimus found in this analysis provides a key
step in the evolution of the manus and pectoral girdle in Ornithomimosauria
... Brochu, 2003;Carr et al., 2005;Brownstein, 2018), this could be related to the large body-size (~5.7 m) and heavier bodyweight (~600 kg) that this dinosaur had to bear. This is the case for ornithomimosaurs Beishanlong grandis (Makovicky et al., 2010) and Deinocheirus mirificus (Lee et al., 2014), which had estimated body lengths of~5.9 m and 11 m, and estimated body weights of 626 kg and 6358 kg, respectively. The pedal phalanges of P. normalensis are comparable in size with the ones of B. grandis from the Early Cretaceous of Asia (Makovicky et al., 2010) (see Table 2). ...
... In contrast, the manual ungual I of Beishanlong grandis is large with deep dorsolateral grooves and although, it has a distally located flexor tubercle divided by a deep transverse sulcus as in P. normalensis, the proximal articular facet is ovoid and the ungual is more highly curved (Fig. 18d) (Makovicky et al., 2010). Deinocheirus mirificus also has a mediolaterally compressed, strongly curved, large manual ungual I with unenclosed dorsolateral grooves; however, unlike P. normalensis, the dorsolateral grooves in D. mirificus are shallow, the proximal articular facet is ovoid and it has a proximally located, undivided flexor tubercle (Fig. 18e) (Lee et al., 2014). On the other hand, the Dinosaur Park specimen (ROM 41844) has a large, moderately curved, broad manual ungual I with deep dorsolateral grooves, a distally located flexor tubercle divided by a sulcus and a deeply concave, oval articular proximal surface (Fig. 18f) (Longrich, 2008). ...
... The presence of an expanded proximal end of metatarsal III in Paraxenisaurus normalensis suggests that the pes of this ornithomimosaur was not arctometatarsalian and was completely exposed in anterior and posterior views ( Fig. 19a1 and 19a2). This nonarctometatarsalian condition has also been found in more primitive clades, such as Nqwebasaurus thwazi (Sereno, 2017) and in one member of the Deinocheiridae family, Deinocheirus mirificus ( Fig. 19b1 and 19b2) (Lee et al., 2014). In other deinocheirids, such as Garudimimus brevipes (Fig. 19c1 and 19c2) and Harpymimus okladnikovi (Fig. 19d1 and 19d2), as well as in two less derived ornithomimosaurs, Beishanlong grandis ( Fig. 19e1 and 19e2) and Arkansaurus fridayi (Fig. 19f1 and 19f2), a submetatarsalian condition was present, where the proximal end of metatarsal III is laterally compressed, but still exposed in anterior view (Xu et al., 2002;Barsbold, 2005a, 2005b; Makovicky et al., 2010;Hunt and Quinn, 2018). ...
New ornithomimosaur material discovered from the Upper Cretaceous Cerro del Pueblo Formation of Coahuila, Mexico is described herein. The material includes postcraneal elements from several individuals, which are assigned to a new genus and species, Paraxenisaurus normalensis. This new taxon is characterized by the presence of a strongly curved and laterally compressed manual ungual I with a distally placed flexor tubercle divided by a deep sulcus and a deeply concave proximal, elliptical-shaped articular surface; a metacarpal III that has an expanded proximal articular end, which is similar in width to metacarpal II; a combination of posterior caudal vertebrae, where the most anterior vertebrae possess low dorsoventral prezygapophyses with nearly vertical articulation surfaces, while the most posterior vertebrae have prezygapophyses that face ventromedially; a non-arctometatarsalian pes, where the proximal end of metatarsal III is expanded and has a proximal ovoid outline; the presence of an attachment site for pedal digit I in the posterior surface of the distal quarter of metatarsal II; an expanded medial condyle of metatarsal II; a transversely wide distal end of metatarsal III, which has a semi-ginglymoid articular surface; distinctively broad and ventrally curved pedal unguals that depending on the digit, the proximodorsal process changes its position adopting a lip-shaped appearance; a rounded, large foramen on the medial side of each pedal ungual and the presence of a deep ventral fossa that surrounds a strongly developed, ridge-like flexor tubercle. This combination of characteristics separate Paraxenisaurus normalensis from other ornithomimosaurs previously described in North America and in other parts of the world. Phylogenetic analysis shows that within Ornithomimosauria, Paraxenisaurus normalensis is recovered as a deinocheirid ornithomimosaur, along with Garudimimus brevipes and Deinocheirus mirificus. Therefore, the finding of Paraxenisaurus normalensis in the Cerro del Pueblo Formation of Coahuila, Mexico represents the first record of the Deinocheiridae family in the Campanian of North America.
... Ornithomimosaurs are one of the most diverse theropod dinosaur groups and their remains are abundant within the formation (Hurum and Sabath, 2003;Makovicky et al., 2004). They are generally characterized by their medium to large body size, proportionately small skulls with large orbits, elongate forelimbs with weakly developed mani, and cursorially adapted powerful hindlimbs (Osborn, 1917;Norell et al., 2001;Makovicky et al., 2004;Lee et al., 2014). To date, four definitive ornithomimosaurs have been described from the Nemegt Formation of Mongolia; namely, Anserimimus planinychus from Bügiin Tsav, Deinocheirus mirificus from Altan Uul III and IV, and from Bügiin Tsav, Gallimimus bullatus from most of localities of the Nemegt Formation, and a new ornithomimid (aff. ...
... Anserimimus planinychus Barsbold, 1988) from Tsagaan Khushuu (Kobayashi and Barsbold, 2006;Bronowicz, 2011) (Fig. 1). Deinocheirus mirificus belongs to the clade Deinocheiridae (Lee et al., 2014), and the other three are positioned within the cursorial clade Ornithomimidae (Makovicky et al., 2004). ...
... Members of this group show high morphological variation in their manual structures, the phalangeal proportions and the shapes of their unguals, including curvature and robustness. These variations may be related to functional diversity (Osmόlska et al., 1972;Russell, 1981, 1985;Makovicky et al., 2004;Barsbold, 2005a, 2005b;Choiniere et al., 2012;Lee et al., 2014;Claessens and Loewen, 2016). ...
... In particular, flanges and spurs descending ventrally are common (Figure 1c,d;Nabavizadeh, 2020a). The zygomatic region bears a large ventral flange in most known iguanodontians (Horner et al., 2004;Norman, 2004), some heterodontosaurids (Sereno, 2012), at least one stegosaurian (Galton & Upchurch, 2004), some sauropods (Sullivan & Xu, 2017, figure 4 therein;Zaher et al., 2011) and at least one theropod (Lee et al., 2014). Many large theropods possess conspicuous ventral 'cornual processes' in the same location (Sullivan & Xu, 2017). ...
... Several of these features have been proposed as entheses in jaw musculature reconstructions, simplified phylogenetic model-based approaches to tissue reconstruction that ignore contrasting osteological signals. (Figure 1c), as well as conservative reconstructions using muscles predicted using the EPB (Figure 1d; Holliday, 2009;Lautenschlager, 2013;Lee et al., 2014). Like those proposed by Sereno et al. (2010) and Sereno et al. (2012), these reconstructions have since been considered unlikely (Sullivan & Xu, 2017). ...
Unlike mammals, reptiles typically lack large muscles and ligaments that connect the zygoma to the mandible. Dinosaur craniomandibular soft tissue reconstructions, often based on the rationale of extant phylogenetic bracketing, follow this general rule. However, descending flanges from the zygomata of hadrosaurs, heterodontosaurids, and psittacosaurids have been used to argue for a masseter‐like muscle in these dinosaur taxa. We examined dinosauriform skulls for osteological indicators of connective tissue entheses on the zygoma and mandible, and subsequently sectioned 10 specimens for histological evidence. Osteological indicators were found on the zygoma in most sampled dinosauriforms, which range from rugosities to large descending processes, and morphologically resemble known muscular and ligamentous entheses. Similarly, rugose features oriented towards the zygoma were found on the mandible in sampled dinosauriforms, many having previously been interpreted as entheses for the adductor mandibulae muscle group. Serial histological sectioning of ceratopsid, hadrosaurid, and tyrannosaurid jugal and surangular rugosities reveals an external cortex rich in collagen fibres, strongly resembling entheseal fibres. Jugal entheseal fibres are usually oriented ventrally towards the surangular, and in hadrosaurids and tyrannosaurids these are parallel to macroscopic striations on the surfaces of the jugal flange. Histological sections of extant chicken buccal regions show similar entheseal fibres in the attachments of the jugomandibular ligament on the jugal and of the adductor musculature on the mandible. We hypothesise a strong connective tissue structure bridging the zygoma and mandible in dinosaurs, termed the ‘exoparia’. This structure's size and proximity to the craniomandibular joint would be advantageous in stabilising the mandible relative to the cranium during jaw movement, particularly in dinosaurs thought to process their masticate. A ligamentous or muscular identity for the exoparia cannot be determined with the available data, but the size and shape of the zygomatic entheses in many dinosaurs are more consistent with a muscular attachment. Possible antecedents in non‐dinosauriform archosaurs and derivations in modern birds may exist, but the homology of the exoparia is currently unknown. These results highlight the complex soft tissue evolution of dinosaurs and caution against simplified phylogenetic model‐based approaches to tissue reconstruction that ignore contrasting osteological signals.
... The anteroposterior narrowness of these neural arches corresponds well to those of large-bodied theropods such as Allosaurus (Gilmore, 1920;Madsen, 1976), Acrocanthosaurus (Harris, 1998), Mapusaurus (Coria and Currie, 2006) and Tyrannosaurus (Brochu, 2003). This is unlike the condition in ornithomimosaurs, in which the dorsals exhibit dorsoventrally shorter neural arches with more elongate anteroposterior proportions, as in Archaeornithomimus, Deinocheirus, Dromiceiomimus, Gallimimus, Garudimimus, Pelecanimimus, Struthiomimus, and others (Parks, 1928;Osm olska et al., 1972;Smith and Galton, 1990;Kobayashi and Barsbold, 2005;Lee et al., 2014;Sues and Averianov, 2016;Macdonald and Currie, 2019;Cuesta et al., 2022). In addition, an anterior tilt of the arch relative to the horizontal plane is also visible in the anterior dorsals of Allosaurus and Acrocanthosaurus (SMU 74646/FWMSH 93B-9; Harris, 1998), but not the other large-bodied theropods mentioned above, in which the arch is closer to vertically oriented. ...
... Although some aspects of tibial anatomy are relevant for identifying different clades within Ornithomimosauria, few tibial features are useful for discriminating ornithomimosaur tibiae from those of other tetanurans and basal coelurosaurs (Kobayashi and Lü, 2003;Makovicky et al., 2004;Makovicky et al., 2010;Choiniere et al., 2012;Sues and Averianov, 2016). A robust, dorsally expanded cnemial crest is present in Deinocheiridae and Garudimimus (Lee et al., 2014), but this is much larger than that seen in USNM 466054 (or any other ornithomimosaurs, for that matter; Sues and Averianov, 2016). ...
... To assess the phylogenetic affinity of Tyrannomimus, type and referred specimens were scored into the latest version of the character-taxon matrix focused on the phylogeny of ornithomimosaurs 7 that is derived from several previous studies 5, 6,8,9 . Some character descriptions and scores were modified based on information from literature. ...
... The final dataset compiled with Mesquite 3.6 73 includes 106 taxa covering an extensive sample of coelurosaurs and outgroups scored for 568 discrete anatomical characters. The following characters were ordered as in previous studies 5 [5][6][7][8][9] , the dataset was analyzed with equally weighted parsimony in TNT 1.5 74 and Herrerasaurus was chosen as the outgroup to root the tree. At first, the dataset was analyzed under the "New Technology" search options, using sectorial search, ratchet, tree drift Springer Nature journal content, brought to you courtesy of Springer Nature Customer Service Center GmbH ("Springer Nature"). ...
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.
... T he Gobi Desert of Mongolia is the source of non-avian theropod dinosaurs that provided important evidence for brooding behaviour 1 , the presence of pygostyles 2 , and a long-armed giant omnivore 3 . A recent study of the dromaeosaurid theropod Halszkaraptor from the Djadochta Formation of this region revealed its semiaquatic ecology, which is unique among non-avian maniraptorans 4 . ...
... nov., is described based on a well-articulated specimen (Figs. 1, 2, 3a-h, 4a, Supplementary Note 1, and Supplementary Figs. [1][2][3][4] from the Baruungoyot Formation at Hermiin Tsav in the southern Mongolian Gobi Desert. This new taxon exhibits anatomical characteristics very similar to the aquatic adaptations in Halszkaraptor 4,7 . ...
Streamlining a body is a major adaptation for aquatic animals to move efficiently in the water. Whereas diving birds are well known to have streamlined bodies, such body shapes have not been documented in non-avian dinosaurs. It is primarily because most known non-avian theropods are terrestrial, barring a few exceptions. However, clear evidence of streamlined bodies is absent even in the purported semiaquatic groups. Here we report a new theropod, Natovenator polydontus gen. et sp. nov., from the Upper Cretaceous of Mongolia. The new specimen includes a well-preserved skeleton with several articulated dorsal ribs that are posterolaterally oriented to streamline the body as in diving birds. Additionally, the widely arched proximal rib shafts reflect a dorsoventrally compressed ribcage like aquatic reptiles. Its body shape suggests that Natovenator was a potentially capable swimming predator, and the streamlined body evolved independently in separate lineages of theropod dinosaurs.
... Given that UCM 87636 is nearly identical to described examples of tyrannosaurid pedal unguals (e.g., Lambe 1917;Brochu 2003;Holtz 2004;Lehman and Wick 2013;Mallon et al. 2020), this specimen is unlikely to pertain to a giant crocodyliform. Among theropods found in the Campanian-Maastrichtian strata of Laramidia, only caenagnathids (e.g., Xu et al. 2007), ornithomimosaurs (Lee et al. 2014;Serrano-Brañas et al. 2020) and tyrannosaurids (e.g., Brochu 2003;Holtz 2004) would have been large enough to have pedal unguals that are similar in size with UCM 87636. UCM 87636 lacks the constricted proximal articular surface and proximally diverging collateral grooves seen in the pedal unguals of large caenagnathids (Xu et al. 2007;Lamanna et al. 2014). ...
... UCM 87636 lacks the constricted proximal articular surface and proximally diverging collateral grooves seen in the pedal unguals of large caenagnathids (Xu et al. 2007;Lamanna et al. 2014). UCM 87636 can be distinguished from ornithomimosaurs by the absence of a distinctive proximal constriction at the base of the ungual as well as the ventral depression with ridge-like flexor tubercle, which are present even in the largest examples of this clade (Longrich 2008;Lee et al. 2014;Serrano-Brañas et al. 2020). The overall form, as well as details of its anatomy in UCM 87636 match those seen in other tyrannosaurid pedal unguals (see below). ...
A right theropod pedal ungual phalanx II-3 from the Campanian Williams Fork Formation of northwestern Colorado is described, and a combination of features, including the large size, tapering distal tip, robust and stout overall form, triangular cross-section, and a relatively flat ventral surface allows a confident referral to Tyrannosauridae Osborn, 1906. Although this specimen was found in a relatively southern state, the proximal articular surface of this ungual is similar to that of Gorgosaurus libratus Lambe, 1914, a taxon found in the northern state, Alberta. Although based on limited evidence, this may suggest that the range of tyrannosaurids considered endemic to the north of Laramidia extended farther south than previously thought.
... In addition, a narrow gap between the fused centra and fused zygapophyses is visible in lateral view (Fig. 29P), which are unreported in other theropods with fused posteriormost caudals. The dorsal margin of the posteriormost caudals bears a narrow, nearly flat dorsal surface (Fig. 32AD), whereas the ventral margin forms a broader, flat or slightly concave ventral surface (Fig. 33AD) as in the preceding caudals ( Fig. 33O-AC) and the pygostyle of Fukuipteryx (Imai et al., 2019), in contrast to other fused posteriormost caudals in non-pygostylian theropods (Lee et al., 2014;Barsbold et al., 2000a: fig. 1). ...
... Fused posteriormost caudals Fused posteriormost caudals is generally known as a shared trait in avialan pygostylians. On the other hand, such feature is also known in the ornithomimosaur Deinocheirus (Lee et al., 2014), therizinosaur Beipiaosaurus (Xu et al., 2003), and oviraptorosaurs Nomingia (Barsbold et al., 2000b), Similicaudipteryx (He et al., 2008), Citipati and Conchoraptor (Persons et al., 2014), as well as the non-pygostylian avialan FIGURE 59. Relationship between olfactory ratio and body mass for selected dinosaurs. Bold and dashed lines represent independent contrast least-squares regression and 95% CI, respectively. ...
A bizarre coelurosaurian theropod Fukuivenator paradoxus is known only from the holotype specimen preserving majority of the skeleton from the Kitadani Dinosaur Quarry of the Lower Cretaceous Kitadani Formation, Tetori Group, Fukui, Japan. With aids of computed tomography techniques, a re-examination of the holotype specimen reveals additional features of Fukuivenator which was unobservable in the original description, such as the presence of parietals and a quadrate, and the fusion of the posteriormost caudal vertebrae. The thorough description in this study results in the emendation of diagnosis including the retraction of the large promaxillary fenestra subequal in size to maxillary fenestra, and the addition of the large maxillary fenestra expanded well dorsally above the suprantral strut. Expansion of morphological information elaborates the phylogenetic dataset, resulting in locating Fukuivenator as an unambiguous member of Maniraptora at the basalmost position of Therizinosauria. This phylogenetic position of Fukuivenator is supported by several therizinosaurian synapomorphies such as the subotic recess on the braincase, 11 cervical vertebrae some of which having two pneumatic foramina, and distal articular condyles on the anterior surface of the humerus. Among numerous diagnostic features, eight characters shared with some non-maniraptoran coelurosaurs and five shared with different clades within Maniraptora, highlighting the notably mosaic condition of Fukuivenator proposed in the original description. The combination of characters for herbivorous and carnivorous diets suggests the omnivory of Fukuivenator, projecting the dietary shift in the earliest evolutionary stage of Therizinosauria. Also, the large olfactory ratio revealed by the revised brain endocast highlights the unusually high olfactory acuity further developed than the plesiomorphic condition, implying that the acute sense of smell might be a characteristic of therizinosaurian theropods.
... This highlights that certain aspects of the feeding strategies of herbivorous theropods are variable to an extent that overlap with those of carnivores. Dietary reversals to omnivory/carnivory are suspected in the ornithomimosaurian Deinocheirus Report and later-diverging caenagnathid oviraptorosaurians [10][11][12] based on direct and anatomical/functional evidence, respectively. Our results add to these studies by showing that later-diverging caenagnathids have some of the most speedefficient mandibles among oviraptorosaurians ( Figure S2), which could have been an adaptation for prey capture. ...
... As in carnivorous theropods, 57 body size might also be a factor affecting feeding mechanics: exceptionally large herbivorous theropods like Deinocheirus and Gigantoraptor display stress/strain distribution patterns that are unlike other members in the same clade (Figures 1 and S1), which supports hypotheses that they were specialized feeders. 10,21,58 The presence of large-bodied members in every herbivorous theropod clade 9 suggests that size-related niche partitioning might have been widespread among them. Such ecological niche partitioning could have contributed to the diversification of theropod dinosaurs, which eventually led to the rise of modern birds. ...
Theropod dinosaurs underwent some of the most remarkable dietary changes in vertebrate evolutionary history, shifting from ancestral carnivory1, 2, 3 to hypercarnivory⁴,⁵ and omnivory/herbivory,6, 7, 8, 9 with some taxa eventually reverting to carnivory.10, 11, 12 The mandible is an important tool for food acquisition in vertebrates and reflects adaptations to feeding modes and diets.¹³,¹⁴ The morphofunctional modifications accompanying the dietary changes in theropod dinosaurs are not well understood because most of the previous studies focused solely on the cranium and/or were phylogenetically limited in scope,¹²,15, 16, 17, 18, 19, 20, 21 while studies that include multiple clades are usually based on linear measurements and/or discrete osteological characters.⁸,²² Given the potential relationship between macroevolutionary change and ontogenetic pattern,²³ we explore whether functional morphological patterns observed in theropod mandibular evolution show similarities to the ontogenetic trajectory. Here, we use finite element analysis to study the mandibles of non-avialan coelurosaurian theropods and demonstrate how feeding mechanics vary between dietary groups and major clades. We reveal an overall reduction in feeding-induced stresses along all theropod lineages through time. This is facilitated by a post-dentary expansion and the development of a downturned dentary in herbivores and an upturned dentary in carnivores likely via the “curved bone effect.” We also observed the same reduction in feeding-induced stress in an ontogenetic series of jaws of the tyrannosaurids Tarbosaurus and Tyrannosaurus, which is best attributed to bone functional adaptation. This suggests that this common tendency for structural strengthening of the theropod mandible through time, irrespective of diet, is linked to “functional peramorphosis” of bone functional adaptations acquired during ontogeny.
... Based on the phylogenetic bracket of the two-chambered stomachs, together with the generality of gastroliths among archosaurs including non-avian dinosaurs, (e.g., Kobayashi et al., 1999;Cerda, 2008;Lee et al., 2014), neornithine style muscular "gizzard" had previously been considered as a plesiomorphic feature of Archosauria (Varricchio, 2001;Fritz et al., 2011). However, the homology of avian and crocodylian "gizzards" is considered ambiguous (Schwenk and Rubega, 2005). ...
... Besides, this study conducts analyses that provide new implications of the digestive function of crocodylian gastroliths. Neornithine gastrolith mass is known to be correlated with a body mass (Wings and Sander, 2007), and the relationship is utilized as a proxy for the digestive use of dinosaur gastroliths (Wings and Sander, 2007;Cerda, 2008;Lee et al., 2014). Furthermore, avian dietary habits are strongly related to the occurrence frequencies of gastroliths (Best and Gionfriddo, 1991;Gionfriddo and Best, 1996;Gionfriddo and Best, 1999). ...
... The earliest definitive ornithomimosaur is known from the Lower Cretaceous (Berriasian-Valanginian) Kirkwood Formation of South Africa (de Klerk et al., 2000), whereas a possible ornithomimosaurian occurrence from the Upper Jurassic (Kimmeridgian) Alcobaça Formation of Portugal has recently been suggested (Hattori et al., 2023). There are two major clades within Ornithomimosauria, which are Ornithomimidae and Deinocheiridae (Choiniere et al., 2012;Lee et al., 2014). These two clades can be hypothesized to have diverged earlier in the Early Cretaceous due to the presence of an oldest deinocheirid Tyrannomimus fukuiensis from the Aptian Kitadani Formation of Fukui, Japan (Hattori et al., 2023), as well as a possible deinocheirid Kinnareemimus khonkaenensis from the Barremian Sao Khua Formation (Samathi, 2024), which is the first-reported ornithomimosaur in Thailand (Buffetaut et al., 2009). ...
The Aptian-Albian Khok Kruat Formation is composed of sediments rich in dinosaur remains occur in Nakhon Ratchasima, Thailand. Here, we report a distal part of right metatarsal III of an ornithomimosaur (NRRU-F01020052) found at the Ban Krok Duean Ha dinosaur locality in 2017. Notable characteristics of this specimen are the subtle mediolateral expansion, the almost triangular cross-section with an extremely narrow posterior plane in distal diaphysis, and the concave posterior surface neighboring to the distal condyle. The combination of these characters indicates that NRRU-F01020052 is attributable to an ornithomimosaur with an incomplete arctometatarsalian pes. This discovery indicates that Thailand had a great diversity of ornithomimosaurs in the early to late Early Cretaceous, corresponds to the Asian ornithomimosaurian diversity.
... An informal supertree of 180 taxa (electronic supplementary material, figure S1), consisting of 158 theropods, eight non-theropod dinosaurs and 14 Mesozoic non-dinosaurian archosaurs, was assembled from numerous literature sources as follows: Choiniere et al. [44], Canale et al. [45], Currie and Evans [46], Funston et al. [47], Hattori et al. [48], Kobayashi et al. [49], Kubo and Kubo [50], Kubo et al. [9], Lee et al. [51], Macdonald and Currie [52], McFeeters et al. [53], Nesbitt et al. [32], Tsuihiji et al. [54], Xing et al. [55] and Zanno et al. [31]. We reconstructed a phylogeny using Mesquite 3.40 [56]. ...
Coelurosauria, including modern birds, represents a successful group of theropod dinosaurs that established a high taxonomic diversity and significant morphological modifications. In the evolutionary history of this group, a specialized foot morphology, the arctometatarsus, evolved independently in several lineages and has been considered an adaptation for cursoriality. While its functional significance has been extensively studied, the temporal pattern of this parallel evolution, as well as its origin and influencing factors, remains largely unresolved. Here, we show the temporal evolution of cursorial traits, including the arctometatarsus and hind limb proportions. Our study reveals that the proportional elongation of distal hind limb segments preceded the evolution of the arctometatarsus in ornithomimosaurs and oviraptorosaurs. In contrast, in tyrannosauroids, alvarezsaurs and troodontids, the proportional elongation of the tibia and metatarsals occurred in parallel with the acquisition of the arctometatarsus. The evolutionary history of the arctometatarsus further highlights the presence of a phylogenetic constraint outside Coelurosauria, as this foot specialization is restricted to members of this group. Finally, our date estimation, based on compiled evolutionary patterns, demonstrates that these cursorial traits emerged during the mid-Cretaceous (93–120 Ma), suggesting selection on theropod locomotor performance throughout this interval.
... Rauhut et al. (2012) interpreted Sciurumimus, and possibly also Juravenator, as immature members of the non-coelurosaurian group Megalosauroidea. Subsequent phylogenetic analyses have not supported a megalosauroid status for Sciurumimus or Juravenator (e.g., Godefroit et al., 2014;Cau, 2018), recovering them among the earliest diverging coelurosaurs. Foth et al. (2020) discussed the possibility that Juravenator was not a coelurosaurian. ...
Known since the 19 th Century, the compsognathids are among the smallest predatory dinosaurs, and include the first feathered non-avian species found. Traditionally, compsognathids have been considered small and unspecialized coelurosaurs, closer to birds than large-bodied forms like allosauroids and megalosaurids. Yet, all known compsognathids are based on skeletally-immature specimens, and this challenges the accuracy of their traditional phyletic placement. Despite the role of heterochrony in dinosaur evolution is widely recognized, the impact of ontogenetic-biased miscodings in shaping theropod phylogenetics is mostly underestimated. Herein, I show that the standard framework of theropod macroevolution is biased by a series of coding artifacts which violate semaphoront equality prescribed by phylogenetic systematics. I introduce "Ontogenetic State Partitioning" (OSP), a novel coding protocol which integrates ontogenetic and morphological variation under a total evidence approach, and apply it to a densely sampled data set focusing on Mesozoic theropods. The phylogenetic analysis dismissed "Compsognathidae" from being a natural group: its members are identified as juvenile morphs nested among several non-maniraptoriform tetanuran lineages. Conservatism in the immature body plan and greater disparity among large-sized adults differentiate the predatory communities dominated by non-coelurosaurian species (e.g., the so called "triumvirates") from the maniraptoriform-tyrannosaurid faunas (herein named "tyrannies"). This clade-specific differentiation among the communities is confirmed by an analysis of the predatory guild structures including all growth stages: triumvirates and tyrannies result as particular cases along a continuum of communities regulated mainly by alternative contributions of the small-and medium-sized classes. The oldest tyrannies (early Late Cretaceous in age) cluster among non-tyranny communities, supporting the hypothesis that tyrannosaurid-dominated faunas acquired their peculiar structure only after the extinction of the non-coelurosaurian components. The macroevolutionary trajectory that led the maniraptoriforms to realize the avian-like biology may have precluded them from occupying hypercarnivorous large-bodied niches: this bauplan constraint would have favored the tyrannosauroids in opportunistically assuming the apex predatory roles in Late Cretaceous Asiamerica but not elsewhere. The large-scale structure of the Cenozoic radiation of birds is coherent with the framework introduced herein.
... Many large land animals became extinct at the end-Triassic, but the dinosaurs survived, allowing them to evolve into various forms and dominate terrestrial ecosystems. Documented dinosaur fossils and tracks have facilitated a better understanding of the evolutionary history of dinosaurs and allowed for the evaluation of biogeographic hypotheses regarding the distribution of middle-late Mesozoic vertebrate fossils in Mongolia, Japan, China, and the Korean Peninsula (Norell and Xu, 2005;Chang et al., 2009a;Lee et al., 2014Lee et al., , 2022Brusatte et al., 2012;Wang et al., 2019a;Tanaka et al., 2020;Baag and Lee, 2022;Pei and Xu, 2022;Yu et al., 2022). Well-preserved feathered dinosaurs have improved our understanding of the transition between the nonavian theropod dinosaurs and birds Turner et al., 2007;Li et al., 2014;Hu et al., 2018;O'Connor et al., 2022), and mammal fossils have demonstrated how early mammals succeeded alongside dinosaurs and occupied niches in the Cretaceous terrestrial ecosystems Yuan et al., 2013;Bi et al., 2014;Luo et al., 2015;Mao et al., 2021). ...
... In Asia, ornithomimids were common in pre-Campanian strata of Uzbekistan and China (Gilmore, 1933;Smith and Galton, 1990;Kobayashi and Lü, 2003;Sues and Averianov, 2016;Yao, Sullivan, Tan, and Xu, 2022), but are rare in the Campanian of Mongolia (Chinzorig et al., 2017). However, the greatest taxonomic diversity of ornithomimosaurs is known from the Maastrichtian Nemegt Formation of Mongolia (Osmólska and Roniewicz, 1970;Osmólska, Roniewicz, and Barsbold, 1972;Barsbold, 1988;Kobayashi and Barsbold, 2006;Bronowicz, 2011;Lee et al., 2014;Chinzorig et al., 2018). Another ornithomimid taxon is present from the contemporary Qiupa Formation in Henan Province, China (Xu et al., 2011). ...
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.
... times as long in anteroposterior length as other posterior caudal vertebrae (Fig 8E and 8F), which likely consisted of more than two fused centra as in other Maniraptoriformes [56][57][58]. ...
Alvarezsauria is a group of early-branching maniraptoran theropods that are distributed globally from the Late Jurassic to the latest Cretaceous. Despite recent increases in the fossil record of this group, the scarcity of complete specimens still restricts interpreting their detailed anatomy, ecology, and evolution. Here, we report a new taxon of derived alvarezsaur, Jaculinykus yaruui gen. et sp. nov., from the Late Cretaceous of Mongolia, which represents a nearly complete and articulated skeleton. Our phylogenetic analysis reveals that Jaculinykus belongs to the sub-clade of Alvarezsauridae, Parvicursorinae, and forms a mononphyletic group with Mononykus and Shuvuuia. Its well-preserved manus has only two fingers, composed of a hypertrophied digit I and greatly reduced digit II, which implies an intermediate condition between the tridactyl manus of Shuvuuia and monodactyl manus of Linhenykus. This highlights a previously unrecognized variation in specialization of alvarezsaurid manus. Notably, the preserved posture of the specimen exhibits a stereotypical avian-like sleeping position seen in the troodontids Mei and Sinornithoides. Evidence of this behavior in the alvarezsaur Jaculinykus suggests that stereotypically avian sleeping postures are a maniraptoran synapomorphy, providing more evidence of bird-like traits being distributed broadly among avian ancestors.
... Although our understanding about the interrelationships between non-avialan theropods and early diverging avialans, respectively, has been advanced by recent studies 20,26,[35][36][37] , a unified study explicitly focusing on this broad phylogeny with sufficient taxonomic representations is lacking. Therefore, an informal supertree was assembled using combined information from recent phylogenetic studies of avialan and non-avialan theropods 13,35,[37][38][39] . To account for taxa with competing phylogenetic placements in different hypotheses, especially taxa close to the origin of avialans whose phylogenetic positions have long been debated, such as Anchiornis and the scansoriopterygids: Anchiornis was assigned to avialans or troodontids 2,20,24,35 and scansoriopterygids were considered as a sister clade uniting avialans and deinonychus, or as sister clade to oviraptorans 12,35,40 . ...
The origin of birds from theropod dinosaurs involves many changes in musculoskeletal anatomy and epidermal structures, including multiple instances of convergence and homology-related traits that contribute to the refinement of flight capability. Changes in limb sizes and proportions are important for locomotion (for example, the forelimb for bird flight); thus, understanding these patterns is central to investigating the transition from terrestrial to volant theropods. Here we analyse the patterns of morphological disparity and the evolutionary rate of appendicular limbs along avialan stem lineages using phylogenetic comparative approaches. Contrary to the traditional wisdom that an evolutionary innovation like flight would promote and accelerate evolvability, our results show a shift to low disparity and decelerated rate near the origin of avialans that is largely ascribed to the evolutionarily constrained forelimb. These results suggest that natural selection shaped patterns of limb evolution close to the origin of avialans in a way that may reflect the winged forelimb ‘blueprint’ associated with powered flight.
... Whereas paleopathological studies of predatory theropods are numerous, those of omnivorous and/or herbivorous theropods are far less common, with only a handful undertaken among non-deinonychosaurian maniraptoriformes such as therizinosaurs, oviraptorosaurs, and ornithomimosaurs (e.g., Beguesse et al., 2019;Rothschild & Lambert, 2019;Rothschild & Tanke, 1991). This is surprising given the relatively abundant record of ornithomimosaurians specifically, whose fossils are known from extensive geographic and temporal distributions and even mass assemblages (Kobayashi & Lü, 2003), and whose paleobiology has been extensively investigated via studies on biomechanics (Nicholls & Russell, 1985;Paul, 1998), myology (Russell, 1972), integumentary structure (Lingham-Soliar, 2016;Zelenitsky et al., 2012), ontogeny (Cullen et al., 2014;Kobayashi & Lü, 2003;Makovicky et al., 2009;Skutschas et al., 2017;Varricchio et al., 2008), and feeding ecology (Chinzorig et al., 2018;Kobayashi et al., 1999;Lee et al., 2014;Norell et al., 2001). ...
Paleopathological diagnoses provide key information on the macroevolutionary origin of disease as well as behavioral and physiological inferences that are inaccessible via direct observation of extinct organisms. Here we describe the external gross morphology and internal architecture of a pathologic right second metatarsal (MMNS VP‐6332) of a large‐bodied ornithomimid (~432 kg) from the Santonian (Upper Cretaceous) Eutaw Formation in Mississippi, using a combination of X‐ray computed microtomography (microCT) and petrographic histological analyses. X‐ray microCT imaging and histopathologic features are consistent with multiple complete, oblique to comminuted, minimally displaced mid‐diaphyseal cortical fractures that produce a “butterfly” fragment fracture pattern, and secondary osteomyelitis with a bone fistula formation. We interpret this as evidence of blunt force trauma to the foot that could have resulted from intra‐ or interspecific competition or predator–prey interaction, and probably impaired the function of the metatarsal as a weight‐bearing element until the animal's death. Of particular interest is the apparent decoupling of endosteal and periosteal pathological bone deposition in MMNS VP‐6332, which produces transverse sections exhibiting homogenously thick endosteal pathological bone in the absence of localized periosteal reactive bone. These distribution and depositional patterns are used as criteria for ruling out a pathological origin in favor of a reproductive one for unusual endosteal bone in fossil specimens. On the basis of MMNS VP‐6332, we suggest caution in their use to substantiate a medullary bone identification in extinct archosaurians.
... In contrast, ornithomimosaur dinosaurs possess a single and strong cnemial crest with a dorsal apex that projects above the level of the articular surface, particularly in members of the Deinocheiridae family [e.g. Beishanlong grandis (FRDC-GS GJ (06) 01-18;Makovicky et al., 2010), Deinocheirus mirificus (MPC-D 100/127;Lee et al., 2014) and Garudimimus brevipes (GIN 100/13;Kobayashi and Barsbold, 2005) (Fig. 7b)]; also, the cnemial crest curves outwards towards the fibula [e. g. ...
Herein we report the first caenagnathid dinosaur (Theropoda, Oviraptorosauria) material from the Upper Cretaceous Cerro del Pueblo (CdP) Formation of Coahuila, Mexico, comprising three partial tibiae. Caenagnathids are an unusual group of oviraptorosaur theropod dinosaurs mostly known by way of their toothless, beak-like jaws. Fossils ascribed to Caenagnathidae are well-known from many Late Cretaceous localities in Asia and North America, with a high number of specimens found in the mid-latitudes of North America. The postcranial material described in this study represents the southernmost Laramidian locality in which caenagnathids have been found to date and adds to the scant number of caenagnathid fossils found in southern North America. Overall, these discoveries underscore the high diversity of the dinosaurian fauna found in the CdP Formation.
... In contrast, ornithomimosaur dinosaurs possess a single and strong cnemial crest with a dorsal apex that projects above the level of the articular surface, particularly in members of the Deinocheiridae family [e.g. Beishanlong grandis (FRDC-GS GJ (06) 01-18;Makovicky et al., 2010), Deinocheirus mirificus (MPC-D 100/127;Lee et al., 2014) and Garudimimus brevipes (GIN 100/13;Kobayashi and Barsbold, 2005) (Fig. 7b)]; also, the cnemial crest curves outwards towards the fibula [e. g. ...
... Many large land animals were wiped out but dinosaurs survived to evolve into a wide range of forms and increase in number. Dinosaur fossils, including footprints and eggs from Jurassic and Cretaceous strata in Mongolia, China, Japan and the Korean Peninsula, have contributed to paradigms of dinosaurian evolution by recording biogeographical distributions of middle-late Mesozoic vertebrates in East Asia (Lee et al. 2014;Currie 2016;Wang et al. 2018;Tanaka et al. 2020;Kim et al. 2022). The discoveries of feathered dinosaurs have filled a critical gap in the non-avian theropod dinosaur-bird transition record to reveal that volant behaviour emerged repeatedly in dinosaurs closely related to birds (Norell and Clarke 2001;Clarke et al. 2005;Turner et al. 2007;Li et al. 2012;Kiat et al. 2020). ...
Since the late twentieth century, palaeontological and geological evidence from East Asia has contributed to significant advances in the understanding of the Mesozoic world. Geological Society Special Publication 521 covers a wide range of topics that subdivide into four themes. These include: (1) clues and evidence from vertebrate fossils; (2) clues and evidence from invertebrate and plant fossils; (3) significant fossils from amber; and (4) palaeoenvironments and palaeoecosystems. The volume features 18 articles by 53 authors from different disciplines, including geochronology, palaeontology, stratigraphy, sedimentology, tectonics and geochemistry.
... thought to be moving in a similar way as a bird. An excellent presentation was published by Lee et al.for Deinocheirus mirificus, which can be watched in a video sequence[24]. ...
... The diversity of tail construction observed among different clades, including short tails in oviraptorosaurs (39), sustained caudal vertebral modification along the avian stem lineage (46), and trellis-like ossified tendons in ornithopods (48), suggests a diversity in dynamic tail functions that remains to be fully understood. Differences in other body proportions, such as very long arms in therizinosaurs (49) and deinocheirids (50), also invite investigation of whole-animal functional integration across Dinosauria more broadly. ...
Locomotion has influenced the ecology, evolution, and extinction of species throughout history, yet studying locomotion in the fossil record is challenging. Computational biomechanics can provide novel insight by mechanistically relating observed anatomy to whole-animal function and behavior. Here, we leverage optimal control methods to generate the first fully predictive, three-dimensional, muscle-driven simulations of locomotion in an extinct terrestrial vertebrate, the bipedal non-avian theropod dinosaur Coelophysis. Unexpectedly, our simulations involved pronounced lateroflexion movements of the tail. Rather than just being a static counterbalance, simulations indicate that the tail played a crucial dynamic role, with lateroflexion acting as a passive, physics-based mechanism for regulating angular momentum and improving locomotor economy, analogous to the swinging arms of humans. We infer this mechanism to have existed in many other bipedal non-avian dinosaurs as well, and our methodology provides new avenues for exploring the functional diversity of dinosaur tails in the future.
... For the second question, although most fossils themselves are not well-preserved, the preserved elements may help to reconstruct the missing parts. Many dinosaur species are named based on limited fossils, for example, Deinocheirus (Dinosauria, Theropoda) was firstly collected in 1965 (Kielan-Jaworowska and Dovchin, 1966), when only forelimbs and several other fragments were discovered, then Ostrom (1972) recognized its affinity with ornithomimosaurs, which was later supported by Senter (2007), and finally the discovery of almost entire skeletons ended most arguments by Lee et al. (2014). ...
The construction of morphological character matrices is central to paleontological systematic study, which extracts paleontological information from fossils. Although the word information has been repeatedly mentioned in a wide array of paleontological systematic studies, its meaning has rarely been clarified nor specifically defined. It is important, however, to establish a standard to measure paleontological information because fossils are hardly complete, rendering the recognition of homologous and homoplastic structures difficult. Here, based on information theory, we show the deep connections between paleontological systematic study and communication system engineering. Information is defined as the decrease of uncertainty and it is the information in morphological characters that allows distinguishing operational taxonomic units (OTUs) and reconstructing evolutionary history. We propose that concepts in communication system engineering such as source coding and channel coding, correspond to the construction of diagnostic features and the entire character matrices in paleontological studies. The two coding strategies should be distinguished following typical communication system engineering, because they serve dual purposes. With character matrices from six different vertebrate groups, we analyzed their information properties including source entropy, mutual information, and channel capacity. Estimation of channel capacity shows character saturation of all matrices in transmitting paleontological information, indicating that, due to the presence of noise, oversampling characters not only increases the burden in character scoring, but also may decrease quality of matrices. We further test the use of information entropy, which measures how informative a variable is, as a character weighting criterion in parsimony-based systematic studies. The results show high consistency with existing knowledge with both good resolution and interpretability.
... The theropod component of this fauna is particularly well known, in contrast to other parts of the world, where the delicate bones of theropods are rarely preserved [8,9]. From the Nemegt Formation alone, a diverse assemblage of alvarezsaurids [10], dromaeosaurs [11], ornithomimids [12,13], oviraptorosaurs [14,15], therizinosaurs [16], troodontids [17], and tyrannosaurs [18,19] is known, comprising nearly 250 associated skeletons [7,20]. Whereas tyrannosaurs and ornithomimids form the bulk of the collected specimens, the oviraptorosaurs are the most diverse component of the fauna, known from at least nine genera [14,15]. ...
The Nemegt Formation of the Gobi Desert of Mongolia has produced one of the most abundant and diverse oviraptorosaur records globally. However, the caenagnathid component of this fauna remains poorly known. Two caenagnathid taxa are currently recognized from the Nemegt Formation: Elmisaurus rarus and Nomingia gobiensis. Because these taxa are known from mostly non-overlapping material, there are concerns that they could represent the same animal. A partial, weathered caenagnathid skeleton discovered adjacent to the holotype quarry of Nomingia gobiensis is referable to Elmisaurus rarus, revealing more of the morphology of the cranium, mandible, pectoral girdle, and pubis. Despite metatarsals clearly exhibiting autapomorphies of Elmisaurus rarus, overlapping elements are identical to those of Nomingia gobiensis, and add to a growing body of evidence that these taxa represent a single morphotype. In the absence of any positive evidence for two caenagnathid taxa in the Nemegt Formation, Nomingia gobiensis is best regarded as a junior synonym of Elmisaurus rarus. Low caenagnathid diversity in the Nemegt Formation may reflect broader coexistence patterns with other oviraptorosaur families, particularly oviraptorids. In contrast to North America, competition with the exceptionally diverse oviraptorids may have restricted caenagnathids to marginal roles in Late Cretaceous Asian ecosystems.
... A series of impressed neurovascular grooves characterizes the medial aspect of the anterior end of the dentary in Harpymimus suggesting this region may have also been covered by a rhamphotheca (Kobayashi and Barsbold, 2005). Besides the Early Cretaceous ornithomimosaurians, all known Late Cretaceous ornithomimosaurians have beaks that were covered with rhamphothecae (Kobayashi et al., 1999;Norell et al., 2001a;Kobayashi and Lü, 2003;Lee et al., 2014a). These data suggest the loss of dentition in ornithomimosaurs proceeds from posterior to anterior (Choiniere et al., 2012) sary to investigate whether the evolutionary tooth reduction in this clade is heterochronically controlled. ...
Recent discoveries of exquisitely preserved nonavialan and avialan theropod dinosaurs have not only prompted studies of theropod tooth morphologies, but have also provided information about the origin and early evolution of avian beaks. Recent studies on beak morphologies and morpho-genesis in Darwin's finches have greatly improved our understanding of how avian beaks adapt to various ecological niches, but the question of how birds lost their teeth during the course of evolution has long been debated. Evolutionary developmental experiments performed on extant bird embryos bridge the gap between paleontological and neontological evidence, suggesting that the avian beak could have originated through heterochronic truncation of odontogenesis over evolutionary time. Here, we systematically review independently evolved regional and complete edentulism present in nonavialan and avialan theropod dinosaurs, and suggest that the tooth-reduction processes of different jaw bones are likely to be independently controlled. Through reviewing the recent advances of molecular regulations involved in tooth and avian beak morphogenic processes, we suggest that several molecules regulating the development of the avian beak also mediate the growth of keratinous rhamphothecae, and the divergence of odontogenic signalling pathways are likely to have accounted for both of these processes.
... This is the case of the tooth-less ornithomimosaur Deinocheirus from the Late Cretaceous of Mongolia. This large-sized theropod, with giant forelimbs and a long spatulated beak, is interpreted as an omnivore, eating fishes and browsing herbaceous plants in rivers that traversed floodplain environments (Fig. 7.5;Lee et al. 2014). ...
If we imagine walking through Mesozoic lands, we would be able to observe vertebrates with peculiar combinations of morphological traits, some of which would seem to be intermediary to animals seen today. We would witness a terrestrial vertebrate fauna dominated by dinosaurs of various sizes and diversity, accompanied by many other animal groups that often are overlooked. Current research suggests that many of the main vertebrate clades existing today originated or diversified sometime in the Triassic or Early to Middle Jurassic. Herein, we profile some of the major transformations in both terrestrial and aquatic vertebrate evolution during the Mesozoic. We highlight: the appearance of features that allowed sauropod dinosaurs to become the largest animals to ever walk on Earth’s continents, the appearance of herbivory among the usually carnivorous theropod dinosaurs, and we follow the specific changes that led to the evolution of avian flight. Our Mesozoic tour across the globe will allow us to see how different evolutionary forces led to convergent shifts to quadrupedality in ornithischian dinosaurs and to an aquatic lifestyle in turtles, crocodiles, and plesiosaurs. Last, but not least, we examine changes in the Mesozoic fauna linked to the rise of mammals, and the diversification patterns in several clades of fishes after the End-Permian Mass Extinction.
... Notably, several ornithomimosaurs, including Harpymimus and Deinocheirus, show one or two pneumatic foramina on the exterior surfaces of the premaxillae (e.g. Makovicky et al., 2004;Kobayashi & Barsbold, 2005;Lee et al., 2014). These pneumatic foramina probably interacted with invading anterior diverticula of the antorbital sinus, such as the promaxillary sinus and maxillary antrum, both of which extend anteriorly in other coelurosaurs (e.g. ...
Dinosaurs are notable for their extensive skeletal pneumaticity, a feature that may have helped facilitate the development of various ‘extreme’ body plans in this group. Despite its relevance to understanding the evolution of the avian body plan, this feature has only been described in detail for a few non-avian dinosaurs, and cranial pneumaticity outside the braincase remains poorly documented. I describe facial pneumatic features in members of the Dromaeosauridae, a clade of hypercarnivorous dinosaurs closely allied to birds. Variation in the pneumaticity of the nasals and jugals, the position and shape of the pneumatic fenestrae of the maxilla and the border of the antorbital fossa shows that facial pneumaticity differed substantially among closely related dromaeosaurids and other bird-like dinosaurs. Ancestral state reconstructions of facial pneumaticity in coelurosaurs suggest a complex evolutionary history for these features. Surprisingly, the general trend along the path towards birds was the loss or reduction of superficial pneumatic features on the snout and cheek. Some facial pneumatic features seem to have evolved secondarily in some derived bird-like forms. The results show superficial facial pneumaticity did not increase in coelurosaurs and emphasize the complexity of the evolution of pneumatization in the lineage leading to birds.
... Furthermore, pneumaticity up to the middle caudals has only been observed, aside from in megaraptorans, in some oviraptorosaurs, selected therizinosauroids and Deinocheirus (Benson et al., 2010;Lee et al., 2014). ...
Aoniraptor libertatem is a mid‐sized megaraptoran that comes from the Late Cretaceous (Turonian) Huincul Formation at Río Negro province, Patagonia, Argentina. In this study, we conducted a detailed analysis of pneumaticity of the sacrum and tail of Aoniraptor . This shows a complex structure within these vertebrae, being composed by small diverticulae surrounding large pneumatic canals and a central chamber that opens outside through pleurocoels or pneumatic canals. Further, we carried out a histologic analysis which confirms the pneumatic nature of these anatomical features. Both analyses found that chevrons in Aoniraptor were invaded by pneumaticity, a feature that appears to be unique to this taxon. In addition, a comparative analysis between Aoniraptor and other theropods (e.g. Gualicho and other megaraptorans) was carried out. This resulted in the modification of previous schemes about the evolution of pneumaticity through Theropoda, the finding of some evolutionary pneumatic traits through Megaraptora, and the usefulness of pneumatic traits as a taxonomic tool.
... Given that prominent hyposphenes are present in at least some anterior caudal vertebrae of many evolutionarily disparate theropods, including (but not limited to) Dilophosaurus (Welles, 1984), Ceratosaurus (Madsen and Welles, 2000), Elaphrosaurus (Rauhut and Carrano, 2016), Masiakasaurus (Carrano et al., 2011), most abelisaurids (Bonaparte et al., 1990;Coria et al., 2002;Méndez, 2014), Monolophosaurus Zhao et al., 2010), Piatnitzkysaurus (Bonaparte, 1986), Baryonyx (Charig and Milner, 1997), Sinraptor , carcharodontosaurids (Canale et al., 2015), Neovenator (Brusatte et al., 2008), Tyrannosaurus (Brochu, 2003), Bagaraatan (Osmólska, 1996) and Fukuivenator (Azuma et al., 2016), the fact that the phylogenetic relevance of this feature was not assessed is perhaps unsurprising. However, Makovicky (1995) explicitly stated that ornithomimosaurs lack hyposphene-hypantrum articulations in their caudal vertebrae, and a survey of the literature relevant to ornithomimosaurs failed to reveal any exceptions to this rule (although hyposphene-hypantrum articulations are present in the dorsal vertebrae of some taxa, like Garudimimus (Kobayashi and Barsbold, 2005), Deinocheirus (Lee et al., 2014) and Struthiomimus (Stefanic and Nesbitt, 2019)). Thus, the referral of NMV P186168 to Ornithomimosauria is untenable, in agreement with Novas et al. (2013). ...
Elaphrosaurinae is an enigmatic clade of gracile ceratosaurian theropod dinosaurs known from the Late Jurassic of Africa (Elaphrosaurus bambergi) and Asia (e.g., Limusaurus inextricabilis), and the early Late Cretaceous of Argentina (Huinculsaurus montesi). Elaphrosaurinae is often placed within Noasauridae as the sister taxon to Noasaurinae, a clade of small-bodied theropods that lived in South America, Africa, Madagascar and India throughout much of the Cretaceous. Herein, we report the first evidence of Elaphrosaurinae from Australia: a nearly complete middle cervical vertebra from the upper Lower Cretaceous (lower Albian) Eumeralla Formation of Cape Otway, Victoria, Australia. The fact that this site would have been situated at ~76°S towards the end of the Early Cretaceous (~110–107 Ma) implies that elaphrosaurines were capable of tolerating near-polar palaeoenvironments, whereas its age indicates that elaphrosaurines persisted in Australia until at least the late Early Cretaceous. The new Australian elaphrosaurine, in tandem with the recently described Huinculsaurus montesi from the Cenomanian–Turonian of Argentina, implies that the spatiotemporal distribution of Elaphrosaurinae has heretofore been greatly underestimated. Historic confusion of elaphrosaurines with coelurosaurs, especially ornithomimosaurs, coupled with our generally poor understanding of noasaurid evolution, might explain the apparent dearth of fossils of this theropod clade worldwide.
Adaptation to specialist ecological niches is a key innovation that has contributed to the evolutionary success of many vertebrate clades, underpinning the acquisition of diverse skull morphologies. Dinosaurs, which dominated Mesozoic terrestrial faunas, acquired herbivory multiple times, and evolution of these herbivorous adaptations is linked to drastic changes in dental and craniomandibular functional morphology, yet whether changes in functionally relevant phenotypic traits occurred more rapidly in herbivorous lineages compared to in carnivorous lineages remains largely untested in a statistical phylogenetic framework. Here, we infer rates of phenotypic evolution using phylogenetic variable‐rate models on relative biting edge (tooth row) lengths of 107 dinosaur taxa to test the hypothesis that the acquisition of herbivory is associated with rapid changes in mandibular biomechanics. We find elevated rates of biomechanical evolution in theropods with foreshortened and beaked skulls (Oviraptorosauria, Limusaurus ), as well as in ceratopsians and Diplodocus . The presence and position of a reduced tooth row and increased jaw efficiency unite these high‐rate lineages, indicating selection for greater efficiency in biting biomechanics. Large departures from the isometric scaling of these mandibular characteristics helps explain the differences in evolutionary rates in these clades and those of other herbivorous theropods (Therizinosauria, Ornithomimosauria). Additionally, we hypothesize that extreme ontogenetic changes within species lifetimes may be behind some instances of branch‐wise elevated rates. Thus, we show how exceptional rates of biomechanical evolution can reveal signatures of ecological adaptations within dinosaur lineages as well as within‐species ontogenetic sequences.
Birds consume a wide variety of food items that must be digested and absorbed. In this chapter, I provide detailed information about avian diets and the different avian dietary guilds, including insectivores, frugivores, invertivores, granivores, carnivores, scavengers, nectarivores, herbivores, and omnivores. The anatomy and physiology of the avian digestive system are also discussed in detail, with information about the interspecific variation in the anatomy and functions of each component of the digestive system, including bills, the esophagus, two-part stomach, small and large intestine ceca, cloaca, and accessory organs, including the pancreas and liver. Information about the phenotypic plasticity of the avian digestive system and regulation of food intake is also provided.
Dinosaur tracks are a key means of determining the palaeoecology and distribution of dinosaurs through time. They provide a highly complementary information source to the body (skeletal) fossil record but differ in preserving direct evidence of animals’ interactions with their environment. The UK has a rich history of ∼200 yrs of dinosaur track discovery but no recent synthesis exists. Here, we present a new dataset of dinosaur tracks in the UK. This dataset shows a close correlation between the distribution of terrestrial sediments and the preservation of dinosaur tracks through the Mesozoic, providing discrete snapshots into dinosaur communities in the Upper Triassic, Middle Jurassic and Lower Cretaceous. The dinosaur track record shows similar broad patterns of diversity and relative abundance of the major dinosaur groups (Theropoda, Sauropodomorpha, Ornithopoda, and Thyreophora) through time to the body fossil record, although differs in that body fossils are found (albeit infrequently) in marine sediments. There is a broad trend towards higher numbers of track occurrences through time and a notable increase in the relative abundance of ornithopod tracks following the Jurassic-Cretaceous boundary. The track record remains an underutilised resource with the potential to provide a much fuller view of Mesozoic dinosaur ecosystems.
Supplementary material: https://doi.org/10.6084/m9.figshare.c.6606634
The reconstruction of behavioural patterns performed by non-avian dinosaurs is an important task of palaeontology in order to globally understand how these animals interacted with their environment. Their relation with aquatic lifestyles has always been an intriguing question that has been extensively studied during the last decades, especially focused on some specific groups. The present work describes a new tracksite with 27 swimming tracks located in a fluvial setting from the Lower Cretaceous Urbion Group of La Rioja (Spain). They are preserved as natural casts with sizes between 8.5 and 29.2 cm and a predominant orientation. The tracks have been classified into 6 different morphotypes according to their morphology, and grouped into 5 different categories depending on the different pes-substrate interactions, following the proposal of Romilio et al. (2013). Some tracks were produced while the animal was moving in partial or complete buoyancy, and displacement was conducted by water and sediment impulsion, not just a mere paddling. Other tracks could be impressed in a bottom-walked, when the trackmaker touched the digit tips on the ground vertically or sub-vertically. This new tracksite confirms the capabilities of some groups of non-avian dinosaurs to interact with shallow water environments where they could print their pedes as they moved, either in complete buoyancy or during a displacement with some vertical component in the water column. It also contributes to the better understanding of swimming track morphologies as especially dependent on pes-sediment interaction and environment more than differences in pes configuration itself, causing the high variability of swimming footprints even when they belong to the same trackway. The classification of swimming tracks and footprints into categories dependent on the pes-substrate interaction could be a good guiding principle to avoid problematics about ichnotaxonomical definition.
The Cretaceous is a critical time interval that encompasses explosive diversifications of terrestrial vertebrates, particularly the period when the earliest-branching birds, after divergence from their theropod ancestors, evolved the characteristic avian Bauplan that led eventually to their global radiation. This early phylogenetic diversity is overwhelmed by the Ornithothoraces, consisting of the Enantiornithes and Ornithuromorpha, whose members evolved key derived features of crown birds. This disparity consequently circumscribes a large morphological gap between these derived clades and the oldest bird Archaeopteryx. The non-ornithothoracine pygostylians, with an intermediate phylogenetic position, are key to deciphering those evolutionary transformations, but progress in their study has been hampered by the limited diversity of known fossils. Here we report an Early Cetaceous non-ornithothoracine pygostylian, Cratonavis zhui gen. et sp. nov., that exhibits a unique combination of a non-avialan dinosaurian akinetic skull with an avialan post-cranial skeleton, revealing the key role of evolutionary mosaicism in early bird diversification. The unusually elongated scapular and metatarsal one preserved in Cratonavis highlights a breadth of skeletal plasticity, stemming from their distinct developmental modules and selection for possibly raptorial behaviour. Mapped changes in these two elements across theropod phylogeny demonstrate clade-specific evolutionary lability. Cratonavis zhui, a bird from the Early Cretaceous of China, preserves a combination of non-avialan theropod skull features and a bird-like post-cranial skeleton.
Giant carnivorous dinosaurs such as Tyrannosaurus rex and abelisaurids are characterized by highly reduced forelimbs that stand in contrast to their huge dimensions, massive skulls, and obligate bipedalism.¹,² Another group that follows this pattern, yet is still poorly known, is the Carcharodontosauridae: dominant predators that inhabited most continents during the Early Cretaceous3, 4, 5 and reached their largest sizes in Aptian-Cenomanian times.6, 7, 8, 9, 10 Despite many discoveries over the last three decades, aspects of their anatomy, especially with regard to the skull, forearm, and feet, remain poorly known. Here we report a new carcharodontosaurid, Meraxes gigas, gen. et sp. nov., based on a specimen recovered from the Upper Cretaceous Huincul Formation of northern Patagonia, Argentina. Phylogenetic analysis places Meraxes among derived Carcharodontosauridae, in a clade with other massive South American species. Meraxes preserves novel anatomical information for derived carcharodontosaurids, including an almost complete forelimb that provides evidence for convergent allometric trends in forelimb reduction among three lineages of large-bodied, megapredatory non-avian theropods, including a remarkable degree of parallelism between the latest-diverging tyrannosaurids and carcharodontosaurids. This trend, coupled with a likely lower bound on forelimb reduction, hypothesized to be about 0.4 forelimb/femur length, combined to produce this short-armed pattern in theropods. The almost complete cranium of Meraxes permits new estimates of skull length in Giganotosaurus, which is among the longest for theropods. Meraxes also provides further evidence that carchardontosaurids reached peak diversity shortly before their extinction with high rates of trait evolution in facial ornamentation possibly linked to a social signaling role.
Little is known about the large‐scale evolutionary patterns of skull size relative to body size, and the possible drivers behind these patterns, in Archosauromorpha. For example, the large skulls of erythrosuchids, a group of non‐archosaurian archosauromorphs from the Early and Middle Triassic, and of theropod dinosaurs are regarded as convergent adaptations for hypercarnivory. However, few investigations have explicitly tested whether erythrosuchid and theropod skulls are indeed disproportionately large for their body size, and whether this trend is driven by hypercarnivory. Here, we investigate archosauromorph relative skull size evolution, examining the scaling relationships between skull and body size of Palaeozoic and Mesozoic archosauromorphs using a robust phylogenetic framework and assessing the influence of potential drivers, such as taxonomy, diet, locomotory mode and inhabited biotope. Our results show that archosauromorph relative skull sizes are largely determined by phylogeny and that the other drivers have much weaker levels of influence. We find negative allometric scaling of skull size with respect to body size when all studied archosauromorphs are analysed. Within specific groups, skull size scales with positive allometry in non‐archosaurian archosauromorphs and, interestingly, scales isometrically in theropods. Ancestral reconstructions of skull–femur size ratio reveal a disproportionately large skull at the base of Erythrosuchidae and proportionately sized skulls at the bases of Theropoda, Carnosauria and Tyrannosauroidea. Relative skull sizes of erythrosuchids and theropods are therefore distinct from each other, indicating that disproportionately large skulls are not a prerequisite for hypercarnivory in archosauromorphs, and that erythrosuchids exhibit a bauplan unique among terrestrial Mesozoic carnivores.
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.
A new ankylosaurid dinosaur, Tarchia tumanovae sp. nov., has been recovered from the Upper Cretaceous Nemegt Formation of Mongolia. It includes a well-preserved skull, dorsal, sacral, caudal vertebrae, sixteen dorsal ribs, ilia, a partial ischium, free osteoderms, and a tail club. The squamosal horns of T. tumanovae are divided into two layers, the external dermal layer and the underlying squamosal horn proper. The irregular ventral margin of the base of the upper dermal layer may represent a resorption surface, suggesting that the squamosal horns of some ankylosaurids underwent extreme ontogenetic remodeling. Localized pathologies on the dorsosacral ribs and the tail provide evidence of agonistic behaviour. The tail club knob asymmetry of T. tumanovae resulted from restricted bone growth due to tail club strikes. Furthermore, T. tumanovae had an anteriorly protruded shovel-shaped beak, which is a morphological character of selective feeders. Ankylosaurid diets shifted from low-level bulk feeding to selective feeding during the Baruungoyot and the Nemegt “age” (middle Campanian-lower Maastrichtian). This ankylosaurid niche shifting might have been a response to habitat change and competition with other bulk-feeding herbivores.
Saurischian dinosaurs evolved seven orders of magnitude in body mass, as well as a wide diversity of hip joint morphology and locomotor postures. The very largest saurischians possess incongruent bony hip joints, suggesting that large volumes of soft tissues mediated hip articulation. To understand the evolutionary trends and functional relationships between body size and hip anatomy of saurischians, we tested the relationships among discrete and continuous morphological characters using phylogenetically corrected regression. Giant theropods and sauropods convergently evolved highly cartilaginous hip joints by reducing supraacetabular ossifications, a condition unlike that in early dinosauromorphs. However, transitions in femoral and acetabular soft tissues indicate that large sauropods and theropods built their hip joints in fundamentally different ways. In sauropods, the femoral head possesses irregularly rugose subchondral surfaces for thick hyaline cartilage. Hip articulation was achieved primarily using the highly cartilaginous femoral head and the supraacetabular labrum on the acetabular ceiling. In contrast, theropods covered their femoral head and neck with thinner hyaline cartilage and maintained extensive articulation between the fibrocartilaginous femoral neck and the antitrochanter. These findings suggest that the hip joints of giant sauropods were built to sustain large compressive loads whereas those of giant theropods experienced compression and shear forces.
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Ornithomimosauria is a group of medium to large, lightly built theropods that are mainly known from Cretaceous sediments of central Asia and western North America. This chapter examines the diagnostic features, evolution, and paleobiology, and phylogenetic relationships among ornithomimid taxa. Ornithomimosaurs are represented by Pelecanimimus, Gallimimus, Garudimimus, Ornithomimus, Struthiomimus, Harpymimus, Archaeornithomimus, Shenzhousaurus, and Anserimimus. They are characterized by short, delicate skulls, elongate forelimbs with a weak, nonraptorial manus, and long hindlimbs. The chapter also compares the biogeographic history of ornithomimosaurs within the broader context of several other dinosaur groups that display a predominantly Asian-North American distribution during the Cretaceous.
Several dinosaurs, notably Ouranosaurus and Spinosaurus, have vertebral columns marked by prominent arrays of elongated neural spines. Using pelycosaurian sailbacks like Dimetrodon as analogies, popular orthodoxy holds that the tall spines served as supporting struts for dorsal sails of purported thermoregulatory function, especially heat dissipation in tropical climates. It is argued here that the neural spines of Ouranosaurus, Spinosaurus, and several other long-spined dinosaurs favor bison-like humps rather than sails: 1) in functional morphology and relative elongation they are dissimilar to pelycosaur spines but homoplastically converge on the spines of high-withered ungulates; 2) the usefulness of a sail in thermoregulation has been exaggerated—in large tetrapods it would have been fairly efficient as a thermal amplifier but ineffective as a radiator; hence large sail-bearing dinosaurs in open tropical climates are improbable; 3) the insulation properties of humps favor gigantothermy, the most likely thermobiological model for large dinosaurs.
Dinosaur humps are probable adaptations for: 1) energy storage, maintenance of gigantothermy, and heat-shielding in unshaded habitats; 2) long-distance migration from feeding to nesting grounds across terrains of variable productivity; and 3) lipid conservation for production of large clutches of eggs at the nesting site. Because sacral, caudal, or dorsal humps were relatively common traits among certain groups, the fashionably anorexic image of many large dinosaurs must be emended.
Interpreting key ecological parameters, such as diet, of extinct organisms without the benefit of direct observation or explicit fossil evidence poses a formidable challenge for paleobiological studies. To date, dietary categorizations of extinct taxa are largely generated by means of modern analogs; however, for many species the method is subject to considerable ambiguity. Here we present a refined approach for assessing trophic habits in fossil taxa and apply the method to coelurosaurian dinosaurs--a clade for which diet is particularly controversial. Our findings detect 21 morphological features that exhibit statistically significant correlations with extrinsic fossil evidence of coelurosaurian herbivory, such as stomach contents and a gastric mill. These traits represent quantitative, extrinsically founded proxies for identifying herbivorous ecomorphology in fossils and are robust despite uncertainty in phylogenetic relationships among major coelurosaurian subclades. The distribution of these features suggests that herbivory was widespread among coelurosaurians, with six major subclades displaying morphological evidence of the diet, and that contrary to previous thought, hypercarnivory was relatively rare and potentially secondarily derived. Given the potential for repeated, independent evolution of herbivory in Coelurosauria, we also test for repetitive patterns in the appearance of herbivorous traits within sublineages using rank concordance analysis. We find evidence for a common succession of increasing specialization to herbivory in the subclades Ornithomimosauria and Oviraptorosauria, perhaps underlain by intrinsic functional and/or developmental constraints, as well as evidence indicating that the early evolution of a beak in coelurosaurians correlates with an herbivorous diet.
Therizinosaurs are a group of herbivorous theropod dinosaurs from the Cretaceous of North America and Asia, best known for their iconically large and elongate manual claws. However, among Therizinosauria, ungual morphology is highly variable, reflecting a general trend found in derived theropod dinosaurs (Maniraptoriformes). A combined approach of shape analysis to characterize changes in manual ungual morphology across theropods and finite-element analysis to assess the biomechanical properties of different ungual shapes in therizinosaurs reveals a functional diversity related to ungual morphology. While some therizinosaur taxa used their claws in a generalist fashion, other taxa were functionally adapted to use the claws as grasping hooks during foraging. Results further indicate that maniraptoriform dinosaurs deviated from the plesiomorphic theropod ungual morphology resulting in increased functional diversity. This trend parallels modifications of the cranial skeleton in derived theropods in response to dietary adaptation, suggesting that dietary diversification was a major driver for morphological and functional disparity in theropod evolution.
Large-scale adaptive radiations might explain the runaway success of a minority of extant vertebrate clades. This hypothesis predicts, among other things, rapid rates of morphological evolution during the early history of major groups, as lineages invade disparate ecological niches. However, few studies of adaptive radiation have included deep time data, so the links between extant diversity and major extinct radiations are unclear. The intensively studied Mesozoic dinosaur record provides a model system for such investigation, representing an ecologically diverse group that dominated terrestrial ecosystems for 170 million years. Furthermore, with 10,000 species, extant dinosaurs (birds) are the most speciose living tetrapod clade. We assembled composite trees of 614-622 Mesozoic dinosaurs/birds, and a comprehensive body mass dataset using the scaling relationship of limb bone robustness. Maximum-likelihood modelling and the node height test reveal rapid evolutionary rates and a predominance of rapid shifts among size classes in early (Triassic) dinosaurs. This indicates an early burst niche-filling pattern and contrasts with previous studies that favoured gradualistic rates. Subsequently, rates declined in most lineages, which rarely exploited new ecological niches. However, feathered maniraptoran dinosaurs (including Mesozoic birds) sustained rapid evolution from at least the Middle Jurassic, suggesting that these taxa evaded the effects of niche saturation. This indicates that a long evolutionary history of continuing ecological innovation paved the way for a second great radiation of dinosaurs, in birds. We therefore demonstrate links between the predominantly extinct deep time adaptive radiation of non-avian dinosaurs and the phenomenal diversification of birds, via continuing rapid rates of evolution along the phylogenetic stem lineage. This raises the possibility that the uneven distribution of biodiversity results not just from large-scale extrapolation of the process of adaptive radiation in a few extant clades, but also from the maintenance of evolvability on vast time scales across the history of life, in key lineages.
We performed additional preparation on the holotype skeleton of Nqwebasaurus thwazi and discovered new skeletal material. We describe this material, which includes a maxilla with small, conical, unserrated teeth and bones of the braincase, as well as parts of the holotype postcranial anatomy that were previously poorly documented. We incorporate this new anatomical information into a broadly sampled matrix designed to test theropod relationships. Our phylogenetic results hypothesize that Nqwebasaurus is the basalmost ornithomimosaur, and recover numerous characters supporting this relationship, including features of the maxilla, frontal, dentition, axial skeleton, forelimb and hindlimb. Nqwebasaurus is the first African ornithomimosaur and the first Gondwanan member of this group known from articulated skeletal material, supporting the hypothesis that coelurosaurian groups were cosmopolitan during their early evolutionary history. The presence of reduced dentition and a gastric mill in Nqwebasaurus strongly suggest that this taxon was herbivorous.
The Cretaceous theropod families Ornithomimidae, Tyrannosauridae, Troodontidae, Elmisauridae, and Avimimidae share an unusual condition of the metatarsus. The central (third) metatarsal is greatly reduced proximally, completely excluded from anterior view and nearly to completely excluded in dorsal aspect. This bone forms a wedge shape distally, triangular in transverse cross section, which is buttressed against the more columnar metatarsals II and IV. This morphology forms a tightly bound structure, here termed the arctometatarsalian condition.Morphometric analysis indicates that the arctometatarsalian structure is significantly more elongate and gracile than underived metatarsi, and this structure is associated with relatively elongate distal hind limbs per unit femoral length. When compared with limb proportions of modern and extinct mammals and flightless birds, these limb proportions are seen to be consistent with a hypothesis of enhanced cursoriality in the derived theropods. In some genera, intrametatarsal mobility in this structure may have served as an energy storage system analogous to the snap-ligaments of modern equids. The wedge-and-buttress morphology would have resulted in a more direct transmission of locomotory forces to the epipodium than in less derived theropods. Biomechanical analysis indicates that this type of relatively gracile pes was not significantly weaker than pedes of underived theropods with regards to bending stresses, due to elongation into the parasagittal plane. To the contrary, these metatarsi were well designed to withstand the forces and stresses associated with enhanced cursorial ability.
Megaherbivorous dinosaur coexistence on the Late Cretaceous island continent of Laramidia has long puzzled researchers, owing to the mystery of how so many large herbivores (6-8 sympatric species, in many instances) could coexist on such a small (4-7 million km(2)) landmass. Various explanations have been put forth, one of which-dietary niche partitioning-forms the focus of this study. Here, we apply traditional morphometric methods to the skulls of megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta to infer the ecomorphology of these animals and to test the niche partitioning hypothesis. We find evidence for niche partitioning not only among contemporaneous ankylosaurs, ceratopsids, and hadrosaurids, but also within these clades at the family and subfamily levels. Consubfamilial ceratopsids and hadrosaurids differ insignificantly in their inferred ecomorphologies, which may explain why they rarely overlap stratigraphically: interspecific competition prevented their coexistence.
Hadrosaur dinosaurs (Ornithischia: Hadrosauridae) were abundant in Late Cretaceous terrestrial environments of North America and Asia. Their derived dental and postcranial specializations for herbivory have led to the suggestion that these dinosaurs were analogous to modem ungulates in lifestyle. Ungulates display a suite of morphological fea-tures that are correlated with diet, habitat preference, and sexual dimorphism. In this paper we examine several of these same features in hadrosaurs in order to determine whether they display similar patterns under multivariate analysis. Initial results confirm the resemblances between hadrosaurs and ungulates but suggest that missing data may considerably affect the outcomes of statistical analyses. Using the hadrosaur dataset as a template, we artificially degrade the (previously complete) ungulate datasets and per-form the same analyses. Results are consistent with earlier results and provide an opportunity to assess the impact of missing data on the original multivariate structure. Our re-sults support the hypothesis that hadrosaurs were similar to ungulates in patterns of ecomorphology.
Abstract Pygostyle was previously considered as a unique structure of ornithothoracine birds, used to maneuver tail feathers. A similar structure from an oviraptorosaurian dinosaur was considered functionally associated with the rectrices as in birds. We report a pygostyle-like structure from a therizinosauroid dinosaur. The presence of filamentous integuments, but absence of rectrices, on the tail of this therizinosauroid, combined with other lines of evidence, suggests that the initial function of the pygostyle was not related to the rectrices.
As gigantic herbivores, sauropod dinosaurs were among the most important members of Mesozoic communities. Understanding their ecology is fundamental to developing a complete picture of Jurassic and Cretaceous food webs. One group of sauropods in particular, Diplodocoidea, has long been a source of debate with regard to what and how they ate. Because of their long lineage duration (Late Jurassic-Late Cretaceous) and cosmopolitan distribution, diplodocoids formed important parts of multiple ecosystems. Additionally, fortuitous preservation of a large proportion of cranial elements makes them an ideal clade in which to examine feeding behavior.
Hypotheses of various browsing behaviors (selective and nonselective browsing at ground-height, mid-height, or in the upper canopy) were examined using snout shape (square vs. round) and dental microwear. The square snouts, large proportion of pits, and fine subparallel scratches in Apatosaurus, Diplodocus, Nigersaurus, and Rebbachisaurus suggest ground-height nonselective browsing; the narrow snouts of Dicraeosaurus, Suuwassea, and Tornieria and the coarse scratches and gouges on the teeth of Dicraeosaurus suggest mid-height selective browsing in those taxa. Comparison with outgroups (Camarasaurus and Brachiosaurus) reinforces the inferences of ground- and mid-height browsing and the existence of both non-selective and selective browsing behaviors in diplodocoids.
These results reaffirm previous work suggesting the presence of diverse feeding strategies in sauropods and provide solid evidence for two different feeding behaviors in Diplodocoidea. These feeding behaviors can subsequently be tied to paleoecology, such that non-selective, ground-height behaviors are restricted to open, savanna-type environments. Selective browsing behaviors are known from multiple sauropod clades and were practiced in multiple environments.
Variation in daily activity patterns facilitates temporal partitioning of habitat and resources among species. Knowledge of temporal niche partitioning in paleobiological systems has been limited by the difficulty of obtaining reliable information about activity patterns from fossils. On the basis of an analysis of scleral ring and orbit morphology in 33 archosaurs, including dinosaurs and pterosaurs, we show that the eyes of Mesozoic archosaurs were adapted to all major types of diel activity (that is, nocturnal, diurnal, and cathemeral) and provide concrete evidence of temporal niche partitioning in the Mesozoic. Similar to extant amniotes, flyers were predominantly diurnal; terrestrial predators, at least partially, nocturnal; and large herbivores, cathemeral. These similarities suggest that ecology drives the evolution of diel activity patterns.
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.
The pre-sacral vertebrae of most sauropod dinosaurs were surrounded by interconnected, air-filled diverticula, penetrating into the bones and creating an intricate internal cavity system within the vertebrae. Computational finite-element models of two sauropod cervical vertebrae now demonstrate the mechanical reason for vertebral pneumaticity. The analyses show that the structure of the cervical vertebrae leads to an even distribution of all occurring stress fields along the vertebrae, concentrated mainly on their external surface and the vertebral laminae. The regions between vertebral laminae and the interior part of the vertebral body including thin bony struts and septa are mostly unloaded and pneumatic structures are positioned in these regions of minimal stress. The morphology of sauropod cervical vertebrae was influenced by strongly segmented axial neck muscles, which require only small attachment areas on each vertebra, and pneumatic epithelia that are able to resorb bone that is not mechanically loaded. The interaction of these soft tissues with the bony tissue of the vertebrae produced lightweight, air-filled vertebrae in which most stresses were borne by the external cortical bone. Cervical pneumaticity was therefore an important prerequisite for neck enlargement in sauropods. Thus, we expect that vertebral pneumaticity in other parts of the body to have a similar role in enabling gigantism.
Historically, ecomorphological inferences regarding theropod (i.e. 'predatory') dinosaurs were guided by an assumption that they were singularly hypercarnivorous. A recent plethora of maniraptoran discoveries has produced evidence challenging this notion. Here, we report on a new species of maniraptoran theropod, Nothronychus graffami sp. nov. Relative completeness of this specimen permits a phylogenetic reassessment of Therizinosauria-the theropod clade exhibiting the most substantial anatomical evidence of herbivory. In the most comprehensive phylogenetic study of the clade conducted to date, we recover Therizinosauria as the basalmost maniraptoran lineage. Using concentrated changes tests, we present evidence for correlated character evolution among herbivorous and hypercarnivorous taxa and propose ecomorphological indicators for future interpretations of diet among maniraptoran clades. Maximum parsimony optimizations of character evolution within our study indicate an ancestral origin for dietary plasticity and facultative herbivory (omnivory) within the clade. These findings suggest that hypercarnivory in paravian dinosaurs is a secondarily derived dietary specialization and provide a potential mechanism for the invasion of novel morpho- and ecospace early in coelurosaurian evolution-the loss of obligate carnivory and origin of dietary opportunism.
Ornithomimosaurs (ostrich-mimic dinosaurs) are a common element of some Cretaceous dinosaur assemblages of Asia and North America. Here, we describe a new species of ornithomimosaur, Beishanlong grandis, from an associated, partial postcranial skeleton from the Aptian-Albian Xinminpu Group of northern Gansu, China. Beishanlong is similar to another Aptian-Albian ornithomimosaur, Harpymimus, with which it shares a phylogenetic position as more derived than the Barremian Shenzhousaurus and as sister to a Late Cretaceous clade composed of Garudimimus and the Ornithomimidae. Beishanlong is one of the largest definitive ornithomimosaurs yet described, though histological analysis shows that the holotype individual was still growing at its death. Together with the co-eval and sympatric therizinosaur Suzhousaurus and the oviraptorosaur Gigantraptor, Beishanlong provides evidence for the parallel evolution of gigantism in separate lineages of beaked and possibly herbivorous coelurosaurs within a short time span in Central Asia.
The independent evolution of a bird-like tail has been discovered in an oviraptorosaur.
Polished pebbles occasionally found within skeletons of giant herbivorous sauropod dinosaurs are very likely to be gastroliths (stomach stones). Here, we show that based on feeding experiments with ostriches and comparative data for relative gastrolith mass in birds, sauropod gastroliths do not represent the remains of an avian-style gastric mill. Feeding experiments with farm ostriches showed that bird gastroliths experience fast abrasion in the gizzard and do not develop a polish. Relative gastrolith mass in sauropods (gastrolith mass much less than 0.1% of body mass) is at least an order of magnitude less than that in ostriches and other herbivorous birds (gastrolith mass approximates 1% of body mass), also arguing against the presence of a gastric mill in sauropods. Sauropod dinosaurs possibly compensated for their limited oral processing and gastric trituration capabilities by greatly increasing food retention time in the digestive system. Gastrolith clusters of some derived theropod dinosaurs (oviraptorosaurs and ornithomimosaurs) compare well with those of birds, suggesting that the gastric mill evolved in the avian stem lineage.
Remains of bipedal saurischians from lacustrine strata of Albian age in the Alxa ("Alashan") Desert of Inner Mongolia represent a new taxon and the most complete remains of an Early Cretaceous theropod so far discovered in Asia. A skeletal reconstruction generally resembles that of a moderately large prosauropod with long arms and a short tail. However, in its detailed morphology the reptile appears to be close to the ancestry of the Therizinosauridae Maleev, 1954 (for which Segno-sauridae Perle, 1979 is probably a junior synonym). These theropods are best referred to the Tetanurae of Gauthier, 1986. However, a provisional analysis of the distribution of therizinosauroid characters within tetanurans suggests the existence of two subordinate groups: the Carnosauria (Allosaurus, dromaeosaurids, and tyrannosaurids) and the Oviraptorosauria (including therizinosauroids, ornithomimids, troodontids, and oviraptorids).
Fancy Feathers
In the past few decades, an increasing number of dinosaurs have been shown to have possessed feathers. While it seems likely that feathers themselves may have evolved for thermoregulation, the original function of wings has been less clear and remained a matter of debate. Based on examination of three Theropod specimens from the genus Ornothomimus , Zelenitsky et al. (p. 510 ) conclude that the feathered wing may have evolved not for locomotion or prey capture (the animals were herbivores), but rather as a courtship display. All of the individuals examined had a covering consisting of short filamentous feathers, but the adult specimens, which would have reached sexual maturity, also had long shafted feathers on their forelimbs.
Repeated intervals of block-faulting across the Gobi Basin produced a complex mosaic of grabens and semigrabens which were infilled with vertebrate-bearing strata of late Mesozoic age. Although it is nowhere preserved in its entirety, superpositional relationships between the major lithostratigraphic units permit the reconstruction of a composite stratigraphic section. Lower through Middle Jurassic volcanics and coarse-grained clastics deposited on alluvial fans occur near the margins of the Gobi Basin and contain few vertebrate fossils. Upper Jurassic and lowermost Cretaceous strata (Sharilinian and Tsagantsabian time) contain coarse-grained fluvial deposits and some fossiliferous fine-grained alluvial plain and lacustrine sediments. Large, perennial lakes prevailed during Shinkhudukian (Aptian) time, to be replaced by vast, fluvially-influenced plains with smaller lakes during Khukhtekian (Aptian-Albian) time. Vertebrate assemblages of Early Cretaceous age are depauperate and characterized by endemic taxa, while during Khukhtekian time they became more diverse owing to immigration from Europe/North America. Fluviolacustrine and lacustrine environments of Baynshirenian (Turonian through early Campanian) time were inhabitated by shamosuchids, segnosaurids and diverse chelonians. The Gobi region was then gradually transformed into semi-arid alluvial plains interrupted by seasonal lakes and dune fields with ephemeral interdune streams and ponds. Semi-arid environments were widespread during Barungoyotian (Campanian) time and supported vertebrate assemblages dominated by lizards, gobiosuchids and protoceratopsids. Increased pluviosity during Nemegtian (Maastrichtian) time is indicated by meandering stream facies containing abundant remains of ornithomimids, tyrannosaurids and hadrosaurids. Available evidence points to a steady increase in dinosaurian diversity to the end of the Cretaceous.
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.
Primitive ornithomimids, a ubiquitous group of specialized Cretaceous dinosaurs nested within a clade of predominantly carnivorous theropods, are known to have had teeth, whereas derived ornithomimids had an edentulous beak, which has prompted speculation about their dietary habits. Here we describe two new ornithomimid specimens in which soft-tissue structures of the beak have been preserved. These creatures probably used their beaks to strain food sediment in an aqueous environment, rather than for predation on large animals.
Deinocheiridae, a new family of theropod dinosaurs
- H Osmólska
- E Roniewicz
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