Onychopterella
| Onychopterella | |
|---|---|
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| Bottom view of the holotype specimen of O. kokomoensis recovered at Kokomo, in the United States | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Order: | †Eurypterida |
| Superfamily: | †Onychopterelloidea |
| Family: | †Onychopterellidae |
| Genus: | †Onychopterella Størmer, 1951 |
| Type species | |
| †Onychopterella kokomoensis Miller & Gurley, 1896
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| Species | |
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| Synonyms | |
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Onychopterella (stages of South Africa.
Its
scales
. The largest species of the genus was O. kokomoensis with a total length of 16 centimetres (6.3 inches) long, followed by O. augusti (14.3 cm, 5.6 in) and O. pumilus (4 cm, 1.6 in).
The first Onychopterella fossils, belonging to O. kokomoensis, were discovered in 1896 at the Waterlime Group of
distal
end of the swimming leg), as well as the lanceolate (lance-shaped) or styliform (pen-shaped) form of the telson and other characteristics.
The exceptional preservation of the fossils of O. augusti has permitted scientists to describe part of the
branchial respiratory system. This turned out to be highly similar to that of the scorpions of today, supporting a eurypterid-scorpion relationship. Onychopterella was a genus that was able to swim. Most of the time it was likely in the stratum
, probably using its spines to walk and its head to dig in the ground.
Description
Like the other
onychopterellids, Onychopterella was a small eurypterid. The smallest species, O. pumilus, measured only 4 centimetres (1.6 inches). The size of the largest one, O. kokomoensis, is estimated at 16 cm (6.3 in), representing the biggest species of the family Onychopterellidae.[1] O. augusti had a similar size, with the largest specimen reaching 14.3 cm (5.6 in).[2]
The
posteriorly,[5] while that of O. augusti was subcordate (almost heart-shaped) anteriorly and rounded posteriorly.[2] The metastoma of O. pumilus is not known in its entirety. Only the posterior part, which was rounded, is known.[4]
In O. kokomoensis, the preabdomen (body
gills) chambers or respiratory tissue of the branchial tract. The postabdomen was short, and its segments gradually narrowed towards the telson. Each of the postabdominal segments had small epimera. The shape of the telson in O. kokomoensis was clavate (resembling a club), in O. pumilus it was styliform (pen-shaped) and in O. augusti it was lanceolate (lance-shaped).[2]
The walking legs (second to fifth pair of
scales, was the same in all species.[6]
History of research
In 1896,
paleontologists Samuel Almond Miller and William Frank Eugene Gurley described a new species of Eurypterus, E. kokomoensis, based on four specimens, three of them well-preserved and a fragmentary one,[3][5] collected at the Waterlime Group at Kokomo, Indiana, in the United States. They noticed differences between the new species and E. remipes, the type species of Eurypterus, such as the proportions of the carapace, the shorter telson and the size and general form of the body. Only two pairs of appendages were described, suggesting the rest broke away during preservation, although the outline of a pair of unusually large swimming legs was reported. Miller and Gurley considered the preserved parts sufficiently similar to assign the species to Eurypterus.[3] FMNH UC6638, an almost complete specimen, was designated as the type specimen.[7]
In 1912, paleontologists
ornithologist Ludwig Reichenbach. Størmer substituted the old name with a new one, Onychopterella.[10]
In 1916, researcher and geologist Thomas Edmund Savage erected the new species Eurypterus pumilus to accommodate one single well-preserved specimen showcasing the
ontogenetic stage (a different developmental stage of the same animal throughout its life) of O. kokomoensis.[2] Due to the lack of a known accession number for the fossil, its re-examination is impossible.[11]
In 1995, paleontologists Braddy,
specific epithet augusti. It differed from the rest of the species by the lack of large epimera in the pretelson, wider body proportions, the short length of the postabdomen and telson, the lanceolate form of the latter, the two projections of the eighth podomere and in a distal spine longer than in the rest of the species. The paratype, GSSA C427, is the largest known specimen. O. augusti was also compared to the enigmatic Silurian eurypterid Marsupipterus sculpturatus, concluding that the differences between the telson (the only known part of Marsupipterus) of both species are probably preservational.[2]
Classification
Onychopterella is classified as part of its own family, Onychopterellidae, the only
superfamily Onychopterelloidea.[12] It was originally described as a subgenus of Eurypterus,[5] but it was recognized as a distinct genus in 1948.[9]
It has been suggested that Onychopterella could represent a
derived members of Eurypterina such as Dolichopterus, ending in a large plate. The species O. pumilus was not included in the analysis because of its possible affiliation with Drepanopterus.[13]
In 2011, Lamsdell recovered Onychopterella as
Moselopteroidea the most basal eurypterine clade. He also erected the new superfamily Onychopterelloidea and family Onychopterellidae, placing within the latter the genera Onychopterella and Tylopterella. This family was characterized by the presence of spines in the second to fourth pairs of appendages, lack of spines in the fifth and sixth (except occasionally a distal spine in the last podomere of the sixth appendage), the shape of the carapace with lateral eyes and a lanceolate or styliform telson, among other features.[7] Alkenopterus was assigned to Onychopterellidae three years later because of the detection of a movable spine in the swimming leg, rather than a simple projection as previously thought.[14] Before the creation of Onychopterellidae, Onychopterella had been classified in the family Erieopteridae since 1989 by paleontologist Victor P. Tollerton, initially together with Erieopterus and Buffalopterus based on similarities of the morphology of the appendages and the opisthosoma.[15]
The cladogram below is based on a larger study (simplified to only show eurypterids) in a 2011 phylogenetic analysis carried out by Lamsdell, showcasing the basal members of the Eurypterina suborder of eurypterids with other derived groups.[7]
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Paleobiology
Only the
organs and their functional adaptation to walk.[2] This reason and the lack of a more modified spike-like distal podomere may suggest Onychopterella was not a very efficient swimmer.[7]
In 1999, Braddy, Aldridge, Theron and Sarah E. Gabbott, a geologist, described a new specimen of O. augusti from the Soom Shale (GSSA C1179, housed at the Geological Survey of South Africa) which preserves four pairs of
synapomorphy (shared characteristic different from that of their latest common ancestor) between both clades and even increasing the possibilities of a sister group relationship (that is, that both clades are the closest relative to each other).[17]
The eurypterid
trackways were medium-sized (largest track 13.6 cm, 5.4 in wide) and consisted of several symmetrical series of four tracks and individual typically oval or tear-shaped marks with small impressions on the sides, sometimes bilobed and intermittent. A median line was occasionally displayed. Several factors support that P. capensis represents the tracks of O. augusti; the average external width of P. capensis is comparable to that of fossils of O. augusti, the distal spines of the swimming leg of O. augusti could have caused such bilobed marks and Onychopterella represents the only Ordovician eurypterid from those deposits. In addition, the median line could have been produced by the telson touching the substrate. O. augusti would have been able to make incursions to the terrestrial surface, but it would have been uncomfortable for it, performing an undulatory gait and keeping its telson in regular contact with the ground, hence the median line. But nevertheless, this can not be completely proven unless a specimen of O. augusti is found alongside similar tracks.[16]
Paleoecology
It is thought that the genus Onychopterella lived in
top predator, feeding on other arthropods, worms and probably conodonts.[2] It lived during the Late Hirnantian (Late Ordovician) to Early Rhuddanian (Early Silurian) stages, in South Africa.[7][18]
The type species, O. kokomoensis, inhabited a
Most of the eurypterids found outside the
sea floor during the periods of sea level descent of the Hirnantian. Onychopterella does not represent the only occurrence of basal genera in Gondwana; Paraeurypterus, a genus known from deposits of the Şort Tepe Formation in southeastern Turkey, probably arrived there by the same method as O. augusti.[18]
See also
References
- .
- ^ a b c d e f g h i j k l m n o Braddy, Simon J.; Aldridge, Richard J.; Theron, Johannes N. (1995). "A new eurypterid from the Late Ordovician Table Mountain Group, South Africa". Palaeontology. 38: 563–581.
- ^ a b c d Miller, Samuel A.; Gurley, William F. E. (1896). "New species of Echinodermata and a new crustacean from the Paleozoic rocks". Illinois State Museum Natural History Bulletin. 10: 1–91. Archived from the original on 10 May 2019.
- ^ from the original on 30 December 2018.
- ^ a b c d e f g h Clarke, John M.; Ruedemann, Rudolf (1912). The Eurypterida of New York. University of California Libraries.
- ^ JSTOR 1300776. (subscription required)
- ^ S2CID 251107327.
- ISBN 9781408133262.
- ^ JSTOR 1299516. (subscription required)
- S2CID 129426407. (subscription required)
- ^ S2CID 84151264.
- Natural History Museum Bern. pp. 1–296.
- S2CID 88413267.
- S2CID 132432538. (subscription required)
- from the original on 24 March 2019.
- ^ PIIS0899-5382(99)00087-1.
- .
- ^ .
- . (subscription required)
- ^ doi:10.1016/j.palaeo.2007.05.011. Archived from the original(PDF) on 18 July 2011.
- ISBN 9780521363983. (subscription required)
External links
Media related to Onychopterella at Wikimedia Commons
Data related to Onychopterella at Wikispecies
