Paris biota

Paris biota
Paris biota
Stratigraphic range: earliest Spathian, ~249 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Lithology
Primary	Shale, limestone, siltstone
Location
Region	Idaho and Nevada, United States
Country	USA
	Paris biota (the United States) Paris biota (Idaho)

The Paris biota is an exceptionally diverse Early Triassic (approximately 249 million years ago)^[1] fossil assemblage described in 2017 from the Lower Shale Member of the Thaynes Group. It was first discovered in Paris Canyon, west of the town of Paris in Bear Lake County, southeastern Idaho, United States.^[2] This biota was later also found in coeval and slightly younger beds in northeastern Nevada (Elko County) and Bear Lake and Caribou counties, southeastern Idaho.^[3]

Age

Bajarunia sp. ammonoid fossil

The Paris biota was found in layers dating back to the earliest Spathian, a substage of the Olenekian stage of the Early Triassic epoch. The biostratigraphy is constrained by the presence of the ammonoids Tirolites and Bajarunia, and conodonts.^[2]^[3] The Tirolites/Columbites beds are dated with 248.853±0.086 Ma.^[1] The Paris biota was later also discovered in slightly younger beds in Immigrant Canyon, northeastern Nevada, associated with the ammonoid index fossils Prohungarites sp. and Neopopanoceras haugi, which point to a middle–late Spathian age.^[3]

Palaeogeography and paleoenvironment

The organisms of the Paris biota lived in a shallow marine epicontinental sea (western USA basin) on the western coast of Pangea. The sites were located in a near-equatorial position during the Early Triassic epoch.^[2]^[3]

Assemblage

The Spathian aged Paris biota is one of the earliest diverse fossil assemblages from the post-extinction interval, about 3 million years^[1]^[4] after the Permian-Triassic mass extinction, and the first one in the wake of the Smithian-Spathian boundary extinction.

The Paris biota comprises fossils belonging to 20 orders or seven phyla: (1) Retaria (foraminifers)^[2] (2) sponges, (3) brachiopods (4) mollusks, (5) arthropods, (6) echinoderms and (7) chordates (vertebrates). The assemblage also contains fossil algae and coprolites (trace fossils). Ammonoids and bivalves dominate the fauna.^[2] It combines Palaeozoic survivors with members of the Modern evolutionary fauna (i.e., groups that are typical for the Mesozoic and Cenozoic). The Paris biota therefore provides a glimpse at the faunal turnover associated with the largest mass extinction in Earth's history. For example, the biota includes leptomitid protomonaxonid sponges, a group that is otherwise known from the early Paleozoic era (e.g. from the Cambrian Burgess Shale of western Canada). Among the modern clades, it contains a gladius-bearing coleoid cephalopod (Idahoteuthis).

The preservation of Paris biota organisms is considered taxon-dependent, but is not fully understood.^[5] The study of some fossils could be improved using synchrotron μXRF imaging.^[6]

Most organisms of the Paris biota were described in a thematic issue of the journal Geobios in 2019,^[7] but new taxa were also subsequently described.

In 2023, another diverse post-extinction biota was presented from South China, the Dienerian aged Guiyang biota,^[8] which includes fossils belonging to twelve classes and 19 orders. The Early Triassic is generally considered as an environmentally unstable and diversity-poor interval,^[2] highlighting the importance of the discovery of such diverse lagerstätten.

The following taxa (animals sorted by phylum) were either reported or described from the Paris biota (not listed are the foraminifera and conodonts, which have not yet been described):