First true mastodon from the Late Miocene of Western Asia

A mammutid is described here for the first time from the Late Miocene (MN12 equivalent) deposits of Abkhareh village, Varzeghan region in the northwestern part of Iran. It is identified as “Mammut” cf. obliquelophus and is represented by an isolated and moderately worn upper third molar with zygodont crown pattern as typical of mammutids. In addition, two upper incisors found associated with the molar and probably belonging to the same individual are assigned as Mammut. The studied material expands the geographic distribution of “Mammut” obliquelophus into western Asia.

The village Abkhareh, located 12 km to the west of Varzeghan town, about 150 km north to the well-known late Miocene fossiliferous areas of Maragheh, yielded a relatively large number of fossil proboscideans (Deinotherium Kaup, 1829; Mammut Blumenbach, 1799) and Hipparions (Hipparion de Christol, 1832). These fossils were excavated more than a decade ago during a renovation of the historical building ՛՛Amir-Arshad Khaneh Bagh՛՛ in Abkhareh village (Fig. 1).

According to Mirzaie Ataabadi et al. (2011b), Deinotheriid is represented in Varzeghan area by cranial and postcranial elements including some Upper molars (right M¹, MMTT-V16; M², MMTT-V11 and M³, MMTT-V14 and left M1, MMTT-V12; M², MMTT-V15 and M³, MMTT-V13), all belong to a single and huge individual attributed to Deinotherium giganteum Kaup, 1829 (Mirzaie Ataabadi et al., 2011b), which later, in more recent researches, was accepted as Deinotherium proavum Eichwald, 1835 (Pickford & Pourabrishami, 2013). Although before, the materials from Abkhareh, Varzeghan were partly studied and identified as Deinotherium gigantissimum Ştefǎnescu 1892 by Pourabrishami 2004, which following more recent studies (Codrea, 1994; Böhme et al., 2012; Pickford & Pourabrishami, 2013) has been shown not to be a valid species, but synonymized by Deinotherium proavum Eichwald 1835.

The fossils occurred on the surface and there was not sediment exposure. So, the nature of the fossil-bearing sequence and especially its sedimentology and depositional environment is not well understood. The fossil site of dinotheres material is a local concentration of bones within a mudstone bed and is restricted to a single horizon (Mirzaie Ataabadi et al., 2011b). The present article only describes the mammutid remains not the entire proboscinean material of the fauna from this locality.

Volcanic activities were major Palaeogene phenomena in East Azerbaijan province in the northwest of Iran. At the end of the early Miocene, lifting of the Iranian land mass resulted in a retreat of the Tethys and as a consequence in the termination of the carbonate depositio and vanishing of the last Tethyan seaway (Aghanabati, 2004). In the Neogene, this domain was therefore above the sea level and was covered by early mountain ranges, basin troughs, and had topography similar to the present conditions (Davoudzadeh et al., 1997). The area located north of Tabriz city underwent major orogenic phases during the Late Miocene-Pliocene. These activities established new erosional cycles, filling the locally close intermontane basins with fluvial and lacustrine deposits (Aghanabati, 2004). The fossil deposits of the Varzeghan area were formed in such local basins. They are environmentally different from the Maragheh Formation, by not being directly influenced by volcanic activities.

The fossiliferous layer in this area was part of fluvial cycles, because channel deposits were present in close proximity of the fossil locality. Similar to other late Miocene mammal fossiliferous localities in Iran, the fossils are, however, preserved in the fine-grained soil horizons possibly belonging to an over bank deposit (Mirzaie Ataabadi et al., 2011a and b; Sakai et al., 2016). The late Miocene sequence in the study area is covered by recent alluvials, and there were no exposures to be studied in detail. Unfortunately, the tiny exposure of sediment near the fossil site, which was checked before, has been covered by new buildings and is no longer available for further studies.

In this study, an isolated upper third cheek tooth, PRCI, V001, previously coded as Varzeghan [MMTT11] and two upper tusks (Varzeghan [MMTT1 a, b]) stored in the Maragheh Vertebrate Paleontology Research Center were investigated. The dentition nomenclature of the occlusal structures of mammutid cheek teeth follows Tobien (1975 and 1996). Göhlich (1998) was followed for measurement purposes. All the measurements are in millimeters.

I², Upper second incisors (Upper tusk in Proboscideans)

MMTT, Muze Melli Tarikh Tabeie (i.e., National Museum of Natural History, in Persian) 

MN, European Neogene Land Mammal Units

M¹, M² and M³; first, second and third upper molars, respectively.

p⁴, m¹, m² and m³; 4^th lower premolar; first, second and third lower molars, respectively.

PRCI, Paleontological Research Center of Iran

Order Proboscidea Illiger, 1811 

Unranked group Elephantimorpha Shoshani and Tassy, 1997

Family Mammutidea Hay, 1922

Genus Mammut Blumenbach, 1799

Type species Mammut americanum Kerr, 1792

“Mammut” cf. obliquelophus Mucha, 1980 

Synonyms: 

Mammut praetypicum Kubiak, 1972, p. 312, pl. XII

Mastodon americanus Kerr, 1792; Hopwood, 1935, pp. 43–46, Pl. 6.5

Mammut praetypicum Schlesinger, 1919; Pl. I, figs. 1-4

Mastodon (Mammut) americanus Pennant forma praetypica Schlesinger,

1922, Pl. XV, figs. 1, 2, 3, 4; Pl. XIX, fig.2

Mammut borsoni (Hays, 1834): Tobien et al., 1988, p. 165–168, figs 57, 58 (see Wang et al., 2017)

Stratigraphic occurrence: MN12and MN13-MN17, Codrea et al., (2005)

Geographic distribution: China (Baode Region), Southern Russia, Ukraine, Slovenia, Macedonia, Moldavia, Greece, Bulgaria, Hungry, Spain and probably Northwest of Iran.

Referred materials: Right M^{3 (}MMTT11 [PRCI/V001]) and a pair of adult upper tusks (MMTT1 a, b) from Abkhareh (Varzeghan), Iran.

Description

The right M³: It has three roots and was preserved enough to reveal the zygodont characters. The tooth has three major lophs plus a reduced 4th loph at the posterior end. A slight furrow (sulcus) separates the pretrite and posttrite lophs.

The anterior cingulum is moderately developed. The protocone (abaxial pretrite conelet of the first loph) is strongly worn down and is connected to the anterior cingulum. The paracone (main posttrite conelet of the first loph) is slightly worn, and the number of mesoconelets seems to be two or three. Hypocone and metacone are worn to some extent, and there are one and two mesoconelets, respectively. Crescentoids are very weak on the first and second pretrite lophs, but the third pretrite loph bears crescentoids on its anterior wall. The posttrite lophs possess zygodont crests on the posterior wall of the first posttrite cusp and on anterior wall of the second posttrite cusp, both of which are hardly developed. The pretrite lateral enamel is well-developed. The pretrite third half loph consist of a cone and one mesoconelet, which are almost worn and carry crescentoids on its anterior slope. The posttrite third loph is worn so that the number of mesoconelets is not clear. The fourth loph is strong and consists of two pretrite and posttrite conelets. The posterior cingulum is moderately weak. The transverse valleys are completely open and broad (Fig. 2).

The cranium described by Kubiak (1972) has two upper molar teeth: M² and M³. The M² is trilophodont, complete, but deeply worn down. The third molar is broken and only 1^st and 2^nd lophs are preserved. The anterior lophs are relatively worn. There are not any conules between ridges in Kubiak’s M³ material and half lophs are almost symmetrical in width but not in morphology. It seems that the first pretrite loph and the first posttrite loph consist of two or three mesoconelets which are relatively worn. However, the morphology of the first and the second lophs of M³ from Balta Sands (Podolia, Ukraine, Kubiak, 1972, pl. XII, fig. 7) are almost similar to the Abkhareh M³. So, the assignments of Abkhareh tooth to “Mammut” cf. “M.”  obliquelophus can be based on its zygodont morphology and its similarity to the Kubiak material.

Upper tusks: A pair of I² (MMTT 1 a, b) was found in Abkhareh village near Varzeghan area proximate to an isolated zygodont cheek tooth. They were prepared especially in their proximal part and were covered by protective material. The left tusk is broken into two parts, but the right one is almost complete and preserved well. In situ, and in lateral view, the upper tusk is curved dorsally and seems to be directed straight or slightly downwards and then bends strongly outwards after secondary medial of its length. So, the tip is turned upwards. Tusks are not helicoidal, without torsion and diverged in anterodorsal view. The tusks are characterized by a polished surface on their distal ends on the medial sides of both of them. Distal tips are almost abraded, forming a partly distinct elliptical shape on each tusk.  Dorsal and ventral wear facets are absent (Fig. 4, a). No enamel band was recognized. There is a clear longitudinal furrow on their lateral (labial) side. Unfortunately, the pulpa of both the right and left tusks was covered with some glue during the reconstruction. So, it is not possible to see the pulpa.

The maximum lengths of MMTT1a and b (taken dorsally tangentially from the proximal end to the distal end (tip) of tusk) are 1310 mm and 1360 mm, and their lengths are 1080mm and 1000mm, respectively. The maximum diameter of MMTT1a (taken at the middle of the tusk) is 480mm, and that of MMTT1b is 440mm (Figs 4-5). 

No sign of crossing Schreger lines was seen on the ivory’s cross section and broken surfaces but, still their absence is not definite as we did not have the possibility to observe the fresh surface of any of them. Although, the best trait to distinguish Elephantimorpha from more basal proboscideans such as deinotheres is the presence of Schreger Lines, so we relied on the tusks morphology. So, Abkhareh materials’ assignment to the genus Mammut sp. is based on their less curved and untwisted morphology and absence of enamel band. 

According to Jafarzadeh and Konidaris (2020), Neogene elephantimorphs from Eurasia generally have straight or less curved and untwisted upper tusks (except Choerolophodon), this is particularly true about mammutids from Miocene including Zygolophodon and Mammut. 

Proboscideans genera known from the late Miocene of the northwest of Iran include the deinotheriid Deinotherium, the choerolophodontid Choerolophodon, the amebelodontid konobelodon and the mammutids Mammut. The morphology of the tusks of Abkhareh, Varzeghan is obviously dissimilar from the strongly curved and robust lower tusks of Deinotherium (e.g., Tassy, 2016). According to Harris (1978), the mandibular tusks of Deinotherium are relatively short (e.g., Mandibular tusk belonging to a very large individual is D. gigantissimum from Pripiceni, Moldova with 978 mm, which is still short in comparison with Abkhareh tusks) and recurved below symphysis and are almost vertically aligned. Normally, adult deinotheres tusks terminate in rounded conical points. Also, lower tusks of Deinotherium often show no signs of wear (Delmer et al., 2005), which is in contrast with that of Abkhareh tusks. However, wear facets have been observed in a few deinotheriid individuals and are found on the anteromedial tip, suggesting wear by abrasion against one object in front of and between the tusks (Harris, 1978). So, it is supposed that the tusks of Abkhareh can be allocated to an upper tusk of an elephantoid sensu (Tassy, 1988); clade Mammutida (Elephantida, proboscideans) (Shoshani, 1996a, 2002).

Moreover, Choerolophodon which is recognizable based on its strong curvature and double twisted (Outwards and upwards) upper tusks is markedly different from Abkhareh tusks. Konobelodon has more curved upper tusks than the Abkhareh one and with no torsion (Pestszentlörinc, Hungry, HNHM-V.79.34; Schlesinger, 1922; Konidaris and Tsoukala, 2020).  

Remarks

The scattered fossil bones found in Abkhareh locality form surface sediments and there were few of them.  The proximate spatial accumulation of the tusks and an isolated cheek tooth of Abkhareh can be interpreted as all belonging to an individual mammutid. This can also be true about the dinothere postcranial materials and maxilla with some teeth which were attributed to an adult individual of Deinotherium gigantissimum because of their close congregating and consistency in size (Pourabrishami, 2004; Pickford & Pourabrishami, 2013; Rasoli Ghaderi, 2008). So, it is supposed that this fossiliferous layer on the surface was the grave of a few contemporaneous taxa which were washed away by seasonal rivers and buried individually. 

Comparison

There are not many reports of “Mammut” obliquelophus. However, Markov (2008) argued that the taxonomically invalid name “Mammut praetypicum” can be senior synonym of “M.” obliquelophus presented by Kubiak (1972).

Among the Balta Sands materials in Podolia, Ukraine (Kubiak, 1972, p. 311) a part of the skull with dextral I² is present. The tusk is relatively large (1000 mm in length) and almost straight. According to his notes, the ivory leaves the skull horizontally. However, “it is directed slightly downwards and markedly outwards and slightly turned upwards at the end”, which is almost the same in the Abkhareh tusks MMTT1a, b. Nevertheless, the tusks from Abkhareh seem to be directed almost downward and they do not leave the skull horizontally. Also, they are dorsally-curved much stronger. 

The cross-section in Kubiak’s I² is circular, and MMTT1 of Abkhareh shows a circular cross-section at its proximal pulp. It is almost circular in the middle of the tusk. Some “regular longitudinal streaks in the outer and inner layers of the dentine” were observed by Kubiak (1972, p. 311, PL. XIII: F.9). However, the same feature on Abkhareh tusks is not noticeable.

The other upper tusk of late Miocene Mammut, representative, “M.” obliquelophus (Mucha, 1980), is known from Neokaisareia (Katerini, Pieria), Turolian, Late Miocene, right I², NKP-1. Its maximum length is 930 mm and its maximum diameter is 87.3 mm which is slightly shorter and slender than Abkhareh tusks (1080 mm in length).

NKP-1 tusk is almost straight with slight upward (dorsal) curvature in lateral view. It is twisted and slender (according to the writer the NKP-1 tusks belong to an ontogenetically young and/or female, which can explain why its diameter is less than the diameter of the Abkhareh one). A longitudinal furrow runs along the tusk of NKP-1 and the enamel band is absent (Konidaris & Tsoukala, 2020). 

Overall, both the Balta Sands tusk (Ukraine; Kubiak, 1972; Markov, 2008) and NKP-1 upper tusk (Greece; Konidaris & Tsoukala, 2020) are almost straight with slight dorsal curvature in lateral view, and therefore are similar to Abkhareh one. So, these similarities permit the attribution to the upper Miocene Mammut cf. obliquelophus. 

As already mentioned, there are only a few I² materials referred to as Mammut obliquelophus. The material from the Hualinsanshe locality, China (almost complete cranium), belongs to a juvenile individual. It has a pair of in situ upper tusks. The tusks are short and slender. The cross-section is round. As it is expected in juveniles, the apical part is covered by enamel. The material of Hualinsanshe, China is attributed to Mammut obliquelophus by Wang et al. (2017). Although this specimen is so young, and on the other hand tusks of Abkhareh belong to an adult individual, some of their characteristics like bending ventrally in lateral view, lacking enamel band in lateral side and torsion, being divergent in anterior view, and becoming slender apically are similar.

The Pliocene-Early Pleistocene “Mammut” borsoni (Hays, 1834) has never been reported from Iran. Besides, it is likely that “M.” borsoni has longer upper tusks than “M.” obliquelophus. However, the symphysis is longer than the tooth row and lower tusks are well-developed in “M.” obliquelophus. As in a specimen of “M.” borsoni reported from Milia in Grevena, Greece (Tsoukala, 2000; Tsoukala & Mol, 2016), the length of its upper tusks reaches 4.39 meters. The upper tusks of “M.” borsoni are approximately straight and slightly curved upright (dorsally), slender, torsioned, without any enamel band. Longitudinal furrows are present on the proximal part, which is expected for genus Mammut. These characteristics are morphologically comparable with NKP-1 upper tusk and Abkhareh one, but the dimensions of the Milia upper tusks are obviously larger than the NKP-1 and Abkhareh ones.

According to Titov & Tesakov (2012) “M.” obliquelophus was reported from several Turolian (late Miocene) vertebrate faunas from Southern European Russia. These materials included an almost complete mandible with p⁴-m³ tooth rows and small, relatively straight lower tusks (Titov and Tesakov, 2012, Fig 24.3, b-d) from Morskaya2 (middle Turolian, MN12- MN13?) and a fragmental left M³ from Yanovka-Obokhovka sand pits (MN12), (Titov and Tesakov, 2012, Fig 24.3, e). In addition to Deinotherium sp., scanty remains of “M.” cf. obliquelophus were found in the Khanskaya locality (middle Turolian) in Russia. 

The left third upper molar of Yanovka-Obokhovka sand pits in Russia (specimen NMIDK KP-10589/P-89 housed in History Museum of Don Cossacks) has close similarity with Zygodont mastodons of European Turolian attributed by Markov (2008) to “M.” obliquelophus and it is almost the same with the material from Abkhareh submitted in this study. The two M³ distal fragments (TCM 19355/C and 19255/D) from Pǎgaia, Bihor District in NW Romania are assigned to Mammut praetypicum (Schlesinger, 1919) by Codrea et.al. 2005 (Pl. I, Fig. 4). Although both are broken, they show zygodont characteristics which are almost comparable with Abkhareh cheek teeth.

According to Markov (2004, 2008), “Mammut” obliquelophus (Mucha, 1980) is a Turolian (Upper Miocene) taxon which has some different characteristics with other members of mammutids like “Mammut” borsoni (Hays, 1834) and Zygolophodon turicensis (Schinz, 1824). 

“Mammut” obliquelophus was a matter of dispute and taxonomical complications before that. According to Tassy (1990), for a long time, Turolian mammutid materials were misidentified as Pliocene one, “Mammut” borsoni, and the more primitive one, Zygolophodon turicensis from Orleanianto-Vallesian (MN3- MN10). The possibility of this misinterpretation was already mentioned by Alexeeva (1965). Markov (2004, 2008) followed his opinion and separated the Pliocene brevirostrine “M.” borsoni from the Upper Miocene moderately longirostrine “M.” obliquelophus. 

Although the morphology of the cheek teeth of “M.” obliquelophus is practically the same as “M.” borsoni, the symphysis is longer than the tooth row, bearing well developed lower tusks in “M.” obliquelophus, while both lower incisors and symphysis are reduced in length in “M.” borsoni. In comparison with more primitive taxon Zygolophodon turicensis which is real longirostrine, symphysis in “M.” obliquelophus is relatively short. In both Zygolophodon and Mammut posterior border of mandibular symphysis is close to the anterior end of the cheek tooth row. Elongated symphysis is plesiomorphy of Elephantimorpha, but it has been largely reduced in length in all of the derived groups (Tassy, 1996a; Shoshani, 1996).

Generally, as asserted by Tobien (1996), Mammut differs from other mammutids in having either straight or upturned tusks. Upper tusks in “M.” obliquelophus in lateral view are dorsally bent with mild curvature.

However, as it is common in primitive taxa of mammutid (Zygolophodon, Eozygodon), the plesiomorphy of upper tusks in Mammutidae bends ventrally. Upper tusks in Zygolophodon are diverged in anterodorsal view and curve ventrally in lateral view and are not helicoidal. Also, upper tusks in taxa like Eozygodon morotoensis and Zygolophodon turicensis are covered with enamel band. Adults “M.” obliquelophus, “M.” borsoni and M.americanum have no enamel band on their upper tusks. As it is mentioned by Tassy (1996a), enamel bands are lost in most derived taxa of Elephantimorpha.

Moreover, according to Tobien (1975), Zygolophodon molarsdiffer with those of Mammut in the increasing number of transverse ridges in the M³ (four lophs) and m³ (four lophids plus talonid) of Mammut. Molar crowns in Mammut are broader and crescentoids (sperrleisten) are reduced. Also, yoke character of the upper and lower molars in genus Mammut is strengthened. Furthermore, “M.” borsoni and “M.” obliquelophus can be distinguished from Z. turicensis by the lower height of the lophids of cheek teeth in relation to their antero-posterior length and the lower lingual cingulum (Garevski et al., 2012).

Another complication is to use the name “Mammut” for Eurasian mammutids. Schlesinger (1922) suggested a European ancestor for Mammut americanum, but the hypothesis was objected to by Tobien (1976) who assumed an independent origin for “M.” borsoni and for M. americanum. Markov (2004) argued that it is not very probable, assuming a second mammutid migration to North America. Hence, he suggested that using the generic name Mammut for Eurasian mastodons might not be justified. Following Markov (2004), the generic name “Mammut” is used in quotation marks for the Eurasian taxa in this study.

To further make the situation difficult regarding “M.” obliquelophus taxonomy, there are quite a number of materials that have been incorrectly referred to as “M. praetypicum”. Markov (2008) accentuated that this name should not be used for the Turolian mammutids. The name was used by Kubiak (1972) for specimens probably from Balta Sands in Podolia in Ukraine. He elevated Schlesinger’s “Mastodon (Mammut) americanus forma praetypica” Schlesinger (1917) to a specific rank which was a taxonomically erroneous opinion (For more explanation, see Markov, 2008). After Kubiak (1972), the name was used by other authors, for example, Göhlich (1999), Lungu & Obada (2001), and Codrea et al. (2005). However, in the case of the findings from Pǎgaia in Romania (Codrea et al., 2005) they lack a mandible and also are assumed to be Pliocene in age. Therefore, the Pǎgaia material might represent“M.” borsoni.

Moreover, it is quite possible that “M.” praetypicum is a senior synonym for “Mammut”cf. borsoni sensu Tassy (1985) for a longirostrine form from Pikermi (Greece) and a mandible from Ahmatove (South Bulgaria) published by Nikolov & Kovacev (1966), and renamed by Markov (2004).

Nevertheless, a proper name for all those moderately longirostrine Turolian mammutids with bigger lower incisors can be “M.” obliquelophus, which is more primitive than the Pliocene “M.” borsoni with a shorter symphysis, but identical to each other in dental morphology (See Markov, 2004).

Paleobiogeography and Palaeoenvironment

There are several exceptional taxa shared by the localities in northern China and the northwest of Iran. These include Iranotherium, Alcicephalus, Honanotherium, Urmiatherium, and Mammut.  

Iranotherium morgani, a large elasmotherium rhinoceros, occurs in the early Late Miocene of the Linxia Basin, in northwestern China (Deng, 2005). It was first recorded in Maragheh, the northwest of Iran in “MN12”. This species first appeared in China during the Vallesian and immigrated to Maragheh later in the Turolian (Mirzaie Ataabadi et al., 2013; Bernor, et al., 2013).

Honanotherium is a giraffid recently recorded from Maragheh fauna in the form of a new species, H. bernori (Solounias & Danowitz, 2016). Moreover, the same authors also resurrected Alcicephalus (A. neumayri) in Maragheh. It is the most abundant giraffid from this locality and northwest Iran. Both genera are known primarily from north China (Nowdatabase, Fortelius, 2017). Therefore, among giraffids the presence of taxa from the eastern end of Pikermian paleobiome (i.e., China) in northwest Iran is significant. 

Urmiatherium, an ovibovine-like bovid, was originally discovered in Iran (Kostopoulos & Bernor, 2011). It was later recorded from other localities in east (China) and west (Eastern Mediterranean). It is now believed that this genus appeared first in Vallesian of northern Greece and dispersed into central and eastern Asia in the form of U. polaki and U. intermedium (Lazaridis et al. 2017). The abundance of this genus in northern China is mostly in Late Miocene, and it is an apparent migrant from West (Mirzaie Ataabadi et al., 2013; Bernor et al,. 2013).

Presence of “M.”cf. M. obliquelophus in the Late Miocene (MN 12 equivalent) of northwest Iran adds another common taxon between these areas. This taxon probably originated from a Zygolophodon turicensis which is widely distributed from middle to early Late Miocene.

The Chinese material of “M.” cf. M. obliquelophus can be an extension of this taxon from west to east, similar to other taxa discussed earlier. As previously shown, middle and late Miocene chronofaunasmoved into East Asia from the West (Mirzaie Ataabadi et al., 2010). The late Miocene faunas had an even higher proportion of immigrants compared to their precursors. Several ruminants (including Urmiatherium) and equid lineages extended from the eastern Mediterranean to China (Watabe, 1992; Fortelius & Zhang, 2006).

They moved across Asia in response to changing climate and humidity patterns, because summer rainfall brought richer resources to northern China in the latest Miocene (Mirzaie Ataabadi et al., 2013; Liu et al., 2013).

This connection of east and west Asia is not restricted to Miocene faunas. Although it seems that the end of the Miocene was coincident with the waning Pikermian chronofauna, there is evidence that the broad east–west connection of mammalian faunas also continued into Pliocene. For example, the presence of derived hipparionine horses like Proboscidipparion in the Early Pliocene of Anatolia shows their extension of range from Anatolia to China (Bernor & Şen, 2017).

As mentioned above, the materials of current study were unearthed almost next to the materials of Deinotherium proavum, coincidently. According to Pickford and Pourabrishami (2013), deinotheres were present in the environments with sub-tropical to tropic (dry season–wet season cycles) climates, and they are absent from basins records during the boreal to sub-boreal (winter–summer cycles) phases. Also, their dental morphology indicates adaptation to an obligate folivorous diet (see Pickford & Pourabrishami, 2013). It was understood that the climate of Varzeghan region in the northwest of Iran was more tropical during MN12 and generalized that it was the preferable paleoenvironment for “M.” obliquelophus, too.

Although “M.” obliquelophus was assumed invalid by some former authors (Lungu and Obada, 2001), according to Konidaris and Koufos (2013) its validity, which was originally erected for a mandible from Romanovka in Ukraine, is reinforced by a mandible with long symphysis and “borsoni” teeth from the Turolian locality of Ahmatove in Bulgaria.

“M.” obliquelophus is reported from different localities in Central and Eastern Europe and also China. Accordingly, the taxon is present in Spain, Hungary, Bulgaria, Macedonia, Greece, Romania, Moldova, Ukraine, Southern Russia (Markov, 2008) and some localities of Linxia Basin and Baode region in China (Wang et al. 2017).

Despite the absence of mandibular material with symphysis in Abkhareh, Iran, which is a distinctive characteristic between “M.” obliquelophus and “M.” borsoni, the molar teeth and upper tusks can be attributed to “M.” cf. obliquelophus based on their morphology and especially Turolian (MN12 equal) age of the fauna (Mirzaie Ataabadi et al., 2013; Zaree et al., 2011; Pickford & Pourabrishami, 2013). This shows the geographic extension of this species to the northwest of Iran and its possible place between populations in the east and west. This is similar to the position observed for Deinotherium proavum from the same locality (Pickford and Pourabrishami, 2013).

Acknowledgments

The authors thank Iran’s Department of Environment (DOE) for permission to study the specimens. We are grateful to the curator of MaraghehVertebrate Paleontology ResearchCenter, Mr. Golamreza Zare, for providing the access to fossil materials and his constant support. Also, we greatly appreciate Dr. Gorge Konidaris (Palaeoanthropology, Senckenberg Centre for Human Evolution and Palaeoenvironment, Eberhard Karls University of Tübingen) for his kind advice and for providing some beneficial references to use in this study. We also thank the Vice-Chancellor's Office for Research of the Ferdowsi University of Mashhad for their supports, and the anonymous reviewers for their valuable comments and suggestions for improving the text. This project was funded by the Ferdowsi University of Mashhad (grant number 3/38769 to S.Y.).

Data Availability Statements

All data used during this study are included in this published article. The data used during the current study include the vertebrate macrofossils available in Maragheh Vertebrate Palaeontology Research Centre, Maragheh, Iran. These data are available via Sadaf Yaghoubi [[email protected]] at the Ferdowsi University of Mashhad.

Conflict of interest

The authors declare that they have no conflict of interest.

Author's contribution

S.Y., and M.M.A., described the specimens. All the authors contributed to the design and implementation of the research, to the analysis of the results and to the writing of the manuscript.

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Table 1