Tuesday January 3, 2012
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Questions and Answers: In-Depth Responses
I was reading recently about a extinct genus of otter that was discovered called Megalenhydris. What is known about this genus of otter? What was its habitat? What did it eat? How did it swim? What was its behavior like? If you were to relate it to an extant species of otter, which species would you choose? Thanks!
Dave Francazio, 19 July 2007
Response from Lesley Wright
Otter fossils are not common because of the environment in which they live. Rivers tend to be poor preservers of remains because of turbulence, erosion rather than deposition of sediments and the presence of a lot of scavengers. Lake-dwelling species tend to be better preserved and hence are better-known. Sardinia and Corsica appear at first glance to be wall-to-wall with extinct otter species, but on the whole these are each known only from a single specimen.
Megalenhydris barbaricina (Willemsen et Malatesta, 1987), the Sardinian Giant Otter, was discovered by Gruppo Grotte Nuorese in a deep cave on the east coast of Sardinia, and briefly reported in their journal, but was first systematically described by Willemsen et Malatesta,1987. It was later discussed again by Willemsen in 1992.
Only this one specimen has ever been found, consisting of the lower jaw, some teeth, the upper arm and some fingers or toes, all of which were recovered from the sediment, and the two hind legs and some of the vertebrae plus tiny fragments of skull, pelvis and ribs, which remained embedded in the substrate. The specimen is now in the Museo Civico di Archeologia e Speleologia in Nuoro, Sardinia.
With only a single, incomplete fossil, a lot has to be read into very little physical material.
The jawbone is massive, much larger than that of Pteronura brasiliensis, the living Giant Otter. The teeth are massive, and very like those of clawless otters (such as Aonyx capensis), which are adapted to eating shellfish. The tail vertebrae are very flattened right from the tail root, which is unlike any living otter. The overall dimensions of the lower jaw, upper arm, thigh bones etc of the animal are greater than the equivalents for Pteronura, which means it was a very large, robust animal - the total length is not known as only the first five tail vertebrae were found in place, so the tail length cannot be estimated.
The teeth are similar to those of the clawless otters, and like them, seem to be adapted for crushing shellfish. On the other hand, the rest of the skeleton indicates more aquatic adaptation than modern river otters, from the way that the attachment of the foreleg allows a strong back-swing, important in swimming, plus the tail is very flattened, allowing it to be actively used for propulsion by thrashing up and down. The backbone is also particularly flexible, again indicating very aquatic adaptation.
It was not possible to date the deposits in which the fossil was found - the authors thought it likely that it dated from the last Ice Age, 70,000 - 10,000 years bp. During this period, sea levels were lower because so much water was locked up in the ice sheets, and the Mediterranean basin would have been lakes, marshes and dry land, with today's islands being mountain ranges, as well as at times the whole basin being marine. It seems that the individual otter found died in a cave on the edge of the mountains that are now Sardinia, but we cannot know how this came about. It may have been lost, or washed in in a flood, or this species might have made use of caves for denning - with only one specimen, we cannot say. Since the animal seems to have had many very aquatic adaptations, it seems likely that there was a large body of water rich in shellfish nearby.
That's pretty much all that can be said about this otter. Whether this was a giant sea otter, or a giant river otter adapted to eating shellfish cannot be determined - either is possible from the nature of the remains. Some authors confidently state it is a sea otter, others that it is the biggest of the river otters. Willensen himself considered that judging from its teeth, it belonged to the tribe of clawless otters, so we can see that the place of this species in otter classification is not clear at all. If forced to choose, I would go for the shellfish-eating giant river otter. Its relationship with today's otters is unclear - it could easily represent an entire tribe of otters that has no modern descendants.
Given the very patchy nature of the fossil record, it is likely that we will never know any more than this. If another specimen is found, perhaps more can be established.
WILLEMSEN, G.F. & A. MALATESTA. (1987). Megalenhydris burbaricina sp. nov., a new otter from Sardinia. Proc. Kon. Ned. Akad. Wet., B, 90: 83-92.
WILLEMSEN, G.F. (1992). A revision of Pliocene and Quaternary Lutrinae from Europe. Scripta Geol., 101: 1-115.
Response provided 22 July 2007
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