Vetulicolia

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Vetulicolia
Temporal range: about 520–501  Ma
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Cambrian Stage 3—Drumian (Possible Ediacaran record) [1]
Vetulicola cuneata uetsurikora kunieta 1.jpg
Vetulicola rectangulata restoration.jpg
Didazoon haoae.jpg
Restorations and fossils of vetulicolians
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade?:† Vetulicolia
Shu et al. 2001
Type species
† Vetulicola cuneata
Hou, 1987
Classes

Vetulicolia is a group of bilaterian marine animals encompassing several extinct species from the Cambrian, [2] and possibly Ediacaran, [1] periods. As of 2023, the majority of workers favor placing Vetulicolians in the stem group of the Chordata, [3] but some continue to favor a more crownward placement as a sister group to the Tunicata. [2] It was initially erected as a monophyletic clade with the rank of phylum in 2001, [4] with subsequent work supporting its monophyly. [5] However, more recent research suggests that vetulicolians may be paraphyletic and form a basal evolutionary grade of stem chordates. [6]

Contents

Etymology

The taxon name, Vetulicolia, is derived from the type genus, Vetulicola , which is a compound Latin word composed of vetuli "old" and cola "inhabitant". It was named after Vetulicola cuneata , the first species of the group described in 1987. [7]

Description

Schematic of V. rectangulata pharynx and alimentary canal: dashed line; ventral food grooves: dotted line; gill slits: pink Ou et al. 2012 f07.jpg
Schematic of V. rectangulata
pharynx and alimentary canal: dashed line; ventral food grooves: dotted line; gill slits: pink

The vetulicolian body plan comprises two parts: a voluminous rostral (anterior) forebody, tipped with an anteriorly positioned mouth and lined with a lateral row of five round to oval-shaped openings on each side, which have been interpreted as gills (or at least orifices in the vicinity of the pharynx); and a caudal (posterior) section that primitively comprises seven body segments and functions as a tail. All vetulicolians lack preserved appendages of any kind, having no legs, feelers or even eye spots. [8] The area where the anterior and posterior parts join is constricted in most genera. [9] [10] Notochord-like structures have been found in some vetulicolian fossils. [11]

Ecology and lifestyle

From their superficially tadpole-like forms, leaf or paddle-shaped tails, and various degrees of streamlining, it is assumed that all vetulicolians discovered to date were swimming animals that spent much, if not all, of their time living in water. [12] Some groups, like the genus Vetulicola, were more streamlined (complete with ventral keels) than other groups, such as the tadpole-like Didazoonidae. [12]

Because all vetulicolians had mouths which had no features for chewing or grasping, it is assumed that they were not predators. [12] Since vetulicolians possessed gill slits, many researchers regard these organisms as planktivores. The sediment infills in the guts of their fossils have caused some to suggest that they were deposit feeders. This idea has been contested, as deposit feeders tend to have straight guts, whereas the hindguts of vetulicolians were spiral-shaped. Some researchers propose that the vetulicolians were "selective deposit-feeders" which actively swam from one region of the seafloor to another, while supplementing their nutrition with filter-feeding. [12]

Taxonomy and evolution

Banffozoans
Banffia constricta.JPG
Artist's reconstruction of Banffia constricta
Skeemella clavula KUMIP 310501.jpg
Fossil of Skeemella clavula

The phylum Vetulicolia was erected in 2001 to group the genera Vetulicola, Didazoon, and Xidazoon (later deemed a junior synonym of Pomatrum). [13] Prior to this the class Vetulicolida had been defined in 1997 to group Vetulicola with the previously enigmatic genus Banffia due to its similar two-part construction, as well as apparent gill slits in a newly discovered specimen. [14] Further work split Banffia into a separate class called Banffozoa, which was soon expanded to encompass similar species such as Heteromorphus. [15] While subsequent studies supported the monophyly of Vetulicolia, it has also been noted that this would preclude vetulicolians representing a stepwise development of deuterostome characteristics, as the genus with the most such characteristics, Vetulicola, is one of the most derived in the group. [13]

A 2024 phylogenetic analysis by Mussini and colleagues found vetulicolians to be a paraphyletic group of stem-chordates, lying outside a clade formed by Yunnanozoon , Cathaymyrus , Pikaia and crown-chordates. [6] This is in part due to the Cambroernida, which are basal stem-ambulacrarians, being discovered to share characteristics such as a terminal anus with vetulicolians, despite such characteristics previously being believed to be present in the last common ancestor of deuterostomes. [16] However, ascidian larvae have been noted to have endoderm extending to the terminal end, which could suggest that the ancestral tunicate also had a terminal anus. [11]

Other possible placements are suggested by the Centroneuralia hypothesis, which features a paraphyletic Deuterostomia with chordates as the sister-group to protostomes. If proven true, pharyngeal slits would no longer require a deuterostome placement and vetulicolians could prove to be stem protostomes that lost the post-anal tail. In such a scenario, Banffozoa could be a more derived stem protostome group than Vetulicolida. [17]

Cladograms

The following cladograms show two possible placements of the Vetulicolia.

First, on the left, a monophyletic Vetulicolia is shown as the sister group to Tunicata, but with all internal relationships unresolved. [18]

Next, on the right, the two proposed classes are shown as the earlier (Banffozoa) and later (Vetulicolida) parts of the vetulicolian grade. [19] Within the Vetulicolida, the family Vetulicolidae as defined by Li et al. (2018) [20] is recovered as monophyletic, while the three widely accepted members of the Didazoonidae [21] are in a polytomy with the clade of crownward chordates.

Simplified from García-Bellido et al. (2014)
Chordata
Ambulacraria
Simplified from Mussini et al. (2024)
Chordata
(total group)
Ambulacraria
(total group)
"Banffozoa"
"Vetulicolida"

Classification

The following classification is taken from Li et al. (2018) [20] except where noted.

History of identification

Evidence for the presence of a pharynx and dorsal/ventral feeding gutters in vetulicolians, supporting their placement among the Deuterostomes. Click through for detailed description. Ou et al. 2012 f06.jpg
Evidence for the presence of a pharynx and dorsal/ventral feeding gutters in vetulicolians, supporting their placement among the Deuterostomes. Click through for detailed description.

The current consensus view is that vetulicolians are stem group chordates, although some researchers continue to raise other possibilities. [3] The possible identification of an endostyle bolstered theories of a tunicate affinity, but was later retracted, while the tentative identification of a notochord in Nesonektris and Vetulicola has further supported overall chordate affinities. [2] [11] Other characters that have been used to support a tunicate affinity include the limiting of the notochord to the tail and the presence of a stiff cuticle (tunic). [11]

Recent research has strengthened the arguments for placing vetulicolians in the chordate stem lineage rather than near the tunicates. Like vetulicolians, members of the basal ambulacrarian clade Cambroernida have a terminal anus rathre than a post-anal tail. Since Ambulacraria is the sister-group of the chordates within the deuterostomes, this suggests that the last common ancestor of both groups lacked a post-anal tail. [16] However, ascidian larvae have been noted to have endoderm extending to the terminal end, which could suggest that tunicates also lacked post-anal tails ancestrally. [11]

Some workers have questioned the inclusion of Banffozoa within this group due to their lack of gill slits and apparent gut diverticula, and have theorized that they may fit within Protostomia instead. [25] Skeemella , in particular, has been noted as having striking arthropod-like characteristics. [28] However, Herpetogaster , the most basal cambroernid, is thought to have non-serialized pores for pharyngial openings. If banffozoans are the most basal vetulicolians, This could explain why they also lack serialized pharyngeal structures. [16] Additionally, a comprehensive review of the Vetulicolia in 2007 did not find evidence of gut diverticula in their material while acknowledging the previous report regarding Banffia. [29] Shenzianyuloma has been interpreted as a vetulicolian with both a notochord (a definitively deuterostome trait) and gut diverticula. However, this fossil has is of unusual provenance (a "crystal and fossil vendor"), and has not yet been examined by other researchers. [30]

Protostomia
Deuterostomia
Adapted from cladograms in Aldridge et al. 2007, showing each possible placement for Vetulicolia considered in the paper; [31] note the presence of the Euchordata clade rather than the now-favored Olfactores.

Vetulicolians were thought to be stem arthropods when Vetulicola was first discovered, but around 2001 the focus of most theories shifted towards stem deuterostomes due to the discovery of pharyngial gill slits (a deuterostome characteristic), as well as the mounting evidence that vetuicolians have no appendages of any kind. [32] A theory grouping both vetulicolians and vetulocystids with Saccorhytus was disproven when the alleged pharyngial openings of Saccorhytus were shown to be remnants of spines that had broken off; the saccorhytids are now considered to be ecdysozoans. [33]

Related Research Articles

<span class="mw-page-title-main">Maotianshan Shales</span> Series of Early Cambrian deposits in the Chiungchussu Formation in China

The Maotianshan Shales (帽天山页岩) are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation, famous for their Konservat Lagerstätten, deposits known for the exceptional preservation of fossilized organisms or traces. The Maotianshan Shales form one of some forty Cambrian fossil locations worldwide exhibiting exquisite preservation of rarely preserved, non-mineralized soft tissue, comparable to the fossils of the Burgess Shale of British Columbia, Canada. They take their name from Maotianshan Hill in Chengjiang County, Yunnan Province, China.

<i>Yunnanozoon</i> Cambrian fossil chordate

Yunnanozoon lividum is an extinct species of bilaterian animal from the Lower Cambrian Chengjiang biota of Yunnan province, China. Its affinities have been long the subject of controversy.

<i>Vetulicola</i> Fossil genus of marine animal

Vetulicola is an extinct genus of marine animal discovered from the Cambrian of China. It is the eponymous member of the enigmatic phylum Vetulicolia, which is of uncertain affinities but may belong to the deuterostomes. The name was derived from Vetulicola cuneata, the first species described by Hou Xian-guang in 1987 from the Lower Cambrian Chiungchussu Formation in Chengjiang, China.

<i>Didazoon</i> Cambrian age animal

Didazoon haoae is an extinct species of vetulicolid vetulicolian described by Shu, et al. based on fossils found in the Qiongzhusi (Chiungchussu) Formation, Yu'anshan Member, Lower Cambrian, in the Dabanqiao area (Kunming), about 60 km northwest of Chengjiang, China.

<i>Pomatrum</i> Cambrian age animal

Pomatrum is an extinct vetulicolian, the senior synonym of Xidazoon; the latter taxon was described by Shu, et al. (1999) based on fossils found in the Qiongzhusi (Chiungchussu) Formation, Yu'anshan Member, Lower Cambrian, Haikou, (Kunming), about 50 km west of Chengjiang, China.

<i>Banffia</i> Extinct genus of Cambrian organisms

Banffia is a genus of animals described from Middle Cambrian fossils. The genus commemorates Banff, Alberta, near where the first fossil specimens were discovered. Its placement in higher taxa is controversial, with it mostly being considered to be a member of the enigmatic phylum Vetulicolia.

<span class="mw-page-title-main">Vetulicolida</span> Extinct Cambrian group of marine animals

Vetulicolida is a class of vetulicolians. It consists of the order Vetulicolata and the genus Nesonektris, which is of uncertain placement. It is distinguished from the Banffozoa by the number and size of posterior segments as well as features of the anterior section.

<span class="mw-page-title-main">Vetulicolidae</span> Extinct Cambrian family of vetulicolian animals

Vetulicolidae is a vetulicolian family from the Cambrian Stage 3 Maotianshan Shale and Sirius Passet Lagerstätte that consists of Vetulicola, Beidazoon, and Ooedigera. It is distinguished from the Didazoonidae by a harder body wall and the lack of an oral disc.

<span class="mw-page-title-main">Didazoonidae</span> Extinct Cambrian family of vetulicolid animals

Didazoonidae is a vetulicolian family within the order Vetulicolata. It is charaterized by a relatively thin-walled, non-biomineralized body and a large, round anterior opening surrounded by an oral disc. It may be paraphyletic, even if the phylum Vetulicolia is monophyletic.

<span class="mw-page-title-main">Banffozoa</span> Extinct Cambrian group of marine animals

Banffozoa 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 as well as a dwarf "Form A" that has not been formally described or named. Skeemella has been placed incertae sedis in this class, but has more recently been placed with the Banffiidae. Banffozoa may be paraphyletic even if Vetulicolia is monophyletic.

<i>Yuyuanozoon</i> Cambrian genus of animals

Yuyuanozoon magnificissimi, from the Cambrian Stage 3 Chengjiang lagerstatte, is the largest known vetulicolian, with specimens up to 20 cm in length compared to 5–14 cm for other vetulicolian species.

<i>Vetulicola cuneata</i> Extinct species of animal

Vetulicola cuneata is a species of extinct marine animal from the Early Cambrian Chengjiang biota of China. It was described by Hou Xian-guang in 1987 from the Lower Cambrian Chiungchussu Formation, and became the first animal under an eponymous phylum Vetulicolia.

<i>Ooedigera</i> Ovoid Cambrian animal with a bulbous tail

Ooedigera peeli is an extinct vetulicolian from the Early Cambrian of North Greenland. The front body was flattened horizontally, oval-shaped, likely bearing a reticulated or anastomosing pattern, and had 5 evenly-spaced gill pouches along the midline. The tail was also bulbous and flattened horizontally, but was divided into 7 plates connected by flexible membranes, allowing movement. Ooedigera likely swam by moving side-to-side like a fish. It may have lived in an oxygen minimum zone alongside several predators in an ecosystem based on chemosynthetic microbial mats, and was possibly a deposit or filter feeder living near the seafloor.

<i>Vetulicola rectangulata</i> Extinct animal from Cambrian of the Chengjiang biota of China

Vetulicola rectangulata is a species of extinct animal from the Early Cambrian of the Chengjiang biota of China. Regarded as a deuterostome, it has characteristic rectangular anterior body on which the posterior tail region is attached. It was described by Luo Huilin and Hu Shi-xue in 1999.

<i>Nesonektris</i> Extinct genus of Cambrian Era Chordate

Nesonektris aldridgei is an extinct vetulicolian from the Late Botomian-aged Emu Bay Shale Lagerstätte in Kangaroo Island, Australia. So far, it is the fourth described vetulicolian that is not restricted to the Maotianshan Shales.

<i>Beidazoon</i> Extinct species of Cambrian organism

Beidazoon venustum is a marine deuterostome from the group Vetulicolia. It originates from the lower Cambrian Chengjiang biota of Yunnan Province, China, and was discovered in 2005. It is known as the smallest described vetulicolian, and for its surface being covered in many small nodes.

<span class="mw-page-title-main">Banffiidae</span> Extinct Cambrian family of animals

Banfiidae is a family of extinct banffozoan animals from North America and China. The family name is sometimes spelt Banffidae. It includes Banffia, Heteromorphus, and possibly Skeemella. The family may be paraphyletic. The family may be paraphyletic. A Heteromorphus-like dwarf "Form A" is allied with this group at the class level, but has not been formally described or assigned to this family.

<i>Shenzianyuloma</i> Species of vetulicolian invertebrate

Shenzianyuloma is an extinct genus of vetulicolian represented by a single species, Shenzianyuloma yunnanense, from the Maotianshan Shale during Stage 3 of the Cambrian period. It is notable for having a compact body shape akin to that of an angelfish. It's exact phylogenetic position is unclear, and it was not included in a 2024 phylogenetic analysis of vetulicolians.

Cheungkongella is a fossil organism from the lower Cambrian Chengjiang lagerstatte, the affinity of which has been the subject of debate. It was announced as a "probable" tunicate, although this affinity was later disputed in a paper announcing the discovery of Shankouclava, also from Chengjiang, as the oldest known tunicate. Cheungkongella has been accepted as a distinct taxon and possible tunicate by multiple workers not involved in its discovery, but the dispute remains unresolved.

<i>Heteromorphus</i> Extinct genus of Cambrian organisms

Heteromorphus is an extinct genus of banffiid from the lower Cambrian Chengjiang lagerstatte. It contains one broadly accepted species, Heteromorphus confusus, as well as a proposed junior synonym, Heteromorphus longicaudatus that may prove to be a separate species as additional specimens are examined. A much smaller species labeled "Form A" is allied with Heteromorphus at the class level but has not been formally described or assigned to Heteromorphus itself.

References

  1. 1 2 3 Liu et al. 2024 (Note that while the paper leaves the classification of Alienum uncertain in its systematic paleontology, it also states on page 4 that "Alienum velamenus might belong to a clade of extinct Vetulicolia that formed during the early evolution of Vetulicola." It is tentatively included here on these grounds.)
  2. 1 2 3 Gee 2018 , pp. 188–189
  3. 1 2 Onai et al. 2023 , p. 202
  4. ↑ Shu et al. 2001
  5. ↑ Aldridge et al. 2007 , p. 154
  6. 1 2 Mussini et al. 2024
  7. ↑ Lacalli 2002 , p. 208
  8. ↑ Chen et al. 2003
  9. ↑ Conway Morris et al. 2015 , pp. 3–4
  10. ↑ Aldridge et al. 2007 , p. 133
  11. 1 2 3 4 5 6 García-Bellido et al. 2014
  12. 1 2 3 4 Aldridge et al. 2007
  13. 1 2 Hou et al. 2017 , p. 272
  14. ↑ Chen & Zhou 1997 , pp. 95–96
  15. ↑ Aldridge et al. 2007 , pp. 151–152(Note: See Banffozoa#Preference for Banffozoa over Heteromorphida regarding whether Banffozoa or Heteromorphida is the preferred name.)
  16. 1 2 3 Mussini et al. 2024 , p. 6
  17. ↑ Kapli et al. 2021 , p. 6
  18. ↑ García-Bellido et al. 2014 , p. 9
  19. ↑ Mussini et al. 2024 , pp. 6–7
  20. 1 2 3 Li et al. 2018 , pp. 1083–1084(Note: See Banffozoa#Preference for Banffozoa over Heteromorphida regarding the use of Heteromorphida in this classification.)
  21. ↑ "†family Didazoonidae Shu and Han 2001". Paleobiology Database. Retrieved December 8, 2024.
  22. ↑ Shu 2005 , p. 2346
  23. ↑ McMenamin 2019 , p. 11
  24. ↑ Shu 2005 , p. 2349(Note: Shu assigned "Form A" to class Heteromorphida, but not to Heteromorphus on account of its very small size, highly sclerotized shell, and details of the anterior section; no order or family was specified; see also Banffozoa#Preference for Banffozoa over Heteromorphida)
  25. 1 2 Caron 2005
  26. ↑ "†family Banffiidae Caron 2006". Paleobiology Database. Retrieved 2024-12-17.
  27. ↑ "†Nesonektris García-Bellido et al. 2014". Paleobiology Database. Retrieved December 8, 2024.
  28. ↑ Shu 2005 , p. 2352
  29. ↑ Aldridge et al. 2007 , pp. 151–152
  30. ↑ McMenamin 2019 , pp. 15–16
  31. ↑ Aldridge et al. 2007, pp. 156, 158
  32. ↑ Giribet & Edgecombe 2020 , p. 105
  33. ↑ Liu et al. 2022

Works cited

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