The apparatuses of Triassic ellisonid conodonts: Cornudina breviramulis, Hadrodontina aequabilis, and Staeschegnathus perrii gen. et sp. nov. from the Taho Formation in Higashiuwa-gun, Ehime Prefecture, Southwest Japan and Furnishius triserratus from the Iwai Formation in Nishitama-gun, Tokyo were reconstructed on the basis of the multielement structure of natural assemblages previously reported. Ellisonia triassica was remarked on this occasion. These species well agree with the general septimembrate apparatus structure containing 15 elements: angulate or pastinate P1, angulate P2, breviform digyrate M, alate S0, extensiform digyrate S1 and S2, and bipennate S3 and S4 elements. Having compared the morphologic features of apparatus elements of the Ellisonidae, I propose herein the new subfamily Hadrodontinae within it. Among the Ellisonidae and other taxa of the Prioniodinina, a phylogenetic relationship is recognized only between E. triassica and Upper Devonian Hibbardella angulata. Other species of the Ellisonidae are more closely related to ozarkodinides with “ozarkodiniform” angulate P1 element than any previously reported prioniodininids with “oulodiniform” extensiform digyrate and carminate P1 elements.
Introduction
Multielement reconstructions of the apparatuses of the Ellisonidae Clark, 1972 have been proposed by several workers. Most of them are, however, incomplete because the S1 and S2 elements were not sufficiently differentiated from each other. The examination of natural assemblages provides valuable information on the determination of the S1, S2, and other elements of ellisonid apparatuses.
I reconstructed on this occasion the following four ellisonid species; Cornudina breviramulis (Tatge, 1956), Hadrodontina aequabilis Staesche, 1964, Staeschegnathus perrii gen. et sp. nov., and Furnishius triserratus Clark, 1959. Cornudina breviramulis occurs in the Smithian (lower Olenekian) through Norian, and H. aequabilis and S. perrii in the Smithian limestone of the Taho Formation in Taho, Shirokawa-cho, Higashiuwa-gun, Ehime Prefecture. Furnishius triserratus Clark was recovered from the Smithian limestone of the Iwai Formation cropping out in the Kaizawa Valley, Iwai, Hinode-machi, Nishitama-gun, Tokyo. I describe the aforementioned four species and review Ellisonia triassica Müller, 1956 which was already reported by Koike et al. (2004) and compare the morphologic characters of the apparatus elements of the Ellisonidae. I discuss the phylogenic relationships among the Ellisonidae and other taxa of the Ozarkodinida.
All of the described conodont specimens are deposited at the Department of Geology and Paleontology, National Museum of Nature and Science, Tsukuba.
Characteristics of the apparatus structure of the Ellisonidae
One of the natural assemblages providing information on the apparatus structure of ellisonids is Hibbardella angulata (Hinde, 1879) described by Nicoll (1977, 1985) on the basis of a cluster recovered from the gut region of a palaeoniscoid fish from the Gogo Formation, Upper Devonian of the Canning Basin, Western Australia. The apparatus carries eight kinds of elements; angulate Pa and Pb, dolabrate N (M), triramous Sa, extensiform digyrate Sb (S2) and Sd (S1), and “ligonodiniform” bipennate Sc elements. The Sb and Sd elements are quite similar in shape and mode of denticulation to each other.
The bedding-plane natural assemblage of Ellisonia cf. triassica Müller, 1956 demonstrated by Koike et al. (2004) from the uppermost Permian claystone in the Mt. Nabejiriyama, Shiga Prefecture, central Japan is significantly important in reconstructing ellisonid apparatuses. Smithian E. triassica was reconstructed based on the natural assemblage and frequent association of ellisonids from limestone of the Taho Formation. The apparatus of E. cf. triassica is composed of angulate P1 and P2, triramous S0, extensiform digyrate S1 and S2, and bipennate S3 and S4 elements. The M element is lost in the apparatus. It is, however, of the breviform digyrate type judging from the M of the reconstructed apparatus of E. triassica. The S1 element is distinguished from the S2 by a slight arching of the processes. The mode of denticulation is, however, common between the two types of elements.
Some natural assemblages of ozarkodinids also valuably inform suggested reconstructions of ellisonid apparatuses. The articulated skeletons of Ozarkodina excavata (Branson and Mehl, 1933) from the upper Silurian Eramosa Member carbonate at Hepworth, Ontario reconstructed by von Bitter and Purnell (2005) contain carminate P1, angulate P2, breviform digyrate M, biramous S0, extensiform digyrate S1 and S2, and bipennate S3/4. The S1 and S2 elements are almost the same in shape and mode of denticulation to each other.
The fused clusters of Ozarkodina eosteinhornensis (Walliser, 1964) from the upper Silurian limestone of the Salina Formation in northern Indiana examined by Nicoll and Rexroad (1987) indicate eight types of elements. The arrangement and morphologic feature of the Sd and Sb elements are particularly suggestive in differentiation of the S1 and S2 of the subfamily Hadrodontinae newly proposed herein.
The arrangement of the Sd and Sb elements in the fused clusters of Nicollidina brevis (Bishoff and Ziegler, 1957) and Polygnathus xylus Stauffer, 1940 from the Upper Devonian Napier Formation of the Canning Basin, western Australia described by Nicoll (1985) provides important information about discrimination of the S1 and S2 in the apparatuses of Cornudina and Staeschegnathus gen. nov.
The Sd and Sb elements in the fused clusters of Polygnathus webbi Stauffer, 1938 from the Upper Devonian Upper Kellwasser horizon at La Serre, Southern France studied by Schülke (1997) are suggestive on differentiation of the very long bending extensiform digyrate S1 and straight extensiform digyrate S2 in Furnishius apparatus. The bedding-plane natural assemblages of the Carboniferous polygnathacean conodonts (Aldridge et al., 1987; Purnell and Donoghue, 1998) contribute to drawing comparisons between the arrangement of apparatus elements of ozarkodinids and ellisonids.
During this study I recognized some fused clusters of Hadrodontina aequabilis and Cornudina breviramulis with T. Maekawa of Kumamoto University from the uppermost Smithian limestone of the Taho Formation. The fused clusters include a straight extensiform digyrate S2 element bounding on the inner side of the bipennate S3 in both H. aequabilis and C. breviramulis apparatuses. The arrangement is the same as that of the Sb and Sc elements in Silurian Ozarkodina eosteinhornensis and Upper Devonian Nicollidina brevis, respectively.
On the basis of the above-mentioned natural assemblages, the morphologic features of the elements of ellisonid apparatuses are summarized as follows: the P1 element is angulate, palmate, pastinate and pastiniplanate; P2 is angulate and palmate; M is breviform digyrate; S0 is alate. The S1 is extensiform digyrate and three morphologic types are recognized in it: arched, short and long straight ones. The arched extensiform digyrate is characterized by gently arched processes without bending in an outer-lateral process and is homologous with the Sd of Hibbardella angulata, S1 of Ellisonia cf. triassica and S1/2 of Ozarkodina excavata. The short extensiform digyrate is characterized by an inwardly bending short outer-lateral process and is homologous with the Sd of Ozarkodina eosteinhornensis. The long extensiform digyrate has a sharply bending relatively long outer-lateral process and is homologous with the Sd of Nicollidina brevis, Polygnathus xylus, and P. webbi. The S2 is extensiform digyrate with a cusp near the middle portion of the processes. The outer-lateral process is straight or gently curves inward and is homologous with the Sb of H. angulata, O. eosteinhornensis, N. brevis, P. xylus, and P. webbi, S1/2 of O. excavata, and S2 of E. cf. triassica. The S3 and S4 are bipennate.
I provide the definitions of Hadrodontina aequabilis, Ellisonia triassica, Cornudina breviramulis, Staeschegnathus perrii gen. et sp. nov., and Furnishius triserrutus, and propose the new subfamily Hadrodontinae which includes Hadrodontina aequabilis, H. anceps Staesche, 1964 and Pachycladina species already described by certain authors.
Phylogenic relationships of the Ellisonidae
As stated above, the straight extensiform digyrate S2 element represents a common morphologic feature among the species of the Ellisonidae. On the other hand, the S1 element shows some morphological variation among the species. Therefore, comparison of the S1 and S2 elements with those of the previously reported multielement species should probably provide an important clue in the phylogenic study of the Ellisonidae.
The conodont apparatuses carrying a straight extensiform digyrate element in both the S1 and S2 positions, which characterize Ellisonia triassica, are upper Silurian Ozarkodina excavata and Upper Devonian prioniodininid Hibbardella angulata. The mode of denticulation of the S1/2 of O. excavata is similar to that of the S1 and S2 elements of E. triassica. The shape and mode of denticulation of the Sd and Sb of H. angulata with angulate Pa and Pb elements exhibit some similarity to the S1 and S2 elements of E. triassica, respectively, which proves the phylogenic relationship between H. angulata and Ellisonia.
The oldest known conodonts carrying bending short extensiform digyrate S1 and straight extensiform digyrate S2 elements, which characterize Hadrodontina aequabilis, are lower Silurian Ozarkodina pirata reconstructed by Uyeno and Barnes (1983) and upper Silurian O. eosteinhornensis. The former possesses simple angulate Pa and dolabrate M and the latter has carminate Pa and breviform digyrate M elements. The Sb and Sb-Sa of O. pirata, and the Sd and Sb of O. eosteinhornensis are closely similar to the S1 and S2 of H. aequabilis, respectively.
The combination of sharply bending long extensiform digyrate S1 and straight extensiform digyrate S2 elements, which characterizes Cornudina breviramulis and Staeschegnathus perrii is recognized in upper Silurian through Lower Devonian Ozarkodina remsheidensis (Ziegler, 1960) reconstructed by Uyeno (1981), Middle Devonian O. raaschi by Klapper and Barrick (1983), and Upper Devonian Nicollidina brevis, which are characterized by segminate, segminiplanate and carminate P1 elements, respectively.
The combination of very long, sharply bending extensiform digyrate S1 and straight extensiform digyrate S2 elements, which characterizes Furnishius triserratus serratus, is known in Middle Devonian Polygnathus semicostatus Branson and Mehl, 1934 reconstructed by Dzik (2002) and Upper Devonian P. webbi.
The oldest known reconstructed prioniodininid, the Late Ordovician species Oulodus roheni Ethington and Furnish, 1959 reconstructed by Sweet (1979), is characterized by sigmoidal extensiform digyrate P1 (Pb by Sweet) and angulate P2 (Pa), dolabrate M and Sc, extensiform digyrate “Sbb” with downwardly directing outerlateral process and deeply arched “zygognathiform” breviform digyrate “Sba” elements. Early Silurian Oulodus sigmoideus reconstructed by Zhang and Barnes (2002) has sigmoidal extensiform digyrate Pa, angulate Pb, dolabrate to extensiform digyrate M, biramous Sa, extensiform digyrate Sb (fig.11.10 of Zhang and Barnes, 2002), breviform digyrate Sb (fig.11.11 of Zhang and Barnes, 2002) and “ligonodiniform” Sc elements. The extensiform digyrate Sb and breviform digyrate Sb are common in their morphologic character with the Sbb and Sba of O. roheni, respectively. Upper Devonian Ligonodina pectinata Bassler, 1925 reconstructed by Dzik (2002) has sigmoidal extensiform digyrate P1, angulate P2, dolabrate M, triramous S0, extensiform digyrate S1, weakly arched breviform digyrate S2 and “ligonodiniform” S3/4 elements. The S1 element exhibits a common feature with the extensiform digyrate Sbb of O. roheni and Sb (fig.11.10 of Zhang and Barnes, 2002) of O. sigmoideus. Devonian Prioniodina cf. recta (Branson and Mehl, 1934) reconstructed by Schülke (1997) has carminate Pa, angulate Pb, triramous Sa, “ligonodiniform” Sc and weakly arched breviform digyrate Sb elements.
Superfamily Gondolellidea Lindström, 1970, the predominant conodont group composed of seven subfamilies in the Triassic (Orchard, 2005, 2007), is characterized by extensiform digyrate S1 with a downwardly directed outer-lateral process and “enantiognathiform” breviform digyrate S2 elements (Goudemand et al., 2012). The S1 is similar to the Sbb of Oulodus roheni and to the S1 of Ligonodina pectinata. Some species of ozarkodinids also have a downwardly directed extensiform digyrate element like the S1 of gondolellids. For example, upper Silurian Ozarkodina confluence (Branson and Mehl, 1933) reconstructed by Uyeno (1981) possesses an inwardly curved breviform digyrate Sa-Sb transitional element and an extensiform digyrate Sb which is similar to the S1 of the gondolellid Cratognathodus sp. A Orchard, 2005. Consequently, it is important to distinguish whether the extensiform digyrate and breviform digyrate elements in some prioniodininids, ozarkodinids, and gondolellids are respectively homologous or not.
Judging from the morphologic comparison among the apparatuses of the Ellisonidae and with other taxa of the Prioniodinina as well, a phylogenic relationship is recognized only, as far as known, between Ellisonia triassica and Upper Devonian Hibbardella angulata. Other species of the Ellisonidae are more closely related to ozarkodinids with “ozarkodiniform” angulate P1 element than they are to other prioniodininids with “oulodiniform” extensiform digyrate and carminate P1 elements.
Among the species of the Ellisonidae, Ellisonia probably appeared first in the Pennsylvanian (von Bitter and Merrill, 1983), crossed the PTB and disappeared in the latest Smithian (Koike et al., 2004). Hadrodontina appeared in the early Griesbachian (early Induan) (Perri, 1991) and disappeared in the uppermost Smithian (Koike et al., 2004). Cornudina appeared in the early Smithian and disappeared in the Norian (Koike, 1996). Staeschegnathus and Furnishius appeared in the early Smithian and disappeared within the Smithian (Solien, 1979; Perri, 1991) (Figure 1). There is no morphologic transition suggesting any phylogenic relationship among the P1 elements of these genera.
Systematic paleontology
Class Conodonta Eichenberg, 1930
Subclass Conodonti Sweet and Donoghue, 2001
Order Ozarkodinida Dzik, 1976
Suborder Prioniodinina Donoghue et al., 2014
Family Ellisonidae Clark, 1972
Subfamily Hadrodontinae subfam. nov.
Characteristics.—The apparatus of the Hadrodontinae is composed of angulate (palmate) P1 and P2, breviform digyrate M, alate S0, extensiform digyrate S1 and S2, and bipennate S3/4 elements. The P1 element carries radial denticles without a distinct cusp. A secondary denticle row is present on the upper margin of the P1 of Hadrodontina anceps Staesche, 1964. The P2 element shows a crescent shape twisting distally without a distinct cusp. The M element has a robust and long cusp, bears discrete denticles on the lateral processes, and exhibits a great deal of variation in the morphologic features of innerand outer-lateral processes. The S0 element is biramous or triramous. The latter carries long antero-lateral processes and a short posterior one. The S1 element is short and bears a distinct cusp. The outer-lateral process is flexed inward at the middle portion and the inner-lateral process gently curves inward. The S2 element is straight extensiform digyrate with a distinct cusp. The S3/4 element possesses a very long and stout cusp and discrete denticles on the anterior and posterior processes. The anterior process represents various degrees of curvature. Zone of recessive basal margin is well developed in all the elements.
I include Hadrodontina aequabilis Staesche, 1964, H. anceps Staesche, 1964, and Pachycladina oblique Staesche, 1964 in the Subfamily Hadrodontinae.
Genus Hadrodontina Staesche, 1964
Type species.—Hadrodontina anceps Staesche, 1964.
Hadrodontina aequabilis
Staesche, 1964
Figure 2
P1 element: Hadrodontina aequabilis Staesche, 1964, p. 275, figs. 43, 44; Hadrodontina aequabilis Staesche, Perri, 1991, p. 36, pl. 2, fig. 2a, b (Pb element by Perri); Pachycladina peculiaris Zhang in Zhang and Yang, 1991, p. 40, pl. 3, figs. 1, 2; Parachirognathus ethingtoni Clark, Wang and Cao, 1993, p. 265, pl. 57, fig. 2; Parapachycladina peculiaris (Zhang), Zhang, 1998, pl. 3, figs. 3–5, pl. 4, figs. 1, 7; Ellisonia aff. triassica Müller, Koike et al., 2004, p. 247, figs. 7.7, 7.8.
P2 element: Pachycladina peculiaris Zhang in Zhang and Yang, 1991, p. 40, pl. 3, figs. 3, 5; Ellisonia aff. triassica Müller, Koike et al., 2004, p. 247, fig. 7.6.
M element: Ellisonia triassica Müller, Koike, 1990, p. 41, pl. 1, figs. 27–39, pl. 2, figs. 1–9 (Pb element by Koike); Hadrodontina aequabilis Staesche, Perri, 1991, p. 36, pl. 2, figs. 3a, b, 4a, b, 5; Pachycladina peculiaris Zhang in Zhang and Yang, 1991, p. 41, pl. 3, figs. 4, 6; Ellisonia aff. triassica Müller, Koike et al., 2004, p. 247, fig. 7.1.
S0 element: Ellisonia triassica Müller, Koike, 1990, p. 39, pl. 1, figs. 1–26: Pachycladina peculiaris Zhang in Zhang and Yang, 1991, p. 41, pl. 3, figs. 7, 9; Ellisonia aff. triassica Müller, Koike et al., 2004, p. 247, fig. 7.2.
S1 element: Pachycladina peculiaris Zhang in Zhang and Yang, 1991, p. 41, pl. 3, figs. 8, 11 (Sb element); Ellisonia aff. triassica Müller, Koike et al., 2004, p. 247, fig. 7.3.
S2 element: Parachyrognathus ethingtoni Clark, 1959, Wang and Cao, 1993, p. 265, pl. 57, fig. 3; Ellisonia aff. triassica Müller, Koike et al., 2004, p. 247, fig. 7.4.
S3/4 element: Ellisonia triassica Müller, Koike, 1990, p. 40, pl. 2, figs. 10–31: Hadrodontina aequabilis Staesche, Perri, 1991, p. 36, pl. 2, figs. 7a–c, 8a, b; Pachycladina peculiaris Zhang in Zhang and Yang, 1991, p. 41, pl. 3, figs. 10, 12; Ellisonia aff. triassica Müller, Koike et al., 2004, p. 247, fig. 7.5.
Description.—Hadrodontina aequabilis Staesche is composed of angulate (palmate) P1 and P2, digyrate M, triramous S0, extensiform digyrate S1 and S2, and bipennate S3/4 elements.
P1 element: Unit is crescent shape with moderately arched upper outline. Cusp is not distinct. Denticles are 8 to 13 in number, discrete and gradually increase in size toward middle portion.
P2 element: Unit is crescent-shaped slightly inclined inward in posterior half. Cusp is not distinct. Denticles are 8 to 12 in number, discrete and increase in size toward middle portion.
M element: Cusp is long and robust. Lateral processes exhibit a great deal of variation in morphologic features as shown by Koike (1990, text-fig. 6). Denticles on inner-lateral process are 5 to 12 in number, they are discrete and curve inward, and tend to increase in size toward cusp. Denticles on outer-lateral process are 4 to 8 in number, they curve inward and tend to increase in size toward cusp, longest denticle is adjacent to the cusp.
S0 element: Unit is triramous type with robust and long cusp. Antero-lateral process carries 5 to 9 discrete denticles. Upper and basal margins of antero-lateral processes curve gently to sharply in reverse U-like shape. Posterior process possesses 4 to 6 discrete denticles of nearly equal size with cusp in middle to posterior third portion. The morphologic variation in S0 element was shown by Koike (1990, text-fig. 2).
S1 element: Unit is short extensiform digyrate with moderately to highly arched upper outline. Outer-lateral process bends inward at middle portion and carries 4 to 5 denticles which tend to be large at middle portion. Inner-lateral process slightly curves inward and possesses 4 to 5 denticles which tend to be large near distal end. Cusp is distinct near middle portion of processes.
S2 element: Unit is crescent-shaped extensiform digyrate and exhibits a great deal of morphologic variation in shape of basal outline. Denticles on outer-lateral process are discrete, 4 to 7 in number and somewhat large at middle portion. Denticles on inner-lateral process are 4 to 7 in number and very large at middle portion. Cusp is distinct near middle portion of processes.
S3/4 element: Cusp is very long and stout. Anterior process carries 2 to 7 discrete denticles. Posterior process is somewhat longer than or about twice as long as anterior one and carries 5 to 7 discrete denticles. The morphologic variation in S3/4 element was shown by Koike (1990, text-fig. 4). On the basis of some clusters obtained from the uppermost Smithian limestone of the Taho Formation, the S3 and S4 elements are morphologically the same in one cluster. The great morphologic variation in the S3/4 elements is not of the apparatus position but of each individual apparatus.
Remarks.—I revise Ellisonia aff. triassica Koike et al., 2004 to Hadrodontina aequabilis Staesche, 1964. The P1, P2, and S1 elements of Ellisonia aff. triassica significantly differ morphologically from those of E. triassica.
The form species Hadrodontina aequabilis proposed by Staesche (1964) from the Lower Triassic in the Southern Alps is crescent-shaped with 10 discrete denticles which gradually increase in height toward middle portion. This morphology well agrees with the P1 element of H. aequabilis apparatus from the Smithian Taho Formation and the Pa element of multielement species Pachycladina peculiaris proposed by Zhang in Zhang and Yang (1991). The holotype of form species H. aequabilis is robust and possesses laterally expanded basal margin. One of the Pa element of P. peculiaris illustrated by Zhang (pl. 3, fig. 3 in Zhang and Yang, 1991) is close to the holotype. I also collected some specimens similar to the holotype from the Taho Formation (Figure 2.1 in this paper). The Sb element of H. aequabilis by Perri et al. (2004) and of P. peculiaris by Zhang in Zhang and Yang (1991) can be correlated with the S1 of the apparatus by Koike (this paper). The M and Sc elements of H. aequabilis apparatus reconstructed by Perri et al. (2004) and of P. peculiaris by Zhang in Zhang and Yang (1991) are robust but fall within the morphological range of the M and S3/4 of the apparatus by Koike (1990 and this paper), respectively. Two kinds of elements of Smithian Parachirognathus ethingtoni Clark reported by Wang and Cao (1993) agree well with the P1 and S2 of H. aequabilis, respectively.
Hadrodontina anceps Staesche, 1964, type species of Hadrodontina Staesche, 1964, from the upper Dienerian (upper Induan) to Smithian in the Southern Alps, Italy was reconstructed as a seximembrate type by Sweet (1981, 1988) and Perri and Andraghetti (1987). The Pa element (form species Hadrodontina biserialis Staesche, 1964) is of angulate type and bears a secondary denticle row. The mode of denticulation of the main row, however, is quite similar to the P1 element of the Hadrodontina aequabilis apparatus. The Pb element is crescent-shaped without a distinct cusp. The denticles increase in height toward the middle portion. This feature of the element accords with the P2 of H. aequabilis. The M element (form species H. anceps Staesche, 1964, type species of Hadrodontina Staesche, 1964) is a breviform digyrate type with almost equal-sized inner- and outer-lateral processes. The feature is close to some M of H. aequabilis. The Sb element (form species Hadrodontina adunca Staesche, 1964) resembles the S1 of H. aequabilis. The Sc element (Hadrodontina n. gen Staesche, 1964) is close to some S3/4 of H. aequabilis. Although the S0 and S2 of H. anceps were not described by Perri and Andragetti (1987), H. anceps is closely related to H. aequabilis, judged from the similarity between the above-mentioned elements of the two species.
Smithian Pachycladina oblique Staesche, 1964 from the Southern Alps was regarded as a seximembrate apparatus by Sweet (1981, 1988) and Perri and Andraghetti (1987). The elements are robust with a wide lower surface and midlateral ribs. The Pa element illustrated by Sweet (1981) and the Pb by Perri and Andraghetti (1987) are palmate and basically close to the P1 of Hadrodontina aequabilis. The Pa element illustrated by Perri and Andraghetti (1987) has a common appearance with the S2 of H. aequabilis. The Sb elements of Sweet (1981) and Perri and Andraghetti (1987) are basically similar to the S1 of H. aequabilis. The M element (form species P. oblique) and Sc elements resemble the M and S3/4 of H. aequabilis, respectively. The Sa element of P. oblique is biramous and different from that of H. aequabilis and other ellisonids.
Early Triassic Pachycladina erromera from Western Guangxi reconstructed by Zhang in Zhang and Yang (1991) possesses six types of elements: Pa, Pb, M, Sa, Sb, and Sc. The morphological features of the elements agree well with those of P. oblique, although the number of denticles on the units tend to be fewer than in the latter. The Sb element of P. erromera possesses an inwardly bending outer-lateral process and is similar to the S1 of Hadrodontina aequabilis.
Dienerian Ellisonia agordina from the Southern Alps, Italy reconstructed as a seximembrate type by Perri and Andraghetti (1987) and Perri (1991) is characterized by the relatively short unit with an inflated rib and blunt discrete denticles. The Pa element is digyrate and basically resembles the S1 of Hadrodontina aequabilis. The Pb element by Perri (1991) is of the angulate type and similar to the P2 of H. aequabilis. The specimen illustrated as Sb is bipennate and probably referable to the Sc element. The M, Sa, and Sc elements are basically similar to those of H. aequabilis. Thus, Ellisonia agordina closely relates to Hadrodontina.
As a result of their cladistics of prioniodininids, Donoghue et al. (2008) concluded that Parapachycladina peculiaris (Zhang, 1991) is the sister taxon of Late Devonian through Late Mississippian Apatognathus and closely related to Early Devonian Erika and Early Ordovician Erraticodon and weakly related to Hadrodontina anceps. They discriminated P. peculiaris following the reconstruction by Zhang in Zhang and Yang (1991) but their definition on some elements (e.g. P2, M and S3/4) differs from that of Zhang in Zhang and Yang (1991) and they did not refer the relationship between P. peculiaris and H. aequabilis. They regarded that H. anceps is the sister taxon of Furnishius triserratus. Donoghue et al. (2008) recognized H. anceps mainly based on the reconstruction of Sweet (1981), Perri and Andraghetti (1987), and F. triserratus of Sweet (1981). The view on the phylogeny of ellisonids (prioniodininids) is very different between Donoghue et al. (2008) and the present author, because of significant differences in the recognition of some elements in the apparatuses.
Figure 2.
Hadrodontina aequabilis Staesche, 1964 from the Taho Formation, Shirokawa-cho, Higashiuwa-gun, Ehime Prefecture. From limestone at Level 1612A and NK01 immediately below the Smithian/Spathian boundary. 1–3, P1 elements; 1, MPC-28781 from NK01; 1a, inner view; 1b, aboral view; 2, 3, inner views, MPC-28782, 28783 from Lev. 1612A; 4, P2 element, inner view, MPC-28784 from Lev. 1612A; 5, 6, S1 elements, inner views, MPC-28785, 28786 from Lev. 1612A; 7, 8, S0 elements MPC-28787, 28788 from Lev. 1612A; 7, posterior view; 8, lateral view; 9–11, S2 elements, inner views, MPC-28789–28791 from Lev. 1612A; 12–14, S3/4 elements, inner views, MPC-28792–28794 from Lev. 1612A; 15, 16, M elements, MPC-28795, 28796 from Lev. 1612A; 15, inner view; 16, outer view.
Table 1.
Occurrence of P1, P2, S0, S1, S2, S3/4 and M elements of Hadrodontina aequabilis Staesche, 1964 obtained from 5 to 10 kg of limestone immediately below the Smithian/Spathian boundary in the Taho Formation.
Subfamily uncertain
Genus
Ellisonia
Müller, 1956
Type species.—Ellisonia triassica Müller, 1956.
Ellisonia triassica
Müller, 1956
Figure 3
P1 element: Ellisonia cf. triassica Müller, Koike et al., 2004, p. 250, figs. 4, 5.
P2 element: Ellisonia cf. triassica Müller, Koike et al., 2004, p. 250, figs. 4, 5. M element: Hibbardella subsymmetrica Müller, 1956, p. 825, pl. 96, fig. 11.
S0 element: Ellisonia triassica Müller, 1956, p. 822, pl. 96, figs. 12–14.
S1 element: Ellisonia triassica Müller, Sweet, 1981, p. W152, pl. 1, fig. 102.3b.
S2 element: Lonchodina triassica Müller, 1956, p. 828, pl. 95, fig. 10.
S3 element: Hindeodella nevadensis Müller, 1956, p. 826, pl. 96, fig. 2 only.
S4 element: Hindeodella radidenticulata Müller, 1956, p. 826, pl. 96, fig. 1.
Remarks.—Ellisonia triassica is composed of angulate P1 and P2 elements with short processes, breviform digyrate M with short processes, triramous S0 with short lateral and posterior processes, extensiform digyrate S1 and S2, and bipennate S3 and S4 with convex basal margin beneath the cusp. The S1 element with slightly arched processes without bending in the outer lateral process is an important clue in distinguishing the genus Ellisonia from other genera of Triassic ellisonids. The S2 is distinguished from the S1 by the almost straight processes but is quite similar in denticulation to the S1 element. The S3 and S4 were distinguished from each other by the number of denticles on the anterior process in the uppermost Permian natural assemblage, Ellisonia cf. triassica Müller, Koike et al. (2004). The number of denticles is two in the S3 and one in the S4 element (Koike et al., 2004). The S4 from the Triassic Taho Formation was illustrated in the previous paper by Koike et al. (2004) but is not shown in this paper because of the poor preservation of all the specimens treated. Denticles of all the elements of E. triassica are generally more discrete than those of other Triassic ellisonids.
The apparatus elements of Pennsylvanian species Ellisonia conflexa (Ellison, 1941) and E. latilaminata reconstructed by von Bitter and Merrill (1983) both have morphologic characters in common with those of E. triassica (Koike et al., 2004). The M element of Pennsylvanian Ellisonia is very short breviform digyrate or dolabrate.
Table 2.
Occurrence of P1, P2, S0, S1, S2, S3/4 and M elements of Ellisonia triassica Müller, 1956 obtained from 1.5 kg of limestone from 12.70–12.90 m depth in a borehole in the Taho Formation.
Figure 3.
Ellisonia triassica Müller, 1956 from the Taho Formation, Shirokawa-cho, Higashiuwa-gun, Ehime Prefecture. From the Smithian limestone in borehole at 12.70–12.90 m. 1, 2, P1 elements, dextral, inner views, MPC-28797, 28798; 3, 4, P2 elements, dextral, inner views MPC-28799, 28800; 5, S0 element, proximal, lateral view, MPC-28801; 6, S1 element, sinistral, inner view, MPC-28802; 7, S2 element, dextral, inner view, MPC-28803; 8, 9, S3 element, dextral, inner views, MPC-28804, 28805; 10, M element, dextral, inner view. MPC-28806.
Genus Cornudina Hirschmann, 1959
Type species.—Ozarkodina breviramulis Tatge, 1956.
Cornudina breviramulis
(Tatge, 1956)
Figure 4
P1 element: Ozarkodina breviramulis Tatge, 1956, p. 139, pl. 5, fig. 12a, b.
P2 element: Cornudina tortilis Kozur and Mostler, 1970, p. 432, pl. 1, figs. 10, 16, 20, 24. M element: Metalonchodina? dinodoides Tatge, 1956, p. 135, pl. 6, fig. 4.
S0 element: Roundya meissneri Tatge, 1956, p. 143, pl. 6, fig. 11.
S1 element: Hindeodella kobayashii Igo, Koike, and Yin, 1965, p. 10, pl. 1, fig. 4.
S2 element: Neoplectospathodus muelleri Kozur and Mostler, 1970, p. 449, pl. 3, figs. 3, 5, 7.
S3/4 element: Hindeodella triassica Müller, 1956, p. 826, pl. 26, figs. 4, 5 only.
Revised characteristics.—The apparatus of Cornudina breviramulis is composed of angulate P1 and P2 with a distinct cusp, short anterior and posterior processes. The M is breviform digyrate with a long inner-lateral process bearing indistinct denticles and a very short outer-lateral one. The S0 is triramous with short lateral processes and a short posterior process. The S1 is extensiform digyrate with an outer-lateral process sharply bending inward at middle portion. The inner-lateral process is about twice the length of the outer-lateral one. The S2 is extensiform digyrate with a straight outer-lateral process which may project downward. The cusp is near the middle potion of the processes. The S3/4 elements are bipennate with a convex basal margin beneath a cusp. The posterior process is about three times as long as the anterior one and bears indistinct denticles.
Remarks.—Cornudina breviramulis (Tatge, 1956) apparatus was reconstructed as of the bimembrate type, composed of Pa and Pb elements by Koike (1996). On the other hand, the M, Sa, Sb, and Sc elements were regarded as components of the apparatus of Ellisonia dinodoides (Tatge, 1956) by Koike (1994). I revise herein that the elements of E. dinodoides by Koike (1994) belong to the apparatus of C. breviramulis by Koike (1996).
The P1 element is morphologically quite similar to that of the Ellisonia triassica apparatus. The denticles on the anterior process of Cornudina breviramulis, however, tend to be more in number and tight. The P2, M, S0, S1, S2, and S3/4 elements of C. breviramulis morphologically differ from those of E. triassica. A marked difference can be observed in the S1 element. The outer-lateral process of the S1 element is not bent in E. triassica.
Orchard (2005) proposed Subfamily Cornudininae in Superfamily Gondolelloidea on the basis of the multielement species Cornudina? igoi (Koike, 1996). According to Orchard (2005) multielement C.? igoi is composed of segminate P1 (form species C. igoi), angulate P2, breviform digyrate M, breviform digyrate (enantiognathiform) S1, bipennate S2?, and bipennate S3–S4. Cornudina igoi was proposed by Koike (1996) as a unimembrate type consisting of the segminate Pa element from the Spathian (upper Olenekian) limestone of the Taho Formation. This time I tried to reconstruct the apparatus including the form species C. igoi but did not succeed in it. I cannot reveal the C. igoi apparatus herein but I presume the apparatus reconstructed by Orchard (2005) is not of the multielement Cornudina because it is not accompanied by the extensiform digyrate S1 and S2 that characterize the apparatus of Cornudina breviramulis, including the type species, Ozarkodina breviramulis Tatge, 1956.
Table 3.
Occurrence of P1, P2, S0, S1, S2, S3/4 and M elements of Cornudina breviramulis (Tatge, 1956) obtained from 5 kg of limestone from Level 1616 of the Taho Formation.
Figure 4.
Cornudina breviramulis (Tatge, 1956) from the Taho Formation, Shirokawa-cho, Higashiuwa-gun, Ehime Prefecture. From limestone at Level 1616, Novispathodus abruptus Zone, Spathian. 1–3, P1 elements, dextral, inner views, MPC-28807–28809; 4, 5, P2 element, inner views, MPC-28810, 28811; 4, dextral; 5, sinistral; 6, 7, S0 elements, proximal, MPC-28812, 28813; 6, posterior view; 7, lateral view; 8, S1 element, dextral, inner view, MPC-28814; 9, 10, S2 elements, inner views, MPC-28815, 28816; 9, dextral; 10, sinistral; 11, S3/4 element, dextral, inner view, MPC-28817; 12, 13, M elements, dextral, inner views, MPC-28818, 28819.
Table 4.
Occurrence of P1, P2, S0, S1, S2, S3/4 and M elements of Staeschegnathus perrii sp nov. obtained from 1.5 to 5 kg of limestone from Level 1601 and from 12.70–12.90 m depth in a borehole in the Taho Formation.
Genus Staeschegnathus gen. nov.
Type species.—Staeschegnathus perrii sp. nov.
Diagnosis.—As for the type species.
Staeschegnathus perrii
sp. nov.
Figure 5
Etymology.—Named in honor of Ulrich Staesche and Maria Cristina Perri for their outstanding and dedicated research on the Lower Triassic conodonts from the Southern Alps.
Description.—Staeschegnathus perrii sp. nov. is composed of angulate P1 and P2, breviform digyrate M, triramous S0, extensiform digyrate S1 and S2, and bipennate S3/4 elements. All elements have a well developed zone of recessive basal margin. Basal cavity and groove are observed.
P1 element: Anterior process somewhat projects downward and gently inclines outward. Cusp is not so distinct. Denticles on anterior process 3 to 6 in number, somewhat longer at middle portion and incline outward. Denticles on posterior process number 6 to 8, stand perpendicularly and are almost the same in size.
P2 element: Anterior process bows downward and curves inward, and bears 3 to 4 denticles. Posterior process is two to three times as long as anterior one, curves inward, and carries 5 to 8 denticles almost the same in size.
M element: Unit composed of very short outer-lateral process, and moderately long and robust inner-lateral process. Outer-lateral process carries one small denticle adjacent to cusp. Inner-lateral process bears 6 to 8 moderate to robust denticles which curve posteriorly and tend to be long in middle portion. Cusp large and slightly curves posteriorly.
S0 element: Lateral processes short and high. Denticles on each lateral process 4 to 5 in number and tend to be long in middle portion. Outline of lower margin of lateral processes slightly arched in anterior and posterior views. Posterior process moderately long, high and bears about 10 denticles. Denticles tend to increase in inclination and length posteriorly and are sometimes thicker than cusp. Cusp is distinct.
S1 element: Outer-lateral process is bent inward at middle portion and carries 5 to 6 short indistinct denticles. Inner-lateral process is twice as long as outer-lateral one and caries 6 to 7 denticles which tend to increase in length distally and sometimes thicker than cusp. Cusp is distinct.
S2 element: Outer-lateral process is almost equal in length with inner-lateral one and straight or slightly curves inward. Denticles on outer-lateral process number 5 to 7 and are relatively long in middle portion. Denticles on inner-lateral process number 5 to 7, increase in inclination and size distally. Cusp is long and curves inward.
S3/4 element: Processes show convex basal margin beneath cusp. Anterior process is high, slightly curves inward and carries 5 to 7 indistinct denticles. Posterior process is about three times as long as anterior one and bears 5 to 10 denticles which tend to increase in inclination and size posteriorly.
Remarks.—The P1 element of Staeschegnathus perrii is morphologically quite different from that of Cornudina breviramulis in having a somewhat twisted crescentshaped unit without a conspicuous cusp. The morphologic features of the P2, M, and S series elements of S. perrii are, however, common to those of C. breviramulis. Staechegnathus perrii is probably closely related to C. breviramulis.
Figure 5.
Staeschegnathus perrii gen. et sp. nov. from the Taho Formation, Shirokawa-cho, Higashiuwa-gun, Ehime Prefecture. From the Smithian limestone at Level 1601 except for 11, 12, from borehole at 12.70–12.90 m. 1–4, P1 elements, dextral, inner views; 4, Holotype, MPC-28820–28823; 5–7, P2 elements, dextral, inner views, MPC-28824–28826; 8–10, S0 elements, proximal, lateral views, MPC-28827–28829; 11, 12, S1 elements, inner views, MPC-28830, 28831; 11, dextral; 12, sinistral; 13–15, S2 elements, dextral, inner views, MPC-28832–28834; 16, 17, S3/4 elements, dextral, inner views, MPC-28835, 28836; 18, 19, M elements, dextral, inner views, MPC-28837, 28838.
Genus Furnishius Clark, 1959
Type species.—Furnishius triserratus Clark, 1959.
Furnishius triserratus
Clark, 1959
Figure 5
All the elements of Furnishius triserratus Clark, 1959 reconstructed herein are newly recognized except for the P1 element. The synonym list of P1 element of F. triserratus was provided in the paper by Koike et al. (1985).
I described only the P1 element of Furnishius triserratus from the Smithian limestone of the Iwai Formation, Nishitama-gun, Tokyo-to (Koike et al., 1985). As a result of the reexamination of ellisonid specimens from the limestone, I distinguished all the elements of the apparatus of Furnishius triserratus. The reconstructed apparatus differs entirely from that of Sweet (1981).
Description.—Furnishius triserratus is composed of pastinate P1, angulate P2, breviform digyrate M, triramous S0, bending very long extensiform digyrate S1, straight extensiform digyrate S2, and bipennate S3/4 elements.
P1 element: Unit is pastinate with blade-like anterior, posterior, and lateral processes. Anterior and lateral processes join at an angle of 60 degrees in oral view. In immature form, anterior process bears 5 to 6 needle-like denticles and lateral process carries 4 to 5 needle-like ones. In mature form, denticles on anterior and lateral processes are 7 to 8 in number and arranged in two rows. Posterior process has 5 to 8 needle-like denticles which gradually decrease in height toward posterior. Cusp is not distinct. Basal groove is well observed beneath three processes.
P2 element: Anterior process inclines outward on upper margin and carries 6 to 7 fine denticles. Posterior process is about two times length of anterior one and bears 8 to 10 fine denticles. Cusp is distinct.
M element: Inner-lateral process is three times length of outer-lateral one and carries 16 to 18 fine denticles. Outer-lateral process slightly inclines posteriorly and possesses 4 to 5 fine denticles. Cusp is distinct. Basal margins of two processes meet at angle of about 120 degrees in anterior view.
S0 element: Anterior-lateral processes are high and carry 4 denticles on each. Posterior process is high and carries more than 7 denticles which gradually increase in length and inclination posteriorly.
S1 element: Cusp is distinct. Outer-lateral process sharply curves inwardly in distal third and bears 10 to 12 fine denticles. Inner-lateral process is somewhat longer than outer-lateral one and carries 10 to 12 fine denticles which gradually increase in length toward distal end. Basal cavity has weakly expanded lip inward.
S2 element: Outer-lateral process is slightly curved inward and carries 7 to 9 fine denticles which tend to be long in middle portion. Inner-lateral process is twice length of outer-lateral one and bears 8 to 9 fine denticles which gradually increase in length toward distal end. Cusp is distinct. Basal cavity has weakly expanded lip inward.
S3/4 element: Anterior process is short and bears 6 to 10 fine denticles which tend to be long at middle portion. Posterior process is about three times length of anterior one and carries 14 to 20 fine denticles which increase in length and inclination toward posterior. Basal cavity lies parallel to outline of posterior process.
Remarks.—Furnishius triserratus was described by many workers but no one noted any ramiform elements of the species except for Sweet (1981). Sweet (1981) reconstructed F. triserratus as a seximembrate apparatus composed of pastinate Pa (fig. 100.2f in Sweet, 1981), angulate Pb (fig. 100.2e in Sweet, 1981), digyrate M (fig. 100.2d in Sweet, 1981), biramous Sa, digyrate Sb, and bipennate Sc elements. The Pa element illustrated by Sweet (1981) is fragmental but comparable to the P1 of Koike et al. (1985). The other elements, however, entirely differ in their morphologic features from F. triserratus from Iwai. More than forty specimens of the F. triserratus pastinate P1 element have been distinguished in the fauna of Iwai. However, no Pb, M, or S series elements of Sweet (1981) have been found in the fauna. The fauna includes four specimens of Neospathodus cf. waageni Sweet, 1970 (pl. 1, fig. 11, Koike et al., 1985), three of P1 and 85 specimens of ramiform elements of Ellisonia triassica (pl. 1, figs. 12.21, Koike et al., 1985) and some large elements of unidentified species. The ramiform elements of F. triserratus can be, consequently, easily distinguished in the fauna. Table 5 shows the number of occurrences of elements of F. triserratus in the fauna.
The elements of Furnishius triserratus from Iwai carry many more denticles than do other Triassic prionoiodininids described herein. The P2, M, S1, S2, and S3/4 elements, however, have features in common with those of Cornudina breviramulis and Staeschegnathus perrii.
Radiatignathus radiatus Tian, 1983 in Tian et al. (1983) from the Lower Triassic of Shichuan Province, Southwest China is of platform type with anterior-posterior process and two anterior processes. The keels are distinct only beneath the anterior-posterior process and the longer anterior process. Therefore, R. radiatus is of pastinate type and agrees well with one of the platform varieties of Furnishius triserratus reported by Clark and Rosser (1976, fig. 5.15) from the Thaynes Formation in western North America. Clark and Rosser (1976) pointed out that a gradual morphologic transition could be observed between the blade-like and platform types of F. triserratus. Solien (1979) emphasized that the two types of F. triserratus indicate a similar stratigraphic position in the Thaynes Formation. The forty specimens referred to the P1 of F. triserratus from Iwai are all of the bladelike type. All of the four illustrated F. triserratus by Buryi (1979) from South Primorye, Russia are also of the blade-like type. The blade-like pastinate P1 from Iwai, South Primorye, and western North America are morphologically close to one another. The denticles on the unit are all needle-like and arranged in two rows on anterior and anterior-lateral processes in mature forms but they are in one row on the posterior one even in mature forms. On the other hand, the denticles on the unit of the platform-type F. triserratus are blunt and node-like, and arranged in two to three rows on the posterior process even in immature forms. Furnishius triserratus and R. radiatus are probably independent taxa but they have a close phylogenetic relationship. I expect that the question will eventually be decided based on the ramiform elements of the two taxa.
Furnishius wangcangensis Dai and Tian, S., 1983 in Tian et al. (1983) from the Lower Triassic in Shichuan Province, Southwest China is of the rounded to quadrangular platform type with irregular-sized node-like denticles on the oral side. Distinct keels are present beneath the anterior, posterior and two internally branching lateral processes. The feature of the keels is coincident with that of blade-like Malaygnathus tetraserratus Igo, Koike, and Yin, 1965 from the Smithian limestone in Gua Panjan hill, Kelantan, Malaysia.
Table 5.
Occurrence of P1, P2, S0, S1, S2, S3/4 and M elements of Furnishius triserratus Clark, 1959 obtained from 2 kg of limestone from Level 1601 and from 12.70–12.90 m depth in a borehole in the Taho Formation.
Figure 6.
Furnishius triserratus Clark, 1959 from the Smithian limestone in the Iwai Formation, Iwai, Nishitama-gun, Tokyo-to. 1, 2, P1 elements, inner views, MPC-28839, 28840; 1, sinistral; 2, dextral; 3, 4, P2 elements, sinistral, inner views, MPC-28841, 28842; 5, 6, S0 elements, proximal, lateral views, MPC-28843, 28844; 7–9, S1 elements, sinistral, inner views, MPC-28845–28847; 10–12, S2 elements, inner views, MPC-28848–28850; 10, 12, dextral; 11, sinistral; 13, 14, S3/4 elements, sinistral, inner views, MPC-28851, 28852; 15–17, M elements, dextral, inner views, MPC-28853–28855.
Acknowledgments
My deep gratitude is expressed to Hisayoshi Igo, Emeritus Professor of Institute of Geoscience, University of Tsukuba, for critical review of the manuscript and valuable suggestions. Thanks are also due to Michael J. Orchard, Geological Survey of Canada and an annonimous reviewer for critically reading the manuscript and providing valuable comments. I thank Shungo Kawagata (Yokohama National University) for his help in preparing the photographs.
