| Spade-toothed whale | |
|---|---|
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Cetacea |
| Family: | Ziphiidae |
| Genus: | Mesoplodon |
| Species: | Mesoplodon traversii |
| Binomial name | |
| Mesoplodon traversii (Gray, 1874) |
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| Locations and dates of specimens | |
| Synonyms | |
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Dolichodon layardii Gray, 1874 |
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The spade-toothed whale, Mesoplodon traversii, is a very little known species of beaked whale. It was first named from a partial jaw found on Pitt Island (New Zealand) in 1872, reported and illustrated in 1873 by James Hector, and described the next year by John Edward Gray, who named it in honor of Henry Hammersley Travers, the collector. This was eventually lumped with the strap-toothed whale, starting as early as 1878 (Hector 1878, who in fact never considered the specimen to be specifically distinct). A calvaria found in the 1950s at White Island (also New Zealand) initially remained undescribed, but later was believed to be from a ginkgo-toothed beaked whale (Baker and van Helden 1999).
In 1986, a damaged calvaria was found washed up on Robinson Crusoe Island (Chile), and was described as a new species, Mesoplodon bahamondi or Bahamonde's beaked whale. The results of DNA sequence and morphological comparisons (van Helden et al. 2002) have shown all three finds came from the same species, which is therefore properly known as M. traversii. This species is remarkable since the external appearance is still completely unknown, and it is likely to be the most poorly known large mammalian species of our time.
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Nothing is known about this species other than cranial and dental anatomy. There are some notable differences between it and other mesoplodonts, such as the relatively large width of the rostrum; altogether it might look most similar to an oversized ginkgo-toothed beaked whale in overall shape, as their skulls are quite alike except in size. The distinguishing character are the very large teeth of the animal, 23 cm (9 inches), close in size to those of strap-toothed whale. The teeth are much wider than the strap-toothed, and a peculiar denticle on the tip of the teeth present on both species is much more pronounced in the spade-toothed whale. The common name was chosen because the part of the tooth that protrudes from the gums, in life, unlike the straplike ones of strap-toothed whales, must have a shape similar to the tip of a flensing spade of 19th-century whalers.
Despite the rather similar dentition, the spade-toothed whale and strap-toothed whale seem only distantly related. The present species' relationships are not known with certainty, though, because it is very distinct morphologically and DNA sequence information is contradictory and unable to propose a robust phylogenetic hypothesis thus far.[2] Judging from the size of the skull, the species may be between 5.0 and 5.5 meters (16 and 18 feet) in length, perhaps a bit larger.
This species has never been seen alive, so nothing is known of its behavior. It is presumably not different from other Mesoplodon of medium size, which are deep-water species living alone or in small groups and which feed on cephalopods and small fish. The young become independent of their mothers probably around one year of age, as in most whales.
The population status of the spade-toothed whale is entirely unknown, but it is unlikely to be abundant.
The sex of the 20th-century specimens is not known. However, by recovering or failing to recover DNA sequences of the Y chromosome, it could, in theory, be resolved. Note that little material is shared between the Pitt Island specimen and the calvariae, making direct anatomical comparisons problematic.