Peter Dodson

Taphonomic investigations of owl pellets

Owls are important consumers of small vertebrates, and because they regurgitate pellets rich in bone, they may be important potential contributors of the concentrated remains of small vertebrates to the fossil record. Owls of three sizes, the large great horned owl ( Bubo virginianus ), the medium-sized barn owl ( Tyto alba ), and the small screech owl ( Otus asio ), were fed a common diet of mice. The bony contents of the pellets were analyzed to determine the amount of bone loss by digestion, bone completeness, and sites of bone breakage. For all three species, only about half the number of bones ingested were recovered in the pellets. Mandibles and femora were most abundant, and pelves and scapulae were the least abundant. Screech owls broke 80% of the cranial and limb elements, barn owls only 30%. Skulls fared poorly in great horned and screech owl pellets, while barn owls returned 80% of the skulls intact, with only the caudal portion of the cranium damaged; barn owls also returned articulated strings of vertebrae and complete paws. These results provide a baseline for the recognition of owls as agents of accumulation of small bones in the fossil record and suggest that the actions of ancient predators may be revealed by species-specific patterns of bone destruction of an assemblage of fossil prey species.

A PROPOSAL FOR A STANDARD TERMINOLOGY OF ANATOMICAL NOTATION AND ORIENTATION IN FOSSIL VERTEBRATE DENTITIONS

Abstract There is little consistency in the notation and orientation terminology used in discussions of non-mammalian fossil vertebrate dentitions. The standardization of this terminology, as done in the medical and dental sciences, would facilitate all future research on fossil teeth. For mammals, we recommend following convention, where incisors, canines, premolars, and molars are abbreviated as In, Cn, Pn, and Mn (n = tooth number) in upper jaws and as in, cn, pn, and mn in lower jaws. Right, left, and deciduous teeth are indicated by R, L, and D (e.g., DP4, Rp2). For non-mammals, which can have dentigerous premaxillae, maxillae, and dentaries, as well as additional tooth-bearing bones (e.g., vomers, palatines, pterygoids, ectopterygoids, sphenoids, splenials, and even parasphenoids), we encourage identifying teeth using the bone abbreviation (e.g., pmn, mxn, dn, vn, paln). A number and slash (/) combination can be used to distinguish between multiple tooth rows (e.g., Pal1/n, Pal2/n), and specimen-specific maps can be created for very complicated dentitions. We suggest the use of the terms mesial and distal to designate tooth surfaces and directions facing toward and away from the mandibular symphysis. Labial is offered for those surfaces and directions facing the lips or cheeks and lingual for those facing the tongue. We offer the terms basal for the direction toward crown bases, apical for the direction toward crown tips, occlusal for views of the occlusal surfaces, and basal and root apical for views of crown bases and roots, respectively.

Taphonomy and paleoecology of the dinosaur beds of the Jurassic Morrison Formation

The Upper Jurassic Morrison Formation has yielded one of the richest dinosaur faunas of the world. Morrison sediments are distributed over more than a million square kilometers in the western United States and represent a mosaic of riverine, lacustrine and floodplain environments developed on a vast alluvial plain nourished by debris from the ancestral Rocky Mountains. Plant productivity must have been reasonably high to support abundant large-bodied herbivores, but the absence of coals, scarcity of small aquatic vertebrates, the abundance of oxidized sediments, and presence of calcretes lead us to believe that water was periodically in short supply. A strongly seasonal climate may have necessitated annual large-scale movements of large herbivores, accounting in part for their remarkably broad and uniform geographic distribution. Dinosaur diversity is lower in the Morrison than in the Late Cretaceous, and taphonomic alteration is higher. Massed accumulations of thousands of bones are characteristic of the Morrison. Morrison dinosaurs were not confined to specific depositional environments but were distributed across the complete spectrum of available habitats, from lakes to dry floodplains; this type of distribution is similar to that of large terrestrial mammals such as elephants and rhinos and is different from that of hippos and crocodiles. Common Morrison taxa were Camarasaurus, Apatosaurus, Diplodocus, Allosaurus and Stegosaurus; these genera probably constituted a true dinosaur community. Stegosaurus may have been partially segregated from the other genera, and Camptosaurus more strongly so. Camarasaurus and Diplodocus were gregarious, with juveniles and subadults of the former particularly common; Apatosaurus was less abundant and more solitary in its habits. Juveniles and subadults are known for a number of dinosaurs.

Trace Metals as Biomarkers for Eumelanin Pigment in the Fossil Record

X-ray maps of fossil feather pigments reveal color patterning in extinct bird species. Well-preserved fossils of pivotal early bird and nonavian theropod species have provided unequivocal evidence for feathers and/or downlike integuments. Recent studies have reconstructed color on the basis of melanosome structure; however, the chemistry of these proposed melanosomes has remained unknown. We applied synchrotron x-ray techniques to several fossil and extant organisms, including Confuciusornis sanctus, in order to map and characterize possible chemical residues of melanin pigments. Results show that trace metals, such as copper, are present in fossils as organometallic compounds most likely derived from original eumelanin. The distribution of these compounds provides a long-lived biomarker of melanin presence and density within a range of fossilized organisms. Metal zoning patterns may be preserved long after melanosome structures have been destroyed.

Estimating the diversity of dinosaurs

Despite current interest in estimating the diversity of fossil and extant groups, little effort has been devoted to estimating the diversity of dinosaurs. Here we estimate the diversity of nonavian dinosaurs at ≈1,850 genera, including those that remain to be discovered. With 527 genera currently described, at least 71% of dinosaur genera thus remain unknown. Although known diversity declined in the last stage of the Cretaceous, estimated diversity was steady, suggesting that dinosaurs as a whole were not in decline in the 10 million years before their ultimate extinction. We also show that known diversity is biased by the availability of fossiliferous rock outcrop. Finally, by using a logistic model, we predict that 75% of discoverable genera will be known within 60–100 years and 90% within 100–140 years. Because of nonrandom factors affecting the process of fossil discovery (which preclude the possibility of computing realistic confidence bounds), our estimate of diversity is likely to be a lower bound.

Mesozoic avian bone microstructure: Physiological implications

We report on the bone microstructure of the Late Cretaceous birds Patagopteryx deferrariisi and members of the Enantiornithes. These birds represent the most primitive birds ever studied histologically. The occurrence of growth rings indicating alternating periods of slowed and fast growth suggests that these basal birds had slower growth rates, and differed physiologically from their modern relatives. Our findings also call into question previous ideas suggesting that nonavian theropods developed a full avian degree of homeothermic endothermy, which was later inherited by birds. On the contrary, our findings suggest that birds developed classic endothermy relatively late in their phylogenetic history.

Biophysical constraints on the thermal ecology of dinosaurs

A physical, model-based approach to body temperatures in dinosaurs allows us to pre- dict what ranges of body temperatures and what thermoregulatory strategies were available to those dinosaurs. We argue that 1. The huge range of body sizes in the dinosaurs likely resulted in very different thermal problems and strategies for animals at either end of this size continuum. 2. Body temperatures of the smallest adult dinosaurs and of hatchlings and small juveniles would have been largely insensitive to metabolic rates in the absence of insulation. The smallest an- imals in which metabolic heating resulted in predicted body temperatures 2 2?C above oper- ative temperatures (TJ) weigh 10 kg. Body temperature would respond rapidly enough to

Titanosaurid (Sauropoda) osteoderms from the Late Cretaceous of Madagascar

ABSTRACT In 1896 Charles Deperet described a fauna of dinosaurs from the Upper Cretaceous (?Campanian) Maevarano Formation from the Mahajanga Basin of northwest Madagascar. Among the dinosaurs was a titanosaurid sauropod that he named Titanosaurus madagascariensis. He attributed to the titanosaurid a large, thick circular osteoderm. His referral of an osteoderm to a sauropod was widely doubted until 1980 when Bonaparte and Powell described Saltasaurus loricatus, an armored titanosaurid from Argentina. Since then titanosaurid osteoderms have been recognized from Spain, France and Malawi. In 1996, we collected three isolated and eight associated osteoderms from the Maevarano Formation, confirming Deperets prescient observation. They range in length from 3 cm to 17 cm, and in thickness up to 6.5 cm. At least one of the two titanosaurids we now recognize from Madagascar was covered with a sparse armor, and that the skin was in places nearly 7 cm thick.

Pelvic and Hindlimb Myology of the Basal Archosaur Poposaurus gracilis (Archosauria: Poposauroidea)

The discovery of a largely complete and well preserved specimen of Poposaurus gracilis has provided the opportunity to generate the first phylogenetically based reconstruction of pelvic and hindlimb musculature of an extinct nondinosaurian archosaur. As in dinosaurs, multiple lineages of basal archosaurs convergently evolved parasagittally erect limbs. However, in contrast to the laterally projecting acetabulum, or “buttress erect” hip morphology of ornithodirans, basal archosaurs evolved a very different, ventrally projecting acetabulum, or “pillar erect” hip. Reconstruction of the pelvic and hindlimb musculotendinous system in a bipedal suchian archosaur clarifies how the anatomical transformations associated with the evolution of bipedalism in basal archosaurs differed from that of bipedal dinosaurs and birds. This reconstruction is based on the direct examination of the osteology and myology of phylogenetically relevant extant taxa in conjunction with osteological correlates from the skeleton of P. gracilis. This data set includes a series of inferences (presence/absence of a structure, number of components, and origin/insertion sites) regarding 26 individual muscles or muscle groups, three pelvic ligaments, and two connective tissue structures in the pelvis, hindlimb, and pes of P. gracilis. These data provide a foundation for subsequent examination of variation in myological orientation and function based on pelvic and hindlimb morphology, across the basal archosaur lineage leading to extant crocodilians. J. Morphol., 2011.

The morphology and systematics of Avaceratops, a primitive horned dinosaur from the Judith River Formation (Late Campanian) of Montana, with the description of a second skull

ABSTRACT The partial skull and skeleton of Avaceratops lammersi, an unusual ceratopsid from the Judith River Formation of central Montana, are described. Avaceratops has several characters that are unique among ceratopsids though not among protoceratopsids. Plesiomorphies include: a primitive squamosal; a solid parietal; lack of a caudo-sagittal indentation on the parietal; weakly developed olecranon process of the ulna; deltopectoral crest of humerus not as distally expanded as in other ceratopsids; pointed pedal unguals; and relatively small size. A second, recently discovered partial skull that incorporates both centrosaurine and chasmosaurine characters is referred to Avaceratops. Lack of parietal fenestrae and the presence of postorbital horncores are probably basal characters within the Ceratopsidae. The inferred adult length of 4.2 m for Avaceratops is the smallest among known ceratopsids. Avaceratops is the least derived known ceratopsid, and hence is close to the ancestry of Triceratops and the C...