Taxonomic revision of the genus Stiptognathus (Conodonta) from the Lower Ordovician of Australia and its biostratigraphical and palaeobiogeographical significance

Abstract

Stiptognathus borealis from the Lower Ordovician Emanuel Formation and correlative subsurface Nambeet Formation of the Canning Basin in Western Australia is examined taxonomically. It is the type and only known species of the genus Stiptognathus, with a stratigraphical range restricted to the lower Floian (Lower Ordovician). The distribution of S. borealis suggests that this species might have inhabited a spectrum of environments, but it was palaeobiogeographically restricted to the tropical zone, possibly because of sea water temperature sensitivity. This study provides a new description of this species and redefines its constituent element types comprising a seximembrate apparatus. This is characterized by a pastinate Pa element and modified angulate Pb element. Stiptognathus borealis is morphologically most closely related to the genus Fahraeusodus. These taxa form a clade that might be phylogenetically basal to Plectodinidae and Cyatoniodontidae, which flourished in Middle and Late Ordovician times.

Yong Yi Zhen [[email protected]], Geological Survey of New South Wales, W.B. Clarke Geoscience Centre, 947-953 Londonderry Road, Londonderry, NSW 2753, Australia.

Key words:

• Conodonta
• supergeneric classification
• evolution
• temporal and spatial distribution

Acknowledgements

Robert Nicoll, John Laurie, and Natalie Schroeder (Geoscience Australia), Kailah Thorn (UWA) and Heidi Allen (GSWA) helped to relocate the specimens of McTavish (1973) and loan of material for study. SEM images were prepared with assistance from Sue Lindsay (Macquarie University). The Editorial Board of Alcheringa, Annalisa Ferretti and an anonymous reviewer provided constructive comments and reviews of the manuscript. This project is part of IGCP Project 735 (Rocks and the Rise of Ordovician Life) and IGCP Project 668 (Equatorial Gondwana History and Early Palaeozoic Evolutionary Dynamics). Y.Y.Z. publishes with the permission of the Head of the Geological Survey of NSW.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.