Eomys minor Comte & Vianey-Liaud, 1987
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publication ID |
https://doi.org/ 10.5252/g2010n2a3 |
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DOI |
https://doi.org/10.5281/zenodo.10543987 |
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persistent identifier |
https://treatment.plazi.org/id/03E18794-0F0D-7246-CCE6-FD7EFDF5FC03 |
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treatment provided by |
Marcus |
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scientific name |
Eomys minor Comte & Vianey-Liaud, 1987 |
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Eomys minor Comte & Vianey-Liaud, 1987 ( Fig. 6 View FIG )
TYPE LOCALITY. — Belgarric (Quercy, France).
OTHER STUDIED LOCALITY. —La Blache ( France).
TEETH SIZE. — Eomys minor was described by Comte & Vianey-Liaud (1987; error as E. minus ) as the smallest eomyid known in the Early Oligocene of Europe. It is indeed a very small species, but it would be actually difficult to separate this species from E. antiquus solely based on size.
Belgarric – m1/2: 0.87 × 0.72 mm; 0.83 × 0.73 mm.
La Blache – M1/2: 0.78 × 0.80 mm; M3: 0.74 × 0.83 mm; p4: 0.79 × 0.70 mm; m1/2: 0.88 × 0.89 mm; 0.91 × 0.80 mm.
DESCRIPTION
The teeth are brachyodont but the tubercles seem to be proportionally high.
M1/2
The rather worn tooth presents a very simple morphology, with massive cusps fused into two transverse and separated crests, no entoloph and no mesoloph. The protocone is directed obliquely backward.
M3
As for the M1/2 the cusps are massive. There are four transverse crests; the labial anteroloph is long and joins an anterocone. Th e entoloph is very thin without mesoloph. Th e posteroloph is long and disconnected from the hypocone at its base. Protocone and hypocone are directed obliquely backward.
p4
As for the other teeth, the morphology is simple; the low ectolophid is very thin, without mesolophid. Th e anterior part is clearly divided into two cusps. Th e posterolophid is weakly developed and represented by a spur on the posterior part of the tooth.
m1/2
The two teeth from Belgarric and the two teeth from La Blache have a very similar morphology, with massive cusps and very simple bunodont morphology. Th e two teeth from Belgarric have no mesolophid and a weakly-developed posterolophid reduced to a spur. One of the two teeth from La Blache has exactly the same morphology whereas the other one is slightly different with no ectolophid and a short spur connected to the hypoconid that could be interpreted as a very weakly-developed mesoconid. On this tooth, the posterolophid is short but clearly more developed than a spur and the anterior root is not completely bifurcated as it is the case for E. antiquus . As in the material from Belgarric, a long anterolophid exists but, as the teeth are unworn, is not connected to the protoconid.
Mandible
It is noteworthy that a second mandible without teeth found in Belgarric is also clearly different from the mandibles of E. antiquus from Möhren 13, 20 and Ronzon. Th e diastema is flat, almost not curved, the ascending coronoid ramus is weakly slant, hiding only the third molar and all the masseter insertions are weakly marked.
DISCUSSION
The size of this species seems to be smaller than E. antiquus but teeth are close to the smallest E. antiquus teeth. Th e measurements, taken directly on the type material (USTL BEL 470) for this study, indicated that part of the values given by Comte & Vianey-Liaud (1987) were underestimated and that the width of the teeth is not clearly smaller than for E. antiquus of Southern Germany ( E. minor , m1: 0.87 × 0.72 mm, m2: 0.83 × 0.73 mm; E. antiquus Ronzon , m1: 0.85 × 0.85 mm, m2: 0.96 × 0.95 mm). However the diagnosis is still valid as the morphology of E. minor can easily be differentiated from that of E. antiquus : the longitudinal crest, often interrupted and centrallylocated on both upper and lower teeth leading to short connections between the cusps; the latter also present a massive morphology, the mesoloph(id)s are absent and the posterolophid is generally short or reduced to a posterior spur.
Based on these features, the teeth from La Blache can undoubtedly be attributed to E. minor and the fact that, in this locality, only this species is present confirms that E. minor is a valid species and not simply the smallest individuals of an E. antiquus population.
In the locality Bumbach1, Engesser (1990) also described a minute P4 (0.58 × 0.64 mm; but a little corroded) as Eomys nov. sp. 3. A single tooth is difficult to assign; it seems unlikely that it could be a P3, such teeth being known in the late Eocene Symplokeomys Emry, Wang, Tjutkova & Lucas, 1997 but it is of interest to notice that the age of Bumbach1 is equivalent to the Quercy level Belgarric (MP 25) where Comte & Vianey- Liaud (1987) described Eomys minor . A further comparison of the material would probably decide if Eomys nov. sp. 3 from Bumbach1 can be related to E. minor . Anyhow the presence of E. minor in at least two localities supports the assumption that E. minor represents an independent lineage as early as the MP 24/25 Oligocene.
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