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Article: Paramonoclimacis sidjachenkoi (Obut & Sobolevskaya) and the evolution of the streptograptid thecal aperture in the Silurian (Graptolithina, Monograptidae)

Papers in Palaeontology - Volume 5 Issue 3 - Cover
Publication: Palaeontology
Volume: 5
Part: 3
Publication Date: August 2019
Page(s): 499 520
Author(s): Jörg Maletz, Michael J. Melchin, Peter Bullock, and Jennifer Russel‐Houston
DOI: 10.1002/spp2.1248
Addition Information

How to Cite

MALETZ, J., MELCHIN, M.J., BULLOCK, P., RUSSEL‐HOUSTON, J. 2019. Paramonoclimacis sidjachenkoi (Obut & Sobolevskaya) and the evolution of the streptograptid thecal aperture in the Silurian (Graptolithina, Monograptidae) . Papers in Palaeontology, 5, 3, 499-520. DOI: /doi/10.1002/spp2.1248

Author Information

  • Jörg Maletz - Institute of Geosciences FU Berlin Malteserstrasse 74‐100 D‐12249 Berlin Germany
  • Michael J. Melchin - Department of Earth Sciences St Francis Xavier University PO Box 5000 Antigonish NS B2G 2W5 Canada
  • Peter Bullock - 67 Queen Mary Road Kingston ON K7M2A3 Canada
  • Jennifer Russel‐Houston - Osum Oil Sands Corp. Suite 1900, 255 – 5th Avenue SW Calgary AB T2P 3G6 Canada

Publication History

  • Issue published online: 20 July 2019
  • Manuscript Accepted: 12 August 2018
  • Manuscript Received: 26 April 2018

Funded By

NSERC Discovery Grant
Polar Continental Shelf Project

Online Version Hosted By

Wiley Online Library
Get Article: Wiley Online Library [Pay-to-View Access] |

Abstract

Chemically isolated specimens of two species of the lower Silurian (Llandovery, mid–upper Aeronian) biform monograptid genus Paramonoclimacis, from Arctic Canada, show tubarium features evolutionarily linking it to the Streptograptus clade. The tubaria, coiled dorsally in the proximal end, show a number of streptograptid thecae with the distinct nozzle of a typical species of Streptograptus. Median thecae retain the nozzle, but are modified first into a wide, proximally directed flange with a shortened hook, while the ventral lobes are reduced. Distally, the thecal apertures form a strong ventral hood and two lateral lobes as an extension of the dorsal wall of the metatheca and not as a secondary construction or addition to a geniculum. The proximal streptograptid thecae of Paramonoclimacis may indicate the evolution of the Streptograptus clade through a Paramonoclimacis ancestor. The cupulae were previously thought to be restricted to the Streptograptus clade but are now also found in some species of Paramonoclimacis. There is a close connection between Paramonoclimacis and the genera Pribylograptus and Pernerograptus in the construction of complexly developed thecae and biform tubaria.

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