Megacricetodon FAHLBUSCH, 1964

Jovells-Vaqué, Sílvia, Ginestí, Montserrrat & Casanovas-Vilar, Isaac, 2017, Cricetidae (Rodentia, Mammalia) From The Early Miocene Site Of Els Casots (Vallès-Penedès Basin, Catalonia), Fossil Imprint 73 (1 - 2), pp. 141-154 : 147-149

Genus Megacricetodon FAHLBUSCH, 1964

Megacricetodon primitivus ( FREUDENTHAL, 1963) Pl. 1, Figs 7–11

1993 Megacricetodon minor primitivus; Agustí and Llenas, p. 70.

M a t e r i a l f r o m e l s C a s o t s l e v e l 7 2. 2 M1 (IPS 45094, IPS 94649); 2 M2 (IPS 45094, IPS 45089) ; 2 M3 (IPS 45094, IPS 45089) ; 3 m 1 (IPS 44995, IPS 44996, IPS 19514) ; 3 m 2 (IPS 19515, IPS 44997, IPS 19523) .

M a t e r i a l f r o m e l s C a s o t s l e v e l 7 3. 7 M1 (IPS 44963 – IPS 44968, IPS 94641); 1 M3 (IPS 94639) ; 6 m 1 (IPS 44969 – IPS 44974) ; 1 m 3 (IPS 94640) .

Material from els Casots level 74.6 M1 (IPS 44936 – IPS 44941); 2 M2 (IPS 44961, IPS 44984) ; 1 M3 (IPS 19479) ; 17 m 1 (IPS 44942 – IPS 44958) ; 15 m 2 (IPS44948 – IPS 44951, IPS 44959, IPS 44960, IPS 44962, IPS 44981 – IPS 44983, IPS 44985, IPS 94255, IPS 94256, IPS 94587, IPS 94588) ; 5 m 3 (IPS 44949, IPS 44991 – IPS 44994) .

M e a s u r e m e n t s. See Tables 4–6.

D e s c r i p t i o n. M 1. All the specimens have three roots. The most mesial root is cylindrical and located under the anterocone; there is a flattened root at the lingual half side and a cylindrical one at the postero-labial corner of the molar. The anterocone is deeply split with the labial cusp conspicuously larger than the lingual one. A few specimens show a faint anterior cingulum at the base of the anterocone, but in most specimens the anterior wall of the anterocone is smooth. The anterolophule connects the protocone with the lingual cusp of the anterocone. There is no labial spur on the anterophule. The protolophule consists of a posterior arm that connects the paracone with the entoloph posteriorly to the protocone. However, four out of 15 M1 show a vestigial extremely short anterior arm of the protolophule that does not reach the paracone. There is a short posterior ectoloph in the paracone spur in three specimens, while this character is absent in the remaining ones. The mesoloph varies from long to absent. It is long in three out of 15 specimens, of medium length in six (for example in IPS 44939; Pl. 1, Fig. 7), short in four and absent in the remaining two. The metalophule consists of a single arm that curves distally and joins the metacone with the posteroloph in a somewhat labial position. This implies that the posterosinus is highly reduced. The posteroloph is thin and partially closes this valley. The sinus is transverse. All the main valleys are closed by cingula, which are more pronounced on the lingual side. However, there is no lingual mesocingulum.

M2. The M 2 have two flattened roots, mesial and distal. The anterior valleys are closed by the well-developed arms of the anterolophule. The labial arm is noticeably higher than the lingual one. The protosinus is very reduced, being vestigial in some specimens (for example in IPS 44961; Pl. 1, Fig. 8). The protolophule and the metalophule are simple, consisting in an anterior arm only. Two specimens (including IPS 44961; Pl. 1, Fig. 8) show a vestige of the posterior arm of the protolophule that can be recognized as a small protuberance posterior to the protocone. The mesoloph is always long, reaching the labial border of the molar although it becomes very low towards its end. In three specimens (for example IPS 44961; Pl. 1, Fig. 8), there is a short to medium-sized posterior ectoloph on the paracone, while it is absent in the remaining one. When present, the ectoloph approaches the mesoloph without contacting with it. The sinus is transverse. The posteroloph is well developed and reaches the base of the metacone, thus resulting in a closed posterosinus. The sinus and mesosinus are closed by relatively well-developed cingula .

M3. The M 3 show a rounded outline and two cylindrical roots (labial and lingual). There is no trace of the protosinus and the lingual anteroloph. The anterosinus is narrow and partially closed by the well-developed labial arm of the anteroloph. The protolophule is simple and connects the paracone with the anteroloph in front of the protocone. The mesoloph and metalophule are highly variable. In one specimen, the mesoloph is long, ending in a prominent mesostyle and the metalophule is parallel to it and ends in a small metacone (IPS 45094). In a second one (IPS 19479; Pl. 1, Fig. 9), this ridge is shorter and isolated from the entoloph and the mesostyle but it shows a weak contact with the metalophule. A third specimen (IPS 45089) shows a peculiar morphology with an arched axioloph and a long, slightly posteriorly-directed mesoloph. The metacone is indistinguishable at the end of the metalophule, and the posterior and labial valleys are closed by a high ridge. The posteroloph is well developed and partially closes the very narrow posterosinus. The sinus is transverse and narrow, being closed by a low cingulum .

m1. The molars have two cylindrical roots, anterior and posterior. In slightly worn specimens, the anteroconid is simple and rounded. The anterior valleys are wide and closed by the arms of the anterolophid, which are low. The anterolophulid is very low and situated in a more or less central position. The anterolophulid shows a labial spur in six out of 26 specimens, it is generally short and low, but in a few instances, it reaches the labial anterolophid. The metalophulid and the hypolophulid are both simple, being defined by a very short anterior arm. The mesolophid is always present, being short in most specimens (20/26; see for example IPS 44950; Pl. 1, Fig. 10) and somewhat longer in a few others (6/26). The sinusid is wide and proverse. It is closed by a pronounced cingulid while the mesosinusid is open. The posterolophid is high and thick and closes a rather wide posterosinusid.

m2. The m2 have two cylindrical roots, mesial and distal. The anterior valleys are closed by the arms of the anterolophid. Unworn molars show a highly reduced to vestigial anterosinusid which quickly disappears because of wear (IPS 44950; Pl. 1, Fig. 10). The mesolophid is always present. Most specimens show a short mesolophid (15/18; see for example IPS 44950; Pl. 1, Fig. 10), although medium-length ones also occur (3/18) and one specimen (IPS 19515) shows a long mesolophid which is extremely low at its lingual end. The sinusid is wide and transverse to slightly proverse. This valley is closed by a cingulid in most specimens, although it is not as well developed as in m1. The remaining morphological features resemble those of the m1 .

m3. The m3 are elongated and show two cylindrical roots. The anterior valleys are reduced, specially the anterosinusid, which is vestigial in some specimens. These valleys are closed by the arms of the anterolophid, which are low. The metalophulid is thick and short, joining the metaconid with the anterolophid in front of the protoconid. The mesolophid is absent in all the molars but one, (IPS 44994), which exhibits a vestige of this ridge just behind the protoconid. The sinusid is relatively wide and mostly retroverse. This valley is closed by a low cingulid as described for the m2. The hypolophulid is very thick and anterior to the hypoconid. The entoconid is reduced. The posterolophid is thick and short, but it closes the posterosinusid. The mesosinusid is closed by a high cingulid.

D i s c u s s i o n. The specimens from els Casots are similar in size to small Megacricetodon species such as M. primitivus, M. minor LARTET, 1851 and M. collongensis MEIN, 1958 ( Text-fig. 3 ; see also Daams and Freudenthal 1988, Oliver and Peláez-Campomanes 2014). However, a number of morphological features allow us to confidently ascribe the material from els Casots to Megacricetodon primitivus. The anterocone in the M1 is clearly divided and not predominantly simple or slightly split as in M. minor. Megacricetodon collongensis ( Mein 1958) is similar in size, but shows a symmetrically split anterocone. In contrast, in M. primitivus and the specimens from els Casots, the labial cusp of the anterocone is generally larger than the lingual one ( Oliver and Peláez-Campomanes 2014). The mesoloph in the M1 is variable, but is mostly of medium length, while in the M2 it is always long and low. Mesoloph development is similar in the type material from Valtorres ( Freudenthal 1963) and in M. primitivus from other Spanish sites ( Daams and Freudenthal 1988, Oliver Pérez et al. 2008, Oliver and Peláez-Campomanes 2014) but the mesoloph in the M2 is most commonly of medium length. The M2 protolophule is simple with only one anterior arm and in a few cases a vestigial posterior arm. Similarly, the protolophule is simple and posterior in the M1 with a vestige of the anterior protolophule occurring in a few specimens. Double protolophules are more common in other Spanish samples from the Calatayud-Montalbán Basin ( Oliver Pérez et al. 2008, Oliver and Peláez-Campomanes 2014) as well as from Bunyol ( Daams and Freudenthal 1974, Adrover et al. 1987) but not in other samples from the Vallès- Penedès Basin such as Can Martí Vell 1 and 2 ( Agustí 1981, 1983) or Les Cases de la Valenciana 1 (Jovells-Vaqué et al. in press). Els Casots specimens perfectly agree in size and morphology with M. primitivus from these Vallès-Penedès sites although a few dental elements (particularly the lower molars) are slightly larger.

Figures

Text-fig. 3. Length/width scatter plot for the molars of Megacricetodon primitivus from different Spanish sites. Locality acronyms are as follows: BU = Bunyol; CMV3 = Can Martí Vell 3; CS72 = els Casots level 72; CS73 = els Casots level 73; CS74 = els Casots level 74; LCV1 = Les Cases de la Valenciana 1; VR1 = Vargas 1. Data for VR1 taken from Daams and Freudenthal (1988), data for BU taken from Daams and Freudenthal (1974).