Venustulus

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Venustulus
Temporal range: Silurian, (Telychian) 437.5–436.5  Ma
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20200814 Venustulus waukeshaensis.png
Reconstruction of Venustulus waukeshaensis
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Clade: Euchelicerata
Clade: Prosomapoda
Genus:† Venustulus
Moore, 2005
Type species
†Venustulus waukeshaensis
Moore, 2005

Venustulus is a genus of synziphosurine, [1] a paraphyletic group of fossil chelicerate arthropods. [2] [3] Venustulus was regarded as part of the clade Prosomapoda. [2] [4] [5] [6] [3] [7] Fossils of the single and type species, V. waukeshaensis, have been discovered in deposits of the Silurian period in Wisconsin, in the United States. [1] [2] [7] Venustulus is one of the few synziphosurine genera with fossil showing evidence of appendages, the other ones being Weinbergina, Anderella and Camanchia . [1] [3] Despite often being aligned close to horseshoe crabs, it has been found that Venustulus and its relatives form a group made up of various basal euchelicerate arthropods more distant to the xiphosurans. [1] [2]

Contents

Description

Venustulus is the third largest member of its grouping just behind Willwerathia and Weinbergina respectively. This arthropod appears to be blind due to the lack of eyes on its carapace, suggesting it lived either in deep water or buried in the sediments. Unlike modern horseshoe crabs, the prosomal appendages of Venustulus covered less of the total carapace length. The animals carapace is semi-circular in shape and has a procurved posterior area. The genal areas (sides of the head) of the arthropod are angular in shape, but are not developed into the genal spines seen on some trilobites and xiphosurans. The opisthosomal region of the arthropod is mainly composed of ten articulating segments. [1] This creature was once considered the earliest known member of its grouping, however more recently synziphosuran fossils have been found in earlier Ordovician deposits. [1] [8] This arthropods five-six pair of appendages contrasts the seven usually seen in other synziphosurans, possibly suggesting that this creature represents a more derived form than other members of its grouping. [1]

History of research

The genus name Venustulus derives from Latin and means "charming". The species name waukeshaensis is derived from the town of Waukesha where the biota containg the fossils is found. [1] This chelicerate, along with many of the other animals of the biota (like Parioscorpio and Thylacares ) were discovered in 1985, but were not given scientific names until decades later. [1] [9] Venustulus was formally described in 2005, and was based on eight specimens that are currently held in the UW–Madison Geology Museum. These specimens vary in quality with three being almost complete and the other five only being the prosoma and opisthosoma of the arthropod. [1]

A fossil of Venustulus Fossil specimen of Venustulus (Synziphosurina) from the Waukesha lagerstatte.jpg
A fossil of Venustulus

Classification

The synziphosuran grouping is divided into multiple families including the Bunodidae, the Pseudoniscidae, and the Weinberginidae. [10] Although the taxonomic relationships of Venustulus are still up for debate, the paper that described it noted that the arthropod has shared characteristics more similar to the weinberginid synziphosurans Weinbergina, Legrandella and Willwerathia. [1] As a group the synziphosurans were first regarded as basal members of the xiphosuran lineage, however more recently they have been found to be more closely related to more primitive chelicerate arthropods and only distantly related to the xiphosurans. [10] [2] [3]

Paleoecology

The oceans that covered Waukesha were a diverse and bustling ecosystem that housed a variety of strange fauna. [9] Arthropods like Venustulus were abundant and diverse with many species of trilobites, a possible cheloniellid, a thylacocephalan, phyllocarids, and several arthropods like Parioscorpio and the "butterfly animal" being enigmatic in their taxonomy. [9] [11] [12] Also inhabiting the area were multiple soft-bodied animals like annelid worms and lobopodians. [9] Multiple chordates also lived in the area evidenced by fossils including an extremely rare body fossil of the conodont Panderodus . [9] [13] Bizarrely, animals like brachiopods, cephalopods, clams, snails and crinoids, which are common in most Silurian environments, are rarely found in this biota, but conulariids are still somewhat common. [9] [14] Interestingly it seems there could be another possible synziphosuran from the same deposits as Venustulus, but the fossils are too fragmentary to consider it a unique genus. [1]

Related Research Articles

<span class="mw-page-title-main">Chelicerata</span> Subphylum of arthropods

The subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids, as well as a number of extinct lineages, such as the eurypterids and chasmataspidids.

<span class="mw-page-title-main">Xiphosura</span> Order of marine chelicerates

Xiphosura is an order of arthropods related to arachnids. They are more commonly known as horseshoe crabs. They first appeared in the Hirnantian. Currently, there are only four living species. Xiphosura contains one suborder, Xiphosurida, and several stem-genera.

<span class="mw-page-title-main">Chasmataspidida</span> Order of arthropods

Chasmataspidids, sometime referred to as chasmataspids, are a group of extinct chelicerate arthropods that form the order Chasmataspidida. Chasmataspidids are probably related to horseshoe crabs (Xiphosura) and/or sea scorpions (Eurypterida), with more recent studies suggest that they form a clade (Dekatriata) with Eurypterida and Arachnida. Chasmataspidids are known sporadically in the fossil record through to the mid-Devonian, with possible evidence suggesting that they were also present during the late Cambrian. Chasmataspidids are most easily recognised by having an opisthosoma divided into a wide forepart (preabdomen) and a narrow hind part (postabdomen) each comprising 4 and 9 segments respectively. There is some debate about whether they form a natural group.

<i>Willwerathia</i> Genus of horseshoe crab relatives

Willwerathia is a genus of Devonian arthropod. It is sometimes classified as synziphosurine, a paraphyletic group of horseshoe crab-like fossil chelicerate arthropods, while some studies compare its morphology to an artiopod. Willwerathia known only by one species, Willwerathia laticeps, discovered in deposits of the Devonian period from the Klerf Formation, in the Rhenish Slate Mountains of Germany.

<i>Bembicosoma</i> Extinct genus of chelicerate

Bembicosoma is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Bembicosoma was regarded as part of the clade Planaterga. Fossils of the single and type species, B. pomphicus, have been discovered in deposits of the Silurian period in the Pentland Hills, Scotland. Bembicosoma had been tentatively assigned as an eurypterid before its synziphosurine affinities revealed.

<i>Bunodes</i> Genus of horseshoe crab relatives

Bunodes is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Bunodes was regarded as part of the clade Planaterga. Fossils of the single and type species, B. lunula, have been discovered in deposits of the Silurian period in Ludlow, England. Bunodes is the type genus of the family Bunodidae, the other genera of the same family being Limuloides. There are 64 direct children of Bunodes.

<i>Cyamocephalus</i> Extinct genus of chelicerate

Cyamocephalus is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Cyamocephalus was regarded as part of the clade Planaterga. Fossils of the single and type species, C. loganensis, have been discovered in deposits of the Silurian-aged Patrick Burn Formation in Lesmahagow, Scotland. Cyamocephalus is one of the two members of the family Pseudoniscidae, the other being Pseudoniscus. Cyamocephalus differ from Pseudoniscus by the fused tergites of 6th and 7th opisthosomal segments.

<i>Legrandella</i> Extinct genus of chelicerate

Legrandella is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Legrandella was regarded as part of the clade Prosomapoda. Fossils of the single and type species, L. lombardii, have been discovered in deposits of the Devonian period in Cochabamba, Bolivia.

<i>Limuloides</i> Genus of horseshoe crab relatives

Limuloides is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Limuloides was regarded as part of the clade Planaterga. Fossils of the genus have been discovered in deposits of the Silurian period in the United Kingdom and potentially in the United States. Limuloides is one of the two genera of the family Bunodidae, the other being the type genus Bunodes. Limuloides is characterized by a carapace with radiated ridges and serrated lateral regions, and an opisthosoma with rows of nodes. Limuloides was once thought to have lateral compound eyes on its carapace, but later investigation did not find any evidence of it.

<i>Pasternakevia</i> Extinct genus of chelicerate

Pasternakevia is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Pasternakevia was regarded as part of the clade Planaterga. Fossils of the single and type species, P. podolica, have been discovered in deposits of the Silurian period in Podolia, Ukraine.

<i>Pseudoniscus</i> Extinct genus of chelicerate

Pseudoniscus is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Pseudoniscus was regarded as part of the clade Planaterga. Fossils of the genus have been discovered in deposits of the Silurian period in the United Kingdom, the United States and Estonia. Pseudoniscus is one of the two members of the family Pseudoniscidae, the other being Cyamocephalus.

<i>Weinbergina</i> Extinct genus of chelicerate

Weinbergina is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Fossils of the single and type species, W. opitzi, have been discovered in deposits of the Devonian period in the Hunsrück Slate, Germany.

<span class="mw-page-title-main">Synziphosurina</span> Group of arthropods

Synziphosurina is a paraphyletic group of chelicerate arthropods previously thought to be basal horseshoe crabs (Xiphosura). It was later identified as a grade composed of various basal euchelicerates, eventually excluded form the monophyletic Xiphosura sensu stricto and only regarded as horseshoe crabs under a broader sense. Synziphosurines survived at least since early Ordovician to early Carboniferous in ages, with most species are known from the in-between Silurian strata.

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

Borchgrevinkium is an extinct genus of chelicerate arthropod. A fossil of the single and type species, B. taimyrensis, has been discovered in deposits of the Early Devonian period in the Krasnoyarsk Krai, Siberia, Russia. The name of the genus honors Carsten Borchgrevink, an Anglo-Norwegian explorer who participated in many expeditions to Antarctica. Borchgrevinkium represents a poorly known genus whose affinities are uncertain.

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

Offacolus is an extinct genus of euchelicerate, a group of chelicerate arthropods. Its only species, O. kingi, has been found in deposits from the Silurian period in the Wenlock Series Lagerstätte of Herefordshire, England. It is the only member of the monotypic family Offacolidae, and classified as a basal ("primitive") genus in the clade Euchelicerata, along with Dibasterium and Prosomapoda. The genus is named after Offa, a king from the ancient kingdom of Mercia, and colus, a person who dwelled among the Offa's Dyke. The species name honors Robert Joseph King, a British mineralogist who found the fossils of Offacolus.

<i>Parioscorpio</i> Extinct genus of enigmatic arthropod

Parioscorpio is an extinct genus of arthropod containing the species P. venator known from the Silurian-aged Waukesha Biota of the Brandon Bridge Formation near Waukesha, Wisconsin. This animal has gone through a confusing taxonomic history, being called an arachnid, crustacean, and an artiopodan arthropod at various points. This animal is one of the more famous fossil finds from Wisconsin, due to the media coverage it received based on its original description in 2020 as a basal scorpion.

<span class="mw-page-title-main">Waukesha Biota</span> Lagerstätte Fossil site in Waukesha County, Wisconsin, U.S.

The Waukesha Biota is an important fossil site located in Waukesha County and Franklin, Milwaukee County within the state of Wisconsin. This biota is preserved in certain strata within the Brandon Bridge Formation, which dates to the early Silurian period. It is known for the exceptional preservation of soft-bodied organisms, including many species found nowhere else in rocks of similar age. The site's discovery was announced in 1985, leading to a plethora of discoveries. This biota is one of the few well studied Lagerstätten from the Silurian, making it important in our understanding of the period's biodiversity. Some of the species are not easily classified into known animal groups, showing that much research remains to be done on this site. Other taxa that are normally common in Silurian deposits are rare here, but trilobites are quite common.

<i>Camanchia</i> Extinct genus of chelicerate

Camanchia is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Camanchia was regarded as part of the clade Prosomapoda. Fossils of the single and type species, C. grovensis, have been discovered in deposits of the Silurian period in Iowa, in the United States. Alongside Venustulus, Camanchia is one of the only Silurian synziphosurine with fossil showing evidence of appendages.

<i>Anderella</i> Extinct genus of chelicerate

Anderella is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Anderella was regarded as part of the clade Prosomapoda. Fossils of the single and type species, A. parva, have been discovered in deposits of the Carboniferous period in Montana, in the United States. Anderella is the first and so far the only Carboniferous synziphosurine being described, making it the youngest member of synziphosurines. Anderella is also one of the few synziphosurine genera with fossil showing evidence of appendages, but the details are obscure due to their poor preservation.

<i>Acheronauta</i> Possible extinct mandibulate arthropod

Acheronauta is a genus of extinct vermiform arthropod that lived in the early Silurian Waukesha biota fossil site in southeast Wisconsin. This arthropod was first discovered alongside the biota in 1985, but was not fully described until October 2022. This creature was recognized and described as a possible early mandibulate. This description is very important as much of the fauna of the biota remain undescribed, and its discovery has allowed for paleontologists to get a better grasp of the diversity of the arthropod fauna at the site. Multiple phylogenetic analyses were performed, and it seems that this arthropod forms a previously undiscovered clade with the Devonian stem-arthropod Captopodus, and the somewhat enigmatic group Thylacocephala.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 Moore, Rachel A.; Briggs, Derek E. G.; Braddy, Simon J.; Anderson, Lyall I.; Mikulic, Donald G.; Kluessendorf, Joanne (2005). "A New synziphosurine (Chelicerata : Xiphosura) from the Late Llandovery (Silurian) Waukesha Lagerstatte, Wisconsin, USA". Journal of Paleontology. 79 (2): 242–250. doi:10.1666/0022-3360(2005)079<0242:ANSCXF>2.0.CO;2. ISSN   0022-3360. S2CID   56570105.
  2. 1 2 3 4 5 Lamsdell, James C. (2013). "Revised systematics of Palaeozoic 'horseshoe crabs' and the myth of monophyletic Xiphosura". Zoological Journal of the Linnean Society. 167 (1): 1–27. doi: 10.1111/j.1096-3642.2012.00874.x . ISSN   0024-4082.
  3. 1 2 3 4 Bicknell, Russell D. C.; Pates, Stephen (2020). "Pictorial Atlas of Fossil and Extant Horseshoe Crabs, With Focus on Xiphosurida". Frontiers in Earth Science. 8: 98. Bibcode:2020FrEaS...8...98B. doi: 10.3389/feart.2020.00098 . ISSN   2296-6463. S2CID   220405124.
  4. ↑ Selden, Paul A.; Lamsdell, James C.; Qi, Liu (2015). "An unusual euchelicerate linking horseshoe crabs and eurypterids, from the Lower Devonian (Lochkovian) of Yunnan, China". Zoologica Scripta. 44 (6): 645–652. doi: 10.1111/zsc.12124 . ISSN   0300-3256. S2CID   55264483.
  5. ↑ Lamsdell, James C.; Briggs, Derek E. G.; Liu, Huaibao P.; Witzke, Brian J.; McKay, Robert M. (2015). "A new Ordovician arthropod from the Winneshiek Lagerstätte of Iowa (USA) reveals the ground plan of eurypterids and chasmataspidids". The Science of Nature. 102 (9–10): 63. Bibcode:2015SciNa.102...63L. doi:10.1007/s00114-015-1312-5. ISSN   0028-1042. PMID   26391849. S2CID   8153035.
  6. ↑ Bicknell, Russell D. C.; Lustri, Lorenzo; Brougham, Tom (2019-12-01). "Revision of "Bellinurus" carteri (Chelicerata: Xiphosura) from the Late Devonian of Pennsylvania, USA". Comptes Rendus Palevol. 18 (8): 967–976. doi:10.1016/j.crpv.2019.08.002. ISSN   1631-0683. S2CID   210315086.
  7. 1 2 Dunlop, J. A.; Penney, D.; Jekel, D. (2020). "A summary list of fossil spiders and their relatives" (PDF). World Spider Catalog. Natural History Museum Bern. pp. 1–296.
  8. ↑ Bicknell, Russell D. C.; Pates, Stephen (2020). "Pictorial Atlas of Fossil and Extant Horseshoe Crabs, With Focus on Xiphosurida". Frontiers in Earth Science. 8: 98. Bibcode:2020FrEaS...8...98B. doi: 10.3389/feart.2020.00098 . ISSN   2296-6463.
  9. 1 2 3 4 5 6 Mikulic, D.G.; Briggs, D.E.G.; Kluessendorf, J. (1985). "A new exceptionally preserved biota from the Lower Silurian of Wisconsin, U.S.A." Philosophical Transactions of the Royal Society of London B. 311 (1148): 75–85. Bibcode:1985RSPTB.311...75M. doi:10.1098/rstb.1985.0140.
  10. 1 2 Moore, Rachel A.; Briggs, Derek E. G.; Bartels, Christoph (2005). "A new specimen of Weinbergina opitzi (Chelicerata: Xiphosura) from the Lower Devonian Hunsriick Slate, Germany". Paläontologische Zeitschrift. 79 (3): 399–408. doi:10.1007/BF02991931. ISSN   0031-0220. S2CID   84994966.
  11. ↑ Anderson, Evan P; Schiffbauer, James D.; Jacquet, Sarah M.; Lamsdell, James C.; Kluessendorf, Joanne; Mikulic, Donald G. (2021). "Stranger than a scorpion: a reassessment of Parioscorpio venator, a problematic arthropod from the Llandoverian Waukesha Lagerstätte". Palaeontology. 64 (3): 429–474. doi:10.1111/pala.12534. ISSN   1475-4983. S2CID   234812878.
  12. ↑ Meyer, Ronald C.; Gunderson, Gerald O. (1986-11-01). "Discovering a New Silurian Soft-Bodied Fauna". Rocks & Minerals. 61 (6): 310–319. doi:10.1080/00357529.1986.11768462. ISSN   0035-7529.
  13. ↑ Murdock, Duncan J. E.; Smith, M. Paul (2021). "Panderodus from the Waukesha Lagerstätte of Wisconsin, USA: a primitive macrophagous vertebrate predator". Papers in Palaeontology . 7 (4): 1977–1993. doi:10.1002/spp2.1389. S2CID   237769553.
  14. ↑ Wendruff, A.J.; Babcock, L.E.; Kluessendorf, J.; Mikulic, D.G. (2020). "Paleobiology and Taphonomy of exceptionally preserved organisms from the Waukesha Biota (Silurian), Wisconsin, USA". Palaeogeography, Palaeoclimatology, Palaeoecology. 546: 109631. Bibcode:2020PPP...546j9631W. doi:10.1016/j.palaeo.2020.109631. S2CID   212824469.
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