Caudicriodus woschmidti ( Ziegler, 1960 )

Suttner, Thomas J., Kido, Erika & Briguglio, Antonino, 2018, A new icriodontid conodont cluster with specific mesowear supports an alternative apparatus motion model for Icriodontidae, Journal of Systematic Palaeontology 16 (11), pp. 909-926 : 912-914

Caudicriodus woschmidti ( Ziegler, 1960)

( Figs 2 , 4 )

1960 Icriodus woschmidti Ziegler : 185, pl. 15, figs 16–18, 20–22.

1962 Icriodus woschmidti Ziegler ; Jentzsch: 967, pl. 1, figs 17–23.

1964 Icriodus woschmidti Ziegler ; Walliser: 38, pl. 9, fig. 22, pl. 11, figs 14–22.

1969 Icriodus woschmidti transiens Carls & Gandl : 174, pl. 15, figs 1–7.

1969 Icriodus woschmidti Ziegler ; Klapper: 10, pl. 2, figs 3–5.

1975 Icriodus woschmidti woschmidti Ziegler ; Carls: 410, pl. 2, figs 19–21.

1976 Caudicriodus woschmidti (Ziegler) ; Bultynck: 21, figs 1, 3–4 [cum syn.].

1977 Caudicriodus woschmidti (Ziegler) ; Bultynck: pl. 39, fig. 10, pl. 40, fig. 24.

1977 Icriodus woschmidti woschmidti Ziegler ; Chatterton & Perry: 793, pl. 3, figs 18–22.

1980 Icriodus woschmidti woschmidti Ziegler ; Jaeger & Schonlaub: pl. 4, figs 4–5/16, 6/16.

1980 Icriodus woschmidti woschmidti Ziegler ; Pickett: 70, fig 3B–D.

1980 Icriodus woschmidti Ziegler ; Serpagli & Mastandrea: 39, figs 2–4.

1981 Caudicriodus woschmidti woschmidti (Ziegler) ; Norris & Uyeno: pl. 5, figs 10–17.

1981 Icriodus woschmidti Ziegler ; Wang: 77, pl. 1, figs 22–25.

1983 Icriodus woschmidti Ziegler ; Broadhead & McComb: 153, figs 2E, 3H–J.

1983 Icriodus woschmidti woschmidti Ziegler ; Serpagli: 155, figs 2, 5–7.

1986 Caudicriodus woschmidti woschmidti (Ziegler) ; Borremans & Bultynck: 52, pl. 1, figs 1–9.

1988 Icriodus woschmidti woschmidti Ziegler ; Denkler & Harris: B8, pl. 1, figs A, B.

1990 Icriodus woschmidti woschmidti Ziegler ; Olivieri & Serpagli: 63, pl. 1, figs 12–14.

1990 aff. Icriodus cf. postwoschmidti Mashkova ; Weyant & Morzadec: 752, pl. 1, figs 1, 3–5.

1994 Icriodus woschmidti woschmidti Ziegler ; Valenzuela-Ŕıos: 87, pl. 8, figs 14, 15, 28.

1995 Icriodus woschmidti woschmidti Ziegler ; Luppold: pl. 2, fig. 11.

1998 Icriodus woschmidti woschmidti Ziegler ; Capkinoglu ¸& Bektas ¸: 167, pl. 5, figs 10, 11.

1999 Caudicriodus woschmidti (Ziegler) ; Benfrika: 318, pl. 1, fig. 10.

2002 Icriodus woschmidti woschmidti Ziegler ; Garćıa-Lopez et al.: pl. 1, figs 5–7.

2003 Caudicriodus woschmidti woschmidti (Ziegler) ; Bultynck: pl. 1, figs 1–3.

2005 Icriodus woschmidti woschmidti Ziegler ; Corradini et al.: fig. 5e.

2009a Icriodus woschmidti woschmidti Ziegler ; Suttner: 77, pl. 1, figs 1–6.

2010 Caudicriodus woschmidti (Ziegler) ; Drygant: 57, pl. 2, figs 3, 6–13.

2012 Caudicriodus woschmidti (Ziegler) ; Drygant & Szaniawski: 846, figs 9B, 10C, D.

Material. NHMW 2011/0374/0001, single conodont cluster including 10 pairs of coniform and both I elements. Additional icriodontan elements from the same locality were described by Suttner (2009a).

Description. The icriodontid conodont cluster consists of crown tissue only and includes one pair of I elements and 20 coniform elements, which can be distinguished in 10 pairs (C1–C5). No basal plate is preserved. Although the cluster shows numerous micro-fractures on the surface of I elements with some coniform elements being broken in two or more pieces (still attached in the cluster) or having lost their tips, it can be reconstructed based on SEM and micro-CT analysis ( Fig. 2 ).

Icriodontan elements are preserved with the oral side opposing each other in an interlocking position. Lateral walls of the basal cavity, especially in the ‘posterior’ part of either element, are adpressed and show strong fractures. Therefore, the lower margin of the basal cavity is very irregular, not reflecting the original outline. However, the basal cavity of this species is widest below the cusp. The initial part of the ‘anterior’ portion of both I elements is broken off. Additionally, the ‘posterior’-most portion of the lateral process is broken too. Four transverse denticle rows are bar-like (denticles are connected by high ridges; Fig. 4B ) with deep interspacing on the rather low spindle. Some of the lateral row denticles show strong fractures. No surface ornamentation is observed.

Coniform elements are clustered in bidirectional orientation around the ‘posterior’ part of the icriodontan elements (‘inner’ side). Few elements are found on the ‘outer’ side of the sinistral I element which indicate post-mortem distortion of the original orientation of the coniform assemblage. Basically, two sets of different-shaped pairs of small (C1, C2a, C2b, C2c, C2d, C4) and large (C2e, C2f, C3, C5) coniform elements are observed. All of these are adenticulate.

C1 elements are small, gracile coniform elements with a recurved cusp and striate surface ornamentation. The cusp and basal outline are elliptical in cross section (‘posterior’ margin more convex than ‘anterior’ margin) with sharp margins that represent costae.

C2 elements (C2a–C2f) differ in size but all possess a circular outline of the basal margin. All are erect or slightly recurved and show a striate surface ornament where preserved. Generally, neither costae nor keels are developed. Some of elements have the base fractured and therefore the basal margin appears elliptically compressed. C2a elements are broken into two parts: base with major part of cusp and tip of cusp preserved close to each other. The tip of the cusp seems elliptical in cross section (‘posterior’ margin more convex than ‘anterior’ margin) with rather sharp margins. This differs somewhat from other C2 elements which have a cusp with a rather round cross section. C2e and C2f elements are larger than other C2 elements, comparable in size to C3 and C5 elements. However, C2 elements can be discriminated easily by having a circular basal outline and a more slender shape in general. Because of recrystallization, surface ornamentation of C2e and C2f is difficult to ascertain.

The largest pair of coniform elements is identified as C3. Both cones have a widely excavated base with an irregular, flared outline. Elements have a keel extending from the base of the cone to the base of the cusp. The angle between the ‘posterior’ lower part and the ‘posterior’ margin of the cusp is about 97 Ǫ. The angle between the lower and ‘anterior’ margin of the element is about 55 Ǫ, slightly curved in the lower one-fifth, continuing rather straight towards the tip of the cusp. No surface ornament is observed.

C4 elements are erect and seem symmetrical with an oval outline of the base. Although it is rather small, one element of the C4 pair is preserved with the same orientation between two large coniform elements, close to the ‘anterior’ margins of C3 and C5.

C5 elements are about half the size of C3 elements, with an erect cusp and a wide, probably oval to circular basal margin. Although the base appears rather conical, the original outline and shape is unknown because of post-mortem deformation. Neither costae nor keels are observed.

Remarks. A chronological summary of the icriodontid element notation ( Fig. 3 ) shows that a bimembrate nature of the apparatus was suggested by Lange (1968) based on the first finding of clusters of Icriodus alternatus . A few years later, coniform elements were termed S 2 (acodinan) elements by Klapper & Philip (1971). Although previously speculated upon by Klapper & Ziegler (1975), Nicoll (1977) was the first to propose a trimembrate apparatus by including an additional type of coniform element (M 2 element). Further evidence to support this model came from statistical analysis of the apparatus reconstruction of Icriodus trojani by Johnson & Klapper (1981). In the same year, Norris & Uyeno (1981) introduced three coniform types (S 2a, S 2b and S 2c) for the apparatus of Icriodus subterminus , of which their S 2a element equates with the classically known S 2 element, and their S 2b element with the M 2 element of Nicoll (1977). Nicoll (1982) set a milestone with his publication on the analysis of hundreds of fused clusters of Icriodus expansus from the Canning Basin in which he revised the apparatus architecture and notation of icriodontid conodonts. His reconstruction includes one pair of opposed platform elements (I elements) and other associated coniform elements (Ca, Cb, Cc, Cd, Ce and Cf elements). No ramiform elements are included within this apparatus. However, the large number of coniform elements counted in single clusters led to the conclusion that these were arranged serially within the apparatus of one individual. Like Icriodus expansus , the fused cluster of Caudicriodus woschmidti did not preserve ramiform elements. The latter elements are part of the apparatus reconstruction suggested by Serpagli (1983). His analysis of disarticulated elements of Caudicriodus woschmidti from the Early Devonian of southern Sardinia ( Italy) resulted in an apparatus that included ramiform (a, b and c), coniform (e and f) and icriodiform (g) elements. These formed two transitional series, each consisting of three morphotypes (a, b, c and e, f, g). This hypothesis followed the analysis of Cypricriodus hesperius from the Silurian to Devonian of north Queensland, Australia, by Simpson (1998), who proposed an apparatus that contained variably ornamented coniform elements (Sa, Sb 1, Sb 2 and Sc elements), M elements, Pb elements and Pa elements. In his model, S elements represent a symmetry transition series. Originally introduced for the skeletal apparatus of Oulodus by Sweet & Schonlaub (1975), this notation scheme was used by Simpson (1998) for documenting the analogous relationship regarding the position occupied by elements in different euconodont apparatuses. The most recent study of Cypricriodus hesperius by Murphy et al. (2016) suggested a new apparatus structure followed by introduction of a new element notation based on statistical analysis of isolated elements. These authors discriminated five elements, including three flared elements: one with plication (Fp), a second with the ‘inner’ wall of the base straighter than the ‘outer’ wall (Fi), and a third with the ‘outer’ wall straighter than the ‘inner’ wall (Fo). The fourth coniform element is denticulate (D) and the fifth is represented by the icriodontan element (I). However, apparatus architecture and notation schemes for Early Devonian icriodontids are based exclusively on statistical analysis of isolated elements, which is expected to suffer a higher bias error compared with analysis of fused conodont clusters (see discussion of ‘bias and biology’ by Purnell & Donoghue 2005). Therefore, these are not applied here.

Figures

Figure 2. Conodont cluster of Caudicriodus woschmidti, Early Devonian, southern Burgenland, Austria; Ki/4/2a-1, NHMW 2011/0374/ 0001. A, SEM scan of the conodont cluster. B, detailed view of the coniform elements (C1–C5) close to the dextral I element. C, D, computer microtomography-based three-dimensional reconstruction with identification of all elements. E, hypothetical arrangement of all elements preserved within the fused conodont cluster.

Figure 3. Chronological listing of notation history for icriodontid apparatus elements. Morphologically similar coniform element types and the icriodontan element evaluated for this study are highlighted in different colours or shades.

Figure 4. A, denticle tip wear of the dextral I element of Caudicriodus woschmidti; Early Devonian, southern Burgenland, Austria; Ki/ 4/2a-1, NHMW 2011/0374/0001. B, detailed view of oral surface of the dextral I element with extent and orientation of tip wear indicated by dotted line and arrow head.