David D. Gillette

Dinosaur tracks and traces

Part I. Introduction Part II. Historical Perspectives Part III. Locomotion and Behaviour Part IV. Eggs and Nests Part V. Paleoecological, Paleoenvironmental and Regional Synthesis Part VI. Biostratigraphy Part VII. Experimentation and Functional Morphology Part VII. Site Reports Part IX. Systematic Ichnology Part X. Conservation and Preservation.

A new North American therizinosaurid and the role of herbivory in ‘predatory’ dinosaur evolution

Historically, ecomorphological inferences regarding theropod (i.e. ‘predatory’) dinosaurs were guided by an assumption that they were singularly hypercarnivorous. A recent plethora of maniraptoran discoveries has produced evidence challenging this notion. Here, we report on a new species of maniraptoran theropod, Nothronychus graffami sp. nov. Relative completeness of this specimen permits a phylogenetic reassessment of Therizinosauria—the theropod clade exhibiting the most substantial anatomical evidence of herbivory. In the most comprehensive phylogenetic study of the clade conducted to date, we recover Therizinosauria as the basalmost maniraptoran lineage. Using concentrated changes tests, we present evidence for correlated character evolution among herbivorous and hypercarnivorous taxa and propose ecomorphological indicators for future interpretations of diet among maniraptoran clades. Maximum parsimony optimizations of character evolution within our study indicate an ancestral origin for dietary plasticity and facultative herbivory (omnivory) within the clade. These findings suggest that hypercarnivory in paravian dinosaurs is a secondarily derived dietary specialization and provide a potential mechanism for the invasion of novel morpho- and ecospace early in coelurosaurian evolution—the loss of obligate carnivory and origin of dietary opportunism.

Geology and taphonomy of the Coelophysis quarry, Upper Triassic Chinle Formation, Ghost Ranch, New Mexico

The Coelophysis dinosaur quarry at Ghost Ranch, near Abiquiu, New Mexico, is unique among Triassic fossil sites for its yield of numerous complete and partial skeletons of a single species of theropod dinosaur ( Coelophysis bauri). Since its discovery in 1947 by E. H. Colbert in the red siltstone beds of the Upper Triassic Chinle Formation, the quarry has yielded the remains of at least 1,000 individuals from approximately 30 cubic meters of excavated material. The main bone-bearing strata are abandoned channel deposits that are part of a siltstone overbank sequence. The Coelophysis remains found at the quarry are remarkably whole and well preserved, though they range in degree of articulation from complete skeletons to isolated limbs and bones. Skeletons, partial skeletons, and bones are crudely aligned and show little evidence of predator or scavenger disturbance or surface weathering. Geologic and taphonomic evidence suggests that the dinosaurs preserved in the Ghost Ranch quarry were transported to the site as carcasses by fluvial currents. The carcasses blocked a small channel and were subsequently buried by silts. Petrographic study and neutron activation analysis reveal no evidence of volcanic ash, paleopathologic osteology, or unusual chemistry in the quarry bone and sediments. The virtual monospecificity, taphonomy, and ecology of the assemblage suggest that the dinosaurs perished due to a regional environmental crisis, such as drought.

PLESIOSAURS FROM THE UPPER CRETACEOUS (CENOMANIAN–TURONIAN) TROPIC SHALE OF SOUTHERN UTAH, PART 2:POLYCOTYLIDAE

Abstract Recent fieldwork in the Tropic Shale of southern Utah has resulted in the recovery of several specimens of short-necked plesiosaurs including both polycotylid plesiosauroids and pliosaurids. This report focuses on the former, whereas the latter are discussed in an accompanying paper. Although the Late Cretaceous Cenomanian/Turonian Stage boundary falls within the lower few meters of the Tropic Shale, all but one of the specimens were found in lower Turonian strata based on molluscan assemblages found in direct association with the skeletal material. The plesiosauroid family Polycotylidae is represented by at least three taxa: (1) the ‘typical’ late Cenomanian/early Turonian Trinacromerum; (2) Eopolycotylus rankini, gen. et sp. nov., a new genus and species that shares synapomorphies with the late Santonian/early Campanian Polycotylus latipinnus; and (3) Palmula quadratus, gen. et sp. nov., another new taxon that shares synapomorphies with unnamed taxa from the late Cenomanian of South Dakota and Japan. Cladistic analysis supports the division of the Polycotylidae into two new subfamilies, here designated the Polycotylinae and the Palmulainae. The Turonian plesiosaur fauna of the Tropic Shale, and consequently the large vertebrate fauna of the Cretaceous Western Interior Seaway, is considerably more diverse than previously realized, and there is no indication that this fauna suffered any negative consequences as a result of global scale oceanographic events, including marine extinctions, that transpired during late Cenomanian-early Turonian time.

PLESIOSAURS FROM THE UPPER CRETACEOUS (CENOMANIAN–TURONIAN) TROPIC SHALE OF SOUTHERN UTAH, PART 1: NEW RECORDS OF THE PLIOSAUR BRACHAUCHENIUS LUCASI

Abstract Recent fieldwork in the Tropic Shale of southern Utah has resulted in the recovery of two new specimens of the short-necked pliosaurid Brachauchenius lucasi Williston, 1903. Both specimens were recovered in Lower Turonian strata a few meters above the Cenomanian-Turonian Stage boundary as determined from molluscan assemblages found in direct association, and both include skull material. The larger of the two also includes pectoral and pelvic elements previously unknown for this taxon. These specimens represent the first records of B. lucasi from the western margin of the Cretaceous Western Interior Seaway; previously recorded specimens were recovered in Kansas and Texas. The Cenomanian through middle Turonian temporal range of B. lucasi, in addition to its geographic range across the seaway, indicates that this taxon suffered few, if any, negative consequences as a result of global scale oceanographic events, including marine extinctions, that transpired during late Cenomanian-early Turonian time.

Seismosaurus halli, gen. et sp. nov., A New Sauropod Dinosaur from the Morrison Formation (Upper Jurassic/Lower Cretaceuos) of New Mexico, USA

ABSTRACT Seismosaurus halli, gen. et sp. nov. (Sauropoda, Diplodocidae) is a new large sauropod from the Brushy Basin Member of the Morrison Formation (Upper Jurassic/Lower Cretaceous) of central New Mexico. The holotype is a partially articulated skeleton consisting to date of approximately 20 caudal vertebrae, five sacral vertebrae, eight dorsal vertebrae, partial pelvis, five chevrons, and ribs. Distinguishing features include the structure of the caudal vertebrae, pelvis, and chevrons. The extraordinary dimensions of these bones indicate an axial length of 39–52 meters.

The Columbian mammoth, Mammuthus columbi, from the Wasatch Mountains of central Utah

A nearly complete and well-preserved skeleton of the Columbian mammoth ( Mammuthus columbi ) and a cranial fragment of a short-faced bear ( Arctodus simus ) were recovered from fossil lake deposits at 2,740 m, near the crest of the Wasatch Plateau, central Utah. The mammoth bones are reliably dated to between 11,500 and 9,500 yr B.P. and may be associated with a late Paleoindian occupation at the site. The mammoth and bear are part of a high elevation Huntington Canyon megafauna including mastodon ( Mammut americanum ), horse ( Equus sp.), and bison ( Bison sp.). The mammoth was an old bull with considerable pathology in the vertebral column, ribs, and legs. Pollen, plant macrofossils, insects, and dung associated with the mammoth suggest this megafauna occupied an essentially modern environmental setting after deglaciation of the Wasatch plateau.

The short-faced bear Arctodus simus from the late Quaternary in the Wasatch Mountains of central Utah

ABSTRACT A partial cranium with upper dentition and an isolated rib of the extinct short-faced bear, Arctodus simus, were associated with a nearly complete skeleton of the Columbian mammoth, Mammuthus columbi, at a high elevation site in Huntington Canyon in the Wasatch Mountains of central Utah. This large A. simus was a decidedly short-faced individual. Radiometric dates for the mammoth cluster around the interval ±11,220–11,400 BP; dates for spruce wood in stratigraphic position above and below the mammoth skeleton cluster around ±9,400 BP. Assuming direct association with the mammoth, the occurrence of Arctodus simus at ≤ 11,400 BP is a new terminal date for the species. The mammoth and bear may have been associated with humans in the Huntington Canyon vicinity. The late Quaternary high elevation fauna of Utah includes 30 genera from sites above 1,950 meters above mean sea level. Late Quaternary high elevation faunas of the central and southern Rocky Mountains included the short-faced bear, and may ha...

Unusual occurrence of gastroliths in a polycotylid plesiosaur from the Upper Cretaceous Tropic Shale, southern Utah

Abstract A polycotylid plesiosaur (Dolichorhynchops sp.), recently discovered in the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale in Glen Canyon National Recreation Area, southern Utah, is associated with 289 gastroliths. This specimen is significant due to the general lack of gastroliths associated with most short-necked plesiosaur skeletons. The skeleton (MNA V10046) was excavated from a stratigraphic interval of marine shale that does not contain coarser-grained material. The stones were generally concentrated in one area of the skeleton, with the majority situated near the back of the skull. The stones are mainly composed of dark grey chert, are smooth and well rounded, and have varying degrees of polish. The majority of the stones are spherical in shape and are likely fluvial in origin. The gastroliths from this animal are similar in shape and number to those documented from elasmosaurid plesiosaurs. The gastroliths from MNA V10046, however, are much smaller and weigh considerably less than most elasmosaurid stomach stones. Given the lack of comparative material from other short-necked plesiosaurs, the size and mass differences are attributed to differences in function of gastroliths between long- and short-necked plesiosaurs.

The geographic and phylogenetic position of sauropod dinosaurs from the Kota formation (Early Jurassic) of India

Abstract The earliest sauropods are the Late Triassic Isanosaurus from Thailand, the Early Jurassic Barapasaurus and Kotasaurus from the Kota Formation of the Pranhita-Godavari Basin of India and Vulcanodon from Zimbabwe, and a variety of Middle Jurassic genera from many localities in Gondwana and Laurasia except North America. These early sauropod genera are related, but their phylogenetic positions remain unresolved. Sauropods originated in Laurasia (Thailand and vicinity) or Pangea (broadly, Thailand, China, India), with at least three additional steps involving expansion and diversification through the Middle Jurassic.