Lisa G. Buckley

A ‘Terror of Tyrannosaurs’: The First Trackways of Tyrannosaurids and Evidence of Gregariousness and Pathology in Tyrannosauridae

The skeletal record of tyrannosaurids is well-documented, whereas their footprint record is surprisingly sparse. There are only a few isolated footprints attributed to tyrannosaurids and, hitherto, no reported trackways. We report the world’s first trackways attributable to tyrannosaurids, and describe a new ichnotaxon attributable to tyrannosaurids. These trackways are from the Upper Cretaceous (Campanian - Maastrichtian) of northeastern British Columbia, Canada. One trackway consists of three tridactyl footprints, and two adjacent trackways consist of two footprints each. All three trackways show animals bearing southeast within an 8.5 meter-wide corridor. Similarities in depth and preservation of the tyrannosaurid tracks indicate that these three trackways were made by track-makers walking concurrently in the same direction. These trackways add significantly to previous osteology-based hypotheses of locomotion and behavior in Tyrannosauridae by providing ichnologic support for gregariousness in tyrannosaurids, and the first record of the walking gait of tyrannosaurids.

Quantifying tooth variation within a single population of Albertosaurus sarcophagus (Theropoda: Tyrannosauridae) and implications for identifying isolated teeth of tyrannosauridsThis article is one of a series of papers published in this Special Issue on the theme Albertosaurus.

Documenting variation in theropod dinosaurs is usually hindered by the lack of a large sample size and specimens representing several ontogenetic stages. Here, variation within 140 disassociated and seven in situ tyrannosaur teeth from the Upper Cretaceous (lower Maastrichtian) monodominant Albertosaurus sarcophagus (Theropoda: Tyrannosauridae) bonebed is documented. This sample represents the largest data set of teeth from one population of A. sarcophagus containing both adult and juvenile specimens. Tooth variation was assessed using multivariate analyses (principal component, discriminant, and canonical variate analyses). Heterodonty in the teeth of A. sarcophagus contributes to the large amount of variation in the data set. Premaxillary teeth are significantly different from maxillary and dentary teeth, but there is no quantifiable difference between a priori identified maxillary and dentary teeth. Juvenile and adult teeth of A. sarcophagus show apparent quantitative differences that are size dependen...

Theropod courtship: large scale physical evidence of display arenas and avian-like scrape ceremony behaviour by Cretaceous dinosaurs

Relationships between non-avian theropod dinosaurs and extant and fossil birds are a major focus of current paleobiological research. Despite extensive phylogenetic and morphological support, behavioural evidence is mostly ambiguous and does not usually fossilize. Thus, inferences that dinosaurs, especially theropods displayed behaviour analogous to modern birds are intriguing but speculative. Here we present extensive and geographically widespread physical evidence of substrate scraping behavior by large theropods considered as compelling evidence of “display arenas” or leks, and consistent with “nest scrape display” behaviour among many extant ground-nesting birds. Large scrapes, up to 2 m in diameter, occur abundantly at several Cretaceous sites in Colorado. They constitute a previously unknown category of large dinosaurian trace fossil, inferred to fill gaps in our understanding of early phases in the breeding cycle of theropods. The trace makers were probably lekking species that were seasonally active at large display arena sites. Such scrapes indicate stereotypical avian behaviour hitherto unknown among Cretaceous theropods, and most likely associated with terrirorial activity in the breeding season. The scrapes most probably occur near nesting colonies, as yet unknown or no longer preserved in the immediate study areas. Thus, they provide clues to paleoenvironments where such nesting sites occurred.

An Ornithopod-Dominated Tracksite from the Lower Cretaceous Jiaguan Formation (Barremian–Albian) of Qijiang, South-Central China: New Discoveries, Ichnotaxonomy, Preservation and Palaeoecology

The historically-famous Lotus Fortress site, a deep 1.5–3.0-meter-high, 200-meter-long horizonal notch high up in near-vertical sandstone cliffs comprising the Cretaceous Jiaguan Formation, has been known since the 13th Century as an impregnable defensive position. The site is also extraordinary for having multiple tetrapod track-bearing levels, of which the lower two form the floor of part of the notch, and yield very well preserved asseamblages of ornithopod, bird (avian theropod) and pterosaur tracks. Trackway counts indicate that ornithopods dominate (69%) accounting for at least 165 trackmakers, followed by bird (18%), sauropod (10%), and pterosaur (3%). Previous studies designated Lotus Fortress as the type locality of Caririchnium lotus and Wupus agilis both of which are recognized here as valid ichnotaxa. On the basis of multiple parallel trackways both are interpreted as representing the trackways of gregarious species. C. lotus is redescribed here in detail and interpreted to indicate two age cohorts representing subadults that were sometimes bipedal and larger quadrupedal adults. Two other previously described dinosaurian ichnospecies, are here reinterpreted as underprints and considered nomina dubia. Like a growing number of significant tetrapod tracksites in China the Lotus Fortress site reveals new information about the composition of tetrapod faunas from formations in which the skeletal record is sparse. In particular, the site shows the relatively high abundance of Caririchium in a region where saurischian ichnofaunas are often dominant. It is also the only site known to have yielded Wupus agilis. In combination with information from other tracksites from the Jiaguan formation and other Cretaceous formations in the region, the track record is proving increasingly impotant as a major source of information on the vertebrate faunas of the region. The Lotus Fortress site has been developed as a spectacular, geologically-, paleontologically- and a culturally-significant destination within Qijiang National Geological Park.

Vertebrate Ichnopathology: Pathologies Inferred from Dinosaur Tracks and Trackways from the Mesozoic

Literature concerning dinosaur footprints or trackways exhibiting abnormal gait or morphology reflecting pathology (ichnopathology) is rare. We report on a number of Jurassic and Cretaceous occurrences of theropod footprints from western North America with unusual morphologies interpreted herein as examples of inferred pathologies, or ichnopathologies. The majority of ichnopathologies are primarily manifested in the digit impressions and include examples of swelling, extreme curvature, dislocation or fracture, and amputation. A number of occurrences are single tracks on ex situ blocks with substantial deformation (inferred dislocation or fracture), or absence of a single digit impression. Two occurrences are from in situ natural mould trackways, one of which is a lengthy trackway of a presumed allosauroid with no noticeable deformation of the digits or feet but with strong inward rotation of the left footprint toward the midline and a pronounced, waddling limp. The other is a tyrannosaurid trackway consisting of three footprints (one right, two left) with the two left prints exhibiting repetitive ichnopathology of a partially missing Digit II impression.

Reanalysis of Wupus agilis (Early Cretaceous) of Chongqing, China as a Large Avian Trace: Differentiating between Large Bird and Small Non-Avian Theropod Tracks

Trace fossils provide the only records of Early Cretaceous birds from many parts of the world. The identification of traces from large avian track-makers is made difficult given their overall similarity in size and tridactyly in comparison with traces of small non-avian theropods. Reanalysis of Wupus agilis from the Early Cretaceous (Aptian-Albian) Jiaguan Formation, one of a small but growing number of known avian-pterosaur track assemblages, of southeast China determines that these are the traces of a large avian track-maker, analogous to extant herons. Wupus, originally identified as the trace of a small non-avian theropod track-maker, is therefore similar in both footprint and trackway characteristics to the Early Cretaceous (Albian) large avian trace Limiavipes curriei from western Canada, and Wupus is reassigned to the ichnofamily Limiavipedidae. The reanalysis of Wupus reveals that it and Limiavipes are distinct from similar traces of small to medium-sized non-avian theropods (Irenichnites, Columbosauripus, Magnoavipes) based on their relatively large footprint length to pace length ratio and higher mean footprint splay, and that Wupus shares enough characters with Limiavipes to be reassigned to the ichnofamily Limiavipedidae. The ability to discern traces of large avians from those of small non-avian theropods provides more data on the diversity of Early Cretaceous birds. This analysis reveals that, despite the current lack of body fossils, large wading birds were globally distributed in both Laurasia and Gondwana during the Early Cretaceous.

Hints of the Early Jehol Biota: Important Dinosaur Footprint Assemblages from the Jurassic-Cretaceous Boundary Tuchengzi Formation in Beijing, China

New reports of dinosaur tracksites in the Tuchengzi Formation in the newly established Yanqing Global Geopark, Beijing, China, support previous inferences that the track assemblages from this formation are saurischian-dominated. More specifically, the assemblages appear theropod-dominated, with the majority of well-preserved tracks conforming to the Grallator type (sensus lato), thus representing relatively small trackmakers. Such ichnofaunas supplement the skeletal record from this unit that lacks theropods thus far, proving a larger diversity of dinosaur faunas in that region. Sauropods are represented by medium to large sized and narrow and wide-gauge groups, respectively. The latter correspond with earlier discoveries of titanosauriform skeletons in the same unit. Previous records of ornithischian tracks cannot be positively confirmed. Purported occurrences are re-evaluated here, the trackways and imprints, except of a single possible specimen, re-assigned to theropods. Palecologically the Tuchengzi ichnofauna is characteristic of semi-arid fluvio-lacustrine inland basins with Upper Jurassic-Lower Cretaceous deposits in northern China that all show assemblages with abundant theropod and sauropod tracks and minor components of ornithopod, pterosaur and bird tracks.

Birding by Foot: A Critical Look at the Synapomorphy- and Phenetic-Based Approaches to Trackmaker Identification of Enigmatic Tridactyl Mesozoic Traces

One of the goals of vertebrate ichnology is to use trace fossils as an additional source of data to determine the palaeoecological makeup of vertebrate paleoecosystems. The features in both the synapomorphy-based and phenetic-based methods of attributing a trace to an osteologic trackmaker are those that are affected by preservational conditions, convergent due to size and/or habitat of the trackmaker, and are morphologically variable within taxa. Despite the drawbacks, the phenetic-based, or “gestalt” method, is still the most comprehensive, if not always synapomorphy-supported, means of using the largest amount of data (morphologic and behavioral) preserved for identifying tracks as avian. To date there are too few synapomorphies that are both pedes specific and are consistently preserved in footprints to be a practical method for attributing tracks to an avian trackmaker. There is still much more comparative ichnological and statistical work to be done to discern novel traits that can be used to delineate between the traces of large avian and small nonavian Mesozoic theropods.

The Sodium Hypochlorite Solution for the Removal of Lichen from Vertebrate Track Surfaces

The removal of extraneous biological materials from vertebrate ichnological specimens may be necessary if they have been exposed to subaerial processes in the field for long periods of time. It is not uncommon for fossil track specimens to be found nearly completely covered with lichen colonies, especially those recovered from alpine areas. This paper describes a technique using a sodium hypochlorite solution (bleach) to remove lichen from a track surface containing numerous avian prints and small theropod prints with skin impressions.