On the determination of the Microchoerus (Omomyidae, Primates) remains from Sant Cugat de Gavadons (Late Eocene, Ebro Basin, NE Spain)

The primate remains from Roc de Santa (Late Eocene, NE Spain) revisited: New taxonomic allocation

The scarce primate remains from the late Eocene locality of Roc de Santa (Central Pyrenees, NE Spain) were first documented in 1975. This material included a mandibular fragment with P₃-M₂ and a maxillary fragment with P³-M³ assigned to Adapis magnus (later transferred to the genus Leptadapis), and an isolated M₃ attributed to Necrolemur antiquus. However, these specimens were never described in detail. We have thoroughly studied these specimens, with the exception of the mandibular fragment, which has been lost. The maxillary fragment is much smaller than in Leptadapis magnus and shows clear morphological differences from that species; this specimen is assigned to Microchoerus hookeri. Similarly, the isolated M₃ resembles that of M. hookeri in size and morphology, and can therefore be attributed to this taxon. In addition, we describe an upper incisor never reported previously, which can also be allocated to M. hookeri, representing the first description of this tooth for the species. Therefore, we conclude that the previous taxonomic determinations were mistaken and all the available primate specimens from Roc de Santa can be confidently assigned to the species M. hookeri, previously described from the same-age localities of Sossís, Spain, and Eclépens-B, Switzerland.

Agerinia marandati sp. nov., a new early Eocene primate from the Iberian Peninsula, sheds new light on the evolution of the genus Agerinia

BACKGROUND

The Eocene was the warmest epoch of the Cenozoic and recorded the appearance of several orders of modern mammals, including the first occurrence of Euprimates. During the Eocene, Euprimates were mainly represented by two groups, adapiforms and omomyiforms, which reached great abundance and diversity in the Northern Hemisphere. Despite this relative abundance, the record of early Eocene primates from the European continent is still scarce and poorly known, preventing the observation of clear morphological trends in the evolution of the group and the establishment of phylogenetic relationships among different lineages. However, knowledge about the early Eocene primates from the Iberian Peninsula has been recently increased through the description of new material of the genus Agerinia from several fossil sites from Northeastern Spain.

METHODS

Here we present the first detailed study of the euprimate material from the locality of Masia de l'Hereuet (early Eocene, NE Spain). The described remains consist of one fragment of mandible and 15 isolated teeth. This work provides detailed descriptions, accurate measurements, high-resolution figures and thorough comparisons with other species of Agerinia as well with other Eurasian notharctids. Furthermore, the position of the different species of Agerinia has been tested with two phylogenetic analyses.

RESULTS

The new material from Masia de l'Hereuet shows several traits that were previously unknown for the genus Agerinia, such as the morphology of the upper and lower fourth deciduous premolars and the P2, and the unfused mandible. Moreover, this material clearly differs from the other described species of Agerinia, A. roselli and A. smithorum, thus allowing the erection of the new species Agerinia marandati. The phylogenetic analyses place the three species of Agerinia in a single clade, in which A. smithorum is the most primitive species of this genus.

DISCUSSION

The morphology of the upper molars reinforces the distinction of Agerinia from other notharctids like Periconodon. The analysis of the three described species of the genus, A. smithorum, A. marandati and A. roselli, reveals a progressive change in several morphological traits such as the number of roots and the position of the P1 and P2, the molarization of the P4, the reduction of the paraconid on the lower molars and the displacement of the mental foramina. These gradual modifications allow for the interpretation that these three species, described from the early Eocene of the Iberian Peninsula, are part of a single evolutionary lineage. The stratigraphical position of Masia de l'Hereuet and Casa Retjo-1 (type locality of A. smithorum) and the phylogenetic analyses developed in this work support this hypothesis.

Microchoerus hookeri nov. sp., a new late Eocene European microchoerine (Omomyidae, Primates): New insights on the evolution of the genus Microchoerus

The study of Eocene primates is crucial for understanding the evolutionary steps undergone by the earliest members of our lineage and the relationships between extinct and extant taxa. Recently, the description of new material from Spain has improved knowledge of European Paleogene primates considerably, particularly regarding microchoerines. Here we describe the remains of Microchoerus from Sossís (late Eocene, Northern Spain), consisting of more than 120 specimens and representing the richest sample of Microchoerus from Spain. This primate was first documented in Sossís during the 1960s, on the basis of scarce specimens that were ascribed to Microchoerus erinaceus. However, the studied material clearly differs from M. erinaceus at its type locality, Hordle Cliff, and shows some characters that allow the erection of a new species, Microchoerus hookeri. This new species is characterized by its medium size, moderate enamel wrinkling, generally absent mesoconid and small hypoconulid in the M₁ and M₂, single paracone in the upper molars and premolars and, particularly, by the lack of mesostyle in most M¹ and M², a trait not observed in any other species of Microchoerus. Some specimens from Eclépens B (late Eocene, Switzerland), determined previously to be Microcherus aff. erinaceus, are also ascribed to M. hookeri. M. hookeri represents the first step of a lineage that differentiated from Necrolemur antiquus and, later, gave rise to several unnamed forms of Microchoerus, such as those from Euzet and Perrière, finally leading to M. erinaceus. This discovery sheds new light on the complex evolutionary scheme of Microchoerus, indicating that it is most probably a paraphyletic group. A detailed revision of the age of the localities containing remains of Microchoerus and the description of the still unpublished material from some European localities, are necessary to clarify the phylogenetic relationships among the members of this microchoerine group.