The theropod dinosaurElaphrosaurus bambergiJanensch, 1920, from the Late Jurassic of Tendaguru, Tanzania

A new abelisaurid dinosaur from the end Cretaceous of Patagonia and evolutionary rates among the Ceratosauria

Gondwanan dinosaur faunae during the 20 Myr preceding the Cretaceous-Palaeogene (K/Pg) extinction included several lineages that were absent or poorly represented in Laurasian landmasses. Among these, the South American fossil record contains diverse abelisaurids, arguably the most successful groups of carnivorous dinosaurs from Gondwana in the Cretaceous, reaching their highest diversity towards the end of this period. Here we describe Koleken inakayali gen. et sp. n., a new abelisaurid from the La Colonia Formation (Maastrichtian, Upper Cretaceous) of Patagonia. Koleken inakayali is known from several skull bones, an almost complete dorsal series, complete sacrum, several caudal vertebrae, pelvic girdle and almost complete hind limbs. The new abelisaurid shows a unique set of features in the skull and several anatomical differences from Carnotaurus sastrei (the only other abelisaurid known from the La Colonia Formation). Koleken inakayali is retrieved as a brachyrostran abelisaurid, clustered with other South American abelisaurids from the latest Cretaceous (Campanian-Maastrichtian), such as Aucasaurus, Niebla and Carnotaurus. Leveraging our phylogeny estimates, we explore rates of morphological evolution across ceratosaurian lineages, finding them to be particularly high for elaphrosaurine noasaurids and around the base of Abelisauridae, before the Early Cretaceous radiation of the latter clade. The Noasauridae and their sister clade show contrasting patterns of morphological evolution, with noasaurids undergoing an early phase of accelerated evolution of the axial and hind limb skeleton in the Jurassic, and the abelisaurids exhibiting sustained high rates of cranial evolution during the Early Cretaceous. These results provide much needed context for the evolutionary dynamics of ceratosaurian theropods, contributing to broader understanding of macroevolutionary patterns across dinosaurs.

Shed teeth from Portezuelo formation at Sierra del Portezuelo reveal a higher diversity of predator theropods during Turonian-Coniacian times in northern Patagonia

The study of thirty-two shed crowns from the Portezuelo Formation (middle Turonian-late Coniacian) at the Sierra del Portezuelo locality, reveals six distinct tooth morphotypes identified through cladistic, discriminant, and cluster analyses. Two morphotypes were identified as belonging to Megaraptoridae, three to Abelisauridae, one to Abelisauroidea, and one to Alvarezsauridae. Additionally, two of the morphotypes exhibit a combination of dental features typically found in megaraptorid and abelisauridtheropods. These results suggest a greater diversity of theropods in the original ecosystem than previously thought, including the presence of a second morphotype of megaraptorid and alvarezsaurid previously undocumented in this formation. Furthermore, the existence of Morphotype 6 indicates the potential coexistence of medium-sized abelisauroids alongside larger abelisaurids in the same ecosystem. These findings underscore the importance of future expeditions to the Sierra del Portezuelo locality to further our understanding of these previously unknown theropod species.

Osteology of the axial skeleton of Aucasaurus garridoi: phylogenetic and paleobiological inferences

Aucasaurus garridoi is an abelisaurid theropod from the Anacleto Formation (lower Campanian, Upper Cretaceous) of Patagonia, Argentina. The holotype of Aucasaurus garridoi includes cranial material, axial elements, and almost complete fore- and hind limbs. Here we present a detailed description of the axial skeleton of this taxon, along with some paleobiological and phylogenetic inferences. The presacral elements are somewhat fragmentary, although these show features shared with other abelisaurids. The caudal series, to date the most complete among brachyrostran abelisaurids, shows several autapomorphic features including the presence of pneumatic recesses on the dorsal surface of the anterior caudal neural arches, a tubercle lateral to the prezygapophysis of mid caudal vertebrae, a marked protuberance on the lateral rim of the transverse process of the caudal vertebrae, and the presence of a small ligamentous scar near the anterior edge of the dorsal surface in the anteriormost caudal transverse process. The detailed study of the axial skeleton of Aucasaurus garridoi has also allowed us to identify characters that could be useful for future studies attempting to resolve the internal phylogenetic relationships of Abelisauridae. Computed tomography scans of some caudal vertebrae show pneumatic traits in neural arches and centra, and thus the first reported case for an abelisaurid taxon. Moreover, some osteological correlates of soft tissues present in Aucasaurus and other abelisaurids, especially derived brachyrostrans, underscore a previously proposed increase in axial rigidity within Abelisauridae.

Macroevolutionary patterns in the pelvis, stylopodium and zeugopodium of megalosauroid theropod dinosaurs and their importance for locomotor function

During the Mesozoic, non-avian theropods represented one of the most successful clades globally distributed, with a wide diversity of forms. An example is the clade Megalosauroidea, which included medium- to large-bodied forms. Here, we analyse the macroevolution of the locomotor system in early Theropoda, emphasizing the Megalosauroidea. We scored the Spinosaurus neotype in a published taxon-character matrix and described the associated modifications in character states, mapping them onto a phylogeny and using these to study disparity. In the evolution of Megalosauroidea, there was the mosaic emergence of a low swollen ridge; enlargement of the posterior brevis fossa and emergence of a posterodorsal process on the ilium in some megalosauroids; emergence of a femoral head oriented anteromedially and medially angled, and appearance of posterolaterally oriented medial femoral condyles in spinosaurids. The greatest morphological disparity is in the ilium of megalosaurids; the ischium seems to have a high degree of homoplasy; there is a clear distinction in the femoral morphospace regarding megalosauroids and other theropods; piatnitzkysaurids show considerable disparity of zeugopodial characters. These reconstructions of osteological evolution form a stronger basis on which other studies could build, such as mapping of pelvic/appendicular musculature and/or correlating skeletal traits with changes in locomotor function.

First definitive record of Abelisauridae (Theropoda: Ceratosauria) from the Cretaceous Bahariya Formation, Bahariya Oasis, Western Desert of Egypt

Numerous non-avian theropod dinosaur fossils have been reported from the Upper Cretaceous (Cenomanian) Bahariya Formation, Bahariya Oasis, Western Desert of Egypt, but unambiguous materials of Abelisauridae have yet to be documented. Here we report Mansoura University Vertebrate Paleontology Center (MUVP) specimen 477, an isolated, well-preserved tenth cervical vertebra of a medium-sized abelisaurid from the Bahariya Formation. The new vertebra shows affinities with those of other Upper Cretaceous abelisaurids from Madagascar and South America, such as Majungasaurus crenatissimus, Carnotaurus sastrei, Viavenator exxoni and a generically indeterminate Patagonian specimen (Museo Padre Molina specimen 99). Phylogenetic analysis recovers the Bahariya form within Abelisauridae, either in a polytomy of all included abelisaurids (strict consensus tree) or as an early branching member of the otherwise South American clade Brachyrostra (50% majority rule consensus tree). MUVP 477, therefore, represents the first confirmed abelisaurid fossil from the Bahariya Formation and the oldest definitive record of the clade from Egypt and northeastern Africa more generally. The new vertebra demonstrates the wide geographical distribution of Abelisauridae across North Africa during the middle Cretaceous and augments the already extraordinarily diverse large-bodied theropod assemblage of the Bahariya Formation, a record that also includes representatives of Spinosauridae, Carcharodontosauridae and Bahariasauridae.

The first edentulous ceratosaur from South America

The recognition of ontogenetic edentulism in the Jurassic noasaurid Limusaurus inextricabilis shed new light on the dietary diversity within Ceratosauria, a stem lineage of non-avian theropod dinosaurs known for peculiar craniomandibular adaptations. Until now, edentulism in Ceratosauria was exclusive to adult individuals of Limusaurus. Here, an exceptionally complete skeleton of a new toothless ceratosaur, Berthasaura leopoldinae gen. et sp. nov., is described from the Cretaceous aeolian sandstones of the Bauru Basin, Southern Brazil. The specimen resembles adult individuals of Limusaurus by the absence of teeth but based on the unfused condition of several elements (e.g., skull, vertebral column) it clearly represents an ontogenetically immature individual, indicating that it might never have had teeth. The phylogenetic analysis performed here has nested Berthasaura leopoldinae as an early-divergent Noasauridae, not closely related to Limusaurus. It represents the most complete non-avian theropod from the Brazilian Cretaceous and preserves the most complete noasaurid axial series known so far. Moreover, the new taxon exhibits many novel osteological features, uncommon in non-avian theropods, and unprecedented even among South American ceratosaurs. These include not only toothless jaws but also a premaxilla with cutting occlusal edge, and a slightly downturned rostral tip. This indicate that B. leopoldinae unlikely had the same diet as other ceratosaurs, most being regarded as carnivorous. As the ontogenetically more mature specimens of Limusaurus, Berthasaura might have been herbivorous or at least omnivorous, corroborating with an early evolutionary divergence of noasaurids from the ceratosaurian bauplan by disparate feeding modes.

Dinosaurs from the Santonian-Campanian Atlantic coastline substantiate phylogenetic signatures of vicariance in Cretaceous North America

During the Cretaceous, diversifications and turnovers affected terrestrial vertebrates experiencing the effects of global geographical change. However, the poor fossil record from the early Late Cretaceous has concealed how dinosaurs and other terrestrial vertebrates responded to these events. I describe two dinosaurs from the Santonian to Early Campanian of the obscure North American paleolandmass Appalachia. A revised look at a large, potentially novel theropod shows that it likely belongs to a new clade of tyrannosauroids solely from Appalachia. Another partial skeleton belongs to an early member of the Hadrosauridae, a highly successful clade of herbivorous dinosaurs. This skeleton is associated with the first small juvenile dinosaur specimens from the Atlantic Coastal Plain. The tyrannosauroid and hadrosaurid substantiate one of the only Late Santonian dinosaur faunas and help pinpoint the timing of important anatomical innovations in two widespread dinosaur lineages. The phylogenetic positions of the tyrannosauroid and hadrosaurid show Santonian Appalachian dinosaur faunas are comparable to coeval Eurasian ones, and the presence of clades formed only by Appalachian dinosaur taxa establishes a degree of endemism in Appalachian dinosaur assemblages attributable to episodes of vicariance.

Sacral co-ossification in dinosaurs: The oldest record of fused sacral vertebrae in Dinosauria and the diversity of sacral co-ossification patterns in the group

The fusion of the sacrum occurs in the major dinosaur lineages, i.e. ornithischians, theropods, and sauropodomorphs, but it is unclear if this trait is a common ancestral condition, or if it evolved independently in each lineage, or even how or if it is related to ontogeny. In addition, the order in which the different structures of the sacrum are fused, as well as the causes that lead to this co-ossification, are poorly understood. Herein, we described the oldest record of fused sacral vertebrae within dinosaurs, based on two primordial sacral vertebrae from the Late Triassic of Candelária Sequence, southern Brazil. We used computed microtomography (micro-CT) to analyze the extent of vertebral fusion, which revealed that it occurred only between the centra. We also assessed the occurrence of sacral fusion in Dinosauria and close relatives. The degree of fusion observed in representatives of the major dinosaur lineages suggested that there may be a sequential pattern of fusion of the elements of the sacrum, more clearly observed in Sauropodomorpha. Our analyses suggest that primordial sacral vertebrae fuse earlier in the lineage (as seen in Norian sauropodomorphs). Intervertebral fusion is observed to encompass progressively more vertebral units as sauropodomorphs evolve, reaching up to five or more fully fused sacrals in Neosauropoda. Furthermore, the new specimen described here indicates that the fusion of sacral elements occurred early in the evolution of dinosaurs. Factors such as ontogeny and the increase in body size, combined with the incorporation of vertebrae to the sacrum may have a significant role in the process and in the variation of sacral fusion observed.

Osteohistology and growth dynamics of the Brazilian noasaurid Vespersaurus paranaensis Langer et al., 2019 (Theropoda: Abelisauroidea)

Although the knowledge of bone histology of non-avian theropods has advanced considerably in recent decades, data about the bone tissue patterns, growth dynamics and ontogeny of some taxa such as abelisauroids are still limited. Here we describe the bone microstructure and growth dynamics of the Brazilian noasaurine Vespersaurus paranaensis using five femora and six tibiae and quantify the annual growth marks through retrocalculation of missing ones to estimate ontogenetic ages. The femoral series comprises four femoral histological classes (FHC I-IV), varying from two annuli or LAGs to seven LAGs. Femora show that sexual maturity was achieved around the seventh to tenth year of life, whereas the tibiae suggest it was earlier (around three to five years old). Tibiae represent three histological classes (THC I-III) displaying from three to nine LAGs. Two tibiae (THC III) exhibit an external fundamental system indicating that these specimens reached full skeletal size. The heterogeneous maturity observed in Vespersaurus hind limb bones could result from differential allometry scaling between femora and tibiae length with the body length. The predominant parallel-fibered bone matrix suggests that Vespersaurus grew more slowly than most theropods, including other abelisauroids, in a pattern shared with the noasaurines Masiakasaurus knopfleri from Madagascar and CPPLIP 1490 from Brazil. This deviation from the typical theropod growth pattern may be mainly correlated with small body size, but also may related to resource limitation imposed by the arid climate prevailing in southwestern Gondwana during Cretaceous. Moreover, given the ecological and phylogenetic similarities among these taxa, such features would probably be apomorphic within Noasauridae.

The first juvenile dromaeosaurid (Dinosauria: Theropoda) from Arctic Alaska

Compared to the osteological record of herbivorous dinosaurs from the Late Cretaceous Prince Creek Formation of northern Alaska, there are relatively fewer remains of theropods. The theropod record from this unit is mostly comprised of isolated teeth, and the only non-dental remains known can be attributed to the troodontid cf. Troodon and the tyrannosaurid Nanuqsaurus. Thus far, the presence of members of Dromaeosauridae has been limited to isolated teeth. Here we describe a symphyseal portion of a small dentary with two ziphodont teeth. Based on tooth shape, denticle morphology, and the position of the Meckelian groove, we attribute this partial dentary to a saurornitholestine dromaeosaurid. The fibrous bone surface, small size, and higher number of mesial denticles compared to distal ones point to a juvenile growth stage for this individual. Multivariate comparison of theropod teeth morphospace by means of principal component analysis reveals an overlap between this dentary and Saurornitholestinae dromaeosaurid morphospace, a result supported by phylogenetic analyses. This is the first confirmed non-dental fossil specimen from a member of Dromaeosauridae in the Arctic, expanding on the role of Beringia as a dispersal route for this clade between Asia and North America. Furthermore, the juvenile nature of this individual adds to a growing body of data that suggests Cretaceous Arctic dinosaurs of Alaska did not undergo long-distance migration, but rather they were year-round residents of these paleopolar latitudes.

Forelimb shortening of Carcharodontosauria (Dinosauria: Theropoda): an update on evolutionary anterior micromelias in non-avian theropods

Evolutionary teratology recognises certain anatomical modifications as developmental anomalies. Within non avian-theropod dinosaurs, the strong forelimb shortening of Tyrannosauridae, Carnotaurinae and Limusaurus - associated with a reduction or loss of autonomy - have been previously diagnosed as evolutionary anterior micromelias. The feature is here examined with Acrocanthosaurus atokensis (Carcharodontosauridae) and Gualicho shinyae (Neovenatoridae). The micromelic diagnosis is confirmed for Acrocanthosaurus, without supplementary malformations. Gualicho is considered as a borderline case, outside of the micromelic spectrum, but shows a total phalangeal loss on digit III. The reduction in the biomechanical range of Acrocanthosaurus' forelimbs was compensated by the skull and jaws as main predatory organs. The same is assumed for Gualicho, but its robust first digit and raptorial claw are to be underlined. Other gigantic-sized and derived representatives of Carcharodontosauridae probably shared the anterior micromelia condition, potentially due to developmental modifications involving differential forelimbs/hindlimbs embryological growth rates, secondarily associated with post-natal growth rates leading to large and gigantic sizes; a converging state with Tyrannosauridae. Nevertheless, whereas developmental growth rates are also considered in the shortened condition of Gualicho, there is no association with post-natal gigantism. Finally, the digit III reduction likely followed the same evolutionary pathways as Tyrannosauridae, potentially involving BMPs, Fgfs and Shh signalling.

Late Jurassic theropod dinosaur bones from the Langenberg Quarry (Lower Saxony, Germany) provide evidence for several theropod lineages in the central European archipelago

Marine limestones and marls in the Langenberg Quarry provide unique insights into a Late Jurassic island ecosystem in central Europe. The beds yield a varied assemblage of terrestrial vertebrates including extremely rare bones of theropod from theropod dinosaurs, which we describe here for the first time. All of the theropod bones belong to relatively small individuals but represent a wide taxonomic range. The material comprises an allosauroid small pedal ungual and pedal phalanx, a ceratosaurian anterior chevron, a left fibula of a megalosauroid, and a distal caudal vertebra of a tetanuran. Additionally, a small pedal phalanx III-1 and the proximal part of a small right fibula can be assigned to indeterminate theropods. The ontogenetic stages of the material are currently unknown, although the assignment of some of the bones to juvenile individuals is plausible. The finds confirm the presence of several taxa of theropod dinosaurs in the archipelago and add to our growing understanding of theropod diversity and evolution during the Late Jurassic of Europe.

Noasaurids are a component of the Australian 'mid'-Cretaceous theropod fauna

The diversity of Australia's theropod fauna from the 'mid'-Cretaceous (Albian-Cenomanian) is distinctly biased towards the medium-sized megaraptorids, despite the preponderance of abelisauroids in the younger but latitudinally equivalent Patagonian theropod fauna. Here, we present new evidence for the presence of ceratosaurian, and specifically abelisauroid, theropods from the Cenomanian Griman Creek Formation of Lightning Ridge, New South Wales. A partial cervical vertebra is described that bears a mediolaterally concave ventral surface of the centrum delimited by sharp ventrolateral ridges that contact the parapophyses. Among theropods, this feature has been reported only in a cervical vertebra attributed to the noasaurid Noasaurus. We also reappraise evidence recently cited against the ceratosaurian interpretation of a recently described astragalocalcaneum from the upper Barremian-lower Aptian San Remo Member of the upper Strzelecki Group in Victoria. Inclusion of the Lightning Ridge cervical vertebra and Victorian astragalocalcaneum into a revised phylogenetic analysis focused on elucidating ceratosaurian affinities reveals support for placement of both specimens within Noasauridae, which among other characters is diagnosed by the presence of a medial eminence on the ascending process of the astragalus. The Lightning Ridge and Victorian specimens simultaneously represent the first noasaurids reported from Australia and the astragalocalcaneum is considered the earliest known example of a noasaurid in the world to date. The recognition of Australian noasaurids further indicates a more widespread Gondwanan distribution of the clade outside of South America, Madagascar and India consistent with the timing of the fragmentation of the supercontinent.

A new desert-dwelling dinosaur (Theropoda, Noasaurinae) from the Cretaceous of south Brazil

Noasaurines form an enigmatic group of small-bodied predatory theropod dinosaurs known from the Late Cretaceous of Gondwana. They are relatively rare, with notable records in Argentina and Madagascar, and possible remains reported for Brazil, India, and continental Africa. In south-central Brazil, the deposits of the Bauru Basin have yielded a rich tetrapod fauna, which is concentrated in the Bauru Group. The mainly aeolian deposits of the Caiuá Group, on the contrary, bear a scarce fossil record composed only of lizards, turtles, and pterosaurs. Here, we describe the first dinosaur of the Caiuá Group, which also represents the best-preserved theropod of the entire Bauru Basin known to date. The recovered skeletal parts (vertebrae, girdles, limbs, and scarce cranial elements) show that the new taxon was just over 1 m long, with a unique anatomy among theropods. The shafts of its metatarsals II and IV are very lateromedially compressed, as are the blade-like ungual phalanges of the respective digits. This implies that the new taxon could have been functionally monodactyl, with a main central weight-bearing digit, flanked by neighbouring elements positioned very close to digit III or even held free of the ground. Such anatomical adaptation is formerly unrecorded among archosaurs, but has been previously inferred from footprints of the same stratigraphic unit that yielded the new dinosaur. A phylogenetic analysis nests the new taxon within the Noasaurinae clade, which is unresolved because of the multiple alternative positions that Noasaurus leali can acquire in the optimal trees. The exclusion of the latter form results in positioning the new dinosaur as the sister-taxon of the Argentinean Velocisaurus unicus.

The oldest ceratosaurian (Dinosauria: Theropoda), from the Lower Jurassic of Italy, sheds light on the evolution of the three-fingered hand of birds

The homology of the tridactyl hand of birds is a still debated subject, with both paleontological and developmental evidence used in support of alternative identity patterns in the avian fingers. With its simplified phalangeal morphology, the Late Jurassic ceratosaurian Limusaurus has been argued to support a II-III-IV digital identity in birds and a complex pattern of homeotic transformations in three-fingered (tetanuran) theropods. We report a new large-bodied theropod, Saltriovenator zanellai gen. et sp. nov., based on a partial skeleton from the marine Saltrio Formation (Sinemurian, lowermost Jurassic) of Lombardy (Northern Italy). Taphonomical analyses show bone bioerosion by marine invertebrates (first record for dinosaurian remains) and suggest a complex history for the carcass before being deposited on a well-oxygenated and well-illuminated sea bottom. Saltriovenator shows a mosaic of features seen in four-fingered theropods and in basal tetanurans. Phylogenetic analysis supports sister taxon relationships between the new Italian theropod and the younger Early Jurassic Berberosaurus from Morocco, in a lineage which is the basalmost of Ceratosauria. Compared to the atrophied hand of later members of Ceratosauria, Saltriovenator demonstrates that a fully functional hand, well-adapted for struggling and grasping, was primitively present in ceratosaurians. Ancestral state reconstruction along the avian stem supports 2-3-4-1-X and 2-3-4-0-X as the manual phalangeal formulae at the roots of Ceratosauria and Tetanurae, confirming the I-II-III pattern in the homology of the avian fingers. Accordingly, the peculiar hand of Limusaurus represents a derived condition restricted to late-diverging ceratosaurians and cannot help in elucidating the origin of the three-fingered condition of tetanurans. The evolution of the tridactyl hand of birds is explained by step-wise lateral simplification among non-tetanuran theropod dinosaurs, followed by a single primary axis shift from digit position 4 to 3 at the root of Tetanurae once the fourth finger was completely lost, which allowed independent losses of the vestigial fourth metacarpal among allosaurians, tyrannosauroids, and maniraptoromorphs. With an estimated body length of 7.5 m, Saltriovenator is the largest and most robust theropod from the Early Jurassic, pre-dating the occurrence in theropods of a body mass approaching 1,000 Kg by over 25 My. The radiation of larger and relatively stockier averostran theropods earlier than previously known may represent one of the factors that ignited the trend toward gigantism in Early Jurassic sauropods.

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.

Ceratosaur palaeobiology: new insights on evolution and ecology of the southern rulers

Ceratosaur theropods ruled the Southern Hemisphere until the end of the Late Cretaceous. However, their origin was earlier, during the Early Jurassic, a fact which allowed the group to reach great morphological diversity. The body plans of the two main branches (Noasauridae and new name Etrigansauria: Ceratosauridae + Abelisauridae) are quite different; nevertheless, they are sister taxa. Abelisaurids have lost the ability to grasp in the most derived taxa, but the reduced forelimb might have had some display function. The ontogenetic changes are well known in Limusaurus which lost all their teeth and probably changed the dietary preference at maturity. The results presented here suggest that abelisaurids had different soft tissues on the skull. These tissues might have been associated with evolution of a strong cervicocephalic complex and should have allowed derived taxa (e.g. Majungasaurus and Carnotaurus) to have low-displacement headbutting matches. The ability to live in different semi-arid environment plus high morphological disparity allowed the ceratosaurs to become an evolutionary success.

The oldest Archaeopteryx (Theropoda: Avialiae): a new specimen from the Kimmeridgian/Tithonian boundary of Schamhaupten, Bavaria

The iconic primeval bird Archaeopteryx was so far mainly known from the Altmühltal Formation (early Tithonian) of Bavaria, southern Germany, with one specimen having been found in the overlying Mörnsheim Formation. A new specimen (the 12th skeletal specimen) from the earliest Tithonian Painten Formation of Schamhaupten (Bavaria) represents the so far oldest representative of the genus. The new specimen shows several interesting anatomical details, including the presence of a postorbital in contact with the jugal, the presence of a separate prefrontal and coronoid, and opisthocoelous mid-cervical vertebrae. Based on observations on the new specimen, we discuss several problematic issues concerning Archaeopteryx, including the monophyly and diagnosis of the genus, the absence/presence of the sternum, the position of the gastralia, and variation in morphometrics and dental morphology in that genus. Based on a new diagnosis for the genus Archaeopteryx, the Berlin, Eichstätt, Solnhofen, Munich, Daiting, Thermopolis, 11th, and 12th specimens can be referred to this genus with high certainty. The Maxberg specimen is very probably also an Archaeopteryx, based on overall similarity, although none of the diagnostic characters can be evaluated with certainty. The ninth specimen (‘chicken wing’) might be Archaeopteryx, but cannot be referred to the genus with any certainty. In comparison with other paravians, the presence of distally thickened anterior pectoral ribs indicates that a rather large cartilagenous sternum was present in this taxon. In contrast to non-opisthopubic theropods, opisthopubic taxa, such as Archaeopteryx and many other paravians, have the posterior end of the gastral basket preserved at about half-length of the pubis, which might reflect the post-mortem collapse of enlarged abdominal air sacs in these taxa. Specimens that can be referred to Archaeopteryx show a high amount of variation, both in the morphometrics of the limb bones as well as in the dentition. In respect to the latter aspect, variation is found in tooth number, spacing, orientation, and morphology, with no two specimens showing the exact same pattern. The significance of this variation is unclear, and possible explanations reach from high intraspecific (and possibly ontogenetic and/or sexual dimorphic) variation to the possibility that the known specimens represent a ‘species flock’ of Archaeopteryx, possibly due to island speciation after the initial dispersal of the genus into the Solnhofen Archipelago.