An ornithomimosaurian from the Upper Cretaceous Prince Creek Formation of Alaska

Watanabe, Akinobu; Erickson, Gregory M.; Druckenmiller, Patrick

doi:10.1080/02724634.2013.770750

“…Therefore, hind limb and foot bones of a single individual would yield different assessments of relative maturity if analysed in isolation. For example, the inference that an Alaskan ornithomimosaur [ 26 ] was approaching somatic maturity at the time of death based on a decreasing pattern of LAG spacing in a single, isolated metatarsal, is poorly substantiated.…”

Section: Discussionmentioning

confidence: 99%

“…Horner et al [ 16 ], or the outer circumferential layer, or OCL, following Cormack [ 17 ]) has been used to infer somatic maturity in sampled individuals [ 7 , 14 , 15 ]. In the absence of an EFS, patterns in the relative spacing of LAGs has been used to infer the ontogenetic stage of an individual, in some cases using a single sectioned element [ 2 , 8 , 18 - 26 ]. On a finer scale, the density of osteocyte lacunae (osteocyte lacunar density, OLD) in the cortex of limb bones of tetrapods has been suggested to be related to mechanical forces and differential loadings, basal metabolic and growth rates, and element structural differences [ 27 - 29 ], and osteocyte lacuna morphology itself has also been shown to be related to these properties [ 27 , 29 , 30 ].…”

Section: Introductionmentioning

confidence: 99%

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

Cullen

¹

,

Evans

²

,

Ryan

³

et al. 2014

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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.

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“…Spacing between lines of arrested growth is often used to qualitatively assess the relative growth rates and maturity in isolated bones, e.g. Tyrannosaurus [5,7], Alioramus [18], Raptorex [23,25,26], and a putative Alaskan ornithomimosaur [26]. This method assumes that a decrease in LAG spacing from the inner cortex to the periosteum corresponds with an individual approaching somatic maturity.…”

Section: Lag Spacingmentioning

confidence: 99%

“…Horner et al [16], or the outer circumferential layer, or OCL, following Cormack [17]) has been used to infer somatic maturity in sampled individuals [7,14,15]. In the absence of an EFS, patterns in the relative spacing of LAGs has been used to infer the ontogenetic stage of an individual, in some cases using a single sectioned element [2,8,[18][19][20][21][22][23][24][25][26]. On a finer scale, the density of osteocyte lacunae (osteocyte lacunar density, OLD) in the cortex of limb bones of tetrapods has been suggested to be related to mechanical forces and differential loadings, basal metabolic and growth rates, and element structural differences [27][28][29], and osteocyte lacuna morphology itself has also been shown to be related to these properties [27,29,30].…”

Section: Introductionmentioning

confidence: 99%

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

Cullen

¹

,

Evans

²

,

Ryan

³

et al. 2014

View full text Add to dashboard Cite

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.

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“…Ornithomimosaurs spanned three orders of magnitude in body size [ 29 ], from an estimated 5.3 kg ( Nqwebasaurus [ 30 ]) to 620 kg ( Beishanlong [ 26 ]) and exceptionally in excess of 6000 kg ( Deinocheirus [ 31 ]). Phylogenetic ghost lineages imply that ornithomimosaurs had originated by the Middle Jurassic, and attained a broad distribution during the Cretaceous [ 32 ], including paleo-arctic [ 33 ] and Gondwanan [ 30 ] occurrences. In this study, we provide a comprehensive description of the vertebral pneumaticity of Archaeornithomimus and survey the degree of pneumaticity in other ornithomimosaurs to determine the macroevolutionary pattern of vertebral pneumaticity in Ornithomimosauria.…”

Section: Introductionmentioning

confidence: 99%

Vertebral Pneumaticity in the Ornithomimosaur Archaeornithomimus (Dinosauria: Theropoda) Revealed by Computed Tomography Imaging and Reappraisal of Axial Pneumaticity in Ornithomimosauria

Watanabe¹,

Gold²,

Brusatte³

et al. 2015

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Among extant vertebrates, pneumatization of postcranial bones is unique to birds, with few known exceptions in other groups. Through reduction in bone mass, this feature is thought to benefit flight capacity in modern birds, but its prevalence in non-avian dinosaurs of variable sizes has generated competing hypotheses on the initial adaptive significance of postcranial pneumaticity. To better understand the evolutionary history of postcranial pneumaticity, studies have surveyed its distribution among non-avian dinosaurs. Nevertheless, the degree of pneumaticity in the basal coelurosaurian group Ornithomimosauria remains poorly known, despite their potential to greatly enhance our understanding of the early evolution of pneumatic bones along the lineage leading to birds. Historically, the identification of postcranial pneumaticity in non-avian dinosaurs has been based on examination of external morphology, and few studies thus far have focused on the internal architecture of pneumatic structures inside the bones. Here, we describe the vertebral pneumaticity of the ornithomimosaur Archaeornithomimus with the aid of X-ray computed tomography (CT) imaging. Complementary examination of external and internal osteology reveals (1) highly pneumatized cervical vertebrae with an elaborate configuration of interconnected chambers within the neural arch and the centrum; (2) anterior dorsal vertebrae with pneumatic chambers inside the neural arch; (3) apneumatic sacral vertebrae; and (4) a subset of proximal caudal vertebrae with limited pneumatic invasion into the neural arch. Comparisons with other theropod dinosaurs suggest that ornithomimosaurs primitively exhibited a plesiomorphic theropod condition for axial pneumaticity that was extended among later taxa, such as Archaeornithomimus and large bodied Deinocheirus. This finding corroborates the notion that evolutionary increases in vertebral pneumaticity occurred in parallel among independent lineages of bird-line archosaurs. Beyond providing a comprehensive view of vertebral pneumaticity in a non-avian coelurosaur, this study demonstrates the utility and need of CT imaging for further clarifying the early evolutionary history of postcranial pneumaticity.

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An ornithomimosaurian from the Upper Cretaceous Prince Creek Formation of Alaska

Cited by 22 publications

References 60 publications

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

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

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

Vertebral Pneumaticity in the Ornithomimosaur Archaeornithomimus (Dinosauria: Theropoda) Revealed by Computed Tomography Imaging and Reappraisal of Axial Pneumaticity in Ornithomimosauria

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