Please cite this article in press as:Jordana, X., et al., Ontogenetic changes in the histological features of zonal bone tissue of ruminants: A quantitative approach. C. R. Palevol (2015), http://dx. a b s t r a c tBone histology is a powerful tool to explore the growth patterns of vertebrates. There is a broad consensus that a deeper understanding of bone development in living taxa is still lacking. Here, we aim to explore the ontogeny of the fibrolamellar (FLC) zonal bone of mammals by studying histological sections of the femoral growth series of 84 wild ruminants.Our results indicate that large ruminants do not preserve a complete ontogenetic record of primary bone growth, so it is necessary to use methods of age retrocalculation. Our study also stresses the ontogenetic variation in histological features of the FLC-zonal bone (vascular orientation, vascular and osteocyte lacunae density) that may reflect the slowdown in growth associated with the onset of physiological maturity. We conclude that the transition from FLC bone to lamellar bone (EFS) in ruminants records the fundamental life history trade-off between growth and reproduction (reproductive maturity).
The island rule entails a modification of the body size of insular mammals, a character related with numerous biological and ecological variables. From the Miocene to human colonization (Holocene), Mediterranean and Canary Islands were unaltered natural ecosystems, with paleofaunas formed with endemic giant rodents among other mammals. Our aim is to create methods to estimate the body masses of fossil island rodents and address the nature of ecological pressures driving the island rule. We created regression equations based on extant rodent data and used these to estimate the body masses of the extinct species. Our results show strong correlations between teeth, cranial and postcranial measurements and body mass, except for the length of the long bones, the transversal diameter of the distal tibia and the anteroposterior diameter of the proximal tibia, where the equations were less reliable. The use of equations obtained from a more homogeneous group (suborder and family) is preferable when analyzing the area of the first molar. The new regressions were applied to estimate the body masses of some Mediterranean and Canarian fossil rodents (Canariomys, C. bravoi 1.5 kg and C. tamarani 1 kg; Hypnomys, H. morpheus 230 g and H. onicensis 200 g; and Muscardinus cyclopeus 100 g). Our results indicate that under absence of predation, resource availability (island area) is the key factor that determines the size of the Canariomys sp. However, under presence of specialized predators (birds of prey), body size evolution is less pronounced (Hypnomys sp.).
Lagomorphs are widespread around the world, but little is known about the biology and ecology of their fossil ancestors. In this case, knowing the body mass of these extinct species is of principal interest because it is correlated with physiological, morphological and life history attributes. Moreover, insular fossil rabbits, hares and pikas, which became spectacular giants with huge weights and dramatic shifts in their life histories, encourage curiosity in the research world. Our principal aim is to create allometric models between skeletal parameters and body weights with extant species of the order Lagomorpha (both ochotonids and leporids). These regressions can then be applied to the fossil register to estimate the body mass of the extinct lagomorphs. The models are satisfactory in all cases, although weaker relationships were obtained when we analyzed dental parameters. Multiple models have slightly better results than bivariate ones, but their use is limited to complete bones or skeletons. These body mass estimation models were tested in three different fossil lagomorphs: Prolagus apricenicus, Prolagus cf. calpensis and Nuralagus rex. In all three cases, the results from dental variables were discarded due to the fact that these species may not follow the allometric relationship between teeth and body mass of standard lagomorphs. Other variables, such as the proximal anteroposterior diameter of the humerus in N. rex, were also removed for their implications in fossorial lifestyle. We ultimately estimated a weight of around 600 g for P. apricenicus, 300 g for P. cf. calpensis and 8000 g for N. rex. Differences in extrinsic mortality explain the important differences in body masses between the two Prolagus species. The results of N. rex cannot be compared with the giant Prolagus due to phylogenetic differences.
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