Forerunners of Mammals
Radiation ? Histology ? Biology
Publication Year: 2011
About 320 million years ago a group of reptiles known as the synapsids emerged and forever changed Earth's ecological landscapes. This book discusses the origin and radiation of the synapsids from their sail-backed pelycosaur ancestor to their diverse descendants, the therapsids or mammal-like reptiles, that eventually gave rise to mammals. It further showcases the remarkable evolutionary history of the synapsids in the Karoo Basin of South Africa and the environments that existed at the time. By highlighting studies of synapsid bone microstructure, it offers a unique perspective of how such studies are utilized to reconstruct various aspects of biology, such as growth dynamics, biomechanical function, and the attainment of sexual and skeletal maturity. A series of chapters outline the radiation and phylogenetic relationships of major synapsid lineages and provide direct insight into how bone histological analyses have led to an appreciation of these enigmatic animals as once-living creatures. The penultimate chapter examines the early radiation of mammals from their nonmammalian cynodont ancestors, and the book concludes by engaging the intriguing question of when and where endothermy evolved among the therapsids.
Published by: Indiana University Press
Series: Life of the Past
Title Page, Copyright
This book brings together a group that has over many years researched various aspects of the evolution and paleobiology of the synapsids. Many of us have collaborated in our research endeavors, and all of us have at some stage shared information and had many hearty discussions about the biology of our...
I am indebted to all the contributors to this book. The successful completion of an edited volume of this nature is directly attributable to the hard work and diligence of the entire team. I count myself as incredibly fortunate to have had the opportunity to collaborate with all of you..
List of Contributors
1. The Origin and Radiation of Therapsids
The earliest fossils of amniotes—the clade that now consists of the reptiles birds and mammals—occur in 320 million-year-old rocks of the Late Carboniferous (sensu Laurin 2004; Laurin and Reisz 1995; Voigt and Ganzelewski 2010). They are characterized by several modifications that...
2. Therapsid Biodiversity Patterns and Paleoenvironments of the Karoo Basin, South Africa
Therapsids lived in Pangaean times and their fossils have been found on every continent (see Plate 1A); however, there is no doubt that the most abundant and diverse collecting grounds are in the main Karoo Basin of South Africa. This 10-km-thick sedimentary succession accumulated in a...
3. The Microstructure of Bones and Teeth of Nonmammalian Therapsids
Bone is a specialized connective tissue. Except for extant jawless fishes (lampreys) and to some extent chondrichthyes (sharks), it composes the skeleton of all vertebrates. It is a composite material with an organic phase and an inorganic mineral phase consisting of carbonate hydroxyl...
4. The Paleobiology and Bone Microstructure of Pelycosaurian-Grade Synapsids
Modern reptilian-grade amniotes (e.g., snakes, lizards, crocodilians) and the lineage that gave way to mammals (Synapsida) diverged more than 320 Mya during the Carboniferous Period. Also called pelycosauriangrade synapsids or “pelycosaurs,” basal synapsids were the dominant...
5. Dicynodont Growth Dynamics and Lifestyle Adaptations
Dicynodontia, a clade of non-mammalian therapsid, diversified into numerous genera and species during the Middle and Late Permian (Lucas 2002). These taxa are considered to be important biostratigraphic markers for global correlation between similar-aged strata (see Plate 1). Apart...
6. Biological Inferences of the Cranial Microstructure of the Dicynodonts Oudenodon and Lystrosaurus [Contains Image Plates]
Dicynodonts were nonmammalian therapsids and the most common herbivores during the Permo-Triassic. The remains of dicynodonts are well documented from therapsid bearing deposits worldwide, and because of their abundance, they have been used as biostratigraphic markers...
7. Bone and Dental Histology of Late Triassic Dicynodonts from North America
Dicynodonts were the dominant terrestrial herbivores during the Late Permian (Hotton 1986). Although diversity declined at the end of the Permian, at least four dicynodont lineages managed to survive the greatest mass extinction of the Phanerozoic (Fröbisch 2007; chapter 1 of this...
8. Bone Histology of Some Therocephalians and Gorgonopsians, and Evidence of Bone Degradation by Fungi
The Theriodontia are the carnivorous nonmammalian therapsids which include the Gorgonopsia, Therocephalia, and Cynodontia (the latter including mammals as a derived subgroup). With respect to crown Mammalia, the Gorgonopsia are considered to be the most plesiomorphic...
9. The Radiation and Osteohistology of Nonmammaliaform Cynodonts
Cynodontia is the last major therapsid lineage to appear in the fossil record (Rubidge and Sidor 2001) and includes mammals as living representatives. The extensive documentation of the acquisition of mammalian features in Paleozoic-Mesozoic nonmammaliaform cynodonts has...
10. The Radiation, Bone Histology, and Biology of Early Mammals
Modern mammals are represented by the monotremes, marsupials, and placentals. However, the fossil record provides a fascinating account of the radiation of mammals from their nonmammalian therapsid ancestors and shows evidence of other lineages of mammals. The evolutionary...
11. The Evolution of Mammalian Endothermy
Whole body endothermy, or “warm-bloodedness,” is a major specialization that has profoundly affected the biology of both mammals and birds and sharply distinguishes them physiologically from reptiles and all other vertebrates. It provides distinct physiological and ecological benefits, and...