Osteohistological variation in growth marks and osteocyte lacunar density in a theropod dinosaur (Coelurosauria: Ornithomimidae)

Abstract

BackgroundOsteohistological examinations of fossil vertebrates have utilized a number of proxies, such as counts and spacing of lines of arrested growth (LAGs) and osteocyte lacunar densities (OLD), in order to make inferences related to skeletochronology and mass-specific growth rates. However, many of these studies rely on samplings of isolated bones from single individuals. These analyses do not take individual variation into account, and as a result may lead to misleading inferences of the physiology of extinct organisms. This study uses a multi-element, multi-individual sampling of ornithomimid dinosaurs to test the amount of individual variation in the aforementioned osteohistological indicators. Based on these results we also assess the conclusions of previous studies that tested paleohistological hypotheses using isolated elements.ResultsLAG number was found to be consistent within the hind limb bones of each individual, with the exception of the fibula, which preserves one additional LAG. Considerable differences in LAG spacing were found between elements of the sampled individuals, with larger variation found in elements of the foot compared with the femur, fibula, and tibia. Osteocyte lacunar density ranged between 29000 and 42000 osteocyte lacunae per mm3, and was found to vary more between hind limb bones of an individual and within bones, than between the average values of individuals.ConclusionsThe variation between hind limb elements in LAG number and LAG spacing suggests that direct comparisons of these elements may be misleading, and that LAG spacing is not a reliable proxy for mass-specific growth rates of an individual. Sampling of multiple bones should be performed as an internal check of model-based LAG retro-calculation and growth equations. The observation that osteocyte lacunar density varies more between individual bone elements than between average individual values suggests that the choice of sampled element can greatly influence the result, and care should be taken to not bias interpretations of the physiology of fossil tetrapods.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-014-0231-y) contains supplementary material, which is available to authorized users.

Diminutive fleet-footed tyrannosauroid narrows the 70-million-year gap in the North American fossil record

“…5b). Doublet to quadruplet LAGs are commonly observed in non-avian theropod dinosaurs 31,34 and we interpret these as single growth events 35 . The predominance of a parallel-fibered bone matrix dominated by longitudinal vascular canals suggests a slow to moderate growth rate for this animal 36 , in contrast with the highly vascularized laminar to plexiform fibrolamellar bone tissues and rapid growth rates observed in large-bodied tyrannosaurids 3 .…”

Maiasaura, a model organism for extinct vertebrate population biology: a large sample statistical assessment of growth dynamics and survivorship

“…This normalization method must be applied cautiously, as comparing different skeletal elements from taxa with different limb allometries, gaits, and ecologies can lead to erroneous conclusions about growth (see Zhao et al 2013;Cullen et al 2014). Tight correlations with limb element dimensions and body length/mass, as well as maximum appositional growth rates, as noted with the alligator femora, must be demonstrated before being utilized in such normalized comparisons to ensure that the same growth characteristics are being compared.…”

“…The tibia was chosen for analysis because it lacks such a process and is therefore less subject to extensive remodeling. Although there is variation in the apposition rates of different bones within a skeleton (Horner et al 1999;Cullen et al 2014;Woodward et al 2014), this study samples only tibiae in order to directly compare variability present in a single element across multiple individuals. Along with the femur, the tibia tends to provide the most consistent skeletochronological results (Horner et al 1999), allowing reasonable estimates of maximum growth rates.…”

Peer Review #1 of "Histological variability in the limb bones of the Asiatic wild ass and its significance for life history inferences (v0.1)"

“…In the present research, we analyzed the histological variability between limb bones in the extant species Equus hemionus for the first time. Previous studies have addressed this issue in isolated bones of fossil vertebrate species (Horner, de Ricqlès and Padian, 2000;Sander & Andrássy, 2006;Cullen et al, 2014;Martínez-Maza et al, 2014), but only a few have studied the histological variation of bone tissue within the same individual (Horner, de Ricqlès and Padian, 1999;García-Martínez et al, 2011;Woodward, Horner & Farlow, 2014;Cambra-Moo et al, 2015). Our analysis of kulan's bone histology contributes to the knowledge of intraskeletal variability in mammals, providing new and important results that are of interest in different scientific areas.…”