Histology and Geochemistry of Allosaurus (Dinosauria: Theropoda) From the Cleveland-Lloyd Dinosaur Quarry (Late Jurassic, Utah): Paleobiological Implications

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Abstract

The Late Jurassic Allosaurus is one of the better-studied dinosaurs. A histological and geochemical study of a tibia and a femur of A. fragilis recovered in the Upper Jurassic Cleveland-Lloyd Dinosaur Quarry, Utah, United States has been done in order to address growth characteristics of this species. The two bones, probably belonging to separate individuals, are among the largest known for this species, which make them suitable to address such issues. The inclusion of our data on femur growth markings in the previously published data reflects a range of growth variability rather than two distinct growth strategies. The tibia has a well-developed external fundamental system indicating somatic maturity achievement. Using a quantitative method of superimposition to retrocalculate missing lines of arrested growth, the tibia appears to correspond to an individual that reached its skeletal maturity at 22 years and died at approximately 26 years. In the tibia, the concentration of zinc, a potential biomarker associated with bone formation, displays a higher concentration in zones of rapid growth compared to annuli. There is no direct relationship between the values of δ ¹⁸O _p and the lines of arrested growth distribution. The absence of relations between the histological organization and an enrichment in REE of the bone, indicates that the variations of δ ¹⁸O _p likely represent a diagenetic process rather than a primordial, biologic composition. However, the geochemical composition of the bones is not homogeneous along the sections, indicating that the signal variations have not been completely erased by diagenesis.

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Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs.

Patricia Erickson, Mark Norell, Peter J Makovicky … (2004)

How evolutionary changes in body size are brought about by variance in developmental timing and/or growth rates (also known as heterochrony) is a topic of considerable interest in evolutionary biology. In particular, extreme size change leading to gigantism occurred within the dinosaurs on multiple occasions. Whether this change was brought about by accelerated growth, delayed maturity or a combination of both processes is unknown. A better understanding of relationships between non-avian dinosaur groups and the newfound capacity to reconstruct their growth curves make it possible to address these questions quantitatively. Here we study growth patterns within the Tyrannosauridae, the best known group of large carnivorous dinosaurs, and determine the developmental means by which Tyrannosaurus rex, weighing 5,000 kg and more, grew to be one of the most enormous terrestrial carnivorous animals ever. T. rex had a maximal growth rate of 2.1 kg d(-1), reached skeletal maturity in two decades and lived for up to 28 years. T. rex's great stature was primarily attained by accelerating growth rates beyond that of its closest relatives.

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Sexual maturity in growing dinosaurs does not fit reptilian growth models.

Sarah Werning, Ren-Shen Lee (2008)

Recent histological studies suggest relatively rapid growth in dinosaurs. However, the timing of reproductive maturity (RM) in dinosaurs is poorly known because unambiguous indicators of RM are rare. One exception is medullary bone (MB), which is an ephemeral bony tissue that forms before ovulation in the marrow cavities of birds as a calcium source for eggshelling. Recently, MB also was described in a single specimen of the saurischian dinosaur Tyrannosaurus rex. Here, we report two other occurrences of MB: in another saurischian dinosaur, Allosaurus, and in the ornithischian dinosaur Tenontosaurus. We show by counting lines of arrested growth and performing growth curve reconstructions that Tenontosaurus, Allosaurus, and Tyrannosaurus were reproductively mature by 8, 10, and 18 years, respectively. RM in these dinosaurs coincided with a transition from growth acceleration to deceleration. It also far precedes predictions based on the growth rates of living reptiles scaled to similar size. Despite relatively rapid growth, dinosaurs were similar to reptiles in that RM developed before reaching asymptotic size. However, this reproductive strategy also occurs in medium- to large-sized mammals and correlates with a strategy of prolonged multiyear growth. RM in actively growing individuals suggests that these dinosaurs were born relatively precocial and experienced high adult mortality. The origin of the modern avian reproductive strategy in ornithuran birds likely coincided with their extreme elevations in growth rate and truncations to growth duration.

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Growth patterns in brooding dinosaurs reveals the timing of sexual maturity in non-avian dinosaurs and genesis of the avian condition.

Xing Xu, Mark Norell, Patricia Erickson … (2007)

The timing of sexual maturation in non-avian dinosaurs is not known. In extant squamates and crocodilians it occurs in conjunction with the initial slowing of growth rates as adult size is approached. In birds (living dinosaurs) on the other hand, reproductive activity begins well after somatic maturity. Here we used growth line counts and spacing in all of the known brooding non-avian dinosaurs to determine the stages of development when they perished. It was revealed that sexual maturation occurred well before full adult size was reached-the primitive reptilian condition. In this sense, the life history and physiology of non-avian dinosaurs was not like that of modern birds. Palaeobiological ramifications of these findings include the potential to deduce reproductive lifespan, fecundity and reproductive population sizes in non-avian dinosaurs, as well as aid in the identification of secondary sexual characteristics.