Non-avian Theropods Research Articles

The rise of feathered dinosaurs:Kulindadromeus zabaikalicus, the oldest dinosaur with ‘feather-like’ structures

Diverse epidermal appendages including grouped filaments closely resembling primitive feathers in non-avian theropods, are associated with skeletal elements in the primitive ornithischian dinosaur Kulindadromeus zabaikalicus from the Kulinda locality in south-eastern Siberia. This discovery suggests that “feather-like” structures did not evolve exclusively in theropod dinosaurs, but were instead potentially widespread in the whole dinosaur clade. The dating of the Kulinda locality is therefore particularly important for reconstructing the evolution of “feather-like” structures in dinosaurs within a chronostratigraphic framework. Here we present the first dating of the Kulinda locality, combining U-Pb analyses (LA-ICP-MS) on detrital zircons and monazites from sedimentary rocks of volcaniclastic origin and palynological observations. Concordia ages constrain the maximum age of the volcaniclastic deposits at 172.8 ± 1.6 Ma, corresponding to the Aalenian (Middle Jurassic). The palynological assemblage includes taxa that are correlated to Bathonian palynozones from western Siberia, and therefore constrains the minimum age of the deposits. The new U-Pb ages, together with the palynological data, provide evidence of a Bathonian age—between 168.3 ± 1.3 Ma and 166.1 ± 1.2 Ma—for Kulindadromeus. This is older than the previous Late Jurassic to Early Cretaceous ages tentatively based on local stratigraphic correlations. A Bathonian age is highly consistent with the phylogenetic position of Kulindadromeus at the base of the neornithischian clade and suggests that cerapodan dinosaurs originated in Asia during the Middle Jurassic, from a common ancestor that closely looked like Kulindadromeus. Our results consequently show that Kulindadromeus is the oldest known dinosaur with “feather-like” structures discovered so far.

Comment on Brocklehurstet al.

Open AccessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Paul Gregory 2019Comment on Brocklehurst et al.R. Soc. open sci.6181872181872http://doi.org/10.1098/rsos.181872SectionSupplemental MaterialOpen AccessCommentComment on Brocklehurst et al. Gregory Paul Gregory Paul http://orcid.org/0000-0002-4493-6092 3100 St Paul St 604, Baltimore, MD 21218, USA [email protected] Google Scholar Find this author on PubMed Search for more papers by this author Gregory Paul Gregory Paul http://orcid.org/0000-0002-4493-6092 3100 St Paul St 604, Baltimore, MD 21218, USA [email protected] Google Scholar Find this author on PubMed Search for more papers by this author Published:27 February 2019https://doi.org/10.1098/rsos.181872 Review history Comment on Brocklehurst et al. Brocklehurst et al. [1] present additional evidence that the osteological features of non-avian theropod dinosaurs are incompatible with the presence of the crocodilian-like liver pump respiratory complex that had been proposed by some palaeobiologists [2,3]. The latter hypothesis is in opposition to the wider consensus that the avian air-sac system first appeared in non-avian dinosaurs. In particular, Brocklehurst et al. detail that the strongly corrugated ceiling of the theropod ribcage should have locked their rigid lungs in place, as in birds, while the much smoother ribcage ceiling of crocodilians facilitates the fore-and-aft expansion and contraction of their compliant lungs through corresponding movement of their large livers. In doing so, Brocklehurst et al. cite earlier studies to the same effect dating back to 2009 by Schachner et al. [4,5].My concern is that Brocklehurst et al. neglected to cite my even earlier work, starting in 2001 [6–8], which as far as I am aware first explicitly and extensively tested the configuration of theropod respiratory apparati by comparing the contrasting topography of dinosaur versus crocodilian ribcage ceilings in the technical literature. The first paper, the subsequent academic book appendix and the later book chapter included comprehensive text backed by the first detailed comparative illustrations of the pertinent vertebra-rib head articulations. These studies were conducted with the direct intent of addressing the problematic Ruben et al. hypothesis [2,3], first published in 1997, that some dinosaurs had crocodilian-like rather than avian-like breathing complexes. Those researchers have since failed to plausibly refute my arguments, a task made increasingly difficult by subsequent and increasingly sophisticated research on the subject. Yet this precedent is not noted by Brocklehurst et al.They are not the first to fail to cite some of my innovative arguments on the subject of archosaur respiration. It is especially pertinent to this discussion that while the two Schachner et al. analyses cite my studies, they too did not explicitly relate that I had previously examined the contrasts between bird and crocodilian ribcage morphologies and came to similar conclusions. Perhaps that failing to cite the precedent literature contributed to Brocklehurst et al.'s ignorance of who first considered and refuted the Ruben et al. hypothesis.I regret that I did not cite the Schachner et al. 2009 and 2011 papers in my 2012 discussion of the subject because I was not aware of them. Had I known of the studies I would have included them, the more to support the anatomical comparative hypothesis I originated.Hopefully, this note will cause those in the future working on this aspect of archosaur evolution to cite the precedent literature properly, whether or not they agree with it.Data accessibilityThere is no data specific to this commentary.Competing interestsI declare no competing interests.FundingThere was no financial support for this commentary.Footnotes© 2019 The Authors.Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends

The distribution of dental features in non-avian theropod dinosaurs: Taxonomic potential, degree of homoplasy, and major evolutionary trends

A diversified dinosaur track assemblage from the Lower Cretaceous Xiaoba Formation of Sichuan Province, China: Implications for ichnological database and census studies

The rapid rate of discovery of Lower Cretaceous tetrapod tracksites in terrestrial sequences on the Sichuan Basin area is such that the 2016 report of 21 sites in the Xiaoba, Feitianshan and Jiaguan Formations is now increased by ∼24%–26 sites. Of these seven occur in the Xiaoba Formation, including two new sites (Luogan and Apuruha) described here. Likewise, there has been a similar increase in reports of sites from the Jiaguan Formation, from 12 to 15 sites (=25%) in the same period. The total of estimated trackmakers, based on trackways, not individual tracks, is ∼598 for all three formations, including∼150 from the Xiaoba Formation, and ∼325 from the Jiaguan Formation. This indicates a two-year increase in the database of ∼20%. To date all tracks from the Xiaoba formation represent saurischians (non-avian theropods and sauropods). However, as the database has increased for all three formations it has been possible to demonstrate that didactyl, presumably deinonychosaurian trackmakers, although rare and in some cases poorly preserved, occur in about 20% of assemblages. Thus, the data base helps differentiate between the relatively low abundance and relatively widespread distribution of deinonychosaurian trackmakers within the non-avian theropod track database. This difference between abundance and distribution is consistent with what is known of patterns in other parts of Asia.

Flightless birds are not neuroanatomical analogs of non-avian dinosaurs

BackgroundIn comparative neurobiology, major transitions in behavior are thought to be associated with proportional size changes in brain regions. Bird-line theropod dinosaurs underwent a drastic locomotory shift from terrestrial to volant forms, accompanied by a suite of well-documented postcranial adaptations. To elucidate the potential impact of this locomotor shift on neuroanatomy, we first tested for a correlation between loss of flight in extant birds and whether the brain morphology of these birds resembles that of their flightless, non-avian dinosaurian ancestors. We constructed virtual endocasts of the braincase for 80 individuals of non-avian and avian theropods, including 25 flying and 19 flightless species of crown group birds. The endocasts were analyzed using a three-dimensional (3-D) geometric morphometric approach to assess changes in brain shape along the dinosaur-bird transition and secondary losses of flight in crown-group birds (Aves).ResultsWhile non-avian dinosaurs and crown-group birds are clearly distinct in endocranial shape, volant and flightless birds overlap considerably in brain morphology. Phylogenetically informed analyses show that locomotory mode does not significantly account for neuroanatomical variation in crown-group birds. Linear discriminant analysis (LDA) also indicates poor predictive power of neuroanatomical shape for inferring locomotory mode. Given current sampling, Archaeopteryx, typically considered the oldest known bird, is inferred to be terrestrial based on its endocranial morphology.ConclusionThe results demonstrate that loss of flight does not correlate with an appreciable amount of neuroanatomical changes across Aves, but rather is partially constrained due to phylogenetic inertia, evident from sister taxa having similarly shaped endocasts. Although the present study does not explicitly test whether endocranial changes along the dinosaur-bird transition are due to the acquisition of powered flight, the prominent relative expansion of the cerebrum, in areas associated with flight-related cognitive capacity, suggests that the acquisition of flight may have been an important initial driver of brain shape evolution in theropods.

Cancellous bone and theropod dinosaur locomotion. Part III-Inferring posture and locomotor biomechanics in extinct theropods, and its evolution on the line to birds.

This paper is the last of a three-part series that investigates the architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is highly sensitive to its prevailing mechanical environment, and may therefore help further understanding of locomotor biomechanics in extinct tetrapod vertebrates such as dinosaurs. Here in Part III, the biomechanical modelling approach derived previously was applied to two species of extinct, non-avian theropods, Daspletosaurus torosus and Troodon formosus. Observed cancellous bone architectural patterns were linked with quasi-static, three-dimensional musculoskeletal and finite element models of the hindlimb of both species, and used to derive characteristic postures that best aligned continuum-level principal stresses with cancellous bone fabric. The posture identified for Daspletosaurus was largely upright, with a subvertical femoral orientation, whilst that identified for Troodon was more crouched, but not to the degree observed in extant birds. In addition to providing new insight on posture and limb articulation, this study also tested previous hypotheses of limb bone loading mechanics and muscular control strategies in non-avian theropods, and how these aspects evolved on the line to birds. The results support the hypothesis that an upright femoral posture is correlated with bending-dominant bone loading and abduction-based muscular support of the hip, whereas a crouched femoral posture is correlated with torsion-dominant bone loading and long-axis rotation-based muscular support. Moreover, the results of this study also support the inference that hindlimb posture, bone loading mechanics and muscular support strategies evolved in a gradual fashion along the line to extant birds.

Dinosaur egg colour had a single evolutionary origin

Birds are the only living amniotes with coloured eggs1-4, which have long been considered to be an avian innovation1,3. A recent study has demonstrated the presence of both red-brown protoporphyrin IX and blue-green biliverdin5-the pigments responsible for all the variation in avian egg colour-in fossilized eggshell of a nonavian dinosaur6. This raises the fundamental question of whether modern birds inherited egg colour from their nonavian dinosaur ancestors, or whether egg colour evolved independently multiple times. Here we present a phylogenetic assessment of egg colour in nonavian dinosaurs. We applied high-resolution Raman microspectroscopy to eggshells that represent all of the major clades of dinosaurs, and found that egg colour pigments were preserved in all eumaniraptorans: egg colour had a single evolutionary origin in nonavian theropod dinosaurs. The absence of colour in ornithischian and sauropod eggs represents a true signal rather than a taphonomic artefact. Pigment surface maps revealed that nonavian eumaniraptoran eggs were spotted and speckled, and colour pattern diversity in these eggs approaches that in extant birds, which indicates that reproductive behaviours in nonavian dinosaurs were far more complex than previously known3. Depth profiles demonstrated identical mechanisms of pigment deposition in nonavian and avian dinosaur eggs. Birds were not the first amniotes to produce coloured eggs: as with many other characteristics7,8 this is an attribute that evolved deep within the dinosaur tree and long before the spectacular radiation of modern birds.

Cancellous bone and theropod dinosaur locomotion. Part I-an examination of cancellous bone architecture in the hindlimb bones of theropods.

This paper is the first of a three-part series that investigates the architecture of cancellous (‘spongy’) bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and has previously been used to infer locomotor biomechanics in extinct tetrapod vertebrates, especially primates. Despite great promise, cancellous bone architecture has remained little utilized for investigating locomotion in many other extinct vertebrate groups, such as dinosaurs. Documentation and quantification of architectural patterns across a whole bone, and across multiple bones, can provide much information on cancellous bone architectural patterns and variation across species. Additionally, this also lends itself to analysis of the musculoskeletal biomechanical factors involved in a direct, mechanistic fashion.On this premise, computed tomographic and image analysis techniques were used to describe and analyse the three-dimensional architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs for the first time. A comprehensive survey across many extant and extinct species is produced, identifying several patterns of similarity and contrast between groups. For instance, more stemward non-avian theropods (e.g. ceratosaurs and tyrannosaurids) exhibit cancellous bone architectures more comparable to that present in humans, whereas species more closely related to birds (e.g. paravians) exhibit architectural patterns bearing greater similarity to those of extant birds. Many of the observed patterns may be linked to particular aspects of locomotor biomechanics, such as the degree of hip or knee flexion during stance and gait. A further important observation is the abundance of markedly oblique trabeculae in the diaphyses of the femur and tibia of birds, which in large species produces spiralling patterns along the endosteal surface. Not only do these observations provide new insight into theropod anatomy and behaviour, they also provide the foundation for mechanistic testing of locomotor hypotheses via musculoskeletal biomechanical modelling.

The first specimen of Archaeopteryx from the Upper Jurassic Mörnsheim Formation of Germany

ABSTRACTFrom an initial isolated position as the oldest evolutionary prototype of a bird, Archaeopteryx has, as a result of recent fossil discoveries, become embedded in a rich phylogenetic context of both more and less crownward stem-group birds. This has prompted debate over whether Archaeopteryx is simply a convergently bird-like non-avialan theropod. Here we show, using the first synchrotron microtomographic examination of the genus, that the eighth or Daiting specimen of Archaeopteryx possesses a character suite that robustly constrains it as a basal avialan (primitive bird). The specimen, which comes from the Mörnsheim Formation and is thus younger than the other specimens from the underlying Solnhofen Formation, is distinctive enough to merit designation as a new species, Archaeopteryx albersdoerferi sp. nov., but is recovered in close phylogenetic proximity to Archaeopteryx lithographica. Skeletal innovations of the Daiting specimen, such as fusion and pneumatization of the cranial bones, well vascularized pectoral girdle and wing elements, and a reinforced configuration of carpals and metacarpals, suggest that it may have had more characters seen in flying birds than the older Archaeopteryx lithographica. These innovations appear to be convergent on those of more crownward avialans, suggesting that Bavarian archaeopterygids independently acquired increasingly bird-like traits over time. Such mosaic evolution and iterative exploration of adaptive space may be typical for major functional transitions like the origin of flight.

The effect of long-term atmospheric changes on the macroevolution of birds

Atmospheric conditions are critical for a range of biological functions—locomotion among others—and long-term changes in these conditions have been identified as causal for different macroevolutionary patterns. Here we examine the influence of variations in atmospheric O2 concentration (AOC), temperature (Tair), and air density (ρair) on the power efficiency, as it relates to locomotion, during the evolutionary history of birds. Specifically, our study centers on four key evolutionary events: (1) the body mass reduction of non-avian theropods prior to the rise of birds; (2) the emergence of flapping flight in the earliest birds; (3) the divergence of basal pygostylians; and (4) the diversification of modern birds. Our results suggest that a marked increase in AOC and ρair during the Middle Jurassic—coeval with a trend in miniaturization—improved the power efficiency of the dinosaurian predecessors of birds. Likewise, an increase in these conditions is hypothesized as having played a major role in the diversification of early pygostylians during the Early Cretaceous. However, our analyses do not identify any significant paleoatmospheric effects on either the emergence of flapping flight or the early cladogenesis of modern birds. Extinct birds flew within the range of atmospheric conditions in which modern birds fly but varying past conditions influenced their flight performance. Our study thus highlights the importance of considering paleoatmospheric conditions when reconstructing the flight efficiency of the forerunners of modern birds.

The function of the alpha rhythm during the solution of complicated mathematical problems

The vertebrate track Laiyangpus liui, from the Lower Cretaceous of Shandong Province in China has been the subject of misunderstanding and misinterpretation since it was discovered and named in 1960, and reposited in the Institute of Vertebrate Paleontology and Paleoanthropology collections in Beijing. It was initially misinterpreted as evidence of a coelurosaurian (non-avian theropod) trackmaker supposedly showing evidence of tridactyl manus and tetradactyl pes. This discredited conclusion was influenced by erroneous 1930s interpretations in the European literature, of tracks later shown to be of turtle affinity. A half century later, when morphologically disparate avian and non-avian theropod tracks were reported from the type locality, it was suggested that the ichnites were most likely crocodilian swim tracks. However, at that date (2010), and for some time previously, the type specimen was believed lost, and in at least one instance the label Laiyangpus had been applied to quite different theropod track specimens in the collections. With the discovery of turtle swim tracks at several Lower Cretaceous sites in China, it was suspected, and later (2015) stated that the tracks were likely attributable to turtles. This, inference was confirmed when the holotype was rediscovered and examined in detail, revealing that Laiyangpus liui is sufficiently similar, morphologically, to Chelonipus to be considered a subjective senior synonym. We therefore propose transferring L. liui to Chelonipus liui, comb. nov. which is diagnostic of tracks attributable to turtles.

Lower Cretaceous sauropod trackways from Lishui City and an overview of dinosaur dominated track assemblages from Zhejiang Province, China

A relatively small number of tetrapod tracksites from Zhejiang Province fills out the fossil record from that region, which is also known to have yielded both saurischian (titanosauriform, coelurosaur) and ornithischian (basal ornithopod, ankylosaurian) body fossils as well as dinosaurian eggs. We use photogrammetry and 3D imaging to reinterpret the sauropod tracks from Lishui City, which revealed the existence of trackways. The track record from three documented sites in Zhejiang Province includes avian and non-avian theropod, sauropod, ornithopod and pterosaur tracks. Previous work showed that the purported new bird ichnospecies Dongyangornipes sinensis is a synonym of Uhangrichnus chuni, while we here consider Pteraichnus dongyangensis as a nomen dubium. Such “provincial ichnotaxonomy” may mask similarities in the ichnofauna across large regions. In fact, we show that the ichnofauna is similar to that found in the Early Cretaceous elsewhere in China.

The distinctive theropod assemblage of the Ellisdale site of New Jersey and its implications for North American dinosaur ecology and evolution during the Cretaceous

AbstractThe Cretaceous landmass of Appalachia has preserved an understudied but nevertheless important record of dinosaurs that has recently come under some attention. In the past few years, the vertebrate faunas of several Appalachian sites have been described. One such locality, the Ellisdale site of the Cretaceous Marshalltown Formation of New Jersey, has produced hundreds of remains assignable to dinosaurs, including those of hadrosauroids of several size classes, indeterminate ornithopods, indeterminate theropods, the teeth, cranial, and appendicular elements of dromaeosaurids, ornithomimosaurians, and tyrannosauroids, and an extensive microvertebrate assemblage. The theropod dinosaur record of the Ellisdale site is currently the most extensive and diverse known from the Campanian of Appalachia. Study of the Ellisdale theropod specimens suggests that at least four or more non-avian theropod taxa are represented at the site, including tyrannosauroids, ornithomimosaurs, several different morphotypes of dromaeosaurids that are the first of that clade described from New Jersey, and indeterminate theropods. The specimens are important for increasing current knowledge about the theropod diversity of the Atlantic Coastal Plain (ACP) during the Campanian by representing the most speciose assemblage of the group during the time in the ACP as well as for shedding light on Appalachian dinosaur ecology and biogeography generally.

Large theropod and small sauropod trackmakers from the Lower Cretaceous Jingchuan Formation, Inner Mongolia, China

At least 16 tetrapod tracksites have been reported from the Cretaceous Jingchuan Formation of the Ordos Basin, in the Chabu area, of Otog Qi, Inner Mongolia. Only a few of these sites, designated as Chabu sites 1–16, have been documented in detail. Most known sites occur in an area of ∼100 km2 and are saurischian dominated, yielding the tracks of sauropods, avian and non-avian theropods. Sites include the type localities of three previously-named theropod ichnotaxa: the non-avian theropod ichnogenus Chapus, (site 8) the avian theropod ichnogenus Tatarornipes (site 4) and the non-avian theropod ichnospecies Asianopodus robustus (site 6). We herein revise the description of ichnogenus Chapus based on the tridactyl holotype, erect the new ichnotaxon Ordexallopus zhanglifui ichnogen. et ichnosp. nov, for a distinctive tetradactyl morphotype, also from site 8, and compare both with A. robustus, and other well known large theropod track ichnotaxa from the Lower Cretaceous. Ordexallopus is shown to represent a large robust tetradactyl trackmaker with foot morphology reminiscent of that registered by the smaller, more gracile tetradactyl maker of Saurexallopus tracks. Both likely represent arctometatarsalians.Previous studies, have shown that many of the of the 16 known sites warrant detailed study, due to the abundance and ichnotaxonomic significance of tracks. We herein show that site 8, which has been developed as an interpretative destination, comprises four different sites (8A–8D), only one of which has previously been described in detail, in Chinese. Site 8D is of special significance as the type locality of Ordexallopus zhanglifui ichnogen et isp. nov. It also reveals evidence of gregarious behavior among juvenile sauropods traveling in the same direction as a large adult. The site also yields the most complete turtle trackway known from the Cretaceous of China. Ongoing studies of the Chabu area tracksites which form part of Otog Geopark indicate that the ichnological potential of the region is as yet only partially realized.

Incubation behaviours of oviraptorosaur dinosaurs in relation to body size.

Most birds sit on their eggs during incubation, a behaviour that likely evolved among non-avian dinosaurs. Several 'brooding' specimens of smaller species of oviraptorosaurs and troodontids reveal these non-avian theropods sat on their eggs, although little is known of incubation behaviour in larger theropod species. Here we examine egg clutches over a large body size range of oviraptorosaurs in order to understand the potential effect of body size on incubation behaviour. Eggshell porosity indicates that the eggs of all oviraptorosaurs were exposed in the nest, similar to brooding birds. Although all oviraptorosaur clutches consist of radially arranged eggs in a ring configuration, clutch morphology varies in that the central opening is small or absent in the smallest species, becomes significantly larger in larger species, and occupies most of the nest area in giant species. Our results suggest that the smallest oviraptorosaurs probably sat directly on the eggs, whereas with increasing body size more weight was likely carried by the central opening, reducing or eliminating the load on the eggs and still potentially allowing for some contact during incubation in giant species. This adaptation, not seen in birds, appears to remove the body size constraints of incubation behaviour in giant oviraptorosaurs.

Multiple parallel deinonychosaurian trackways from a diverse dinosaur track assemblage of the Lower Cretaceous Dasheng Group of Shandong Province, China

Many newly-discovered dinosaur tracksites have recently been reported from the Lower Cretaceous Dasheng Group of Shandong Province. These are proving valuable as tools for characterizing the fauna in deposits almost devoid of body fossils. Here we report on a new Cretaceous site, the 14th documented in recent years, with multiple track-bearing levels, that adds ∼300 tracks to a growing database. At least two morphotypes tentatively labelled as cf. Menglongpus isp., representing a deinonychosaur, and cf. Tatarornipes isp., representing an avian theropod, add to the list of at least seven named ichnogenera attributed to avian and non-avian theropods reported from the Dasheng Group in Shandong Province. Combined with two sauropodomorph and two ornithopod ichnogenera, and unnamed turtle tracks, the genus-level ichnodiversity (∼14) is one of the highest reported for any Cretaceous unit either regionally in China or globally.The tracks identified as cf. Menglongpus isp. occur in four parallel trackways indicating a group of small didactyl bipeds of inferred deinonychosaurian affinity. Despite the lack of body fossils from the Dasheng Group in Shandong Province, a high diversity of deinonychosaur body fossils is known from the contemporary Jehol Biota from northeastern China. This similarity underscores the importance of the Shandong track assemblage as indicators of regional, tetrapod biodiversity during the Cretaceous.

The trophic habits of early birds

Although direct associations that reveal diet are extremely rare in the fossil record, the rich Lower Cretaceous Jehol Lagerstätte has produced dozens of specimens preserving ingested items, which together reveal important information regarding the early evolution of the avian alimentary canal. Direct evidence indicates Jeholornis and Sapeornis ate seeds and like living granivores utilized a gastric mill although only the more derived Sapeornis possessed a crop for food storage. Despite their smaller numbers in the Early Cretaceous, most direct evidence pertains to the Ornithuromorpha, indicating a structurally and functionally modern alimentary canal was present in even the earliest members of this clade. Similar evidence is altogether lacking in the Enantiornithes suggesting this clade was characterized by a primitive alimentary canal, potentially factoring into the ultimate extinction of this successful Cretaceous lineage. The role of the gizzard in the loss of teeth in Aves is more complex than in non-avian theropod lineages. As in neornithines, the presence of gastroliths in basal ornithuromorphs may not be entirely indicative of herbivory although this diet does appear to correlate with complete tooth loss in this clade. Positive selection for specialized tooth morphologies persists throughout the evolution of Aves and in the Ornithuromorpha appears to be linked to piscivory. Although represented by the greatest numbers, no direct indicator of diet preference is preserved in any confuciusornithiform or enantiornithine suggesting these clades utilized different nutritional strategies. The absence of teeth and gastroliths in all confuciusornithiforms suggest this lineage may have secondarily switched to a non-herbivorous, soft diet. Similarly, the absence of gizzard stones in enantiornithines also suggests a soft diet while their small body size suggests Early Cretaceous species would have fed on invertebrates. The diversity of recognized dental patterns including enamel specializations observed in Jehol enantiornithines suggests effective resource partitioning of available invertebrate faunas and that teeth had an active participation in enantiornithine feeding strategies.

The influence of speed and size on avian terrestrial locomotor biomechanics: Predicting locomotion in extinct theropod dinosaurs.

How extinct, non-avian theropod dinosaurs moved is a subject of considerable interest and controversy. A better understanding of non-avian theropod locomotion can be achieved by better understanding terrestrial locomotor biomechanics in their modern descendants, birds. Despite much research on the subject, avian terrestrial locomotion remains little explored in regards to how kinematic and kinetic factors vary together with speed and body size. Here, terrestrial locomotion was investigated in twelve species of ground-dwelling bird, spanning a 1,780-fold range in body mass, across almost their entire speed range. Particular attention was devoted to the ground reaction force (GRF), the force that the feet exert upon the ground. Comparable data for the only other extant obligate, striding biped, humans, were also collected and studied. In birds, all kinematic and kinetic parameters examined changed continuously with increasing speed, while in humans all but one of those same parameters changed abruptly at the walk-run transition. This result supports previous studies that show birds to have a highly continuous locomotor repertoire compared to humans, where discrete ‘walking’ and ‘running’ gaits are not easily distinguished based on kinematic patterns alone. The influences of speed and body size on kinematic and kinetic factors in birds are developed into a set of predictive relationships that may be applied to extinct, non-avian theropods. The resulting predictive model is able to explain 79–93% of the observed variation in kinematics and 69–83% of the observed variation in GRFs, and also performs well in extrapolation tests. However, this study also found that the location of the whole-body centre of mass may exert an important influence on the nature of the GRF, and hence some caution is warranted, in lieu of further investigation.

Theropod assemblages and a new ichnotaxon Gigandipus chiappei ichnosp. nov. from the Jiaguan Formation, Lower Cretaceous of Guizhou Province, China

A newly discovered Jiaguan Formation (Lower Cretaceous) tracksite from the Linjiang region of Guizhou Province, China, reveals the first example of a Cretaceous track morphotype attributable to the non-avian theropod ichnogenus Gigandipus, here named Gigandipus chiappei ichnosp nov. The theropod dominated locality also reveals the second report of the avian theropod ichnogenus Wupus, one of the largest avian traces currently known from the Lower Cretaceous. The Linjiang site provides evidence to support previous interpretations of a distinctive Lower Cretaceous theropod-dominated ichnofauna that was widespread in China and East Asia and highlights the similarity between Lower Cretaceous theropod ichnotaxa in East Asia and those found in the Lower Jurassic both in East Asia and elsewhere. These similarities in turn create various ichnotaxonomic challenges familiar to researchers working on theropod tracks, and we recommend caution in the naming of new theropod ichnotaxa at the ichnogenus level.

Living avian theropods in the extinct non-avian theropod's feathers!?

Living avian theropods in the extinct non-avian theropod's feathers!?