Modern Animal - Otters Future Animal - Enhydra Australis

Otter Previous Animal - Bear Otter Enhydriodon Dikikae


IntroductionScientists believe that otter-like creatures have existed on Earth for the past 30 million years. A theory has developed, stating that otters were once only land animals which later adapted to be semi-aquatic, to reduce their number of predators. However, scientists have not been able to obtain enough information about the evolution of the otter because of the limited fossil specimens.
A fossil record shows that Endriodon dikikae is a likely ancestor of the modern otter. It is an oversized mammal, described as a gigantic otter, and commonly named as the bear otter, because of its large skull. The scientific name is derived from the name of the region in which the fossil was found. Bones that make up the skull and the teeth of this creature were discovered in the Afar Region of Ethiopia at the fossil site situated in the lower Awash valley.
Scientific Classification
Level
Classification
Kingdom
//Animalia//
Phylum
//Chordata//
Subphylum
//Vertebrata//
Class
//Mammalia//
Order
//Carnivora//
Suborder
//Caniformia//
Infraorder
Arctoidea
Family
//Mustelidae//
Subfamily
//Lutrinae//
Genus
Enhydriodon
Species
Enhydriodon dikikae
Habitat

Geological TimescaleThe Enhydriodon dikikae would have lived around 2.4 – 5.4 million years ago, in the Pliocene Epoch. According to the continental drift theory, by the time of the Pliocene ages, the continents of the world would have already spread out, from Pangea, and the map of the world today is very similar to how it would have been during the Pliocene.
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ClimateThe Pliocene Epoch was a period of earth cooling. This came after the Miocene, where there were warmer global climates, and led to the ice age of the Pleistiocene. The cooling process changed the climate, becoming drier, leading to the formation of grassland and savannah biomes . However, the mean temperature during this time is estimated to be 2-3°C higher than today’s modern climate, as it was a period of transition from the warm climates of the Miocene, to the ice age of the Pleistiocene.
EnvironmentThe Endriodon dikikae fossils were found in Ethiopia. The African environment was considerably different at the Pliocene epoch. The conditions were moister, and had greater forest areas and tree cover than today’s present conditions. The vegetation in Ethiopia would have been tropical with forest areas, and woodland vegetation, in contrast with the present semi-desert conditions.
Food ChainIn the same level of strata of the fossil site at Dikika, other aquatic species of fishes, crocodiles and hippos were found, with the fossils of the bear otter. Scientists suggest that the otters preyed on bivalves. Bivalves are a class of molluscs which have two part shells. Examples of bivalves are clams, oysters and scallops.
Adaptations

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Structural Adaptation 1 – SizeThe Enhydriodon dikikae is a gigantic otter. This otter is estimated by scientists to be over 2 metres (seven feet) in length. The Journal of Vertebrate Paleontology studied 2 specimen of teeth for weight estimates, which come to suggest that the bear otter had a weight range of 77-126kg. This is by far, greater than any of the modern species of otter. A reason for the large size of this animal would be its position in the food web, being at least, secondary consumers, by preying on crocodiles. Additionally, there would not be as many predators for the bear otter, because of its large size.
Structural Adaptation 2 – TeethThe bear otter had very large canines. These teeth were very robust. Canine teeth are relatively long, and are useful for holding food and tearing it apart. They can also be used as a weapon. In a high position in the food web, being a predator to many animals in the environment these canine teeth are very useful. The diet of the animal would have been an environmental push factor to this adaptation. They would have needed very strong teeth to pierce the shells of bivalves.
Structural Adaptation 3 – Skullbear-otter.jpg
The size of its skull, approximately 25cm in length, was very surprising to scientists. The common name, the bear otter has come from this. The structure of its skull shares more similarities to that of a bear, than to modern day otters. The purpose of the skull of an animal is for protecting the brain. The large size of its skull would enable the Enhydriodon dikikae to consume quite large animals.
Structural Adaptation 4 – FemurThe Enhydriodon dikikae has more slender femurs than the truly aquatic modern otters of genus Enhydra and Pteronura. This is a feature which is associated with a semi-aquatic lifestyle. The bear otter might have this similar structure for it to remain semi-aquatic. It is advantageous for an animal to be able to survive in different environments.
Behavioural 1 – Mostly TerrestrialThe humerus of the bear otter is different to the modern semi-aquatic species of otter. For this reason, scientists believe that they were mostly terrestrial animals. An environmental pressure for this could be that the large size of the bear otter meant that they would not be as efficient in the water, and adapted to spend more time on the land, than some modern species of otter .
ExtinctionScientific research fails to explain the extinction of the Enhydriodon dikikae. They are thought to have become extinct before the end of the Pliocene epoch. The following epoch, the Pleistocene is characterised by glaciations. The changing environment might have put too much pressure on the bear otter. The creature would be used to the warm and dry conditions of the environment. It might not have been able to adapt to the cold environment which lead to the ice age. As it is quite high in the food chain, this species would be dependent on the survival of other organisms in the same ecosystem. Perhaps, with its great size, the population of bivalves was not enough to support the population of otters, and the species starved to death.
References
Switek, B. (2011). The Bear Otter. Retrieved June 25, 2011, from,
http://www.wired.com/wiredscience/2011/03/the-bear-otter/
Adams, J. (Unknown). Pliocene Quick Guide. Retrieved June 25, 2011, from,
http://www.esd.ornl.gov/projects/qen/pliocene.html
Enhydriodon dikikae. (2011). Retrieved June 25, 2011, from,
https://webspace.utexas.edu/dnr266/www/pdfs/Geraads_et_al_2011_Enhydriodon_dikikae.pdf