Jerald D. Harris

A Nearly Modern Amphibious Bird from the Early Cretaceous of Northwestern China

Three-dimensional specimens of the volant fossil bird Gansus yumenensis from the Early Cretaceous Xiagou Formation of northwestern China demonstrate that this taxon possesses advanced anatomical features previously known only in Late Cretaceous and Cenozoic ornithuran birds. Phylogenetic analysis recovers Gansus within the Ornithurae, making it the oldest known member of the clade. The Xiagou Formation preserves the oldest known ornithuromorph-dominated avian assemblage. The anatomy of Gansus, like that of other non-neornithean (nonmodern) ornithuran birds, indicates specialization for an amphibious life-style, supporting the hypothesis that modern birds originated in aquatic or littoral niches.

The significance of SUUWASSEA EMILIEAE (Dinosauria: Sauropoda) for flagellicaudatan intrarelationships and evolution

Synopsis Suuwassea emilieae is a recently described dinosaur taxon discovered in the Upper Jurassic Morrison Formation of the western United States and the only non‐diplodocid flagellicaudatan (Dinosauria: Sauropoda) known from North America. It retains sauropod symplesiomorphies that are unexpected in a Late Jurassic taxon and thus sheds light on the evolutionary origins of the Flagellicaudata. Despite being comparatively small, the holotype of Suuwassea demonstrates hallmarks of relatively advanced age. A phylogenetic analysis of 30 taxa and 331 characters retains Suuwassea in a trichotomy with the Diplodocidae (Apatosaurus + (Diplodocus + Barosaurus)) and the Dicraeosauridae (Dicraeosaurus +Amargasaurus). This lack of resolution is probably due to a combination of missing data, character conflict and poor incorporation of specimens referred to diplodocid taxa that differ from their holotype specimens and species holotypes. Middle Jurassic palaeobiogeographical reconstructions conflict with the hypothetical distribution of flagellicaudatans in the Middle and Late Jurassic based on their phylogeny, implying that physical barriers, such as epeiric seas, were not responsible for limiting their initial radiation. The postparietal foramen shared by Suuwassea, Dicraeosaurus, Tornieria and Amargasaurus may correlate to preferred existence in near‐shore, terrestrial environments.

A Review of the Tetrapod Track Record in China, with Special Reference to Type Ichnospecies： Implications for Ichnotaxonomy and Paleobiology

“Splitting” and “lumping” are perpetual problems in vertebrate, especially dinosaur, ichnotaxonomy. Chinese dinosaur ichnotaxonomy, which began in 1940, provides a series of interesting case studies, highlighting the dual problems of historical and dubious ichnotaxonomy. Chinese Mesozoic tetrapod track types have been placed into 63 ichnospecies (one Triassic, 28 Jurassic, and 34 Cretaceous), exclusive of other, non-type ichnospecies or ichnotaxa identified from China. Fifty-two (∼83%) of these 63 tetrapod ichnospecies were placed in monospecific ichnogenera. At the ichnogenus level, we prune—either by recognizing nomina dubia or by synonymy—17 from the list of 53 dinosaurian ichnogenera (a 32% reduction), leaving 36 ichnotaxa that we consider valid. Most of the cuts affect Jurassic theropod ichnotaxa, which are reduced from 23 to only nine because most ichnogenera are subjective junior synonyms of Grallator and Eubrontes. Fewer Chinese Cretaceous ichnotaxa (only six of 21 ichnogenera) are obvious nomina dubia or subjective synonyms, suggesting greater east Asian endemism during this time. Because ichnospecies differences are subtle, we provisionally retain ichnospecies as valid pending detailed comparative analyses of congeneric ichnospecies. This synthesis is long overdue and is necessary to address problems of historical and provincial ichnotaxonomy, which severely hamper comparisons of tetrapod ichnofaunas in space and time.

Behavioral and faunal implications of Early Cretaceous deinonychosaur trackways from China

Deinonychosaurian theropods, the dinosaurian sister group of birds, are characterized by a large raptorial claw borne on a highly modified second digit that was thought to be held in a retracted position during locomotion. In this study, we present new trackway evidence for two coeval deinonychosaurian taxa from the Early Cretaceous of Shandong, China that indicate a hitherto unrecognized body size diversity for this period and continent. These fossil tracks confirm diversity and locomotory patterns implied by phylogeny and biogeography, but not yet manifested in the body fossil record. Multiple parallel and closely spaced trackways generated by the larger track maker provide the best evidence yet discovered for gregarious behavior in deinonychosaurian theropods.

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 (∼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.

Earliest zygodactyl bird feet: evidence from Early Cretaceous roadrunner-like tracks

Fossil footprints are important in understanding Cretaceous avian diversity because they constitute evidence of paleodiversity and paleoecology that is not always apparent from skeletal remains. Early Cretaceous bird tracks have demonstrated the existence of wading birds in East Asia, but some pedal morphotypes, such as zygodactyly, common in modern and earlier Cenozoic birds (Neornithes) were unknown in the Cretaceous. We, herein, discuss the implications of a recently reported, Early Cretaceous (120–110 million years old) trackway of a large, zygodactyl bird from China that predates skeletal evidence of this foot morphology by at least 50 million years and includes the only known fossil zygodactyl footprints. The tracks demonstrate the existence of a Cretaceous bird not currently represented in the body fossil record that occupied a roadrunner (Geococcyx)-like niche, indicating a previously unknown degree of Cretaceous avian morphological and behavioral diversity that presaged later Cenozoic patterns.

A Gigantic, Exceptionally Complete Titanosaurian Sauropod Dinosaur from Southern Patagonia, Argentina

Titanosaurian sauropod dinosaurs were the most diverse and abundant large-bodied herbivores in the southern continents during the final 30 million years of the Mesozoic Era. Several titanosaur species are regarded as the most massive land-living animals yet discovered; nevertheless, nearly all of these giant titanosaurs are known only from very incomplete fossils, hindering a detailed understanding of their anatomy. Here we describe a new and gigantic titanosaur, Dreadnoughtus schrani, from Upper Cretaceous sediments in southern Patagonia, Argentina. Represented by approximately 70% of the postcranial skeleton, plus craniodental remains, Dreadnoughtus is the most complete giant titanosaur yet discovered, and provides new insight into the morphology and evolutionary history of these colossal animals. Furthermore, despite its estimated mass of about 59.3 metric tons, the bone histology of the Dreadnoughtus type specimen reveals that this individual was still growing at the time of death.

A DREPANOSAURID PECTORAL GIRDLE FROM THE GHOST RANCH (WHITAKER) COELOPHYSISQUARRY (CHINLE GROUP, ROCK POINT FORMATION, RHAETIAN), NEW MEXICO

Abstract An isolated but three-dimensionally preserved pectoral girdle from the Rock Point Formation (Rhaetian) of New Mexico represents the youngest known drepanosaurid. The specimen preserves, in articulation, both scapulae, coracoids, clavicles, and sternal plates; clavicles and sternal plates were previously poorly documented or unknown in the Drepanosauridae. The elongate, thin, dorsally-oriented scapular blades are distinctive autapomorphies of the clade and strongly support the drepanosaurid origin of the specimen. The paired clavicles resemble the furculae of some theropod dinosaurs and basal birds, but the morphology of the remainder of the girdle demonstrates that it cannot belong to either group. The specimens three dimensional preservation provides new information concerning the pectoral morphology of drepanosaurids.

Cranial osteology of Suuwassea emilieae (Sauropoda: Diplodocoidea: Flagellicaudata) from the Upper Jurassic Morrison Formation of Montana, USA

Abstract Cranial elements of Suuwassea emilieae (Sauropoda: Diplodocoidea) from the Upper Jurassic Morrison Formation of Montana, U.S.A., represent one of only a few flagellicaudatan skulls known. Preserved elements include a left premaxilla, a fragment of right maxilla, a right squamosal, a right quadrate, a basicranium and skull roof lacking only the rostral end of the frontals, basipterygoid processes, and parasphenoid rostrum. Autapomorphic features of the skull include: premaxillary teeth projecting parallel to long axis of premaxilla; single optic nerve foramen; postparietal foramen present and larger than parietal foramen; supraoccipital with elongate ventral process contributing little to dorsal margin of foramen magnum; basioccipital not contributing to floor of median condylar incisure; and antotic processes with no dorsal contact with frontals. The basicranium more closely resembles that of Apatosaurus rather than Diplodocus and is also unlike the skull of Dicraeosaurus, despite its possession of a similar postparietal foramen, a feature unique among Morrison Formation sauropods. Pending reanalysis of Tornieria africana, which also possesses it, the postparietal foramen must be viewed as a symplesiomorphic retention in the Dicraeosauridae, with its loss a synapomorphy of the Diplodocidae, or at least of the North American members of the latter clade.

A New Deinonychosaurian Track from the Lower Cretaceous Hekou Group, Gansu Province, China

Herein we describe deinonychosaurian (Dinosauria: Theropoda) tracks in the Lower Cretaceous Hekou Group at sites I and II of Liujiaxia Dinosaur National Geopark, Gansu Province, China. The site preserves 71 didactyl tracks, the largest concentration of deinonychosaurian tracks in Asia. The tracks pertain to a new dromaeopodid ichnospecies: Dromaeosauripus yongjingensis ichnosp. nov., which is diagnosed by: a digital pad formula of x-1-3-4-x and a mean divarication angle between digits III and IV of 19°, and having the proximal portion of digit II contacting the anterior margin of a large, rounded metatarsophalangeal pad. Six Dromaeosauripus trackways from site II comprise at least two, and possibly three, turning trackways in which the track maker(s) turned without slowing down. None of the Dromaeosauripus trackways are parallel or closely spaced, suggesting that they were made by solitary track makers. Estimates of dromaeopodid track-maker sizes are between 61–300 cm, well within the size range established by body fossils of both dromaeosaurids and troodontids.