Allactaga fru, Nesin & Kovalchuk, 2017
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publication ID |
https://doi.org/ 10.26879/751 |
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publication LSID |
lsid:zoobank.org:pub:6A340E9B-DBCB-47D7-B84C-993407C24C32 |
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persistent identifier |
https://treatment.plazi.org/id/FDDE9966-58BC-4439-98C0-791673AF62E6 |
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taxon LSID |
lsid:zoobank.org:act:FDDE9966-58BC-4439-98C0-791673AF62E6 |
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treatment provided by |
Felipe |
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scientific name |
Allactaga fru |
| status |
sp. nov. |
Allactaga fru sp. nov.
Figure 3.1 View FIGURE 3 -21
zoobank.org/ FDDE9966-58BC-4439-98C0-791673AF62E6
1979 Paralactaga complicidens sp. n (nomen nudum); Topachevsky and Skorik, p. 15.
1998 Paralactaga complicidens ; Topachevsky, Nesin, Topachevsky, p. 83, tab. 3.
2001 Paralactaga complicidens ; Nesin and Nadachowski, p. 124, tab. 3.
2013 Allactaga View in CoL (= Paralactaga ) aff. varians ( Savinov, 1970) ; Nesin, p. 20, 153.
Topachevsky and Skorik (1979) provided a systematic review of late Miocene and early Pliocene rodents of the northern Black Sea region.
They proposed new names for two species of the genus Paralactaga , one of which ( P. complicidens )
was mentioned as occurring in the locality Frunzovka 2. However, no type material was allocated and neither description nor figures were presented by Topachevsky and Skorik (1979). Later, this name was repeatedly used (e.g., Topachevsky et al., 1998; Nesin and Nadachowski, 2001) without any substantiation. We therefore consider P. complicidens as a nomen nudum. The material from Frunzovka 2 was reclassified into the genus Allactaga by Nesin (2013) and considered as belonging to a species closely related to A. varians . Here we assign the material from Frunzovka 2 to Allactaga fru sp. nov.
Etymology. The name refers to the initial letters of the type locality name.
Holotype. NMNHU-P 41/5549, left M1 ( Figure 3.1 View FIGURE 3 ). Department of Palaeontology, National Museum of Natural History, National Academy of Sciences of Ukraine, Kyiv.
Additional material. One P4 ( NMNHU-P 41/ 5548), ten M1 ( NMNHU-P 41/5550-5559), seven M2 ( NMNHU-P 41/5560-5566); ten m1 ( NMNHU-P 41/5567-5576), six m2 ( NMNHU-P 41/ 5577-5582), five m3 ( NMNHU-P 41/5583-5587).
Type locality. Frunzovka 2, Odesa region, southern Ukraine ( Figure 1 View FIGURE 1 ).
Geological age. Late Miocene, early Turolian, MN 11, ca. 8.7 Ma.
Measurements. Length × width: (holotype NMNHU-P 41/5549) M 1 – 2.35 mm × 1.70 mm. For other teeth – see Table 1 View TABLE 1 .
Diagnosis. A small-sized Allactaga which differs from other extinct and extant species of this genus in the following unique combination of characters: (1) the anterior part of the M1 crown is wider than the main portion of the tooth due to the strong development of anterostyle, anteroloph, and anterocone; (2) the labial arm of the posteroloph is well developed; (3) strongly developed paracone connected with mesocone and mesostyle; (4) metaconid of m1 is isolated on the unworn teeth; (5) entoconid and mesostylid are also separated; (6) the presence of one major anterior cusp on P4, completely isolated from the posterior ridge (which is arc-shaped).
Differential diagnosis. Allactaga fru sp. nov. differs from:
• A. irgizensis Zazhigin and Lopatin, 2000b by (1) strongly developed anterostyle; (2) winding (S-shaped) configuration of the medial ridge; (3) less flattened lingual tubercles of M1 and more shifted outward labial cusps; (4) earlier (in most cases) junction of the metaconid with protoconid through wear as well as a connected hypoconid and ectostylid on m1; (5) the ridges in the middle part of the m1 do not display a cruciform shape; (6) more developed ectomesolophid of the m1; (7) ectostylid and hypoconid are strongly displaced labially from the longitudinal axis of the tooth, so the posterior part of the crown is much broader than the anterior one;
• A. minor ( Zheng, 1982) by (1) more developed anterocone, anteroloph, and anterostyle, metaconule and labial posteroloph on M1 and M2; (2) developed ectostylid on m1 but not on m2;
• A. anderssoni ( Young, 1927) by (1) smaller size (see Table 1 View TABLE 1 ); (2) close contact of paracone and endoloph on M1 and M2; (3) closer location of paracone and anterior endoloph; (4) more developed anteroloph and anterostyle on M1;
• A. varians ( Savinov, 1970) by (1) significantly smaller size (see Table 1 View TABLE 1 ); (2) less expressed lophiodonty; (3) less developed lingual semihypsodonty; (4) mesodont teeth with lower crowns; (5) bigger and completely isolated anterior cusp on P4; (6) more developed anterostyle and anteroloph on M1; (7) wider anterior part of M1;
• A. suni ( Teilhard and Young, 1931) by (1) significantly smaller size (see Table 1 View TABLE 1 ); (2) close contact of paracone with other elements of tooth crown; (3) the presence of anteroconid on m1; (4) less developed anterocone but more developed anteroloph and anterostyle on M1.
Description
P4 ( Figure 3.21 View FIGURE 3 ) is rounded, with well-developed anterior cusps, covering approximately a third of the occlusal tooth surface. The posterior ridge is lower, bordering posterior and lingual edges of the crown. The labial valley is very narrow.
M1 and M2 ( Figure 3.1 View FIGURE 3 -8) are similar both in size and morphology. M1 differs from M 2 in the following characters: extended anterior part of the crown; narrow facet formed by the contact with P4; more developed anterostyle, anteroloph, and anterocone forming an arcuate crest, framing the anterior edge of the tooth crown. The anterocone on these teeth is well defined and bigger than the anterostyle. The anteroloph is very short and narrow. The protocone on slightly worn teeth is separated from the posterior part of the tooth; it joins the posterior arm of the endoloph when the crown is worn. The paracone is connected with the mesocone; the latter is often weakly expressed. The hypocone is large and connected in its anterior part with the mesocone via the long posterior arm of the endoloph. On slightly worn teeth, the hypocone is separated posteriorly from the joined metacone and metaconule. On worn teeth, the hypocone is connected with the two latter cusps by its short posterior arm. The metacone is also large, compressed longitudinally, and connected with a small metaconule by a short metaloph. The pointed apex of the metaconule is always directed labially, the longitudinal ridge is weakly expressed on slightly worn teeth. This ridge is clearly visible on the strongly worn M1-M 2 specimens, and forms a wide arc, whose convex apex is directed anterolabially. The hypoflexus is wide, its apex pointing forward. Para- and metaflexuses are also wide; however, they curl posteriorly. The mesoflexus, and especially the posteroflexus, are narrower and shorter; they are arranged perpendicular to the longitudinal axis of the tooth.
In m1 ( Figure 3.9 View FIGURE 3 -14), the anterior lobe is narrower than the posterior one due to its smaller size and more closely spaced adjacent cusps. Major and minor folds are well developed and identified at all stages of the tooth wear. Lophiodonty is moderately developed. The anteroconid is reduced in most cases, but sometimes is present in the form of a very small cusp on the anterior edge of the crown. The protoconid is connected to the weakly expressed mesoconid or to the short endolophid. Sometimes (in 10 % of the teeth), the metaconid is in contact with the posterior part of the protoconid. The metaconid is usually connected with the mesolophid or mesostylid. The anterior arm of the entoconid is in contact with the mesoconid. On strongly worn crowns, all of these elements form a distinctive, five-petal corolla, connecting with the hypoconid through its anterior arm. The hypoconid is the largest among all cusps of this tooth; it is directly associated anteriorly with the ectostylid and posteriorly with the bucco-labially flattened hypoconulid. The postero-anterior ridge on m1 is traced only with the strongly worn teeth.
The m2 ( Figure 3.15 View FIGURE 3 -17) is quite easily identified and differs from the m1 by its subsquare outline in occlusal view, the lack of an ectostylid, and the moderate development of the labial and lingual anterolophid arms. The main cusps have approximately the same size and are arranged symmetrically on the crown. On slightly worn teeth, the anteroconulid is connected with the metaconid and anterolophid. The latter disappears on strongly worn teeth, and the anteroconulid flattens anteroposteriorly. The protoconid adjoins anteriorly the anteroconulid and posteriorly the entoconid and the mesolophid, even on slightly worn teeth. An enamel island can form in the place of such connection as the tooth gets worn. The hypoconid is connected anteriorly with the entoconid, and posteriorly with the hypoconulid; the latter adjoins the longitudinally flattened posterolophid, whose pointed apex is directed anterolabially.
The m3 ( Figure 3.18 View FIGURE 3 -20) is very small, with a triangular outline of the crown. Lingual and labial basic conids are well developed, similar in size, and individualized at all stages of the tooth wear. The lingual anterolophid is absent; the labial anterolophid is well-developed and in contact with the metaconid. This part is separated from the posterior part of the crown on unworn teeth. On the worn teeth, the anteroconulid is connected with the protoconid. The posterior fossetid forms an enamel island that quickly disappears as wear increases. At the same time, the lingual fossetid closes on the lingual edge of the crown forming a big anterior enamel island, which persists until advanced tooth wear.
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