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| Cotylocara macei | |
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| Tweet Topic Started: Mar 13 2014, 11:45 AM (1,683 Views) | |
| Taipan | Mar 13 2014, 11:45 AM Post #1 |
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Cotylocara macei![]() Scientific classification Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Cetacea Suborder: Odontoceti Family: Xenorophidae Genus: Cotylocara Species: Cotylocara macei Age 28 million years old, Oligocene Epoch. Range The only known specimen of Cotylocara macei was found in the vicinity of present-day Charleston, South Carolina. Size The skeleton is largely unknown for Cotylocara macei; however, the length of its body can be estimated from the size of its skull. Living cetaceans with a similarly sized skull are about 10 to 11 feet in length. Anatomy Two aspects of the skull of Cotylocara are surprising: its asymmetry and degree of telescoping. In the skulls of all living odontocete, bones that are restricted to the rostrum of other mammals have spread out over the bones of the braincase. The term used for this evolutionary process is “telescoping” and is derived from the collapsible, nautical telescopes; just as the nested cylinders of a telescope slide past each other, the bones of odontocete skulls have slid past each other through evolution. Cotylocara has by far the most telescoped skull of any Oligocene odontocete (those living between 24-35 million years ago), and in fact its degree of telescoping is on par with that of many living species. Even more surprising is that Cotylocara belongs to an extinct family, the Xenorophidae, that also includes species with relatively untelescoped skulls. Thus the highly telescoped skull of Cotylocara evolved convergently and separately from those of living odontocetes. Features shared by Cotylocara and other xenorophids are: excavation on the rostrum for an air sinus; transverse and backward expansion of the premaxillae (the front tooth-bearing bones of the skull) over the orbits; expansion of the lacrimal, a bone that typically forms the front wall of the orbit, over the orbit; and a prong of bone that firmly attaches the inner ear bone to the rest of the skull. The skull of Cotyolocara is distinctly asymmetric, and it is the most asymmetric of any Oligocene odontocete. Asymmetry occurs in several places of the skull including: the entire face is twisted counterclockwise when viewed head-on, the right and left air sinus basins on the rostrum are very different sizes, and sutures between paired bones on the skull are shifted towards the left side, instead of being centered. All living cetaceans have asymmetric faces, and in most cases the asymmetry is also reflected in the skull. The functional significance of the asymmetry is unclear; some have suggested it may be involved in the production of complex vocalizations for echolocation, others think that it may lead to improved hearing for echolocation, and one study suggested that it may allow for larger prey to be swallowed whole. The significance of the pronounced asymmetry in Cotylocara is unknown. Locomotion The forelimbs and tail of Cotylocara have not been found, so there is little direct evidence for how it moved through the water. That said, there is ample evidence to suggest that by this time all cetaceans had a tail fluke, flippers for forelimbs, and vestigial hindlimbs that likely ended in the body wall. Sensory Abilities The discovery of Cotylocara macei has important implications for the evolution of echolocation. All living odontocetes echolocate; whereby they produce high-frequency vocalizations and then use delays in hearing the echoes to build an acoustic image of their environment. Their vocalizations are produced in the face at the phonic lips, not the larynx as is typical of other mammals. The phonic lips are a constriction in the nasal passage between the blowhole and the skull, and sounds are produced as air rushes past this constriction, much like letting air out of a balloon. The use of high-frequency sound allows for small objects to be detected, thus odontocetes can use echolocation to find prey. Several features indicate that Cotylocara could echolocate. The cavities at the base of the rostrum and the top of the skull were likely formed by air sinuses. In living odontocetes these air sinuses are thought to have two important functions in echolocation: 1) they are situated on either side of the phonic lips and allow air to be continuously cycled past the phonic lips, allowing for uninterrupted vocalizations, 2) they redirect sound waves traveling backward, thus amplifying a forward–projecting beam of sound. The air sacs reflect sound waves because of the great density difference between air and tissue (for a similar reason, a person underwater hears little of the sounds traveling in the air above). High-density bone can also reflect sound, and the rostrum of Cotylocara is quite dense. Finally the maxilla (the main tooth-bearing bone of the skull) is exceptionally large and spread out over the braincase. This bone serves as an anchor for the large and complex muscles that control the sound-producing apparatus in the face of living odontocetes. Thus by inference, Cotylocara had large facial muscles that functioned in echolocation. If Cotylocara macei echolocated, as the evidence suggests, then it appears that this behavior evolved between 35 and 32 million years ago. After it evolved, the skull of Cotylocara and those of other fossil odontocetes suggest that the air sinuses and the facial muscles enlarged and odontocetes evolved a more sophisticated form of echolocation. Diet Cotylocara likely ate fish, as is the case for many living odontocetes. Its long and narrow snout, tall interlocking teeth, and worn tooth cusps suggest that it grabbed prey with its front teeth before swallowing prey whole. Some living odontocetes capture prey with suction-feeding; where they suck prey and water into the mouth. This feeding strategy works best if the snout is relatively short and mouth wide, such as seen in a beluga. It is unlikely that Cotylocara used suction feeding given its long and narrow rostrum. http://www.nyit.edu/medicine/research/cetacean_family_tree_cotylocara_macei Edited by Taipan, Mar 13 2014, 11:51 AM.
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| Taipan | Mar 13 2014, 11:50 AM Post #2 |
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Ancient Whale Fossils Reveal Early Origin of Echolocation By Tia Ghose, Staff Writer | March 12, 2014 02:00pm ET ![]() An illustration of the new species, Cotylocara macei. An ancient whale used sound beams to navigate and stalk prey 28 million years ago, an analysis of a new fossil suggests. The new whale species, called Cotylocara macei, contains air pockets in the skull similar to those used by porpoises and dolphins to send out focused sound beams. The discovery pushes back the origins of the ability, called echolocation, to at least 32 million years ago, said study co-author Jonathan Geisler, an anatomist at the New York Institute of Technology. "It suggest echolocation evolved very, very early in the history of the group that involved toothed whales," a group that includes sperm whales and killer whales, as well as dolphins and porpoises, Geisler said. Fossil whale About 10 years ago, scientists unearthed a complete toothed whale skull, along with a few neck vertebrae and some ribs in a fossil-rich region near Charleston, S.C. An international collector named Mace Brown acquired the find, and then invited Geisler to take a look at it. (The new species is named after the collector.) The ancient whale, which was about 28 million years old, grew to about 10 feet (3 meters) long and looked somewhat similar to modern-day dolphins or small cetaceans, though they are not closely related. It likely lived in shallow marine environments, such as the mouth of an estuary or a little further offshore, Geisler said. Early echolocation C. macei also had several distinctive features, including bone density variations and several deep air cavities, including one on top of the skull and one on either side of the base of the snout, Geisler said. ![]() The skull of the ancient whale C. macei, reveals distinctive density variation and shapes suggestive of echolocation. Those air sinuses looked similar in purpose to those found in toothed whales, or odontocetes. In odontocetes, the air sinsuses help them form nearly continuous, focused sound beams to investigate or search for prey in dark or muddy water. They then process the reflections of those sound beams through internal ears on the side of their heads, or through air spaces between their jaws, to create a sound-based map of the world around them. "Odontocetes don't produce sound in their voice box, it's originated in the face," Geisler told Live Science. The ear bones and soft tissue from the whale weren't preserved, so they don't know for sure how the whale's echolocation would have sounded or how it processed the reflections from sound beams they sent out, Geisler said. The new discovery suggests that echolocation evolved very early in whale evolution, likely soon after odontocetes diverged from the ancestors of baleen whales. The findings were published today (Mar. 12) in the journal Nature. http://www.livescience.com/44056-whale-evolved-echolocation-early.html Journal Reference: Jonathan H. Geisler, Matthew W. Colbert, James L. Carew. A new fossil species supports an early origin for toothed whale echolocation. Nature, 2014; DOI: 10.1038/nature13086 Abstract Odontocetes (toothed whales, dolphins and porpoises) hunt and navigate through dark and turbid aquatic environments using echolocation; a key adaptation that relies on the same principles as sonar1. Among echolocating vertebrates, odontocetes are unique in producing high-frequency vocalizations at the phonic lips, a constriction in the nasal passages just beneath the blowhole, and then using air sinuses and the melon to modulate their transmission2, 3. All extant odontocetes seem to echolocate2, 4; however, exactly when and how this complex behaviour—and its underlying anatomy—evolved is largely unknown. Here we report an odontocete fossil, Oligocene in age (approximately 28 Myr ago), from South Carolina (Cotylocara macei, gen. et sp. nov.) that has several features suggestive of echolocation: a dense, thick and downturned rostrum; air sac fossae; cranial asymmetry; and exceptionally broad maxillae. Our phylogenetic analysis places Cotylocara in a basal clade of odontocetes, leading us to infer that a rudimentary form of echolocation evolved in the early Oligocene, shortly after odontocetes diverged from the ancestors of filter-feeding whales (mysticetes). This was followed by enlargement of the facial muscles that modulate echolocation calls, which in turn led to marked, convergent changes in skull shape in the ancestors of Cotylocara, and in the lineage leading to extant odontocetes. http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13086.html |
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12:02 AM Jul 12