James O. Farlow

Speculations about the diet and digestive physiology of herbivorous dinosaurs

Like living herbivorous lizards, chelonians, birds, and mammals, plant-eating dinosaurs probably relied on a symbiotic gut microflora, housed in a hindgut fermentation chamber, to break down plant cell wall constituents. Large body sizes in most herbivorous dinosaurs resulted in low mass-specific metabolic rates and low rates of digesta passage through the gut; the effects of large body size were probably enhanced by the low metabolic rates of large dinosaurs as compared with large mammals. The long residence time of digesta in the gut permitted long exposure of refractory plant materials to the microflora, probably enabling even those dinosaurs with unsophisticated dentitions to survive on fodder with high fiber content. Large herbivorous dinosaurs probably fed on plants whose allelochemical defenses were geared more toward reducing digestibility than attacking the herbivores metabolism directly, obviating the need for a foregut fermentation chamber and permitting these large herbivores to take advantage of the energetic benefits of hindgut fermentation for digestion of low-quality fodder. Differences in dentitions among the groups of herbivorous dinosaurs may correlate with differences in standard metabolic rate, activity level, body size, or food quality, or combinations of these factors, but the relative importance of each is difficult to assess. Because the mass of the fermentation contents was probably large in big herbivorous dinosaurs, the heat of fermentation may have been a significant source of thermoregulatory heat for these reptiles.

Body mass, bone “strength indicator,” and cursorial potential of Tyrannosaurus rex

ABSTRACT We describe a new life restoration of Tyrannosaurus rex, based on a fairly complete skeleton (Museum of the Rockies [MOR] 555). From the volume of this model, we estimate the live mass of the full-sized dinosaur as approximately 6,000 kg. Because MOR 555 is a representative of the gracile morph of T. rex, the mass of the robust morph may have been substantially greater. The “indicator of athletic ability” or “strength indicator” of MOR 555 is 7.5–9.0 meter2/giganewton, similar to previously reported results. The implication is that the cursorial potential of Tyrannosaurus was limited, a conclusion consistent with observed declines in sprint speed with increasing body mass in living animals, and also consistent with the tibia/femur length ratio, and the construction of the hip joint, of the dinosaur. Furthermore, mathematical models of the impact forces and decelerations that would affect a Tyrannosaurus, were it to fall while running at a high speed (20 meters/second), suggest that the animal wou...

Body Size Overlap, Habitat Partitioning and Living Space Requirements of Terrestrial Vertebrate Predators: Implications for the Paleoecology of Large Theropod Dinosaurs

Ecological studies of extant tetrapod predators indicate that morphologically similar species which coexist in the same habitats routinely reduce interspecific competition for food by regular spacing of body size. The biggest predator species in the assemblage often differ more from one another in size than the smallest species. When coexisting carnivore species do not differ greatly in size, they commonly show morphological differences related to prey handling that may reduce dietary overlap. If carnivore species are very similar in both size and morphology, competition is avoided by habitat partitioning. Two tyrannosaurid species from the late Campanian Dinosaur Park Formation of western Canada are similar in both size and morphology, suggesting that they were segregated on the basis of habitat and/or biogeographic province. However; consideration of the living-space requirements of predator species of such large body size suggests that this kind of spatial separation would only have been possible had tyrannosaurids been more like ectotherms than endotherms in their metabolic rates. Distribution of different large theropod species across different, and surprisingly small (for the size of the animals) portions of Mesozoic landscapes may also account for the remarkably high diversity of morphologically similar large theropods in other dinosaur faunas.

Osteohistological Evidence for Determinate Growth in the American Alligator

Abstract An external fundamental system (EFS) is a form of bone microstructure present in the outermost cortex of long bones in animals that have attained skeletal maturity. It indicates an effective cessation of any significant periosteal growth (i.e., growth in circumference or girth). Although an EFS has been noted in several reptile taxa, the idea that reptiles grow continually throughout their lives remains popular. Examination of femoral bone microstructure from captive American Alligators (Alligator mississippiensis) reveals parallel-fibered tissue terminating periosteally in an EFS, thus confirming determinate growth in another reptile taxon. The results of this study have several important implications for both modern and fossil tetrapods: first, because many birds, nonavian dinosaurs, pterosaurs, and basal pseudosuchians all produce an EFS, it can be concluded that determinate growth is a shared characteristic of Archosauria; second, because the captive alligators were not senescent, an EFS should not be associated with “old age” when interpreting growth histories of extinct animals; third, if no EFS is present, this should not immediately suggest indeterminate growth but rather that skeletal maturity was not attained prior to death. In addition, this study highlights the need for more osteohistological studies to establish exactly how widespread determinate growth is within both extinct and extant members of Sauropsida, because this form of growth may be the rule rather than the exception.

Transport-induced abrasion of fossil reptilian teeth: Implications for the existence of Tertiary dinosaurs in the Hell Creek Formation, Montana

The experimental transport-induced abrasion of five fossil teeth from a crocodilian and the tyrannosaurid dinosaur Albertosaurus demonstrates that enamel-coated teeth are minimally affected by abrasion associated with sediment-transport processes. After the equivalent of 360–480 km of transport, two teeth showed slight loss of weight, scratches were developed on the surface of one tooth, there were slight enlargements of the areas between adjacent serrations of one tooth, and a pit in the exposed dentine of one tooth was abraded smooth. These changes would have been difficult to recognize if the teeth had not been examined before the start of the experiment. Our results suggest that dinosaur teeth are abraded so slowly by transport processes that they provide equivocal evidence for limited transport and reworking.

Growth and function of Stegosaurus plates; evidence from bone histology

Histological examination of Stegosaurus dorsal bony plates shows a thin wall of incompletely remodeled bone surrounding a large cancellous region containing some large “pipes” delineated by thin bony walls. Growth proceeded mainly from the basal region of the plates. Histological observations provide a test against which several functional interpretations of the plates are checked. While some interpretations (e.g., plates as armor) are clearly falsified, others (linked to thermoregulatory functions) seem to be more robust, although by no means can they be viewed as clearly vindicated on the basis of the evidence presently available.

Quantification of intraskeletal histovariability in Alligator mississippiensis and implications for vertebrate osteohistology

Bone microanalyses of extant vertebrates provide a necessary framework from which to form hypotheses regarding the growth and skeletochronology of extinct taxa. Here, we describe the bone microstructure and quantify the histovariability of appendicular elements and osteoderms from three juvenile American alligators (Alligator mississippiensis) to assess growth mark and tissue organization within and amongst individuals, with the intention of validating paleohistological interpretations. Results confirm previous observations that lamellar and parallel fibered tissue organization are typical of crocodylians, and also that crocodylians are capable of forming woven tissue for brief periods. Tissue organization and growth mark count varies across individual skeletal elements and reveal that the femur, tibia, and humerus had the highest annual apposition rates in each individual. Cyclical growth mark count also varies intraskeletally, but data suggest these inconsistencies are due to differing medullary cavity expansion rates. There was no appreciable difference in either diaphyseal circumference or cyclical growth mark circumferences between left and right element pairs from an individual if diaphyses were sampled from roughly the same location. The considerable intraskeletal data obtained here provide validation for long-held paleohistology assumptions, but because medullary expansion, cyclical growth mark formation, and variable intraskeletal growth rates are skeletal features found in tetrapod taxa living or extinct, the validations presented herein should be considered during any tetrapod bone microanalysis.

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.

Historical Photogrammetry: Bird's Paluxy River Dinosaur Chase Sequence Digitally Reconstructed as It Was prior to Excavation 70 Years Ago

It is inevitable that some important specimens will become lost or damaged over time, conservation is therefore of vital importance. The Paluxy River dinosaur tracksite is among the most famous in the world. In 1940, Roland T. Bird described and excavated a portion of the site containing associated theropod and sauropod trackways. This excavated trackway was split up and housed in different institutions, and during the process a portion was lost or destroyed. We applied photogrammetric techniques to photographs taken by Bird over 70 years ago, before the trackway was removed, to digitally reconstruct the site as it was prior to excavation. The 3D digital model offers the opportunity to corroborate maps drawn by R.T. Bird when the tracksite was first described. More broadly, this work demonstrates the exciting potential for digitally recreating palaeontological, geological, or archaeological specimens that have been lost to science, but for which photographic documentation exists.

LATE NEOGENE (LATE HEMPHILLIAN) RODENTS FROM THE PIPE CREEK SINKHOLE, GRANT COUNTY, INDIANA

Abstract Spermophilus cf. howelli, Spermophilus sp., Castor or Dipoides sp., Geomys cf. adamsi, Symmetrodontomys daamsi, sp. nov., Bensonomys hershkovitzi, sp. nov., Ogmodontomys pipecreekensis, sp. nov., and Pliophenacomys koenigswaldi n. sp. are reported from the Pipe Creek Sinkhole of Grant County, Indiana. The Geomys sample demonstrates a variable sulcus morphology of the upper incisor, suggesting it stands near the Geomys—Pappogeomys boundary. Symmetrodontomys daamsi is characterized by its short lower molars and small mandible. Bensonomys hershkovitzi has a unique m1, with an anteroconid that with little wear connects deeply with the labial cingulum, and a mesolophid. O. pipecreekensis, with relatively low dentine tracts and no enamel atoll on m1, may be related to both Ogmodontomys sawrockensis and Ogmodontomys poaphagus, although it is probably not ancestral to either of them. Ogmodontomys Hibbard is considered an endemic North American genus distinguished from Mimomys Forsyth Major on the basis of a suite of dental features, including absence of a full lamellar enamel layer on leading edges of the molar triangles. The dentition of Pliophenacomys koenigswaldi exhibits a set of features suggesting a close relationship with Pliophenacomys finneyi of the early Blancan Fox Canyon local fauna of Kansas. Together with the rhinoceros Teleoceras, the rodent assemblage collectively suggests an early Pliocene (latest Hemphillian) age for the Pipe Creek biota. This is the first report of a late Neogene rodent fauna from Indiana.