No abstract

No abstract

Molecular preservation in non-avian dinosaurs is controversial. We present multiple lines of evidence that endogenous proteinaceous material is preserved in bone fragments and soft tissues from an 80-million-year-old Campanian hadrosaur, Brachylophosaurus canadensis [Museum of the Rockies (MOR) 2598]. Microstructural and immunological data are consistent with preservation of multiple bone matrix and vessel proteins, and phylogenetic analyses of Brachylophosaurus collagen sequenced by mass spectrometry robustly support the bird-dinosaur clade, consistent with an endogenous source for these collagen peptides. These data complement earlier results from Tyrannosaurus rex (MOR 1125) and confirm that molecular preservation in Cretaceous dinosaurs is not a unique event.

Finite element analysis (FEA) is used by industrial designers and biomechanicists to estimate the performance of engineered structures or human skeletal and soft tissues subjected to varying regimes of stress and strain. FEA is rarely applied to problems of biomechanical design in animals, despite its potential to inform structure-function analysis. Non-invasive techniques such as computed tomography scans can be used to generate accurate three-dimensional images of structures, such as skulls, which can form the basis of an accurate finite element model. Here we have applied this technique to the long skull of the large carnivorous theropod dinosaur Allosaurus fragilis. We have generated the most geometrically complete and complex FEA model of the skull of any extinct or extant organism and used this to test its mechanical properties and examine, in a quantitative way, long-held hypotheses concerning overall shape and function. The combination of a weak muscle-driven bite force, a very 'light' and 'open' skull architecture and unusually high cranial strength, suggests a very specific feeding behaviour for this animal. These results demonstrate simply the inherent potential of FEA for testing mechanical behaviour in fossils in ways that, until now, have been impossible.

Twelve different bones from the skeleton of the holotype specimen of the hadrosaurian dinosaur Hypacrosaurus stebingeri were thin-sectioned to evaluate the significance of lines of arrested growth (LAGs) in age assessments. The presence of an external fundamental system (EFS) at the external surface of the cortex and mature epiphyses indicate that the Hypacrosaurus specimen had reached adulthood and growth had slowed considerably from earlier stages. The number of LAGs varied from none in the pedal phalanx to as many as eight in the tibia and femur. Most elements had experienced considerable Haversian reconstruction that had most likely obliterated many LAGs. The tibia was found to have experienced the least amount of reconstruction, but was still not optimal for skeletochronology because the LAGs were difficult to count near the periosteal surface. Additionally, the numbers of LAGs within the EFS vary considerably around the circumference of a single element and among elements. Counting LAGs from a single bone to assess skeletochronology appears to be unreliable, particularly when a fundamental system exists.Because LAGs are plesiomorphic for tetrapods, and because they are present in over a dozen orders of mammals, they have no particular physiological meaning that can be generalized to particular amniote groups without independent physiological evidence. Descriptions of dinosaur physiology as “intermediate” between the physiology of living reptiles and that of living birds and mammals may or may not be valid, but cannot be based reliably on the presence of LAGs.

Histological evidence of the bones of pterosaurs and dinosaurs indicates that the typically large forms of these groups grew at rates more comparable to those of birds and mammals than to those of other living reptiles. However, Scutellosaurus, a small, bipedal, basal thyreophoran ornithischian dinosaur of the Early Jurassic, shows histological features in its skeletal tissues that suggest relatively lower growth rates than in those of larger dinosaurs. In these respects Scutellosaurus, like other small dinosaurs such as Orodromeus and some basal birds, is more like young, rapidly growing crocodiles than larger, more derived ornithischians (hadrosaurs) and all saurischians (sauropods and theropods). Similar patterns can be seen in small, mostly basal pterosaurs such as Eudimorphodon and Rhamphorhynchus. However, superficial similarities to crocodile bone growth belie some important differences, which are most usefully interpreted in phylogenetic and ontogenetic contexts. Large size evolved secondarily in several dinosaurian and pterosaurian lineages. We hypothesize that this larger size was made possible by rapid growth strategies that are reflected by characteristic highly vascularized fibro-lamellar bone tissues that comprise most of the cortex. Dinosaurs and pterosaurs, like other tetrapods, generally grew more quickly in early stages and more slowly as growth neared completion. As in other vertebrate groups, taxa of small adult size may have grown at lower rates or for shorter durations than larger taxa did. Phylogenetic patterns suggest that by themselves, the low vascularity and inferred low growth rates seen in small dinosaurs and pterosaurs are not good indicators of thermometabolic regime, because they are correlated so strongly with size. They may reflect mechanical exigencies of small size rather than especially lower growth rates, tied to the process of deposition of particular kinds of bone tissues. The evolution of life history strategies in dinosaurs and pterosaurs, as they relate to rates of growth and adult body sizes, will be better understood as more complete histological studies place these data into phylogenetic and ontogenetic contexts.

Dinosaurs, like other tetrapods, grew more quickly just after hatching than later in life. However, they did not grow like most other non-avian reptiles, which grow slowly and gradually through life. Rather, microscopic analyses of the long-bone tissues show that dinosaurs grew to their adult size relatively quickly, much as large birds and mammals do today. The first birds reduced their adult body size by shortening the phase of rapid growth common to their larger theropod dinosaur relatives. These changes in timing were primarily related not to physiological differences but to differences in growth strategy.

No abstract