An illustration showing the size of an average human next to a 50-ton Leviathan killer whale. 1996;190:186. Evo Edu Outreach 2, 272288 (2009). 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. 2001, 2007). The tympanic bulla, a bone which forms the floor of the middle ear cavity, was less connected to the rest of the skull as compared to more primitive whales. Geisler JH, Theodor JM, Uhen MD, Foss SE. The rete mirabile depends on countercurrent blood flow within the net (blood flowing in opposite directions.) 9). Dentally, remingtonocetids are specialized (Thewissen and Bajpai 2001a); their molars have lost the crushing basins of pakicetids and ambulocetids. "Bone-Breaking Bite Force of, Gingerich P.D., Smith B.H., Simons E.L. (1990). 2023 BioMed Central Ltd unless otherwise stated. 27). It is possible that these relatives are also closely related to hippopotamids, which would make molecular and morphological phylogenies consistent. In Eocene Basilosaurus-bearing fossil sites in Egypt, many fossils of the smaller basilosaurid Dorudon bear large puncture marks, which are potentially caused by the teeth of Basilosaurus. From Digital Library of Dolphin Development coordinated and spearheaded by the Northeastern Ohio Universities College of Medicine we find the following images: In most mammals, the nose opening is located near the tip of the snout. Modern representatives of artiodactyls include pigs, hippos, camels, deer, sheep, cattle, and giraffe, and, of these, hippos are thought to be the closest living relatives of cetaceans (Nikaido et al. A 50-mL graduated cylinder contains 20.0 mL of water. David Polly is a vertebrate paleontologist at Indiana University-Bloomington and a Research Associate at the Field Museum in Chicago. 3). 4), has a hinge joint, called a trochlea, where it articulates with the tibia (shin bone). https://www.thoughtco.com/facts-about-basilosaurus-king-lizard-whale-1093325 (accessed March 4, 2023). The skull of Ambulocetus has a long snout, as evidenced by the long lower jaw (much of the upper jaw is not preserved). Good introductions to the evolutionary history of odontocetes and mysticetes have been published (Fordyce and Muizon 2001; Bianucci and Landini 2007). Kellogg R. A review of the Archaeoceti. Until recently, practically nothing was known about the morphogenetic processes concealed in this metamorphosis, about what cranial structures take part in it, and about the exact way in which the cetacean skull becomes transformed during embryogeny. Hulbert RC Jr, Petkewich RM, Bishop GA, Burky D, Aleshire DP. Educator app for Contr Mus Pal Univ Michigan. Archaeocete whales have been found from early to middle Eocene (52-42 Ma) deposits in Africa and North America but are best known from Pakistan and India. 1900;23:32731. 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. Nasal Drift in Early Whales Whales breathed with more ease when they no longer had to lift a snout above water. In spite of the variation in body size, all modern Cetacea are relatively similar in shape: they have a horizontal tail fluke used in swimming; their forelimbs are flippers; there are no external hind limbs; their neck is short, and their body is streamlined. At the time, of course, no one knew that these petrified artifacts were actually the bones of a long-extinct prehistoric whale. Madar SI, Thewissen JGM, Hussain ST. Additional holotype remains of Ambulocetus natans (Cetacea, Ambulocetidae), and their implications for locomotion in early whales. (2002), Annual Reviews). Odontocetes and mysticetes conquered nearly all of the oceans: they include coastal and off-shore forms, arctic and tropical waters, shallow water, deep sea, and riverine forms. There are no external hind limbs in normal modern cetaceans, although, very rarely, an anomalous individual with such limbs is born (Fig. Unlike modern cetaceans, the skull of Basilosaurus has bony external ear canals, suggesting that it may have retained some form of highly reduced external ear. 1995a, b; Fig. 19). 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]. 2004;430:7768. 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). 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). In Eocene Basilosaurus-bearing fossil sites in Egypt, many fossils of the smaller basilosaurid Dorudon bear large puncture marks, which are potentially caused by the teeth of Basilosaurus. We dont have your requested question, but here is a suggested video that might help. The hindlimbs are tiny, and the pelvis lacked any bony connection to the vertebral column (and must have floated in the muscles of the belly), indicating that these elements could not support any weight out of water. Phylogenetic relationships of cetaceans to terrestrial artiodactyls. Experts are tested by Chegg as specialists in their subject area. Corrections? Pakicetids are related to artiodactyls, as was shown by the cladistic analysis (Gatesy and O'Leary 2001; Geisler et al. In modern dolphins, on the other hand, it is located on the top of the head, above the eyes. So first that shark whales and the dolphins. Gatesy J, O'Leary MA. Madar SI. 1997; Bajpai and Thewissen 1998; Gingerich et al. 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. Notice the similarities between hippos and whales. X-ray computed tomographic (CT) scanning has been . Whales, dolphins, and porpoises together constitute the Cetacea (English: cetaceans). Nummela S, Thewissen JGM, Bajpai S, Hussain ST, Kumar K. Sound transmission in archaic and modern whales: anatomical adaptations for underwater hearing. True or False: All living things on Earth are related? Some paleontologists speculate that Basilosaurus both looked and swam like a giant eel, undulating its long, narrow, muscular body close to the water's surface. Other features are even more impressive indicators of the land ancestry of cetaceans. In details of ear anatomy too, remingtonocetids are more specialized than pakicetids and ambulocetids (Nummela et al. In all mammals, this foramen carries the nerves and blood vessels to the lower teeth and chin, but this does not account for its size in cetaceans. Rodhocetus nostrils were higher on the skull, intermediate between its ancestors and modern whales. Eg: the nasal opening of the basilosaurid whale shows that this animal is an intermediate species between land mammal and modern whale. 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 . Paleobiology. Together with other basilosaurid whales, Basilosaurus is frequently referred to as a transitional form between the four-legged . Like other mammals and unlike other vertebrates, they nurse their young; they have three ear bones that are involved in sound transmission (hammer, anvil, and stirrup), and their lower jaws consist of a single bone (the dentary). . However, the first basilosaurid specimenBasilosaurus, whose Latin name is translated king lizardwas originally classified as a lizard when it was first described. Pakicetids are only known from a few sites in northern Pakistan and Western India, and these are approximately 50 million years old (middle Eocene). Middle Eocene cetaceans from the Harudi and Subathu Formations of India. Protocetids are a diverse group, with approximately 15 genera described. The ectotympanic of Indohyus has a thickened internal lip, a powerful indicator that Indohyus is closely related to cetaceans. The ectotympanic of artiodactyls roughly has the shape of half a walnut shell, enclosing the air-filled middle ear cavity. Toothed whales, the odontocetes, have access to rich marine food resources down to depths of 2000 m and achieve a biomass turnover larger than that of human fisheries combined ().The key to this success is their ability to locate, track, and capture fast-moving prey underwater in complete darkness at depths of, routinely, >100 m using echolocation, a feat that critically depends on the . 1998;72:90525. Skulls and skeletons are known for a single raoellid: Indohyus (Thewissen et al. Here, we report a small cetacean vertebra tentatively referred to as Neoceti from the late Eocene of Seymour Island. Modular evolution of the Cetacean vertebral column. 482. Raoellid teeth are very different from those of early cetaceans, suggesting that a dietary shift took place after the habitat change and may have been critical in the early diversification of cetaceans but not in their entry into the water. From Milan Klima, Development of the Cetacean Nasal Skull 1999 Springer. Washington: Carnegie Institute of Washington; 1936. p. 1366. However, the details of the pakicetid skeleton tell a different story; this was not an ordinary land predator. In our view, classifications of animals above the species level are mostly vehicles for communication between scientists, and communication is greatly hampered by classifications that are not stable: changing the content of Cetacea by including Indohyus leads to instability of Cetacea. In spite of our advances in understanding of the pattern of cetacean origins, it remains unclear which process caused this pattern: Why did cetaceans enter the oceans? Gingerich PD, Arif M, Bhatti MA, Raza HA, Raza M. Protosiren and Babiacetus (Mammalia, Sirenia and Cetacea) from the middle Eocene Drazinda Formation, Sulaiman Range, Punjab (Pakistan). 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. Be that as it may, Basilosaurus is the official state fossil of both Mississippi and Alabama (at least Mississippi divides the honor between Basilosaurus and another prehistoric whale, Zygorhiza). 2001). volume2,pages 272288 (2009)Cite this article. The study of differences and similarities between living things. In the second embryo, hind limbs have started to form, but their development ceases and they slowly disappear as the embryo grows (third and fourth embryos). 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. Our editors will review what youve submitted and determine whether to revise the article. Instead it is located further posterior on the snout, foreshadowing the formation of the blowhole of later whales (Fig. Journal of Vertebrate Paleontology 10:455-466. Range: Ambulocetid fossils are approximately 49 million years old (middle Eocene). This, however, would place it so far outside the mainstream of cetacean evolution that other experts remain skeptical. 2001b). 1997; Williams 1998; Geisler et al. Modified from Spoor et al. The only known fossils dated to the Oligocene have been found in Peru and New Zealand. Peters, S.E., Antar, M.S.M., Zalmout, I.S., and Gingerich, P.D. 16), roughly the size of a large male sea lion. Manage cookies/Do not sell my data we use in the preference centre. 2006;26:74659. Deciphering whale origins with molecules and fossils. In the past, the presence of an ectotympanic with an involucrum was the main character supporting the inclusion of a species in Cetacea, and it is therefore sometimes advocated that Indohyus (or Raoellidae) be included in Cetacea. While we believe that there are some benefits to this view, we lean against it. Thewissen JGM, Nummela S. Sensory evolution in aquatic tetrapods: toward and integrative approach. Form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve, form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end, form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle, the arithmetic average of a distribution, obtained by adding the scores and then dividing by the number of scores. The morphology of the sense organs suggests that hearing was important for Remingtonocetus but that vision was not. As such, these teeth are not suitable for crushing food. Preliminary evaluation of Kuldana paleosols and implications for interpreting vertebrate fossil assemblages, Kuldana Formation, Northern Pakistan. 2002;417:1636. 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). is started on 4L4 \mathrm{~L}4L oxygen by nasal cannula and an IV of D5W at 15mL/hr15 \mathrm{~mL} / \mathrm{hr}15mL/hr. 1997). Ectotympanic bones of Pakicetus and the modern dolphin Lagenorhynchus. Omissions? We focus on the evolution of cetacean organ systems, as these document the transition from land to water in detail. The reduced connections, plus the development of air-filled sinuses around the middle ear, helped isolate the inner ear from bone-conducted sound waves. The phylogeny among fossil animals can be determined by coding their morphology and having a computer program determine the greatest similarities in significant characters. The fins of dolphins and whales have a circulatory system which works as a heat exchanger. ANSWER 1. Updates? 2002). Oxygen-16 is by far the more common isotope (over 99% in nature), but the ratio between Oxygen-16 and Oxygen-18 varies in different environments, and animals living in water have a different ratio compared to animals living on land (Roe et al. 1998; Hulbert 1998). Size: Complete skeletons of Basilosaurus indicate that it measured at least 17 meters (56 feet) in length. Large rear teeth are triangular in shape with distinct serrations and two large, heavy roots. In most mammals, its walls are made of a bone called the ectotympanic, as is the case in artiodactyls and cetaceans. 23), suggesting that they hunted different prey. In: Thewissen JGM, editor. River otters swim with their hind limbs and tail, and it is likely that Ambulocetus did the same. The limb proportions (relative length of the thighs, feet, and hands, etc.) 7). In the forelimb, basilosaurids resemble modern cetaceans, in that their elbow joint is not separately mobile and their hand webbed with individual digits not recognizable (Uhen 2004). Locomotion: Although Basilosaurus has rudimentary hindlimbs, they were useless for any sort of terrestrial locomotion. Their molars differed greatly from those of protocetids and ambulocetids, there not being a central depression surrounded by three cusps in the upper molars (O'Leary and Uhen 1999). The presence of hair or fur, for instance, is characteristic of mammals. The stream bed broke up into shallow pools most of the year, and water was only flowing during the rainy periods. Cetaceans originated from land mammals (Thewissen and Williams 2002; Fordyce and Muizon 2001). Thewissen JGM, Hussain ST, Arif M. Fossil evidence for the origin of aquatic locomotion in archaeocete whales. Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan. Once cetacean hindlimbs were no longer needed, it could have taken millions of years before they were lost entirely, with a protracted period of highly reduced hindlimbs. Bajpai S, Thewissen JGM. The evolution of the blowhole in whales, which according to the fossil evidence moved from the tip to the vertex of the head, has caused some concerns amongst our creationist readers who wonder how such a feat could have taken place. 1st ed. Cookies policy. New York: Plenum; 1998. p. 399421. . This skeleton includes the skull and the vertebral column, one forelimb and parts of both hind limbs. Although Basilosaurus was only officially named in the early 18th century, its fossils had been extant for decadesand were used by residents of the southeastern U.S. as andirons for fireplaces or foundation posts for houses. 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 Instead it is located further posterior on the snout, foreshadowing the formation of the blowhole of later whales (Fig. From Land to Water: the Origin of Whales, Dolphins, and Porpoises. The rich fossil record that has emerged can now be used to enrich other subfields of evolutionary science, including developmental biology, comparative anatomy, and molecular systematics. In fact, they are quite similar, belong to the same family, and are thought to be the first fully aquatic cetaceans. While hunting in these deep and murky waters, they use short, powerful, ultrasonic echolocation clicks to find, follow, and catch . "10 Facts About Basilosaurus." In all mammals, this bone, the astragalus or talus (Fig. Outlines indicate where specific fossils were buried, and the hammer provides a scale (image from Thewissen and Williams (2002), Annual Reviews), Four skulls of pakicetid cetaceans. From Land to Water: the Origin of Whales, Dolphins, and Porpoises, https://doi.org/10.1007/s12052-009-0135-2, http://www.neoucom.edu/audience/about/departments/anatomy/AnatFaculty/media, www.neoucom.edu/DEPTS/ANAT/Thewissen/whale_origins/whales/Pakicetid.html, http://www.neoucom.edu/DEPTS/ANAT/publ.html, http://www.neoucom.edu/DEPTS/ANAT/Thewissen/whale_origins/index.html, www.neoucom.edu/DEPTS/ANAT/Thewissen/whale_origins/whales/Remi.html, https://creativecommons.org/licenses/by/2.0. Hand and foot of the protocetid Rodhocetus (modified from Gingerich et al. _______________________________ Where is the nasal opening in have come from the common ancestor. This feature disappeared entirely in later whales and is today retained only by the distantly related marine mammals known as pinnipeds. 2007; Thewissen et al. In: Thewissen JGM, editor. The blowhole in modern cetaceans is located between the eyes on the forehead, an adaptation for breathing while remaining submerged. Basilosaurus is one of the few fossil marine mammals for which preserved gut contents are known. Univ Michigan Pap Pal. 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. Science. Frank Fish (1996) discussed the evolution of different swimming modes in mammals (Fig. 2006;26:40010. Just like Pakicetus, ambulocetids had osteosclerotic limb bones (Madar 1998). Fetus of the pantropical dolphin (LACM 94389, Stenella attenuata) with whiskers along the rostrum. A modern gray whale can emerge from the water, inhale and resubmerge without stopping or tilting its snout to breathe. 2001b;5:103749. New archaeocetes (Mammalia, Cetacea) from the middle Eocene Domanda Formation of the Sulaiman Range, Punjab, Pakistan. In life, the peg like front teeth were used to seize prey and the rear triangular teeth were used to dispatch and process prey. This explains the unusual length and flexibility of Basilosaurus' front flippers, which retained their rudimentary elbows. Eg: in Australia, which was the first island that had been isolated by oceans from the others, a great diversity of pouched mammals evolved, while on the rest of the continents placental evolved and diversified. Paleo-scientists actually mistook this species for a juvenile Basilosaurus. Although not positioned at the tip of the snout like more primitive whales (e.g. Palaios 24:290-302. Therefore, skeletons of pakicetids are composites based on bones from a number of different individuals, identified based on their size, their similarity to other primitive whales, the chemical composition of the bones, and the relative abundance at their locality. another animal is to ? 2001a). In all these features, basilosaurids are more similar to modern cetaceans than to protocetids, and it is likely that they did not leave the oceans and were the first obligate cetaceans (Kellogg 1936; Uhen 2004). This could then lead to overstimulation of the semicircular canals, especially in acrobatic animals. Pictured are five families of archaeocetes, the oldest being the pakicetids, while the youngest are the basilosaurids (modified from Thewissen et al. Cranial anatomy of Pakicetidae (Cetacea, Mammalia). with a long rostrum and nasal opening retracted to a position above the first premolars. 2007). Baltimore: Johns Hopkins Univ Pr; 2007. p. 1931. 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). Cetaceans (whales, dolphins, and porpoises) are an order of mammals that originated about 50 million years ago in the Eocene epoch. Comparing things that are similar and different. 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. (C) The pelvis is attached to the femur with a synovial joint, and a small cartilaginous tibia is also present (B. mysticetus, 06B4; Lucas 1900; Struthers 1893). Pakicetids are the most archaic cetaceans known. 2003-2023 Chegg Inc. All rights reserved. 22). Most modern cetaceans have a relatively stiff neck, and it is likely that this reflex, if present at all, cannot stabilize the head because the neck is already relatively immobile. Basilosaurus drazindai and Basiloterus hussaini, new Archaeoceti (Mammalia, Cetacea) from the middle Eocene Drazinda Formation, with a revised interpretation of ages of whale-bearing strata in the Khirthar Group of the Sulaiman Range, Punjab (Pakistan). Eg: when we looking at the whales's anatomy, we can see that they evolved from an ancien 4 legged land mammal. 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. It is possible that it fed on water plants, but it is also possible that it came on land to feed on land plants, in a way similar to modern hippos. Aslan A, Thewissen JGM. 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. Figure2 shows four embryos arranged from young to old. Clementz, M.T., Goswami, A., Gingerich, P.D., and P.L. Am Zool. It had a long snout and a long tail and long slender limbs. Basilosaurids are usually referred to as archaeocetes, the ancient whales, but in modern classifications they are members of the Pelagiceti, the fully aquatic whales. Nature. Use specific examples of known genes (e.g., \beta globin and other genes) when making your list. Gingerich PD, Arif M, Clyde WC. Correspondence to Modern giant South American river otters (Pteronura brasiliensis) have a long tail that is flat dorsoventrally and that is swept up and down during swimming. All modern Cetacea live in water and cannot survive out of the water. Basilosaurid genera are separated into four subfamilies: Dorudontinae, Basilosaurinae, Kekenodontinae, and Stromeriinae. whales skeletally and may be close to the ancestry of the mysticetes and odontocetes. They are more similar to a wolf with a long nose and tail (Thewissen et al. 1997;30:5581. New York: Plenum; 1998. p. 32552. Anatomy: Basilosaurus looked vastly different from all modern whales and dolphins. Such a diagram is called a cladogram. Unlike all modern cetaceans, Basilosaurus also retained external hindlimbs with a functional knee and toes. However, the hind limbs are greatly reduced in size and the pelvis is not attached to the vertebral column, making the hind limbs unsuitable to support the body weight of these whales. de., Ray, C.E., and D.P. Locomotor abilities in water may also differ between protocetids. However, under closer examination, scientists . The first occurs in the genus Basilosaurus which had a snake-like body with a maximum length of approximately 17m long. Pakicetids have teeth with cusps (the elevated bumps on a tooth) that are high, separated by deep valleys from other cusps (Fig. It exchanges heat, ions, or gases between vessel walls so that the two bloodstreams within the rete maintain a gradient with respect to temperature, or concentration of gases or solutes. 2004. 23) with large teeth, suggestive of a diet that includes hard elements (such as bones of large fish or other vertebrates). The blowhole in modern cetaceans is located between the eyes on the forehead, an adaptation for breathing while . Basilosaurus is characterized by extremely elongate vertebrae (three times as long as those in most other basilosaurids, relative to vertebral width), a very high degree of flexibility in the vertebral column, a high number of vertebrae, and an incredibly elongate body form in general. Buchholtz EA. 1995a;29:33157. The skeleton of A. natans (H-GSP 18507) had a large pelvis that supported the animal as it walked on land, but the tail and hind limbs were used during swimming (http://www.neoucom.edu/DEPTS/ANAT/publ.html, J.G.M. Remingtonocetids and all cetaceans higher on the cladogram have small canals, but pakicetids have large canals. This eye position occurs in aquatic mammals such as hippopotamus. If Basilosaurus had positive buoyancy, it would be difficult for it to dive and swim effectively. 2007). [12] They were characterized by elongated distal thoracic vertebrae, lumbar, and proximal sacrococcygeal. Protocetids are known from low latitudes of Asia, Africa, Europe, and North America, and it is likely that they had a worldwide distribution in the middle Eocene between 49 and 40 million years ago (Gingerich et al. In all, there are four or five genera of remingtonocetids, characterized by a long snout, which makes up nearly two thirds of the length of the skull. reptile-like creatures ____ Do both have multi-chambered stomachs? Thewissen JGM, Fish FE. Thewissen). However, sharks have gills for breathing, while whales and dolphins have lungs. where is basilosaurid whales nasal opening. Contr Mus Pal Univ Michigan. While toothed whales generally have one hole, baleens are split into two. "Eocene Antarctica: a window into the earliest history of modern whales". 2002). Basilosaurines are the archetypal basilosaurids, with elongated vertebrae and long tails. The canals are not preserved in any Ambulocetus specimen. J Vert Pal. 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. The three voice registers of a bottlenose dolphin in sequence. coat of fur ____________ ______________Both have? The earliest cetaceans had nasal bones (gray) and a nasal opening (black) near the tip of the snout.