Megacricetodon hellenicus, Oliver & Peláez-Campomanes, 2016

Oliver, Adriana & Peláez-Campomanes, Pablo, 2016, Early Miocene evolution of the rodent Megacricetodon in Europe and its palaeobiogeographical implications, Acta Palaeontologica Polonica 61 (1), pp. 211-219 : 212-215

Megacricetodon hellenicus sp. nov.

Figs. 1 , 2 .

1979 Megacricetodon primitivus ( Freudenthal, 1963) ; De Bruijn and Van der Meulen 1979: 209, fig. 1.

1980 Megacricetodon primitivus ( Freudenthal, 1963) ; De Bruijn et al. 1980: 243.

1981 Megacricetodon primitivus ( Freudenthal, 1963) ; Katsikatsos et al. 1981: 511.

1982 Megacricetodon primitivus ( Freudenthal, 1963) ; Benda and De Bruijn 1982: 130.

1988 Megacricetodon primitivus ( Freudenthal, 1963) ; Klein Hofmeijer and De Bruijn 1988: 185, 192, 193, 196, 198, 199, text-fig. 4, pl. 2.

Etymology: After Hellenic i.e., Ancient Greek Megacricetodon .

Type material: Holotype: m1 dextral, IAUU AL-N-2096 ( Fig. 1O ;

SOM 1, 2, Supplementary Online Material available at http://app.pan.

pl/SOM/app61-Oliver_PelaezCampomanes_etal_SOM.pdf). Paratypes:

M1: IAUU AL-N-2051–2063, 2069; M2: IAUU AL-N-2071–2073,

2076–2078; m1: IAUU AL-N-2091–2093, 2097, 2098; m2: IAUU AL-

N-2101–2107, 2111–2114; m3: IAUU AL-N-2126.

Type locality: Aliveri North quarry, Island of Evia, Aliveri-Kymi Basin ,

Greece.

Type horizon: Underclay of the lignite occurring North of Aliveri along the eastern edge of the basin where the lignite wedges out against Me-

sozoic limestone ( De Bruijn et al. 1980); Early Miocene (MN4).

Other material.— Isolated teeth from Aliveri South quarry: 4 M1, 1 M2, 3 M 3, 2 m 1, 3 m 3 ( Fig. 2A–I ).

Diagnosis.— Small-sized species of Megacricetodon . It shows slender crests and well-developed mesolophs and mesolophids (generally of medium length). Lower first molars with rounded and simple anteroconid, being lower than the other four main cusps. Upper molars with long and angular entoloph and transverse sinus.

Megacricetodon hellenicus sp. nov. differs from the medium- and large-sized group of Megacricetodon defined by Peláez-Campomanes and Daams (2002) by its significantly smaller dimensions.

Megacricetodon hellenicus sp. nov. differs from M. debruijni Freudenthal, 1968 , M. freudenthali García Moreno (in Álvarez-Sierra and García-Moreno, 1986), M. minutus Daxner, 1967 , and M. pussillus Qiu, 1996 by its bigger dimensions.

Megacricetodon collongensis ( Mein, 1958) is similar in size to M. hellenicus sp. nov., but, it differs from it by the frequent presence of double anteroconid and double protolophule and metalophule in the M1 and M2.

The medium-sized Megacricetodon , M. sinensis Qiu, Li, and Wang, 1981 has a similar size to Megacricetodon hellenicus sp. nov., however, differs by the morphology of the anterocone (anterocone deeply split in more than 75% of the specimens), shorter mesolophid in the m1, m3 with longer lingual anterolophid and absent mesolophid.

Megacricetodon minor ( Lartet, 1851) has a similar size to M. hellenicus sp. nov., but differs from it by having the M1 with a higher percentage of ectolophs connected with the mesoloph; M2 with a higher percentage of double protolophules; and m1 with a higher percentage of double anteroconids and longer mesolophids.

Megacricetodon tautavelensis Lazzari and Aguilar, 2007 differs from Megacricetodon hellenicus sp. nov. by its smaller size, in the M1 with a lower percentage of labial spurs of the anterolophule and the higher percentage of posterior protolophules; M2 with more variability in the morphotypes of the metalophule and protolophule; m1 with a higher percentage of subdivided anteroconid and more variability in the mesolophid.

Megacricetodon primitivus ( Freudenthal, 1963) has a similar size to M. hellenicus sp. nov., however, it differs by having M1 with deeply split anterocone, shorter mesoloph and short entoloph; M2 with a higher percentage of ectoloph absent; short entoloph in the M3; in the lower molars all the cusps of the m1 have the same height, shorter mesolophids in the m1 and m2, and a shorter lingual anterolophid of the m2.

Measurements. —See Table 1.

Description.— M1: The anterocone is slightly subdivided in five (5/12), it is slightly subdivided with a small platform in front of the furrow in two (2/12), the anterocone is deeply split with a small platform in front of the furrow in four (4/12) or it is deeply split with a small cingulum ridge in front it in one (1/12). The labial cone of the anterocone is larger than the lingual one in seven specimens, the two cones are equal in size in four specimens and in the remaining one the lingual cone is larger than the labial. In 12 out of 14 specimens, the anterolophule is connected to the lingual cone of the anterocone, and it is connected between the two lobes of the anterocone in two. The labial spur of the anterolophule is present in eight specimens (in three of them there are two labial spurs) and absent in four. In two teeth, there is a forward paracone spur. The protolophule is posterior (6/11), posterior almost double (4/11) or double (1/11). The entoloph is long and symmetrical, and the sinus is transverse. The ectoloph is strong in one specimen, short in six, and absent in the remaining six. One specimen shows a crest inside the sinus that starts from the entostyl. One out of 13 teeth has a lingual mesocingulum that connects the protocone to the hypocone. The mesoloph is long in two out of 13, medium in nine and short in two. The ectoloph and the mesoloph are never connected. The metalophule is posterior and points backwards in all the specimens (see SOM 3: tables 1–11).

M2: The protolophule is anterior in three specimens and it is anterior almost double in the remaining three. The entoloph is long and angular, with the posterior arm of the protocone better developed than the anterior arm of the hypocone. The sinus is transverse. The ectoloph is strong in four out of six and it is short in two. The mesoloph is long in one, medium in four (in one of them there are two medium mesolophs, Fig. 1J ), and short in the remaining one. In three out of six, the ectoloph is connected with the mesoloph. One specimen shows a short crest inside the sinus that starts from the entostyl. The metalophule is anterior (5/6) or it is posterior and points backwards (1/6) (see SOM 3: tables 12–16).

M3: Klein Hofmeijer and De Bruijn (1988) attributed some very large specimens of M3 from North and South quarries to Megacricetodon . In our opinion, their morphology and large dimensions (M3 length> 0.80 mm) suggest that they belong to Democricetodon franconicus Fahlbusch, 1966 instead of to Megacricetodon hellenicus sp. nov., therefore, there are no M3 known from the type locality. The following description refers to the material from Aliveri South quarry: the labial anteroloph is always present and extends to the paracone. The lingual anteroloph is incipient in one, and long but not connected to the protocone in two specimens. The paracone is well developed. The metacone is present in two out of three specimens. The hypocone is present in the three specimens. The metalophule is connected to the neo-entoloph in two specimens, and it is connected to the neo-entoloph and the protolophule in one. The mesoloph is absent in two out of three specimens. The second protolophule is present in one and incipient in the remaining two. The posterior arm of the protocone is absent. The neo-entoloph and the sinus are always present. The posterosinus is always present (see SOM 3: table 17).

m1: The anteroconid is always rounded and simple. The metalophulid is anteriorly connected in three specimens and is double in one. The lingual mesocingulid is incipient in two and absent in two specimens. The labial mesocingulid is present in three specimens (in one of them the mesocingulid is not connected to the hypoconid), and incipient in two. The mesolophid is medium (2/5) or short (3/5). In one out of six, there is an ectomesolophid. The hypolophulid is always anterior (see SOM 3: tables 18–22).

m2: The lingual anterolophulid is long (5/10) or short (5/10). The labial anterolophulid is long and connected to the protoconid in six specimens or long but disconnected in the remaining four. The lingual mesocingulid is present in four specimens (in three of them, the mesocingulid is not connected to the entoconid), incipient in two and absent in the remaining four. Only one specimen (1/10) has an incipient mesostylid. The labial mesocingulid is well-developed and connected to the hypoconid in two, well-developed and not connected to the hypoconid in four and incipient in the remaining four specimens. In one out of 11 the mesolophid is long, in four it is medium, and in six it is short. The hypolophulid is always anterior (see SOM 3: tables 23–24).

m3: As for the M3, Klein Hofmeijer and De Bruijn (1988) attributed some very large specimens of m3 to Megacricetodon ,thatshouldbeattributedto Democricetodon (m3 L> 1 mm). Therefore, in our opinion, there is only one available tooth and it is highly corroded. The lingual anterolophulid is short and the labial anterolophulid is long, but not connected to the protoconid. The labial mesocingulid is incipient. The mesoloph is absent (see SOM 3: table 25). To complete the m3 descriptions the material from Aliveri South quarry is included in the following paragraph: The lingual anterolophulid does not reach the antero-lingual corner of the metaconid in two specimens and reaches it in one specimen. The three specimens have mesolophid, one of them have two (one long, connected to the lingual mesocingulid and the other incipient).

Stratigraphic and geographic range.—Lower Aragonian, Lower Miocene, Greece.

Figures

Fig. 1. Cricetodontid rodent Megacricetodon hellenicus sp. nov. from type locality Aliveri North quarry, Greece (MN4, Early Miocene). A. IAUU AL-N-2051, M1 left. B. IAUU AL-N-2052, M1 left. C. IAUU AL-N-2053, M1 left. D. IAUU AL-N-2055, M1 left. E. IAUU AL-N-2056, M1 left. F. IAUU AL-N-2057, M1 left. G. IAUU AL-N-2059, M1 left. H. IAUU AL-N-2060, M1 left. I. IAUU AL-N-2071, M2 left. J. IAUU AL-N-2072, M2 left. K. IAUU AL-N-2077, M2 right. L. IAUU AL-N-2078, M2 right. M. IAUU AL-N-2091, m1 left. N. IAUU AL-N-2092, m1 left. O. Holotype IAUU AL-N-2096, m1 right. P. IAUU AL-N-2097, m1 right. Q. IAUU AL-N-2101, m2 left. R. IAUU AL-N-2102, m2 left. S. IAUU AL-N-2104, m2 left. T. IAUU AL-N-2105, m2 left. U. IAUU AL-N-2111, m2 right. V. IAUU AL-N-2126, m3 right.

Fig. 2. Cricetodontid rodent Megacricetodon hellenicus sp. nov. from the Aliveri South quarry, Greece (MN4, Early Miocene). A. IAUU AL- S-1112, M1 right. B. IAUU AL-S-1114, M1 left. C. IAUU AL-S-1118, M3 left. D. IAUU AL-S-1119, M3 left. E. IAUU AL-S-1122, m1 left. F. IAUU AL-S-1124, m1 right. G. IAUU AL-S-1115, M2 left. H. IAUU AL-S-1128, m3 right. I. IAUU AL-S-1129, m3 right.