''Nesonektris aldridgei'' is an extinct

vetulicolian Vetulicolia is a group of bilaterian marine animals encompassing several extinct species from the Cambrian, and possibly Ediacaran, periods. As of 2023, the majority of workers favor placing Vetulicolians in the stem group of the Chordata, but ...

from the Late

Botomian Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission ...

-aged

Emu Bay Shale The Emu Bay Shale is a Formation (stratigraphy), geological formation in Emu Bay, South Australia, containing a major Konservat-Lagerstätte (fossil beds with soft tissue preservation). It is one of two in the world containing Redlichiidan trilob ...

Lagerstätte A Fossil-Lagerstätte (, from ''Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that preserves an exceptionally high amount of palaeontological information. ''Konzentrat-Lagerstätten'' preserv ...

Kangaroo Island Kangaroo Island (, ) is Australia's third-largest island, after Tasmania and Melville Island, Northern Territory, Melville Island. It lies in the state of South Australia, southwest of Adelaide. Its closest point to the mainland is Snapper Poi ...

, Australia. So far, it is the fourth described

vetulicolia Vetulicolia is a group of bilaterian marine animals encompassing several extinct species from the Cambrian, and possibly Ediacaran, periods. As of 2023, the majority of workers favor placing Vetulicolians in the stem group of the Chordata, but ...

n that is not restricted to the

Maotianshan Shales The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized orga ...

(the other three being '' Ooedigera'' of

Sirius Passet Sirius Passet is a Cambrian Lagerstätte in Peary Land, Greenland. The Sirius Passet Lagerstätte was named after the Slædepatruljen Sirius, Sirius sledge patrol that operates in North Greenland. It comprises six places in Nansen Land, on the eas ...

, '' Banffia'' of the

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

, and '' Skeemella'' of the Pierson Cove Formation above the

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 ...

Description

''N. aldridgei'' is known from several incomplete fossils which suggest that, in life, it was a fairly large animal (when compared to other vetulicolians). The largest fossil is about 150 millimetres ( 5.9 inches) long, leading researchers to estimate that that individual was about 170 millimetres (6.7 inches) long. The exquisitely preserved fossils show that running the length inside the tail was a

notochord The notochord is an elastic, rod-like structure found in chordates. In vertebrates the notochord is an embryonic structure that disintegrates, as the vertebrae develop, to become the nucleus pulposus in the intervertebral discs of the verteb ...

, thereby demonstrating the animal's chordate affinities as being related to

tunicate Tunicates are marine invertebrates belonging to the subphylum Tunicata ( ). This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time ...

s. The forebody, and overall form are similar to vetulicolids of Vetulicolidae, though, its researchers do not have confidence to place ''N. aldridgei'' within either of the families within

Vetulicolida Vetulicolida is a class of vetulicolians. It consists of the order Vetulicolata (which contains the families Vetulicolidae and Didazoonidae) and the genus '' Nesonektris'', which is of uncertain placement. It is distinguished from the Banff ...

(Vetulicolidae or Didazoonidae).

Etymology

The genus name translates as "island swimmer" in reference to both its obvious adaptations for a

nekton Nekton or necton (from the ) is any aquatic organism that can actively and persistently propel itself through a water column (i.e. swimming) without touching the bottom. Nektons generally have powerful tails and appendages (e.g. fins, pleopods, ...

ic lifestyle in the water column, and the great distance between Kangaroo Island and China, the primary center of vetulicolian diversity, even during Cambrian times. The specific name commemorates the efforts and memory of Richard "Dick" Aldridge for his crucial research in resolving vetulicolian affinities.

Taxonomy

The discoverers of ''Nesonektris'' placed it in the class Vetulicolida outside of any order or family. While a 2018 paper placed it in the Didazoonidae, it did not discuss the reassignment in the text. The reassignment has not been broadly accepted, even by sources that accept the paper's other reassignment (of '' Yuyuanozoon'' to Didazoonidae). A phylogenetic analysis by the discoverers of ''Nesonektris'' placed

Vetulicolia Vetulicolia is a group of bilaterian marine animals encompassing several extinct species from the Cambrian, and possibly Ediacaran, periods. As of 2023, the majority of workers favor placing Vetulicolians in the stem group of the Chordata, but ...

as the sister-group of Tunicata, but was unable to resolve any internal relationships within the group: However, several trees used to produce the cladogram above placed ''Nesonektris'' as an intermediate form between ''Banffia''-type and ''Vetulicola''-type forms, and a 2024 phylogenetic analysis agreed with that placement. ''Nesonektris'' is shown as the basal-most member of a paraphyletic

vetulicolida Vetulicolida is a class of vetulicolians. It consists of the order Vetulicolata (which contains the families Vetulicolidae and Didazoonidae) and the genus '' Nesonektris'', which is of uncertain placement. It is distinguished from the Banff ...

n grade, crownward from

Banffozoa Banffozoa (also called Heteromorphida) is an extinct class of bilaterians. Most workers place it in the Vetulicolia, but the protostome-like features of some members have motivated ongoing debate. Banffozoa consists of the order Banffiata (whi ...

but outside of either Vetulicolidae (labeled based on Li ''et al.'' 2018) or Didazoonidae. This study recovered Vetulicolia as a basal

evolutionary grade A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Phylogenetics The concept of evolutionary grades ...

along the chordate

stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...

, rather than next to the tunicates:

References

Works cited

* * * {{Taxonbar, from=Q20712554 Vetulicolia Paleozoic animals of Australia Fossils of Australia Paleontology in South Australia Fossil taxa described in 2014