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Helenodora

Helenodora is an extinct basal onychophoran or lobopodian genus known from the Carboniferous Carbondale Formation of Illinois. The only known species described is H. inopinata. The ecology of this animal is not well known, but it is thought that it may have lived on land and/or underwater.

Discovery and naming

At the moment, Helenodora is known from ten specimens found in the Middle Pennsylvanian, Francis Creek Shale of Illinois.[2][3] All were found in siderite concretions from Mazon Creek fossil beds, a lagerstätte that contains animals like the famous "Tully Monster".[2][4]

The first specimens found (the holotype FMNH PE 29049 and paratype FMNH PE 29050) were described during the 80's and are composed of both a part and counterpart. These were deposited in the invertebrate fossil collection of the Field Museum of Natural History of Chicago, Illinois.[2] Other specimens include FMNH PE 13966, 33380, 33822, 45049, and 49784 and FMNH ROM 47513, 45565, and 47978.[3]

Helenodora was suggested by some authors to be a junior synonym of Ilyodes Scudder 1890, a fossil genus that includes two species and was originally described as a myriapod. A re-examination of the type material of Helenodora inopinata and the Ilyodes species found significant differences between them. Additionally, neither species of Ilyodes were adequately diagnosed, so they and the genus are all considered nomina dubia.[3]

The genus name "Helenodora" is Greek for "Helen’s gift". This name honors Mrs. Helen Piecko of Chicago, Illinois for finding both the holotype and paratype. The species name "inopinata" is Latin and means "unexpected".[2]

Description

Restoration of H. inopinata

Head

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Trunk

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Lobopods

While originally thought to have more or less,[2] Helenodora is now known to possess 20 pairs of legs known as lobopods. In complete specimens with a differentiated front and back, this number is certain.[3] These lobopods are preserved as stubby triangles that taper off towards the end.[2] They had a mean length of 1.7 millimeters, and a mean width at their base of 2.1 millimeters.[3] Other than a single leg on the paratype (appendage 11), none of Helenodora’s lobopods preserve any part of the cuticle. However, even where it exists, the cuticle is poorly preserved. Because of this, whether the lobopods had any annulations or limb ornaments is unknown.[2][3]

Claws

When it was first described, the paratype was found to preserve seven pairs of claws on the tips of its lobopods. One of the pairs was well defined, while the rest were less so. All claws were on the left row of the body and were preserved on either side of the concretion.[2] These claws were preserved as long small dark patches are were composed of a thin film of carbon and framboidal pyrite.[3]

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Classification

Paleobiology

References

  1. ^ Thompson, I.; Jones, D. S. (May 1980). "A Possible Onychophoran from the Middle Pennsylvanian Mazon Creek Beds of Northern Illinois" (PDF). Journal of Paleontology. 54 (3): 588–596. Bibcode:1974JPal...48..524M. JSTOR 1304204.
  2. ^ a b c d e f g h Thompson, Ida; Jones, Douglas S. (1980). "A Possible Onychophoran from the Middle Pennsylvanian Mazon Creek Beds of Northern Illinois". Journal of Paleontology. 54 (3): 588–596. ISSN 0022-3360.
  3. ^ a b c d e f g Murdock, D. J. E.; Gabbott, S. E.; Purnell, M. A. (2016). "The impact of taphonomic data on phylogenetic resolution: Helenodora inopinata (Carboniferous, Mazon Creek Lagerstätte) and the onychophoran stem lineage". BMC Evolutionary Biology. 16 (19): 19. Bibcode:2016BMCEE..16...19M. doi:10.1186/s12862-016-0582-7. PMC 4722706. PMID 26801389.
  4. ^ Clements, Thomas; Purnell, Mark; Gabbott, Sarah (2018-10-04). "The Mazon Creek Lagerstätte: a diverse late Paleozoic ecosystem entombed within siderite concretions". Journal of the Geological Society. 176 (1): 1–11. doi:10.1144/jgs2018-088. hdl:2381/44761. ISSN 0016-7649.