| Hyolitha Fossil range: Cambrian–Permian[1] |
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| Hyolithes cerops, Spence Shale, Idaho (Middle Cambrian) | |
| Scientific classification | |
| Kingdom: | Animalia |
| Subkingdom: | Metazoa |
| Superphylum: | Lophotrochozoa |
| Phylum: | Mollusca?[2] |
| Class: | Hyolitha |
Hyolitha are enigmatic animals with small conical shells known from the Palaeozoic Era.
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Shell morphology
The calcareous shells have a cover (operculum) and two curved supports known as helens. Most are one to four centimeters in length and are triangular or elliptical in cross section. Some species have rings or stripes.
Taxonomy & ecology
Because hyoliths are extinct and do not obviously resemble any extant group, it is unclear which living group they are most closely related to. They may be molluscs; authors who suggest that they deserve their own phylum do not comment on the position of this phylum in the tree of life.[1] Fossil traces showing a twisted, looped, intestine bear some resemblance to the gut of sipunculan worms.[3]
Despite the fact that hyolithid shells are quite common as fossils, next to nothing is known about their ancestry and internal structures. They were obviously benthic (bottom-dwellers), and there is some evidence that they were carnivores.[citation needed]
Fossil record
The first hyolith fossils appeared about in the Purella antiqua Zone of the Nemakit-Daldynian Stage of the Siberia and in its analogue the Paragloborilus subglobosus–Purella squamulosa Zone of the Meishucunian Stage of the China. Hyolith abundance and diversity attain a maximum in the Cambrian, followed by a progressive decline up to their Permian extinction.[4]
References
- ^ a b Malinky, j. 2009 "Permian Hyolithida from Australia: The Last of the Hyoliths?" Journal of Paleontology 83(1):147-152.
- ^ Wotte, T. 2006. "New Middle Cambrian mollucs from the Láncara Formation of the Cantabrian Mountains (north-western Spain)". Revista Española de Paleontología 21(2):145-158
- ^ Introduction to Sipuncula
- ^ Michael Steiner, Guoxiang Li, Yi Qian, Maoyan Zhu and Bernd-Dietrich Erdtmann (2007). "Neoproterozoic to early Cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the Yangtze Platform (China)". Palaeogeography, Palaeoclimatology, Palaeoecology 254: 67–99.
External links
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