Hallucigenia

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Hallucigenia
Temporal range: Cambrian Stage 3–Middle Cambrian
USNM PAL 83935 Hallucigenia sparsa Image 1.jpg
Fossil holotype of Hallucigenia sparsa from the Burgess Shale
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
(unranked): Panarthropoda
Phylum:† "Lobopodia"
Clade:† Hallucishaniids
Family:† Hallucigeniidae
Genus:† Hallucigenia
Conway Morris, 1977 [1]
Species
  • H. sparsa(Walcott, 1911) (type)
  • H. fortisHou & Bergström, 1995 [2]
  • H. hongmeiaSteiner et al 2012 [3]
Synonyms

Canadia sparsa

Hallucigenia is a genus of lobopodian known from Cambrian aged fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. [4] The generic name reflects the type species' unusual appearance and eccentric history of study; when it was erected as a genus, H. sparsa was reconstructed as an enigmatic animal upside down and back to front. [1] Lobopodians are a grade of Paleozoic panarthropods from which the velvet worms, water bears, and arthropods arose. [5] [4]

Contents

Description

Reconstructions of H. fortis, H. hongmeia, and H. sparsa in scale. 20210000 Hallucigenia diagrammatic reconstruction.png
Reconstructions of H. fortis, H. hongmeia, and H. sparsa in scale.

Hallucigenia is a 0.5–5.5 cm (3⁄16–2+3⁄16 in) [6] [7] long tubular animal with up to ten pairs of slender legs (lobopods). The first 2 or 3 leg pairs are slender and featureless, [6] [7] [8] while the remaining 7 or 8 pairs each terminate with 1 or 2 claws. [9] [7] [8] Above the trunk region are 7 pairs of rigid conical sclerites (spines) corresponding to the 3rd–9th leg pairs. [9] [6] [7] [8] The trunk is either featureless (H. sparsa) [7] or divided by heteronomous annulations (H. fortis [2] and H. hongmeia). [9] [10] The "head" and "tail" end of the animal are difficult to identify; one end extends some distance beyond the legs and often droops down as if to reach the substrate. Some specimens display traces of a simple gut. [7]

Research in the mid-2010s clarified that the longer end is a head with anteroventral mouth and at least a pair of simple eyes. [11] [6] [7] The shape of head differs between species – elongated in H. sparsa, rounded in H. fortis, [6] [7] while those of H. hongmeia remain unknown. [9] At least in H. sparsa, the head possesses radial teeth and pharyngeal teeth within the front of the gut. [7] [12]

Hallucigenia's spines are made up of one to four nested elements. The spine surface of H. sparsa is covered in an ornament of minute triangular 'scales', [13] while the spine surface of Hallucigenia hongmeia is a net-like texture of microscopic circular openings, which can be interpreted as the remains of Papillae. [9]

History of study

Various interpretations of Hallucigenia sparsa throughout the history of study 20210917 Hallucigenia sparsa interpretations.png
Various interpretations of Hallucigenia sparsa throughout the history of study

Hallucigenia sparsa was originally described by Charles Walcott as a species of the polychaete worm Canadia . [14] In his 1977 redescription of the organism, Simon Conway Morris recognized the animal as something quite distinct, for which he proposed the name Hallucigenia because of the "bizarre and dream-like appearance of the animal." No specimen was available that showed both rows of legs, so Conway Morris reconstructed the animal walking on its spines, with its single row of legs interpreted as tentacles on the animal's back. A dark stain at one end of the animal was interpreted as a featureless head. Only the forward tentacles could easily reach to the 'head', meaning that a mouth on the head would have to be fed by passing food along the line of tentacles. Conway Morris suggested that a hollow tube within each of the tentacles might be a mouth. [1] This raised questions, such as how it would walk on the stiff legs, but it was accepted (with reservations) as the best available interpretation. [15]

Specimen with obvious spines HallucigeniaSparsa-ROM-June11-10.jpg
Specimen with obvious spines

An alternative interpretation considered Hallucigenia to be an appendage of a larger, unknown animal. There had been precedent for this, as Anomalocaris had been originally identified as three separate creatures before being identified as a single huge (for its time) 34.1-centimetre (1.12 ft) to 37.8-centimetre-long (1.24 ft) creature. [15]

In 1991, Lars Ramskold and Hou Xianguang, working with additional specimens of a "hallucigenid", Microdictyon , from the lower Cambrian Maotianshan shales of China, reinterpreted Hallucigenia as a lobopodian, a legged worm-like taxon which were still thought to be exclusively related to onychophoran (velvet worm) at that time. [16] [5] They inverted it, interpreting the tentacles, which they believe to be paired, as walking structures and the spines as protective. [16] Further preparation of fossil specimens showed that the 'second legs' were buried at an angle to the plane along which the rock had split, and could be revealed by removing the overlying sediment. [17] Ramskold and Hou also believe that the blob-like 'head' is actually a stain that appears in many specimens, not a preserved portion of the anatomy. [16] This stain may be an artifact of decomposition. [7]

Affinity

Restoration of H. sparsa H. sparsa.jpg
Restoration of H. sparsa
External videos
Nuvola apps kaboodle.svg Hallucigenia: The worm with the missing head Nature Video, YouTube.

Since the revisions around 1990s, [16] [17] [2] Hallucigenia is unquestionably a lobopodian panarthropod, although the relationship with other panarthropods remains controversial. Hallucigenia has long been interpreted as a stem-group onychophoran (velvet worms) – a position that has found support from multiple phylogenetic analysis. [10] [7] [18] [19] A key character demonstrating this affinity is the cone-in-cone construction of Hallucigenia claws, a feature shared only with modern onychophorans. [10] On the other hand, some analysis rather support the position of Hallucigenia as a basal panarthropod outside of onychophoran stem-group. [20] [8] [21] Under this scenario, the cone-in-cone structure shared between Hallucigenia and onychophorans represent panarthropod plesiomorphy. [8] [21] Hallucigenia also exhibits certain characters inherited from the ancestral ecdysozoan, but lost in the modern onychophorans – in particular its distinctive foregut armature. [7]

Below is a cladogram for Hallucigenia according to Yang et al., 2015: [18]

Microdictyon

Cardiodictyon

Hallucigenia sparsa

Hallucigenia fortis

Diversity

In 2002, Desmond Collins informally suggested that new Hallucigenia fossils from the Burgess Shale showed male and female forms, one with "a rigid trunk, robust neck and a globular head" and the other thinner, and with a small head. [22]

Three species of Hallucigenia have been described. The first specimen, Hallucigeniasparsa, was discovered in Canada. Two other species, H. fortis and H. hongmeia, are represented by the Maotianshan Shales' fossils of Chengjiang. [2] [3]

Distribution

Hallucigenia was first described from the Burgess Shale in southeastern British Columbia, Canada. 109 specimens of Hallucigenia are known from the Greater Phyllopod bed, where they comprise 0.3% of the community. [23] Hallucigenia also forms a minor component of Chinese lagerstätten. Isolated hallucigeniid spines, however, are widely distributed in a range of Cambrian deposits, preserved both as carbonaceous and mineralized fossils. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Lobopodia</span> Group of extinct worm-like animals with legs

Lobopodians are members of the informal group Lobopodia, or the formally erected phylum Lobopoda Cavalier-Smith (1998). They are panarthropods with stubby legs called lobopods, a term which may also be used as a common name of this group as well. While the definition of lobopodians may differ between literatures, it usually refers to a group of soft-bodied, marine worm-like fossil panarthropods such as Aysheaia and Hallucigenia. However, other genera like Kerygmachela and Pambdelurion are often referred to as “gilled lobopodians”.

<i>Opabinia</i> Extinct stem-arthropod species found in Cambrian fossil deposits

Opabinia regalis is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte of British Columbia. Opabinia was a soft-bodied animal, measuring up to 7 cm in body length, and its segmented trunk had flaps along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a clawed proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using the proboscis to seek out small, soft food. Fewer than twenty good specimens have been described; 3 specimens of Opabinia are known from the Greater Phyllopod bed, where they constitute less than 0.1% of the community.

<i>Aysheaia</i> Extinct genus of soft-bodied animals

Aysheaia is an extinct genus of soft-bodied lobopodian, known from the Middle Cambrian Burgess Shale of British Columbia, Canada

<i>Xenusion</i> Extinct genus of panarthropods

Xenusion auerswaldae is an early lobopodian known from two specimens found in glacial erratics on the Baltic coast of Germany. They probably originated in the Kalmarsund Sandstone of Southern Sweden, which was deposited in the Lower Cambrian. It is the oldest currently known lobopodian with soft body fossils.

<span class="mw-page-title-main">Panarthropoda</span> Animal taxon

Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada and Onychophora. Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphyletic group where the last common ancestor and basal members (stem-group) of each extant panarthropod phylum are thought to have risen. However the term "Lobopodia" is sometimes expanded to include tardigrades and onychophorans as well.

<span class="mw-page-title-main">Dinocaridida</span> Extinct class of basal arthropods

Dinocaridida is a proposed fossil taxon of basal arthropods, which flourished during the Cambrian period and survived up to Early Devonian. Characterized by a pair of frontal appendages and series of body flaps, the name of Dinocaridids refers to the suggested role of some of these members as the largest marine predators of their time. Dinocaridids are occasionally referred to as the 'AOPK group' by some literatures, as the group compose of Radiodonta, Opabiniidae, and the "gilled lobopodians" Pambdelurion and Kerygmachelidae. It is most likely paraphyletic, with Kerygmachelidae and Pambdelurion more basal than the clade compose of Opabiniidae, Radiodonta and other arthropods.

<i>Pambdelurion</i> Extinct genus of Arthropod

Pambdelurion is an extinct genus of panarthropod from the Cambrian aged Sirius Passet site in northern Greenland. Like the morphologically similar Kerygmachela from the same locality, Pambdelurion is thought to be closely related to arthropods, combining characteristics of "lobopodians" with those of primitive arthropods.

<i>Parapeytoia</i> Extinct genus of arthropods

Parapeytoia is a genus of Cambrian arthropod. The type and only described species is Parapeytoia yunnanensis, lived over 518 million years ago in the Maotianshan shales of Yunnan, China. Unidentified fossils from the same genus also had been discovered from the nearby Wulongqing Formation.

<span class="mw-page-title-main">Megacheira</span> Extinct class of arthropods

Megacheira is an extinct class of predatory arthropods defined by their possession of spined "great appendages". Their taxonomic position is controversial, with studies either considering them stem-group euarthropods, or stem-group chelicerates. The homology of the great appendages to the cephalic appendages of other arthropods is also controversial. Uncontested members of the group were present in marine environments worldwide from the lower Cambrian to the upper Ordovician.

<i>Diania</i> Extinct genus of Cambrian animals

Diania is an extinct genus of lobopodian panarthropod found in the Lower Cambrian Maotianshan shale of China, represented by a single species - D. cactiformis. Known during its investigation by the nickname "walking cactus", this organism belongs to a group known as the armoured lobopodians, and has a simple worm-like body with robust, spiny legs. Initially, the legs were thought to have a jointed exoskeleton and Diania was suggested to be evolutionarily close to early arthropods, but many later studies have rejected this interpretation.

<span class="mw-page-title-main">Luolishaniidae</span> Extinct family of worm-like animals

The Luolishaniidae or Luolishaniida are a group of Cambrian and Ordovician lobopodians with anterior 5 or 6 pairs of setiferous lobopods. Most luolishaniids also have posterior lobopods each with a hooked claws, and thorn-shaped sclerites arranged as three or more per trunk segment. The type genus is based on Luolishania longicruris Hou and Chen, 1989, from the Chengjiang Lagerstatte, South China. They are presumed to have been benthic suspension or filter feeders.

Collinsium was a genus of lobopodian from the Early Cambrian. It is represented by a single fossil species, Collinsium ciliosum, found in the Xiaoshiba Lagerstätte of China. Similar to the later Hallucigenia it was a small worm-like creature with spikes along its back and feeding tentacles near its head. Unlike Hallucigenia, Collinsium had 9 walking appendages and 6 fine anterior appendages. Its body was covered in hair-like papillae and its fine anterior appendages were lined with setae. The generic name honors paleontologist Desmond Collins.

<i>Onychodictyon</i> Extinct genus of worms

Onychodictyon is a genus of extinct lobopodian known from the Lower Cambrian Chengjiang Maotianshan Shales in the Yunnan Province in China. It was characterized by a stout body covered by fleshy papillae and pairs of sclerotized plates with spines, representing part of the diverse "armoured lobopodians" alongside similar forms such as Microdictyon and Hallucigenia.

<i>Collinsovermis</i> Extinct genus of lobopodians

Collinsovermis is a genus of extinct panarthropod belonging to the group Lobopodia and known from the middle Cambrian Burgess Shale in British Columbia, Canada. It is monotypic having only one species, Collinsovermis monstruosus. After its initial discovery in 1983, Desmond H. Collins popularised it as a unique animal and was subsequently dubbed "Collins' monster" for its unusual super armoured body. The formal scientific description and name were given in 2020. A similar lobopodian is known from the Emu Bay Shale, however it remains unnamed.

<i>Acinocricus</i> Extinct genus of lobopodians

Acinocricus is a genus of extinct panarthropod belonging to the group Lobopodia and known from the middle Cambrian Spence Shale of Utah, United States. As a monotypic genus, it has one species Acinocricus stichus. The only lobopodian discovered from the Spence Shale, it was described by Simon Conway Morris and Richard A. Robison in 1988. Owing to the original fragmentary fossils discovered since 1982, it was initially classified as an alga, but later realised to be an animal belonging to Cambrian fauna.

Luolishania is an extinct genus of lobopodian panarthropod and known from the Lower Cambrian Chiungchussu Formation of the Chengjiang County, Yunnan Province, China. A monotypic genus, it contains one species Luolishania longicruris. It was discovered and described by Hou Xian-Guang and Chen Jun-Yuan in 1989. It is one of the superarmoured Cambrian lobopodians suspected to be either an intermediate form in the origin of velvet worms (Onychophora) or basal to at least Tardigrada and Arthropoda. It is the basis of the family name Luolishaniidae, which also include other related lobopods such as Acinocricus, Collinsium, Facivermis, and Ovatiovermis. Along with Microdictyon, it is the first lobopodian fossil discovered from China.

<i>Thanahita</i> Extinct genus of Lobopodian

Thanahita is a genus of extinct lobopodian and known from the middle Silurian Herefordshire Lagerstätte at the England–Wales border in UK. It is monotypic and contains one species, Thanahita distos. Discovered in 2018, it is estimated to have lived around 430 million years ago and is the only known extinct lobopodian in Europe, and the first Silurian lobopodian known worldwide.

<span class="mw-page-title-main">Hallucigeniidae</span> Extinct family of lobopodian worms

Hallucigeniidae is a family of extinct worms belonging to the group Lobopodia that originated during the Cambrian explosion. It is based on the species Hallucigenia sparsa, the fossil of which was discovered by Charles Doolittle Walcott in 1911 from the Burgess Shale of British Columbia. The name Hallucigenia was created by Simon Conway Morris in 1977, from which the family was erected after discoveries of other hallucigeniid worms from other parts of the world. Classification of these lobopods and their relatives are still controversial, and the family consists of at least four genera.

Carbotubulus is a genus of extinct worm belonging to the group Lobopodia and known from the Carboniferous Carbondale Formation of the Mazon Creek area in Illinois, US. A monotypic genus, it contains one species Carbotubulus waloszeki. It was discovered and described by Joachim T. Haug, Georg Mayer, Carolin Haug, and Derek E.G. Briggs in 2012. With an age of about 300 million years, it is the first long-legged lobopodian discovered after the period of Cambrian explosion.

<i>Lenisambulatrix</i> Extinct genus of Lobopodian

Lenisambulatrix is a genus of extinct worm belonging to the group Lobopodia and known from the Lower Cambrian Maotianshan shale of China. It is represented by a single species L. humboldti. The incomplete fossil was discovered and described by Qiang Ou and Georg Mayer in 2018. Due to its missing parts, its relationship with other lobopodians is not clear. It shares many structural features with another Cambrian lobopodian Diania cactiformis, a fossil of which was found alongside it.

References

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  10. 1 2 3 Smith, M. R.; Ortega-Hernández, J. (2014). "Hallucigenia's onychophoran-like claws and the case for Tactopoda" (PDF). Nature. 514 (7522): 363–366. Bibcode:2014Natur.514..363S. doi:10.1038/nature13576. PMID   25132546. S2CID   205239797.
  11. ↑ Ma, Xiaoya; Hou, Xianguang; Aldridge, Richard J.; Siveter, David J.; Siveter, Derek J.; Gabbott, Sarah E.; Purnell, Mark A.; Parker, Andrew R.; Edgecombe, Gregory D. (1 September 2012). "Morphology of Cambrian lobopodian eyes from the Chengjiang Lagerstätte and their evolutionary significance". Arthropod Structure & Development. 41 (5): 495–504. doi:10.1016/j.asd.2012.03.002. ISSN   1467-8039. PMID   22484085.
  12. ↑ Morelle, Rebecca, Face of bizarre sea creature Hallucigenia revealed, BBCNews, Science and Environment, 2015.06.25
  13. 1 2 Caron, Jean-Bernard; Smith, Martin R.; Harvey, Thomas H. P. (September 2013). "Beyond the Burgess Shale: Cambrian microfossils track the rise and fall of hallucigeniid lobopodians". Proceedings of the Royal Society B: Biological Sciences. 280 (1767): 20131613. doi:10.1098/rspb.2013.1613. PMC   3735267 . PMID   23902914.
  14. ↑ WALCOTT, C. 1911. Cambrian Geology and Paleontology II. Middle Cambrian annelids. Smithsonian Miscellaneous Collections, 57(5): 109–145.
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  19. ↑ Zhang, Xi-Guang; Smith, Martin R.; Yang, Jie; Hou, Jin-Bo (2016). "Onychophoran-like musculature in a phosphatized Cambrian lobopodian". Biology Letters. 12 (9): 20160492. doi:10.1098/rsbl.2016.0492. ISSN   1744-9561. PMC   5046927 . PMID   27677816.
  20. ↑ Caron, Jean-Bernard; Aria, Cédric (31 January 2017). "Cambrian suspension-feeding lobopodians and the early radiation of panarthropods". BMC Evolutionary Biology. 17 (1): 29. doi: 10.1186/s12862-016-0858-y . ISSN   1471-2148. PMC   5282736 . PMID   28137244.
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  23. ↑ Caron, Jean-Bernard; Jackson, Donald A. (October 2006). "Taphonomy of the Greater Phyllopod Bed community, Burgess Shale". PALAIOS. 21 (5): 451–65. Bibcode:2006Palai..21..451C. doi:10.2110/palo.2003.P05-070R. JSTOR   20173022. S2CID   53646959.

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