Glikmanius myachkovensis ( Lebedev, 2001 )

Ginter, Michał, Ivanov, Alexander & Lebedev, Oleg, 2005, The revision of “ Cladodus ” occidentalis, a late Palaeozoic ctenacanthiform shark, Acta Palaeontologica Polonica 50 (3), pp. 623-631 : 627-630

Glikmanius myachkovensis ( Lebedev, 2001)

Figs. 2C , 3.

? Symmorium myachkovensis [sic] Lebedev, sp. nov.; Lebedev 2001: 196–197, pl. 41: 4.

“ Cladodus ” sp.: Nekrylov 1997: 52.

“ Symmorium ” sp.: Keltsiyan 2002: 25.

Original material.— The original description was founded on about 50 teeth from the Moscovian and Kasimovian of the Moscow and Riazan Regions in Russia. The holotype, PIN 1704 /180 ( Lebedev 2001, pl. 41: 4a), comes from the vicinities of the village of Myachkovo, Moscow Region; its stratigraphic position is uncertain: either Myachkovian Regional Stage, Moskovian, or Krevyakinian Regional Stage, Kasimovian .

New material.— 28 teeth, CM 44549 , from Peru, Nebraska , Indian Cave Sandstone , Onaga Formation , Upper Pennsylvanian; generally well preserved, with only slight traces of overall abrasion. Two teeth partly embedded in white limestone, MB.f.9452.1−2, from the type locality at Myachkovo, probably Moscovian .

Specimens belonging to the same species were described by Nekrylov (1997) as “ Cladodus ” sp. and Keltsiyan (2002) as “ Symmorium ” sp. Material studied by these two authors includes about 200 unnumbered teeth in the collection of the Geography Department of the Lugansk Pedagogical University (Lugansk, Ukraine) from the Gurkovaya Ravine close to Kalinovo village, Popasnya District, Lugansk Region, Ukraine. The age of the fossil−bearing layer is regarded as limestone M 7 1, Formation C 2 7 according to the local Donetsk Basin stratigraphical scheme (corresponding to the Podolskian–Myachkovian Regional Stages of the Russian Platform General unified scheme), Moscovian, Middle Carboniferous ( Nekrylov 1997; Keltsiyan 2002). Material from this collection was examined by one of the authors of the present paper (O. L.) and is currently under description by V. Keltsiyan (Lugansk, Ukraine).

Description.—This species of Glikmanius is characterised by small teeth with a relatively long and narrow median cusp and in most cases more than one, usually two to three, intermediate lateral cusplets on each side, smaller than the outermost ones. All the cusps in the crown are more in line than in G. occidentalis . The basolabial depression, projections, and rounded oral−lingual buttons are relatively weakly developed. The buttons are rather far from the lingual rim and can be connected by a thin and vague ridge. The part of the base lingual to the line connecting the buttons is folded downwards.

The level of heterodonty in this species is rather low. However, several differences, particularly between smaller and larger teeth in the collection, can be pointed out. The smaller teeth (2–4 mm in the mesio−distal dimension) often have more than two intermediate cusplets on each side (up to four; Fig. 3A); the larger ones (4–6 mm; Figs. 2C , 3C, F) have one or two such cusplets, and in the latter case the more lateral cusplet is the higher ( Fig. 3C 2 , C 3, F 2 ). There are specimens, usually of intermediate size (3–4 mm), which possess more cusplets on one side than on the other, e.g., two and three or three and four ( Fig. 3B 2 , E). Because the teeth are otherwise virtually symmetrical, it is impossible to say, whether the larger number of cusps is strictly side−related.

The ornamentation of the median cusp is typical of Glikmanius , with only a few vertical cristae in the lower half and a smooth upper part of the labial side, whereas the lingual side is covered with 12 and more cristae, almost reaching the tip ( Fig. 3C 1, F 1 ).

There is a single specimen in the collection from the Peru site, in all aspects of form resembling typical teeth of G. myachkovensis , but much larger than the rest. It is broken, but when complete must have measured well above 1 cm across the base. We think that it belonged to a particularly large individual of the same species.

Comparisons.—The teeth of G. myachkovensis are consider− Some other teeth figured by Lund (1985: fig. 8) are also ably smaller than G. occidentalis , with a more slender, uni− similar to G. myachkovensis , but their possible relationship is formly narrowing median cusp throughout its length, and even less certain than in the case of that mentioned above. usually with a larger number of intermediate cusplets which The large tooth in Lund (1985: fig. 8E) probably belongs to are more in line than in the other species. The basolabial de− “ Cladodus ” striatus Agassiz, 1843.

pression is shallower in G. myachkovensis , the buttons are Distribution.— Upper Carboniferous , Pennsylvanian of the less prominent, situated further from the lingual rim, and of− Moscow Syneclise, Donetsk Basin, and Nebraska.

ten connected with a low ridge; the latter feature is rather rare in G. occidentalis . Also the sloping lingual part of the base is a diagnostic feature of G. myachkovensis . Discussion

Remarks.—This small form of Glikmanius was first noted by

Ossian (1974) in the Peru site in Nebraska in his unpublished There are several taxa, whose tooth morphology is close to dissertation. He attributed an enormous number of such teeth Glikmanius gen. nov. Two of them, viz. Heslerodus diver− (1325), which he found at Peru, to the upper dentition of gens ( Trautschold, 1879) (= Phoebodus heslerorum Wil− Cladodus occidentalis . He also decided to include consider− liams, 1985) and “ Ctenacanthus ” costellatus Traquair, 1884, ably different teeth (467), with three almost equal main cusps, share general basal features with Glikmanius , such as the in the same species, as representing its lower dentition. We deep median depression, two pad−like basolabial projections consider the “upper teeth” to represent G. myachkovensis and and two prominent buttons, but their crowns are considerably the “lower teeth” as belonging to Heslerodus divergens . It is a different. Heslerodus has gentle, thin, phoebodont−like main tempting idea to treat G. myachkovensis and H. divergens cusps, with the central cusp only slightly larger than the laterteeth as coming from the same fish, because indeed there are als; that was the reason why Williams (1985) attributed it to several similarities, particularly in the structure of the base the genus Phoebodus . In the holotype of “ C. ” costellatus, (two buttons and basolabial projections, and the median de− there is only one imperfect tooth ( Traquair 1884: pl. 2: 6), but pression). However, there exist quite a few contradictory argu− the second specimen, described by Moy−Thomas (1936; see ments. Firstly, the semi−articulated specimens of H. divergens Ginter 2002 : figs. 4A, 5), provides much better material for described by Williams (1985, under the name of Phoebodus comparison. Its teeth can have up to three pairs of lateral heslerorum ) from the Pennsylvanian Black Shales of Indiana cusps, which can be observed in Glikmanius myachkovensis , are associated with only one type of tooth. Secondly, teeth of but all the cusps are in line and very coarsely ornamented H. divergens are, on average, smaller than those of G. myach− with cristae converging at various heights. Moreover, the kovensis. It is also notable that the number of G. myachko− teeth of “ C. ” costellatus and Heslerodus are much smaller, vensis teeth, collected by Ossian, is more than twice as large as on average, than those of Glikmanius .

that of H. divergens , and the numbers are so extreme, that this On the other hand, the size and the tooth−crown form are observation is evidently statistically significant. This ratio in shared features of Glikmanius occidentalis and the Lower Carthe sample studied by us, housed at the Carnegie Museum, is boniferous Cladodus sensu stricto (as noted above, the re−esless striking (28:19), but also in favour of G. myachkovensis tablishment of this genus is under way, Duffin and Ginter in teeth. press). In particular, the crown of C. bellifer (St. John and It is probable that a tooth from the Namurian of Bear Worthen 1875: pl. 4: 10), with its large, gently striated central Gulch in Montana, illustrated by Lund (1985: fig. 8A, B) as cusp, and intermediate cusplets moved labially off the line Stethacanthus sp. , belongs to some species related to G. connecting the bases of the main cusps, resembles that of myachkovensis (see Fig. 1B for a similar tooth from the same Glikmanius . However, in this case the basal articulation delocality). It has two intermediate cusplets on each side, and vices are different: in Cladodus , instead of two buttons there is the other features are typical of Glikmanius . However, a single, slightly curved ridge, and instead of two basolabial Lund’s figure suggests that the more median cusplet is the projections, there occurs a long, unbroken shelf or parapet.

larger, which is opposite to the situation observed in the teeth There are two more cladodont genera which have a deep from Peru. The tooth from Montana is much larger than the median basolabial depression in their teeth, two basolabial average size of G. myachkovensis teeth (the width of the base projections, and may or may not have two buttons. These are reaches 1.5 cm), but does not exceed the size of the largest Cladoselache Dean, 1894 , and Squatinactis Lund and Zanspecimen from Peru. It also ought to be remembered that gerl, 1974. Although their tooth−bases are superficially simi− Lund’s specimen was collected as a macrofossil and speci− lar to those of Glikmanius teeth, examination reveals that the mens from Peru come from processed conodont samples. nature of the basolabial projections is different. The projec− The latter method usually reveals smaller teeth. tions in Cladoselache ( Ginter 2002: fig. 4B) and Squatinactis Ą ( Lund 1988: fig. 1; MG, personal observations), as well as in “ Symmorium ” glabrum Ginter, 1999 (whose real generic assessment is yet undetermined), are simply specifically formed parts of the labial rim of the base; in contrast, such projections in Glikmanius , Heslerodus , and “ Ctenacanthus ” costellatus appear to be independent entities. This suggests that in the mentioned two groups of taxa the overall appearance of tooth−bases developed convergently.

Despite our belief that Glikmanius possessed ctenacanthiform spines, there is no direct evidence on that. Therefore, Glikman’s (1964a, b) decision to assign G. occidentalis as Ctenacanthus appears to be premature. The type species of Ctenacanthus , C. major Agassiz, 1837 , is based on a fin spine from the Lower Carboniferous Limestone of the British Isles. It is probable, considering the size of the spine, that one of the big tooth−based cladodont taxa from the same formation, such as Cladodus mirabilis , is conspecific with C. major . However, no such undoubted association, indicative of which particular tooth form it could be, has yet been found. Therefore, the only shark possessing true Ctenacanthus fin−spines (sensu Maisey 1981) and associated teeth is C. compressus Newberry, 1889 (= C. clarki Newberry, 1889 ; see Dean 1909, Williams 2001), from the late Famennian Cleveland Shale of Ohio. Its teeth, although definitely similar to those of Cladodus sensu stricto, are also distinctly different from those of Glikmanius , e.g., by lacking two buttons and two basolabial projections.

We temporarily refrain from defining a new family for Glikmanius sp. nov., because some more comparative work on presumably related genera must be done. However, the above discussion suggests that, of all mentioned taxa, such a family should also include Heslerodus and “ Ctenacanthus ” costellatus.

In this paper, we could confidently distinguish only two species of Glikmanius from the Permo−Carboniferous. However, future detailed studies, particularly on the material from the Serpukhovian of Montana and Moscow Syneclise, may show that more species deserve to be recognised. Several specimens, such as “ Cladodus girtyi ” ( Hay 1900: fig. 2) and a part of “ Cladodus lamnoides ” teeth figured by Trautschold (1874: pl. 28: 3c–e), also differ in certain aspects from the classic model of G. occidentalis . It seems an irony that such a well known tooth form is known only from isolated teeth and never even a partial dentition was recorded. This makes an account of probable ontogenetic and position−related heterodonty, and distinguishing it from an inter−specific variation, virtually impossible.

Figures

Fig. 2. A, B. Glikmanius occidentalis (Leidy, 1859). A. Specimen PF 8240, from the Pennsylvanian black shales of the Hesler Quarry, Indiana, in oral/lingual view (same as Williams 1985: pl. 7: 7). B. Specimen PCh/425a, from the Moscovian of Myachkovo, Moscow District, in oral (B1) and aboral (B2) views. C. Glikmanius myachkovensis (Lebedev, 2001), specimen MB.f.9452.1, from the Moscovian of Myachkovo, in labial (C1), labial/aboral (C2), and aboral (C3) views.

Fig. 1. A. Glikmanius occidentalis (Leidy, 1859), holotype, specimen ANSP 8394, from the upper Coal Measures (Pennsylvanian) of Manhattan, Kansas, in lingual (A1), aboral (A2), and labial/aboral (A3) views. B. Glikmanius sp., specimen CM 44504B, from the Namurian E3, Bear Gulch, Montana, in lingual view. C–E. G. occidentalis. C. Specimen USNM 14107, from undetermined Carboniferous of Illinois, labial view. D. Specimen BMNH P.7043 (labelled as Cladodus impressus Woodward), from the Moscovian of Myachkovo, Moscow District, in lateral view. E. The first ever published specimen, BMNH P.7364, from the Chance Pennystone, Coal Measures of Donnington, Coalbrook Dale, Shropshire, UK, labial view. F, G. Glikmanius sp., photographs in aniseed oil, parts of occlusal view, specimen MP30−1, from the Serpukhovian of the Kalinovskie Vyselki Quarry, Moscow District. F. Lingual part of the base. G. Intermediate cusp. H. Lateral cusp.