Mitrate
| Mitrate Temporal range: Cambrian to Carboniferous (500-360 Ma)[1] | |
|---|---|
| Scientific classification | |
| Domain: | Eukarya |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
Mitrates are an extinct group of stem group echinoderms, which may be closely related to the hemichordates.
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 other 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
- 1 2 3 4 5 6 7 8 9 10 Gee, H. (2000). "Mitrates on the move.". Nature. 407 (6806): 849–851. doi:10.1038/35038193. PMID 11057650. 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.