Megacheira

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Megacheira
Temporal range: Cambrian Stage 3–Katian
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[1] Possible Silurian and Devonian records
20191028 Megacheirans Leanchoilia Haikoucaris Yohoia Fortiforceps.png
Alalcomenaeus (top left), Fortiforceps (top right), Haikoucaris (middle), Leanchoilia (bottom left) and Yohoia (bottom right).
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class:† Megacheira
Hou and Bergström, 1997
Groups

See text

Megacheira ("great hands", also historically great appendage arthropods) is an extinct class of predatory arthropods defined by their possession of spined "great appendages". [2] Their taxonomic position is controversial, with studies either considering them stem-group euarthropods, or stem-group chelicerates. [3] [4] 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.

Contents

Morphology

20190911 Megacheira Great Appendages.png
Comparison of megacheiran great appendages
20210701 Yohoia tenuis great appendage mobility.gif
Movement range of the great appendage of Yohoia
3D model of Tanglangia longicaudata. en=endopod, ex=exopod Tanglangia longicaudata reconstruction.png
3D model of Tanglangia longicaudata. en=endopod, ex=exopod


Megacheirans are defined by their possession of uniramous "great appendages", which are their first pair of head appendages. The first one or two proximalmost segments/podomeres are spineless (it has been argued that the supposed first of the two proximal podomeres is actually an arthrodial membrane [5] ), while the remaining 3–4 more distal podomeres each typically bear a single upward pointing spine attached towards the distal end of the segment, with the spineless proximal segment/s typically being connected to the spined distal segments by an elbow-like joint, which curled upwards. [6] [5] The great appendages have been interpreted as raptorial limbs involved in predation, with those of some genera such as Yohoia being structurally comparable to the raptorial maxillipeds of mantis shrimp. [6] The spines on the great appendages of leanchoilid megacheirans such as Leanchoilia and Yawunik are elongated into flagella-like structures, suggesting a sensory role alongside predatory function. [7] The body is divided into the head and the trunk. The biramous limbs of megacheirans are homonomous (i.e. having little differentiation from each other), with endopods typically divided into seven segments/podomeres, and paddle-shaped exopods, which are fringed with thin lamellae. The morphology of the terminal telson segment is variable. [5] The biramous limbs of at least some megacheirans have been suggested bear exites. [8]

Taxonomy

Several subdivisions within the group are recognised including Jianfengiidae (including Fortiforceps , Jianfengia , Sklerolibyon and possibly Parapeytoia ) which are known from the Early Cambrian of China, as well as the Cheiromorpha (containing at least Yohoia , Haikoucaris , and Leanchoiliidae), known with certainty from the Early-Mid Cambrian of North America, China and Australia, which is distinguished from Jianfengiidae by having a fewer number of body segments (20+ in Jianfengiidae, as compared to typically only 11 to 13 in Cheiromorpha). The monophyly of Megacheira is uncertain, with some studies recovering the group as paraphyletic. [5] The latest unambiguous megacheiran is the leanchoiliid Lomankus from the Upper Ordovician of North America. [9]

Parapeytoia from the Cambrian of China which formerly misinterpreted as a radiodont was later suggested to be a member of this group. [10] [11] [12] Possible megacheirans include Enalikter described from the Silurian of the United Kingdom, and Bundenbachiellus from the Early Devonian of Germany; [13] [14] due to their possession of great appendage-like cephalic appendages. However, their relationship to megacheirans has been questioned, due to the uncertain homology of their appendages. [15] Kootenichela has been suggested to be a chimera of various arthropod taxa. [5] Previous inclusion of some "bivalved" genera such as Forfexicaris , Ovalicephalus , and Occacaris to Megacheira was questioned by later investigations. [16] The Late Cambrian Orsten taxon Oelandocaris typically considered to be a crustacean relative, has also been suggested in some studies to be a megacheiran. [17]

List of genera

Relationship to other arthropods

Megacheirans are either suggested to be stem-group chelicerates or stem-group arthropods, [3] with the former hypothesis based on the chelicerae-like morphology of the great appendages [18] [19] [20] alongside neuroanatomy [21] and the presence of a reduced labrum [22] resembling those of modern chelicerates, it being argued that chelicerae and the great appendages are homologous structures. [23] Other studies suggest that the megacheirans are stem-group arthropods based on the argument that the great appendages are homologous to the frontal appendages of stem-group arthropods like Isoxys and radiodonts. This identity is disputed, with other authors suggesting that the frontal appendages of radiodonts are homologous to the labrum of modern arthropods. [5]

Related Research Articles

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

Yohoia is an extinct genus of megacheiran arthropod from the Cambrian period that has been found as fossils in the Burgess Shale formation of British Columbia, Canada. The type species, Yohoia tenuis, was described in 1912 by Walcott, who considered it an anostracan crustacean. 711 specimens of Yohoia are known from the Greater Phyllopod bed, where they comprise 1.35% of the community. In 2015, Conway Morris et al. reported another species, Y. utahana, from the Marjum Formation, Utah.

<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>Jianfengia</i> Extinct genus of arthropods

Jianfengia is an extinct genus of Middle Cambrian (Atdabanian) megacheiran arthropod found in the Maotianshan Shale Lagerstätte of China. It contains the single species Jianfengia multisegmentalis. The body is extremely elongated, though the animal itself was relatively small at less than 4 centimetres (1.6 in) in length. The head has a pair of stalked eyes, a hypostome/labrum complex, a pair of great appendages with five podomeres, and four pairs of biramous limbs. The maximum known number of trunk segments is 27, though most known specimens have 20, which are associated with pairs of biramous appendages, and the body ends with a telson spine. It has been placed as a member of the family Jiangfengiidae, alongside Fortiforceps and Sklerolibyon as well as possibly Parapeytoia.

<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.

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

Fuxianhuia is a genus of Lower Cambrian fossil arthropod known from the Chengjiang fauna in China. Its purportedly primitive features have led to its playing a pivotal role in discussions about the euarthropod stem group. Nevertheless, despite being known from many specimens, disputes about its morphology, in particular its head appendages, have made it one of the most controversial of the Chengjiang taxa, and it has been discussed extensively in the context of the arthropod head problem.

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

Chuandianella ovata is an extinct bivalved arthropod that lived during Cambrian Stage 3 of the Early Cambrian. It is the only species classified under the genus Chuandianella. Its fossils were recovered from the Chengjiang Biota in Yunnan, China.

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

Haikoucaris is a genus of megacheiran arthropod that contains the single species Haikoucaris ercaiensis. It was discovered in the Cambrian Chengjiang biota of China.

<span class="mw-page-title-main">Kunmingella</span>

Kunmingella is genus of Cambrian bradoriid from the Chengjiang biota, containing the single species K. douvillei. Kunmingella had 12 appendages, including a pair of antennae as well pairs of biramous limbs, including four anterior pairs of appendages bearing double rows of endites on their endopods, and a posterior 5 with only a single row of endites, as well as two terminal pairs of uniramous limbs. Eggs have been found preserved attached to the posteriormost three pairs of biramous limbs, suggesting it engaged in brood care. Around 50–80 eggs, each around 150–180 μm across were attached in total.

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

Occacaris oviformis is an extinct nektonic predatory arthropod from the Lower Cambrian Maotianshan shale Lagerstätte. It bears a superficial resemblance to the Cambrian arthropod, Canadaspis, though, was much smaller, and had a pair of "great appendages", with which it may have grasped prey. It was originally considered to belong to Megacheira, however it is questioned in later study.

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

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 used for a variety of functions. Radiodonts are among the earliest large predators, but they also included sediment sifters and filter feeders. Some of the most famous species of radiodonts are the Cambrian taxa Anomalocaris canadensis, Hurdia victoria, Peytoia nathorsti, Titanokorys gainesi, Cambroraster falcatus and Amplectobelua symbrachiata. The later surviving members include the subfamily Aegirocassisinae from the Early Ordovician of Morocco and the Early Devonian member Schinderhannes bartelsi from Germany.

<i>Cucumericrus</i> Extinct genus of arthropod

Cucumericrus ("cucumber-leg") is an extinct genus of stem-arthropod. The type and only species is Cucumericrus decoratus, with fossils discovered from the Maotianshan Shales of Yunnan, China.

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

The Artiopoda is a grouping of extinct arthropods that includes trilobites and their close relatives. It was erected by Hou and Bergström in 1997 to encompass a wide diversity of arthropods that would traditionally have been assigned to the Trilobitomorpha. Trilobites, in part due to abundance of findings owing to their mineralized exoskeletons, are by far the best recorded, diverse, and long lived members of the clade. Other members, which lack mineralised exoskeletons, are known mostly from Cambrian deposits.

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

Hymenocarina is an order of extinct arthropods known from the Cambrian. They possess bivalved carapaces, typically with exposed posteriors. Members of the group are morphologically diverse and had a variety of ecologies, including as filter feeders and as predators. Recent research has generally considered them to be stem or crown group members of Mandibulata, due to the presence of mandibles in some species.

<i>Kylinxia</i> Genus of fossil arthropod

Kylinxia is a genus of extinct arthropod described in 2020. It was described from six specimens discovered in Yu'anshan Formation in southern China. The specimens are assigned to one species Kylinxia zhangi. Dated to 518 million years, the fossils falls under the Cambrian period. Announcing the discovery on 4 November 2020 at a press conference, Zeng Han of the Nanjing Institute of Geology and Paleontology, said that the animal "bridges the evolutionary gap from Anomalocaris to true arthropods and forms a key ‘missing link’ in the origin of arthropods," which was "predicted by Darwin’s evolutionary theory." The same day the formal description was published in Nature.

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.

<span class="mw-page-title-main">Deuteropoda</span> Clade of arthropods

Deuteropoda is a proposed clade of arthropods whose members are distinguished from more basal stem-group arthropods like radiodonts by an anatomical reorganization of the head region, namely the appearance of a differentiated first appendage pair, a multisegmented head, a hypostome/labrum complex, and by bearing pairs of segmented biramous limbs.

<i>Enalikter</i> Extinct arthropod genus

Enalikter is an extinct arthropod described from the middle Silurian Herefordshire Lagerstätte at the England–Wales border in UK. This genus is known from only one species, E. aphson. Enalikter is described as late-living example of Megacheira, "great-appendage arthropod". It subsequently suggested to be an annelid by other researchers, however subsequent studies rejected this interpretation. Its interpretation as megacheiran arthropod has been questioned in later studies.

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

Fortiforceps is an extinct genus of Cambrian megacheiran arthropod known from the Chengjiang biota of Yunnan, China. It was originally described by Hou and Bergström in 1997, and redescribed in 2020. It was relatively small, at 4 centimetres (1.6 in) or less in length. The head had a large pair of stalked eyes, a pair of frontal projections, as well as a pair of great appendages, like other megacheirans, along with two other cephalic appendages. The trunk had either 20 or 22 segments, depending on the specimen. These segments had pronounced blade-like spines on their upper-outer edge. Each of the trunk segments were associated with pairs of biramous limbs, which probably have seven podomeres and like other megacheirans, have paddle-shaped exopods. The trunk terminated with a forked tailpiece, which on their outer edges had rod-like structures. The two lobes were separated by a rectangular central piece. It has been placed as a member of the family Jiangfengiidae, alongside Jianfengia, Sklerolibyon and possibly Parapeytoia.

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

Enaliktidae is an extinct family of elongate arthropods known from the Silurian and Devonian periods, containing two genera, Enalikter and Bundenbachiellus. The taxonomic position of the family is uncertain. In its original description it was attributed to the Megacheira, a group of arthropods otherwise known from the Cambrian and Ordovician periods, due to them possessing uniramous frontal appendages with whip-like exensions, similar to the great appendages of megacheirans belonging to the family Leanchoiliidae like Leanchoilia. However, their placement as megacheirans has been questioned, as they arguably lack any defining apomorphies of that group, as whether the great appendages of megacheirans and the frontal appendages of enaliktids are homologous is unclear.

References

  1. ↑ Parry, Luke A.; Briggs, Derek E.G.; Ran, Ruixin; O'Flynn, Robert J.; Mai, Huijian; Clark, Elizabeth G.; Liu, Yu (29 October 2024). "A pyritized Ordovician leanchoiliid arthropod". Current Biology. doi: 10.1016/j.cub.2024.10.013 .
  2. ↑ Stein, Martin (March 2010) [26 February 2010]. "A new arthropod from the Early Cambrian of North Greenland, with a 'great appendage'-like antennula". Zoological Journal of the Linnean Society . 158 (3): 477–500. doi:10.1111/j.1096-3642.2009.00562.x.
  3. 1 2 Aria, Cédric (26 April 2022). "The origin and early evolution of arthropods". Biological Reviews. 97 (5): 1786–1809. doi:10.1111/brv.12864. ISSN   1464-7931. PMID   35475316. S2CID   243269510. Archived from the original on 8 May 2024. Retrieved 8 May 2024.
  4. ↑ Liu, Cong; Fu, Dongjing; Wu, Yu; Zhang, Xingliang (July 2024). "Cambrian euarthropod Urokodia aequalis sheds light on the origin of Artiopoda body plan". iScience. 27 (8): 110443. Bibcode:2024iSci...27k0443L. doi: 10.1016/j.isci.2024.110443 . PMC   11325232 . PMID   39148713.
  5. 1 2 3 4 5 6 Aria, Cédric; Zhao, Fangchen; Zeng, Han; Guo, Jin; Zhu, Maoyan (December 2020). "Fossils from South China redefine the ancestral euarthropod body plan". BMC Evolutionary Biology. 20 (1): 4. Bibcode:2020BMCEE..20....4A. doi: 10.1186/s12862-019-1560-7 . ISSN   1471-2148. PMC   6950928 . PMID   31914921.
  6. 1 2 Haug, Joachim T.; Waloszek, Dieter; Maas, Andreas; Liu, Yu; Haug, Carolin (March 2012). "Functional morphology, ontogeny and evolution of mantis shrimp-like predators in the Cambrian: MANTIS SHRIMP-LIKE CAMBRIAN PREDATORS". Palaeontology. 55 (2): 369–399. doi: 10.1111/j.1475-4983.2011.01124.x .
  7. ↑ Aria, Cédric; Caron, Jean-Bernard; Gaines, Robert (2015). "A large new leanchoiliid from the Burgess Shale and the influence of inapplicable states on stem arthropod phylogeny". Palaeontology. 58 (4): 629–660. Bibcode:2015Palgy..58..629A. doi: 10.1111/pala.12161 . S2CID   86443516.
  8. ↑ Liu, Yu; Edgecombe, Gregory D.; Schmidt, Michel; Bond, Andrew D.; Melzer, Roland R.; Zhai, Dayou; Mai, Huijuan; Zhang, Maoyin; Hou, Xianguang (30 July 2021). "Exites in Cambrian arthropods and homology of arthropod limb branches". Nature Communications. 12 (1): 4619. Bibcode:2021NatCo..12.4619L. doi: 10.1038/s41467-021-24918-8 . ISSN   2041-1723. PMC   8324779 . PMID   34330912.
  9. ↑ Parry, Luke A.; Briggs, Derek E.G.; Ran, Ruixin; O’Flynn, Robert J.; Mai, Huijuan; Clark, Elizabeth G.; Liu, Yu (October 2024). "A pyritized Ordovician leanchoiliid arthropod". Current Biology. doi: 10.1016/j.cub.2024.10.013 .
  10. ↑ Stein, Martin (1 March 2010). "A new arthropod from the Early Cambrian of North Greenland, with a 'great appendage'-like antennula" . Zoological Journal of the Linnean Society. 158 (3): 477–500. doi:10.1111/j.1096-3642.2009.00562.x. ISSN   0024-4082. Archived from the original on 3 November 2019. Retrieved 29 October 2019.
  11. ↑ Xian-Guang, Hou; Siveter, David J.; Siveter, Derek J.; Aldridge, Richard J.; Pei-Yun, Cong; Gabbott, Sarah E.; Xiao-Ya, Ma; Purnell, Mark A.; Williams, Mark (24 April 2017). The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life. John Wiley & Sons. ISBN   9781118896389. Archived from the original on 8 May 2024. Retrieved 10 May 2021.
  12. ↑ Daley, Allison C.; Budd, Graham E.; Caron, Jean-Bernard; Edgecombe, Gregory D.; Collins, Desmond (20 March 2009). "The Burgess Shale Anomalocaridid Hurdia and Its Significance for Early Euarthropod Evolution". Science. 323 (5921): 1597–1600. Bibcode:2009Sci...323.1597D. doi:10.1126/science.1169514. ISSN   0036-8075. PMID   19299617. S2CID   206517995.
  13. ↑ Siveter, Derek J.; Briggs, Derek E. G.; Siveter, David J.; Sutton, Mark D.; Legg, David; Joomun, Sarah (7 March 2014). "A Silurian short-great-appendage arthropod". Proceedings of the Royal Society B . 281 (1778): 20132986. doi:10.1098/rspb.2013.2986. PMC   3906945 . PMID   24452026.
  14. ↑ Derek J. Siveter; Derek E. G. Briggs; David J. Siveter; Mark D. Sutton; David Legg; Sarah Joomun (2015). "Enalikter aphson is an arthropod: a reply to Struck et al. (2014)". Proceedings of the Royal Society B . 282 (1804): 20142663. doi:10.1098/rspb.2014.2663. PMC   4375861 .
  15. ↑ Aria, Cédric (October 2022). "The origin and early evolution of arthropods". Biological Reviews. 97 (5): 1786–1809. doi:10.1111/brv.12864. ISSN   1464-7931. PMID   35475316. S2CID   243269510. Archived from the original on 8 May 2024. Retrieved 8 May 2024.
  16. ↑ Ortega-Hernández, Javier; Janssen, Ralf; Budd, Graham E. (1 May 2017). "Origin and evolution of the panarthropod head – A palaeobiological and developmental perspective". Arthropod Structure & Development. Evolution of Segmentation. 46 (3): 354–379. Bibcode:2017ArtSD..46..354O. doi: 10.1016/j.asd.2016.10.011 . ISSN   1467-8039. PMID   27989966.
  17. ↑ Aria, Cédric; Caron, Jean-Bernard (May 2017). "Burgess Shale fossils illustrate the origin of the mandibulate body plan" . Nature. 545 (7652): 89–92. Bibcode:2017Natur.545...89A. doi:10.1038/nature22080. ISSN   0028-0836. PMID   28445464. S2CID   4454526. Archived from the original on 23 September 2022. Retrieved 12 January 2023.
  18. ↑ Chen, Junyuan; Waloszek, Dieter; Maas, Andreas (2004). "A new 'great-appendage' arthropod from the Lower Cambrian of China and homology of chelicerate chelicerae and raptorial antero-ventral appendages". Lethaia. 37 (1): 3–20. Bibcode:2004Letha..37....3C. doi:10.1080/00241160410004764. ISSN   1502-3931.
  19. ↑ Chen, Jun-Yuan (2009). "The sudden appearance of diverse animal body plansduring the Cambrian explosion". The International Journal of Developmental Biology. 53 (5–6): 733–751. doi: 10.1387/ijdb.072513cj . ISSN   1696-3547. PMID   19557680.
  20. ↑ Haug, Joachim T.; Waloszek, Dieter; Maas, Andreas; Liu, Yu; Haug, Carolin (March 2012). "Functional morphology, ontogeny and evolution of mantis shrimp-like predators in the Cambrian: MANTIS SHRIMP-LIKE CAMBRIAN PREDATORS". Palaeontology. 55 (2): 369–399. doi: 10.1111/j.1475-4983.2011.01124.x . S2CID   82841481.
  21. ↑ Tanaka, Gengo; Hou, Xianguang; Ma, Xiaoya; Edgecombe, Gregory D.; Strausfeld, Nicholas J. (17 October 2013). "Chelicerate neural ground pattern in a Cambrian great appendage arthropod". Nature . 502 (7471): 364–367. Bibcode:2013Natur.502..364T. doi:10.1038/nature12520. PMID   24132294. S2CID   4456458.
  22. ↑ Liu, Yu; Ortega-Hernández, Javier; Zhai, Dayou; Hou, Xianguang (25 June 2020). "A Reduced Labrum in a Cambrian Great-Appendage Euarthropod". Current Biology. 30 (15): 3057–3061.e2. Bibcode:2020CBio...30E3057L. doi: 10.1016/j.cub.2020.05.085 . ISSN   0960-9822. PMID   32589912. S2CID   220057956.
  23. ↑ Tanaka, Gengo; Hou, Xianguang; Ma, Xiaoya; Edgecombe, Gregory D.; Strausfeld, Nicholas J. (17 October 2013). "Chelicerate neural ground pattern in a Cambrian great appendage arthropod" . Nature. 502 (7471): 364–367. Bibcode:2013Natur.502..364T. doi:10.1038/nature12520. ISSN   0028-0836. PMID   24132294. S2CID   4456458. Archived from the original on 16 October 2022. Retrieved 12 January 2023.
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