A review of Neogene and Quaternary pikes of southeastern Europe and a new species from the early Pleistocene of Nogaisk, Ukraine

OLEKSANDR M. KOVALCHUK, MARK V.H. WILSON, and TERRY GRANDE

Kovalchuk, O.M., Wilson, M.V.H., and Grande, T. 2017. A review of Neogene and Quaternary pikes of southeastern Europe and a new species from the early Pleistocene of Nogaisk, Ukraine. Acta Palaeontologica Polonica 62 (1): 121–135.

The fish genus Esox (Teleostei, Esocidae) has been recorded from thirty late Miocene, Pliocene, and Pleistocene localities where forty-one bone-bearing strata are exposed in the territory of Ukraine, Russian Federation, and Republic of Moldova. From eight localities the genus is reported or described for the first time. A detailed description and morphological analysis of the currently available osteological material demonstrates the presence of four species in the studied area: (i) Esox sibiricus (late Miocene–early Pliocene); (ii) Esox moldavicus (early Pliocene–early Pleistocene); (iii) Esox nogaicus sp. nov. (early Pleistocene, Calabrian); (iv) Esox lucius (early–middle Pleistocene). The Northern Pike (Esox lucius) is recorded for the first time in the early Pleistocene fossil record of southeastern Europe. The new species E. nogaicus is characterized by a massive dentary with deep symphysis and the possible presence of a pair of fixed canine-like teeth near the anterior end of the vomer. Such canine teeth are seen also in certain species known only from North America, the extant Esox masquinongy, the fossil species E. columbianus, and an unnamed Miocene form. However, unlike in E. nogaicus, in the three North American species fixed canines also occur anteriorly on the palatines. The Miocene, Pliocene, and Pleistocene pikes from southeastern Europe document a greater diversity of morphologies in the past than exists today in the pike species of Europe. Changes in the predominant species of Esox in southeastern Europe are hypothesized to be driven by changing global and regional climates.

Key words: Esociformes, Esocidae, Esox, Miocene, Pliocene, Pleistocene, Ukraine, Russia, Moldova.

Oleksandr M. Kovalchuk [biologiest@ukr.net], Department of Paleontology, National Museum of Natural History at the National Academy of Sciences of Ukraine, 15 Bogdan Khmelnitsky str., Kyiv 01601 Ukraine.

Mark V.H. Wilson [mvwilson@ualberta.ca], Department of Biological Sciences, University of Alberta, Edmonton, ­Alberta T6G 2E9, Canada.

Terry Grande [tgrande@luc.edu], Department of Biology, Loyola University Chicago, Chicago, Illinois 60660, USA.

Received 28 September 2016, accepted 5 December 2016, available online 26 January 2017.

Copyright © 2017 O.M. Kovalchuk et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License (for details please see http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Introduction

The genus Esox Linnaeus 1758 (i.e., pikes and pickerels) is a group of freshwater fishes known for its duck-billed snout, elongated body and voracious feeding behavior. The family Esocidae (with only one extant genus) has a rich fossil record dating to the Late Cretaceous (Wilson et al. 1992), although all known species are restricted to the Northern Hemisphere. Based on morphological (Nelson 1972; Sytchevskaya 1976; Grande 1999; Grande et al. 2004) and molecular data (López et al. 2000; Grande et al. 2004), species of Esox are divided between two subgenera: Kenoza, the pickerels, and Esox, the pikes. Species within the subgenus Esox are restricted to northern latitudes and include the following extant taxa. Esox lucius (Northern Pike) exhibits a circumpolar distribution through eastern and central United States, throughout Canada, Europe and into Asia. In eastern and central North America, Esox masquinongy (Muskellunge) is also found. Despite their many similarities and partly overlapping distributions, E. lucius and E. masquinongy display significantly different behavioral traits and developmental trajectories (Burdi and Grande 2010; McCormick et al. in press). In Asia, Esox reichertii (Amur Pike) is restricted to the Amur River basin. In Europe, two additional species have been named recently. One recently named species is the Southern Pike Esox cisalpinus (Bianco and Delmastro 2011) with junior synonym E. flaviae (Lucentini et al. 2011) of Italy. The other recently named species is the Aquitanian Pike Esox aquitanicus (Denys et al. 2014) from France. Omitting those two recently named European species, phylogenetic relationships among the extant forms are as follows: [[E. niger [E. americanus americanus, E. americanus vermiculatus]] [E. masquinongy [E. reichertii, E. lucius]]] (Grande et al. 2004). The molecular study of Denys et al. (2014) suggested that both E. cisalpinus and E. aquitanicus are more closely related to E. lucius than to other extant pike species.

Fossil esocids expand the morphological diversity and biogeographic history of the group (Cavender et al. 1970; Gaudant 1979, 2002; Wilson 1980, 1981, 1984; Wilson et al. 1992; Grande 1999; Smith et al. 2000). Late Cretaceous records of Esocidae from North America classified in different genera include Estesesox and Oldmanesox, the latter being more closely related to Esox than the former (Wilson et al. 1992). There are at least twelve nominal species of Esox known only as fossils, beginning with Esox tiemani Wilson, 1980, from the Paleocene of North America. Two other species, Esox longkouensis Chang and Zhou, 2002, late Paleocene or early Eocene of China, and Esox kronneri Grande, 1999, early Eocene of North America, are slightly younger. Two relatives of E. masquinongy are Esox columbianus of Pliocene age (Smith et al. 2000) from southern Washington and a related form referred only to Esox sp. from the Miocene of southeastern Oregon (Cavender et al. 1970).

In Europe the skeletal fossil record begins with the Oligocene E. primaevus (see Gaudant 1978) and E. papyraceus (see Gaudant 1988) and includes the middle Miocene E. lepidotus (see Gaudant 1980). Esox moldavicus was described from the early Pliocene of Eastern Europe (Sytchevskaya 1974). Diversity of Asian fossil pike species is also high and includes E. aralensis from the middle Oligocene–early Miocene, as well as the late Oligocene E. borealis and E. dispar (see Sytchevskaya 1976). Many remains from the Miocene and Pliocene strata of Western Siberia belong to Esox sibiricus (see Sytchevskaya 1974, 1976). In addition, Esox aff. sibiricus and Esox cf. sibiricus were defined from the early–middle Pliocene of Western Mongolia and Altai (Sytchevskaya 1976). Lebedev (1959) described Esox (lucius?) from the late Miocene of the Zaisan locality; however, as clearly stated by Sytchevskaya (1976), these are remains of E. sibiricus. Bones of pikes are very numerous in the late Neogene deposits of Eastern Europe and usually determined as Esox lucius and Esox sp. (see Tarashchuk 1962; Dubrovo and Kapelist 1979; Böhme and Ilg 2003; Kovalchuk 2011, 2015; Kovalchuk et al. 2014a, 2015), but some of them (as is shown below) belong to fossil species (e.g., E. sibiricus, E. moldavicus, etc.).

The earliest record of extant species of Esox in North America might be the palatine tentatively assigned to E. masquinongy from the late Miocene of Oregon (Cavender et al. 1970), although a Pliocene fossil from Washington State represents an extinct species (Smith et al. 2000). In Europe Esox cf. lucius appears first in the Pliocene of Willershausen clay pit in Germany (Gaudant 1997). This species was also described from the late Pleistocene of the Russian Federation (Sytchevskaya et al. 2015). Esox lucius has been collected from Pleistocene localities in England (Schreve et al. 2002; Böhme 2010), Germany (Bloos et al. 1991; Böttcher 1994), Hungary (Jánossy 1986), Netherlands (Gaudant 1979), Poland (Pawłowska 1963) and Slovenia (Križnar and Kovalchuk 2016), as well as from the Holocene of Bulgaria (Böhme and Ilg 2003). Bones identified as Esox aff. reichertii come from the early Pliocene of the Russian Federation (Sytchevskaya 1989).

In southeastern Europe a wealth of esocid fossil material documents the diversity of species of Esox represented by fossils. Some of these fossils can be referred to species previously named by Sytchevskaya (1974), and others cannot. This study addresses the morphology and diversity of all of the available fossil esocids from southeastern Europe, for the purpose of clarifying their morphological characteristics, their taxonomy, and their stratigraphic occurrences.

Institutional abbreviations.—NMNHU-P, Department of Paleontology of the National Museum of Natural History, Kyiv, Ukraine.

Other abbreviations.—DDC, diameter of the vomerine canine teeth; DFA, diameter of the fossa articularis; DT, tooth depth; HS, height of dentary symphysis; L, length; LM, maxillar length; LT, tooth length; W, width; WCV, width of the vomerine head; WDF, maximum width of the vomerine dental field; WPSa, width of the anterior part of parasphenoid; WPSp, width of the posterior part of parasphenoid; WS, width of the dentary near the symphysis; WT, tooth width; WTR, width of tooth row.

All investigated fish-bearing strata are of alluvial origin, but the accumulations of bones occurred in different water bodies—rivers, lakes, estuaries, and lagoons. Popovo, Lobkovo, Verkhnya Krynitsya, Vasylivka, Novoukrainka, Andreevka, Novopetrovka, and Obukhovka yielded numerous fish bones in gravel lenses, interlayered with ferruginized sands and clays (Rekovets and Pashkov 2009; Krochmal and Rekovets 2010; Nesin 2013; Kovalchuk 2013, 2014, 2015). Remains of pikes and other freshwater fish remains from the Mykhailivka locality were obtained from clay and siltstone with interbedded sand, limestone, and gravel lenses (Nesin 2013). The same situation is found at the Frunzovka (Kovalchuk 2015), Palievo (Sinitsa 2008a), Egorovka (Sinitsa 2008b, 2010), Cherevichne (Nesin 2013), Sinyaya Balka (Krochmal and Rekovets 2010). Coarse-­grained or fine- to medium-grained crossbedded sand and gravel of the Orekhovka (Nesin 2013), Pontian Lectostratotype (Topachevsky et al. 1988), Vinogradovka (Nesin and Nadachowski 2001; Nesin 2013), Kamenskoe (Tarashchuk 1965), Tiligul, Kryzhanovka, Nogaisk, Kairy, Semibalka (Krochmal and Rekovets 2010), and Lysa Gora (Rekovets et al. 2014) also contain pike remains. Freshwater fish bones of the Kotlovina, Zhevakhova Gora, Nova Etuliya, Protopopovka, Bol’shevik, and Medzhibozh are derived from the layered, partly ferruginized clayey sand and gravel with small carbonate concretions and/or sandstone pebbles (Topachevsky and Nesin 1989; Krochmal and Rekovets 2010; Nesin 2013).

Material and methods

The material under study is represented by disarticulated bones, housed in the Department of Paleontology of the National Museum of Natural History, National Academy of Sciences of Ukraine (collections NMNHU-P No. 27, 29, 33, 35, 37, 38, 41, 42, 45, 53). Comparative material is listed in Appendix 1. Isolated bones were identified based on comparisons with extinct and modern taxa from the literature (Lebedev 1959; Sytchevskaya and Lebedev 1971; Sytchevskaya 1974, 1976, 1980, 1989; Gaudant 1978; Smith et al. 2000). Determination of elements was accomplished using diagnostic features based on comparative observations and literature summaries (Grande 1999; Grande et al. 2004). The taxonomic hierarchy in the systematics section follows Nelson et al. (2016). Correlation of the Eastern Paratethys stages with European Mammal Neogene Zones follows Topachevsky et al. (1997, 1998), as well as Nesin and Nadachowski (2001). General stratigraphic scale of Quaternary deposits (Head et al. 2015) has been used for correlation of the Pleistocene sediments containing pike fossils. The specimens were measured using a digital caliper with 0.1 mm precision. Bone terminology follows Sytchevskaya (1976) and Lepiksaar (1994).

Systematic palaeontology

Subdivision Teleostei Müller, 1845

Order Esociformes Bleeker, 1859

Family Esocidae Rafinesque, 1815

Genus Esox Linnaeus, 1758

Type species: Esox lucius Linnaeus, 1758, Pleistocene–Recent, Eurasia and North America.

Esox sibiricus Sytchevskaya, 1974

Fig. 2.

1959 Esox (lucius?); Lebedev 1959: 50, fig. 25.

1971 Esox sp.; Sytchevskaya and Lebedev 1971: 49, pl. 1, pl. 2: 5b.

1974 Esox sibiricus sp. nov.; Sytchevskaya 1974: 227, pl. 1: 8, pl. 2: 12, pl. 3: 1–4, pl. 4: 1–8.

1976 Esox sibiricus Sytchevskaya, 1974; Sytchevskaya 1976: 107, pl. 6: 6–9; 108, figs. 1–11; 109, fig. 8; 110, fig. 1.

1980 Esox sibiricus Sytchevskaya, 1974; Sytchevskaya 1980: 201, 202, pl. 9: 8, pl. 10: 1–5.

1989 Esox sibiricus Sytchevskaya, 1974; Sytchevskaya 1989: 22–23, pl. 1: 3–11.

Material.—Late Miocene: one left and two right dentaries (NMNHU-P 29/1678–1680, Popovo 3); one left dentary (NMNHU-P 29/3965, Lobkovo); one left dentary (NMNH-P 45/5690, Cherevichne 3); one parasphenoid, three dentary fragments (NMNHU-P 29/1033–1036, Verkhnya Krynitsya 2); one left and three right dentaries, one right articular (NMNHU-P 41/4323–4326, 4525, Egorovka 2); one left dentary (NMNHU-P 41/2847, Orekhovka); one right dentary (NMNHU-P 41/2741, Vinogradovka 1). Early Pliocene: one left dentary (NMNHU-P 37/2554, Novopetrovka); one left dentary (NMNHU-P 29/1583, Popovo 2).

Emended diagnosis.—Esox sibiricus differs from other Eur­asian taxa by a number of characters: (i) predominance of double tooth row at symphysis of dentary; (ii) narrow and weak dental shelf; (iii) absence of symphysial notch; (iv) very large articular angle (nearly or more than 70°); (v) clearly visible grooves of carotid arteries on parasphenoid; (vi) short and flat facet of maxillar process on palatine.

Description.—The parasphenoid from the Verkhnya Kryni­tsya 2 locality is presented by caudally extended anterior part (Fig. 2E). The bone is massive; grooves of the carotid arteries are clearly visible. Measurements of the medial part of the parasphenoid are width 5.9 mm, height 3.5 mm, width of anterior medial crest 1.2 mm.

The dentary, which is not deep, has a moderately developed dental shelf, which smoothly rises into the medial wall (Fig. 2A–D, F–H, J–L). Teeth at the symphysis are arranged in two rows, and internal one being better developed. Teeth are completely broken in the fossils, but C-shaped crown bases are visible. There is a gradual increase in their diameter in the direction towards the symphysis. A clear lateral groove separates the anterior edge of the dentary and forms a ventral bulge in the symphysis. The anterior edge of the dentary is straight and thickened at the symphysis. Pores for the sensory canal (Nelson 1972) are clearly visible at the ventral edge. Two small hook-shaped teeth with rounded crowns are preserved on one dentary from Popovo 3. Measurements of dentaries of Esox sibiricus from late Miocene and Pliocene strata of Ukraine are presented in the Table 2.

Table 2. Measurements (in mm) of dentaries of Esox sibiricus Sytchevskaya, 1974. N, number of specimens.

The articular bone is massive (Fig. 2I), with a high wall (anguloarticular angle is 67°). The posterior process of the bone is elongated, laterally compressed and has a narrow ventral keel. The articular facet is wide (W 4.5 mm; L 6.1 mm), with a thick raised edge. The anteroventral angle is smooth. The height of the bone at the front edge of the articular facet is 7.3 mm.

Remarks.—The described remains from the late Miocene and Pliocene localities of southeastern Europe correspond closely in morphology to those of Esox sibiricus from Kazakhstan (Sytchevskaya 1976) and Mongolia (Sytchevskaya 1989). This species is similar to Esox reichertii in the structure of the anterior median crest of the parasphenoid. As compared to that in Esox aralensis, the dentary of the described species has a smaller dental shelf, a two-row dentition, and lacks a symphysial notch (Sytchevskaya 1976). The limited variety of skeletal elements of Esox sibiricus from the described localities (i.e., dentary, parasphenoid and articular bone only) does not allow comparison with some other extinct species. The presence of Esox sibiricus in the early Pleistocene strata of Popovo 2 could have been caused by the redeposition of these remains from an older layer (probably Popovo 3).

Stratigraphic and geographic range.—Early Miocene–late Pliocene of Western Siberia; late Miocene–early Pliocene of southeastern Europe.

Esox moldavicus Sytchevskaya, 1974

Fig. 3.

1974 Esox moldavicus sp. nov.; Sytchevskaya 1974: 229, pl. 1: 2–6, pl. 2: 10.

1976 Esox moldavicus Sytchevskaya, 1974; Sytchevskaya 1976: 110, pl. 9: 2–9.

1980 Esox moldavicus Sytchevskaya, 1974; Sytchevskaya 1980: 36–37, pl. 10: 6–9.

2014 Esox moldavicus Sytchevskaya, 1974; Kovalchuk et al. 2014b: 51, fig. 7a–c.

Material.—Early Pliocene: one right dentary (NMNHU-P 53/4245, Obukhovka 1); one left and two right dentaries (NMNHU-P 42/513, 532, 1252, Kamenskoe). Late Pliocene: two palatines (NMNHU-P 53/4246, 4247, Obukhovka 2); one left dentary (NMNHU-P 53/4248, Kryzhanovka); one left and one right dentary (NMNHU-P 45/6017, 6018, Chere­vichne 2). Early Pleistocene: one left dentary and one palatine (NMNHU-P 41/2452, 2453, Kotlovina 2); two left dentaries and two palatines (NMNHU-P 41/2454–2457, Kotlovina 3).

Emended diagnosis.—Esox moldavicus differs from other esocids by (i) the predominance of one-row dentition on dentary; (ii) moderately developed dental shelf; (iii) high articular wall (articular angle more than 60°); (iv) caudally narrowed anterior medial crest on parasphenoid; (v) weakly visible grooves of carotid arteries on parasphenoid; (vi) presence of groove on anterior part of palatine.

Description.—The dentary has a moderately developed shelf, without symphysial notch (Fig. 3A, C–F, H; Table 3). There is one complete tooth row at the symphysis, and a few small teeth in a second row. The profile of the dentary is low, and the ventral bulge near the symphysis is almost not expressed. The ventral keel is narrow, as is especially clearly visible in the symphysial area.

The toothed surface on the palatine is short and not concave, extending under the maxillary process. The dorsal surface of the bone is curved. There are four or five rows of small tooth bases on the ventral side of the palatine (Fig. 3B, G). Widths of bones from the Obukhovka 2 are 3.1 and 4.2 mm, and from Kotlovina 2 4.7 mm.

Table 3. Measurements (in mm) of dentaries of Esox moldavicus Sytchevskaya, 1974. N, number of specimens.

Locality	N	Height of dentary symphysis		Width of the dentary near the symphysis		Width of tooth row
		range	mean	range	mean	range	mean
Kotlovina 3	2	2.4; 2.7	–	2.3; 2.5	–	0.9; 2.1	–
Kotlovina 2	1	–	2.2	–	2.6	–	0.9
Cherevichne 2	2	1.4; 2.5	–	0.9; 2.4	–	0.7; 2.0	–
Kryzhanovka	1	–	5.0	–	4.3	–	2.0
Kamenskoe	3	2.5–4.3	3.4	1.7–3.2	2.5	0.9–2.0	1.4
Obukhovka 1	1	–	–	–	–	–	2.7

Remarks.—Described bones are comparable in morphology to those of Esox moldavicus. This species resembles Esox sibiricus in the structure of the dentigerous surface of the palatine, but differs in the predominance of the one-row dentition at the dentary symphysis. The orientation of the maxillary process on the palatine and the low dentary are similar to those in Esox lucius, but differ from features of E. reichertii (Sytchevskaya, 1976).

Stratigraphic and geographic range.—Early Pliocene–early Pleistocene of southeastern Europe.

Esox nogaicus sp. nov.

Fig. 4.

Etymology: Derived from the name of the type locality.

Type material: Holotype: NMNHU-P 27/1697, almost complete right dentary (Fig. 4A). Paratypes: NMNHU-P 27/1001, right dentary, NMNHU-P 27/998, left dentary.

Type locality: Nogaisk, Zaporozhye region, Ukraine (Fig. 1).

Type horizon: Calabrian (early Pleistocene).

Material.—NMNHU-P 27/1088–1092, vomers; NMNHU-P 27/1124–1128, frontals; NMNHU-P 27/1129, parietal; NMNHU-P 27/1047–1054, parasphenoids; NMNHU-P 27/1036–1046, maxillae; NMNHU-P 27/1102–1106, 1108, 1110–1115, 1117–1121, palatines; NMNHU-P 27/1012–1021, 1040, quadrates; NMNHU-P 27/1022–1033, 1038, articular bones; NMNHU-P 27/992–995, 997, 1000, 1006, 1007, left dentaries; NMNHU-P 27/1004, 1005, 1008, 1009, 1463, right dentaries; NMNHU-P 27/1093–1096, 1099, hyomandibulars; NMNHU-P 27/1056–1069, ceratohyals; NMNHU-P 27/986–989, 1097, opercular bones; NMNHU-P 27/1035, 1071–1076, 1614, cleithra. All material from the type locality and horizon.

Diagnosis.—Esox nogaicus sp. nov. differs from other esocids in the following combination of characters: (i) massive dentary with wide dental shelf and high symphysis; (ii) well-developed antero-ventral crest on frontal; (iii) large angle between horizontal crest and preopercular process of opercle and wide foramen on hyomandibula; (iv) low anguloarticular with wide retroarticular process; (v) long and flat dentigerous surface on palatine; (vi) wide articular crest on cleithrum.

Description.—The dentary (Fig. 4A) is massive, with a well-developed wide dental shelf, a deep symphysis, and uniserial dentition. The anterior (toothed) edge of the dentary is straight and thickened near the symphysis. The oral margin is relatively high. C-shaped tooth bases occupy the anterior two-thirds of the tooth row, with bases of fixed teeth and large replacement pits in the posterior third. A shallow lateral groove divides the anterior edge of the dentary and forms a ventral bulge in the symphysis. On the lateral surface, four pores for the mandibular sensory canal (Nelson 1972) are clearly visible near the ventral edge while, near the tooth row, the trigeminal foramen opens toward the posterior (see Wilson et al. 1992). Measurements of dentaries of the new species are as follows: height of dentary symphysis, 6.6–9.1 mm; width of the dentary near the symphysis, 3.9–5.0 mm; width of tooth row, 4.2–4.5 mm.

The posterior part of the medial suture edge of the frontal (Fig. 4B) is slightly thickened, with a wide sphenotic ledge, a clearly expressed antero-ventral crest, and a narrow side branch of the supraorbital canal. The dorsal surface of the bone is sculptured by radial smooth plates.

The parietal (Fig. 4C) is massive, with a wide postero-­lateral process and a well-developed ventral crest.

The front edge of the vomer (Fig. 4D) is smooth. The anterior premaxillary process of the vomer forms an angle of 115° with the longitudinal axis of the bone. The elongate dental field on the shaft of the vomer is relatively wide (WDF 5.1–6.8 mm) and has numerous very small C-shaped tooth bases. The dental field tapers anteriorly, and connects at a small neck to the triangular anterior dental field on the vomerine head (WCV 11.1–14.3 mm). There are several larger, medial C-shaped tooth bases (DDC 2.3–2.4 mm) on the vomerine head, their sizes increase laterally. A single pair of even larger replacement pits suggests the presence of fixed teeth (Fig. 4D). Similar replacement pits can be seen in several other vomers of E. nogaicus sp. nov.

Both anterior and posterior parts of the parasphenoid (Fig. 4E) are long: WPSa 7.3–9.5 mm, WPSp 6.9–8.6 mm. The narrow anterior median crest passes without a neck into the posteriorly extended dorsal medial crest. Carotid grooves are clearly expressed and deepened anteromedially. The angle between the postcarotid crests is about 110–120°.

The upper edge of the hyomandibula (Fig. 4F1, F2) and the horizontal crest on the medial surface are almost parallel. The angle between the horizontal crest and the preopercular process is about 120°. There is a deep notch between the wall and the upper edge of the preopercular process.

The maxilla (Fig. 4G) is highly elongated (LM 50.3–61.5 mm), with wider posterior and narrower anterior parts. The short medial process has a rounded tip.

The articular (Fig. 4H) is characterized by a low wall (the anguloarticular angle is 40–45°), an uvular notch of the articular facet (LAF 4.9–5.6 mm), and a wide and elevated retroarticular process. There is an elongated keel at the posteroventral edge of the bone.

The palatine (Fig. 4I) has a large maxillary process with a wide fossa articularis and a small notch beside it. The dentigerous surface is long and flat. There are C-shaped bases from six rows of small, depressible teeth on the ventral surface, the largest bases located anteriorly in the medial row. The width of the bone is in the range 5.7–7.2 mm, DFA 3.2–4.8 mm.

The opercular (Fig. 4J) is flat and almost rectangular, with smooth edges. The articular facet is lenticular.

The massive barbell-shaped ceratohyals (Fig. 4K) are mostly represented by their medial parts with broken ends; they have weekly expressed branchiostegal pits and a wide main shaft.

The quadrate (Fig. 4L) is more or less triangular. The articular condyle is doubled, with medial and lateral lobes, and forms an oblique articulation with the articular bone. In lateral view, the angle between the articular condyle and the body of the quadrate is about 80°. The notch of the anterior edge just above the condyle is narrow and elongated.

The cleithrum (Fig. 4M) is massive and characterized by a wide and well-developed, medially bending articular crest. The width of the main plate is 10.2–12.1 mm.

Remarks.—Esox nogaicus sp. nov. is similar to E. lucius in the uniserial dentition of the dentary, the well-developed anteroventral crest of the frontal, and in the structure of parietal, vomer, parasphenoid and opercular, but differs in its wider dental shelf and higher dentary symphysis, as well as its lower anguloarticular angle, flat dentigerous surface on palatine, and wider articular crest of the cleithrum. Esox moldavicus is close to E. nogaicus sp. nov. in the structure of the dentary, but it differs in its weakly visible carotid grooves on parasphenoid, higher anguloarticular angle, and short toothed surface on the palatine. As compared to those in E. nogaicus sp. nov. the dentaries of Esox sibiricus and E. reichertii are characterized by a small and weakly developed dental shelf, two-row dentition, a larger anguloarticular, a relatively short dentigerous surface on the palatine, and a wider articular crest on the quadrate; on the other hand, these species resemble E. nogaicus sp. nov. in the structure of the frontal and parasphenoid.

Stratigraphic and geographic range.—Type locality and horizon only.

Fig. 4. Isolated elements assigned to a pike Esox nogaicus sp. nov. from Southeastern Europe, Nogaisk; Pleistocene. A. Holotype, right dentary (NMNHU-P 27/1697), occlusal (A1) and lateral (A1) views. B. Left frontal (NMNHU-P 27/1124), lateral view. C. Left parietal (NMNHU-P 27/1129), dorsal view. D. Vomer (NMNHU-P 27/1088), ventral view. E. Parasphenoid (NMNHU-P 27/1047), ventral (E1) and dorsal (E2) views. F. Left hyomandibular (NMNHU-P 27/1093), lateral (F1) and medial (F2) views. G. Left maxilla (NMNHU-P 27/1036), lateral view. H. Right articular (NMNHU-P 27/1024), medial view. I. Right palatine (NMNHU-P 27/1115), ventral (I1), lateral (I2), and dorsal (I3) views. J. Right opercular (NMNHU-P 27/986), medial view. K. Left ceratohyal (NMNHU-P 27/1059), medial view. L. Right quadrate (NMNHU-P 27/1012), medial view. M. Left cleithrum (NMNHU-P 27/1035), medial view. A2, G, H, I1, I2, M, anterior to right; A1, B, I3, J, L, anterior to left; C–F, K, anterior towards top. Scale bars 5 mm.

Esox lucius Linnaeus, 1758

Fig. 5.

Material.—Early Pleistocene: one left cleithrum (NMNHU-P 53/4249, Nova Etuliya); one fragment of cleithrum (NMNHU-P 53/4250, Sinyaya Balka). Middle Pleistocene: one left palatine and two left dentaries (NMNHU-P 53/4253, Semibalka 1); one parasphenoid, two right palatines, two left and six right dentaries (NMNHU-P 53/4254–4264, Medzhibozh).

Emended diagnosis.—Esox lucius is characterized by a number of features distinguishing it from other species: (i) only uniserial dentition of dentary; (ii) narrow dental shelf; (iii) presence of symphysial notch; (iv) clearly expressed and anteromedially deepened carotid grooves on parasphenoid; (v) rounded articular facet on palatine; (vi) weakly expressed dorsal crest on cleithrum.

Description.—The posterior part of the parasphenoid and the dorsal medial crest are extended caudally (Fig. 5G). The broad anterior medial crest is well developed. There is a dorsally directed process at the base of the posterior crest. The bone is wide (6.0 mm in the medial part and 7.8 mm in the posterior part). Two shallow longitudinal grooves are expressed in the medial part of the ventral side of the bone. There is a large angle between the postcarotid crests.

The dentaries (Fig. 5E, F) are low, with a uniserial dentition of depressible teeth near the symphysis and a narrow dental shelf. Width of the dentary near the symphysis of these bones from Medzhibozh is 1.2–2.9 mm (M 1.5 mm); height of dentary symphysis, 1.9–5.2 mm (M 3.1 mm); and width of tooth row, 1.0–3.1 mm (M 1.9 mm). Dentaries from Semibalka 1 are comparable in size: width of the dentary near the symphysis, 2.2 and 3.0 mm; height of dentary symphysis, 3.8 and 5.6 mm; width of tooth row, 1.6 and 2.0 mm.

The palatine has a rounded fossa articularis and an uvular articular process (Fig. 5B, C). The dentigerous surface is relatively long and concave. There are C-shaped bases from five rows of small depressible teeth on the ventral surface of the bone (the largest of them located in the medial row). The width of the palatine from Semibalka 1 is 7.0 mm, with DFA 3.5 mm.

Cleithra are represented by their caudal parts (Fig. 5A, D). The thickened dorsal crest is weakly expressed. The width of the plate is 6.2 mm for those from Nova Etuliya and 7.2 mm for the cleithrum from Sinyaya Balka.

Remarks.—All described bones are indistinguishable in morphology and size from those of Esox lucius.

Stratigraphic and geographic range.—Early Pleistocene–Recent, Eurasia and North America.

Esox spp.

Fig. 6.

Material.—Late Miocene: thirty teeth (NMNHU-P 29/ 1681–1710, Popovo 3); eleven teeth (NMNHU-P 33/554–564, Mykhailivka 2); one dentary fragment, two teeth (NMNHU-P 41/3015–3017, Frunzovka 2); two teeth (NMNHU-P 41/3472, 3473, Palievo); one palatine fragment and three teeth (NMNHU-P 29/3966–3969, Lobkovo); eight teeth (NMNHU-P 45/5691–5698, Cherevichne 3); one tooth (NMNHU-P 29/3970, Vasylivka 1); two teeth (NMNHU-P 29/1467, 1468, Vasylivka 3); seventy teeth (NMNHU-P 29/1037–1106, Verkhnya Krynitsya 2); twenty-seven teeth (NMNHU-P 41/4498–4524, Egorovka 2); five teeth (NMNHU-P 41/4327–4331, Egorovka 1); one dentary fragment and twenty-four teeth (NMNHU-P 38/1964–1988, Novoukrainka 1); eight teeth, one palatine (NMNHU-P 33/514–522, Andreevka); three teeth (NMNHU-P 41/2848–2850, Orekhovka); ten teeth (NMNHU-P 41/2465–2474, Pontian Lectostratotype); twenty-three teeth (NMNHU-P 41/2742–2764, Vinogradovka 1). Early Pliocene: two teeth (NMNHU-P 37/2555, 2556, Novopetrovka); fourteen teeth (NMNHU-P 53/4265–4278, Obukhovka 1); one tooth (NMNHU-P 42/2458, Vinogradovka 2); five teeth (NMNHU-P 42/2459–2463, Kotlovina 1). Late Pliocene: fifty-nine teeth (NMNHU-P 53/4279–4338, Obukhovka 2); six teeth (NMNHU-P 53/4342–4347, Zhevakhova Gora); one left dentary and four teeth (NMNHU-P 45/6020–6024, Cherevichne 2); fourteen teeth (NMNHU-P 29/626–639, Verkhnya Krynitsya 1). Early Pleistocene: nine teeth (NMNHU-P 42/2463–2471, Kotlovina 2); forty-seven teeth (NMNHU-P 42/2472–2518, Kotlovina 3); twenty teeth (NMNHU-P 1584–1603, Popovo 2); two teeth (NMNHU-P 29/1533, 1534, Popovo 1); two teeth (NMNHU-P 29/1472, 1473, Popovo 0); one left dentary fragment and eight teeth (NMNHU-P 53/4348–4356, Tiligul); three teeth (NMNHU-P 53/4357–4359, Nova Etuliya); thirteen teeth (NMNHU-P 53/4360–4372, Sinyaya Balka); fourteen teeth (NMNHU-P 53/4373–4386, Kairy); eight teeth (NMNHU-P 45/6025–6032, Cherevichne 1). Middle Pleistocene: ten teeth (NMNHU-P 42/2519–2528, Protopopovka 2); six teeth (NMNHU-P 53/4388–4393, Semibalka 1); five teeth (NMNHU-P 29/380–384, Lysa Gora 1); one palatine fragment and six teeth (NMNHU-P 53/4394–4400, Bol’she­vik 2); one hundred and five teeth (NMNHU-P 53/4401–4505, Medzhibozh).

Description.—Palatines from Lobkovo and Bol’shevik 2 are represented by small fragments; their width is 2.4 mm and 5.8 mm, respectively. The toothed surface on the palatine (Fig. 6H) is very long and slightly concave, extending under the maxillary process. The dorsal surface of the bone is somewhat curved. The diameter of the tooth crowns on the palatines averages 0.6 mm.

It is not possible to measure some dentaries because they are fragmentary. WTR of the more complete dentaries varies from 2.1 mm (Frunzovka 2) to 3.1 mm (Novoukrainka 1); the WTR for the dentary from Tiligul (2.2 mm) is close to the smaller one.

Elongate, dagger-shaped jaw teeth (Fig. 6A–G, I–T) are laterally compressed, with slightly curved crowns and rounded bases. Tips of the teeth are sharp and cutting edges are slightly narrowed. Measurements of isolated jaw teeth of pikes are presented in Table 4.

Remarks.—These jaw teeth and other bones undoubtedly belong to the genus Esox. Their species attribution is uncertain because of the bones are significant fragmented and the teeth are not diagnostic to species.

Table 4. Measurements (in mm) of jaw teeth of pikes (Esox sp.) from the Mio-Pleistocene of southeastern Europe. N, number of specimens.

Locality	n	Tooth length		Tooth width		Tooth		Tooth width / depth
		range	mean	range	mean	range	mean
Medzhibozh	105	3.2–10.9	7.6	1.5–4.4	2.7	0.9–3.1	1.9	1.4
Bol’shevik 2	6	4.8–11.0	7.3	1.9–3.9	2.9	1.2–3.0	1.9	1.5
Lysa Gora 1	5	4.2–11.1	6.3	1.7–4.3	2.4	1.0–3.3	1.6	1.5
Semibalka 1	6	5.9–12.3	7.5	1.8–3.7	2.7	1.3–2.7	2.1	1.3
Protopopovka 2	10	4.7–8.4	6.1	1.7–2.7	2.3	0.9–2.0	1.4	1.6
Cherevichne 1	8	4.1–7.5	6.2	1.8–3.4	2.6	1.1–1.9	1.6	1.6
Kairy	14	3.1–7.2	5.9	1.4–2.8	2.2	0.8–2.1	1.5	1.5
Sinyaya Balka	13	4.6–8.4	6.9	1.9–3.4	2.6	1.2–2.2	1.7	1.5
Nova Etuliya	3	6.7–7.5	7.1	2.1–3.3	2.6	1.3–1.8	1.6	1.6
Tiligul	8	4.4–7.1	5.8	1.5–2.9	2.2	1.0–2.1	1.6	1.4
Popovo 0	2	5.3; 5.5	–	2.1; 2.5	–	1.2; 1.8	–	1.5
Popovo 1	2	4.3; 5.9	–	1.6; 2.3	–	1.1; 1.6	–	1.4
Popovo 2	20	4.7–10.8	6.9	1.8–4.1	2.5	1.2–2.9	1.8	1.4
Kotlovina 3	47	4.9–12.6	7.9	1.9–4.1	2.9	1.3–3.3	2.1	1.4
Kotlovina 2	9	4.0–8.2	6.2	1.8–3.0	2.4	0.9–2.1	1.6	1.5
Verkhnya Krynitsya 1	14	4.0–8.8	5.9	1.6–3.4	2.2	1.1–2.7	1.6	1.4
Cherevichne 2	4	4.7–8.1	7.0	1.6–2.8	2.4	1.2–1.8	1.6	1.5
Zhevakhova Gora	6	3.5–8.8	5.3	1.3–2.5	1.9	0.7–2.3	1.4	1.4
Obukhovka 2	59	4.0–12.2	7.2	1.7–4.6	2.8	1.0–3.0	1.7	1.6
Kotlovina 1	5	2.8–6.0	4.5	1.4–1.9	1.7	0.8–1.3	1.1	1.5
Vinogradovka 2	1	–	11.4	–	4.5	–	3.2	1.4
Obukhovka 1	14	4.4–11.6	6.2	2.1–4.0	2.3	1.1–3.2	1.6	1.4
Novopetrovka	2	6.2; 7.9	–	2.2; 3.4	–	1.6; 2.2	–	1.5
Vinogradovka 1	23	3.3–9.4	6.0	1.4–3.5	2.2	0.9–2.6	1.7	1.3
Pontian Lectostratotype	10	3.4–8.8	5.7	1.4–3.5	2.3	1.0–2.4	1.6	1.4
Orekhovka	3	3.1–4.2	3.7	1.5–2.1	1.8	0.9–1.2	1.1	1.6
Andreevka	9	5.2–8.3	7.3	2.0–3.6	3.0	1.2–2.3	1.9	1.6
Novoukrainka 1	24	4.6–8.9	6.6	1.7–3.1	2.4	1.1–2.4	1.6	1.5
Egorovka 1	5	3.5–5.2	4.3	1.6–2.0	1.8	1.3–1.5	1.4	1.3
Egorovka 2	27	2.7–7.2	4.6	1.1–2.2	1.6	0.8–1.5	1.1	1.5
Verkhnya Krynitsya 2	70	5.2–9.0	7.3	1.8–3.2	2.7	1.2–2.4	2.0	1.4
Vasylivka 1	1	–	6.6	–	2.1	–	1.5	1.4
Vasylivka 3	2	6.8; 7.6	–	2.3; 2.6	–	1.8; 2.1	–	1.3
Cherevichne 3	8	3.1–6.3	4.8	1.5–2.3	1.9	0.9–1.7	1.2	1.6
Lobkovo	3	5.0–6.6	5.5	1.9–2.6	2.3	1.1–1.5	1.3	1.8
Palievo	2	3.6; 5.6	–	1.6; 1.9	–	1.3; 1.3	–	1.5
Frunzovka 2	2	3.3; 4.7	–	1.3; 1.6	–	0.8; 1.0	–	1.6
Mykhailivka 2	11	3.5–6.7	5.2	1.4–2.1	1.9	1.1–1.6	1.3	1.5
Popovo 3	30	3.7–10.2	7.0	2.2–3.2	2.7	1.5–2.7	1.9	1.4

Concluding remarks

Pikes were an important element in freshwater fish complexes of southeastern Europe during the late Neogene and Anthropogene. At least three developmental stages for these assemblages (in respect to the presence of certain Esox species) can be defined: (i) late Miocene to earliest Pliocene; (ii) early Pliocene to earliest Pleistocene; (ii) early–middle Pleistocene to present.

The first stage is characterized by the wide geographic distribution of E. sibiricus. Such a situation, as in the case of Leobergia (see Kovalchuk and Murray 2016) and some other freshwater fishes (e.g., catfishes; see Kovalchuk and Ferraris 2016), may be related to the Miocene climatic optimum (Böhme et al. 2008). It can be also explained by a prochoresis of esocids from North America to Asia and Europe, with their subsequent incorporation into local fish complexes.

In the second stage, the later appearance of E. moldavicus and the extinction of E. sibiricus (as well as other thermophilic species) could have been caused by geographical vicariance and is interpreted here as a response to gradual global climate cooling during the Pliocene and early Pleistocene. The landscape was undergoing major changes associated with the collision of the Afro-Arabian and Eurasian plates causing changes to ocean circulations with the closing of the Tethys, as well as uplift of mountain ranges in Europe (Ivanov et al. 2011). This was also a period of significant climate change with the onset of polar glaciation causing a cooling and drying phase (see Syabryaj et al. 2007; Kovalchuk and Murray 2016 for more details).

Subsequent changes in freshwater fish complexes of south­eastern Europe also occurred against the background of significant cooling, which favoured cold-adapted fishes, such as E. nogaicus sp. nov. and, finally, E. lucius. Similar climatic events have been hypothesized to explain changing geographic and stratigraphic ranges of Cretaceous, Paleogene, and Neogene esocids in North America (Newbrey et al. 2008).

Esox nogaicus sp. nov. presents a distinctive morphology including a stout dentary with deep symphysis and the possible presence of a pair of fixed canine-like teeth near the anterior end of the vomer. Fixed “canine” teeth on the vomer are seen also in certain species known only from North America: the extant Esox masquinongy, the related Pliocene fossil species E. columbianus Smith, Morgan, and Gustafson, 2000, and an unnamed Miocene form (Cavender et al. 1970). However, the North American species have fixed “canine-like” teeth also anteriomedially on the palatines, unlike E. nogaicus sp. nov. which lacks fixed teeth on its palatines.

The Miocene, Pliocene, and Pleistocene pikes from southeastern Europe, taken together, document a greater diversity of morphologies in the past than exists today in the pike species of Europe, and record a series of changes in the predominant esocid species during the Neogene in that region that we hypothesize were driven by climatic change.

Acknowledgements

The authors express sincere thanks to Eugenia K. Sytchevskaya (Boris­siak Paleontological Institute, Moscow, Russian Federation) for inspiring discussion on the taxonomy and systematics of pikes from the Miocene and Pliocene of Eastern Europe. We are indebted to Leonid I. Rekovets (Wrocław University of Environmental and Life Sciences, Poland), Valentin A. Nesin (National Museum of the Natural History NAS, Kyiv, Ukraine) and Maxim V. Sinitsa (Ural Federal University, Yekaterinburg, Russian Federation) for collecting fish fossils in localities of Ukraine and for bringing them to our attention. The authors thank all curators for allowing access to osteological collections. We are very grateful to Gerald R. Smith (University of Michigan, Museum of Palaeontology, Ann Arbor, USA) for his useful comments and advice. This research was supported in part by NSERC (Canada) Discovery Grant A9180 to MVHW and by NSF (USA) grant DEB-0732589 to TG.

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Appendix 1

Comparative material derived from the Field Museum of Natural History (FMNH), Loyola University Chicago Fish Collection (LUC-F), Cornell University Museum of Vertebrates (CU), and NMNHU-P. Specimens are either dried bones and skeletons or cleared and stained (c&s) for bone or for both bone and cartilage. Each number represents an individual specimen.

Esox lucius: FMNH 32734, 9760, 51360, 9964 (dried skeletons); NMNHU-P 1/127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 217 (dried skeletons); NMNHU-P 1/138, 1/163 (c&s).

Esox masquinongy: FMNH 72177 (dried skeleton); CU9118 (c&s).

Esox reichertii: CU 64227, 64228, 64229, 64231 (alcohol and c&s); FMNH 109221.

Esox niger: FMNH 21811 (c&s); LUF 082291-082293 (c&s).

Esox americanus: FMNH 31768 (c&s).

Esox americanus americanus: FMNH 10424 (c&s).

Esox americanus vermiculatus: FMNH 7187 (c&s).

Acta Palaeontol. Pol. 62 (1): 121–135, 2017

https://doi.org/10.4202/app.00311.2016