Protoprioniodus McTavish, 1973

Zhen, Yong Yi, Percival, Ian G. & Webby, Barry D., 2003, Early Ordovician Conodonts from Far Western New South Wales, Australia, Records of the Australian Museum 55 (2), pp. 169-220 : 209-210

Protoprioniodus McTavish, 1973

Type species. Protoprioniodus simplicissimus McTavish, 1973 .

Remarks. As pointed out by Smith (1991), interpretations of the apparatus composition of the genus and its phylogenetic relationships vary considerably. It is clear that at least three distinct species groups have been previously assigned to Protoprioniodus . The first group, represented by the type species, P. simplicissimus McTavish, 1973 , and P. yapu Cooper, 1981 , have a pastinate P element with a robust cusp, similar to the P elements of Prioniodus but with adenticulate processes in this and all other elements. Based on this interpretation, which was followed by Cooper (1981), Ethington & Clark (1982), and Smith (1991), the apparatus has a ramiform-pectiniform configuration. Material from the western New South Wales collections supports the interpretation of Sweet (1988: 61) who

[continuation of Fig. 23 caption]… C1612, G, inner lateral view, H, basal inner lateral view at the base; I–K, Pa element, AMF 120432, C1611, I, basal view, J, inner lateral view, K, outer lateral view; L–N, Pa element, AMF 120433, C1611, L, inner lateral view, M, outer lateral view, N, basal view; O,P, Pb element, AMF 120434, C1611, O, inner lateral view, P, outer lateral view. Q, Protopanderodus nogamii? ( Lee, 1975) : Sa element, AMF 120435, C1612, lateral view. Scale bars 100 µm.

envisaged the apparatus as consisting of pectiniform P elements , makellate M element and adenticulate ramiform S elements .

The second group, including P. nyinti and P. aranda from the Amadeus Basin previously referred to the genus by Cooper (1981), have the P positions occupied by pectiniform elements, but in lacking a recognizable cusp they do not conform to the concept of Protoprioniodus . These species are now distinguished as the new genus Cooperignathus , in which the anterior, posterior and outer lateral processes are characterized by having blade-like crests on upper surfaces, rather than rows of nodes in more derived forms like Eoplacognathus .

The third species group is represented by P. papiliosus ( van Wamel, 1974) and P. cowheadensis Stouge & Bagnoli, 1988 . These latter authors, as well as Johnston & Barnes (2000), regarded the genus as including oistodiform elements in both the P and M positions, implying a ramiform-ramiform configuration.

Some authors ( McTavish, 1973; Cooper, 1981) have suggested that Protoprioniodus might have evolved from Acodus based on general similarity of their P elements , although in Protoprioniodus these have a more strongly developed adenticulate outer-lateral process. An alternate proposal ( Sweet, 1988: 61) related Protoprioniodus more closely to Oistodus , citing the geniculate nature of their skeletal elements.

Figures

Fig. 23. A–P, Protopanderodus nogamii (Lee, 1975): A, Sa element, AMF120430, C1611, basal view showing the basal cavity; B, Sa element,AMF120428, C1612, lateral view; C,D, Sb element,AMF120427, C1612, C, lateral view of the basal part showing furrow and striation, D, lateral view; E,F, Sc element,AMF120431, Y4–2, E, inner lateral view, F, outer lateral view; G,H, Sd element,AMF120429,