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

Cullen TM, Evans DC, Ryan MJ, Currie PJ, Kobayashi Y - BMC Evol. Biol. (2014)

Bottom Line: These analyses do not take individual variation into account, and as a result may lead to misleading inferences of the physiology of extinct organisms.Based on these results we also assess the conclusions of previous studies that tested paleohistological hypotheses using isolated elements.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada. thomas.cullen@mail.utoronto.ca.

ABSTRACT

Background: Osteohistological 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.

Results: LAG 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 mm(3), and was found to vary more between hind limb bones of an individual and within bones, than between the average values of individuals.

Conclusions: The 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.

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Range of intra- and inter-individual variation in osteocyte lacunar density (OLD) in Horseshoe Canyon Formation (HCF) ornithomimid taxon compared with point-sampling of species from Stein & Werner[29]. Mammal data from Stein & Werner 2013 primarily derived from Bromage et al. [44]. Purple box indicates range of measured variation in Horseshoe Canyon Formation Ornithomimid taxon.
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Fig7: Range of intra- and inter-individual variation in osteocyte lacunar density (OLD) in Horseshoe Canyon Formation (HCF) ornithomimid taxon compared with point-sampling of species from Stein & Werner[29]. Mammal data from Stein & Werner 2013 primarily derived from Bromage et al. [44]. Purple box indicates range of measured variation in Horseshoe Canyon Formation Ornithomimid taxon.

Mentions: For an estimated ornithomimid body size range of 90–125 kg [37], the minimum and maximum, average OLD values of the Horseshoe Canyon Formation ornithomimids plot midway between birds/mammals and non-avian theropod dinosaurs [29], but show considerable variation when individual bone measurements are plotted (Figure 7). This variation is illustrated further through a comparison of the range of OLD values for each element of the three bonebed individuals against the mean OLD values for the species derived from the individual averages (Figure 8A), a comparison of the variation in OLD within (via medial and lateral sampling) and between elements of CMN 12068 (Figure 8B), and a detailed comparison of the OLD values across a transect through the inner, middle, and outer cortex of the fibula of ROM 852 (Figure 8C). The latter comparison was also assessed via a series of ANOVAs, which found no significant differences in the OLD between the inner and middle cortex (p = 0.79), between the inner and outer cortex (p = 0.06), or between the middle and outer cortex (p = 0.97).Figure 7


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

Cullen TM, Evans DC, Ryan MJ, Currie PJ, Kobayashi Y - BMC Evol. Biol. (2014)

Range of intra- and inter-individual variation in osteocyte lacunar density (OLD) in Horseshoe Canyon Formation (HCF) ornithomimid taxon compared with point-sampling of species from Stein & Werner[29]. Mammal data from Stein & Werner 2013 primarily derived from Bromage et al. [44]. Purple box indicates range of measured variation in Horseshoe Canyon Formation Ornithomimid taxon.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4269922&req=5

Fig7: Range of intra- and inter-individual variation in osteocyte lacunar density (OLD) in Horseshoe Canyon Formation (HCF) ornithomimid taxon compared with point-sampling of species from Stein & Werner[29]. Mammal data from Stein & Werner 2013 primarily derived from Bromage et al. [44]. Purple box indicates range of measured variation in Horseshoe Canyon Formation Ornithomimid taxon.
Mentions: For an estimated ornithomimid body size range of 90–125 kg [37], the minimum and maximum, average OLD values of the Horseshoe Canyon Formation ornithomimids plot midway between birds/mammals and non-avian theropod dinosaurs [29], but show considerable variation when individual bone measurements are plotted (Figure 7). This variation is illustrated further through a comparison of the range of OLD values for each element of the three bonebed individuals against the mean OLD values for the species derived from the individual averages (Figure 8A), a comparison of the variation in OLD within (via medial and lateral sampling) and between elements of CMN 12068 (Figure 8B), and a detailed comparison of the OLD values across a transect through the inner, middle, and outer cortex of the fibula of ROM 852 (Figure 8C). The latter comparison was also assessed via a series of ANOVAs, which found no significant differences in the OLD between the inner and middle cortex (p = 0.79), between the inner and outer cortex (p = 0.06), or between the middle and outer cortex (p = 0.97).Figure 7

Bottom Line: These analyses do not take individual variation into account, and as a result may lead to misleading inferences of the physiology of extinct organisms.Based on these results we also assess the conclusions of previous studies that tested paleohistological hypotheses using isolated elements.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, ON, M5S 3B2, Canada. thomas.cullen@mail.utoronto.ca.

ABSTRACT

Background: Osteohistological 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.

Results: LAG 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 mm(3), and was found to vary more between hind limb bones of an individual and within bones, than between the average values of individuals.

Conclusions: The 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.

Show MeSH
Related in: MedlinePlus