Occitanomys brailloni Michaux, 1969

Colombero, Simone, Pavia, Giulio & Carnevale, Giorgio, 2014, Messinian rodents from Moncucco Torinese, NW Italy: palaeobiodiversity and biochronology, Geodiversitas 36 (3), pp. 421-475 : 434-436

Occitanomys brailloni Michaux, 1969 ( Fig. 4 G-L)

Occitanomys brailloni Michaux, 1969: 8 , pl. 1, figs 6-11. — van de Weerd 1979: 132, pl. 1, figs 3-9. — de Bruijn 1989: 191. — Vasileiadou et al. 2003: 553, fig. 4I, J. — Minwer-Barakat et al. 2005: 434, fig. 3H. — Hordijk & de Bruijn 2009: 33, pl. 8, figs 1-7, pl. 9, figs 1-11.

Hansdebruijnia sp. – Angelone et al. 2011: 99, fig. 6 (11).

aff. Huerzelerimys – Angelone et al. 2011: 99, fig. 6 (13).

TYPE LOCALITY. — Layna, Spain.

OCCURRENCE IN THE STUDIED LAYERS. — MCC3, MCC4, MCC5, MCC7.

REFERRED MATERIAL. — Two maxillary fragments bearing M1 and M2; one maxillary fragment bearing M2 and M3; two mandibular fragments bearing m1, m2 and m3; two mandibular fragments bearing m1 and m2; 79 isolated M1; 79 isolated M2; 26 isolated M3; 64 isolated m1; 61 isolated m2; 31 isolated m3. See Appendix 1 for further details.

MEASUREMENTS. — Table 3.

DESCRIPTION

M1

t1bis present; t1 very close to t5; t3 exhibits a posterior spur that touches the base of the t5 or t5-t6

connection in 35% of the specimens; labial tubercles (t3-t6-t9) aligned, forming a straight labial margin; posterior tubercles (t4; t5; t6; t9; t8) connected in a stephanodont crest; t4-t8 connection low or absent; t12 weakly developed.

M2

Ovoid shape; t1 close to t5, t3 small; t1bis rarely present, posterior tubercles (t4; t5; t6; t9; t8) connected in a stephanodont crest; t12 absent or very poorly developed.

M3

t1 connected to t5; t3 generally absent even if a small swelling of the enamel occurs in few specimens; t8 isolated or weakly connected to t6.

m1

A low longitudinal spur develops from the entoconidhypoconid complex, barely reaching the base of the protoconid-metaconid complex without constituting a complete crest (75% of the specimens) or remaining free (25%); the labial cingulum bears a c1 and an additional cusplet between protoconid and anteroconid.

m2

Well-developed anterolabial cuspid; a low longitudinal spur is present but it does not form a complete crest; labial cingulum departs from c1 and reaches a cusplet near the protoconid.

m3

The anterolabial cuspid is a small swelling of the enamel; posterior complex transversally elongated and isolated from the protoconid-metaconid complex.

REMARKS

The material described herein can be referred to the genus Occitanomys Michaux, 1969 because of its moderately developed longitudinal connections between the tubercles of lower and upper molars, a less pronounced stephanodonty than Stephanomys Schaub, 1938 and Castillomys Michaux, 1969 and the position of t1 close to t5 ( Michaux 1969). In addition, Stephanomys usually displays higher- crowned teeth with better developed longitudinal connections, the tubercles of upper molars are more pointed than in Occitanomys in which, on the contrary, the tubercles are more rounded and the overall aspect is more bunodont. Moreover, in the M1 of Stephanomys the t6 is more voluminous, usually protruding over the labial outline of the tooth, whereas in the specimens from MCC the t6 is always well aligned with t3 and t9, forming a straight labial border. However, few upper molars of Stephanomys ramblensis van de Weerd, 1976 from some Messinian localities of the Teruel Basin ( van de Weerd 1976; Adrover et al. 1993a) and the Granada Basin (García-Alix et al. 2008b) including Valdecebro 3, Villastar and Purcal 23 roughly resemble those from MCC in displaying less developed t3-t5 connections in some M1 and t1-t5 connections in some M2. Nonetheless the lower molars of this species clearly differ from the studied material in the significantly more developed longitudinal connections that are present even in the m3. Moreover, even if the size ranges partially overlap, the mean-size of the molars of S. ramblensis is slightly larger than that of Occitanomys brailloni from MCC.

The size of the molars of Occitanomys from MCC falls in the range of Occitanomys brailloni Michaux, 1969 from some Pliocene localities of western and eastern Europe including Layna, Nîmes ( Michaux 1969), Kardia, Ptolemais 1 and 3 ( van de Weerd 1979) and Tollo de Chiclana-1B (Minwer-Barakat et al. 2005). The measurements are also very similar to those of O. brailloni from Vorio 1 and Vorio 2 ( Hordijk & de Bruijn 2009), even though the mean size of the M2 is slightly larger in MCC. However, the size variability of M2 is poorly known for this species. Comparisons with material referred to O. brailloni from Layna housed at the IVAU and from the UCBL collections revealed a very similar morphology of the molars that fall in the range of variation of the type assemblage. Slight differences can be found in the M1 since the specimens from MCC display less frequent longitudinal connections. In particular, in the examined M1 from Layna the t3- t5 connection is present in 60% of the specimens whereas this connection only appears in 35% of the specimens from MCC. In our opinion these differences are not significant and can be related to the older age of the assemblages from MCC since the longitudinal connections seem to become more frequent in younger assemblages such as that from Layna. Therefore, the material from MCC is referred herein to Occitanomys brailloni .

Teeth of Occitanomys montheleni Aguilar, Calvet & Michaux, 1986 reported in the Pliocene French localities of Mont Hélène and Serrat d’en Vaquer ( Aguilar 1982; Aguilar et al. 1986) show a larger overall size; moreover, on the grounds of morphological comparisons with some specimens of O. montheleni , the posterior spurs of the t 3 in the M1 of O. brailloni are more developed and the m1 shows a more developed labial cingulum.

Occitanomys adroveri (Thaler, 1966) , a species occurring in Europe during the Late Miocene, differs from the studied material in displaying slender and less rounded cusps and much more developed t 12 in M1 and M2. In addition, the connections in the upper teeth, especially t3-t5 connections in M1, are less developed than those occurring in the studied material. Moreover, the measures of the teeth of this species are usually smaller than those of the studied material. According to Michaux (1969), O. adroveri and O. brailloni belong to the same lineage that, from the Miocene to the Pliocene, should be characterized by a general size increase of the teeth in addition to a volume-increase of the cusps and a reduction of the t12. Moreover, as observed in the type assemblage of O. brailloni from Layna, the longitudinal connections of the upper molars are slightly more developed in the younger species. The earliest record of O. brailloni is that of Rema Marmara, a Greek locality dating back to the MN12 ( de Bruijn 1989). This species is also reported in other Greek localities with an age close to the Mio-Pliocene boundary, such as Silata (Va- sileiadou et al. 2003) and Kardia ( van de Weerd 1979) and it appeared in France ( Michaux 1969) and Spain ( Michaux 1969; Minwer-Barakat et al. 2005) during the Pliocene. The record of MCC represents one of the oldest reports of this taxon documenting its presence in the central sectors of southern Europe at the end of the Miocene.

In a previous cursory analysis of the fossil assemblage from MCC ( Angelone et al. 2011), a small sample of Occitanomys brailloni was tentatively assigned to Hansdebruijna sp. Nonetheless, Hansdebruijna Storch & Dahlmann, 1995 clearly differs in the more developed t12, poorly developed t1bis and a general smaller size. In the same paper, another very small sample of O. brailloni was tentatively attributed to aff. Huerzelerimys Mein, Martín-Suárez & Agustí, 1993 . This genus can be distinguished from Occitanomys by its lesser degree of stephanodonty, more developed t6 and t12, and less developed t1 bis. In summary, all these specimens previously assigned to other taxa are now referred to Occitanomys brailloni .

Figures

FIG. 4. — Isolated teeth of Paraethomys Petter, 1968, Occitanomys Michaux,1969, Centralomys De Giuli,1989 and Micromys Dehne, 1841 from Moncucco Torinese. A-F, Paraethomys meini (Michaux, 1969); A, MGPT-PU128032, M1 dex.; B, MGPT-PU128040, M2 sin.; C, MGPT-PU127602, M3 sin.; D, MGPT-PU127146, m1 sin.; E, MGPT-PU127302, m2 sin.; F, MGPT-PU127603, m3 sin.; G-L, Occitanomys brailloni Michaux, 1969; G, MGPT-PU127062, M1 sin.; H, MGPT-PU127447, M2 dex.; I, MGPT-PU127657, M3 dex.;J, MGPT- MGPTPU127166,m1 dex.; K, MGPT-PU127305,m2 dex.; L, MGPT-PU127658,m3 sin.;M-R, Centralomys benericettii (De Giuli, 1989); M, MGPT-PU128090, M1 sin.; N, MGPT-PU128278, M2 sin.; O, MGPT-PU128115, M3 sin.; P, MGPT-PU128272, m1 sin.; Q, MGPT-PU128321, m2 sin.; R, MGPT-PU128144, m3 dex.; S-V, Micromys bendai van de Weerd, 1979; S, MGPT-PU127434, M1 dex.; T, MGPT-PU127251, M2 dex.; U, MGPT-PU127600, m1 dex.; V, MGPT-PU127601, m2 sin. Scale bar: 1 mm.