Re-evaluation of the Haarlem Archaeopteryx and the radiation of maniraptoran theropod dinosaurs

Archaeopteryx is an iconic fossil that has long been pivotal for our understanding of the origin of birds. Remains of this important taxon have only been found in the Late Jurassic lithographic limestones of Bavaria, Germany. Twelve skeletal specimens are reported so far. Archaeopteryx was long the only pre-Cretaceous paravian theropod known, but recent discoveries from the Tiaojishan Formation, China, yielded a remarkable diversity of this clade, including the possibly oldest and most basal known clade of avialan, here named Anchiornithidae. However, Archaeopteryx remains the only Jurassic paravian theropod based on diagnostic material reported outside China

Ontogenetic, macroevolutionary and morphofunctional patterns in archosaur skulls

The Archosauria represent the most successful clade within tetrapods, having a large diversity in terms of species, diet spectra, body plans and locomotion styles. This is also true for the skull morphology, which shows a wide variety in shape and size, as well as in the common formation of beaks, crests, domes or horns. Archosaur skulls have been studied intensively in terms of their morphology, ontogeny, function, ecology and behavior in the past, but most of these studies have largely been restricted to case studies of single species or only a small number of taxa. The aim of the current thesis is to obtain better and comprehensive insight into skull shape diversity of archosaurs by using a two-dimensional geometric morphometric approach, with a special focus on ontogenetic and macroevolutionary patterns and their relation to function and ecology. Skull shape variation was quantified for Crocodylomorpha (including an ontogenetic series of the recent caimanine alligatorid Melanosuchus niger), Pterosauria, Sauropodomorpha and Theropoda. The material used for the analyses consists of skull reconstructions published in the scientific literature and photographs of skull material. The most important results of the thesis are summarized as follows: •The use of different skull reconstructions of the same specimen from the scientific literature has no significant influence on the results of morphometric analyses. However, the results could be potentially falsified by the use of reconstructions based on highly incomplete, strongly deformed or pathologic specimens. •In some cases the degree of intraspecific variation of one species can be as great as the interspecific variation of closely related species with similar ecological niches. Thus, species with great intraspecific diversity could have an impact on the results of morphometric analyses. •The skull shape of Archosauria is strongly correlated with function. A closer examination within theropod skulls reveals that the shape of the postrostrum is probably more affected by functional constraints than the snout, but the greatest correlation to the function was found in the orbital shape. The latter result supports previous studies on the biomechanics of theropod skulls. A comparison of the ontogenetic bite force performance with the cranial growth in the alligatorid Melanosuchus and biomechanical studies on crocodile skulls reveals that ontogenetic shape changes, especially in the orbital and postorbital region, are functional constrained. •Both ontogenetic and interspecific skull shape variation in archosaurs is correlated to diet preferences and feeding behaviour. A comparison between carnivorous and non-carnivorous (i.e. omnivorous and herbivorous) theropods reveals that both ecological groups occupy large areas within the morphospace without showing a significant overlap. Furthermore, small-bodied theropods tend to have a larger diet spectrum, suggesting that diet preferences within theropods are probably size related. •The distribution of taxa within the morphospace of Crocodylomorpha, Pterosauria, Sauropodomorpha and Theropoda is strongly correlated with the phylogenetic interrelationship of these clades: Closely related taxa appear closer to one another within the morphospace than more distantly related taxa. This result indicates that skull shape in archosaurs is further constrained by phylogeny. •When inferred from geometric morphometric data, disparity results proved to be similar to those based on limb measurements and discrete characters from phylogenetic analyses. This results justifies the use of geometric morphometric data as a further and equally useful proxy for addressing disparity. •Early archosaur hatchlings share features of the skull shape, including short, pointed snouts, enlarged orbits and large postorbital regions. However, ontogenetic shape changes are only congruous in terms of a relative increase of the snout length and a relative decrease of the orbit size. The degree of these changes is not uniform, so that adult specimens of different species can vary substantially in snout length or orbit shape. Furthermore, archosaurs show a huge variability of changes in the snout depth, the length of the postorbital region as well as the relative size of the antorbital fenestra and the lateral temporal fenestra during ontogeny. This variability in ontogenetic trajectories probably causes the large skull shape diversity found in archosaurs. •Due to the great variability in ontogenetic trajectories, cranial evolution of archosaurs is strongly affected by heterochronic events. Skull shape evolution of Crocodylomorpha, Sauropodomorpha, basal theropods, Tyrannosauroidea as well as derived Oviraptoridae, Dromaeosauridae and Troodontidae was probably influenced by peramorphosis. However, within Crocodylia the short skull of Osteolaemus might result from a paedomorphic event. This is also likely for the short-snouted basal theropods Daemonosaurus and Limusaurus. The great similarity in the skull shapes of the juvenile megalosaurid Sciurumimus and basal coelurosaurs reveals that the skull shapes of the latter might be also caused by paedomorphosis. Further paedomorphic trends are suspected for the skull evolution of basal Maniraptora and Avialae. The heterochronic events found seem to correlate with body size evolution.Die Archosaurier repräsentieren die erfolgreichste Gruppe unter den Tetrapoden, die durch eine große Diversität an Arten, Nahrungspektren, Bewegungsformen und im Körperbau gekennzeichnet ist. Dies gilt auch für die Schädelmorphologie, die durch eine große Variation in Größe und Formen sowie der häufigen Ausbildung von Schnäbeln, Hörnern, Hauben und Kämmen gekennzeichnet ist. Die Schädel der Archosaurier wurden in der Vergangenheit intensiv hinsichtlich ihrer Morphologie, Ontogenese, Funktion, Ökologie und Verhalten untersucht, jedoch beschränken sich die meisten Arbeiten auf Fallstudien zu einzelnen Arten bzw. einer kleinen Auswahl von Taxa. In der vorliegenden Arbeit soll die Diversität der Schädelmorphologie innerhalb der Archosaurier mit Hilfe von zwei-dimensionaler geometrischen Morphometrie auf breiterer Ebene untersucht werden. Dabei sollen sowohl ontogenetische als auch makroevolutive Muster und ihre Beziehung zu Funktion und Ökologie näher betrachtet werden. Eine Quantifizierung der Schädelform erfolgte für Crocodylomorpha (inklusive einer ontogenetischen Serie des rezenten Alligatoriden Melanosuchus niger), Pterosauria, Sauropodomorpha und Theropoda. Als Grundlage dienten publizierte Schädelrekonstruktionen aus der wissenschaftlichen Literatur sowie Fotos von Schädelmaterial. Die wichtigsten Ergebnisse der Arbeit sind wie folgt zusammengefasst: •Die Verwendung von verschiedenen Schädelrekonstruktionen desselben Individuums aus der wissenschaftlichen Literatur hat keinen signifikanten Einfluss auf die Ergebnisse von morphometrischen Analysen. Die Ergebnisse können jedoch durch die Verwendung von Rekonstruktionen verfälscht werden, die auf unvollständigem, stark verformtem oder pathologisch verändertem Material basieren. •In einigen Fällen kann das Maß der innerartlichen Variation vergleichbar sein mit der zwischenartlichen Variation von nah-verwandten Arten mit ähnlichen ökologischen Nischen. Daher können Arten mit großer innerartlichen Variation die Ergebnisse von morphometrischen Analysen beeinträchtigen. •Die Schädelform der Archosaurier korreliert stark mit der Funktion. Eine detaillierte Untersuchung an Theropoden-Schädeln zeigt, dass die Form des Hinterhaupts stärker durch Funktion beeinflusst wird als die Form der Schnauze. Die größte Korrelation zwischen Form und Funktion findet sich in der Augenhöhle, was die Ergebnisse früherer Arbeiten zur Biomechanik von Theropoden-Schädeln unterstützt. Ein Vergleich der ontogenetischen Beißkraftleistung mit dem Schädelwachstum bei Melanosuchus mit biomechanischen Studien an Krokodilschädeln zeigt, dass ontogenetische Veränderungen der Schädelform, speziell im Augen- und Hinterhauptsbereich, funktional beeinträchtigt sind. •Sowohl ontogenetische als auch interspezifische Variation der Schädelform korrelieren bei Archosauriern mit Nahrungspräferenzen und Fressverhalten. Ein Vergleich zwischen karnivoren und nicht-karnivoren (d.h. omnivoren und herbivoren) Theropoden zeigt, dass beide ökologischen Gruppen große Bereiche im „Morphospace“ einnehmen, jedoch nicht signifikant miteinander überlappen. Kleinere Theropoden besitzen hier ein breiteres Nahrungspektrum, so dass Präferenzen in der Nahrung wahrscheinlich größenabhängig sind. •Die Verteilung der Taxa im „Morphospace“ der Crocodylomorpha, Pterosauria, Sauropodomorpha und Theropoda korreliert stark mit dem phylogenetischen Verwandtschaft dieser Gruppen, d.h. das näher verwandte Taxa im „Morphospace“ näher beieinander liegen als entfernt verwandte Taxa. Dieses Ergebnis zeigt weiterhin, dass die Schädelform der Archosaurier auch durch die phylogenetische Verwandtschaft beeinträchtigt ist. •Übereinstimmungen in den Ergebnissen von Disparitätsanalysen basierend auf geometrischer Morphometrie mit solchen basierend auf Längenmessungen und diskreten Merkmalen aus phylogenetischen Analysen zeigen, dass Disparität über mehrere Proxies gemessen werden kann, inklusive geometrisch morphometrischer Daten. •Die Schädelformen von verschiedenen Archosaurier-Schlüpflingen ähneln einander durch das Vorhandensein einer kurzen Schnauze, großen Augenhöhlen und einer vergrößerten Hinterhauptsregion. Allgemeine ontogenetische Veränderungen betreffen die relative Verlängerung der Schnauze und die relative Verkleinerung der Augenhöhle. Diese Veränderungen sind allerdings nicht einheitlich in ihrer Intensität, so dass ausgewachsene Individuen verschiedener Arten sich deutlich in der Länge der Schnauze und der Form der Augen unterscheiden können. Des Weiteren besitzen Archosaurier ein große ontogenetische Variabilität hinsichtlich der Höhe der Schnauze, der Länge des Hinterhaupts sowie der relativen Größe des Antorbitalfensters und des lateralen Temporalfensters. Die große Variabilität der ontogenetischen Trajektorien ist wahrscheinlich für die große Diversität an Schädelformen innerhalb der Archosaurier verantwortlich. •Aufgrund der großen Variabilität ontogenetischer Trajektorien ist die Schädelevolution der Archosaurier sehr stark durch heterochronische Ereignisse geprägt. Die Schädelevolution von Crocodylomorpha, Sauropodomorpha, basalen Theropoden, Tyrannosauroidea sowie abgeleiteten Oviraptoridae, Dromaeosauridae und Troodontidae ist wahrscheinlich durch Peramorphose beeinflusst. Innerhalb der Crocodylia resultiert der kurze Schädel von Osteolaemus wahrscheinlich aus einer Pädomorphose. Das ist wahrscheinlich auch der Fall für die beiden kurzschnauzigen basalen Theropoden Daemonosaurus und Limusaurus. Die große Übereinstimmung der Schädelform des juvenilen Megalosauriden Sciurumimus mit dem von basalen Coelurosauriern könnte ebenfalls ein Hinweis sein, dass die Schädelform der basalen Coelurosaurier das Resultat einer Pädomorphose ist. Weitere pädomorphe Ereignisse könnten in der Schädelevolution der Maniraptora und Avialae aufgetreten sein. Die heterochronischen Ereignisse scheinen in enger Beziehung zur Evolution der Körpergröße zu stehen

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

Preliminary observations on the bone histology of the Middle Triassic pseudosuchian archosaur Batrachotomus kupferzellensis reveal fast growth with laminar fibrolamellar bone tissue

The bone tissue of femur, rib, and gastralia from three different individuals of the Middle Triassic pseudosuchian Batrachotomus kupferzellensis from southern Germany is studied. The femoral bone tissue comprises laminar fibrolamellar bone tissue throughout and is stratified by three annual growth cycles, indicating that the individual died early in its fourth year of life, at which time it had reached 87% of maximum known femur length. Thus, compared with most other Pseudosuchia (e.g., phytosaurs, aetosaurs, and most crocodylomorphs, including marine taxa), Batrachotomus achieved its large body size in a very short time by fast, although interrupted, growth and not by protracted longevity. Such fast growth as well as the organization of the tissue is similar to the condition observed in ornithodirans. The pseudosuchians Effigia and Postosuchus also show fibrolamellar tissue, but vascular density is lower when compared with Batrachotomus and dominated by a longitudinal organization of primary osteons. The rib and gastralium of Batrachotomus both show an inner spongious organization surrounded by a ring of compact, avascular, highly organized parallel-fibered and/or lamellar bone largely covered by short fibers. Maximal growth cycle count in the proximal rib sample suggests an age of at least 11 years for this individual with a reduction of growth rate after the sixth cycle.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVPCitation for this article: Klein, N., C. Foth, and R. R. Schoch. 2017. Preliminary observations on the bone histology of the Middle Triassic pseudosuchian archosaur Batrachotomus kupferzellensis reveal fast growth with laminar fibrolamellar bone tissue

Cranial ontogenetic variation in early saurischians and the role of heterochrony in the diversification of predatory dinosaurs

Non-avian saurischian skulls underwent at least 165 million years of evolution and shapes varied from elongated skulls, such as in the theropod Coelophysis, to short and box-shaped skulls, such as in the sauropod Camarasaurus. A number of factors have long been considered to drive skull shape, including phylogeny, dietary preferences and functional constraints. However, heterochrony is increasingly being recognized as an important factor in dinosaur evolution. In order to quantitatively analyse the impact of heterochrony on saurischian skull shape, we analysed five ontogenetic trajectories using two-dimensional geometric morphometrics in a phylogenetic framework. This allowed for the comparative investigation of main ontogenetic shape changes and the evaluation of how heterochrony affected skull shape through both ontogenetic and phylogenetic trajectories. Using principal component analyses and multivariate regressions, it was possible to quantify different ontogenetic trajectories and evaluate them for evidence of heterochronic events allowing testing of previous hypotheses on cranial heterochrony in saurischians. We found that the skull shape of the hypothetical ancestor of Saurischia likely led to basal Sauropodomorpha through paedomorphosis, and to basal Theropoda mainly through peramorphosis. Paedomorphosis then led from Orionides to Avetheropoda, indicating that the paedomorphic trend found by previous authors in advanced coelurosaurs may extend back into the early evolution of Avetheropoda. Not only are changes in saurischian skull shape complex due to the large number of factors that affected it, but heterochrony itself is complex, with a number of possible reversals throughout non-avian saurischian evolution. In general, the sampling of complete ontogenetic trajectories including early juveniles is considerably lower than the sampling of single adult or subadult individuals, which is a major impediment to the study of heterochrony on non-avian dinosaurs. Thus, the current work represents an exploratory analysis. To better understand the cranial ontogeny and the impact of heterochrony on skull evolution in saurischians, the data set that we present here must be expanded and complemented with further sampling from future fossil discoveries, especially of juvenile individuals

Rapid Initial Morphospace Expansion and Delayed Morphological Disparity Peak in the First 100 Million Years of the Archosauromorph Evolutionary Radiation

Adaptive radiations have played a major role in generating modern and deep-time biodiversity. The Triassic radiation of the Archosauromorpha was one of the most spectacular vertebrate radiations, giving rise to many highly ecomorphologically varied lineages—including the dinosaurs, pterosaurs, and stem-crocodylians—that dominated the larger-bodied land fauna for the following 150 Ma, and ultimately gave rise to today’s > 10,000 species of birds and crocodylians. This radiation provides an outstanding testbed for hypotheses relating to adaptive radiations more broadly. Recent studies have started to characterize the tempo and mode of the archosauromorph early adaptive radiation, indicating very high initial rates of evolution, non-competitive niche-filling processes, and previously unrecognized morphological disparity even among non-crown taxa. However, these analyses rested primarily either on discrete characters or on geometric morphometrics of the cranium only, or even failed to fully include phylogenetic information. Here we expand previous 2D geometric morphometric cranial datasets to include new taxa and reconstructions, and create an analogous dataset of the pelvis, thereby allowing comparison of anatomical regions and the transition from “sprawling” to “upright” posture to be examined. We estimated morphological disparity and evolutionary rates through time. All sampled clades showed a delayed disparity peak for sum of variances and average nearest neighbor distances in both the cranium and pelvis, with disparity likely not saturated by the end of the studied time span (Late Jurassic); this contrasts with smaller radiations, but lends weight to similar results for large, ecomorphologically-varied groups. We find lower variations in pelvic than cranial disparity among Triassic-Jurassic archosaurs, which may be related to greater morphofunctional constraints on the pelvis. Contrasting with some previous work, but also confirming some previous findings during adaptive radiations, we find relatively widespread evidence of correlation between sampled diversity and disparity, especially at the largest phylogenetic scales and using average displacement rather than sum of variances as disparity metric; this also demonstrates the importance of comparing disparity metrics, and the importance of phylogenetic scale. Stem and crown archosauromorphs show a morphological diversification of both the cranium and pelvis with higher initial rates (Permian–Middle Triassic and at the base of major clades) followed by lower rates once diversification into niches has occurred (Late Triassic–Jurassic), indicating an “early burst” pattern sensu lato. Our results provide a more detailed and comprehensive picture of the early archosauromorph radiation and have significant bearing on the understanding of deep-time adaptive radiations more broadly, indicating widespread patterns of delayed disparity peaks, initial correlation of diversity and disparity, and evolutionary early bursts.Fil: Foth, Christian. University of Fribourg; Alemania. Staatliches Museum fur Naturkunde Stuttgart; AlemaniaFil: Sookias, Roland B.. Université de Liège; Bélgica. University of Oxford; Reino Unido. Staatliches Museum fur Naturkunde Stuttgart; AlemaniaFil: Ezcurra, Martin Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentin

A non-archaeopterygid avialan theropod from the Late Jurassic of southern Germany

The Late Jurassic 'Solnhofen Limestones' are famous for their exceptionally preserved fossils, including the urvogel Archaeopteryx, which has played a pivotal role in the discussion of bird origins. Here we describe a new, non-archaeopterygid avialan from the Lower Tithonian Mornsheim Formation of the Solnhofen Archipelago, Alcmonavis poeschli gen. et sp. nov. Represented by a right wing, Alcmonavis shows several derived characters, including a pronounced attachment for the pectoralis muscle, a pronounced tuberculum bicipitale radii, and a robust second manual digit, indicating that it is a more derived avialan than Archaeopteryx. Several modifications, especially in muscle attachments of muscles that in modern birds are related to the downstroke of the wing, indicate an increased adaptation of the forelimb for active flapping flight in the early evolution of birds. This discovery indicates higher avialan diversity in the Late Jurassic than previously recognized

A non-archaeopterygid avialan theropod from the Late Jurassic of southern Germany

The Late Jurassic 'Solnhofen Limestones' are famous for their exceptionally preserved fossils, including the urvogel Archaeopteryx, which has played a pivotal role in the discussion of bird origins. Here we describe a new, non-archaeopterygid avialan from the Lower Tithonian Mornsheim Formation of the Solnhofen Archipelago, Alcmonavis poeschli gen. et sp. nov. Represented by a right wing, Alcmonavis shows several derived characters, including a pronounced attachment for the pectoralis muscle, a pronounced tuberculum bicipitale radii, and a robust second manual digit, indicating that it is a more derived avialan than Archaeopteryx. Several modifications, especially in muscle attachments of muscles that in modern birds are related to the downstroke of the wing, indicate an increased adaptation of the forelimb for active flapping flight in the early evolution of birds. This discovery indicates higher avialan diversity in the Late Jurassic than previously recognized