ThePeronopsidae(which may also be calledperonopsids) comprise the earliest family of the Agnostina suborder. Species of this family occurred on allpaleocontinents.The earliest representatives of this family first occur just before the start of theMiddle Cambrian,and the last disappeared just after the start of theUpper Cambrian.
| Peronopsidae Temporal range:
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| Itagnostus interstrictus,until recently known asPeronopsis interstricta,from the Wheeler Shale, Utah | |
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| Family: | Peronopsidae Westergård, 1936
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| genera | |
| Synonyms | |
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Archaeagnostinae, Quadragnostinae | |
Distribution
editPeronopsidae arecosmopolitan.
Temporal distribution
editTemporal distribution:
- Archaeagnostus,Toyonian(Nephrolenellus multinodus-zone) andAmgaian(Ovatoryctocara-zone).
- Eoagnostus,Toyonian (Nephrolenellus multinodus-zone) and Amgaian (Ovatoryctocara-zone).
- Peronopsis (Proacadagnostus),Amgaian (Ovatoryctocara- and lowerKounamkites-zones).
- Diplorrhina,Amgaian (Ovatoryctocara- andKounamkites-zones)
- Peronopsis (Peronopsis),Amgaian (Ovatoryctocara-,Kounamkites- andTriplagnostus gibbus-zones).
- Pentagnostus (Pentagnostus),Amgaian (Ovatoryctocara-,Kounamkites- andTriplagnostus gibbus-zones).
- Pentagnostus (Meragnostus),Amgaian (Kounamkites- andTriplagnostus gibbus-zones).
- Peronopsis (Vulgagnostus),Amgaian (Kounamkites-,Triplagnostus gibbus- andT. fissus/Ptychagnostus atavus-zones).
- Itagnostus,Amgaian (Kounamkites-,Triplagnostus gibbus- andT. fissus/Ptychagnostus atavus-zones) toMayanian(Ptychagnostus punctuosus-zone).
- Quadragnostus,Amgaian (Kounamkites-,Triplagnostus gibbus- andT. fissus/Ptychagnostus atavus-zones) to Mayanian (Ptychagnostus punctuosus- andGoniagnostus nathorsti-zones).
- Peronopsis (Svenax),Amgaian (T. fissus/Ptychagnostus atavus-zones) to Mayanian (Ptychagnostus punctuosus- andGoniagnostus nathorsti-zones).
- Micagnostus,Amgaian (Triplagnostus gibbus-zone).
- Redeagnostus,Amgaian (T. fissus/Ptychagnostus atavus-zones) to Mayanian (Ptychagnostus punctuosus-,Goniagnostus nathorsti- andLejopyge laevigata-zones).
- Gratagnostus,Amgaian (T. fissus/Ptychagnostus atavus-zones) to Mayanian (lowestPtychagnostus punctuosus-zone).
- Acadagnostus,Amgaian (Triplagnostus gibbus- andT. fissus/Ptychagnostus atavus-zones) to Mayanian (Ptychagnostus punctuosus-zone).
- Baltagnostus,Amgaian (Triplagnostus gibbus- andT. fissus/Ptychagnostus atavus-zones) to lowest Ayusok-Kanskian.[1]
Taxonomy
editThe Peronopsidae are considered to be the earliest family of the Agnostina. This implicates that the earliest Peronopsid genus (Archaeagnostus) probably descended directly from theEodiscoidgenusTannudiscus(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
edit
Many lineages are thought to have evolved within the Peronopsidae, six of which gave rise to later Agnostina families.
- Archaeagnostusdeveloped intoPentagnostus,which sprouted thePtychagnostidaefamily early on, and also developed into the advanced subgenusPentagnostus (Meragnostus).Archaeagnostusalso developed into the effaced genusEoagnostus.Archaeagnostusis finally the ancestor of the subgenusPeronopsis (Peronopsis).
- The early nominate subgenus ofPeronopsisgave rise to the generaQuadragnostusandDiplorrhina,either of which developed intoGratagnostus.
- Peronopsis (Peronopsis)contains the ancestor ofIniospheniscus.
- Peronopsis (Peronopsis)fathered the subgenusPeronopsis (Svenax),which early on sprouted the genusRedeagnostus,itself the ancestor of theAgnostidaefamily. LaterPeronopsis (Svenax)probably developed intoItagnostus,which is transitional to theDoryagnostidaefamily.
- Peronopsis (Peronopsis)brought forth the subgenusPeronopsis (Vulgagnostus),itself the ancestor ofBaltagnostusfrom which theAmmagnostidaedescended. The effaced genusEoagnostusalso descends fromPeronopsis (Vulgagnostus).
- A further lineage fromPeronopsis (Peronopsis)includesPeronopsis (Proacadagnostus),Acadagnostus,andPseudoperonopsis,the earliest genus of theDiplagnostidaefamily.
- Peronopsis palmadonis transitional to theCondylopygoideasuperfamily.[1]
Genera previously assigned to the Peronopsidae
edit- Connagnostusis reassigned to theAgnostidae
- Euagnostusis reassigned to theDoryagnostidae
- Pseudoperonopsisis reassigned to theDiplagnostidae[1]
Description
editLike all Agnostida, members of the Peronopsidae are diminutive, with the headshield (orcephalon) and tailshield (orpygidium) of approximately the same size (orisopygous) 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 (orglabella) - is lacking or incomplete. The cephalon carries no spines. The border around the pygidium is not forked.[1]
References
edit- ^abcdeNaimark, E.B. (2012). "Hundred species of the GenusPeronopsisHawle et Corda, 1847 ".Paleontological Journal.46(9): 945–1057.Bibcode:2012PalJ...46..945N.doi:10.1134/S0031030112090018.S2CID85130465.
- ^Whittington, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997
- ^Shergold, John H. (1991). "Protaspid and early meraspid growth stages of the eodiscoid trilobitePagetia ocellataJell, and their implications for classification ".Alcheringa: An Australasian Journal of Palaeontology.15(1): 65–86.Bibcode:1991Alch...15...65S.doi:10.1080/03115519108619010.
- ^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.