Springer Nature. Science. The presence of basilosaurids in . the Basilosaurid whale? Let's hear questions in a question they were asking that so that's a shark, whales and dolphins. Tr Ecol Evol. Notice the similarities between hippos and whales. So they both share the similar features which includes the border shape and position orphans. When you visit the site, Dotdash Meredith and its partners may store or retrieve information on your browser, mostly in the form of cookies. Department of Anatomy and Neurobiology, Northeastern Ohio Universities College of Medicine, Rootstown, OH, 44272, USA, School of Biomedical Sciences, Kent State University, Kent, OH, 44242, USA, Department of Wildlife Management, North Slope Borough, Box 69, Barrow, AK, 99723, USA, Department of Earth Sciences, Indian Institute of Technology, Roorkee, 247 667, Uttarakhand, India, You can also search for this author in 3). Ambulocetus fossils have only been found in rocks that were formed in a shallow sea, possibly in a coastal swamp or forest. In: Thewissen JGM, editor. In hunting behavior, Ambulocetus may have been similar to a modern crocodile, and, externally, Ambulocetus may have looked like a crocodile (http://www.neoucom.edu/DEPTS/ANAT/Thewissen/whale_origins/index.html). Because of a shortage of forelimb fossils from other archaeocetes, it is not known if this arrangement is unique to basilosaurids, as some of the characteristics are also seen in Georgiacetus.[3]. The green line indicates the minimal width of the skull. "Bone-Breaking Bite Force of, Gingerich P.D., Smith B.H., Simons E.L. (1990). 27). David Polly is a vertebrate paleontologist at Indiana University-Bloomington and a Research Associate at the Field Museum in Chicago. another animal is to ? https://www.thoughtco.com/facts-about-basilosaurus-king-lizard-whale-1093325 (accessed March 4, 2023). another animal is to ? This changed in the early 1990s, when paleontologists unearthed the first of a series of fossil cetaceans, mostly in India and Pakistan, documenting the transition from land to water in detail in the Eocene Period (which lasted from approximately 54 to 34 million years ago). The more similar the DNAs are, the closer related the organisms are. (D) Pelvis and femur of the juvenile male specimen figured in C. (E) Another pelvis and femur from an adult specimen (B. mysticetus, 98B5) for comparison. The Dinosaurs and Prehistoric Animals of Alabama, The Dinosaurs and Prehistoric Animals of Alaska, 10 Facts About Elasmosaurus, Ancient Marine Reptile, Most Important Dinosaurs and Prehistoric Animals of Italy, The Dinosaurs and Prehistoric Animals of Virginia, The Dinosaurs and Prehistoric Animals of Washington. Curiously, the ribs of Basilosaurus are very dense and thickened, which is a specialization that probably allowed it to achieve slight negative buoyancy. Indian Remingtonocetus probably lived in a muddy bay protected from the ocean by islands or peninsulas. common ancestor with. The former species were larger and had larger eyes (Fig. Pakicetus They were, however, very small and did not articulate with the vertebral column, which also lack true sacral vertebrae. Corrections? Similarly the left ear heard sounds that originated on the left side earlier than those that originated on the right side. Basilosaurus (a.k.a. Modern whales emerge Mysticetes and Odontocetes (33-28 mya) The ancestors of toothed and baleen whales diverged as the world's climate rapidly cooled and opened up new opportunities for basilosaurid diets. The bones of Indohyus were found high in the Himalaya mountains near the border between Pakistan and India. The phylogeny among fossil animals can be determined by coding their morphology and having a computer program determine the greatest similarities in significant characters. Sirenians are most closely related to elephants, and pinnipeds are related to land carnivores (e.g., dogs and bears). Berkeley: Univ Calif Press; 2008. p. 25786. These results suggest that Indohyus was aquatic and thus that cetaceans originated from aquatic ancestors. 1995a;29:33157. Lucas FA. Aslan A, Thewissen JGM. In: Thewissen JGM, editor. Rains came only a few times per year, but they were torrential. 14). Basilosaurids have a nasal opening that has shifted back far toward the eyes to form a blowhole and have flippers for forelimbs, a fluke at the end of the tail, and tiny hind limbs, too tiny to support the body weight on land. Skeletal evidence indicates that Basilosaurus could perceive the direction of origin for underwater sounds. 2006;26:40010. The transition from land to water is documented by a series of intermediate fossils, many of which are known from India and Pakistan. Stromerius nidensis was described in 2007 and dated to the late Eocene of Egypt; it is the only species classified in subfamily Stromeriinae. This helps the animal walk on the bottom of rivers, where the extra bone mass serves as ballast. As such, these teeth are not suitable for crushing food. Summarizing, pakicetids inherited the aquatic lifestyle from their raoellid ancestors. It contains a small group of species, most of which are only known from teeth and jaws (Thewissen et al. a Outline ellipses and regression of body size (on x-axis, as 10-log in grams) against semicircular canal radius (on y-axis, as 10-log in mm) for modern land mammals (maroon) and modern cetaceans (blue). 2007;290:71633. Zeuglodon) is a genus of primitive whale from the Late Eocene. Counter current heat exchange evidence is also found for the tongue and the testes of dolphins. Vestibular evidence for the evolution of aquatic behaviour in early cetaceans. Struthers MD. A good example is the giant killer whale Leviathan (Livyatan), which lived about 25 million years later (during the Miocene epoch), weighed as much as 50 tons, and made a worthy opponent for the contemporaneous prehistoric shark Megalodon. Unlike modern whales, basilosaurids possessed small hindlimbs with well defined femur, lower leg and feet. But the animals, known as toothed whales, also produce other sounds for social . 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. 12). This bone surrounds the middle ear cavity like a bowl. Variation in the skeleton behind the skull is hard to assess because these bones are only known in a few species, specifically Rodhocetus and Artiocetus from Pakistan (Gingerich et al. CAS The blowhole in modern cetaceans is located between the eyes on the forehead, an adaptation for breathing while remaining submerged. The Front Flippers of Basilosaurus Retained Their Elbow Hinges, The Vertebrae of Basilosaurus Were Filled With Fluid, Basilosaurus Wasn't the Largest Whale That Ever Lived. 1990. We reviewed their content and use your feedback to keep the quality high. In this photo we are looking down at the top of a basilosaurid skull. The first occurs in the genus Basilosaurus which had a snake-like body with a maximum length of approximately 17m long. One of the first identified prehistoric whales, Basilosaurus, the "king lizard," has been a part of American culture for literally hundreds of years, especially in the southeastern U.S. 25 and 26). Eg: the nasal opening of the basilosaurid whale shows that this animal is an intermediate species between land mammal and modern whale. 2003-2023 Chegg Inc. All rights reserved. Basilosaurids are usually referred to as archaeocetes, the ancient whales, but in modern classifications they are members of the Pelagiceti, the fully aquatic whales. Correspondingly, the conical incisors and canines are aligned anteroposteriorly, rather . This cetacean is the first large-bodied macroraptorial dolphin and highlights widespread locomotor convergence between baleen and toothed whales. Both remingtonocetids and protocetids are found in the same areas of India, Eye size in cetaceans and extinct marine reptiles (ichthyosaurs; modified from Thewissen and Nummela (2008), University of California Press). Article The first embryo is 6mm, the last one 17.5mm in length. Science 249:154-157. ____ Do both have multi-chambered stomachs? Washington: Carnegie Institute of Washington; 1936. p. 1366. 1st ed. "During vocal fry, the vocal folds are only open for a very short . Molecular biology came to the rescue, identifying genetic similarities between cetaceans and artiodactyls (English: even-toed ungulates) that were not present in other mammals. have come from the common ancestor. 2006) abound in some remingtonocetids, protocetids are usually found in clearer water deposits that are more exposed to wave action. Fig 3. [7] Some genera tend to show signs of convergent evolution with mosasaurs by having long serpentine body shape, which suggests that this body plan seems to have been rather successful. A stable isotope study of the teeth of Indohyus also suggested that it lived in water (Thewissen et al. Scientists are still trying to understand what exactly these differences mean, but they must have affected function of the animals in a major way. This affects the attachment of the masticatory muscles but also the path of the nerves going to eyes and nose. This type of locomotion may be a good model for swimming in Remingtonocetus. Toothed whales can use vocal registers like humans to communicate and hunt. The Bowhead whale specimens were collected under NMFS marine mammal collection permit 814-1899. Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan. On the other hand, it is not clear what raoellids ate, and neither raoellid nor early cetacean dentitions have good modern analogs. Even though all modern cetaceans are obligate aquatic mammals, early cetaceans were amphibious, and their ancestors were terrestrial artiodactyls, similar to small deer. 2006;26:35570. This happened in 2007, when skeletons for raoellids were found in the Himalayas that were shown to be the closest relatives to whales (Thewissen et al. 1998; Hulbert 1998). Humans and chimpanzees share a recent common ancestor. While toothed whales generally have one hole, baleens are split into two. It may seem odd that a 47-million-year-old artiodactyl that looks like a tiny deer is aquatic, but this behavior is reminiscent of one species of modern artiodactyl. Bones shown here are derived from several individuals and were found scrambled with many other bones near the border area between Pakistan and India by geologist A. Ranga Rao ( J.G.M. 1998). Also unlike earlier cetaceans, the nasal opening is not at the tip of the snout (Thewissen and Bajpai 2001b). Deciphering whale origins with molecules and fossils. Archaeocetes are important because they represent the earliest radiation of cetaceans and because they include the ancestors of the two modern suborders of cetaceans, the Mysticeti (baleen whales) and Odontoceti (toothed . The ectotympanic of artiodactyls roughly has the shape of half a walnut shell, enclosing the air-filled middle ear cavity. Diet: The skull of Basilosaurus is superficially crocodilian in shape, exhibits large jaw muscle attachment areas, and a fearsome set of teeth with canine-shaped incisors in front, and flattened, serrated triangular molars in back. VIDEO ANSWER:Hello. 1997; Bajpai and Thewissen 1998; Gingerich et al. 6 (RR 208). In raoellids and other artiodactyls (and in extinct cetaceans), the astragalus has a second trochlea, which is located on the opposite end of the first trochlea, and this second trochlea articulates with the remaining bones of the ankle. The emergence of whales: evolutionary patterns in the origin of Cetacea. In most mammals, its walls are made of a bone called the ectotympanic, as is the case in artiodactyls and cetaceans. 22). report the skeleton of a stem toothed whale, from the Oligocene of South Carolina, with intermediate locomotor adaptations between modern toothed whales and the earliest pelagic whales. 2001). 21), and Georgiacetus from North America (Hulbert et al. Range: A disruption of the normal sequence of expression of genes that make these organs is responsible for this (Thewissen et al. Age: 34-40 million years old, Eocene Epoch. Curr Sci (New Delhi). Contr Mus Pal Univ Michigan. 1996;190:186. It has been suggested that early cetaceans ate fish (O'Leary and Uhen 1999). Middle Eocene cetaceans from the Harudi and Subathu Formations of India. This could then lead to overstimulation of the semicircular canals, especially in acrobatic animals. While every effort has been made to follow citation style rules, there may be some discrepancies. Hind flippers present in a single anomalous dolphin housed at the Taiji Whale Museum, Diagram showing the approximate location of the pelvis and hind limb of a male bowhead whale (Balaena mysticetus) in (A) lateral view and (B) dorsal view. Ann Rev Ecol Syst. Anyone you share the following link with will be able to read this content: Sorry, a shareable link is not currently available for this article. Omissions? In some regards, all cetaceans, sirenians, and pinnipeds are similar; they are all adapted to life in water. By Robert Boessenecker (@CoastalPaleo) and Sarah Boessenecker (tetrameryx) Happy Fossil Friday! 1998; Clementz et al. Fig 2. Pakicetids are the most archaic cetaceans known. 16), roughly the size of a large male sea lion. 5 consists of bones of a number of different individuals. In: Thewissen JGM, Nummela S, editors. 2004;430:7768. Nature. 8), the marrow cavity of the femur (the thighbone) makes up more than 60% of the total thickness of the bone, and the bony walls, called cortex, are thin. The hind limbs of basilosaurids retain the bones present in earlier whales and indeed land mammals: the femur, tibia, fibula, tarsals, metatarsals, and phalanges (Gingerich et al. View the full answer. In details of ear anatomy too, remingtonocetids are more specialized than pakicetids and ambulocetids (Nummela et al. Educator app for Ambulocetus is much larger than any pakicetid (Fig. The emergence of whales: evolutionary patterns in the origin of Cetacea. Almost as soon as scientists realized that cetaceans had land ancestors, they tried to identify what the closest relatives of cetaceans were. 2001a). As cetaceans became more aquatic, the nasal bones retracted and the nasal opening migrated to the top of the skull and became the blowhole (modified from Thewissen and Bajpai 2001b). We hope that a detailed understanding of evolutionary patterns will allow us to determine the processes that drove cetacean evolution. The cheek teeth have well-developed accessory denticles. Basilosaurid genera are separated into four subfamilies: Dorudontinae, Basilosaurinae, Kekenodontinae, and Stromeriinae. However, the oldest whale fossils known are approximately 50 million years old, and it is unlikely that the closest relatives of whales are still living. ", Basilosaurus Was Once Mistaken for a Prehistoric Reptile, The Brain of Basilosaurus Was Comparatively Small, Basilosaurus Bones Were Once Used as Furniture, Basilosaurus Is the State Fossil of Mississippi and Alabama, Basilosaurus Was the Inspiration for the Hydrarchos Fossil Hoax. Their dentition is easily distinguishable from that of . 2002;417:1636. . 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 postcranial skeleton of pakicetid cetaceans. Humans and chimpanzees share a recent common ancestor. Diagram showing the relationships among cetaceans and their land relatives. Pakicetids are only known from a few sites in northern Pakistan and Western India, and these are approximately 50 million years old (middle Eocene). The African mouse deer (Hyemoschus aquaticus) lives on the forest floor of central Africa, feeding mostly on fruits and flowers. In general, the diameter of these tubes, the semicircular canals, scales with body size (Spoor and Thewissen 2008), but the canals are extremely reduced in modern cetaceans. 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. Clementz, M.T., Goswami, A., Gingerich, P.D., and P.L. J Vert Pal. Anat Rec. True or False: All living things on Earth are related? Thewissen JGM, Madar SI, Hussain ST. Ambulocetus natans, an Eocene cetacean (Mammalia) from Pakistan. 20). Comparative anatomy The study of differences and similarities between living things. 2001, 2007). The study of how organisms are related to each other is called phylogenetic inference, and hypotheses regarding phylogeny are indicated by a cladogram, a branching diagram that links more-and-more closely related groups as closer-and-closer branches. Given its morphology, it appears that Indohyus is more aquatic than Hyemoschus and may have spent much of its life in water. The intermediate fossil of the Basilosaurid whale contains a nasal hole at _____. Nature. 1st ed. All this evidence suggests that Basilosaurus was fully marine; additionally, Basilosaurus has only been discovered in marine sedimentary deposits, and oxygen isotope chemistry of its teeth indicate that it lived in saltwater. This eye position occurs in aquatic mammals such as hippopotamus. The bones of one individual were found together, partly articulated. At depths over 100m, whale lungs collapse to avoid compression sickness and are thus no good for air supply, and the remaining air is found in the nasal passages of the skull. Retrieved from https://www.thoughtco.com/facts-about-basilosaurus-king-lizard-whale-1093325. Gatesy J, O'Leary MA. 1997). Specimens courtesy of John Craighead George and the Barrow Whaling Captains Association, Diagram showing changes in the pelvis of Indohyus (RR 256) and cetaceans. He appears anxious and says that he is short of breath. This pad was also present in remingtonocetids, suggesting that underwater sound transmission was effective in remingtonocetids, a clear aquatic adaptation (Nummela et al. They are all . 2001; Nummela et al. de., Ricqles, A. The rocks in which these fossils are preserved indicate that the bones were buried in a freshwater stream. The phylogenetic relations among groups are best expressed by a cladogram, and classifications cannot accurately reflect phylogenetic relationships anyway (because an ancestor species would have to include all its descendant species). Basilosaurids occurred worldwide during most of their history, and important fossils have been recovered in Egypt and the southern United States. As huge as Basilosaurus was, it still occupied a fairly low branch on the whale evolutionary tree, plying the oceans only 10 million years or so after its earliest ancestors (such as Pakicetus) were still walking on land. "10 Facts About Basilosaurus." Stable isotope data indicate that Ambulocetus lived in environments that were partly freshwater, possibly implying that they were near a river mouth (Roe et al. statement and There are approximately seven genera of basilosaurid cetaceans, but basically they can be divided into two body types. 2002). A rete mirabile (Latin for wonderful net; plural retia mirabilia) is a complex of arteries and veins lying very close to each other, found in some vertebrates. 2007; Geisler and Uhen 2003; Geisler et al. 2007). Also unlike earlier cetaceans, the nasal opening is not at the tip of the snout (Thewissen and Bajpai 2001b). Form, function, and anatomy of Dorudon atrox (Mammalia, Cetacea): an archaeocete from the middle to late Eocene of Egypt. have come from the common ancestor. At the earliest embryonic stages the nasal openings are still situated at the rostra tip like those of land mammals; they are gradually shifted more and more towards the vertex of the head at the older stages. Nature. The marrow cavity of the femur of Ambulocetus makes up 57% of the cross section of the bone. His current research is on trait-based community dynamics in vertebrates, Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. This feature makes the bones heavy, and heavy bones make running on land more difficult. 2007). Both are missing a Preliminary evaluation of Kuldana paleosols and implications for interpreting vertebrate fossil assemblages, Kuldana Formation, Northern Pakistan. River otters swim with their hind limbs and tail, and it is likely that Ambulocetus did the same. A new protocetid whale (Cetacea, Archaeoceti) from the late middle Eocene of South Carolina. It would be reasonable to infer from this fact that Basilosaurus was native to North America exclusively, but fossil specimens of this whale have been discovered as far afield as Egypt and Jordan. One hearing-related feature is the size of the mandibular foramen, a perforation of the lower jaw behind the teeth. The teeth in the tip of the snout are roughly similar to those of modern fish-eating toothed whales, although the teeth are extremely robust and deeply rooted. Together with other basilosaurid whales, Basilosaurus is frequently referred to as a transitional form between the four-legged . Cookies policy. BioSci. Thewissen). In spite of this, cetaceans are mammals. structures that have different mature forms in different organisms but develop from the same embryonic material, A structure that is present in an organism but no longer serves its original purpose, the study of the formation, early growth, and development of different organisms, provides evidence about the history of lfe on Earth, also shows the adaption of animals over time, the study of the earth's physical and cultural features, David N. Shier, Jackie L. Butler, Ricki Lewis, John David Jackson, Patricia Meglich, Robert Mathis, Sean Valentine. The emergence of whales, evolutionary patterns in the origin of Cetacea. evolutionary change within a species or small group of organisms, especially over a short period. About 50 million years ago, during the evolution from (raoellid) artiodactyls to (pakicetid) cetaceans, a remarkable transformation took place. In growth it was similar to today's Killer whales, but Basilosaurus was muchlenthier than killer whales(twice the size of the killer whale).There was a co-existence between this huge c. They were probably the first fully aquatic cetaceans. It was a shallow stream, and the climate was hot and dry. Some dolphins can exceed speeds of 50 km/h, a feat accomplished by thrusting the flukes while adjusting attack angle with their flippers [].These movements are driven by robust axial musculature anchored to a relatively rigid torso consisting of numerous short . However, the rest of Basilosaurus hearing adaptations indicate it was fully marine, and thus any retention of adaptations for hearing airborne sound was probably vestigial. University of Michigan Papers on Paleontology 34:1-222. In: Thewissen JGM, editor. _____________ ____________Mammals Spoor F, Thewissen JGM. Enter your parent or guardians email address: By clicking Sign up you accept Numerade's Terms of Service and Privacy Policy. This creates greater mobility in the foot in the anteroposterior direction. J Pal. Provided by the Springer Nature SharedIt content-sharing initiative. Strauss, Bob. Over the next few decades, various specimens of Basilosaurus were assigned as species of Zeuglodon, most of which either reverted back to Basilosaurus or received new genus designations (Saghacetus and Dorudon being two notable examples). However, all modern cetaceans lack a hair coat, presumably an adaptation to reduce friction and improve locomotion. B.T's wife drove him to the clinic when his wheezing was unresponsive to fluticasone/salmeterol (Advair) and ipratropium bromide (Atrovent) inhalers, he was unable to lie down, and he began to use accessory muscles to breathe. The fact that the cetacean nose moved, in the course of evolution, from the tip of the rostrum up to the vertex of the head, is among the most perfect of adaptations to aquatic life. Coen Elemans was . Privacy Fossils attributed to the type species B. cetoides were discovered in the United States. We will discuss these following the order of the cladogram. In modern cetaceans, this foramen carries, in addition to the nerves and blood vessels mentioned, a long pad of fat which connects the lower jaw to the middle ear and transmits underwater sounds. What type of medicine addresses imbalances of qiq iqi ? Fewer than ten fossils of ambulocetids have been discovered, but one of these is a relatively complete skeleton of Ambulocetus natans (Fig. 2001a;30:269319. Sensory Abilities: Land mammals (including humans) can hear underwater, but they cannot tell which direction the sound comes from because sound waves travel through the bones of the skull and arrive at both inner ears at the same time. Creationists have moved the goal posts to other questions which I will attempt to address as an addition to my original posting since they require graphics and comments do not allow for pictures to be included. These may So let's see. Let us know if you have suggestions to improve this article (requires login). The proportions of the vertebrae at the tip of the tail suggest that Basilosaurus had small tail flukes. Roe LJ, Thewissen JGM, Quade J, O'Neil JR, Bajpai S, Sahni A, et al. By using this website, you agree to our In the genus Remingtonocetus, the eyes are very small (Thewissen and Nummela 2008), but the ears are large and set far apart on the skull, a feature that enhances directional hearing. In fact, they are quite similar, belong to the same family, and are thought to be the first fully aquatic cetaceans. While early reports on protocetid skeletons proposed that a fluke was present (Gingerich et al. Edward Babinski has some good pages. Just like raoellids and all cetaceans, pakicetids have an involucrum, the thickened inner lip on the tympanic bone (Fig. _______________________________ Where is the nasal opening in Nasal Drift in Early Whales Whales breathed with more ease when they no longer had to lift a snout above water. The canals are not preserved in any Ambulocetus specimen. Cour Forsch Inst Senckenberg. Form, function, and anatomy of Dorudon atrox (Mammalia, Cetacea) from the Middle to Late Eocene of Egypt. The nostrils migrated upward toward the top of their . 2001b;5:103749. Journal of Vertebrate Paleontology 10:455-466. The involucrum is not present in other mammals, except for one: Indohyus (Fig. 1997; Williams 1998; Geisler et al. 2006;103:84148. Gingerich PD, Haq M, Zalmout IS, Khan IH, Malkani MS. 1995b;29:291330. This shape of the astragalus, with a proximal trochlea (hinge joint) as well as distal trochlea, only occurs in even-toed ungulates (artiodactyls). Get 5 free video unlocks on our app with code GOMOBILE, _______________________________ Where is the nasal opening in The tail vertebrae are robust, suggesting that the tail was muscular. The stream bed broke up into shallow pools most of the year, and water was only flowing during the rainy periods. These may Land locomotion must have been slow since the semicircular canals were small (Spoor et al. However, unlike earlier, more primitive whales, many of the joints in the ankle and foot are fused and others have limited mobility. Raoellidae has been a family of artiodactyls for more than 20years; the recent finding by one group of authors (Thewissen et al. The changing cetacean body plan during the first ten million years of cetacean evolution. The sheer volume of bones of unrelated animals at one locality makes it impossible to identify all the bones of one individual. The hammer provides a scale. the Basilosaurid whale? This early whale has short and powerful legs, with five fingers in the hand and four toes in the foot. reptile-like creatures Basilosaurus (meaning "king lizard") is a genus of large, predatory, prehistoric archaeocete whale from the late Eocene, approximately 41.3 to 33.9 million years ago (mya). These are two species of extinct basilosaurid whales! Basilosaurid forelimbs have broad and fan-shaped scapulae attached to a humerus, radius, and ulna which are flattened into a plane to which the elbow joint was restricted, effectively making pronation and supination impossible. Google Scholar. In some species, pelvis, femur, and tibia are present (Figs. New whale from the Eocene of Pakistan and the origin of cetacean swimming. For instance, cetaceans and sirenians lack (nearly all) body hair, whereas pinnipeds have dense fur. [3] While they were unable to support body weight on land, they might have assisted as claspers during copulation. 1998). The hind limbs of basilosaurids consisted of a femur (thighbone), a patella (kneecap), tibia and fibula, ankle bones, and toes.

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