Peronopsidae
| Peronopsidae Temporal range: terminal Toyonian to earliest Batyrbayan |
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|---|---|
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| Itagnostus interstrictus, until recently known as Peronopsis interstricta, from the Wheeler Shale, Utah | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Trilobita |
| Order: | Agnostida |
| Suborder: | Agnostina |
| Superfamily: | Agnostoidea |
| Family: |
Peronopsidae Westergård, 1936 |
| genera | |
| Synonyms | |
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Archaeagnostinae, Quadragnostinae |
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Archaeagnostinae, Quadragnostinae
The Peronopsidae (which may also be called peronopsids) comprise the earliest family of the Agnostina suborder. Species of this family occurred on all paleocontinents. The earliest representatives of this family first occur just before the start of the Middle Cambrian, and the last disappeared just after the start of the Upper Cambrian.
Peronopsidae are cosmopolitan.
Temporal distribution:
The Peronopsidae are considered to be the earliest family of the Agnostina. This implicates that the earliest Peronopsid genus (Archaeagnostus) probably descended directly from the Eodiscoid genus Tannudiscus (Weymouthiidae). Some scholars do not consider the Agnostina true trilobites, and consequently rejected the idea that they were related to the Eodiscina.
Many lineages are thought to have evolved within the Peronopsidae, six of which gave rise to later Agnostina families.
Like all Agnostida, members of the Peronopsidae are diminutive, with the headshield (or cephalon) and tailshield (or pygidium) of approximately the same size (or isopygous) and outline. Like all Agnostina, Peronopsidae have only two thorax segments. The cephalon and pygidium usually have a complete set of furrows. The preglabellar furrow - between the front and the central raised area of the cephalon (or glabella) - is lacking or incomplete. The cephalon carries no spines. The border around the pygidium is not forked.
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