Introduction If you asked a native South African to take you to the Karoo Basin today, he or she might give you a puzzled look and wonder why you would want to visit this desolate region spanning 153,000 square miles. Like a seemingly endless desert, the Karoo is hot and barren, showing little vegetation or life of any kind. However, if we were able to travel back in time and visit the same area, we would come upon a Karoo which would be completely different in composition, one which showed abundant life and left behind an unsurpassed record in the development of mammals. Climate With the retreat of the ice sheet in Southern Africa 250 million years ago during the late Permian period, a low lying Basin surrounded by uplands and mountains was revealed, and eventually came to be called the Karoo Basin. As the mass of ice melted, rivers flowed from high snow-capped mountains into the Basin. Extremely wet conditions would follow, especially in the early Triassic period, with periodic heavy rainfall and flooding of swamplands, giving way to extremely lush vegetation. This was extremely important considering the majority of animal life that roamed these lands were herbivores which would consume the ferns and gymnosperms (eg. cycads, cycadeoids, ginkgos, and conifers) that dominated the land. The final stages of early synapsid evolution took place in a Karoo environment very different from earlier times. Once called mammal-like reptiles, synapsids were the first terrestrial vertebrates to truly dominate the landscape. There were two main waves, the Pelycosaurs during the Permian period and the Therapsids during the Triassic. During the Late Triassic period, the Red Beds and the Cave Sandstone would be the last of the fossil-bearing Karoo strata. The climate during the Red Beds became increasingly hot and dry, and the succeeding Cave Sandstone was laid down in semi-arid conditions where wind-blown sand covered large areas of the Karoo. Many of the earlier synapsids could not handle these conditions and became extinct. Others continued to survive, such as the Archosaurs, Tritylodon, and the Cynodonts. Soon all life in the Karoo Basin was swept away by a series of great volcanic outbursts that would lead to the formation of the Drakensburg basalts that formed out of the hardened lava outflows. The Karoo Basin today is that of a desert - vast, desolate, and dry. The sparse grasslands of the Karoo get as little as 400mm of rain annually, while the upper Karoo receives less than 200mm per year. It is no wonder the name "Karoo" is derived from the Khoisan word meaning "land of thirst." Fauna of the Karoo As periodic heavy rainfalls changed the climate changed to allow for abundant vegetation to cover the Karoo, the possibility for terrestrial animal life increased. Although aquatic animals such as Mesosaurus were discovered to have lived during the Early Permian Period (286 to 258 million years ago), it was not until roughly 240 million years ago during the Middle Permian that terrestrial reptiles dominated the landscape of the Karoo. Studies of fossils have indicated that a small number of carnivores were ecologically balanced by a large number of herbivores. Moreover, an eastern European origin of the Karoo fauna has been discovered through studying fossils from the Permian period. Supporting Alfred Wegener's continental drift theory by assuming that continents today were once fused together as the supercontinent Pangaea ("all-earth"), fossils from South Africa's terrestrial animals have been located on most continents today. It is believed the initial population of land animals found in the Karoo Basin came after a series of migrations from the Northern hemisphere. The Pelycosaurs, one of the first Synapsid groups to evolve, composed an estimated 70% of the tetrapod population during the early Permian and was common to North America, but has also been found in the Karoo. Early Karoo animals were broken down into two main groups, Pareiasauria (early turtle relatives) and Therapsida (early mammal ancestors). Although the Karoo may be best recognized for providing evidence as to how mammals evolved in the course of Therapsid evolution, it is also important to realize that Pareiasaurs were once thought to be the predecessors for all modern-day reptiles. However, it is now better understood that these primitive herbivorous reptiles are most closely related to modern-day turtles based on morphological structure and did not give rise to reptiles or mammals. The second group of early Karoo residents, Therapsida, were a group of synapsids which included mammals and dominated the early Karoo. Unlike Pareisauria, this group of animals was quite diverse, and therefore will be broken down and spoken about individually: Dinocephalia The Dinocephalians are the largest therapsids of the upper Permian and the first large tetrapods to walk on land. The group includes both herbivores and carnivores. The primitive traits for therapsids include the pattern of the skull bones, a smaller temporal fenestra (caused by an enlargement of the slit between the skull roof and the cheek, and it evolved to be used as a window for jaw-closing muscles to bulge into when contracted allowing for larger muscles; it also provided anchorage for jaw muscles), and the structure of the lower jaw. All synapsids have a temporal fenestra, but the size varies from group to group. Their large size and thick skull bones cause them to be considered monophyletic. The teeth of the Dinocephalians included interlocking upper and lower incisors. The anterior teeth were specialized and the posterior teeth were reduced, providing better means for collecting food. Carnivorous dinocephalians still relied on their lower jaws like their Pelycosaur ancestors. The expansion of the temporal fenestra (enabling large jaw muscles) is a characteristic of the Dinocephalians. In earlier Dinocephalians the intertemporal part of the skull became narrower, which changed as more advanced herbivorous Dinocephalians evolved. In these more advanced Dinocephalians, the bones expanded and increased the width of the intertemporal area. Dicynodontia Some speculate that Dicynodonts came from an Ostheria-like ancestor. The earliest known Dicynodont is Eodicynodon who is from the area around the Tapinocephalis zone, a strata during the Middle Permian located south of Beaufort West. This region included parts of Laingsburg, Prince Albert, and Sutherland. Dicynodonts are the longest surviving of the main groups of early synapsids (surviving for about 55 million years). They were relatively small, ranging from less than 20cm to over 2 meters. They had bulky bodies with four short legs (like many herbivores) and the claws at the end of their digits were flat. They resemble large tortoises and turtles and most likely lived in groups or herds. Dicynodonts have many modifications to their skull for an herbivorous diet. Their incisors and lower canine teeth are absent and upper canines are found as enlarged tusks for searching for food. Postcanines are either very small or absent, instead jaws were probably covered with a hard layer, like turtles. A sharp ridge around the snout formed a horny beak. The temporal fenestra is larger than with the Dinocephalia, and the Dicynodonts had very short jaws. Gorgonopsids Gorgonopsids first appeared in the Tapinocephalis zone and were relatively rare and in fairly small forms. They were quadrupedal (they walked on four legs), and their body length could be as long as 10 feet. Even though they had short necks and relatively small dog-like heads, Gorgonopsids were dominant predators, feeding on prey as large as themselves. They had enlarged canines to aid them in catching and eating their prey. Most of the Gorgonopsids are not well known except for the primitive member, Hipposaurus. They had lightly built limbs that were very long. They were much smaller than the Dinocephalus carnivores that they descended from. Therocephalians They are another group of carnivorous therapsids which is often compared to the Gorgonopsids, though they are not in the same taxon. Some Therocephalians were small enough to be insectivorous (feeding on insects), and some have been found to be herbivorous. They first appeared in the Tapinocephalus zone. Unlike the other early synapsids, a few survived the Permian extinction. The Therocephalians and the Gorgonopsids have much in common, including a large canine tooth, high jaw articulation, and a coronoid process (a long bone in the dentary area that is located around the area of jaw articulation). Like all the other therapsids, the temporal fenestra has been enlarged. The snout of most forms is relatively large and heavily built. They, along with the Gorgonopsids and their ancestors did not chew their prey, but swallowed everything whole. They are believed to have had a poisonous bite because their skulls contained chambers that could have been used for venom glands. At the end of the Permian some 248 million years ago, a mass extinction wiped out nearly all the species in the Karoo Basin. The Karoo is one of the few places where the mass extinction is recorded in the fossil record. Scientists have proposed four main hypotheses to the cause of the mass extinction. Many believe the extinction was caused by plate tectonics that created the supercontinent Pangaea. The formation of one supercontinent greatly affected the environment and life because it resulted in a loss of shoreline, increasing competition for shelter. Also, a change in the climate and the salinity of the ocean resulted in a drastic change in the environments of several living organisms. Most organisms had small ranges of tolerance for environmental changes. This disrupted the ecosystems of several organisms. For example, many species of fish could not even survive a slight change in the temperature of water. One of the most probable explanations is that volcanic eruptions caused the Permian extinction. Lava flows dating back to the Permian age indicated that volcanic eruptions sent clouds of sulfur and ash into the atmosphere, subsequently altering the climate and environment. Nearly all land and marine organisms were wiped out by the extinction. The two main species that survived in the Karoo Basin are the Lystrosaurs and the Cynodonts. Eventually the Lystrosaurs died out, but the Cynodonts are believed to be part of the lineage of mammals. The Lystrosaurs, a member of the Dicynodontidae family, share similar traits with the Dicynodonts, such as the prominent two tusks, heavy limbs, and stout bodies. The body of Lystrosaurus was about 3 feet long. Its skull, which is small to medium sized, had much a shorter and deeper snout with nostrils on the top. Lystrosaurus had a jaw adapted to cut, not to grind. This species was a herbivore that could forage under water surfaces and plant roots. Though the Lystrosaurs survived the Permian extinction, the lineage ended in the Triassic period. Along with the Lystrosaurs, the Cynodonts survived the Permian extinction. Because mammals likely descended from the Cynodonts, they share several characteristics. The Cynodont had similar features on the skull such as the secondary plate found on the underside of the skull separating the nasal and oral cavaties. This plate allows for simultaneous breathing and eating, making eating much more efficient. They also had differentiated teeth, jawbones, and jaw muscles that enabled them to chew. While some Cynodonts were herbivorous, others were carnivorous. The body of a Cynodont looked much like the Lystrosaurus—stout and thick-limbed. Many scientists are debating whether Cynodonts had any hair. Because hair is a soft tissue, the fossil record is not likely to answer the question. However, some have claimed that some remains of Cynodonts had whiskers, which probably meant that they had hair. Advent of the Dinosaurs in the Karoo Along with the Permian mass extinction, the ecology was further changed as Archosauria dominate the Karoo and other parts the land during the Mesozoic era. Known as "ruling reptiles," Archosaurs took over habitats left vacant by the extinct herbivores and carnivores and became the direct ancestors of dinosaurs through adaptive radiation. As they evolved, major groups of animals based on the structure of the ankle joint started branching off and forming new populations. One of these groups endemic to the Karoo were the Euparkeria. Euparkeria was close relatives of Archosaurs and were thought to be morphologically representative of the first Archosaurs. With a semi-erect posture, these carnivores have been suggested to have been able to run bipedally because of their small forelimbs and relatively long hind limbs. Furthermore, they had a more primitive structure and contained many ancestral features of both dinosaurs and crocodiles. As Archosauria in the Karoo evolved, the dinosaurs were divided into two main groups based on their pelvic structure. Ornithschia included exclusively herbivorous Archosaurs were more closely related to birds and dinosaurs than crocodiles. Examples found in the Karoo include Fabrosaurus and Heterodontosaurus. Saurischia, on the other hand, was one of two groups within the dinosaurs which included the birds, and were either herbivores or carnivores. Today, the only remnants of the Karoo fauna which existed so many million years ago are birds and crocodiles which have slowly evolved. For the most part, primitive crocodilians share many similar characteristics with crocodiles which live today. Fossils of the Karoo Basin: The Karoo Basin is important because of the wealth of information that has been uncovered by the fossils that have been found there. It is said to be the "richest known repository" of fossil therapsids (Bartlett, 1998). It is also the "longest uninterrupted reptile fossil record in the world, chronicling more than 100-million years of evolution (Bartlett, 1998)." Robert Broom wrote in 1932 that, "The mammal-like reptiles from South Africa may be safely regarded as the most important fossil animals ever discovered, and their importance lies chiefly in the fact that there is little or no doubt that among them we have the ancestors of mammals, and the remote ancestors of man." The director of the Bernard Price Institute of Paleontology at the University of the Witwatersrand, Bruce Rubridge, describes it as having the whole jigsaw or the whole story, because of the ability to physically trace back in history where mammal ancestors first began. A hypothesis about the inhabitants of the Karoo is that they immigrated into the Karoo by way of a north-south migration. Evidence that supports this hypothesis is the fact that in the past the oldest fossils have always been found in Russia. More recently, however, new finds in deeper rocks of the Karoo have uncovered some of the oldest, most primitive synapsids ever found to date. This new evidence is in support of what Rubridge has called "global faunal interchange" (Bartlett, 1998). Fossil hunts in South Africa, South America and India have turned up some of the first " conclusive corroborative evidence that the continents had once been joined". Fossil therapsids counterparts were found on all three continents, providing support for the theory of continental drift. There are a total of five groups that can be found at the Karoo Basin. Each group consists of zones and correlating formations. The combination of all the zones, represent about 50 million years. Zones are characterized by the different plants and animals that are found there, and by the different types of sedimentary rocks it contains. The type of rock found is indicative of the type of climate of the period, thus looking at the many of intermediate type rocks that are found, the Karoo went through many climatic changes. The Beaufort is an important group of the Karoo. Of the five groups Beaufort consists of the longest geological period. Zones of the Beaufort group indicate many interesting and significant events and "facts". The total extinction of the Dinocephalia, at the end of the Tapinocephalus zone, is one example. Within the Endothiodon and Cistecephelus Zones, Diconodonts were quite common. Gorgonopsians are also found in the Cistecephelus Zone, along with the Daptocephalus. In fact, suggestions have been made to change the current zone name, Cistecephelus, to the Daptocephalus Zone. The end of the Permian and Paleozoic is marked by the end of this zone. The Lystrosaurus Zone, the proceeding zone, indicates a dramatic change in the climate, a wetter one with periodic flooding as well. It is during this time that the Gorgonopsia and the Pareiasaurs go extinct. Chinle Formation The Chinle Formation of Arizona has many similarities to that of the Karoo Basin. Many of the fossils that come from this time coincide with that of the Karoo, during the Triassic period. It's no wonder considering that at this time, Pangaea was still intact, and the two locations were much closer than they ever could be today. With similar environments, one that was extremely wet, and about the same variety of vegetation with ferns and gymnosperms, many fossil forms, especially those of synapsids and archosauromophs have been found at both sites. Conclusion As it can be seen, life in the Karoo Basin has evolved and changed greatly since the Permian period. What is now a desolate desert used to be a place which overflowed with various life forms. Fossil records from the Karoo have helped us see the progression and evolution of various fauna of the Karoo Basin