Helenodora inopinata
| Helenodora inopinata | ||||||||||||
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Photos and drawing of the holotype of Helenodora inopinata |
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| Temporal occurrence | ||||||||||||
| Westfalium D ( Moskovium , Oberkarbon ) | ||||||||||||
| 309 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Helenodora inopinata | ||||||||||||
| Thompson & Jones , 1980 |
Helenodora inopinata is an extinct species of columbus (Onychophora) from the geological period of the Upper Carboniferous . Their fossil remains were found in siderite concretions in the famous deposit on Mazon Creek in the US state of Illinois . The species is considered to be the earliest, undisputed fossil record of the velvet worms.
Helenodora inopinata was first described in 1980 and is named after Helen Piecko, who found the fossils. The name means something like 'Helene's unexpected gift'. Both the holo and paratype of the species are now in the Field Museum of Natural History in Chicago .
features
The two known specimens of the species are characterized by a worm-shaped body about six centimeters long and one centimeter wide, on which there are up to 20 stubby pairs of legs positioned on the abdomen at regular intervals. On one of these legs, which are about two to three millimeters long, two small, about half a millimeter long claws could be identified.
On the body surface, around nine rings can be made out per segment, on which there are numerous small elevations that are interpreted as papillae. These are arranged in longitudinal rows that are about a third of a millimeter apart.
The head region is poorly preserved. Although a clear assignment is not possible, a black spot near the (assumed) front end of the body is interpreted as a jaw; if this identification applies, the mouth was already on the belly side, as in the modern representatives of the animal line. However, it is quite unclear whether the two front pairs of extremities can already be interpreted as antennae or as oral papillae. (The former are used by modern velvet worms to track down potential prey, the latter by spraying sticky slime to catch prey.)
Site and habitat
Helenodora inopinata was found in siderite, which comes from the so-called Francis Creek Shale in the north of the US state of Illinois. It is assigned to the geological period of the Middle Pennsylvanian , which in turn falls into the Carboniferous, and is more than 300 million years old.
The animal's habitat can no longer be precisely reconstructed today, as land, freshwater and marine forms can be found in the Francis Creek slate. However, similarities to the modern, exclusively rural forms speak predominantly in favor of a terrestrial way of life.
Systematic classification
Helenodora was temporarily regarded as a younger synonym of Ilyodes Scudder in 1890. In 2016, however, a revision based on additional evidence confirmed the status of Helenodora inopinata as a type species of an independent genus.
Due to the large number of stubby feet, it can be considered relatively certain that Helenodora inopinata belongs to the columbus (Onychophora) named after this property. The species is the earliest undisputed find of a representative of this taxon .
From the Cambrian and Ordovician epochs , however, a whole series of fossils are known that are traditionally also regarded as members of the velvet worms , such as Aysheaia pedunculata , Xenusion auerswaldae or Hallucigenia fortis . In cladistic principles based studies of these and similar forms but sometimes seen as lineages representatives of a taxon from water bears (tardigrades) and arthropods (Arthropoda - insects, spiders, crustaceans and others). If this view were to be correct, then Helenodora inopinata would actually be the earliest known form of the true colobus.
If, however, the traditional view out to be correct, the type includes at least a huge time gap between the Cambrian and Ordovician forms one hand and the Cretaceous kind cretoperipatus burmiticus , resulting in amber from Myanmar has received, on the other. Together with two species, Succinipatopsis balticus and Tertiapatus dominicanus from the Tertiary , they make up the entire fossil record of the velvet worms.
literature
- J. Thompson, DS Jones, A possible onychophoran from the Middle Pennsylvanian mazon creek beds of Northern Illinois , Journal of Paleontology, 54 (3), 588
Individual evidence
- ^ A b D. JE Murdock, SE Gabbott & MA Purnell: The impact of taphonomic data on phylogenetic resolution: Helenodora inopinata (Carboniferous, Mazon Creek deposit) and the onychophoran stem lineage. In: BMC Evolutionary Biology. Vol. 16, 2016, item no. 19. doi : 10.1186 / s12862-016-0582-7
- ^ AA Hay, S. Kruty: Onychophora. In: CW Shabica, AA Hay (Ed.): Richardson's Guide to The Fossil Fauna of Mazon Creek. Pp. 215-218, Northeastern Illinois University, 1997, ISBN 978-0-9250-6521-6 .