Trigonotarbida Fossil range: 419–290 Ma PreЄ Є O S D C P T J K Pg N Late Silurian to Early Permian
Palaeotarbus jerami
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Arachnida
Order:	Trigonotarbida † Petrunkevitch, 1949
Families
Palaeocharinidae Anthracomartidae Anthracosironidae Trigonotarbidae Lissomartidae Aphantomartidae Kreischeriidae Eophrynidae

The Order Trigonotarbida is an extinct group of arachnids whose fossil record extends from the late Silurian to the early Permian (c. 419 - 290 million years). 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 millimeters to a few centimetres in body length and had a segmented abdomen, with the tergites across the back of the animal's abdomen 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.

Contents 1 Historical background 1.1 A new arachnid order 2 Relationships 2.1 Pantetrapulmonata 2.2 Trigonotarbids and ricinuleids 3 Anatomy 3.1 Prosoma 3.1.1 Mouthparts 3.1.2 Pedipalps 3.1.3 Legs 3.2 Opisthosoma 3.2.1 Locking ridge 3.2.2 Tergites 3.2.3 Sternites 3.2.4 Book lungs 3.3 Ornamentation 4 Systematics 5 References

[edit] Historical background

The first trigonotarbid was described in 1837 from the Coal Measures of Coalbrookdale in England by the famous English geologist Dean William Buckland^[1]. 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 (geologist)^[2], he correctly identified it as an arachnid and renamed it Eophrynus prestvicii - whereby the genus name comes from Eo, meaning 'dawn', and Phrynus, a genus of living whip spider (Amblypygi). Woodward subsequently described another trigonotarbid, Brachypyge carbonis, from the Coal Measues of Mons in Belgium^[3]; although this fossil is only known from the abdomen and was initially mistaken for the back end of a crab.

[edit] A new arachnid order

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 völkelianus^[4] in honour of Herr Völkel, the foreman of the mine where it was discovered. This species was raised to a new, extinct, arachnid order which Karsch called Anthracomarti. The name is derived from 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^[5], although he interpreted it as a fossil pseudoscorpion. Johann Kušta described Anthracomartus krejcii^[6] from Rakovník in the Czech Republic, and published further descriptions in a number of subsequent papers^[7][8][9]. Samuel Hubbard Scudder described Anthracomartus trilobitus^[10] from Fayetteville, Arkansas, USA; the first trigonotarbid from North America.

[edit] Relationships

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.

[edit] Pantetrapulmonata

In the 1980s, Bill Shear and colleagues^[11]. carried out an important study on well preserved Mid Devonian trigonotarbids from Gilboa, New York, USA. 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^[12]. has become most widespread. Tetrapulmonates include spiders, whip spiders, whip scorpions and schizomids 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^[13] the Shear et al. hypothesis was largely supported and a group Pantetrapulmonata was proposed which comprises Trigonotarbida + Tetrapulmonata.

[edit] Trigonotarbids and ricinuleids

In 1892, Ferdinand Karsch suggested that the rare and rather bizarre-looking ricinuleids (Ricinulei) were the last living descendants of the trigonotarbids ^[14]. A similar hypothesis was reintroduced by Dunlop^[15] 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 opisthoosma which 'locks' the two halves of the body together. Although cladistic anylsis has tended to recover ricinuleids in their traditional position closely related to mites and ticks, further discoveries ^[16][17] have revealed that in trigonotarbids and ricinuleids the tip of the pedipalp ends in a small claw.

[edit] Anatomy

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^[18]. 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 ^[19].

[edit] Prosoma

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^[20], appear to have borne a series of individual lenses. In this sense palaeocharinids seem to be in the process of reducing a compound eye.

[edit] Mouthparts

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 ^[21] formed from hairs or platelets which strongly suggests that trigonotarbids (like spiders and many other arachnids) could only eat preorally digested, liquified prey.

[edit] Pedipalps

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.

[edit] Legs

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^[22], presumably to help catch prey. The legs end in three claws, two large ones and a smaller median claw.

[edit] Opisthosoma

The trigonotarbid opisthosoma (or abdomen) consists of twelve segments. The first forms a so called 'locking ridge' and the last two a small pygidium.

[edit] Locking ridge

A quite unusual feature, again shared with Ricinulei, is that the first tergite of the opisthosoma has a half-moon shape and fits into a pocket created by a fold at the back of the carapace. In this way the two halves of the body seem to have been 'locked' together. The function of this system is unknown and some of the more derived trigonotarbids seem to have lost it.

[edit] Tergites

The first tergite usually forms the locking ridge (see above). In many trigonotarbids the second and third tergites have fused together to form a single larger plate, sometimes called a 'diplotergite'. Further tergites from segments 4 to 9 follow. Tergites 2-8 (2-9 in some families) are divided into median and lateral plates and this is one of the most instantly recognisable trigonotarbid features. In most families each tergite is divided into three plates, but in Anthracomartidae there are five.

[edit] Sternites

Ventrally, the first sternite seems to be missing. The next two sclerites (segments 2-3) bear the lungs and are probably highly modified and flattened appendages. The third and sometimes the fourth segments also bear raised structures which may be equivalent to the ventral sacs seen in some living arachnids like whip spiders (Amblypygi). The last three segments of the abdomen comprise a flat element surrouding two small ring-like segments forming a postabdomen or pygidium. No trigonotarbid has yet been found with a telson.

[edit] Book lungs

Remarkable and well-preserved trigonotarbid fossils from the Rhynie chert of Scotland show that these animals had two pairs of book lungs^[23]. At ca. 410 million years, these are the oldest known examples of lungs in any animal group and clearly indicate that trigonotarbids lived on land. The detailed structure of these fossil book lungs is almost identical to the book lungs of modern arachnids ^[24].

[edit] Ornamentation

Some trigonotarbids, especially Carboniferous species in the families Aphantomartidae, Kreischeriidae and Eophrynidae have a heavily armoured body covered with tubercles and occasionally sharp spines. In some ways they resemble harvestmen of the Laniatores suborder, although the two groups are not closely related.

[edit] Systematics

• TRIGONOTARBIDA Petrunkevitch, 1949
  • = Anthracomarti Karsch, 1882
  • = Meridogastra Thorell & Lindström, 1885
  • = Eurymarti Matthew, 1895

• plesion taxa
• Palaeotarbus Dunlop, 1999
  • = Eotarbus Dunlop, 1996 [preoccupied]
  • Palaeotarbus jerami (Dunlop, 1996) — Late Silurian, England
• Alkenia Størmer, 1970
  • Alkenia mirabilis Størmer, 1970 — Early Devonian, Germany

• PALAEOCHARINIDAE Hirst, 1923
• Aculeatarbus Shear, Selden & Rolfe, 1987
  • Aculeatarbus depressus Shear, Selden & Rolfe, 1987 — Mid Devonian, USA
• Gelasinotarbus Shear, Selden & Rolfe, 1987
  • Gelasinotarbus bifidus Shear, Selden & Rolfe, 1987 — Mid Devonian, USA
  • Gelasinotarbus bonamoae Shear, Selden & Rolfe, 1987 — Mid Devonian, USA
  • Gelasinotarbus heptops Shear, Selden & Rolfe, 1987 — Mid Devonian, USA
  • Gelasinotarbus reticulatus Shear, Selden & Rolfe, 1987 — Mid Devonian, USA
• Gigantocharinus Shear, 2000
  • Gigantocharinus szatmaryi Shear, 2000 — Late Devonian, USA
• Gilboarachne Shear, Selden & Rolfe, 1987
  • Gilboarachne griersoni Shear, Selden & Rolfe, 1987 — Mid Devonian, USA
• Palaeocharinus Hirst, 1923
• = Palaeocharinoides Hirst, 1923
  • Palaeocharinus calmani Hirst, 1923 — Early Devonian, Scotland
  • Palaeocharinus hornei (Hirst, 1923) — Early Devonian, Scotland
  • Palaeocharinus kidstoni Hirst, 1923 — Early Devonan, Scotland
  • Palaeocharinus rhyniensis Hirst, 1923 — Early Devonian, Scotland
  • Palaeocharinus scourfieldi Hirst, 1923 — Early Devonian, Scotland
  • Palaeocharinus tuberculatus Fayers, Dunlop & Trewin, 2005 — Early Devonian, Scotland

• ANTHRACOMARTIDAE Haase, 1890
  • = PROMYGALIDAE Frič, 1904
  • = BRACHYPYGIDAE Pocock, 1911
  • = CORYPHOMARTIDAE Petrunkevitch, 1945
  • = PLEOMARTIDAE Petrunkevitch, 1945
• Anthracomartus Karsch, 1882
  • Anthracomartus granulatus Frič, 1904 — Late Carboniferous, Poland
  • Anthracomartus voelkelianus Karsch, 1882 — Late Carboniferous, Poland
• Brachylycosa Frič, 1904
  • = Perneria Frič, 1904
  • Brachylycosa carcinoides (Frič, 1901) — Late Carboniferous, Czech Republic
    • = Promygale rotundata Frič, 1901
    • = Perneria salticoides Frič, 1904
  • Brachylycosa kustae Petrunkevitch, 1953 — Late Carboniferous, Czech Republic
• Brachypyge Woodward, 1878
  • Brachypyge carbonis Woodward, 1878 — Late Carboniferous, Belgium
• Cleptomartus Petrunkevitch, 1949
  • Cleptomartus denuiti (Pruvost, 1922) — Late Carboniferous, Belgium
  • Cleptomartus hangardi Guthörl, 1965 — Late Carboniferous, Germany
  • Cleptomartus plautus Petrunkevitch, 1949 — Late Carboniferous, England
  • Cleptomartus planus Petrunkevitch, 1949 — Late CArboniferous, England
• Coryphomartus Petrunkevitch, 1945
  • Coryphomartus triangularis (Petrunkevitch, 1913) — Late Carboniferous, Canada
• Cryptomartus Petrunkevitch, 1945
  • Cryptomartus hindi (Pocock, 1911) — Late Carboniferous, England
  •  ?Cryptomartus meyeri Guthörl, 1964 — Late Carboniferous, Germany
  • Cryptomartus presti Pocock, 1911 — Late Carboniferous, England
  • Cryptomartus radvanicensis Opluštil, 1985 — Late Carboniferous, Czech Republic
  • Cryptomartus rebskei Brauckmann, 1984 — Late Carboniferous, Germany
• Maiocercus Pocock, 1911
  • Maiocercus celticus (Pocock, 1902) — Late Carboniferous, Europe
    • = Maiocercus orbicularis Gill, 1911
• Oomartus Petrunkevitch, 1953
  • Oomartus nyranensis Petrunkevitch, 1953 — Late Carboniferous, Czech Republic
• Pleomartus Petrunkevitch, 1945
  • Pleomartus palatinus (Ammon, 1901) — Late Carboniferous, Germany
  • Pleomartus trilobitus (Scudder, 1884) — Late Carboniferous, USA
• Promygale Frič, 1901
  • Promygale bohemica (Frič, 1901) — Late Carboniferous, Czech Republic
  • Promygale elegans Frič, 1901 — Late Carboniferous, Czech Republic
  • Promygale minor Kušta, 1884 — Late Carboniferous, Czech Republic
    • = Anthracomartus socius Kušta, 1888
  • Promygale janae Opluštil, 1986 — Late Carboniferous, Czech Republic

• ANTHRACOSIRONIDAE Pocock, 1903
• Anthracosiro Pocock, 1903
  • Anthracosiro fritschii Pocock, 1903 — Late Carboniferous, Europe
    • = Anthracosiro elongatus Waterlot, 1934
  • Anthracosiro woodwardi Pocock, 1903 — Late Carboniferous, Europe
    • = Anthracosiro corsini Pruvost, 1926
    • = Anthracosiro latipes Gill, 1909)
• Arianrhoda Dunlop & Selden, 2004
  • Arianrhoda bennetti Dunlop & Selden, 2004 — Early Devonian, Wales

• TRIGONOTARBIDAE Petrunkevitch, 1949
• Archaeomartus Størmer, 1970 — Early Devonian, Germany
  • Archaeomartus levis Størmer, 1970 — Early Devonian, Germany
  • Archaeomartus roessleri Dunlop & Brauckmann, 2006 — Late Carboniferous, Germany
  • Archaeomartus tuberculatus Størmer, 1970 — Early Devonian, Germany
• Trigonotarbus Pocock, 1911
  • Trigonotarbus arnoldi Petrunkevitch, 1955 — Late Carboniferous, France
  • Trigonotarbus johnsoni Pocock, 1911— Late Carboniferous, England
  • Trigonotarbus stoermeri Schultka, 1991 — Early Devonian, Germany

• LISSOMARTIDAE Dunlop, 1995
• Lissomartus Petrunkevitch, 1949
  • Lissomartus carbonarius (Petrunkevitch, 1913) — Late Carboniferous, USA
  • Lissomartus schucherti (Petrunkevitch, 1913) — Late Carboniferous, USA

• APHANTOMARTIDAE Petrunkevitch, 1945
  • = TRIGONOMARTIDAE Petrunkevitch, 1949
• Aphantomartus Pocock, 1911
• = Trigonomartus Petrunkevitch, 1913
• = Phrynomartus Petrunkevitch, 1945
  • Aphantomartus areolatus Pocock, 1911 — Early/Late Carboniferous, Europe
    • = Aphantomartus pococki Pruvost, 1912
    • = Trigonomartus dorlodoti Pruvost, 1930
    • = Eophrynus waechteri Guthörl, 1938
    • = ?Trigonomartus pruvosti van der Heide, 1951
    • = ?Brachylycosa manebachensis Müller, 1957
  • Aphantomartus ilfeldicus (Scharf, 1924) — Permian, Germany
  • Aphantomartus pustulatus (Scudder, 1884) — Late Carboniferous, Europe, North America
    • = ?Kreischeria villeti Pruvost, 1912
    • = Cleptomartus plötzensis Simon, 1971

• KREISCHERIIDAE Haase, 1890
• Anzinia Petrunkevitch, 1953
  • Anzinia thevenini (Pruvost, 1919) — Late Carboniferous, France
• Gondwanarache Pinto & Hünicken, 1980
  • Gondwanarache argentinensis Pinto & Hünicken, 1980 — Late Carboniferous, Argentina
• Hemikreischeria Frič, 1904
  • Hemikreischeria geinitzi (Thevenin, 1902) — Late Carboniferous, France
• Kreischeria Geinitz, 1882
  • Kreischeria wiedei Geinitz, 1882 — Late Carboniferous, Germany
• Pseudokreischeria Petrunkevitch, 1953
  • Pseudokreischeria pococki (Gill, 1924) — Late Carboniferous, England
    • = Eophrynus varius Petrunkevitch, 1949
• EOPHRYNIDAE Karsch, 1882
  • = HEMIPHRYNIDAE Frič, 1904
• Areomartus Petrunkevitch, 1913
  • Areomartus ovatus Petrunkevitch, 1913 — Late Carboniferous, USA
• Eophrynus Woodward, 1871
  • Eophrynus prestvicii (Buckland, 1837) — Late Carboniferous, England
  • Eophrynus udus Brauckmann, Koch & Kemper, 1985 — Late Carboniferous, Germany
• Nyranytarbus Harvey & Selden, 1995
• = Hemiphrynus Frič, 1901 [preoccupied]
  • Nyranytarbus hofmanni (Frič, 1901) — Late Carboniferous, Czech Republic
  • Nyranytarbus longipes (Frič, 1901) - Late Carboniferous, Czech Republic
• Petrovicia Frič, 1904
  • Petrovicia proditoria Frič, 1904 — Late Carboniferous, Czech Republic
• Planomartus Petrunkevitch, 1953
  • Planomartus krejcii (Kušta, 1883) — Late Carboniferous, Czech Republic
    • = Anthracomartus affinis Kušta, 1885
• Pleophrynus Petrunkevitch, 1945a
  • Pleophrynus verrucosus (Pocock, 1911) — Late Carboniferous, UK, USA
    • = Eophrynus warei Dix & Pringle, 1930
    • = Pleophrynus ensifer Petrunkevitch, 1945
    • = Eophrynus jugatus Ambrose & Romano, 1972
• Pocononia Petrunkevitch, 1953
  • Pocononia whitei (Ewing, 1930) — Early Carboniferous, USA
• Somaspidion Jux, 1982
  • Somaspidion hammapheron Jux, 1982
• Stenotrogulus Frič, 1904
• = Cyclotrogulus Frič, 1904
• = Pseudoeophrynus Příbyl, 1958
  • Stenotrogulus salmii (Stur, 1877)— Late Carboniferous, Czech Republic
    • = Cyclotrogulus sturii Frič, 1904 [non Hasse, 1890]
    • = Pseudoeophrynus ostraviensis Příbyl, 1958
• Vratislavia Frič, 1904
• Vratislavia silesica (Roemer, 1878) — Late Carboniferous, Poland

Trigotarbida incertae sedis

• Anthracophrynus Andrée, 1913
  • Anthracophrynus tuberculatus Andrée, 1913 — Late Carboniferous, Germany
• ‘Eophrynus’
  • ‘Eophrynus’ scharfi 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, USA

[edit] References