Tenuicricetodon arcemis, Maridet & Codrea & Fărcaș & Solomon & Venczel & Tissier, 2025

Maridet, Olivier, Codrea, Vlad A., Fărcaș, Cristina, Solomon, Alexandru A., Venczel, Márton & Tissier, Jérémy, 2025, The record of cricetid rodents across the Eocene-Oligocene transition in Transylvania, Romania: implications for the “ Grande Coupure ” at European scale, Acta Palaeontologica Polonica 70 (2), pp. 291-327 : 306-308

Tenuicricetodon arcemis sp. nov.

Figs. 9E–N, 10.

Zoobank LSID: urn:lsid:zoobank.org:act:.

Etymology: From Arcem the latin name of the locality Cetățuie, in Latin arcemis .

Holotype: Right M1 (MPSUBB v1116).

Type locality: Cetățuie, Transylvanian Basin, Romania.

Type horizon: Rupelian, lower Oligocene, Dâncu Formation, Gilău sedimentary area,

Species diagnosis.—Same as the generic diagnosis.

Material.—Eight upper molars and three lower molars, all from the type locality and horizon.

Measurements.—See Table 6. Description.—The molars are characterized by a low crown and small narrow cusp(id)s and loph(ids) providing a slightly lophodont aspect; in lateral view the cusp(id)s have either an angular shape when the wear is weak, or a low rounded shape when the wear is strong.

The M1s display a short and narrow mesial lobe. The anterocone is small, crescent-like and transversally elongated; the lingual anteroloph ends with a protostyle connected to the protocone. The protocone spur (sensu Maridet and Ni 2013) is either short (ending in the anterosinus), or long and prolonged by an anterolophule reaching the anterocone. Both the mesosinus and the sinus are closed respectively labially and lingually by a cingulum; additionally, there is a mesostyle on the labial cingulum, with or without a spur. The mesial protoloph is complete (connected to the anterolophule) in one M1 ( Fig 10A) and interrupted in the other Fig. 10B). The distal protoloph is short and it connects to the paracone in one M1. The entoloph and the distal protoloph form a continuous oblique crest between the hypocone and the distal protolophule whereas the connection between the protocone and the entoloph is less developed. The protocone and its mesial spur being oblique, the sinus is also oblique. The mesoloph starts from a small mesocone and it reaches the mesostyle spur in one M1. The metalophule is straight and connects the hypocone. The posteroloph is inflated. In one M1 a posterostyle extends from the posteroloph lingually in the posterosinus ( Fig. 10A). The M1s have three roots.

In M2s, the lingual anteroloph is much shorter and lower than the lingual one, it can reach the protocone and close the protosinus (3/5). The mesial protolophule is complete and better developed than the distal one; the distal protolophule is long but does not reach the paracone. Like in M1s, the entoloph and the distal protoloph form a continuous oblique crest between the hypocone and the paracone whereas the connection between the protocone and the entoloph is shorter; also, the protocone is elongated distally and the sinus is strongly curved. The paracone spur is located on the labial border, it is long and closes the mesosinus in all but one M2 ( Fig. 10E). The mesoloph is long, it either reach directly the labial cingulum (3/5) or merges with a somewhat lower and thinner mesostyle spur. The sinus either is closed by a low and weakly developed cingulum (2/5) or labially open (3/5). The metalophule is slightly oblique and connects mesially to the hypocone. The posteroloph is long and generally closes the posterosinus (3/5), but the posterosinus can also remain open labially (1/5), and the postero-labial corner of one M2 is broken so the labial end of the posterosinus is not discernable (1/5). The M2s have three roots.

The M3 ( Fig. 10G) has a well-developed labial anteroloph, the lingual one being absent. The mesial protolophule is strong, connects the anterolophule whereas the distal protolophule is short, and does not reach the paracone. Like in M1s and M2s, the entoloph forms a continuous oblique crest between the hypocone and the distal protolophule, and the connection between the protocone and the entoloph is interrupted. The mesoloph is long and reaches the labial cingulum; the metacone is reduced to a postero-labial bulge on the cingulum. The metalophule connects distally the metacone and mesially the hypocone. The roots are not preserved.

The m1 ( Fig. 10H) has both equally developed anteroconid and metastylid. The lingual anterolophid, between the metastylid and the metaconid, is very short whereas the labial one is long and closes the protosinusid labially. A small spur starts distally to the anteroconid but there is no anterolophulid connecting the anteroconid to the protoconid. The protoconid hind arm is well developed and long, and connects to the metaconid. Both the metaconid ridge and the entoconid spur are long; they join each other lingually and close the mesosinusid. Likewise, a strong ridge starting from the hypoconid is prolonged by a cingulid reaching the protoconid so the sinusid is closed labially. The entolophid, mesolophid and ectomesolophid are all thick and form a cross in the middle of the molar. The mesolophid is long and reaches the lingual cingulid whereas the ectomesolophid ends in the middle of the sinusid. The hypolophulid is straight, transverse, and connects mesially to the hypoconid. The hypoconid hind arm is long and connects to the posterolophid, delimiting a small pit distally to the hypoconid. This small pit is itself divided by an additional spur (second hypoconid hind arm) between the hypoconid hind arm and the distal border ( Fig. 10H). The roots are not preserved.

The m2 ( Fig. 10I) has both strong lingual and labial anterolophid closing the anterosinusid and protosinusid respectively. The metalophulid is oblique and connects on the anterolophulid; the protoconid hind arm is long, bends mesially and connects to the metaconid distal slope. The metaconid ridge and the entoconid spur are long and join each other along the lingual border, forming a cingulid that closes the mesosinusid. A spur extends in the mesosinusid from this lingual cingulid, but does not reach the mesolophid; additionally, a crest is present in the middle of the mesosinusid, isolated between this spur and the mesolophid. A strong cingulid also closes the sinusid labially. The ectomesolophid is long and merges with a ridge connected to the hypoconid. The hypolophulid is oblique, parallel to the metalophulid, and connect on the ectolophid, mesially to the hypoconid. The posterosinusid is very large, and closed lingually by a long posterolophid; the hypoconid hind arm is short but well developed and ends in the middle of the posterosinusid. A second minute hypoconid hind arm is present next to the first one. The roots are not preserved.

The m3 ( Fig. 10J) displays clearly separated metaconid and protoconid, indeed the metalophid connects on the lingual anterolophid whereas the anterolophulid connects on the labial anterolophid, and the protoconid hind arm does not connect to the metaconid, but on the metaconid distal ridge next to minute mesostylid. There is no mesolophid, and the ectomesolophid is very weak, limited to a fold of the enamel labially to the entolophid. The mesosinusid and the sinusid are open respectively lingually and labially. The posterolophid is long and merges with the entoconid distal ridge that closes the posterosinusid lingually. The m3 has two roots.

Remarks.— Hugueney (1980) and later Comte (1985) discussed in detail the differences between Eucricetodon huberi ( Schaub, 1925) and Pseudocricetodon incertus (Schlosser, 1884) . Indeed, the two species are large and present similar sizes, but some morphological differences can be observed that, in turn, can also secure the identification at generic level. These differences led Engesser (1987) to refer these genera to two different subfamilies, Eucricetodontinae and Pseudocricetodontinae respectively.

The teeth described above differ from Eucricetodon aff. Eu. huerzeleri from the same locality by being slightly smaller, having a M3 with a less reduced distal part, and having a lower crown with thinner and narrower cusp(id)s and loph(ids) which gives it a more lophodont aspect. These characteristics are usually associated with Pseudocricetodon Engesser 1987 ; Hugueney 1999). They also display a long mesoloph in M2 and M3 which is characterictic of Ps. incertus and absent in Eu. huberi (Comte 1985) , a short and narrow anteroloph usually characteristic of Pseudocricetodon Engesser 1987 ), a long mesial arm of the protocone in M1 more frequent in Pseudocricetodon (Engesser 1987; Hugueney 1999), and a concave labial border whereas it is rather convexe in M1 of Eu. huberi (Comte 1985; and more generally in Eucricetodontinae , Engesser 1987), and a divided anteroconid in m1 which is rare in Eucricetodon Hugueney 1999 ). Among Pseudocricetodontinae this population from Cetățuie otherwise strongly differs from Heterocricetodon Schaub, 1925 , in having a much lower crown and less elongated molars, especially the third molars; it also strongly differs from Adelomyarion Hugueney, 1969 , in being less lophodont (thicker crests and larger cusps and cuspids), and missing the often strongly oblique or interrupted entoloph(id).

In contrast these teeth from Cetățuie also display characters that are usually associated with Eucricetodon : The mesial lobe is short and narrow, and the mesial protolophule more developed than the distal one in M1 (Engesser 1987; Hugueney 1999); the anterolophulid absent in m1 whereas it is usually long and complete in Ps. incertus ( Hugueney 1980) ; the mesolophid of m1 is long and oblique in Eu. huberi whereas it is usually small or even absent in Ps. incertus ( Hugueney 1980) ; and the hypoconid hind arm is always absent in Pseudocricetodon and more generally in all Pseudocricetodontinae (Engesser 1987; Hugueney 1999).

The ambiguous association of morphological characters on molars led to refering this population from Cetățuie to a new genus: Tenuicricetodon gen. nov. However, the question of the subfamily it belongs to remains open. Most of the characters mentioned above present a noticeable variability when taking into account large populations (e.g., Freudenthal 1994; Freudenthal et al. 1994; Maridet et al. 2009), but not all of them. The short and narrow mesial lobe in M1, the absence of anterolophulid in m1 and the presence of a hypoconid hind arm in m1 seem to be consistent features differentiating Eucricetodontinae from Pseudocricetodontinae Freudenthal et al. 1994; Hugueney 1999). Despite the morphological similarities with Pseudocricetodon , we refer this new genus to the subfamily Eucricetodontinae .

Stratigraphic and geographic range.—Dâncu Formation Rupelian), Transylvania ( Romania).