Studying Fossil Horses

The horse has frequently been used as a classic example of long-term evolution because it possesses an extensive fossil record. This book synthesizes the large body of data and research relevant to an understanding of fossil horses from perspectives such as biology, geology, paleontology.

This book provides an update on the phylogeny, systematics and ecology of horses in South America based on data provided over the past three decades. The contemporary South American mammalian communities were shaped by the emergence of the Isthmus of Panama and by the profound climatic oscillations during the Pleistocene. Horses were a conspicuous group of immigrant mammals from North America that arrived in South America during the Pleistocene. This group is represented by 2 genera, Hippidion and Equus, which include small species (Hippidion devillei, H. saldiasi, E. andium and E. insulatus) and large forms (Equus neogeus and H. principale). Both groups arrived in South America via 2 different routes. One model designed to explain this migration indicates that the small forms used the Andes corridor, while larger horses used the eastern route and arrived through some coastal areas. Molecular dating (ancient DNA) suggests that the South American horses separated from the North American taxa (caballines and the New World stilt-legged horse) after 3.6 - 3.2 Ma, consistent with the final formation of the Panamanian Isthmus. Recent studies of stable isotopes in these horses indicate an extensive range of 13C values cover closed woodlands to C4 grasslands. This plasticity agrees with the hypothesis that generalist species and open biome specialist species from North America indicate a positive migration through South America.

Everything you were taught about evolution is wrong.

How can we bring together the study of genes, embryos and fossils? Embryos in Deep Time is a critical synthesis of the study of individual development in fossils. It brings together an up-to-date review of concepts from comparative anatomy, ecology and developmental genetics, and examples of different kinds of animals from diverse geological epochs and geographic areas. Can fossil embryos demonstrate evolutionary changes in reproductive modes? How have changes in ocean chemistry in the past affected the development of marine organisms? What can the microstructure of fossil bone and teeth reveal about maturation time, longevity and changes in growth phases? This book addresses these and other issues and documents with numerous examples and illustrations how fossils provide evidence not only of adult anatomy but also of the life history of individuals at different growth stages. The central topic of Biology today—the transformations occurring during the life of an organism and the mechanisms behind them—is addressed in an integrative manner for extinct animals.