Life History Evolution in Extant and Extinct Laurasiatheria – Case Studies Elucidating the Junctions among Selective Forces, Disparity,and Trait Evolution

Abstract

Abstract This thesis presents several case studies on life history evolution in Laurasiatheria, a diverse group of mammals occupying a wide range of habitats. The respective group in each case study was chosen based on its suitability to answer an underlying question. Additionally, one case study investigates domestication as driver for variation within a species. The first case study aims for a closer look on the Schultz’s rule and heterochro -ny in the relative eruption sequence of the permanent dentition in lower jaws of deer, Cervidae. Cervids were chosen because of their relative uniform mandibular architecture. Schultz’s rule implies that slower growing animals replace their deciduous teeth earlier in relative sequence compared to molar eruption to counterbalance tooth decay and maintain a functional tooth set during growth. The study revealed several heterochronic shifts in tooth eruption during the evolution of deer and resulted in an ancestral tooth eruption sequence, which can also be found in the fossil record. In contrast, the relative eruption sequence is not correlated with any life history variable and thus it does not provide in formation about the life history of cervids. The second study investigated the brain size of cave bears and compared it to extant bear species. Encephalization, or brain size in relation to body size, is linked to some life history variables in Ursidae such as gestation time, newborn mass, weaning mass, and litter size. The results suggest that cave bears had a small brain compared to body size, due to a decoupled body and brain size evolution in which the increase of body size outpaced the one of brain size. Additionally, the trade-off between fat storage and brain size as well as diet might have impacted the relative brain size of cave bears. The degree of encephalization of cave bears suggests that this species gave birth to many, light weighted cubs and had prolonged gestation; mass at weaning was small. The growth of different bear species was investigated using histological thin sections of the midshaft of femora. The growth rate of cave bears from different European localities was investigated and compared to the one of black bears, brown bears, polar bears, sloth bears, and sun bears. The bone cortex of all bear species exhibits a fibrolamellar complex and mostly varies in amounts of parallel-fibered and lamellar bone. Cave bears exhibit a high growth rate and late maturity. The altitude of the locality in which the cave bear remains were found was correlated with growth rate. The growth rate of cave bears indicates that this species gave birth to many, small offspring. In the final case study presented in this thesis, the aim was to investigate how domestication affects variation within a species. For this, the extinct Niata cattle from South America was used as case study. The Niata was a heavy brachycephalic cattle variety. It was described by Darwin and sparked debates among scientists in Europe due to its peculiar appearance. These debates are addressed in an integrative investigation of the Niata using anatomical description, geometric morphometrics, finite element analysis, and genetic analysis. The anatomical description shows clear distinctions between the Niata traits and lethal malformations with which its brachycephaly was compared. The morphometric and genetic analyses show the distinctiveness of the Niata compared to other cattle and places it close to the European taurine breeds. Additionally, the finite element analysis revealed released stress on the Niata skull during bilateral bite. The Niata is an illustrative case on how human intervention shapes domesticated species. To summarize, the case studies presented in this thesis exemplify how bones and teeth can be used to infer life history of extant and extinct animals as well as how humans shape animals during domestication. Keywords: heterochrony, Schultz’s rule, encephalization, hibernation, palaeohistology, growth rate, domestication, chondrodysplasia