Sunday, June 7, 2015
Opabinia the Alien
Opabinia is one of the rarest fossils found in today’s world. There are less than twenty quality specimens of the creature, and archaeologists hope to discover more in time. The known fossils were mostly found in the Burgess Shale of British Columbia. Opabinia isn’t what you’d expect when you think about prehistoric ages. This species, known to live on the seafloor, had a soft body that was about seven centimeters long. They had a head with five eyes and a mouth underneath that was backwards. The backwards mouth is said to coincide with the fact that the creature had a proboscis, which was more than likely used to pass food to the mouth, as its length indicates. The creature also had a segmented body that was finished off by a fan-shaped tail.
Opabinia regalis is an extinct stem-arthropod found in the Middle Cambrian Burgess Shale Lagerstätte of British Columbia, Canada. Fewer than twenty good specimens have been described; 3 specimens of Opabinia are known from the Greater Phyllopod bed, where they comprise less than 0.1% of the community. Opabinia was a soft-bodied animal of modest size, and its segmented body had lobes along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using the proboscis to seek out small, soft food.
When the first thorough examination of Opabinia in 1975 revealed its unusual features, it was thought to be unrelated to any known phylum, although possibly related to a hypothetical ancestor of arthropods and of annelid worms. However other finds, most notably Anomalocaris, suggested that it belonged to a group of animals that were closely related to the ancestors of arthropods and of which the living animals onychophorans and tardigrades may also be members.
In the 1970s there was an ongoing debate about whether multi-celled animals appeared suddenly during the Early Cambrian, in an event called the Cambrian explosion, or had arisen earlier but without leaving fossils. At first Opabinia was regarded as strong evidence for the "explosive" hypothesis. Later the discovery of a whole series of similar lobopod animals, some with closer resemblances to arthropods, and the development of the idea of stem groups suggested that the Early Cambrian was a time of relatively fast evolution but one that could be understood without assuming any unique evolutionary processes.