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

<p>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, <i>Aldridgeognathus manniki</i> and <i>Omanognathus daiqaensis</i>, 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 <i>Omanognathus</i> is similar to the bedding plane assemblage-defined genus <i>Notiodella</i> (= <i>Icriodella</i>) but differs in that as yet only 15 elements rather than 17 have been identified. <i>Aldridgeognathus</i> has similar P elements to the early Silurian apparatus <i>Pranognathus</i> but differs in the possession of a geniculate M element and a <i>Baltoniodus</i>-like S element array. <i>Aldridgeognathus</i> does not easily fit with either the 17-element <i>Notiodella</i> (<i>Icriodella</i>) or the 19-element <i>Promissum</i> 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 <i>Arianagnathus</i>, are more derived than <i>Baltioniodus</i> and <i>Prioniodus</i> but ancestral to <i>Icriodella</i>, <i>Sagittodontina</i>, <i>Promissum</i> and <i>Notiodella</i>. The exact position of <i>Aldridgeognathus</i> is not well resolved in respect to the newly described <i>Arianagnathus</i> or <i>Omanognathus</i>. 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.</p> <p><a href="http://zoobank.org/urn:lsid:zoobank.org:pub:84C8267D-76E8-4DD3-92F3-0B72CA976DEC" target="_blank">http://zoobank.org/urn:lsid:zoobank.org:pub:84C8267D-76E8-4DD3-92F3-0B72CA976DEC</a></p