Hydrodamalis cuestae (lat.) Is a species of extinct marine mammals from the family of dugong (Dugongidae) sirens , a probable ancestor of the Steller's cow ( Hydrodamilis gigas ) [1] . He lived 5-2 million years ago along the coasts of the southern United States , Mexico and Japan . It was first described in 1978 by Daryl Domning when fossils were discovered in California . Representatives reached a length of up to 9 meters, which made them the largest sirens that have ever lived [2] . Appearance and behavior are largely based on Steller's well-documented sea cow, which, unlike H. cuestae , lived in our time and was well described.
† Hydrodamalis cuestae |
Hydrodamalis cuestae , skull |
Scientific classification |
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No rank : | Bilateral symmetric |
Subfamily : | † Hydrodamalinae |
View: | † Hydrodamalis cuestae |
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International Scientific Name |
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Hydrodamalis cuestae Domning , 1978 |
Synonyms |
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- Hydrodamalis spissus
Furusawa, 1988
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Content
Taxonomy and DisappearanceHydrodamalis cuestae was described in 1978 from residues from Upper Pliocene sediments ( ) of the Pismo Formation in California (USA) [2] . Today, the fossils of this animal are known from other California sites and are dated from the Upper Miocene to the Upper Pliocene (gemfillium-blank). Finds made in Baja California (northern Mexico) are of Upper Pliocene age. The remains of this animal were also found in the Lower Pliocene sediments of the island of Hokkaido (Japan). Some of the finds from there in 1988 were described under the species name Hydrodamalis spissa Furusawa, 1988 [3] , there were also other remains from Hokkaido of indeterminate species (Sirenia indet. Illiger, 1811 ). Today it is established that these Japanese finds also belong to the species Hydrodamilis cuestae .
EvolutionThe ancestors of H. cuestae are more ancient and smaller in size representatives of the genus Dusisiren ( Dusisiren ). The most likely candidate for this role is D. takasatensis , found in sediments of the middle part of the island of Honshu (Japan), having a Upper Miocene age (about 10–6 Ma). According to some morphological features (reduction of the dentition, the shape of the palate, the structure of the occipital articular surface, etc.) it occupies an intermediate position between the earlier D. jordani and H. cuestae .
View extinct at the end of the Pliocene, about 2 million years ago. It seems likely that the disappearance of H. cuestae was somehow related to the onset of the ice age , accompanied by cooling and, as a result, changes in the ranges of many marine plant and animal organisms, a decrease in feeding areas and the spread of new species of competitors and predators. However, before its complete disappearance, Hydrodamalis cuestae apparently gave rise to a steller's cow, somewhat more specialized and much better adapted to life in the cool shallow waters of the Pacific North [2] .
DescriptionThe maximum length of the body Hydrodamalis cuestae reached more than 9 m, the skull had a length of about 79 cm, the mass according to some data could reach 10 tons. Thus, he was the largest representative of the siren squad known to us throughout its existence. The animal had a relatively small head, a massive spindle-shaped body, ending in a powerful tail fin. The skeleton was heavy, the bones had considerable density and served as a kind of ballast that prevented the body from being pushed onto the water surface. The forelimbs were shortened, the skeleton of the hand was greatly reduced, many phalanges were missing. Probably, as with the steller's cow, there were hoof-like formations consisting of the epidermis at the ends of these cult-like limbs. The animal moved, alternately moving its forelimbs along the bottom surface or gently waving its broad tail fin. The habitats of these large animals were shallow areas of the inland seas, bays, bays and estuaries, where they could find protection from the weather and abundant food - algae and sea grasses . In the mouth, the food was ground with the help of two special horny plates that were located on the palate and lower jaw. The teeth of these sirens were completely absent, however, their embryos had alveoli of the upper molars, which were later filled with connective tissue . With high probability we can assume that H. cuestae was a herd animal and was kept by family groups [2] [4] .
Notes- ↑ Marsh H., O'Shea TJ Reynolds JE III. Sirenian Steller's sea cow: discovery, biology and ecology // Ecology and Conservation of Sirenia: Dugongs and Manatees . - New York: Cambridge University Press, 2011. - P. 18-35.
- 2 1 2 3 4 Doming, Daryl P. An Ecological Model for the Tertiary Sirenian Evolution in the North Pacific Ocean (Eng.) // Systematic Zoology: journal. - 1978. - Vol. 25 - P. 352-362 . - DOI : 10.2307 / 2412510 .
- ↑ Furusawa, H. A new species of hydrodamaline Sirenia from Hokkaido, Japan. - Takikawa Museum of Art and Natural History, 1988. - P. 1-73.
- ↑ Hydrodamalis cuestae ( Neop .) . Age of Mammals (2013). The date of circulation is September 2, 2016. Archived April 17, 2013.