Emuellidae
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Emuellidae Temporal range: 517 Ma late Botomian |
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Balcoracania dailyi of the Emuellidae family Lower Cambrian Emu Shale Kangaroo Island, South Australia © Dave Simpson |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Trilobita |
| Order: | Redlichiida |
| Suborder: | Redlichiina |
| Superfamily: | Emuelloidea |
| Family: |
Emuellidae Pocock, 1970 |
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Emuellidae are a small family of trilobites, a group of extinct marine arthropods, that lived during the late Lower Cambrian (late Botomian) of the East Gondwana supercontinent, in what are today South-Australia and Antarctica. Emuellidae can be recognized among trilobites in having a set of unique features. The headshield or cephalon has large genal spines reaching back as far as the 3rd to 6th segment of the thorax. The eye-ridges contact the back of the frontal lobe of the glabella and extend laterally and backwards, roughly parallel to the frontal and lateral rim of the cephalon. There are small, clearly incised pits at the junction between the eye-ridge and the frontal lobe of the cephalic axis (or glabella). The thorax reaches its greatest width at the 6th segment. The frontal part or prothorax consists of 6 segments, with number 5 and 6 fused, and the 6th carrying very large trailing spines. The rear part or opistothorax consists of a variable but extremely large number of seqments (up to 97).
(See the Trilobite article for a definition of morphological terms)
Cephalon: Cranidium subquadrate, glabella cylindrical, slightly contracted at S3, three pairs of glabellar furrows, preglabellar field short or absent, eye ridge wide, long, directed slightly postero-laterally, palpebral lobe cresentic, posterior area of fixigena with fulcrum, free cheeks (or librigenae) with long spines; hypostome conterminant, attached to a narrow rostral plate.
The thorax is divided into a prothorax of six segments (the 6th carrying very large, trailing, pleural spines and extremely long opisthothorax of up to 97 segments (Balcoraciana dailyi holds the record for greatest number of thoracic segments in a trilobite species).
Pygidium: A minute, segmented disc.
Fossils now assigned to the Emuellidae were first discovered by Dr. B. Daily, of the Geology Department, University of Adelaide in 1956.
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