Sunday 30 August 2009

British Wildlife: H

Hypsilophodon foxii Huxley, 1869
Hypsilophodontidae; Ornithischia; Sauropsida; Chordata

Hypsilophodon is one of the most well-known small ornithischian (bird-hipped) dinosaurs. It was first thought to be a juvenile Iguanodon until it was studied in detail by T. H. Huxley, who formally named it twenty years after its discovery. It is known from many locations in England, most notably the Isle of Wight.

Hypsilophodon foxii mounted skeleton
Dinosaur Isle Museum, Isle of Wight
May 2008

Historically, it was thought that dinosaurs like Hypsilophodon were partially arboreal, that is, spending some time in the trees, in a method somewhat akin to tree kangaroos. We now know, through study of the bones, especially the pelvis, limbs and tail bones, that it would have been a mostly bipedal, and wholly terrestrial, animal.

Restored skull of Hypsilophodon foxii at Dinosaur Isle museum (it spins!)

One of the more unusual traits of the Hypsilophodontidae in general (the family which also contains Zephyrosaurus, Thescelosaurus, Parksosaurus and their kin) is their "primitive" hands and feet. They retain five 'fingers' and four 'toes', which other contemporary ornithopod groups had reduced to these somewhat. This is supposedly due to the fact that hypsilophodontids were doing well as they are and there were no selective pressures put on them to change this.

Grey seal
Halichoerus grypus (Fabricius, 1791)
Phocidae; Carnivora; Mammalia; Chordata

There are two species of seal that have breeding colonies in the UK; the common or harbour seal (Phoca vitulina) and the grey seal. Ironically, the grey seal is more common than the common seal in the UK; indeed I've never seen the common seal in the wild. Grey seals, however, are plentiful around many of Britain's rocky coasts and even some of the more protected sandy beaches, such as Donna Nook in Lincolnshire, where their breeding has been studies for decades.

I have illustrated a male grey seal here, who can be distinguished by his "Roman nose"; the female's snout is more like a dog's. The 'grey' in their names is also a misnomer: they are more likely to be dark with pale blotches or vice-versa, and the calves are pure white. The lanugo (the name for the white fur in a young seal, or any woolly covering in an infant, even human babies) is shed by the time the young is a month old, at which time it is also weaned and able to enter the water. As you can imagine, the lanugo is not waterproof, so a very young seal cannot swim. It is also imperative that a seal pup must put on enough weight in order to insulate it from the cold waters (seal pups are oddly enough born in winter), so the mother's milk is very high in fat (something like 60%, more like clotted cream than milk!). In the four weeks or so before weaning, the pup has put on enough weight to keep itself warm. It's not just the pup that changes drastically in those four weeks; the mother does too. The female after giving birth is quite a large object: her weight is displaced to her offspring through suckling.

Harvest mouse
Micromys minutus (Pallas, 1771)
Muridae; Rodentia; Mammalia; Chordata

The harvest mouse is Europe's smallest rodent. In Britain, only shrews beat it to the title of smallest mammal. It truly is a tiny creature, constructing a nest out of grass the same shape and size of a cricket ball. Inside the ball-like nest would not only be the mother mouse, but a whole litter of young.

The harvest mouse will spend most of its time in arable fields amongst the crops. It is not a pest, unlike house mice (Mus musculus), which would probably strip the field of all grain in a single season, as its numbers are low and it is generally a rare animal. In order to manoeuvre through the tall grasses, the mouse uses its prehensile tail as a fifth limb.

For I, another ornithopod, a damselfly and a moth. I is not a good letter for extant vertebrates, it seems.

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