Euthycarcinoidea

Euthycarcinoidea
Euthycarcinus kessleri , reconstruction drawing by Anton Handlirsch 1914 (today's reconstructions differ in numerous details)
Temporal occurrence
Furongium to anisium
485 to 247 million years
Locations
Europe (UK, France, Germany), North and South America, Australia
Systematics
Bilateria Primordial mouths (protostomia) Molting animals (Ecdysozoa) Arthropod (arthropoda) Mandibulata Euthycarcinoidea
Scientific name
Euthycarcinoidea
Gall & Grauvogel , 1964

The Euthycarcinoidea are a seldom found group of extinct arthropods, from the most recent Cambrian to the Middle Triassic . So far, 16 species have been described . Although there are some fossils with excellent preservation, their exact taxonomic classification is still a mystery. It has been suggested that they belong to the stem group of the millipede , to the crustaceans or as a sister group of the Hexapoda . While the oldest known representatives come from marine sediments and probably lived in the sea, all later fossils come from limnic or terrestrial deposits. Fossilized footprints (trace or Ichnofossils ) from the late Cambrian and Ordovician , which are assigned to the group, are considered to be the oldest unambiguous evidence of life on land .

anatomy

They were medium-sized, flattened arthropods. The smallest species was Heterocrania rhyniensis with a body length of around 15 millimeters. Schramixerxes gerem from Montceau-les-Mines reached a body length of 60 millimeters. The largest species described so far is Mosineia macnaughtoni with about 10 centimeters.

The body of the Euthycarcinoidea was divided into three separate body sections ( tagmata ): head, pre-abdomen (sometimes also thorax or trunk) and post-abdomen. On closer inspection, the head consists of two sections. The anterior one, the Procephalon, carried two long, simple articulated antennas and two hemispherical "spheroidal appendages", which almost all investigators believe to have been eyes (although facets have never been observed). The posterior one, called the gnathocephalon, carried the mouth limbs. This most often consisted of one, two pair usually plate-like structures, which are under the current interpretation of mandibles has acted in some types of in the middle of the head (unpaired) arranged plate according to some editors the labrum of the insect homolog be could. In some fossils this is the only recognizable structure, the mandibles are then completely absent; in other fossils the mouthparts are not recognizable due to preservation. The middle section, the pre-abdomen, was covered on the top and bottom by sclerites . The upper tergites were considerably wider than the lower sternites and almost completely covered the legs from above. On the side of each sternite sat a pair of legs, which were presumably anchored in the body with an apodeme . The number of sternites, and thus the legs, and those of the tergites did not match; there were two pairs of legs per tergite or sometimes three pairs of legs for the posterior segments, often eleven pairs of legs. The legs were single-branched (uniram), they were divided into numerous (up to 14) simple, uniform, ring-shaped segments that became slightly smaller towards the tip, and ended in an end spine. In some species they had fine, long bristles ( Kottyxerxes gloriosus ) or a short, spiky extension. The rear section of the body, the post-abdomen, was narrower than the pre-abdomen and consisted mostly of five, sometimes four or six segments without legs or other appendages and a long end spine of variable length, often called a telson . In the genera Sottyxerxes and Pieckoxerxes (found in Carboniferous of deposits Montceau-les Mines, France and Mazon Creek, USA) Präabdomen was elongated, relatively narrow and contributed 14 and 28 Tergites running pairs of legs, the animals were similar by recent centipedes. In the other genera it was much wider than the post-abdomen, sometimes, as in the genera Euthycarcinus and Heterocrania, laterally rearward tooth-shaped. Usually five tergites were recognizable, in some genera ( Mosineia ) up to seven; the number of pairs of legs was also variable.

Way of life

The physique and the circumstances of the find suggest that the Euthycarcinoidea were soil-living ( benthic ) organisms that lived in the shallow bank zone of water. The species with finely bristled legs were possibly also able to swim. According to the accompanying flora and fauna, the populated waters were in almost all cases freshwater or brackish water habitats. The species Apankura machu from the Cambrian of Argentina and the species found in Quebec, i.e. especially the earliest known representatives of the group, can be assumed to be marine habitats. The group originally comes from the sea and seems to have later withdrawn to limnic habitats. Fossilized intestinal contents were found in animals of the species Heterocrania rhyniensis from the Windyfeld Chert in Scotland (very close to the famous Rhynie fossil deposit ). This consists of fibrous material of undoubtedly vegetable origin. Due to the spinous processes of the legs, there is also speculation about a possible predatory diet. For other species, a filtering diet is considered due to the fine hair bristles on the legs.

Trace fossils

In fossilized soils of marine tidal tidal flats, for example from Canada and Australia, trace fossils are known which consist of lateral impressions of numerous pairs of legs and a central grinding track. These have been given numerous names as Parataxa depending on their expression ( Cruziana , Didymaulichus , Diplichnites , Protichnites ). In many cases these can be related to Euthycarcinoidea with a high degree of probability. While it is not possible to differentiate with certainty that trace fossils in very shallow water from those on land, the most common interpretation is that the animals left the water either to graze on algae floodplains or to migrate from one shallow tidal pool to the next . At this point in time, there are no other fossils or trace fossils of land-living animals. It is possible that the Euthycarcinoidea were the first animals to leave the waters of the oceans to make at least short excursions on land. At least in two species, Synaustrus brookvalensis and Kottyxerxes gerem , simple tracheal- like structures have also been described, which could indicate air breathing.

Traces of rest of arthropods on the sediment surface from the red sandstone of Germany have been described as Tripartichnus triassicus . Although it is of course not clearly possible to identify the trace producer, the evidence speaks for a representative of the group, possibly Euthycarcinus kessleri .

relationship

When Anton Handlirsch described the first representative of the group, Euthycarcinus kessleri , from the red sandstone near Saarbrücken, he assumed that it belonged to an extinct order of crustaceans with a relationship to copepods . Gall and Grauvogel described this species anew, now as a representative of their own order of crustaceans, for which they introduced the name Euthycarcinoidea. Later editors assumed relationships with the Merostomata ( horseshoe crabs and sea scorpions), which belong to the arachnids , others saw them again as crustaceans or as primeval relatives and possible sister groups of the Hexapoda.

A phylogenetic analysis based on morphological features showed a position basal within the mandibular, with crustaceans, millipedes and hexipedes together as a sister group . Their actual position, however, is still unclear and depends critically above all on the interpretation of the head with its attachments. They are therefore to be regarded as Arthropoda incertae sedis , presumably belonging to the mandibulata.

swell

• Javier Ortega-Hernández, David A. Legg, Jonathan Tremewan, Simon J. Braddy (2010): Euthycarcinoids (Fossils explained 59). Geology Today Vol. 26, No. 5: 195-198.
• Patrick R. Racheboeuf, Jean Vannier, Frederick R. Schram, Dominique Chabard, Daniel Sotty (2008): The euthycarcinoid arthropods from Montceau-les-Mines, France: functional morphology and affinities. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 99: 11-25. doi : 10.1017 / S1755691008006130

Individual evidence

1. ↑ ^{a b c} Lyall I.Anderson, & Nigel H. Trewin (2003): An Early Devonian arthropod fauna from the Windyfield cherts, Aberdeenshire, Scotland. Palaeontology, Volume 46, Number 3: 467-509.
2. ^ ^{A b} Joseph H. Collette: Three-Dimensionally Preserved Arthropods from the Cambrian (Furongian) of Quebec and Wisconsin: Systematics, Phylogeny, Ichnology, and Taphonomy. Masters Thesis 1896 - February 2014. Paper 322. download
3. ^ ^{A b} Frederick R. Schram & WD Ian Rolfe (1982): New Euthycarcinoid Arthropods from the Upper Pennsylvanian of France and Illinois. Journal of Paleontology Vol. 56, No. 6: 1434-1450.
4. ↑ ^{a b} N.E. Vaccari, GD Edgecombe, C. Escudero (2004): Cambrian origins and affinities of an enigmatic fossil group of arthropods. Nature vol. 430: 554-557.
5. ^ Gregory J. Retallack (2008): Cambrian-Ordovician non-marine fossils from South Australia. Alcheringa 33 (4): 355-391. doi : 10.1080 / 03115510903271066
6. ↑ Joseph H. Collette, James W. Hagadorn, Mario A. Lacelle (2010): Dead in their tracks - Cambrian arthropods and their traces from intertidal sandstones of Quebec and Wisconsin. Palaios 25: 475-486. doi : 10.2110 / palo.2009.p09-134r
7. ↑ Joseph H. Collette, Kenneth C. Gass, James W. Hagadorn (2012): Protichnites eremita Unshelled? Experimental Model-Based Neoichnology and New Evidence for A Euthycarcinoid Affinity for These Ichnospecies. Journal of Paleontology vol. 86: 442-454. doi : 10.1666 / 11-056.1
8. ↑ Lothar H. Vallon & Martin Röper (2008): Reading traces - From print to producer. Fossils 2008: 230-234. download ( Memento of the original from October 19, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. 
9. ^ Anton Handlirsch (1914): An interesting crustacean shape from the Triassic of the Vosges. Negotiations of the Zoological-Botanical Society in Vienna 64: 1-8. PDF
10. ↑ Jean-Claude Gall & Léa Grauvogel-Stamm (2005): The early Middle Triassic 'Grès à Voltzia' Formation of eastern France: a model of environmental refugium. Comptes Rendus Palevol 4: 637-652. doi : 10.1016 / j.crpv.2005.04.007