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

Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace

BACKGROUND: Fossil tracks made by non-avian theropod dinosaurs commonly reflect the habitual bipedal stance retained in living birds. Only rarely-captured behaviors, such as crouching, might create impressions made by the hands. Such tracks provide valuable information concerning the often poorly understood functional morphology of the early theropod forelimb. METHODOLOGY/PRINCIPAL FINDINGS: Here we describe a well-preserved theropod trackway in a Lower Jurassic ( approximately 198 million-year-old) lacustrine beach sandstone in the Whitmore Point Member of the Moenave Formation in southwestern Utah. The trackway consists of prints of typical morphology, intermittent tail drags and, unusually, traces made by the animal resting on the substrate in a posture very similar to modern birds. The resting trace includes symmetrical pes impressions and well-defined impressions made by both hands, the tail, and the ischial callosity. CONCLUSIONS/SIGNIFICANCE: The manus impressions corroborate that early theropods, like later birds, held their palms facing medially, in contrast to manus prints previously attributed to theropods that have forward-pointing digits. Both the symmetrical resting posture and the medially-facing palms therefore evolved by the Early Jurassic, much earlier in the theropod lineage than previously recognized, and may characterize all theropods

Tracking Dinosaurs on the Isle of Wight: a review of tracks, sites, and current research

The Wealden exposures on the Isle of Wight have long been noted for their dinosaur footprints and trackways and represent a unique ichnological resource. However, with a few notable exceptions, these ichnites remain largely unstudied and documentation has been sporadic and often concentrated on a few particular sites. Thus, their context within the Lower Cretaceous is poorly understood. The vertebrate ichnological record of the Wessex Sub-basin is currently being re-assessed. We review the main sites containing dinosaur footprints on the Isle of Wight. We also look at previously-known sites, and present new research using techniques such as photogrammetry to accurately record, preserve, and distribute ichnological data, especially data recorded in the dynamic foreshore and cliff environments, where many trace fossils are frequently lost as a result of human activity, weathering, erosion, and changing marine dynamics. Although the ichnoassemblages of the island's Wealden facies are dominated by ornithopod tracks including Caririchnium and Amblydactylus, we also report the first occurrence of the ankylosaurian track Tetrapodosaurus in both the Wessex and Vectis Formations, alongside the previously reported stegosaurian Deltapodus, as well as the occurrence of tracks left by saurichian tracemakers

Measurements (in cm; ° as noted) of SGDS.18.T1 <i>Eubrontes</i> trackway and corresponding tail drag marks.

<p>Roman numerals = divarication angles between indicated pedal digits, L/R = left/right, MTD = maximum track depth, P = pace or step length, PA = pace angulation, S = stride length, TL = track length (excluding metatarsal impression, if any), TTL = total track length (including metatarsal impression, if any), TW = track width, * = more accurate measurements taken from 2000 M.G. Lockley tracing (CU Denver Tracks Museum Tracing # T472), although tracing provides little data and present track is much more weathered, – = measurement not applicable or unobtainable.</p><p>Measurements in parentheses are approximations due to incompleteness, poor preservation of trace, or ambiguity in discerning track margin from surface sedimentary structures; subscripted numbers indicate tracks between which P, PA, and S measurements are given.</p

Restoration of Early Jurassic environment preserved at the SGDS, with the theropod <i>Dilophosaurus wetherilli</i> in bird-like resting pose, demonstrating the manufacture of SGDS.18.T1 resting trace.

<p>By Heather Kyoht Luterman.</p

<i>Eubrontes</i> trackway with resting trace (SGDS.18.T1) in the Whitmore Point Member of the Moenave Formation, St. George, Utah.

<p>A, Overhead, slightly oblique angle photograph of SGDS.18.T1 resting trace. Note normal <i>Eubrontes</i> track cranial to resting traces (top center) made by track maker during first step upon getting up. Scale bar equals 10 cm. B, Schematic of SGDS.18.T1 to scale with A: first resting traces (manus, pes, and ischial callosity) in red, second (shuffling, pes only) traces in gold, final resting traces (pes and ischial callosity) in green, and tail drag marks made as track maker moved off in blue. Note long metatarsal (“heel”) impressions on pes prints. C, Direct overhead photograph and D, computerized photogrammetry with 5 mm contour lines of <i>Eubrontes</i> trace SGDS.18.T1. Color banding reflects topography (blue-green = lowest, purple-white = highest); a portion of the berm on which the track maker crouched is discernible. Abbreviations: ic = ischial callosity, lm = left manus, lp = left pes, rm = right manus, rp = right pes, td = tail drag marks.</p

Stratigraphic section of the Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm.

<p>Resting trace and trackway SGDS.18.T1 is in the “Top Surface” of the Main Track-Bearing Sandstone Bed (indicated by the blue arrow) in the Whitmore Point Member of the Moenave Formation.</p