basilosaurid
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What is a basilosaurid?
A basilosaurid is any member of the family Basilosauridae, an early group of whales that existed from the middle Eocene to the late Oligocene Epoch, roughly 41 million to 23 million years ago. They are usually referred to as archaeocetes, the ancient whales. Basilosaurids have a closer affinity to living whales than any other extinct group.
Basilosaurids had flukes similar to those of modern whales, but they differed from living whales because they had triangle-shaped teeth, small hind limbs, and an elongated body with an extended tail. The largest basilosaurids could grow up to 25 meters (82 feet) long. The Basilosaurus genus belongs to this family. Basilosaurus skeletons averaged approximately 17 metres (about 56 feet) in length, with skulls about 1.5 metres (about 5 feet) long.
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When and where did basilosaurids live?
Basilosaurids, early whale members of the family Basilosauridae, existed from the middle Eocene to the late Oligocene Epoch, roughly 41 million to 23 million years ago. During most of their history, basilosaurids could be found worldwide, with significant fossils discovered in Egypt and the southern United States. The only fossils dating to the Oligocene Epoch have been discovered in Peru and New Zealand. Basilosaurus was a common genus throughout the late Eocene seas.
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What did basilosaurids look like?
Basilosaurids were early whales that existed from the middle Eocene to the late Oligocene Epoch, approximately 41 million to 23 million years ago. Though the first discovered basilosaurid, Basilosaurus, was initially classified as a lizard, these mammals have a closer relation to modern whales than any other extinct group.
These whales had flukes similar to those of modern whales, triangle-shaped teeth, small hind limbs, and an elongated body with an extended tail. The largest could reach 25 meters (82 feet) in length, with skulls averaging about 1.5 meters (5 feet) long. The tail comprised as much as three-quarters of their total body length. Though likely non-functional, the hind limbs had a femur, kneecap, tibia and fibula, ankle bones, and toes.
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How are basilosaurids related to modern whales?
Basilosaurids are an early group of whales that lived from the middle Eocene to the late Oligocene Epoch. They have a closer affinity to living whales than any other extinct group. Basilosaurids had flukes similar to those of modern whales, but differed in having triangle-shaped teeth, small hind limbs, and an elongated body with an extended tail. They are referred to as archaeocetes, the ancient whales, but in modern classifications they are members of the Pelagiceti, the fully aquatic whales.
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What have scientists learned from basilosaurid fossils?
Basilosaurid fossils, dating from the middle Eocene to the late Oligocene Epoch (approximately 41 million to 23 million years ago), have given scientists key insights into the evolution of whales. These early whales had flukes like modern whales but also had triangle-shaped teeth, small hind limbs, and an elongated body with an extended tail.
Analysis of basilosaurid remains, some as long as 25 meters (82 feet), indicates they were the first widespread, fully aquatic whale group. Their hind limbs, though likely non-functional for walking, show well-formed joints and muscle attachments, suggesting they may have been used for mating. The earliest basilosaurids had long skulls and relatively short bodies, while later forms had elongated vertebrae and long tails.
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Why are basilosaurids important for understanding whale evolution?
Basilosaurids are vital to understanding whale evolution because they represent a transitional group between early, amphibious whales and modern, fully aquatic whales. They are more closely related to living whales than any other extinct group. Basilosaurids are the first widespread, fully aquatic whale group, too large to move on land, with forelimbs specialized for swimming.
Although basilosaurids had flukes like modern whales, they also had features that highlight their transitional nature, such as small hind limbs, triangle-shaped teeth, and an elongated body. The existence of well-formed joints and muscle attachments on their hind limb bones suggests that the limbs may have been functional, or they may have been completely atrophied. Some scientists suggest that basilosaurid hind limbs may have acted as claspers to help guide the long bodies of the males and females into position for mating.
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basilosaurid, any member of the family Basilosauridae, an early group of whales that lived from the middle Eocene to the late Oligocene Epoch (about 41 million to 23 million years ago). Basilosaurids occurred worldwide during most of their history, and important fossils have been recovered in Egypt and the southern United States. Their diversity was highest during the Eocene Epoch. The only known fossils dated to the Oligocene have been found in Peru and New Zealand. The basilosaurids have a closer affinity to living whales than any other extinct group. However, the first basilosaurid specimen—Basilosaurus, whose Latin name is translated “king lizard”—was originally classified as a lizard when it was first described.
Basilosaurids had flukes similar to those of modern whales, but they differed from living whales in having triangle-shaped teeth, small hind limbs, and an elongated body with an extended tail. The largest basilosaurids may have been as long as 25 metres (82 feet). The remains of some representatives of the genus Basilosaurus measured approximately 17 metres (about 56 feet) in length; the skulls of these animals averaged approximately 1.5 metres (about 5 feet) long. The tail made up as much as three-quarters of the total body length of Basilosaurus.
The hind limbs of basilosaurids were not connected to the rest of the skeleton and were likely too small to have assisted in swimming. The earliest whales—which were thought to have evolved from terrestrial ancestors in the order Artiodactyla (a group that contains living pigs, hippopotamuses, and even-toed ungulates), most likely the raoellid artiodactyls (aquatic artiodactyls from South Asia that lived during the Eocene)—had relatively long back legs and were probably amphibious in their lifestyle. Basilosaurids, however, were the first widespread truly aquatic group of whales. They were too large to have hauled themselves out of the water, and they possessed forelimbs that were too specialized for swimming to have supported them on land. The hind limbs of basilosaurids consisted of a femur (thighbone), a patella (kneecap), tibia and fibula, ankle bones, and toes. Although the pelvis was characterized by a reduced ilium (the bone that connects to the sacrum, which forms the base of the vertebral column, in terrestrial animals), it possessed a proportionally large pubis. Whether the hind limbs were functional is unclear; well-formed joints and evidence of muscle attachments on the bones suggest that they may have been functional, but they also may have been completely atrophied. In addition, the hind limbs may have been used as claspers to help guide the long bodies of the males and females into position for mating.
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Basilosaurids are usually referred to as archaeocetes, the ancient whales, but in modern classifications they are members of the Pelagiceti, the fully aquatic whales. Basilosaurid genera are separated into four subfamilies: Dorudontinae, Basilosaurinae, Kekenodontinae, and Stromeriinae. The earliest dorudontines were the earliest basilosaurids, with long skulls and relatively short bodies. Basilosaurines are the archetypal basilosaurids, with elongated vertebrae and long tails. The kekenodontines consist of the single genus Kekenodon, which was only poorly known and is the only basilosaurid dating from the Oligocene Epoch. Stromerius nidensis was described in 2007 and dated to the late Eocene of Egypt; it is the only species classified in subfamily Stromeriinae.