Peronopsidae

Peronopsidae
Temporal range: terminal Toyonian to earliest Batyrbayan
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

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.

Distribution

Peronopsidae are cosmopolitan.

Temporal distribution

Temporal distribution:

Taxonomy

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).[2] Some scholars do not consider the Agnostina true trilobites, and consequently rejected the idea that they were related to the Eodiscina.[3][4]

Relations within the Peronopsidae

Relations between the subgenera of Peronopsis (light green), other peronopsid genera (darker green), the ancestral (orange) and descending families (other colors)

Many lineages are thought to have evolved within the Peronopsidae, six of which gave rise to later Agnostina families.

Genera previously assigned to the Peronopsidae

Description

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.[1]

References

  1. 1 2 3 4 5 Naimark, E.B. (2012). "Hundred species of the Genus Peronopsis Hawle et Corda, 1847". Paleontological Journal 46 (9): 945–1057. doi:10.1134/S0031030112090018.
  2. Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997
  3. Shergold, John H. (1991). "Protaspid and early meraspid growth stages of the eodiscoid trilobite Pagetia ocellata Jell, and their implications for classification". Alcheringa: An Australasian Journal of Palaeontology 15 (1): 65–86. doi:10.1080/03115519108619010.
  4. Westrop, S.R.; Landing, E. (2012). "Lower Cambrian (Branchian) eodiscoid trilobites from the lower Brigus formation, Avalon Peninsula, Newfoundland, Canada". Memoirs of the Association of Australasian Palaeontologists 42: 209–262.
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