Evolution of spiders

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A spider in Baltic amber Spider in amber.jpg
A spider in Baltic amber

Spiders have existed since at least 380 million years. The group's origins lie within an arachnid sub-group defined by the presence of book lungs (the tetrapulmonates); [1] [2] the arachnids as a whole evolved from aquatic chelicerate ancestors. More than 45,000 extant species have been described, organised taxonomically in 3,958 genera and 114 families. [3] There may be more than 120,000 species. [3] Fossil diversity rates make up a larger proportion than extant diversity would suggest with 1,593 arachnid species described out of 1,952 recognized chelicerates. [4] Both extant and fossil species are described annually by researchers in the field. Major developments in spider evolution include the development of spinnerets and silk secretion.

Contents

Early spider-like arachnids

Among the oldest known land arthropods are Trigonotarbids, members of an extinct order of spider-like arachnids. [5]

Trigonotarbids share many superficial characteristics with spiders, including a terrestrial lifestyle, respiration through book lungs, and walking on eight legs, [6] with a pair of leg-like pedipalps near the mouth and mouth parts. They lacked the ability to spin silk: there is no evidence for either spigots or spinnerets within the group. An unpublished fossil exists which has distinct microtubercles on its hind legs, akin to those used by spiders to direct and manipulate their silk, but given the lack of any structures associated silk production, it seems unlikely the structures were associated with silk.

Trigonotarbids are not true spiders, and the trigonotarbids have no living descendants. [7]

Emergence of true spiders

Geratonephilad attacking Cascoscelio incassus preserved in amber, c. 100 million years ago. Nephila burmanica attacking Cascoscelio incassa in Burmese amber.jpg
Geratonephilad attacking Cascoscelio incassus preserved in amber, c.  100  million years ago.

According to a 2020 study using a molecular clock calibrated with 27 chelicerate fossils, spiders most likely diverged from other chelicerates between 375 and 328 million years ago. [8]

At one stage, Attercopus was claimed as the oldest fossil spider which lived 380  million years ago during the Devonian. Attercopus was placed as the sister-taxon to all living spiders, but has now been reinterpreted as a member of a separate, extinct order Uraraneida which could produce silk, but did not have true spinnerets. [9] The discovery of Chimerarachne in early Late Cretaceous (Cenomanian) aged Burmese amber has also demonstrated that taxa existed until the Cretaceous that had both spinnerets, and a whip-like telson. [10] [11]

The oldest reported spiders date to the Carboniferous Period, or about 300  million years ago. Most of these early segmented fossil spiders from the Coal Measures of Europe and North America probably belonged to the Mesothelae, or something very similar, a group of spiders with the spinnerets placed underneath the middle of the abdomen, rather than at the end as in modern spiders. They were probably ground-dwelling predators, living in the giant clubmoss and fern forests of the mid-late Palaeozoic, where they were presumably predators of other primitive arthropods. Silk may have been used simply as a protective covering for the eggs, a lining for a retreat hole, and later perhaps for simple ground sheet web and trapdoor construction. They co-existed with a range of spider-like forms which had some, but not all, the characters associated with the true spiders. [12]

As plant and insect life diversified so also did the spider's use of silk. Spiders with spinnerets at the end of the abdomen (Mygalomorphae and Araneomorphae) appeared more than 250  million years ago, presumably promoting the development of more elaborate sheet and maze webs for prey capture both on ground and foliage, as well as the development of the safety dragline. The oldest mygalomorph, Rosamygale , was described from the Triassic of France. Megarachne servinei from the Permo-Carboniferous was once thought to be a giant mygalomorph spider and, with its body length of 34 cm (1.1 ft) and leg span of above 50 cm (20 in), the largest known spider ever to have lived on Earth, but subsequent examination by an expert revealed that it was actually a relatively small sea scorpion.

By the Jurassic period, the sophisticated aerial webs of the orb-weaver spiders had already developed to take advantage of the rapidly diversifying groups of insects. A spider web preserved in amber, thought to be 110 million years old, shows evidence of a perfect "orb" web, the most famous, circular kind one thinks of when imagining spider webs. An examination of the drift of those genes thought to be used to produce the web-spinning behavior suggests that orb spinning was in an advanced state as many as 136  million years ago. One of these, the araneid Mongolarachne jurassica , from about 165  million years ago, recorded from Daohuogo, Inner Mongolia in China, is the largest known fossil of a spider.

The 110 million year-old amber-preserved web is also the oldest to show trapped insects, containing a beetle, a mite, a wasp's leg, and a fly. [13] The ability to weave orb webs is thought to have been "lost", and sometimes even re-evolved or evolved separately, in different species of spiders since its first appearance.

Around half of modern spider species belong to the RTA clade, a group of spiders linked by the shared morphological trait of the retrolateral tibial apophysis (RTA) on the male pedipalp. Despite their modern diversity, there is no unambiguous evidence of the clade from the Mesozoic, though molecular clocks suggest that diversification of the group began in the Late Cretaceous. There appears to be a faunal turnover in the Cretaceous-Cenozoic interval, with the Cretaceous dominated by Synspermiata and Palpimanoidea, as well as enigmatic extinct families like the lagonomegopids, while the Cenozoic is dominated by RTA clade and araneoid spiders. [14]

See also

Related Research Articles

<span class="mw-page-title-main">Merostomata</span> Class of arthropods

Merostomata is a class of chelicerate arthropods that contains the extinct Eurypterida and the extant Xiphosura. The term was originally used by James Dwight Dana to refer to Xiphosura only, but was emended by Henry Woodward to cover both groups.

<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">Arachnid</span> Class of arthropods

Arachnids are arthropods in the class Arachnida of the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.

<span class="mw-page-title-main">Ricinulei</span> Order of obscure arachnids

Ricinulei is a small order of arachnids. Like most arachnids, they are predatory; eating small arthropods. They occur today in west-central Africa (Ricinoides) and the Americas from South America to as far north as Texas, where they either inhabit leaf-litter or caves. As of 2022, 103 extant species of ricinuleids have been described worldwide, all in the single family Ricinoididae. In older works they are sometimes referred to as Podogona. Due to their obscurity they do not have a proper common-name, though in academic literature they are occasionally referred to as hooded tickspiders.

<span class="mw-page-title-main">Dipluridae</span> Family of spiders

The family Dipluridae, known as curtain-web spiders are a group of spiders in the infraorder Mygalomorphae, that have two pairs of booklungs, and chelicerae (fangs) that move up and down in a stabbing motion. A number of genera, including that of the Sydney funnel-web spider (Atrax), used to be classified in this family but have now been moved to Atracidae.

<span class="mw-page-title-main">Mesothelae</span> Suborder of spiders

The Mesothelae are a suborder of spiders. As of April 2024, two extant families were accepted by the World Spider Catalog, Liphistiidae and Heptathelidae. Alternatively, the Heptathelidae can be treated as a subfamily of a more broadly circumscribed Liphistiidae. There are also a number of extinct families.

<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.

<i>Plesiosiro</i> Extinct genus of arachnids

Plesiosiro is an extinct arachnid genus known exclusively from nine specimens from the Upper Carboniferous of Coseley, Staffordshire, United Kingdom. The genus is monotypic, represented only by the species Plesiosiro madeleyi described by Reginald Innes Pocock in his important 1911 monograph on British Carboniferous arachnids. It is the only known member of the order Haptopoda.

<span class="mw-page-title-main">Trigonotarbida</span> Extinct order of arachnids

The order Trigonotarbida is a group of extinct arachnids whose fossil record extends from the late Silurian to the early Permian. These animals are known from several localities in Europe and North America, as well as a single record from Argentina. Trigonotarbids can be envisaged as spider-like arachnids, but without silk-producing spinnerets. They ranged in size from a few millimetres to a few centimetres in body length and had segmented abdomens (opisthosoma), with the dorsal exoskeleton (tergites) across the backs of the animals' abdomens, which were characteristically divided into three or five separate plates. Probably living as predators on other arthropods, some later trigonotarbid species were quite heavily armoured and protected themselves with spines and tubercles. About seventy species are currently known, with most fossils originating from the Carboniferous coal measures.

<span class="mw-page-title-main">Tetrapulmonata</span> Clade of arachnids

Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Uropygi, Schizomida, Amblypygi and Araneae (spiders). It is the only supra-ordinal group of arachnids that is strongly supported in molecular phylogenetic studies. Two extinct orders are also placed in this clade, Haptopoda and Uraraneida. In 2016, a newly described fossil arachnid, Idmonarachne, was also included in the Tetrapulmonata; as of March 2016 it has not been assigned to an order.

<span class="mw-page-title-main">Harvestman phylogeny</span> Order of arachnids

Harvestmen (Opiliones) are an order of arachnids often confused with spiders, though the two orders are not closely related. Research on harvestman phylogeny is in a state of flux. While some families are clearly monophyletic, that is share a common ancestor, others are not, and the relationships between families are often not well understood.

<i>Attercopus</i> Extinct genus of spider-like arachnids

Attercopus is an extinct genus of arachnids, containing one species Attercopus fimbriunguis, known from flattened cuticle fossils from the Panther Mountain Formation in Upstate New York. It is placed in the extinct order Uraraneida, spider-like animals able to produce silk, but which lacked true spinnerets and retained a segmented abdomen bearing a flagellum-like tail resembling that of a whip scorpion. They are thought to be close to the origins of spiders.

<i>Eophrynus prestvicii</i> Extinct species of arachnid

Eophrynus prestvicii is an extinct species of arachnid belonging to the order Trigonotarbida.

<span class="mw-page-title-main">Spider</span> Order of arachnids

Spiders are air-breathing arthropods that have eight limbs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except Antarctica, and have become established in nearly every land habitat. As of September 2024, 52,309 spider species in 134 families have been recorded by taxonomists. However, there has been debate among scientists about how families should be classified, with over 20 different classifications proposed since 1900.

<i>Palaeocharinus</i> Extinct genus of spiders

Palaeocharinus is a genus of extinct trigonotarbid arachnids known from the Devonian of western Europe. The genus was first found and described in the Rhynie chert in the 1920s by Arthur Stanley Hirst and S. Maulik. The family to which the genus belongs may be paraphyletic.

Rosamygale is a genus of extinct Triassic spiders, with a single described species, Rosamygale grauvogeli. It is the oldest known member of the Mygalomorphae, one of the three main divisions of spiders, which includes well known forms such as tarantulas and Australian funnel-web spiders. It was described by Selden and Gall in 1992, from specimens found in the Middle Triassic aged Gres a Meules and Grès à Voltzia geological formations in France. It is also considered to be the oldest known member of the Avicularioidea, one of the two main divisions of Mygalomorphae.

<span class="mw-page-title-main">Uraraneida</span> Order of arachnids

Uraraneida is an extinct order of Paleozoic arachnids related to modern spiders. Two genera of fossils have been definitively placed in this order: Attercopus from the Devonian of United States and Permarachne from the Permian of Russia. Like spiders, they are known to have produced silk, but lack the characteristic spinnerets of modern spiders, and retain elongate telsons.

<i>Idmonarachne</i> Extinct genus of arachnids

Idmonarachne is an extinct genus of arachnids, containing one species, Idmonarachne brasieri. It is related to uraraneids and spiders.

This list of fossil arthropods described in 2011 is a list of new taxa of trilobites, fossil insects, crustaceans, arachnids and other fossil arthropods of every kind that have been described during the year 2011. The list only includes taxa at the level of genus or species.

<i>Chimerarachne</i> Extinct genus of spider-like arachnids

Chimerarachne is a genus of extinct arachnids, containing five species. Fossils of Chimerarachne were discovered in Burmese amber from Myanmar which dates to the mid-Cretaceous, about 100 million years ago. It is thought to be closely related to spiders, but outside any living spider clade. The earliest spider fossils are from the Carboniferous, requiring at least a 170 myr ghost lineage with no fossil record. The size of the animal is quite small, being only 2.5 millimetres (0.098 in) in body length, with the tail being about 3 millimetres (0.12 in) in length. These fossils resemble spiders in having two of their key defining features: spinnerets for spinning silk, and a modified male organ on the pedipalp for transferring sperm. At the same time they retain a whip-like tail, rather like that of a whip scorpion and uraraneids. Chimerarachne is not ancestral to spiders, being much younger than the oldest spiders which are known from the Carboniferous, but it appears to be a late survivor of an extinct group which was probably very close to the origins of spiders. It suggests that there used to be spider-like animals with tails which lived alongside true spiders for at least 200 million years.

References

  1. ↑ Garwood, Russell J.; Dunlop, Jason (2014). "Three-dimensional reconstruction and the phylogeny of extinct chelicerate orders". PeerJ. 2: e641. doi: 10.7717/peerj.641 . ISSN   2167-8359. PMC   4232842 . PMID   25405073.
  2. ↑ Garwood, Russell J.; Dunlop, Jason A.; Knecht, Brian J.; Hegna, Thomas A. (2017). "The phylogeny of fossil whip spiders". BMC Evolutionary Biology. 17 (1): 105. doi: 10.1186/s12862-017-0931-1 . ISSN   1471-2148. PMC   5399839 . PMID   28431496.
  3. 1 2 Garrison, Nicole L.; Rodriguez, Juanita; Agnarsson, Ingi; Coddington, Jonathan A.; Griswold, Charles E.; Hamilton, Christopher A.; Hedin, Marshal; Kocot, Kevin M.; Ledford, Joel M.; Bond, Jason E. (2016). "Spider phylogenomics: untangling the Spider Tree of Life". PeerJ. 4: e1719. doi: 10.7717/peerj.1719 . ISSN   2167-8359. PMC   4768681 . PMID   26925338.
  4. ↑ Jason A. Dunlop; et al. (2008), "How many species of fossil arachnids are there?", The Journal of Arachnology, 36 (2): 267–272, doi:10.1636/ch07-89.1, S2CID   42371883
  5. ↑ Garwood, Russell J.; Edgecombe, Gregory D. (September 2011). "Early Terrestrial Animals, Evolution, and Uncertainty". Evolution: Education and Outreach. 4 (3): 489–501. doi: 10.1007/s12052-011-0357-y . ISSN   1936-6426.
  6. ↑ Garwood, Russell; Dunlop, Jason (2015). "The walking dead: Blender as a tool for paleontologists with a case study on extinct arachnids". Journal of Paleontology. 88 (4): 735–746. doi:10.1666/13-088. ISSN   0022-3360. S2CID   131202472.
  7. ↑ Garwood, Russell J.; Dunlop, Jason A. (2010). "Fossils Explained: Trigonotarbids". Geology Today. 26 (1): 34–37. doi:10.1111/j.1365-2451.2010.00742.x. S2CID   247708509 . Retrieved June 12, 2015.
  8. ↑ Lozano-Fernandez, Jesus; Tanner, Alastair R.; Puttick, Mark N.; Vinther, Jakob; Edgecombe, Gregory D.; Pisani, Davide (11 March 2020). "A Cambrian–Ordovician Terrestrialization of Arachnids". Frontiers in Genetics. 11: 182. doi: 10.3389/fgene.2020.00182 . PMC   7078165 . PMID   32218802.
  9. ↑ Selden, P.A.; Shear, W.A.; Sutton, M.D. (2008). "Fossil evidence for the origin of spider spinnerets, and a proposed arachnid order". Proceedings of the National Academy of Sciences . 105 (52): 20781–20785. doi: 10.1073/pnas.0809174106 . ISSN   0027-8424. PMC   2634869 . PMID   19104044.
  10. ↑ Wang, Bo; Dunlop, Jason A.; Selden, Paul A.; Garwood, Russell J.; Shear, William A.; Müller, Patrick; Lei, Xiaojie (2018). "Cretaceous arachnid Chimerarachne yingi gen. et sp. nov. illuminates spider origins". Nature Ecology & Evolution. 2 (4): 614–622. doi:10.1038/s41559-017-0449-3. ISSN   2397-334X. PMID   29403075. S2CID   4239867.
  11. ↑ Huang, Diying; Hormiga, Gustavo; Cai, Chenyang; Su, Yitong; Yin, Zongjun; Xia, Fangyuan; Giribet, Gonzalo (2018). "Origin of spiders and their spinning organs illuminated by mid-Cretaceous amber fossils". Nature Ecology & Evolution. 2 (4): 623–627. doi:10.1038/s41559-018-0475-9. ISSN   2397-334X. PMID   29403076. S2CID   3268135.
  12. ↑ Garwood, Russell J.; Dunlop, Jason A.; Selden, Paul A.; Spencer, Alan R.T.; Atwood, Robert C.; Vo, Nghia T.; Drakopoulos, Michael (2016). "Almost a spider: A 305 million year-old fossil arachnid and spider origins". Proceedings of the Royal Society B: Biological Sciences. 283 (1827): 20160125. doi:10.1098/rspb.2016.0125. ISSN   0962-8452. PMC   4822468 . PMID   27030415.
  13. ↑ "Oldest known spider web discovered in amber". Live Science (LiveScience.com). 22 June 2006. Retrieved 25 June 2006.
  14. ↑ Magalhaes, Ivan L. F.; Azevedo, Guilherme H.F.; Michalik, Peter; Ramírez, Martín J. (February 2020). "The fossil record of spiders revisited: Implications for calibrating trees and evidence for a major faunal turnover since the Mesozoic". Biological Reviews. 95 (1): 184–217. doi:10.1111/brv.12559. ISSN   1464-7931. PMID   31713947. S2CID   207937170.
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