Danielsen and Over—Lower Silurian conodonts, Shine Jinst region, Mongolia
Remarks.—The recovered elements of Panderodus unicostatus range from rounded and circular in cross section, to compressed with lenticular cross sections. The compressed specimens are densely striated at the base; striations extend the length of the cusp along the sides of a longitudinal, posterior-lateral groove that extends from a notch in the posterior edge of the base. The rounded specimens display a similar striation pattern, and have a costa that begins at the top of the basal striations.
Panderodus sp. Figure 3.12, 3.13
Remarks.—Simple cone specimens are placed in Panderodus sp. because of their general shape or presence of the longitudinal groove. The specimen in Figure 3.12 is more robust and has coarser, more abundant striations than Pa. unicostatus. The specimen in Figure 3.13 has striation patterns and longitudinal groove similar to those in specimens of Pa. unicostatus, athough it has sharp anterolateral margins and a subtriangular cross section.
Family Prioniodinidae Bassler, 1925 Genus Pseudolonchodina Zhou, Zhai, and Xian, 1981
Type Species.—Pseudolonchodina irregularis Zhou, Zhai, and Xian, 1981.
Remarks.—Based on the observations of Simpson and Talent (1995) and Wang and Aldridge (2010), Aspelundia Savage, 1985 is a junior synonym of Pseudolonchodina. Thus, Pseudolonchodina takes precedence.
Pseudolonchodina expansa (Armstrong, 1990) Figure 3.15–3.18
1990 Aspelundia expansa Armstrong, p. 50, pl. 3, figs. 13–20. 1995 Pseudolonchodina expansa; Simpson and Talent, p. 111, pl. 1, fig. 3 (see for synonymy).
1997 Aspelundia expansa; Dumoulin et al., fig. 4BB–DD.
1998 Aspelundia expansa; Männik and Malkowski, pl. 1, figs. 34–35.
2002 Oulodus? expansus; Zhang and Barnes, p. 21, fig. 10.1–10.14 (see for synonymy).
2009 Aspelundia? expansa; Männik et al., fig. 5bb, cc. 2010 Aspelundia? expansa; Loydell et al., fig. 9c, d, h. ?2010 ?Pseudolonchodina expansa; Wang and Aldridge, p. 82, pl. 20, fig. 1.
Schuchert, Washington Land, western North Greenland (Armstrong, 1990, pl. 3, fig. 13).
Occurrence.—Occurs globally. First occurrence marks the base of the Pseudolonchodina (Aspelundia) expansa Zone that spans the upper Rhuddanian to lower Aeronian (Loydell et al., 2003).
2003 Aspelundia expansa; Loydell et al., fig. 14z, aa. 2007a Aspelundia expansa; Zhang and Barnes, fig. 12.14– 12.17.
Remarks.—Elements of Pseudolonchodina expansa have a broad basal cavity and widely spaced denticles, distinguished from elements of Ps. fluegeli, which have a narrow basal cavity and a greater number of more closely packed denticles (Simpson and Talent, 1995).
Pseudolonchondia sp. Figure 3.19
Remarks.—Several fragments are placed within Pseudolonchodina
Holotype.—Aspelundia expansa (P2 element), MGUH 17.687, sample GGU 216837, Cape Schuchert Formation, Kap
because of general outline or the presence of the characteristic basal flare under the cusp, although they do not fully conform to species diagnoses or descriptions. The figured S element has a basal flare characteristic of Pseudolonchodina although the element is straighter, much more compressed and denticles are more closely packed than typical Pseudolonchodina Selements.
Family Pseudooneotodidae Wang and Aldridge, 2010 Genus Pseudooneotodus Drygant, 1974
87
Occurrences have been found to range into the Distomodus staurognathoides Zone (Männik, 2007) and to the mid-Telychian (Zhang and Barnes, 2002).
Description.—P2 element: Consists of a cusp and two lateral denticulate processes. Outer lateral process is straight and down- turned, forming a 100° angle with the inner lateral edge of the cusp, bearing 4–10 compressed denticles; inner lateral process is shorter, twisted anteriorly, and bears up to 10 compressed denti- cles, and occasionally a short unornamented, inward-directed projection beneath the first proximal denticles (Armstrong, 1990); processes are incomplete in YamaanUs
specimen.Cusp is usually the same width as the denticles, laterally compressed with a flat- tened, lenticular cross section, and inclined toward the inner lateral process. Wide basal cavity, rounded in aboral view, expands broadly under the cusp; posterior edge is upturned and inclined toward the inner lateral process, and tapers into narrow grooves under the processes (Armstrong, 1990). M element: Cusp is large, laterally compressed, with a
sharp anterior and rounded posterior edge. It is inwardly twisted, inclined posteriorly, and slightly separated from the denticles on the posterior process. Posterior process is inwardly bowed and bears 6–8 compressed, posteriorly inclined denticles. Basal cavity is shallowly excavated and upturned on the inner side, where it flares laterally beneath the posterior edge of the cusp and process (Armstrong, 1990). Occasionally specimens with an anterior process are known to occur (Simpson and Talent, 1995); this does not occur in the Mongolian fauna, nor was it described in the Greenland fauna (Armstrong, 1990). S0 element: Cusp is oval in cross section and highly inclined
toward the posterior. Compressed lateral processes of equal length extend downward fromthe anterolateral edges of the cusp, creating an angle of 160° between the lower edges in posterior view, and bowposteriorly, each bearing up to five partially fused, compressed denticles. Basal cavity is laterally expanded, extends posteriorly as a broad groove under the cusp, and laterally as narrow grooves under the processes (Armstrong, 1990).
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