Reese E. Barrick

Thermophysiology of Tyrannosaurus rex: Evidence from Oxygen Isotopes

The oxygen isotopic composition of vertebrate bone phosphate (δp) is related to ingested water and to the body temperature at which the bone forms. The δp is in equilibrium with the individuals body water, which is at a physiological steady state throughout the body. Therefore, intrabone temperature variation and the mean interbone temperature differences of well-preserved fossil vertebrates can be determined from the δp variation. Values of δp from a well-preserved Tyrannosaurus rex suggest that this species maintained homeothermy with less than 4�C of variability in body temperature. Maintenance of homeothermy implies a relatively high metabolic rate that is similar to that of endotherms.

Comparison of thermoregulation of four ornithischian dinosaurs and a varanid lizard from the Cretaceous Two Medicine Formation; evidence from oxygen isotopes

The 180 values of vertebrate bone phosphate are dependent upon the 180O values of their body water and the temperature of bone deposition. This allows the measurement of the temperature fluctuation during bone deposition for individual skeletal elements within any individual. 8180 results for bones from a varanid lizard and four Late Cretaceous ornithischian dinosaurs (Orodromeus makelai, Hypacrosaurus stebingeri, Montanaceratops sp., and a juvenile Achelousaurus horneri) from the Campanian Two Medicine Formation in Montana are compared. Results from the varanid indicate that bone deposition occurred over a range of 10-15?C, as expected for an ectotherm. Results from the dinosaurs indicate that bone deposition occurred over a range 2-7?C within the body core and 3-8 C in the extremities. The intrabone and interbone pattern of 6180 values suggests that these dinosaurs were primarily homeotherms with all but Orodromeus exhibiting regional heterothermy. Homeothermy over the size range of the individual dinosaurs suggests that they had metabolic rates elevated above those of modern ectotherms and the range of isotopic variability suggests intermediate endothermy.

Oxygen isotopes from turtle bone; applications for terrestrial paleoclimates?

The oxygen isotope values (8) of turtle-bone phosphate for two freshwater emydid genera from the United States vary linearly with isotopic values (8J of environmental water. Mud, box, and snapping turtles do not fall on this regression line, while a soft-shelled turtle and marine loggerhead and leatherback turtles do. Although ectothermic, emydid turtles depend upon basking to raise their body temperatures. The mean temperature of bone growth is similar (3133?C) in emydid individuals analyzed as indicated by their bone and body-water oxygen isotopes. Unlike regressions for mammals, the slope of 8p versus 8, for these emydid turtles is unity, suggesting that the divergence from equilibrium is due to simple fractionation between environmental water and body water. Thus, bone 8, values from these genera of turtles (and potentially others) may be used to reconstruct local meteoric water 8w values in the fossil record. Concurrent study of fossil freshwater fish or molluscs may then be used to reconstruct local paleotemperatures.

Oxygen isotope variability in juvenile dinosaurs (Hypacrosaurus): evidence for thermoregulation

Small terrestrial vertebrates are not capable of maintaining a constant body temperature (±2°C) without a relatively high metabolism. The amount of temperature variability during bone growth can be determined using oxygen isotopes from bone phosphate because fractionation of oxygen isotopes between body fluid and bone phosphate is dependent upon temperature. Fluctuation of body temperature during the early phase of growth in juvenile ectotherms should result in high intra- and interbone isotopic variability, whereas juvenile endotherms should have low isotopic variability resulting from the maintenance of homeothermy. Analyses of juvenile Hypacrosaurus individuals indicate a pattern of low isotopic heterogeneity suggestive of endothermy.

Ankylosaurs from the Price River Quarries, Cedar Mountain Formation (Lower Cretaceous), east-central Utah

Abstract A new large nodosaurid ankylosaur, Peloroplites cedrimontanus, is described from a partial skull and postcranial skeleton found at the PR-2 Quarry located at the base of the Mussentuchit Member of the Cedar Mountain Formation in central Utah. The specimen is about the same size as the contemporary nodosaurid Sauropelta edwardsorum from the Cloverly Formation of Montana, and is of an individual approximately 5–5.5 m long. The skull of Peloroplites differs from that of Sauropelta in the vertical orientation of the suspensorium, non-domed cranium and broad, square premaxillary beak. The quarry is near and roughly at the same level as the CEM Quarry that produced the holotype of the ankylosaurid Cedarpelta bilbeyhallorum. The postcrania of Cedarpelta is described and illustrated based on the paratype and new material. These elements clearly establish that Cedarpelta is closer to Ankylosaurus than to Sauropelta. As a primitive ankylosaurid, there is no a priori reason to assume that the tail club was present. Based on recent finds in China, a hypothesis is presented that the tail club is a derived feature in non-shamosaurine (i.e., ankylosaurine) ankylosaurids.

Dinosaur skin impressions and associated skeletal remains from the upper Campanian of southwestern New Mexico: new data on the integument morphology of hadrosaurs

ABSTRACT Skin impressions from the tail region of an indeterminate hadrosaur recently excavated from the Upper Cretaceous Ringbone Formation, southwest New Mexico represent the first known dinosaur specimen from New Mexico with impressions of the integument preserved in association with skeletal remains. The mid- to distal-caudal region is represented by 20 articulated centra, other disarticulated centra, a single chevron, ossified tendons and fragmentary bone, including poorly preserved neural spines. The skin impressions are preserved in negative and positive relief between two very fine-grained sandstone beds, interpreted as part of a fluvio-lacustrine facies package. The impression surface is directly below the ossified tendons, and 2.5 m from the articulated vertebral column. The skin impressions are six discrete patches characterized by predominantly apical, circular to ovate tubercles. Measurements of the long and short axes of individual tubercles demonstrate that a distribution of relatively homo...

The thermoregulatory functions of the Triceratops frill and horns: heat flow measured with oxygen isotopes

ABSTRACT Variability of body temperature within fossil vertebrates can be measured by the oxygen isotopie composition of bone phosphate (δp). Intrabone and interbone δp variations indicate heat flow within an individual and can be used to establish thermoregulatory strategies such as homeothermy and regional heterothermy. This method is applied to an individual Triceratops skeleton where the results suggest very high and uniform heat flow through the parietal frill, maintaining mean frill temperatures between 0–4°C below the body core. Heat flow to the postorbital horn-core is much more variable. The frill and horn cores of Triceratops were used as thermoregulatory structures with the horn cores interpreted as being especially important in the stabilization of brain temperatures at extreme ambient temperatures and the frill serving a more consistent role in body temperature regulation.

ESCALATION AND EXTINCTION SELECTIVITY: MORPHOLOGY VERSUS ISOTOPIC RECONSTRUCTION OF BIVALVE METABOLISM

Abstract Studies that have tested and failed to support the hypothesis that escalated species (e.g., those with predation‐resistant adaptations) are more susceptible to elimination during mass extinctions have concentrated on the distribution and degree of morphological defenses in molluscan species. This morphological approach to determining level of escalation in bivalves may be oversimplified because it does not account for metabolic rate, which is an important measure of escalation that is less readily accessible for fossils. Shell growth rates in living bivalves are positively correlated with metabolic rate and thus are potential indicators of level of escalation. To evaluate this approach, we used oxygen isotopes to reconstruct shell growth rates for two bivalve species (Macrocallista marylandica and Glossus markoei) from Miocene‐aged sediments of Maryland. Although both species are classified as non‐escalated based on morphology, the isotopic data indicate thatM. marylandica was a faster‐growing species with a higher metabolic rate and G. markoei was a slower‐growing species with a lower metabolic rate. Based on these results, we predict that some morphologically non‐escalated species in previous tests of extinction selectivity should be reclassified as escalated because of their fast shell growth rates (i.e., high metabolic rates). Studies that evaluate the level of escalation of a fauna should take into account the energetic physiology of taxa to avoid misleading results.

Oxygen isotope variability in bones of wild caught and constant temperature reared sub-adult American alligators.

(1) The mean delta18O(BP) ( per thousandSMOW) for any given bone sampled from captive alligators maintained at high constant temperature was lower (indicative of higher temperatures of bone deposition) than that of the same bone from wild alligators caught in Northern Florida, but these differences were only greater than two standard deviations from the mean for the thoracic vertebrae and metatarsal bones. (2) Inter-bone variability of delta18O(BP) ( per thousandSMOW) was similar for captive alligators maintained at constant temperatures and the wild alligators, but intra-bone variability was much greater in wild alligators. (3) The order of mean delta18O(BP) ( per thousandSMOW) of bones (from highest to lowest) differed between treatment groups. However, intra-bone variability obscured the significance of those differences. Nevertheless, the thoracic vertebra had the highest mean delta18O(BP) ( per thousandSMOW), indicative of lower temperatures, and the lowest variability of bones in both groups of alligators. Conversely, the tibia was one of the warmest and more variable bones in both groups of alligators. (4) The pattern of delta18O(BP) ( per thousandSMOW) values across sites within long bones were identical between alligator treatment groups for the femur and humerus but differed between groups for the tibia and metatarsus, and differed between different long bones. The predicted intra-bone pattern for long bones of increasing delta18O(BP) ( per thousandSMOW) indicative of lower temperatures in more distal sampling sites was only obtained from the femurs. (5) Paired cortical and cancellous bone samples from the same site from all individuals in both treatment groups were available for proximal humeri and distal femurs. delta18O(BP) ( per thousandSMOW) values from cortical bone were more variable than those from cancellous bone for both bones. (6) Cortical bone had lower delta18O(BP) ( per thousandSMOW) values indicative of warmer temperatures than cancellous bone at sites sampled on the proximal humeri and distal femurs of all three animals from both treatment groups.

Paleotemperatures versus sea level: Oxygen isotope signal from fish bone phosphate of the Miocene Calvert Cliffs, Maryland

The use of skeletal oxygen isotopic records for use in paleotemperature reconstruction has been hampered by the lack of independent evidence for ocean water oxygen isotopic composition. The δ18O record from homeothermic cetaceans has provided an independent estimate of ocean δ18O values represented by the Calvert and Choptank formations of Maryland. Fish teeth and bones (especially shark and ray teeth) were also collected from these sediments and provide the basis for paleotemperature estimates for represented time slices of the middle Miocene. Trends in δ18O values of the fish phosphate throughout the Calvert Formation are of opposite polarity to the trends from the cetacean bone phosphate. Paleotemperatures calculated using the cetacean proxies for ocean δ18O values sharpen the already present trend, indicating that ocean temperatures increased during episodes of greater glaciation and decreased during periods of lesser or no glaciation. When using modern average ocean values of 0‰ SMOW in the paleotemperature calculation, however, corrected paleotemperatures for the Choptank Formation do not alter the existing pattern of temperatures.