Two new early balognathid conodont genera from the Ordovician of Oman and comments on the early evolution of prioniodontid conodonts

Abstract

Reports of Ordovician conodonts from the Arabian region of the Gondwanan margin are extremely rare. Here we provide a description of the apparatus of two new conodont genera and species, Aldridgeognathus manniki and Omanognathus daiqaensis, based on discrete elements recovered from the Am5 Member of the Amdeh Formation, Darriwilian, Ordovician of the Sultanate of Oman. The apparatuses contain 17 and 15 elements, respectively, and both possess three pairs of P elements. The apparatus structure of Omanognathus is similar to the bedding plane assemblage-defined genus Notiodella (= Icriodella) but differs in that as yet only 15 elements rather than 17 have been identified. Aldridgeognathus has similar P elements to the early Silurian apparatus Pranognathus but differs in the possession of a geniculate M element and a Baltoniodus-like S element array. Aldridgeognathus does not easily fit with either the 17-element Notiodella (Icriodella) or the 19-element Promissum templates and suggests that there may be other 17-element Ordovician apparatus templates with very similar or duplicated elements in the P element positions. A cladistic analysis based on the data set of Donoghue (2008) confirms that both new genera should be classified with the Balognathidae and suggests that they, along with another newly described three P element bearing genus Arianagnathus, are more derived than Baltioniodus and Prioniodus but ancestral to Icriodella, Sagittodontina, Promissum and Notiodella. The exact position of Aldridgeognathus is not well resolved in respect to the newly described Arianagnathus or Omanognathus. These new taxa add little to attempts to correlate the Arabian Peninsula with other palaeogeographic regions, but may prove useful for future correlation within the region and provide data to test the hypothesis of Dzik (2015) that the origins for prioniodontid conodonts lie in high latitudes during the Ordovician.http://zoobank.org/urn:lsid:zoobank.org:pub:84C8267D-76E8-4DD3-92F3-0B72CA976DEC