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Ordovician trilobites from Taimyr and the identity of Taimyraspis Balashova, 1959
Natural History Museum, London.
Uppsala University, Music and Museums, Museum of Evolution.ORCID iD: 0000-0001-8769-3572
2017 (English)In: 6th International Conference on Trilobites and their Relatives. Tallinn, Estonia,  7-10 July 2017 / [ed] Helje Pärnaste, Tallinn: Libris Est OU, Tallinn , 2017, 18- p.Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

Ordovician and Silurian trilobites from the Taimyr Peninsula were described by Balashova (1959, 1960), who identified 31genera and 60 species through the Middle and Upper Ordovician part of the succession. New material from the Ordovician succession was collected during a multidisciplinary expedition arranged by the Swedish Polar Research Institute in 1998. Three localities along the eastern shore of the Upper Taimyr River were sampled. The trilobites include some Siberian endemics in shelf limestones, with more widespread faunas representing a different biofaces. The most diverse Upper Ordovician fauna was recovered from the Mutninskaya Formation, and a rich sample collected from the locality at Fisherman's Bend is similarin many ways to 'open shelf' Upper Ordovician faunas described particularly from the Scotland-Appalachian Caledonides. Of particular interest is excellent new material of the hitherto incompletely known genus Taimyraspis. Balashova associated an incorrect thorax and pygidium with the cephalic parts when she described this taxon. Furthermore, she assigned Taimyraspis to the Family Isocolidae, which has been followed by subsequent authors. However, recognition of the correct thoracic segments and pygidium in the new collections makes this familial assignment implausible. Since Balashova (1959) several other trilobitegenera have been erected which are relevant to the relationships of Taimyraspis. Dean (1972) proposed a new genus Effnaspis for a species originally described by B. N. Cooper (1953) from Virginia as lsbergia virginica and also placed in lsocolidae. Cooper had assigned a pygidium to this species, which Dean subsequently rejected as being inappropriate for an isocolid. However, this pygidium is more compatible with that of Taimyraspis, and the cranidium of Effnaspis is also so similar to that of Taimyraspis that it is considered likely that Effnaspis is its synonym. Chang and Fan (1960) erected a third relevant genus Yumenaspis, from the Chilien Mountains, China; this genus was placed in Family Hapalopleuridae. Again, there are considerable similarities to Taimyraspis, and a pygidium attributed to Yumenaspis is also appropriate. Yumenaspis has since been reportedin several localities in Scotland and Ireland, but never from good material. We consider that all of these trilobites are closely related, with a wide distribution similar to that of other genera from Fisherman's Bend. The familial relationships of this group are less easily resolved. Taimyraspis is neither isocolid nor hapalopleurid. However, we recognise significant similarities to a rare Ordovician genus described from Norway by Nikolaisen (1965) as Frognaspis. Nikolaisen assigned this genus to the previously monogeneric Family Ityophoridae, based on ltyophorus from the latest Ordovician Boda Limestone of Sweden. The higher-level relationships of this family are controversial. However, small growth stages of Taimyraspis in the new collections suggest aplacement within the corynexochoids sensu lato.

Place, publisher, year, edition, pages
Tallinn: Libris Est OU, Tallinn , 2017. 18- p.
Keyword [en]
Taimyr, trilobites, Ordovician, Taimyraspis, Yumenaspis, Effnaspis
National Category
Other Earth and Related Environmental Sciences
Research subject
Earth Science with specialization in Historical Geology and Palaeontology
Identifiers
URN: urn:nbn:se:uu:diva-337464ISBN: 978-9949-81-861-7 (print)OAI: oai:DiVA.org:uu-337464DiVA: diva2:1169669
Conference
6th International Conference on Trilobites and their Relatives. Tallinn, Estonia
Available from: 2017-12-29 Created: 2017-12-29 Last updated: 2017-12-29

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