- Mitrate
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Mitrate
Temporal range: Cambrian to Carboniferous (500-360 Ma)[1]Scientific classification Domain: Eukarya Kingdom: Animalia Phylum: Echinodermata Mitrates are a group of stem group Echinoderms, which may be closely related to the hemichordates.
Contents
Morphology
The organisms were a few millimetres long.[1] Like the echinoderms, they are covered in armour plates, each of which comprises a single crystal of calcite. However, this is arguably the only feature they share with the latter group; they don't have, for example, fivefold symmetry or a water vascular system.[1]
Their heads had two sides; one, flat, was covered with large "pavement-like"[1] plates, the other, convex, bore smaller plates.[1] Their tails were long and segmented, resembling the stalk of a crinoid or the arm of a brittlestar.[1] At the opposite end was a hole which may have been mouth or anus - or both.[1]
They also bear features reminiscent of pharyngeal slits,[2] a character lost in echinoderms but present in hemichordates,[1] causing R.P.S. Jefferies to hold them as the ancestor of all chordates.
Behaviour
Mitrates^ have been found with associated trace fossils.[3] Their interpretation requires an understanding of how the animal was oriented in life; it's not agreed whether the convex side of the head was up or down, or indeed whether the "tail" was at the front or back of the organism![1] The trace fossils suggest that they pulled themselves through the mud with their "tail", and were flat-side up.[1]
Notes
^ Rhenocystis latipedunculata
References
- ^ a b c d e f g h i j Gee, H. (2000). "Mitrates on the move.". Nature 407 (6806): 849–851. doi:10.1038/35038193. PMID 11057650. http://www.nature.com/nature/journal/v407/n6806/full/407849a0.html. Retrieved 2008-02-02.
- ^ Jefferies, R.P.S. (1986). The Ancestry of the Vertebrates. British Museum (Natural History).
- ^ Sutcliffe, O.E.; Südkamp, W.H.; Jefferies, R.P.S. (2000). "Ichnological evidence on the behaviour of mitrates: two trails associated with the Devonian mitrate Rhenocystis". Lethaia 33 (1): 1–12. doi:10.1080/00241160050150267.
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