Amanda R. Falk

Model tests of gliding with different hindwing configurations in the four-winged dromaeosaurid Microraptor gui

Fossils of the remarkable dromaeosaurid Microraptor gui and relatives clearly show well-developed flight feathers on the hind limbs as well as the front limbs. No modern vertebrate has hind limbs functioning as independent, fully developed wings; so, lacking a living example, little agreement exists on the functional morphology or likely flight configuration of the hindwing. Using a detailed reconstruction based on the actual skeleton of one individual, cast in the round, we developed light-weight, three-dimensional physical models and performed glide tests with anatomically reasonable hindwing configurations. Models were tested with hindwings abducted and extended laterally, as well as with a previously described biplane configuration. Although the hip joint requires the hindwing to have at least 20° of negative dihedral (anhedral), all configurations were quite stable gliders. Glide angles ranged from 3° to 21° with a mean estimated equilibrium angle of 13.7°, giving a lift to drag ratio of 4.1:1 and a lift coefficient of 0.64. The abducted hindwing model’s equilibrium glide speed corresponds to a glide speed in the living animal of 10.6 m·s−1. Although the biplane model glided almost as well as the other models, it was structurally deficient and required an unlikely weight distribution (very heavy head) for stable gliding. Our model with laterally abducted hindwings represents a biologically and aerodynamically reasonable configuration for this four-winged gliding animal. M. gui’s feathered hindwings, although effective for gliding, would have seriously hampered terrestrial locomotion.

The birdlike raptor Sinornithosaurus was venomous

We suggest that some of the most avian dromaeosaurs, such as Sinornithosaurus, were venomous, and propose an ecological model for that taxon based on its unusual dentition and other cranial features including grooved teeth, a possible pocket for venom glands, and a groove leading from that pocket to the exposed bases of the teeth. These features are all analogous to the venomous morphology of lizards. Sinornithosaurus and related dromaeosaurs probably fed on the abundant birds of the Jehol forests during the Early Cretaceous in northeastern China.

Tree climbing – a fundamental avian adaptation

There have been a number of studies on the claws of Mesozoic birds, largely driven by interest in the habitat of Archaeopteryx. Many Mesozoic avians have large, well formed manual claws, largely absent in contemporary birds. Juvenile hoatzins are the only living birds with claws that are large enough to be generally functional, but not equivalent to those of Mesozoic birds. When birds developed an effective backstroke permitting easy ascent from flat surfaces, the need for manual claws disappeared, which would suggest that they were primarily used for climbing tree trunks and had little function in prey capture. This hypothesis has both phylogenetic and functional implications. The numerous claw studies to date are based primarily on measurements taken of the bony core, all that is usually preserved in fossils. Examination of contemporary birds shows that this is a poor estimator of the size and shape of the horny sheath that actually forms the functional claw. The discovery of vast numbers of exceptionally preserved fossil birds from the Late Jurassic and Early Cretaceous of China means that we now have an opportunity to compare actual horny claw data from the earliest birds with that of modern birds and test hypotheses on climbing, terrestrial activity, and predation.

Feeding traces associated with bird tracks from the Lower Cretaceous Haman Formation, Republic of Korea

Abstract The bird track localities of the Republic of Korea are among the richest and most diverse avian tracksites in the world; however, no behavioral studies have been conducted with them. This paper examines the association of invertebrate traces, avian footprints, and small, enigmatic elongate and double-oval traces from silicone casts (KS001 and KS064) taken from two specimens from the Haman Formation near Jinju. Two distinct types of bird tracks are present: a larger type with a well-defined hallux impression on the majority of the tracks, Koreanaornis isp., and a smaller type without a clear hallux impression, K. hamanensis. Elongate traces interpreted to be peck marks and double-oval traces interpreted to be probe marks were found on KS001. The peck marks range from 4.0 to 11.2 mm long and average 7.6 mm in width. There are two distinct morphologies of probe marks which may represent different species or genera of birds. The large probe mark is 6.9 mm long and 2.9 mm wide, whereas the smaller probe marks are 4.5 mm long by 2.2 mm wide and 5.7 mm long by 3.0 mm wide, respectively. Invertebrate traces associated with the bird tracks and feeding traces include Cochlichnus, Steinichnus, and Arenicolites. This represents the first report of peck marks from a fossil bird track locality.

A morphologic criterion to distinguish bird tracks

Few anatomical criteria have been proposed to distinguish bird tracks from dinosaur tracks. The most commonly used criterion is the angle of divarication between toes II and IV, which is usually greater in birds than dinosaurs. The angle of divarication as related to some skeletal feature in modern birds may provide additional information about the trackmaker and its evolutionary relationships. A total of 186 bird tarsometatarsi (11 orders, 21 families, 39 genera, 41 species) from 8 morphotypes—shorebirds, wading birds, perching birds, zygodactyl birds, birds of prey, ground foragers, webbed-footed birds, and syndactyl birds—were sampled to test the hypothesis that the morphology of the distal end of the tarsometatarsus is the primary influence on the angle of divarication of the toes. Skeletal limb anatomy was also studied for correlations with stride length in an effort to predict pivot point height in birds from their trackways. Analysis shows a pronounced correlation between a large trochlea arc angle, and a small angle of divarication. Distinct differences in the trochlear arc angle and the angle of divarication could be correlated to such avian morphotypes as shorebirds, waders, ground foragers, and perching birds. No correlations between limb length and stride length could be established, and the equations commonly used for most vertebrate trackways did not hold for birds, most likely due to their unique hindlimb anatomy.ZusammenfassungBisher wurden wenige anatomische Kriterien aufgestellt, um Vogel- von Dinosaurierspuren zu trennen. Das am häufigsten verwendete Kriterium verwendete den Winkel der Divarication zwischen der II. und IV. Zehe, der bei Vögeln in der Regel größer ist als bei Dinosauriern. Der Winkel der Divarikation in Beziehung gesetzt zu einigen Skelettmerkmalen moderner Vögel liefert womöglich zusätzliche Informationen über den Spurenverursacher und seine evolutionäre Stellung. Insgesamt wurden die Tarsometatarsi von 186 Vögeln (11 Ordnungen, 21 Familien, 39 Gattungen, 41 Arten) von 8 Morphotypen—Küstenvögeln, Watvögeln, Ansitzjägern, zygodactylen Vögeln, Greifvögeln, am Boden nach Nahrung suchenden Vögeln, Vögeln mit Schwimmhäuten und syndactylen Vögeln—untersucht, um die Hypothese zu testen, dass die Morphologie des distalen Endes des Tarsometatarsus primär den Winkel der Divarikation der Zehen beeinflusst. Darüber hinaus wurde auch die Lauf-Anatomie auf Korrelationen mit der Schrittlänge untersucht, um die Drehpunkthöhe der Vögel aus ihren Spuren vorherzusagen. Die Analyse erbrachte eine deutliche Korrelation zwischen einem großen Winkel des Trochlearbogens und einem kleinen Winkel der Divarikation. Deutliche Unterschiede im Winkel des Trochlearbogens und dem Winkel der Divarikation konnten mit Vogel-Morphotypen wie Küstenvögeln, Watvögeln, am Boden nach Nahrung suchenden Vögeln und Ansitzjägern in Beziehung gebracht werden. Zwischen Hinterlauf- und Schrittlänge konnten keine Korrelationen festgestellt werden, und die Gleichungen, die für die meisten Vertebratenspuren häufig verwendet werden, waren auf Vögel nicht anwendbar, höchstwahrscheinlich aufgrund ihrer einzigartigen Hinterlauf-Anatomie.

Laser-Stimulated Fluorescence in Paleontology

Fluorescence using ultraviolet (UV) light has seen increased use as a tool in paleontology over the last decade. Laser-stimulated fluorescence (LSF) is a next generation technique that is emerging as a way to fluoresce paleontological specimens that remain dark under typical UV. A laser’s ability to concentrate very high flux rates both at the macroscopic and microscopic levels results in specimens fluorescing in ways a standard UV bulb cannot induce. Presented here are five paleontological case histories that illustrate the technique across a broad range of specimens and scales. Novel uses such as back-lighting opaque specimens to reveal detail and detection of specimens completely obscured by matrix are highlighted in these examples. The recent cost reductions in medium-power short wavelength lasers and use of standard photographic filters has now made this technique widely accessible to researchers. This technology has the potential to automate multiple aspects of paleontology, including preparation and sorting of microfossils. This represents a highly cost-effective way to address paleontologys preparatory bottleneck.

Basal paravian functional anatomy illuminated by high-detail body outline

Body shape is a fundamental expression of organismal biology, but its quantitative reconstruction in fossil vertebrates is rare. Due to the absence of fossilized soft tissue evidence, the functional consequences of basal paravian body shape and its implications for the origins of avians and flight are not yet fully understood. Here we reconstruct the quantitative body outline of a fossil paravian Anchiornis based on high-definition images of soft tissues revealed by laser-stimulated fluorescence. This body outline confirms patagia-bearing arms, drumstick-shaped legs and a slender tail, features that were probably widespread among paravians. Finely preserved details also reveal similarities in propatagial and footpad form between basal paravians and modern birds, extending their record to the Late Jurassic. The body outline and soft tissue details suggest significant functional decoupling between the legs and tail in at least some basal paravians. The number of seemingly modern propatagial traits hint that feathering was a significant factor in how basal paravians utilized arm, leg and tail function for aerodynamic benefit.

Tracking Mesozoic birds across the world

Early Cretaceous bird tracks have been found in North America, China, South Korea and Japan. The identification of many of the tracemakers as ornithurine birds rather than enantiornithines is supported by the overall morphological and behavioural similarity to tracks left by modern shorebirds, as well as indicators of ground-to-air takeoff. Various morphologies found in Asia, including web-footed, anisodactyl and zygodactyl tracks, indicate a very high diversity of birds. The most common are anisodactyl shorebird-like tracks represented by Aquatilavipes, Koreanaornis, Ignotornis and others. Such ichnogenera as Aquatilavipes and, more recently, Koreanaornis, have been discovered on both sides of the Pacific Ocean. Koreanaornis is more specific in its distinguishing criteria, unlike Aquatilavipes, which may be a taxonomic wastebasket. The appearance of the same ichnogenera across great distances implies that either ornithurine birds evolved long-distance migration in or before the Early Cretaceous, or that ornithurine birds arose before the Cretaceous. Molecular data support an Early Cretaceous origin for modern bird families, and shorebird-like tracks have been reported from very near the Jurassic–Cretaceous boundary. Shorebird-like trackways have been reported from the Early Jurassic of Africa and North America (e.g. Trisaurpodiscus), suggesting an even earlier origin for ornithurine birds.

First Record of Cenozoic Bird Footprints from East Asia (Tibet, China)

Cenozoic bird tracks are known largely from North America, Europe, and the Middle East. There have been no reports of Cenozoic bird tracks from East Asia. This paper describes a series of two trackways produced by a galliform-like or gruiform-like bird from the Oligocene to Early Miocene of Tibet. The tracks are represented by tracings collected from a coal mine in Shigatse, Tibet, during the late 1970s. The tracks are comparable to Ornithoformipes and Pavoformipes and likely represent a medium-sized to large cursorial or flightless bird. In relation to modern bird tracks, the tracks bear a striking resemblance to those produced by the North American Wild Turkey (Meleagris gallopavo) except that M. gallopavo tracks often possess a small, elevated hallux impression. Due to the fact that these are tracings, however, a hallux may have been present and simply have been overlooked. The Shigatse trackways were, unfortunately, lost when the mine was closed and then backfilled during the 1980s, and there is little to no likelihood of recovery. Casts can be catalogued as holotype specimens but tracings cannot; however, all the original tracings have been donated to a public institution by their discoverer, Yimin Wu.

Laser Fluorescence Illuminates the Soft Tissue and Life Habits of the Early Cretaceous Bird Confuciusornis

In this paper we report the discovery of non-plumage soft tissues in Confuciusornis, a basal beaked bird from the Early Cretaceous Jehol Biota in northeastern China. Various soft tissues are visualized and interpreted through the use of laser-stimulated fluorescence, providing much novel anatomical information about this early bird, specifically reticulate scales covering the feet, and the well-developed and robust pro- and postpatagium. We also include a direct comparison between the forelimb soft tissues of Confuciusornis and modern avian patagia. Furthermore, apparently large, fleshy phalangeal pads are preserved on the feet. The reticulate scales, robust phalangeal pads as well as the highly recurved pedal claws strongly support Confuciusornis as an arboreal bird. Reticulate scales are more rounded than scutate scales and do not overlap, thus allowing for more flexibility in the toe. The extent of the pro- and postpatagium and the robust primary feather rachises are evidence that Confuciusornis was capable of powered flight, contrary to previous reports suggesting otherwise. A unique avian wing shape is also reconstructed based on plumage preserved. These soft tissues combined indicate an arboreal bird with the capacity for short-term (non-migratory) flight, and suggest that, although primitive, Confuciusornis already possessed many relatively advanced avian anatomical characteristics.