| Yamatocetus Temporal range: Late Oligocene | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | † Eomysticetidae |
| Genus: | † Yamatocetus Okazaki, 2012 |
| Species: | †Y. canaliculatus |
| Binomial name | |
| †Yamatocetus canaliculatus Okazaki, 2012 | |
Yamatocetus canaliculatus is an extinct species of eomysticetid baleen whale from the Late Oligocene of Japan.
The holotype specimen, a partial skeleton, was discovered by curator Toshiyuki Kamei in October 1981 in the Ashiya Group of the Jinnobaru Formation on the island of Kyushu, and stored in the Kitakyushu Museum of Natural History and Human History. The genus name honors the old name of Japan, Yamato, and Latin cetus, "whale." The species name translates to "with groove" in reference to the grooves in its mouth which indicate functional baleen. It was placed into the family Eomysticetidae, a primitive group of baleen whales. [1]
As in other baleen whales, the skull is wide and flat. The skull, along the sides, has several narrow, straight grooves–eight in total–and there are several foramina in the skull used as passage for blood vesselsthough not as many as modern baleen whales–which indicate it had baleen in its mouth. The skull contains several tooth sockets, but no teeth were discovered; it is possible these sockets were vestigial and held no teeth, or the teeth naturally fell out over the course of the animal's life. The blowhole was located midway along the snout, near the position of eyes. Unlike the closely related Eomysticetus , the head is relatively flat, and the snout is blunt. The auditory bulla in the ear is more similar to primitive baleen whales and archaeocetes. [1]
Yamatocetus had seven neck vertebrae, and the complete series was preserved. The neural spine projecting up from the vertebra increases along the series. Thoracic vertebrae one through seven and nine were preserved. The ribs had a double-headed joint with the vertebrae. The shoulder blade was concave on the side facing the ribs, a primitive feature for baleen whales. [1]
The left forearm and fragments of the right were discovered. As in modern whales, the elbow joint probably could not rotate. The humerus is proportionally longer than that of modern baleen whales, a characteristic of eomysticetid whales, suggesting eomysticetids had less swimming capabilities. [1]
Yamatocetus was an early filter feeder, and its teeth, if it had any, were likely vestigial and served no purpose. Since the whale had several double-headed vertebral joints, and modern baleen whales have a reduced number of these to increase the flexibility of the ribcage to aid in deep-sea diving, Yamatocetus likely stayed near the surface. [1]
Several marine vertebrates were found in the Ashiya Group: the baleen whales " Metasqualodon ," Chonecetus , and an unidentified aetiocetid; and an unidentified squalodontid dolphin; a Trionyx softshell turtle; the tortoise Indotestudo takasago ; an unidentified sea turtle; an unidentified crocodile; the seabirds Copepteryx and an unknown pelagornithid; and unknown dugong. An unknown amynodontid, a terrestrial hippo-like animal, was also found. [1]
Baleen is a filter-feeding system inside the mouths of baleen whales. To use baleen, the whale first opens its mouth underwater to take in water. The whale then pushes the water out, and animals such as krill are filtered by the baleen and remain as a food source for the whale. Baleen is similar to bristles and consists of keratin, the same substance found in human fingernails, skin and hair. Baleen is a skin derivative. Some whales, such as the bowhead whale, have longer baleen than others. Other whales, such as the gray whale, only use one side of their baleen. These baleen bristles are arranged in plates across the upper jaw of whales.
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Mammalodon is an extinct genus of archaic baleen whale belonging to the family Mammalodontidae.
Mammalodontidae is a family of extinct whales known from the Oligocene of Australia and New Zealand.
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Anthracosuchus is an extinct genus of dyrosaurid crocodyliform from the Paleocene of Colombia. Remains of Anthracosuchus balrogus, the only known species, come from the Cerrejón Formation in the Cerrejón mine, and include four fossil specimens with partial skulls. Anthracosuchus differs from other dyrosaurids in having an extremely short (brevirostrine) snout, widely spaced eye sockets with bony protuberances around them, and osteoderms that are smooth and thick. It is one of the most basal dyrosaurids along with Chenanisuchus and Cerrejonisuchus.
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Waharoa is a genus of eomysticetid baleen whale from the Late Oligocene (Chattian) of New Zealand. It was identified with the discovery of Waharoa ruwhenua by Boessenecker and Fordyce (2015), which added a new genus and species to a monophyletic family Eomysticetidae.
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Coronodon is a genus of toothed (transitional) baleen whales from the Early Oligocene Ashley and Chandler Bridge formations of South Carolina. The genus contains three species: the type species C. havensteini, and additional species C. newtonorum and C. planifrons.
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