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Journal of Paleontology 92(5):920–937
Material.—SV2-99, right P4; SV3-47, left M3; SV3-125, right M1; SV3-317, right M1; SV3-565, right M3.
Remarks.—Antunes (1981) first reported the presence of paromomyids in Portugal by including Phenacolemur in his faunal list of Silveirinha. It was not until Estravís’s work (1992, 2000) that the Portuguese fossils were included in the genus Arcius and assigned to a new species. Arcius zbyszewskii was suggested by Estravís (2000) to represent a primitive lineage of European paromomyids due to its mosaic of Arcius characters together with primitive paromomyid characters. Our interpretation of the Portuguese fossils differs from
Estravís (2000) in that SV1-24 is interpreted as anM1, instead of an M2. We argue that the paraconid on SV1-24 is no smaller than that of the other M1 (SV3-125), which is typical for paromomyids. There is also no difference in the mesiodistal length of the trigonid between the two specimens, while it is a common trait for paromomyids to have a shorter M2 trigonid. Smith et al. (2011) described a diminutive upper tooth of a
paromomyid from Sotteville-sur-Mer (Normandy, France) that they considered to be a broken M1. The authors acknowledged the similarities of this tooth to the Portuguese fossils but did not ascribe it to any particular species of Arcius. The poor state of preservation of the tooth and the fact that Arcius is characterized by having molariform upper premolars makes it difficult to assign the specimen to a tooth position, but its very weak postprotocrista suggests it is a P4 rather than an M1. Arcius zbyszewskii is the only species of the genus in which the P4 has a very weak postprotocrista instead of it being completely absent. This trait, paired with the similarity in the small size of the specimen from Sotteville-sur-Mer compared to the collection from Silverinha, supports attribution of the Normandy specimen to A. zbyszewskii. Sotteville-sur-Mer and Silveirinha are considered to be of very similar age (Smith et al., 2011) and are the oldest sites in Europe that yield paromomyid fossils, which would be consistent with grouping the Arcius from both sites under the same species.
Arcius hookeri new species Figures 2.9, 8
1980 Phenacolemur cf. P. fuscus Hooker and Insole, p. 38. 1996 Arcius fuscus Hooker, p. 209. 1998 Arcius fuscus Hooker, p. 449.
2003 Arcius lapparenti (in part) Aumont, appendix A, tables 3, 4.
2010 Arcius lapparenti Hooker, p. 48. Holotype.—BMNH.M 44945, right dentary with M2–M3.
Diagnosis.—Buccal cingulids present on M2, but weaker than those found in A. fuscus and A. lapparenti and not extended onto the talonid. Trigonid wider, with a greater difference in height between the metaconid and the protoconid, than in other species of Arcius. Mesial inflection of the trigonid not as pronounced as in species of other paromomyid genera, but not as vertical as in A. rougieri and A. ilerdensis n. sp. Differs from all other species of Arcius, except for A. ilerdensis n. sp., in having a taller
Figure 8. Micro-CT scan images of the holotype of Arcius hookeri n. sp. (BMNH.M 44945) in (1) occlusal, (2) buccal, (3) lingual views. Arrows indicate the presence of a double entoconid. Scale bar=1mm.
metaconid than the protoconid on M2 and M3. Differs from A. zbyszewskii in not having a paraconid on M3. Double entoconid present on M3, unlike all other species of Arcius.
Horizon and locality.—Blackheath Beds from Abbey Wood (type locality, PE III), England, UK.
Biostratigraphy.—Abbey Wood is a reference locality for PE III using mammalian biostratigraphy (Hooker, 1996).
Description.—BMNH.M 44945 is the only specimen known of this species. It is composed of a partial dentary with an associated M2 andM3 in place. The complete distal alveolus of M1 is preserved, as well as the distal aspect of the mesial alveolus of M1. The mandibular ramus is partially preserved, and it retains the anterior edge of the masseteric fossa (Hooker, 2010). Arcius hookeri n. sp. shows typical paromomyid characteristics such as reduced paraconids, a protoconid- metaconid notch that is obscured by a fold of enamel, and an expanded hypoconulid on M3 that forms an additional lobe (Silcox and Gunnell, 2008). It shares with other Arcius species features such as taller cusps than in Ignacius, trigonids not as inclined as in other paromomyid genera, and the presence of a simple rounded hypoconulid lobe onM3 (instead of the bilobed hypoconulid lobe seen in other paromomyids; Fig. 2).
Etymology.—Named after Dr. Jeremy J. Hooker of the British Museumof Natural History for his unparalleled contributions to the study of the mammalian paleontology of England.
Remarks.—The record of paromomyids from England is very limited, with BMNH.M 44945 being the only specimen of a
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