Body Size Distribution of the Dinosaurs

The distribution of species body size is critically important for determining resource use within a group or clade. It is widely known that non-avian dinosaurs were the largest creatures to roam the Earth. There is, however, little understanding of how maximum species body size was distributed among the dinosaurs. Do they share a similar distribution to modern day vertebrate groups in spite of their large size, or did they exhibit fundamentally different distributions due to unique evolutionary pressures and adaptations? Here, we address this question by comparing the distribution of maximum species body size for dinosaurs to an extensive set of extant and extinct vertebrate groups. We also examine the body size distribution of dinosaurs by various sub-groups, time periods and formations. We find that dinosaurs exhibit a strong skew towards larger species, in direct contrast to modern day vertebrates. This pattern is not solely an artefact of bias in the fossil record, as demonstrated by contrasting distributions in two major extinct groups and supports the hypothesis that dinosaurs exhibited a fundamentally different life history strategy to other terrestrial vertebrates. A disparity in the size distribution of the herbivorous Ornithischia and Sauropodomorpha and the largely carnivorous Theropoda suggests that this pattern may have been a product of a divergence in evolutionary strategies: herbivorous dinosaurs rapidly evolved large size to escape predation by carnivores and maximise digestive efficiency; carnivores had sufficient resources among juvenile dinosaurs and non-dinosaurian prey to achieve optimal success at smaller body size. © 2012 O'Gorman, Hone

Wpływ stada, sezonu i płci na wiek osiągania dojrzałości okrywy włosowej szynszyli

The aim of this study was to determine the effect of herd, birth season, slaughter season, and sex on the age of reaching a full maturity of fur in chinchilla. The data on 566 chinchillas (104 females and 462 males) slaughtered for pelt in the years 1997 to 2002 were collected from 4 farms. The linear model of fur maturity age in the analysis of variance included birth month, herd (farm), and sex as factors. The results showed that the age of animals at fur maturity (assumed to be the age at slaughter) averaged 284 days. Significant differences between the herds indicate that the conditions of housing and the system of breeding influenced this trait. The differences between males and females were not significant. The month of birth had a significant effect on the age of fur maturity: chinchillas born in October were the first to reach fur maturity (253 days), followed by chinchillas born from May to August and in November (275-279 days), while those born from January to April as well as in September and December were the latest (295-302 days). Chinchillas born in March were an exception to the general pattern: 51% of the animals reached fur maturity in the period from December to March (64.4% from December to April).Celem pracy było określenie wpływu stada, sezonu urodzenia i uboju oraz płci na wiek osiągnięcia pełnej dojrzałości okrywy włosowej szynszyli. Zebrano dane o 566 szynszylach (104 samice i 462 samce) poddanych ubojowi na skóry w latach 1997-2002. Model linowy analizy wariancji uwzględniał: miesiąc urodzenia, stado (fermę) i płeć ubijanych zwierząt. Stwierdzono, że wiek szynszyli przy osiągnięciu dojrzałości okrywy włosowej (utożsamiany z wiekiem przy uboju) wynosił średnio 284 dni. Istotne różnice między stadami wskazują na wpływ sposobu utrzymania i systemu chowu na tę cechę. Nie stwierdzono istotnych różnic między płciami. Miesiąc urodzenia wpływał istotnie na wiek osiągania dojrzałości okrywy włosowej. Szynszyle urodzone w październiku najwcześniej osiągały dojrzałość okrywy włosowej (253 dni), następnie szynszyle urodzone w miesiącach od maja do sierpnia i w listopadzie (275-279 dni), a najpóźniej szynszyle urodzone od stycznia do kwietnia oraz we wrześniu i w grudniu (295-302 dni). Wyjątek stanowią jedynie szynszyle urodzone w marcu. 51% szynszyli osiągnęło dojrzałość okrywy włosowej w okresie od grudnia do marca, a uwzględniając kwiecień, wskaźnik ten dochodził do 64,4%