Sunday 20 December 2009

British Wildlife: X

Xenoposeidon proneneukos Taylor and Naish, 2007
Family incertae sedis; Saurischia; Sauropsida; Chordata

Xenoposeidon was one of the largest animals ever to live in what is now the United Kingdom. It is known from only one bone, found in East Sussex in the last decade of the 19th century, geologically dating from the early Cretaceous period, some 140 million years ago. This bone is a vertebra from the rear portion of the animal, and it is incomplete; the neural arch (spine at the top of the bone) and part of the centrum (solid part at the middle) are missing. This makes it extremely difficult (if not impossible) to place the animal systematically, other than it is definitely a dinosaur, and more specifically a sauropod.

My reconstruction is based on members of the Brachiosauridae, such as Brachiosaurus and Sauroposeidon from North America, and Giraffatitan from Tanzania. Of course, it might not even be a brachiosaurid, in which case it probably was more elongated in body form, looking like the diplodocoids (including Apatosaurus and of course Diplodocus).

Xanthogramma pedissequum (Harris, 1776)
Syrphidae; Diptera; Insecta; Arthropoda

This wasp-like insect is in fact a true fly of the order Diptera. Dipterans have only two wings (hence the name), unlike most other winged insects which have an extra pair. The hind wings are vestigial, being made only of a much reduced pair of halteres, drumstick-shaped organs which are believed to aid flight. Hoverflies make up a family of dipterans which are known for their hovering flight, seen as they search for flowers from which to sip nectar. Young hoverflies, known simply as maggots, are usually more carnivorous, eating aphids and other small insects, being an important biological control agent. Other hoverfly maggots will live in dung and stagnant water, using a long breathing tube extending from the anus as a snorkel to breathe fresh air.

The featured hoverfly, Xanthogramma pedissequum, is not a common species in the UK. More widespread syrphids include Syrphus ribesii and Episyrphus balteatus, both of which are similarly patterned. This is obviously an example of Batesian mimicry: when a harmless organism mimics the warning coloration of a more dangerous one. Other examples include the milk snakes (Lampropeltis spp.) copying the coral snakes (Micrurus spp.), and the viceroy butterfly (Limenitis archippus) copying the monarch (Danaus plexippus). This works because predators learn to avoid the dangerous/toxic organism because of its warning coloration (known as aposematism) and previous experience. When the same predator sees the mimic, it will avoid that too.

Black carpenter bee
Xylocopa violacea (Linnaeus, 1758)
Apidae; Hymenoptera; Insecta; Arthropoda

OK, so its common name doesn't begin with 'X', but I'll have to make an exception for this and 'Z'. Carpenter bees are so called because they make their nests in wood. They are partially social, but nowhere near as much as the bumblebees and honey bees to which they are related. Carpenter bees are large, with Xylocopa violacea being a glossy purple-black colour. Like other bees, carpenter bees are important pollinators, visiting flowers for nectar and cross-pollinating them in the process. However, carpenter bees often 'rob' flowers of their nectar by slitting the side of the flower where the nectar is kept, hence avoiding being 'used' by the flower as a pollen-carrier. Females do sting, but won't unless provoked. The males, like other bees, lack stings as this organ is a modified ovipositor (egg-laying tube).

Next week, Y: a pachycephalosaur that probably isn't really a pachycephalosaur, a lemon-yellow warbler and a furry musteline moth.

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