Trigonotarbida

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Trigonotarbida
Temporal range: 419–290Ma
Late Silurian to Early Permian
Palaeotarbus jerami.png
Palaeotarbus jerami
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Trigonotarbida
Petrunkevitch, 1949
Families
Synonyms
  • Anthracomarti Karsch, 1882
  • Meridogastra Thorell & Lindström, 1885
  • Eurymarti Matthew, 1895

The Order Trigonotarbida is an extinct group of arachnids whose fossil record extends from the late Silurian to the early Permian (c.419 to 290 million years ago). 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, with the 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. In July 2014 scientists used computer graphics to re-create the animal's walk.[1]

Historical background[edit]

Kreischeria fossil in Vienna

The first trigonotarbid was described in 1837 from the Coal Measures of Coalbrookdale in England by the famous English geologist Dean William Buckland.[2] He believed it to be a fossil beetle and named it Curculoides prestvicii. A much better preserved example was later discovered from Coseley near Dudley; also in the English West Midlands conurbation. Described in 1871 by Henry Woodward,[3] he correctly identified it as an arachnid and renamed it Eophrynus prestvicii – whereby the genus name comes from ἠώς (eos, meaning 'dawn'), and Phrynus, a genus of living whip spider (Amblypygi). Woodward subsequently described another trigonotarbid, Brachypyge carbonis, from the Coal Measures of Mons in Belgium;[4] although this fossil is only known from the abdomen and was initially mistaken for the back end of a crab.

A new arachnid order[edit]

In 1882 The German zoologist Ferdinand Karsch described a number of fossil arachnids from the Coal Measures of Neurode in Silesia (now Poland), including one he named Anthracomartus voelkelianus in honour of Herr Völkel, the foreman of the mine where it was discovered.[5] This species was raised to a new, extinct, arachnid order which Karsch called Anthracomarti. The name is derived from ἄνθραξ (anthrax), the Greek word for coal. A number of other fossils which would eventually be placed in Trigonotarbida were discovered around this time. Hans Bruno Geinitz described Kreischeria wiedei from the Coal Measures of Zwickau in Germany,[6] although he interpreted it as a fossil pseudoscorpion. Johann Kušta described Anthracomartus krejcii[7] from Rakovník in the Czech Republic, and published further descriptions in a number of subsequent papers.[8][9][10] In 1884, Samuel Hubbard Scudder described Anthracomartus trilobitus from Fayetteville, Arkansas – the first trigonotarbid from North America.[11]

Relationships[edit]

Early studies tended to confuse trigonotarbids with other living or extinct groups of arachnids; particularly harvestmen (Opiliones). Petrunkevitch's division of the trigonotarbids into two, unrelated, orders was noted above. In detail, he divided the arachnids into suborders based on the width of the division between the two parts of the body (the prosoma and opisthosoma). Anthracomartida and another extinct order, Haptopoda, were grouped into a subclass Stethostomata defined by a broad division of the body and downward-hanging mouthparts. Trigonotarbida was placed in its own subclass Soluta and defined as having a division of the body which was variable in width. Petrunkevitch's scheme was largely followed in subsequent studies of fossil arachnids.

Pantetrapulmonata[edit]

In the 1980s, Bill Shear and colleagues[12] carried out an important study on well preserved Mid Devonian trigonotarbids from Gilboa, New York. They questioned whether it was appropriate to define a group of animals on a variable character state and carried out the first cladistic analysis of fossil and living arachnids. They showed that trigonotarbids are closely related to a group of arachnids which have gone under various names (Caulogastra, Arachnidea, etc.), but for which the name Tetrapulmonata has become most widespread.[13] Members of the Tetrapulmonata include spiders, whip spiders, whip scorpions and Schizomida and, together with trigonotarbids, share characters like two pairs of book lungs and similar mouthparts with fangs operating rather like a pocket knife. In the most recent study of arachnid relationships, the Shear et al. hypothesis was largely supported and a group Pantetrapulmonata was proposed which comprises Trigonotarbida + Tetrapulmonata.[14]

Trigonotarbids and ricinuleids[edit]

In 1892, Ferdinand Karsch suggested that the rare and rather bizarre looking ricinuleids (Ricinulei) were the last living descendants of the trigonotarbids.[15] A similar hypothesis was reintroduced by Dunlop,[16] who pointed out distinct similarities between these arachnid groups. Both have opisthosomal tergites divided into median and lateral plates and both have a complicated coupling mechanism between the prosoma and the opisthosoma which 'locks' the two halves of the body together. Although cladistic analysis has tended to recover ricinuleids in their traditional position closely related to mites and ticks, further discoveries have revealed that the tip of the pedipalp ends in a small claw in both trigonotarbids and ricinuleids.[17][18]

Description[edit]

Trigonotarbids superficially resemble spiders, but can be easily recognised by having tergites on the dorsal side of the abdomen divided into median and lateral plates.[19] This character is shared with ricinuleids (Ricinulei) (see also Relationships). As in other arachnids, the body is divided into a prosoma (or cephalothorax) and opisthosoma (or abdomen). Body length ranges from a couple of millimetres up to about 5 cm (2.0 in).[20]

Prosoma[edit]

The prosoma is covered by the carapace and always bears a pair of median eyes. In the probably basal families Palaeocharinidae, Anthracomartidae – and perhaps also Anthracosironidae – there is an additional pair of lateral eye tubercles which, at least in palaeocharinids,[21] appear to have borne a series of individual lenses. In this sense palaeocharinids seem to be in the process of reducing a compound eye.

The chelicerae resemble those of a mygalomorph spider and are of the 'pocket-knife' type consisting of a basal segment and a sharp, curving fang. There is no evidence in well-preserved fossils for the opening of a venom gland, thus trigonotarbids were probably not venomous. The chelicerae seem to have hung underneath the body and may have been slightly retractable into the prosoma. Well preserved palaeocharinids show evidence for a small, slit-like mouth with an upper lip (a labrum or rostrum) and a lower lip (or labium). Inside the mouth there is some sort of filtering system[22] formed from hairs or platelets which strongly suggests that trigonotarbids (like spiders and many other arachnids) could only eat preorally digested, liquified prey.

The pedipalps have the typical arachnid structure with a coxa, trochanter, femur, patella, tibia and tarsus. They are pediform, i.e. they look like small legs and were not modified into pincers. There is no evidence for a special sperm transfer device as in the modified palpal organ of male spiders. Interestingly, in at least the palaeocharinids and anthracomartids the tip of the pedipalp is modified into a small claw formed from the tarsal claw (or apotele) and a projection from the tarsus. As mentioned above, a very similar arrangement is seen at the end of the pedipalp in Ricinulei.

The walking legs again follow the typical arachnid plan with a coxa, trochanter, femur, patella, tibia, metatarsus and tarsus. The coxae surround a single sternum. In well preserved palaeocharinids there is a ring, or annulus, around the trochanter–femur joint which may be the remains of an earlier leg segment. The legs are largely unmodified, although in Anthracosironidae the forelegs are quite large and spiny,[23] presumably to help catch prey. The legs end in three claws, two large ones and a smaller median claw.

Taxonomy[edit]

plesion taxa
Palaeocharinidae Hirst, 1923
Anthracomartidae Haase, 1890
Anthracosironidae Pocock, 1903
Trigonotarbidae Petrunkevitch, 1949
Lissomartidae Dunlop, 1995
Aphantomartidae Petrunkevitch, 1945
Kreischeriidae Haase, 1890
Eophrynidae Karsch, 1882
incertae sedis
  • Anthracophrynus Andrée, 1913
    • Anthracophrynus tuberculatus Andrée, 1913 – Late Carboniferous, Germany
  • Eophrynusscharfi Scharf, 1924 – Early Permian, Germany
nomina dubia
  • Anthracomartus buchi (Goldenberg, 1873) – Late Carboniferous, Germany
  • Anthracomartus hageni (Goldenberg, 1873) – Late Carboniferous, Germany
  • Elaverimartus pococki Petrunkevitch, 1953 – Late Carboniferous, Scotland
  • Eurymartus latus Matthew, 1895 – Late Carboniferous, Canada
  • ?Eurymartus spinulosus Matthew, 1895 – Late Carboniferous, Canada
  • Trigonomartus woodruffi (Scudder, 1893) – Late Carboniferous, United States

References[edit]

  1. ^ Jonathan Amos (9 July 2014). "Ancient arachnid 'walks again'". BBC News. Retrieved 9 July 2014. 
  2. ^ William Buckland (1837). Treatise IV. Geology and mineralogy with reference to natural theology. The Bridgewater treatises on the power, wisdom and goodness of God as manifested in the creation. (2nd ed.). London: William Pickering. 
  3. ^ H. Woodward (1871). "On the discovery of a new and very perfect Arachnide from the ironstone of the Dudley Coal-field". Geological Magazine 8 (9): 1–4. doi:10.1017/s0016756800192817. 
  4. ^ H. Woodward (1878). "Discovery of the remains of a fossil crab (Decapoda–Bracyura) in the Coal Measures of the Environs of Mons, Belgium". Geological Magazine. new series 2 (5): 433–436. 
  5. ^ F. Karsch (1882). "Ueber ein neues Spinnenthier aus der Schlesischen Steinkohle und die Arachnoiden überhaupt". Zeitschrift der Deutschen geologischen Gesellschaft (in German) 34: 556–561. 
  6. ^ H. B. Geinitz (1882). "Kreischeria wiedei, ein Pseudoskorpion aus der Steinkohlenformation von Zwickau". Zeitschrift der Deutschen geologischen Gesellschaft (in German) 34: 238–242. 
  7. ^ Johann Kušta (1883). "Anthracomartus krejcii, eine neue Arachnide aus dem Böhmischen Karbon". Sitzungsberichte der Königlich Böhmischen Gesellschaft der Wissenschaften, Mathematisch-Naturwissenschaftliche Klasse (in German) 1883: 7. 
  8. ^ Johann Kušta (1884). "Neue Arachniden aus der Steinkohlenformation von Rakonitz". Sitzungsberichte der Königlich Böhmischen Gesellschaft der Wissenschaften, Mathematisch-Naturwissenschaftliche Klasse (in German) 1884: 398–401. 
  9. ^ Johann Kušta (1885). "Neue fossile Arthropoden aus dem Noeggarathienschiefer von Rakonitz". Sitzungsberichte der Königlich Böhmischen Gesellschaft der Wissenschaften, Mathematisch-Naturwissenschaftliche Klasse (in German) 1885: 1–7. 
  10. ^ Johann Kušta (1888). "O nových arachnidech z karbonu Rakovnického. (Neue Arachniden aus der Steinkohlenformation bei Rakonitz)". Sitzungsberichte der Königlich Böhmischen Gesellschaft der Wissenschaften, Mathematisch-Naturwissenschaftliche Klasse (in Czech) 1888: 194–208. 
  11. ^ Samuel H. Scudder (1884). "A contribution to our knowledge of Paleozoic Arachnida". Proceedings of the American Academy of Arts and Sciences 20: 13–22. doi:10.2307/25138764. JSTOR 25138764. 
  12. ^ William A. Shear, Paul A. Selden, W. D. I. Rolfe, Patricia M. Bonamo & James D. Grierson (1987). "New terrestrial arachnids from the Devonian of Gilboa, New York". American Museum Novitates 2901: 1–74. 
  13. ^ Jeffrey W. Shultz (1990). "Evolutionary morphology and phylogeny of Arachnida". Cladistics 6 (1): 1–38. doi:10.1111/j.1096-0031.1990.tb00523.x. 
  14. ^ Jeffrey W. Shultz (2007). "A phylogenetic analysis of the arachnid orders based on morphological characters". Zoological Journal of the Linnean Society 150 (2): 221–265. doi:10.1111/j.1096-3642.2007.00284.x. 
  15. ^ Ferdinand Karsch (1892). "Ueber Cryptostemma Guèr. als einziger recenter Ausläufer der fossilen Arachnoideen-Ordnung Meridogastra Thor". Berliner Entomologische Zeitschrift (in German) 37 (1): 25–32. doi:10.1002/mmnd.18920370108. 
  16. ^ Jason A. Dunlop (1996). "Evidence for a sister group relationship between Ricinulei and Trigonotarbida" (PDF). Bulletin of the British Arachnological Society 10 (6): 193–204. 
  17. ^ Jason A. Dunlop, Carsten Kamenz and Giovanni Talarico (2009). "A fossil trigonotarbid arachnid with a ricinuleid-like pedipalpal claw". Zoomorphology 128 (4): 305–313. doi:10.1007/s00435-009-0090-z. 
  18. ^ Russell Garwood, Jason A. Dunlop & Mark D. Sutton (2009). "High-fidelity X-ray micro-tomography reconstruction of siderite-hosted Carboniferous arachnids". Biology Letters 5 (6): 841–844. doi:10.1098/rsbl.2009.0464. PMC 2828000. PMID 19656861. 
  19. ^ Stephen R. Fayers, Jason A. Dunlop & Nigel H. Trewin (2005). "A new early Devonian trigonotarbid arachnid from the Windyfield chert, Rhynie, Scotland". Journal of Systematic Palaeontology 2 (4): 269–284. doi:10.1017/S147720190400149X. 
  20. ^ Ronny Rößler & Jason A. Dunlop (1997). "Redescription of the largest trigonotarbid arachnid – Kreischeria wiedei Geinitz 1882 from the Upper Carboniferous of Zwickau, Germany". Paläontologische Zeitschrift 71 (3–4): 237–245. doi:10.1007/BF02988493. 
  21. ^ Stanley Hirst & S. Maulik (1926). "On some arthropod remains from the Rhynie Chert (Old Red Sandstone)". Geological Magazine 63 (2): 69–71. doi:10.1017/S0016756800083692. 
  22. ^ Jason A. Dunlop (1994). "Comparative anatomy of filtration mechanisms in tetrapulmonate arachnids (Trigonotarbida, Araneae, Amblypygi, Uropygi and Schizomida)". Bulletin of the British Arachnological Society 9: 267–273. 
  23. ^ R. I. Pocock (1903). "A new Carboniferous arachnid". Geological Magazine. Decade 4 10 (6): 247–251. doi:10.1017/S001675680011252X.