''Pahvantia'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of

hurdiid Hurdiidae (synonymous with the previously named Peytoiidae) is an extinct cosmopolitan distribution, cosmopolitan Family (biology), family of radiodonts, a group of Crown group#Stem groups, stem-group marine arthropods, which lived during the Pal ...

radiodont Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety ...

from the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

period. It is known by a single species, ''Pahvantia hastata'', described from

Wheeler Shale The Wheeler Shale (named by Charles Walcott) is a Cambrian ( 507 Ma) fossil locality world-famous for prolific agnostid and ''Elrathia kingii'' trilobite remains (even though many areas are barren of fossils) and represents a Konzent ...

and

Marjum Formation The Marjum Formation is a Cambrian geological formation that overlies the Wheeler Shale in the House Range, Utah. It is named after its type locality, Marjum Pass, and was defined in 1908. The formation is known for its occasional preservation of ...

Utah Utah is a landlocked state in the Mountain states, Mountain West subregion of the Western United States. It is one of the Four Corners states, sharing a border with Arizona, Colorado, and New Mexico. It also borders Wyoming to the northea ...

. Although it was once considered as a

filter feeder Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a s ...

based on the large number of putative

seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...

e on the frontal appendage, these structures were later interpreted as fossil material of the "trunk" section.

Description

File:20210516 Radiodonta head sclerites Pahvantia hastata.png, Head

sclerite A sclerite (Greek language, Greek , ', meaning "hardness, hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instea ...

s File:20210909 Radiodonta frontal appendage Pahvantia hastata.png, Frontal appendage File:20210218 Pahvantia size.png, Size estimation ''Pahvantia'' is named after the

Pahvant The Pahvant or Pahvants (''Pavant, Parant, Pahva-nits'') were a band of Ute people that lived in present-day Utah. Called the "Water People", they fished and hunted waterfowl. They were also farmers and hunter-gatherers. In the 18th century they w ...

people of western Utah. It was originally described as a possible arthropod of unknown affinity (evolutionary relatives). One specimen was described as a specimen of ''Proboscicaris agnosta'', which was originally interpreted as a bivalved arthropod, but is now considered as the head sclerites of ''

Hurdia ''Hurdia'' is an extinct genus of Hurdiidae, hurdiid radiodont that lived 505 million years ago during the Cambrian Period. Fossils have been found in North America, China, and the Czech Republic. Taxonomic history ''Hurdia'' was named in 1912 ...

''. ''Pahvantia'' is a relatively small radiodont with an estimated length between . Similar to most other hurdiids, ''Pahvantia'' had a large dorsal head sclerite (H-element), and it was more than twice as long than it is wide. Based on the frontal appendage, its morphology is most close to that of ''Hurdia'', although the sclerites' forms are different enough (diagnostic) to consider ''Pahvantia'' a distinct genus.

Interpretation of frontal appendage

Lerosey-Aubril and Pates (2018) considered the fossil specimen KUMIP 314089 as the frontal appendage of the animal, with a multitude of long hair-like structures tentatively interpreted as

e. It was interpreted that frontal appendage had two different types of

endite The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, : ...

s; two proximal short ones with robust, plate-like structures of different widths, and five apparently unpaired endites that are two to three times wider and around three times longer, with anterior margins fringed by numerous setae. However, Moysiuk and Caron (2019) questioned this interpretation, arguing that unnatural fossil preservation against flexibility of structures, no differentiation between the supposed

podomere The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, : ...

s and endites interpreted by Lerosey-Aubril and Pates (2018), and what would be much bigger frontal appendages compared to other hurdiids. It was considered that the morphology of the "frontal appendage" shows several bands of lamellae, possibly representing disarticulated endites. Due to preservation status, researchers considered the morphology of the frontal appendage to be uncertain. In 2021, Moysiuk and Caron reinterpreted the morphology of ''Pahvantia hastata'' by comparison with ''

Titanokorys ''Titanokorys'' is a genus of extinct hurdiid (peytoiid) radiodont (a grouping of primitive stem arthropods which lived during the early Paleozoic) that lived during the Miaolingian epoch of the middle Cambrian. It is the largest member of its ...

''; through comparison of the part and counterpart of specimen KUMIP 314089, they found that these actually show a ''Hurdia''-like frontal appendage, with "two proximal short endites with different widths". Lerosey-Aubril and Pates' interpretation (2018) was of one endite and three overlapped endites. The 2021 paper shows that the supposed "five endites with numerous setae" are more comparable to gill blades ( setal blades) on the trunk segments.

Palaeoecology

''Pahvantia'' was originally interpreted as an example of

suspension feeding Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a specia ...

radiodont taxa alongside ''

Aegirocassis ''Aegirocassis'' is an extinct genus of giant radiodont arthropod belonging to the family Hurdiidae that lived 480 million years ago during the early Ordovician in the Fezouata Formation of Morocco. It is known by a single species, ''Aegirocassis ...

'' and ''

Tamisiocaris ''Tamisiocaris'' (from Latin ''tamisium'', sieve, and Greek ''karis'', crab, shrimp) is a radiodont genus from the Cambrian period. The taxon was initially described in 2010 based on frontal appendages discovered from the Sirius Passet lagerstat ...

'', using the numerous setae on frontal appendage to capture microscopic food particles and

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

suspended in the water column.Dryad Data
However, after the morphology of the frontal appendage was reinterpreted, it is now thought that ''Pahvantia'' probably had a nekto-

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

lifestyle; it may have captured larger prey living along or in the sediment, similar to what is thought for ''Hurdia'', which had a comparable frontal appendage anatomy.

References

{{Taxonbar, from=Q113550283 Cambrian arthropods Radiodonta Fossil taxa described in 1981 Cambrian genus extinctions