Type species

Arcius rougieri.

Other species

A. fuscus, A. lapparenti, A. zbyszewskii, Arcius hookeri n. sp., Arcius ilerdensis n. sp. (see descriptions below).

Emended diagnosis (modified from Godinot, Reference Godinot1984)

Presence of a molariform P⁴ (i.e., metacone approaching the size of paracone, expanded distolingual basin), not observed in any other paromomyid. Upper molars with distolingual basins less expanded distally than in Phenacolemur. Incisor with a lingual and a buccal crest, in contrast to Ignacius. The computed two-dimensional (2-D) area (max length × width of the crown in occlusal view) of P₄ is similar to that of M₁, in contrast to Ignacius. Lower molar cusps relatively taller relative to the base of the crown than those of Ignacius. Lower molar trigonids not as mesially inclined relative to the level of the base of the talonid basin as in any other paromomyid genus. Large third molar hypoconulid with a simple rounded lobe, in contrast to Phenacolemur, Ignacius, Acidomomys, and some species of Paromomys, which exhibit a central invagination (evident from a distal view) that runs mesiodistally on the hypoconulid lobe.

Occurrence

Neustrian (early Eocene) of France, United Kingdom, Portugal, and Spain; Grauvian (middle Eocene) of France.

Remarks

Following the classification of fossils from Condé-en-Brie to the genus Phenacolemur by Louis (Reference Louis1966), Russell et al. (Reference Russell, Louis and Savage1967) subsequently described new fossils from Mutigny and Avenay and classified them under that genus based on their resemblance to some of the North American representatives known at that time, such as Phenacolemur jepseni Simpson, Reference Simpson1955; Phenacolemur praecox Matthew, Reference Matthew1915; and Phenacolemur citatus Matthew, Reference Matthew1915. Russell et al. (Reference Russell, Louis and Savage1967) referred to the development of the hypoconulid in M₃ in the European forms as reminiscent of that in Phenacolemur citatus and Phenacolemur jepseni, and the lack of ectocingulum in upper molars as similar to Phenacolemur jepseni. However, Russell et al. (Reference Russell, Louis and Savage1967) also mentioned that the P₄ in the European specimens is smaller in size than the M₁, a trait that is characteristic of Ignacius rather than Phenacolemur.

Following this line of reasoning, Godinot (Reference Godinot1984), in his paper naming the genus Arcius, suggested that it was closely related to Ignacius instead, specifically to Ignacius graybullianus Bown and Rose, Reference Bown and Rose1976 from the early Eocene of Wyoming. One of the characters that Godinot (Reference Godinot1984) highlighted as diagnostic of the genus was that the mandible (or, more appropriately, the alveolar ridge) reaches its highest point in the area of P₄ and M₁ alveoli, but at that time, the only mandible known was that of Arcius rougieri (Fig. 1). Still today, Arcius gnathic fossils are extremely rare, with the only ones reported being the mandible and maxillary fragments of A. rougieri (PAT1, PAT1 bis, and PAT2), two mandibles of A. lapparenti from Condé-en-Brie (CBX1-ph and an uncatalogued specimen [for the uncatalogued specimen, see Aumont, Reference Aumont2003, appendix G, pl. 3, fig. 3]), a maxilla and a mandible of Arcius sp. from Fournes (FNR43 and FNR54), an uncatalogued mandible of Arcius sp. from Le Quesnoy (Aumont, Reference Aumont2003, appendix G, pl. 3, fig. 4), and a mandible with M_2-3 from Abbey Wood. The only lower jaw specimen known to exhibit the character described by Godinot (Reference Godinot1984) is PAT2 (Fig. 1; Arcius rougieri), and it is not present in other species (Aumont, Reference Aumont2003, appendix G, pl. 3, figs. 3 and 4). Therefore, this character is an autapomorphy of A. rougieri, and should not be considered diagnostic of the genus, but rather solely diagnostic of A. rougieri (see the following).

Figure 1

Micro-CT scan images of a cast of the mandible of Arcius rougieri Godinot, Reference Godinot1984 (PAT2) (1) in occlusal, (2) buccal, and (3) lingual views. Note that the strong line cutting through the mandible is a feature of the cast, not on the original specimen. Scale bar=0.5 cm.

Later, Robinson and Ivy (Reference Robinson and Ivy1994) suggested that Arcius was not monophyletic and classified this genus in the subfamily ‘Phenacolemurinae.’ According to Robinson and Ivy (Reference Robinson and Ivy1994), this subfamily contained the genera Phenacolemur, Ignacius, and Elwynella Rose and Bown, Reference Rose and Bown1982, along with their proposed genera ‘Simpsonlemur,’ ‘Pulverflumen,’ and ‘Dillerlemur,’ whose validity has been a source of debate (Silcox and Gunnell, Reference Silcox and Gunnell2008). By contrast, Aumont (Reference Aumont2003) recovered a monophyletic Arcius in her cladistic analysis, with the North American Acidomomys Bloch et al., Reference Bloch, Boyer, Gingerich and Gunnell2002 as its sister taxon.

Diagnostic characters for Arcius included here that have not been discussed previously in the literature include the simple enlarged hypoconulid lobe, the molariform P⁴, and the weak mesial inflection of the molar trigonids. With the exception of primitive representatives of the paromomyid clade (i.e., Paromomys farrandi), a markedly enlarged M₃ hypoconulid lobe is typical of paromomyids. There are, however, two types of morphology of these lobes: simple and divided. Simple lobes, as observed in all species of Arcius, have a rounded shape in distal view, with a concave outline (Fig. 2.6–2.9). Divided lobes, as observed in Phenacolemur, Ignacius, Edworthia Fox et al., Reference Fox, Scott and Rankin2010, some species of Paromomys Gidley, Reference Gidley1923, and to a lesser extent, Acidomomys, exhibit an invagination of the occlusal surface that runs mesiodistally through the center of the lobe (Fig. 2.1–2.5). This gives the lobe a heart-shaped appearance in distal view. Arcius is also characterized by having a P⁴ that resembles a molar, more so than in other genera (Figs. 3.13, 3.17, 4.1). Although the P⁴ metacone is smaller than the paracone, it approaches the size of the paracone. This, combined with the similarity in size of P⁴ to M¹ makes the premolar very molar-like. The similarity between the adult P⁴ to the M¹ in Arcius parallels the resemblance in morphologies between the deciduous P⁴ and the M¹ observed in other paromomyids, such as Phenacolemur (Rose, Reference Rose1981; Silcox et al., Reference Silcox, Rose and Bown2008) and Acidomomys (Bloch et al., Reference Bloch, Boyer, Gingerich and Gunnell2002). This might suggest that Arcius underwent a process of retention of a deciduous P⁴. Arcius rougieri shows a possible retention of the deciduous upper central incisor (see the following).

Figure 2

Distal view of micro-CT scan images of the M₃ of various species of North American and European paromomyids. (1) Phenacolemur citatus Matthew, Reference Matthew1915, USGS 21712, right; (2) Paromomys depressidens Gidley, Reference Gidley1923, USNM 9677; (3) Edworthia lerbekmoi Fox et al., Reference Fox, Scott and Rankin2010, UALVP 50990, right; (4) Ignacius frugivorus Matthew and Granger, Reference Matthew and Granger1921, YPM-PU 20690, left; (5) Acidomomys hebeticus Bloch et al., Reference Bloch, Boyer, Gingerich and Gunnell2002, UM 108206, left; (6) Arcius fuscus Russell et al., Reference Russell, Louis and Savage1967, MU 6507, left; (7) Arcius lapparenti Russell et al., Reference Russell, Louis and Savage1967, AV 5849, left; (8) Arcius zbyszewskii Estravís, Reference Estravís2000, SV3-47, left; (9) Arcius hookeri n. sp., BMNH.M 44945, right. The paromomyids on the top row (1–5) have an invagination at the top central area of the hypoconulid lobe; all Arcius species (6–9) lack this feature. Scale bar=1 mm.

Figure 3

Micro-CT scan images; (1–4, 9, 10, 13–16) Arcius fuscus Russell et al., Reference Russell, Louis and Savage1967; (5–8, 11, 12, 17–19) Arcius lapparenti Russell et al., Reference Russell, Louis and Savage1967. (1) CB 2560, left P₄, occlusal view; (2) MU 6458, right M₁, occlusal view; (3) AV 422-L, left M₂, occlusal view; (4) MU 6507, holotype, left M₃, occlusal view; (5) CB 4162, left P₄, occlusal view; (6) AV 7716, right M₁, occlusal view; (7) AV 7707, right M₂, occlusal view; (8) AV 5849, left M₃, holotype, occlusal view; (9, 10) AV 6838, left I¹, (9) lingual view, (10) mesial view; (11, 12) AV 7714, right I¹, (11) lingual view, (12) mesial view; (13) CB 1914-L, left P⁴, occlusal view; (14) UCMP 71976, left M¹, occlusal view; (15) AV 610-BN, left M², occlusal view; (16) UCMP 71982, left M³, occlusal view; (17) CB 232-BN, left P⁴, occlusal view; (18) AV 1306-Ph, right M¹, occlusal view; (19) AV 1092-BN, right M², occlusal view. Scale bar=1 mm.

Figure 4

Micro-CT scan images of Arcius zbyszewskii Estravís, Reference Estravís2000. (1) SV2-99, right P⁴, occlusal view; (2) SV3-125, right M¹ fragment, occlusal view; (3) SV1-29, right M², holotype, occlusal view; (4) SV3-317, right M₁, occlusal view; (5) SV3-47, left M₃, occlusal view. Scale bar=1 mm.

Based on the two most complete specimens that belong to the genus Arcius, PAT1 and PAT2, the dental formula for this genus would be ${{2.1.2.3} \over {1.0.1.3}}$ . See also Table 1 for estimated body masses for all the species in the genus.

Table 1

Estimated average body masses of all species of Arcius Godinot, Reference Godinot1984 based on data from Aumont (Reference Aumont2003) and the current study (for A. hookeri n. sp. and A. ilerdensis n. sp.). The regression equation used for Conroy’s (Reference Conroy1987) estimates was the one based on the prosimian sample.

Arcius rougieri Godinot, Reference Godinot1984

Figures 1, 5

Figure 5

Micro-CT scan images of Arcius rougieri Godinot, Reference Godinot1984. Maxilla (PAT1, holotype) in (1) occlusal, (2) oblique occlusal, (3) oblique frontal views; (4) PAT5, right M₂, occlusal view; (5) PAT3, left M³, occlusal view. (1–3) Scale bar=0.5 cm; (4, 5) scale bar=1 mm.

1981 Arcius cf. A. fuscus Godinot, Reference Godinot1981, p. 77.

1984 Arcius rougieri Godinot, Reference Godinot1984, p. 85.

1991 ?Arcius rougieri; Marandat, Reference Marandat1991, p. 92.

2003 Arcius rougieri; Aumont, Reference Aumont2003, pl. 3, fig. 5, pl. 6, fig, 5, 6. Pl. 18, fig. 1, pl. 19, 23.

Holotype

PAT1, partial maxilla with right I¹–C and left I¹–M¹.

Emended diagnosis (modified from Godinot, Reference Godinot1984)

Smaller M₂ than Arcius lapparenti, A. hookeri n. sp., and A. ilerdensis n. sp., but larger M₁ than A. zbyszewskii. Further differs from A. fuscus and A. lapparenti in having a more apically extended (taller) anterocone than mediocone on I¹, with a significantly smaller posterocone, and laterocone proximally shifted relative to the anterocone. Further differs from all other species of Arcius in having a more buccally extended parastylar region on M¹ and a stepped postvallid on M₁ and M₂. Further differs from A. fuscus in having a more distally expanded distolingual basin on M³. Further differs from A. fuscus in having two crests, instead of three, on the P₄ postvallid. Paraconid of M₁ is smaller than in A. fuscus and A. lapparenti but larger than in A. zbyszewskii. Mesial inflection of M₁ and M₂ trigonids weaker than in A. ilerdensis n. sp. but stronger than in the other known species of Arcius. Further differs from A. zbyszewskii and A. ilerdensis n. sp. in having a cingulid on the buccal half of the distal aspect of M₁ that runs up to the hypoconulid. Highest point of the alveolar ridge between P₄ and M₁; this has not been observed in any other species of Arcius.

Horizon and locality

Palette (type locality, PE II, see Biostratigraphy in the following), Bouches-du-Rhône, France; Fordones (PE II, see Biostratigraphy), Aude, France; Rians (PE II; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), Var, France.

Biostratigraphy

There is some disagreement as to the age of Palette and Fordones. Marandat et al. (Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012) assigned Palette and Fordones to Paleocene-Eocene biozone I (PE I) and considered them intermediate in age between Silveirinha (older) and Rians/Fournes (younger). However, there seems to be a consensus that Silveirinha is very close in age to Sotteville-sur-Mer, probably slightly younger (Smith et al., Reference Smith, Dupuis, Folie, Quesnel, Storme, Iacumin, Riveline, Missiaen, Ladevèze and Yans2011; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012; Hooker, Reference Hooker2015), and Hooker (Reference Hooker2015) assigned Sotteville-sur-Mer to PE II, close to the onset of the carbon isotope excursion (CIE). Rians and Fournes have been calibrated to be of similar age to the site of Meudon (Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), and Hooker (Reference Hooker2015) suggested PE II as the age for Meudon as well. Therefore, based on the correlations suggested by Hooker (Reference Hooker2015), Palette and Fordones would be considered to be PE II in age.

Materials

PAT2, mandible with right I₁–M₁; PAT3, left M³; PAT5, right M₂.

Remarks

In this paper, all diagnoses for the six species of Arcius include diagnostic features of the referred material along with the holotype. The reason behind this decision is that the holotypes for A. fuscus and A. lapparenti are M₃ specimens (Russell et al., Reference Russell, Louis and Savage1967), and this tooth position is probably the most variable in paromomyids, in particular with respect to the relative proportions of the hypoconulid lobe with the rest of the tooth. This would make the diagnosis for these species solely based on M₃ morphology very limited and not very diagnostic.

The holotype of Arcius rougieri, along with PAT1 bis and PAT2, represent the first described gnathic fossils with associated teeth in a European paromomyid. The I¹ of A. rougieri differs greatly from those of A. fuscus and A. lapparenti (Rose et al., Reference Rose, Beard and Houde1993) and is more similar to the deciduous I¹ of A. fuscus and A. lapparenti (Fig. 6) in that the anterocone is the tallest cusp rather than the mediocone (tallest in adult specimens attributed to A. fuscus and A. lapparenti). In addition, the laterocone is more proximally located to the mediocone in juveniles of A. fuscus and A. lapparenti than in adult representatives of the tooth, as is observed in the adult form of A. rougieri. There are some differences, however, between the I¹ of A. rougieri and the deciduous I¹ of A. fuscus and A. lapparenti in that the mediocone is better developed in juveniles of A. fuscus and A. lapparenti while the posterocone is less so, although the posterocone is still poorly expressed in A. rougieri compared to the condition in most adult paromomyid I¹s. PAT1 is inferred to pertain to an adult because all of its adult teeth have erupted. The second upper incisor and the fourth upper premolar erupt after I¹ in the North American paromomyid Acidomomys (Bloch et al., Reference Bloch, Boyer, Gingerich and Gunnell2002), and both teeth are fully erupted in PAT1. Although it is possible that the dental eruption sequence varied in Arcius from that observed in Acidomomys, it would be surprising for it to vary so much that I¹ would erupt after all the adult teeth, particularly since no primate species is known to have I¹ as the last tooth to erupt. Indeed, I¹ is usually one of the first teeth to erupt (López-Torres et al., Reference López-Torres, Schillaci and Silcox2015, table 1). Therefore, it seems that the upper central incisors of A. rougieri were retained. Interestingly, as noted, the genus Arcius also has an adult P⁴ that resembles a deciduous P⁴ (or an adult molar).

Figure 6

Drawing of a decidious upper central incisor of Arcius lapparenti Russell et al., Reference Russell, Louis and Savage1967 (GR10029) in (1) medial view, (2) lingual view, (3) oblique (mediolingual) view. Original photograph in Aumont (Reference Aumont2003, appendix G, pl. 9, fig. 8). Scale bar=1 mm. Drawing by V. Bodo.

Previous to the description of Arcius, Godinot (Reference Godinot1981) described a paromomyid M₁ from Rians (RI225) that he tentatively ascribed to Phenacolemur cf. P. fuscus. Godinot (Reference Godinot1981) highlights some differences between the Rians specimen and the specimens from Mutigny (type locality of Arcius fuscus), such as the Rians specimen having a paraconid closer to metaconid, a paracristid curved downward, and a greater mesiodistal length of the whole tooth. Godinot (Reference Godinot1981) admits that high intraspecific variability for A. fuscus could allow this tooth to be attributed to that species but suggests that new fossils could shed light on “l’espèce de Rians” (“the species of Rians”; Godinot, Reference Godinot1981, p. 78). The paraconid on RI225 is weak, which contrasts with the fairly strong paraconids on the M₁ of A. fuscus and A. lapparenti. The only Arcius species with poorly expressed paraconids on M₁ and a size comparable to A. fuscus is A. rougieri. Therefore, we suggest that the RI225 belongs to A. rougieri.

Marandat (Reference Marandat1991) tentatively ascribed to A. rougieri fossils found in the locality of Fordones. The Fordones fossils include the only known M₃ for this species (FDN28). This specimen is missing the hypoconulid lobe, which is particularly relevant in determining which species of Arcius it belongs to. Aumont (Reference Aumont2003) suggested that the only way to know the correct ascription of FDN28 is to find an M₃ from the type locality for A. rougieri (Palette), but the size, the metric proportions, and the fact that other A. rougieri fossils have been found in Fordones support the inference that FDN28 is the first M₃ known of A. rougieri (Marandat, Reference Marandat1991; Aumont, Reference Aumont2003).

Arcius fuscus Russell, Louis, and Savage, Reference Russell, Louis and Savage1967

Figures 2.6, 3.1–3.4, 3.9, 3.10, 3.13–3.16, 7.2, 7.5

Figure 7

Micro-CT scan images of three paromomyid P₄s. (1, 2, 4, 5) The ‘prehypoflexid cristid’ (white arrow) as seen on the P₄ of (1, 4) Paromomys maturus Gidley, Reference Gidley1923 and (2, 5) Arcius fuscus Russell et al., Reference Russell, Louis and Savage1967. (3, 6) Arcius lapparenti Russell et al., Reference Russell, Louis and Savage1967 is shown as an example of a paromomyid with no prehypoflexid cristid. When the prehypoflexid cristid is present, the postprotocristid (black arrow) is shifted to a central position across the postvallid. The main difference between the prehypoflexid cristid of Paromomys maturus and that of A. fuscus is that in (4) Paromomys maturus it is located more mesially, contrary to (5) A. fuscus, in which the three cristids are in the same plane on the postvallid. Scale bar=1 mm.

1962 ‘Phenacolemuridae’ gen. indet. sp. indet. Reference Louis and MichauxLouis and Michaux, p. 171.

1966 Phenacolemur sp. Reference MatthewLouis, p. 51.

1967 Phenacolemur fuscus (in part) Reference Russell, Louis and SavageRussell et al., figs. 2a–j, l, 3d, g.

1981 Phenacolemur cf. P. fuscus Reference GodinotGodinot, p. 77.

1984 Arcius fuscus Reference GodinotGodinot, fig. 2b.

1991 Phenacolemur cf. P. fuscus Reference MarandatMarandat, p. 92.

2003 Arcius fuscus; Reference AumontAumont, pl. 1, figs. 3, 4, 8, pl. 2, figs. 9–12, pl. 4, figs. 4, 5, pl. 5, figs. 5, 6, 10, pl. 7, figs. 8–15, pl. 8, figs. 3, 8, 9, 13, 14, pl. 10, figs. 6–8, pl. 11, fig. 2, pl. 12, figs. 4, 6, pl. 13, figs. 3–5, 10, pl. 14, fig. 3.

2004 Arcius fuscus; Reference AumontAumont, fig. 3.5–3.9, 3.14–3.16.

Holotype

MU 6507, left M₃.

Emended diagnosis (modified from Russell et al., Reference Russell, Louis and Savage1967 and Aumont, Reference Aumont2003)

Smaller M₂ than those of Arcius lapparenti, A. hookeri n. sp., and A. ilerdensis n. sp. but larger M₁ than those of A. rougieri and A. zbyszewskii. Further differs from A. rougieri in having a more apically extended (taller) mediocone than anterocone on I¹, no expansion of the parastylar area of M³, presence of ‘prehypoflexid cristid’ on the P₄, a concave mesial border of P₄ in lateral view, stronger mesial inflection of molar trigonids, and lacking a stepped postvallid on M₁. Further differs from A. zbyszewskii and A. ilerdensis n. sp. in having a cingulid on the buccal half of the distal aspect of M₁ that runs up to the hypoconulid. Further differs from A. zbyszewskii in not having a paraconid on M₃.

Occurrence

Mutigny (type locality, PE IV; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), Marne, France; Fournes (PE II; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), Hérault, France; Var, France; Gland (PE V; Aumont, Reference Aumont2003), Aisne, France; Avenay (PE V; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), Marne, France; Sézanne (PE V; Aumont, Reference Aumont2003), Aisne, France; Condé-en-Brie (PE V; Hooker and Russell, Reference Hooker and Russell2012), Aisne, France; St. Agnan (MP10; Hooker, Reference Hooker1996), Aisne, France.

Materials

AV 422-L, left M₂; AV 610-BN, left M²; AV 6838, left I¹; CB 1914-L, left P⁴; CB 2560, left P₄; MU 6458, right M₁; UCMP 71976, left M¹; UCMP 71982, left M³.

Remarks

Arcius fuscus, along with A. lapparenti, is one of the most common species of the genus found in Europe. When it was first described by Russell et al. (Reference Russell, Louis and Savage1967), A. fuscus was thought to come just from its type locality, Mutigny (Marne, France). Arcius lapparenti was also described for the first time by Russell et al. (Reference Russell, Louis and Savage1967) and at that time was thought to come only from its type locality, Avenay (Marne, France). However, Aumont (Reference Aumont2003, Reference Aumont2004) argued these two species were sympatric across many sites in France. Aumont (Reference Aumont2003) also interpreted the Arcius fuscus sample from Russell et al. (Reference Russell, Louis and Savage1967) to be a mixture of both A. fuscus and A. lapparenti and considered the only two P₄ specimens (MU5627 and MU6294) found at Mutigny to belong to A. lapparenti, which is significant since P₄ is generally the most diagnostic tooth for paromomyids. Aumont (Reference Aumont2003) came to that conclusion after studying the large sample from Condé-en-Brie (Aisne, France), where there are two distinct P₄ sizes and morphs.

Russell et al. (Reference Russell, Louis and Savage1967) did not choose a P₄ as the holotype for Arcius fuscus but instead selected an M₃. They used differences in the inclination of the M₃ postvallid, and in the degree of lateral projection of the entoconid, to differentiate A. fuscus from A. lapparenti. However, after the study of the large collection from Condé-en-Brie, it seems as though there is too much variability in these characters for them to be considered diagnostic of species of Arcius. Although form of the M₃ hypoconulid is diagnostic for the genus as a whole, variability in this tooth position implies that distinguishing among species in the genus Arcius also requires consideration of characters from the premolars and other molars.

There are two genera of paromomyids that have three distinct crests on the postvallid of the P₄ of some species: Arcius and Paromomys. These crests are interpreted here as a metacristid (this term used in preference to premetacristid or postmetacristid because of the absence of a metaconid; in this case, ‘metacristid’ is used for a crest in the metaconid position), a postprotocristid, and a third crest that we are referring to here as a ‘prehypoflexid cristid.’ These crests can be distinguished in the following way: (1) the metacristid runs lingually from the protoconid to the entocristid or to the lingual aspect of the bottom of the postvallid (if no entocristid is present); (2) the postprotocristid runs buccally or centrally from the protoconid to the cristid obliqua; and (3) the ‘prehypoflexid cristid’ runs buccally from the protoconid to the hypoflexid. The main difference between these two taxa is that all three crests are in the same plane in Arcius fuscus, but the ‘prehypoflexid cristid’ is less well defined and more distally located in Paromomys (Fig. 7). Only two crests are visible on the postvallid in all other known paromomyid species.

Arcius lapparenti Russell, Louis, and Savage, Reference Russell, Louis and Savage1967

Figures 2.7, 3.5–3.8, 3.11, 3.12, 3.17–3.19, 6, 7.3, 7.6

1967 Phenacolemur lapparenti (in part) Reference Russell, Louis and SavageRussell et al., figs. 2k, 3a–c, e, f.

1984 Arcius lapparenti Reference GodinotGodinot, fig. 2c–f.

2003 Arcius lapparenti; Reference AumontAumont, pl. 1, figs. 1, 2, 5–7, pl. 2, figs. 1–8, pl. 3, figs. 1–3, pl. 4, figs. 1–3, 6–8, pl. 5, figs. 1, 2, 7–9, pl. 6, figs. 1–4, pl. 7, figs. 1–7, pl. 8, figs. 1, 2, pl. 9, pl. 10, figs. 1–5, pl. 11, figs. 1, 9, pl. 12, figs. 1–3, 5, 7–12, pl. 13, figs. 1, 2, 6–9, 11–13, pl. 14, figs. 1, 2, 4–8, pl. 15, figs. 1, 2, pl. 16, 17, pl. 18, figs. 3, 4.

2004 Arcius lapparenti; Reference AumontAumont, fig. 3.1–3.4, 3.10–3.13.

Holotype

AV 5849, left M₃.

Emended diagnosis (modified from Russell et al., Reference Russell, Louis and Savage1967 and Aumont, Reference Aumont2003)

Largest species of Arcius. Further differs from A. rougieri in having a more apically extended (taller) mediocone than anterocone on I¹, no expansion of the parastylar area of M³, and stronger mesial inflection of molar trigonids and lacking a stepped postvallid on M₁. Further differs from A. fuscus in lacking a ‘prehypoflexid cristid.’ Well-developed paraconid on M₁, but proportionally smaller relative to the metaconid than in A. fuscus. Further differs from A. zbyszewskii and A. ilerdensis n. sp. in having a cingulid on the buccal half of the distal aspect of M₁ that runs up to the hypoconulid. Further differs from A. zbyszewskii in not having a paraconid on M₃.

Occurrence

Avenay (type locality, PE V; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), Marne, France; Fournes (PE II; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), Hérault, France; Meudon (PE II; Hooker, Reference Hooker2015), Hauts-de-Seine, France; Pourcy (PE III [55.12 mya]; Hooker, Reference Hooker2010), Marne, France; Mutigny (PE IV; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), Marne, France; Gland (PE V; Aumont, Reference Aumont2003), Aisne, France; Sézanne (PE V; Aumont, Reference Aumont2003), Aisne, France; Condé-en-Brie (PE V; Hooker and Russell, Reference Hooker and Russell2012), Aisne, France; Venteuil (MP10; Aumont, Reference Aumont2003), Marne, France; St. Agnan (MP10; Hooker, Reference Hooker1996), Aisne, France; Prémontré (MP10 [48.4 mya]; Franzen, Reference Franzen2005), Aisne, France.

Materials

AV 1092-BN, right M²; CB 232-BN, left P⁴; AV 7707, right M₂; AV 7714, right I¹; AV 7716, right M₁; CB 3583, right M³; CB 4162, left P₄; CBX 2-Ph, I₁; AV 1306-Ph, right M¹.

Remarks

Along with A. fuscus, A. lapparenti is one of the most common species of this European genus. While Russell et al. (Reference Russell, Louis and Savage1967) described A. fuscus as appearing at Mutigny, A. lapparenti was argued by the same authors to have been present in Avenay, very close geographically to Mutigny.

When Aumont (Reference Aumont2003, Reference Aumont2004) suggested the sympatry of these two species, she also reported that the samples from the type localities of both species were mixed. In addition, the molariform morphology of Arcius fourth upper premolars led to misidentification in the original Russell et al. (Reference Russell, Louis and Savage1967) paper. AV 5775, reported in Russell et al. (Reference Russell, Louis and Savage1967) as an M¹ of A. lapparenti, is interpreted here to be a P⁴ based on its poorly developed postprotocrista, a feature of P⁴ in other species of Arcius. These two teeth can be distinguished mainly by the lack of a postprotocrista and by the slightly convex mesial aspect of the tooth on P⁴. Whereas relative size of the metacone to the paracone is often used to discriminate between M¹ and P⁴ in primate species, the paracone of the P⁴ is so close in size to the metacone in A. lapparenti that it is quite challenging to see a size difference between these two cusps.

Arcius zbyszewskii Estravís, Reference Estravís2000

Figures 2.8, 4

1981 Phenacolemur sp. Reference AntunesAntunes, p. 257.

1981 Phenacolemur cf. P. fuscus Reference Antunes and RussellAntunes and Russell, p. 1101.

2000 Arcius zbyszewskii Reference EstravísEstravís, p. 283.

2003 Arcius zbyszewskii; Reference AumontAumont, pl. 24.

2011 Arcius sp.; Reference Smith, Dupuis, Folie, Quesnel, Storme, Iacumin, Riveline, Missiaen, Ladevèze and YansSmith et al., fig. 19A, B.

Holotype

SV1-29, right M².

Emended diagnosis (modified from Estravís, Reference Estravís2000)

Smallest species of Arcius, approaching the size of A. rougieri. Distolingual basin of M³ somewhat expanded distally, more than in A. rougieri but less than in A. fuscus. Small but patent paraconid on M₁, stronger paraconid on M₃ than in other species of Arcius. The hypoconulid lobe on M₃ is enlarged, as typical of paromomyids, but is the smallest lobe in proportion to the rest of the tooth relative to any other paromomyid, with the exception of Paromomys farrandi.

Horizon and locality.—

Silveirinha (type locality, PE II; see Biostratigraphy), Baixo Mondego, Portugal; Sotteville-sur-Mer (PE II; Hooker, Reference Hooker2015), Normandy, France.

Biostratigraphy

Silveirinha has been considered to belong to MP 7 (PE I) (Estravís, Reference Estravís1992; López-Martínez et al., Reference López-Martínez, Smith, Peláez-Campomanes and Smith2006; Badiola et al., Reference Badiola, Checa, Cuesta, Quer, Hooker and Astibia2009; Smith et al., Reference Smith, Dupuis, Folie, Quesnel, Storme, Iacumin, Riveline, Missiaen, Ladevèze and Yans2011; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), but also to be very close in age to Sotteville-sur-Mer, probably slightly younger (Smith et al., Reference Smith, Dupuis, Folie, Quesnel, Storme, Iacumin, Riveline, Missiaen, Ladevèze and Yans2011; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012). Recently, Hooker (Reference Hooker2015) assigned Sotteville-sur-Mer to PE II, so Silveirinha is here considered to be PE II in age following his temporal framework.

Material

SV2-99, right P⁴; SV3-47, left M₃; SV3-125, right M₁; SV3-317, right M¹; SV3-565, right M³.

Remarks

Antunes (Reference Antunes1981) 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 (Reference Estravís2000) 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 (Reference Estravís2000) in that SV1-24 is interpreted as an M₁, 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. (Reference Smith, Dupuis, Folie, Quesnel, Storme, Iacumin, Riveline, Missiaen, Ladevèze and Yans2011) 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., Reference Smith, Dupuis, Folie, Quesnel, Storme, Iacumin, Riveline, Missiaen, Ladevèze and Yans2011) 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

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=1 mm.

1980 Phenacolemur cf. P. fuscus Reference Hooker and InsoleHooker and Insole, p. 38.

1996 Arcius fuscus Reference HookerHooker, p. 209.

1998 Arcius fuscus Reference HookerHooker, p. 449.

2003 Arcius lapparenti (in part) Reference AumontAumont, appendix A, tables 3, 4.

2010 Arcius lapparenti Reference HookerHooker, 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 metaconid than the protoconid on M₂ and M₃. Differs from A. zbyszewskii in not having a paraconid on M₃. Double entoconid present on M_3, 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, Reference Hooker1996).

Description

BMNH.M 44945 is the only specimen known of this species. It is composed of a partial dentary with an associated M₂ and M₃ 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, Reference Hooker2010). 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, Reference Silcox and Gunnell2008). 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 on M₃ (instead of the bilobed hypoconulid lobe seen in other paromomyids; Fig. 2).

Etymology

Named after Dr. Jeremy J. Hooker of the British Museum of 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 paromomyid to have ever been found in northwestern Europe. Hooker and Insole (Reference Hooker and Insole1980) tentatively reported BMNH.M 44945 as pertaining to Phenacolemur cf. P. fuscus, making this specimen the first known representative of Arcius outside continental Europe. Since then, the specific classification of this specimen has been problematic; it has been suggested to pertain to either A. fuscus (Hooker, Reference Hooker1996, Reference Hooker1998) or A. lapparenti (Aumont, Reference Aumont2003, Hooker, Reference Hooker2010). Hooker (Reference Hooker2010) noted that the English specimen has a small M₃ that falls within the size range of A. fuscus for that tooth. He also noted that the M₂, although not strictly falling within the size range for that tooth reported by Aumont (Reference Aumont2003, Reference Aumont2004), is closer in size to that of A. lapparenti than to that of A. fuscus. This suggests differences in terms of the relative proportions of these two teeth, but there are no specimens known for either A. lapparenti or A. fuscus in which the M₂ and M₃ are preserved in series to assess this possibility. Hooker (Reference Hooker2010) also pointed out the presence of two entoconids on the M₃, a trait never seen in paromomyids before. When considered alongside the contrasts newly noted here (listed in the diagnosis), it seems as though the best solution is to consider the English specimen to pertain to a new species. See also Table 2 for diagnostic comparisons.

Table 2

Diagnostic characters for Arcius Godinot, Reference Godinot1984 species. Question marks indicate nonobservable characters.

Arcius ilerdensis new species

Figure 9

Figure 9

Micro-CT scan images of Arcius ilerdensis n. sp. (1) IPS 57508, left M², occlusal view; (2) IPS 57510, lower right M₂, holotype, occlusal view; (3) IPS 57511, right M₃, occlusal view. Scale bar=1 mm..

2012 Arcius sp. Reference Marigó, Minwer-Barakat, Moyà-Solà and López-TorresMarigó et al.

Holotype

IPS 57510, right M₂.

Diagnosis

Larger M₂ than A. rougieri, larger M² than A. zbyszewskii, similar areas of M₂ to A. hookeri n. sp., and smaller M₂ than A. lapparenti. Absence of distal cingulid on M₂, unlike A. fuscus, A. lapparenti, and A. rougieri. Differs from all other species of Arcius in lacking a buccal cingulid on M₂ and having a short buccal cingulid on the M₃ trigonid. Paraconid present on M₂, but weakly expressed. Mesial inflection of the trigonid on M₂ weaker than any other species of Arcius, with the trigonid being completely vertical. Differs from all other species of Arcius, except A. hookeri n. sp., in having a taller metaconid than the protoconid on M₂ and M₃. Further differs from A. zbyszewskii in not having a paraconid on M₃.

Horizon and locality

Masia de l’Hereuet (MP10?), Lleida, Spain.

Biostratigraphy

Marigó et al. (Reference Marigó, Minwer-Barakat, Moyà-Solà and López-Torres2012) described this site as MP8+9, but most genera found in Masia de l’Hereuet usually appear in younger deposits (e.g., Eogliravus, MP10-13 [Escarguel, Reference Escarguel1999]; Lophiodon, MP 10 and later [Cuesta, Reference Cuesta1994], although it is present but rare in MP8+9 [Checa, Reference Checa1997]).

Description

Arcius ilerdensis n. sp. is represented only by four isolated teeth: two left M² (one of which is damaged; IPS57509), a right M₂, a right M₃. 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 on M₃ (instead of the bilobed hypoconulid lobe seen in other paromomyids; Fig. 2). The M² (IPS57508) has a strong postparacrista and premetacrista, with deep basins. A very small paraconule and metaconule are present, typical of paromomyids (Silcox and Gunnell, Reference Silcox and Gunnell2008). The distal margin of the tooth is straight, with a distolingual basin that is fairly expanded, but less so than in Phenacolemur, a typical Arcius trait. The buccal cingulum is broad. The parastylar region is expanded, forming a parastyle, but no metastyle is present. A precingulum is present, but short (Marigó et al., Reference Marigó, Minwer-Barakat, Moyà-Solà and López-Torres2012). The M₂ (IPS57510) exhibits a trigonid and talonid of similar width and a concave postvallid on the trigonid. The protoconid is lower than the metaconid, and the paraconid is reduced, as is typical of paromomyids (Silcox and Gunnell, Reference Silcox and Gunnell2008). On the talonid, the hypoconulid and the entoconid are poorly distinguishable (Marigó et al., Reference Marigó, Minwer-Barakat, Moyà-Solà and López-Torres2012). The M₃ (IPS57511) has a more buccally positioned cristid obliqua than on the M₂, with more clearly demarcated entoconid and hypoconid (Marigó et al., Reference Marigó, Minwer-Barakat, Moyà-Solà and López-Torres2012). It lacks a paraconid and has a very broad hypoconulid lobe, which are typical features of paromomyids (Silcox and Gunnell, Reference Silcox and Gunnell2008).

Etymology

From the Latin Ilerda (ancient name of the city of Lleida), in allusion to its province of origin.

Materials

IPS 57508, left M²; IPS 57511, right M₃.

Remarks

The Masia de l’Hereuet specimens were described by Marigó et al. (Reference Marigó, Minwer-Barakat, Moyà-Solà and López-Torres2012) as members of the genus Arcius, but those authors did not give them a specific ascription due to the scarcity of the material. Although we agree with Marigó et al. (Reference Marigó, Minwer-Barakat, Moyà-Solà and López-Torres2012) that it would be beneficial for more fossils to be recovered from that site, the few fossils known show enough distinctive traits to be discerned from other species.

Lower molars of paromomyid species that do not belong to the genus Arcius have trigonids that are strongly mesially inflected, while Arcius shows weak levels of inflection. However, Arcius ilerdensis has a uniquely vertical trigonid, even relative to other members of the genus. It is also uncommon among Arcius that the metaconid is clearly taller than the protoconid in lower molars, a feature also seen in A. hookeri n. sp. The lack of a distal cingulid on the buccal half of the distal aspect of the M_1-2 also contrasts with the more derived members of the genus (A. fuscus, A. lapparenti, and A. rougieri), suggesting that A. ilerdensis still retains somewhat primitive characters in the Arcius lineage.

Results of the phylogenetic analysis

In the tree from Analysis 1, Arcius is found to be monophyletic, with A. fuscus and A. lapparenti forming a clade. Arcius rougieri appears as the sister group to the A. fuscus-A. lapparenti clade. Arcius zbyszewskii is placed as the most basal European paromomyid, which agrees with the inference by Estravís (Reference Estravís2000) that A. zbyszewskii is a primitive lineage of European paromomyids, opening up the possibility of it being an ancestral species to all European paromomyids. In terms of the rest of paromomyid relationships, all of the trees from this paper agree with Bloch et al. (Reference Bloch, Boyer, Gingerich and Gunnell2002) and Aumont (Reference Aumont2003) that Phenacolemur and Ignacius are closely related and that Paromomys is a very primitive member of the family. However, the position of Acidomomys seems more contentious. Whereas Acidomomys makes a clade with Ignacius in our trees, Bloch et al. (Reference Bloch, Boyer, Gingerich and Gunnell2002) found Acidomomys to be the sister taxon of the clade Ignacius+Phenacolemur, and Aumont’s (Reference Aumont2003) analysis resulted in Acidomomys being the sister taxon to Arcius. Aumont (Reference Aumont2003) stated that the two characters that support the Acidomomys-Arcius clade are “l’absence de la p3” (absence of P₃) and “la presence d’une P3 uniradiculée” (presence of a single-rooted P³) (Aumont, Reference Aumont2003, p. 364). However, Acidomomys hebeticus does have a P₃ (Bloch et al., Reference Bloch, Boyer, Gingerich and Gunnell2002), and therefore that trait seems to be incorrectly coded in Aumont’s (Reference Aumont2003) matrix. In addition, the other character (presence of a single-rooted P³) seems to be misreported because P³ is coded in the matrix as being double rooted for both Acidomomys hebeticus and Arcius rougieri and not observable (i.e., question mark) in the rest of Arcius species. While it is clear that Acidomomys hebeticus had a double-rooted P³ (Bloch et al., Reference Bloch, Boyer, Gingerich and Gunnell2002), as coded, the number of roots for P³ in Arcius is difficult to assess. Only a small piece of the distobuccal aspect of the P³ of A. rougieri is preserved (Godinot, Reference Godinot1984), and the alveoli for that tooth are not preserved. It is, therefore, impossible to determine how many roots would have been present. In light of these considerations, we would argue that there is no support for an Acidomomys-Arcius clade, which Aumont (Reference Aumont2003) tentatively named as the tribe Arciini (incorrectly reported by Aumont [Reference Aumont2003, p. 364] as ‘Arciusini’). In addition, the fact that Acidomomys appears as the sister taxon to Arcius might explain why Aumont’s phylogeny differs from those reported here in that Arcius rougieri represents the most primitive lineage of European paromomyids in her analysis, instead of Arcius zbyszewskii as found here.

When Arcius hookeri n. sp. is included in the analysis (Analysis 2; Fig. 10.2), it also yields one tree unequivocally. Arcius hookeri is placed as the sister taxon of a clade that includes A. fuscus, A. lapparenti, and A. rougieri. This result supports the inference that the Arcius specimen from England pertains to a separate lineage and therefore should be named as a distinct species. The clade that includes A. hookeri, A. fuscus, A. lapparenti, and A. rougieri is supported by the loss of the paraconid on the M₃, which is clearly present in the more primitive A. zbyszewskii.

The addition of the paromomyid specimen from Sotteville-sur-Mer (Normandy, France) also results in a single most parsimonious tree (Analysis 3; Fig. 10.3). In this case, the Normandy specimen (MAM 6 STV 2008) forms a clade with Arcius zbyszewskii. This result is consistent with the morphological resemblance between the fossils from Portugal and the one from Normandy and supports the inference that all these specimens belong to the same species, A. zbyszewskii.

When including Arcius ilerdensis n. sp. in the analysis (Analysis 4), the clade A. fuscus-A. lapparenti-A. rougieri, present in the results from Analyses 1–3, collapses (Fig. 10.4). In three of the six trees recovered from this analysis (Fig. S1.1, S1.2, S1.6), A. ilerdensis falls out as being most closely related to A. rougieri. Arcius ilerdensis also appears in two other trees (Fig. S1.4, S1.5) as the sister group to the clade A. fuscus-A. lapparenti-A. rougieri, and as most closely related to A. lapparenti in another tree (Fig. S1.3).

When all species are included in the analysis (Analysis 5; Fig. 11), most Arcius lineages collapse, likely because of the large amounts of missing data for several taxa. However, it is important to note that the clade including A. fuscus and A. lapparenti still holds in this cladogram.

In terms of the other genera of paromomyids, our results show that the sister group of Arcius is not Acidomomys, as reported in Aumont (Reference Aumont2003), but the clade that includes Phenacolemur, Ignacius, and Acidomomys. The genus Acidomomys is most closely related to Ignacius. Paromomys and Edworthia appear as members of the most primitive lineage of paromomyids. These results also support the idea from Gunnell (Reference Gunnell1989) that the family Paromomyidae could be subdivided into two subfamilies: the Paromomyinae and the Phenacolemurinae. According to Gunnell (Reference Gunnell1989), based on the genera described at that time, paromomyines would only be composed of the genus Paromomys, and phenacolemurines would include Phenacolemur, Ignacius, and Elwynella. Here, Paromomyinae would be extended to include Paromomys and Edworthia, and Phenacolemurinae would include Phenacolemur, Ignacius, Arcius, and possibly Elwynella. However, to assess this question more fully, additional North American paromomyid species should be included in the analysis of the family.

Biogeographic implications

The results of the phylogenetic analyses, which consistently support the monophyly of Arcius, would suggest that there was only one dispersal event of paromomyids between North America and Europe. This dispersal would have been possible through land bridges between North America and Europe. The volcanic activity and regional uplift in eastern Greenland closed the Greenland Strait (or Denmark Strait) between Europe and Greenland, making it much narrower during the Paleocene and Eocene (Knox, Reference Knox1998). In addition, the English Channel was bridged, allowing dispersal between the British Isles and continental Europe, and in particular with France (King, Reference King2006).

One of the oldest occurrences of Arcius comes from the site of Sotteville-sur-Mer in Normandy, France. That region of Normandy could have been the entry point to continental Europe from the Greenland land bridge (Fig. 12), which would be consistent with finding the oldest representative of the genus in that area. However, Arcius zbyszewskii is also found at Silveirinha, which is inferred to be of nearly equivalent age to Sotteville-sur-Mer (i.e., PE II according to Hooker, Reference Hooker2015) and is quite distant in space. Iberia was isolated from continental Europe by the Carcassonne Strait already by the earliest Eocene (Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012), and the intercontinental dispersal of paromomyids is argued to have occurred during the PETM (Hooker, Reference Hooker2015), making the dispersal of A. zbyszewskii into southwestern Europe rather difficult. However, other sources (Plaziat, Reference Plaziat1981; Badiola et al., Reference Badiola, Checa, Cuesta, Quer, Hooker and Astibia2009) illustrate a land connection between Iberia and continental Europe during the early Eocene, suggesting that faunal dispersal from continental Europe into Iberia might have been possible by the earliest Eocene. In any case, the broad biogeographic range of Arcius zbyszewskii across western Europe suggests that this species might have undergone rapid dispersal across the continent in a short period of time. Even if the fossils from Silveirinha and Normandy did not belong to the same species, it would be one of the first cases of finding similar species in northern and southern Europe, which goes against the strong trend of north–south regionalism in this continent (Marandat, Reference Marandat1997).

Figure 12

Paleogeography of Western Europe and Greenland during the earliest Eocene and location of some selected paromomyid-bearing locations (modified from Eberle and Greenwood, Reference Eberle and Greenwood2012, fig. 3; Marandat et al., Reference Marandat, Adnet, Marivaux, Martinez, Vianey-Liaud and Tabuce2012, fig. 1; and Hooker, Reference Hooker2015, fig. 8). (1) Eureka Sound Group, Canada; (2) Abbey Wood, UK; (3) Sotteville-sur-mer, France; (4) Paris Basin, France; (5) Palette, France; (6) Masia de l’Hereuet, Spain; (7) Silveirinha, Portugal.

In terms of the origins of Arcius, the phylogenetic results unequivocally support the existence of a long ghost lineage. The oldest member of the Phenacolemur-Ignacius-Acidomomys clade is Ignacius cf. I. fremontensis from Torrejonian 2 (To2; Rose, Reference Rose1981; Silcox and Williamson, Reference Silcox and Williamson2012). Therefore, the Arcius lineage is inferred to have branched off prior to To2. The absence of Arcius-like species in the well-sampled western North American record during the Torrejonian, Tiffanian, and Clarkforkian suggests that the evolution of this lineage might have happened in more northern latitudes and closer to the land bridges that would later connect North America with Europe. In fact, undescribed Ignacius-like paromomyids have been reported from the Eocene of Ellesmere Island, in the Canadian Arctic (West and Dawson, Reference West and Dawson1977; Eberle and Greenwood, Reference Eberle and Greenwood2012), hinting at the potential of this region, and of other areas in the Greenland land bridge (e.g., the east coast of Greenland; Larsen et al., Reference Larsen, Bjerager, Nedkvitne, Olaussen and Preuss2001, Reference Larsen, Piasecki and Stemmerik2002), to rewrite our understanding of paromomyid evolution and biogeography.