Institutional acronyms and acronyms of paleontological collections.

OCP DEK/GE: Collections of the Office Chérifien des Phosphates, Khouribga, Morocco.

CPSGM, Collections Paléontologiques du Service Géologique du Maroc; deposited in the OCP Collections, Khouribga, Morocco.

MNHN.F: Collections of the Muséum National d'Histoire Naturelle (F: Paleontology), Paris, France.

MHNT PAL: Muséum National d'Histoire Naturelle of Toulouse, France, collection of Paleontology.

PM: Phosphate of Morocco, localities of the Ouled Abdoun Basin, Morocco.

TZT, THR and NTG2: material from localities of respectively Talazit, Adrar Mgorn 1 and N'Tagourt 2, Ouarzazate Basin, Morocco; collection of the University Montpellier II, France.

BD, locality of M'Bodione Dadere, Senegal, collections of the University Montpellier II, France.

Other abbreviations.

Primitive and derived states are abbreviated (p) and (d) in the text; they refer with respect to the generalized eutherian condition, except when mentioned (e.g., placental and paenungulate conditions). The primitive eutherian condition is represented by Cretaceous taxa such as Eomaia, Acristatherium, Asioryctes, Maelestes, Zalambdalestes, cimolestids, zhelestids, etc… (see Text S1, Part II, Taxa analyzed). These polarized states are established following our preliminary comparisons, as primary homologies for the matrix and before the cladistic analysis that results is the identification of secondary homologies (e.g., synapomorphies). The autapomorphic states are abbreviated (a).

Material.

The new material reported here allows the first description of the skull and upper dental morphology of Ocepeia daouiensis. Two partial skulls of Ocepeia daouiensis, MNHN.F PM45 and MNHN.F PM54, are known. They show important differences in size and general robustness related to intraspecific individual variations.

MNHN.F PM45, a relatively complete cranium, is the best preserved specimen. This is the only and best known mammal skull from the Paleocene of Arabo-Africa. It preserves most part of the cranium, except for a small part of left side (left maxillary, palatine, jugal), the premaxillae, the distal part of the right zygomatic arch (jugal) and the right maxillary tuberosity bearing M₃. MNHN.F PM45 belongs to a small individual with low sagittal crest. The preserved teeth (right P^3–4, M^1–2) are unworn and it is possible that M³ was still in crypt or just erupting in this specimen, indicating a young individual. However, the sutures are strongly fused and in many cases hardly distinct; together with the low sagittal crest, it might suggest a young adult female.

MNHN.F PM 54 corresponds to most of the rostrum of a cranium preserving the permanent cheek teeth (left and right C¹, P^2–4, M^1–3), the anteriormost part of the parietal, the nasal, the frontal, a fragment of left premaxillary (with a large incisor), most of the right maxillary and the palatine, and part of the left maxillary. It belongs to a larger individual than MNHN.F PM45. It is also characterized by a more robust general construction with much stronger sagittal and temporal crests, and a large canine, all features probably related to sexual dimorphism. These characters suggest that MNHN.F PM54 belongs to a large male adult, in contrast to the individual represented by MNHN.F PM45. The lower jaw PM41 fits better in occlusion with MNHN.F PM 54 than with MNHN.F PM45, which might indicate that it also belongs to a male (young individual).

General morphology.

Our reconstruction of the cranium of Ocepeia daouiensis is based on the specimen MNHN.F PM45 (Figs. 1–2, Fig. S1), with help of 3D digital modeling of tomographic image data. It should be noted that this specimen is most likely female individual with a more gracile morphology than MNHN.F PM54 (Fig. 3). The size of the skull is close to that of Meniscotherium chamense (estimated length 90 mm; width  = 65 mm).

The overall cranium shape is noticeably robust, with a broad outline in dorsal view (W/L = 70%). The most remarkable feature is that the rostrum is short and wide, whereas the cranial region (especially mesocranial region) is elongated. This is illustrated by a noticeably high ratio (82%) of the width of the snout at the canine level versus the preorbital length. This primate-like robust short and broad snout is autapomorphic in Ocepeia. The short rostrum might be related to the occurrence of enlarged upper incisors, as illustrated by specimen MNHN.F PM 54 for I². The face (rostrum) is about 1/3 the total length, and the frontal and nasal are short. A short frontal is known is some Paleocene taxa such as Meniscotherium (e.g., Gazin [44], pl. 2) and Pleuraspidotherium, but in Ocepeia the orbital process of the frontal is unusually reduced. For instance, the orbitosphenoid has an original long suture with the elongated parietal and only a small antero-dorsal suture with the frontal. The elongation of the braincase and the mesocranial region is illustrated by the long basisphenoids and pterygoids, by the choanae located very anterior relative to the skull length, by the very long parietal and sagittal crest, and by the anterior position of the pars cochlearis of the petrosal. The postorbital constriction of the skull is strong as illustrated especially in PM 54; the skull and braincase are narrowest near the mid skull length.

Another remarkable feature of the cranium of Ocepeia daouiensis, that is evidenced by the CT scan sections, is the extensive pneumatization of the bones such as the supraoccipital, the parietal, the basisphenoid, the basioccipital and the periotic. This is most striking for the supraoccipital which is considerably thickened and expanded below the parietal, and which shows extensive diploë (Fig. 4). The pars mastoidea of the petrosal, the basisphenoid and the basioccipital are also noticeably pneumatized. This is a probable autapomorphy of Ocepeia.

After correction of the post-mortem distortion (based on 3D digital model and drawings; see §4), the zygomatic arches appear not strong flared laterally (see reconstruction and Fig. S2), in contrast to tethytheres, Phosphatherium, and also Namatherium. There is no postorbital process, so that the orbit is poorly individualized and widely confluent with the temporal fossa. The tooth row does not extend behind the skull mid-length (it extends about 45% of skull length). The skull is low and the dorsal profile is long and straight, as in pantolestids and in contrast to the generalized eutherian construction. The sagittal crest is moderate (MNHN.F PM45) to strong (MNHN.F PM 54), but it does not form a high blade-like structure; the nuchal (lambdoid) crests are strong and salient dorsally and laterally.

Dorsal view.

The most striking feature is the short rostrum relative to the long cranial region. This is illustrated in dorsal view (Fig. 1) by a very short frontal and a contrastingly very long parietal that extends close to the orbit level and that bears a sagittal crest nearly as long as half the skull length. The anterior extension of the parietal in the skull roof resembles that of Pleuraspidotherium [7] and the primate Adapis; Pleuraspidotherium differs however by having much more developed orbito-temporal process of the frontal and by having the orbits that are more anterior with respect to the parietal; Adapis has also more anterior orbits, but it is closer to Ocepeia in the somewhat reduced orbito-temporal process of the frontal. The CT scan sections show that in fact the parietal extends anteriorly considerably above the frontal, on an estimated length of 10 mm.

The squamosal (pars squamosa) is also elongated. The premaxillary was probably short (see reconstruction). The nasal cavity seen in MNHN.F PM54 is high and wide, as in primitive proboscideans; this is probably a paenungulate trait. The nasals are broadened posteriorly. They do not penetrate deep in the frontals. The naso-frontal suture is transverse; it is located at the level between M¹ and M², as in the generalized eutherian condition. The maxillae are well-developed, with a high processus frontalis as in primitive proboscideans; the maxillo-nasal suture is long. The maxillary tuberosity was small and located close to the anterior rim of the orbit. The frontal is flat; it extends anteriorly from the temporal line, up to about 1 cm in front the maxillary tuberosity (M³ location).

The zygomatic process of the maxilla is well-developed laterally and it extends posteriorly on the medial part of the jugal up to the level of the beginning of the sagittal crest. The temporal fossa and zygomatic arches are longer than wide. The lacrimal is broken but its development can be inferred from surrounding preserved bones in MNHN.F PM45. The lacrimal forms the upper rim of the orbit with a large facial process (pars facialis), in the generalized eutherian condition. A slight bone inflation might indicate the presence of a lacrimal tubercle close to the jugal. The lacrimal has sutures with frontal and nasal dorsally. It is not clear if the lacrimal has a suture with the jugal or with the maxillary along the orbit rim. However, the jugal is narrowed in its anterior extremity (MNHN.F PM 45) as a short and flat bony blade above the zygomatic process of the maxillary. This suggests that the contact between the lacrimal and jugal was either slight or interrupted by a short intermediate extension of the maxillary onto the orbital rim; in other words, the jugal was slightly withdrawn posteriorly. The condition of Ocepeia is not far from that of basal paenungulates such as hyracoids where the lacrimal it is separated from the jugal by a narrow orbital process of the maxillary. The lacrimal foramen is present (MNHN.F PM 54) and located in the orbit above the maxillary foramen of the infraorbital canal. The infraorbital canal extends from the P³ to M² levels, above the tooth row.

The postorbital constriction is strong and maximal at the transverse level where the temporal crests meet and unite with the sagittal crest. The parietals are remarkably long, even longer than in Pleuraspidotherium and Hyopsodus. The fronto-parietal suture follows the temporal crest. The postorbital process of the frontal is strikingly absent, as in Hyopsodus and primitive eutherians. The temporal fossa is very large. The zygomatic arches are moderately expanded laterally. There are two discrete but distinct ridges on the posterior part of the parietals that diverges anteriorly on the skull roof from the sagittal crest near the junction with the nuchal crest; this original feature might be autapomorphic. The braincase is well-developed (e.g., wide transversely).

Lateral view.

The skull roof profile is very straight. The nasal and the muzzle are high. The maxilla extends high above the tooth row. The infraorbital foramen is much smaller than in Phosphatherium and in Eritherium. It is located not very high above P³, in the primitive eutherian condition. The orbit is noticeably posterior, with its anterior rim located at the level of M^2–3, as in Hyopsodus and in contrast to primitive proboscideans (Eritherium: P⁴) and even hyracoids (Dimaitherium: P⁴; Saghatherium: distal part of M²). The jugal extends below the orbit but does not contact the lacrimal, because of the presence of a short intermediate process of the maxillary. The maxillary participates in the zygomatic apophysis, as a short medial process extending 1,5 cm posteriorly. There is no submaxillary fossa. The zygomatic apophysis diverges low with respect to the dental row. There is a robust (wide) ventral postorbital process of the zygomatic arch, that is made mostly by the jugal; this is reminiscent of primitive proboscideans such as Numidotherium. The jugal extends anteriorly up to the level of M² parastyle. It forms a high and narrow vertical bony blade. The distal part of the zygomatic arch, broken in MNHN.F PM54, remains unknown in Ocepeia.

The parietal extends very anteriorly at the expense of the frontal. The area of the orbitotemporal fossa, medial to the zygomatic arch (sphenoid region), is not completely preserved, making difficult the identification of bones and their topographic relations. This is especially true of the orbital process of the frontal, the orbital process of the palatine, the orbitosphenoid, and the alisphenoid that is nearly entirely broken. The orbitosphenoid is small and located anteriorly, as in some primitive eutherians such as Uchkudukodon nessovi [45]; it extends dorsally above the postpalatine torus and the choana. The orbital process of the frontal is reduced in relation to the anterior development of the parietal; this is illustrated by a long parietal-orbitosphenoid suture and an anteriorly restricted orbitosphenoid-frontal suture. Among extant afrotherians, the condition of a parietal-orbitosphenoid suture associated with a reduced orbitosphenoid-frontal suture occurs in macroscelidids, and variably in Orycteropus [46]. Although broken, the alisphenoid was probably elongated, sharing a long suture with the parietal, in contrast for instance to Phosphatherium which has a long suture between the frontal and alisphenoid. Such extended relation of the parietal with at least the alisphenoid and possibly also with the orbitosphenoid is an original construction among the eutherians and the placentals (e.g., [46]).

At the base of the orbitosphenoid, five millimeters behind the choana and above it, there is a large semi-lunar and anteriorly oriented opening which might be either the optic foramen or the sphenorbital fissure (f. lacerus anterius), or both. Its large size would agree with a common opening for both the sphenorbital fissure and the optic foramen (and possibly also for the foramen rotundum) as in Phosphatherium; it resembles in shape that of Phosphatherium, but it is located much more anteriorly. According to Cox [46], the optic foramen is located anteriorly on the orbitosphenoid in most extant afrotherians, except in tenrecids. Among extant afrotherians, the fused sphenorbital fissure and optic foramen is a derived condition known in chrysochlorids [46]. A small subcircular foramen is located above the latter foramen, probably the ethmoidal foramen; it is located below an oblique bony crest corresponding to the posterior extension of the crista orbitotemporalis, as in Phosphatherium.

The distal part of basicranium is not elevated with respect to the anterior part of the skull (mesocranium), in contrast to Phosphatherium and other proboscideans. The squamosal dermal part is elongated, and shares long subhorizontal suture with the parietal. There is no contact between the squamosal and the frontal, as in primitive eutherians, and in contrast to Phosphatherium. The alisphenoid canal is probably absent in contrast to Phosphatherium; this is the primitive eutherian state. The postglenoid process is well-developed and higher than the posttympanic process of the squamosal which is closely appressed to the mastoid process. The external auditory meatus is widely opened ventrally (not compressed). The nuchal crests are well-developed and salient posteriorly behind the occiput. However, they are not so expanded posteriorly as in many primitive eutherians such as arctocyonids. The nuchal crests are formed by the supraoccipital which extends anteriorly for a short distance (3–5 mm).

Ventral view.

The palate is wide. The occlusal surface of the cheek tooth series appears relatively large (e.g. breadth extension) with respect to the palatal area, which emphasizes the prominence of the dentition in Ocepeia daouiensis and indicates this is a megadont mammal. This is related to the herbivorous diet and this is another primate (anthropoid) convergence. Comparison of predictive equations of body mass based on various dental measurement (length, width, area) shows that the teeth are especially enlarged transversely. This derived morphology is well distinctive from many artocyonids such as Tricentes and Arctocyon; it is possibly autapomorphic.

The tooth row remains restricted mesially on the skull; it does not extend behind the orbit and the middle skull length. The cheek tooth row is aligned closely parallel to the longitudinal axis. Although broken apart in the known material, the premaxillaries are reconstructed as short and wide, by reference to the occlusion of the lower (anterior) dentition. No palatine fenestra are present in the maxillary. The posterior palatine foramen (f. palatinus majus) is located in front of M². From this foramen, a well-developed palatine groove extends anteriorly up to the P³ level, similarly to primitive hyraxes; it housed the greater palatine nerve (V2) and blood vessels. The palatines are very short (comparable to the premaxillae) and posterior, in the primitive eutherian condition. They do not extend more anteriorly than M², in contrast to Eritherium (M¹, anterior part), and to Pleuraspidotherium (P³). They are even slightly more posterior than in Hyopsodus. The choana opens at mid-length level of M³. Its mesial rim is inflated as a lip-like structure indicating the presence of a postpalatine torus (attachment for tensor palate). The zygomatic process of the maxilla is well-developed laterally but short. It diverges between mid-length of M² and M³, and it extends as a thin a bony blade medial to the anterior part of the jugal, and well behind M³. The temporal fossa and zygomatic arches are wide laterally and also long. The zygomatic process of the squamosal does not diverge very posteriorly, but at the level of the basisphenoid-basioccipital suture (i.e., 27% of skull length).

The pterygoid processes are well-developed, very long (e.g., versus Pleuraspidotherium) and widely separated. Consequently, the pterygoid fossa is wide and large, similarly to Meniscotherium. The large development of this fossa, which accommodates the medial pterygoid muscle, is in agreement with the enlarged angle of the dentary in the species. Just behind the pterygoid processes, opens the small foramen ovale within a longitudinal groove at the basis of the pterygoid crest. It is located anterior to the basisphenoid-basioccipital suture and to the postglenoid process, in contrast to Pleuraspidotherium. The pterygoid, basisphenoid and basioccipital are elongated, resulting in the overall long basicranial region of Ocepeia. The basiphenoid is especially long (e.g., versus Hyopsodus); it extends posteriorly to the pterygoid process. The basioccipital area is large and long, although wider than long. The presphenoid and vomer are poorly distinct. However, the CT scans suggest that the presphenoid was short, high and pneumatized, and that the vomer is crossed by a large canal.

The glenoid surface of the squamosal is poorly excavated, more extended transversely than longitudinally and opened anteriorly which makes possible wide antero-posterior movements of the dentary in Ocepeia. This morphology, known in Paleogene hyracoids and proboscideans, is paenungulate-like. The glenoid fossa is located partly on the braincase, in contrast for instance to Arctocyon. The postglenoid process is tall, higher than in Phosphatherium. It is mainly posterior to the glenoid fossa. The postglenoid foramen opens medially to the high postglenoid process; it is more medial than in Phosphatherium, in the primitive eutherian condition seen in Daulestes, Maelestes, Zalambdalestes [47]; contra [37]). The external auditory meatus is large, with a broadly concave suprameatal surface of the squamosal for the auditory tube. The posttympanic process of the squamosal is present but small. It is much smaller and lower than the postglenoid process, in contrast to Phosphatherium. It is widely separated from the paroccipital apophysis by the elongated mastoid region that is exposed ventrally (proboscidean feature).

The basioccipital is convex with a ventrally salient median keel which is also seen in several other condylarth-like taxa such as Meniscotherium and Hyoposodus. The median crest vanishes before joining the occipital condyles, but this is probably related to post-mortem damage. The hypoglossal foramen houses two small openings; it is smaller than the jugular foramen, and it is located more posteriorly from the jugular foramen than in Phosphatherium; it is 2.5 mm anterior to the occipital condyle. This eutherian-like construction differs from advanced proboscideans in which the two foramens tend to fuse. The hypoglossal foramen has an oval shape with a long axis parallel to the petrosal-basioccipital suture. The paroccipital process is low and located very posterior (behind the hypoglossal foramen and foramen magnum), as in Phosphatherium.

The braincase is wide, especially caudally (up to the alisphenoid-squamosal suture level), in contrast for instance to the arctocyonids and phenacodontids.

Periotic (Figs. 5–6). Both the right and left petrosals are present in MNHN.F PM45, although the structural details in ventral view are poorly preserved. The petrosal of Ocepeia is large and especially long: 1) the pars cochlearis is small and very anterior with a strong rostral tympanic process extending to the level of the anterior margin of the postglenoid process; 2) the pars mastoidea is very long and widely exposed ventrally between posttympanic (squamosal) and paroccipital processes (both separated from about 10 mm). The enlarged pars mastoidea is a remarkable feature of Ocepeia that is shared with proboscideans. The pars cochlearis and promontorium are ovoid, long, and slightly oblique with respect to the longitudinal axis. The promontorium extends posteriorly to the postglenoid process level, and it is more ventral than the basioccipital. It is inflated and located anteriorly. Its almond shape resembles that of Hyopsodus (p). The promontorium has a smooth surface and it bears a stout ridge that is oblique postero-laterally. This ridge is bounded antero-laterally by a sulcus probably for the internal carotid artery (d). The promontorium sulcus for stapedial artery is absent. The rostral tympanic process of the petrosal is salient anteriorly to the promontorium. The epitympanic wing of the periotic medial to the promontorium is absent (p). The fenestra vestibuli (oval window) is very small (area  = 0.312 mm²), and much smaller than the fenestra cochleae. The size of the fenestra vestibuli of Ocepeia daouiensis, and correlatively of its stapes, is well below the regression line for fenestra vestibuli area versus body mass in modern mammals [48]. In fact, the small size of the fenestra vestibuli of Ocepeia daouiensis is in close proportion to Numidotherium koholense [49]. This is a possible derived feature shared with paenungulates, although sirenians show an early divergent trend to hypertrophy of the ear ossicles. It should be noted that the small size of the f. vestibuli correlates with that of the promontorium and inner ear (see below). The fenestra vestibuli is elliptical with a high stapedial ratio (2.05) which is generalized in placentals [42], [50].

The fenestra cochleae (round window) is located postero-medial to the fenestra vestibuli, in the eutherian state. It is larger than the fenestra vestibuli, but smaller than the jugular foramen. It is vertical and elongated transversely (p), and it faces posteriorly as in Phosphatherium and the primitive eutherian or placental condition. The presence of the cochlear canaliculus (aquaeductus cochleae) is evidenced by the CT scan observations. It opens, in the primitive condition, ventro-medially in the jugular fossa, below and more medially than the cochlear fenestra; this differs from Phosphatherium where it is more ventral and anterior. This canal is unusually large in section and its opening is dilated transversely. The stylomastoid foramen for n. faciale (VII) is distinct postero-laterally to the fenestra cochleae. The jugular foramen (f. lacerus posterius for glossopharyngeal nerve, IX) is the largest foramen of the basicranium; it is located just behind the promontorium. Its shape is oval with an oblique postero-lateral to antero-medial long axis. The caudal tympanic process of the petrosal is well-developed, which is generalized in eutherians according to McPhee [51]. However, a large and inflated caudal tympanic process is a trait of the Paenungulata, known for instance in Phosphatherium and Numidotherium.

The tympanohyal is large. The tegmen tympani is remarkably inflated and pneumatized; it forms a large and robust barrel-like bony structure located antero-lateral to the promontorium, and it partially covers the epitympanic recess. An inflated tegmen tympani is a derived feature among Eutheria [51], [52], [53]. It was considered as an ungulate [53] and a tethytherian feature [54], [55]. The barrel-vault like shape of the tegmen tympani is known in tethytheres. The hyperinflated tegmen tympani is known in Meniscotherium, Mesonyx, anthracotheriids, hippopotamids and cetaceans [56], [57]. The tympanohyal is large. No trace of an ossified tympanic bulla is seen in MNHN.F PM45.

In dorsal view (CT scan 3D model: Fig. 6C, Video S2), the internal meatus and the subarcuate fossa are well distinct and comparable in size. The subarcuate fossa is moderately large and deep. The internal meatus shows two distinct openings separated by a short crista transversa: the f. acusticum superius for the facial nerve (VII), and the f. acusticum inferius for the vestibulo-cochlear nerve (VIII). The f. acusticum inferius is posterior and circular, and it shows distinct link with the cochlea (cochlear canal) close to f. cochleae. The f. acusticum superius is anterior and elongated (bean-like outline). In dorsal to dorso-lateral view, there is a large opening that extends medially as a canal in the inflated tegmen tympani and that might correspond to the foramen for the ramus superior of the stapedial artery. Its opening is as large as that of the internal acoustic meatus.

Inner ear (Figs. 6B, 7). The endocast of the bony labyrinth of Ocepeia daouiensis was successfully reconstructed with the help of the computed X-ray micro-tomography analysis of the skull MNHN.F PM45. We reconstructed the whole inner ear endocast of the left petrosal (Fig. 6B), as well as also the semicircular canals of the right petrosal. The perfect alignment of the semicircular canals of the right and left petrosal in lateral view indicates that the bony labyrinth is well preserved and not distorted in the skull MNHN.F PM45. The detailed description of the bony labyrinth system of Ocepeia daouiensis will be presented separately with a functional analysis (ms in prep); here we report a comparative description of the main morphological traits of the inner ear that are of systematic and phylogenetic values. The number of coils of the cochlea measured following method of West [43] is 2.12 (765°). Most placentals have at least 2 turns, with some exceptions such as erinaceids and some sirenians [58]; Cretaceous eutherians are plesiomorphic with fewer turns (1 to 1.5 turns) than crown placentals [58], [59]. Numidotherium has a smaller number of turns than Ocepeia according to Court [60] (1.5) and Benoit et al. [61] (1.62). The spiral plane of the cochlea is much more oblique antero-dorsally with respect to the horizontal plane (50–60°) than in Mesozoic eutherian mammals. The coiling is subplanar as in the primitive eutherian condition seen for instance in the zhelestids [59]. In the coiling plane, the spiral turns are well separated from each other as in primitive Late Cretaceous eutherians such as zhelestids [59]. The ventral coil has a diameter comparable to the dorsal coil, and the apex of the cochlear canal (helecotrema) is large. This is distinct from Notostylops, but of unknown polarity among eutherians. The secondary bony spiral lamina is present on the basal coil (340 to 360° from f. vestibuli). In several late Cretaceous eutherians [58] and in Notostylops [50], it is primitively restricted to half of the basal coil. However, the secondary bony spiral lamina extends to the whole basal coil in some other primitive Mesozoic eutherians such as zhelestids, as in Ocepeia. The anterior semicircular canal is the larger semicircular canal as in most eutherians. The posterior segment of the lateral semi-circular canal is coalescent with the posterior ampula of the posterior semi-circular canal on a short distance from the vestibule. However, the lateral semi-circular canal separates from the posterior ampula before its ends, and the lumen of both lateral semicircular canal and posterior semicircular canal PSC remains distinct, which indicates that there is no true secondary crus commune. The absence of a secondary crus commune is a generalized condition shared by crown placentals in contrast to stem eutherians that have a secondary crus commune [59]. However, it is noticeable that several placentals retain a secondary crus commune, such as the aardvark, some carnivorans, the primitive macroscelidean Chambius [61], and the primitive proboscidean Numidotherium [62]. The crus commune of the anterior semicircular canal and posterior semicircular canal is less long than in generalized eutherians such as zhelestids and Zalambdalestes [59].

Occipital view.

The supraoccipital is well-developed. Transverse and longitudinal CT sections show that it is very thickened and pneumatized (Fig. 4). It extends anteriorly below the parietal, not far from the level of the basisphenoid-basioccipital suture. The foramen magnum is large, comparable in size to “condylarths” such as Hyopsodus; it is wider than high. The occipital condyles are salient posteriorly, and they join ventrally as in Meniscotherium (and Zalambdalestes). The nuchal crest is salient posteriorly all around the occiput; it does not form the peculiar posterior upper expansion seen in many eutherians and primitive placentals such as arctocyonids, pleuraspidotheriids, pantodonts, pantolestids and others. Below the nuchal crest, the occiput appears slightly inclined anteriorly (eutherian trait).

The occipital surface is depressed between the nuchal crest and the condyles. There is a small condylar foramen. The paroccipital process is small. There is no mastoid exposure in the occipital side (amastoid structure).

Skull measurements: see Table 1.

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Table 1. Ocepeia daouiensis, skull measurements, specimens MNHN.F PM45 and PM54 (mm).

https://doi.org/10.1371/journal.pone.0089739.t001

Incisors (Fig. 8).

A broken piece of left premaxillary of the specimen MNHN.F PM54 bears an enlarged root belonging to a broken incisor that lacks the crown (Fig. 8). The root is hypertrophied and compressed laterally; it is larger than the canine root (L = 7 mm). It indicates an enlarged incisor that is identified as a left I² (e.g., no trace symphysis in associated preserved bone). The crown was probably procumbent. It is inferred that this is the larger upper incisor as in early proboscideans such as Numidotherium and Moeritherium.

As in the lower dentition known in O. daouiensis [26], the third upper incisor was probably very small and vestigial.

Canine (Figs. 3, 10).

The canine preserved in MNHN.F PM54 is separated from the I² by a small diastema. The canine is stout, low, but sharp. The root was inflated and larger than the crown. The crown is convex laterally and concave lingually. It bears a small anterior crest and a longer (higher) distal crest. A faint trace of lingual cingulum is present, but it is much smaller than in the lower canine which is more anthropoid-like in this respect.

Premolars (Figs. 9–10).

The two first premolars are absent, as in the lower dentition. They are not replaced by a significant diastema in the tooth row: P³ is very close to C¹.

P³ and P⁴ are sub-molarized with a developed protocone, three roots, and a more or less transverse occlusal outline. As a consequence, the whole cheek dentition is rather homodont.

The labial cingulum is inflated, especially at anterior and distal ends. Traces of stylar cusps are present, most distinctly as a metastyle, and more variably as a D cusp. The paracone is the main labial cusp: it is large, low and nearly as wide as long. It bears long V-shaped shearing anterior and posterior crests that are underlined by a distinct wear facet. Shearing function with trigonid of occlusal relative teeth P^3-4 was enhanced in Ocepeia. There is no trace of metacone. The protocone is much smaller than the paracone. It bears symmetric and well-developed pre- and post-protocristae that enclose a well delimited protofossa. The preprotocrista joins a very small parastyle; the postprotocrista, well distinct in both P³ and P⁴, joins the postparacrista. One or more variable cuspules are inflated on the postprotocrista behind the protocone. Their position is reminiscent of the molar metaconule. A small but distinct transverse crest crosses the protofossa in its anterior part and links the internal flank of paracone and protocone. The lingual flank of the protocone is convex. A very slight enamel bulging of the crown below and behind the protocone of P⁴ suggests trace of postcingulum.

P³ and P⁴ are very similar in morphology, but the former is slightly smaller, less transverse and has a smaller protocone.

Molars (Figs. 9–10).

M^1-3 are bunoselenodont, with a W-like (selenodont) ectoloph that is linked to an inflated mesostyle. They lack a hypocone.

The styles are remarkably well-developed and inflated, and located labial to paracone and metacone. Parastyle and mesostyle are the larger styles, they form inflated cusps on the labial side of the crown. Additional small stylar crests and cuspules are variably present in front of the paracone and metacone (e.g., D cusp). The stylar shelf is present but not so wide. The paracone and metacone are low and linked by a dilambdodont ectoloph that is typically joined to the large mesostyle. The two arms of the centrocrista are united labially just before joining the mesostyle.

The preparacrista joins the parastyle; the postmetacrista, well-developed, joins the metastyle. The labial flank of the paracone and metacone is convex. The paracone is larger than the metacone, and more so from M¹ to M³. The protocone is remarkably low and expanded mesio-distally; its crests are widely divergent. Its labial flank is convex. The protofossa is vast, and especially long, and shallow. A very short transverse crest is present at the base of the lingual flank of the paracone. The preprotocrista joins the parastyle below the preparacrista. The postmetacrista joins the base of the postmetacrista below the metacone. The paracingulum is much more developed than the metacingulum. A metaconule is more or less inflated on the postprotocrista where it is salient disto-lingually; it is more developed on M¹ than on M². The metaconule is doubled lingually by a small additional conular cuspule. There is also a small paraconule on the preprotocrista; it is located more labially than the metaconule. The lingual flank of the protocone is strongly canted labially. A more or less distinct trace of continuous lingual cingulum is present on M^1–3, around the protocone, but it lacks a hypocone. Three roots are present, including in M³.

The selenodont pattern of the ectoloph is functionally underlined by well-developed related semi-lunar shearing facets such as wear facets 3 and 4, 1a and 1b (nomenclature of Crompton [63]).

The occlusal outline is more or less square in M¹, and wider transversely in M² and M³. The molar size increases slightly from M¹ to M³.

Dental measurements: see Tables 2–3.

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Table 2. Ocepeia daouiensis, dimensions of upper dentition: upper teeth (mm).

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Table 3. Ocepeia daouiensis, dimensions of upper dentition: Length (L) of upper tooth row (mm); r: right; l: left.

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Body mass estimates (Table 11).

Estimates based on the length of M1-3 cannot be calculated because none of the known specimens of O. grandis preserves well the molar series. The best body mass estimate of Ocepeia grandis based on available material (lower dentition) is slightly more than ten kilograms (Table 11). O. grandis was indeed close in size to Phosphatherium escuilliei, and much larger than O. daouiensis.

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Table 11. Body mass estimates of Ocepeia grandis n. sp. (in grammes; *estimation  =  minimal size).

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Common nodes and topological patterns.

There are several recurrent nodes that are shared among all resulting trees from our different analyses. We discuss these successively from the base to the higher part of the trees.

Todralestes always has the basalmost position, as sister-group of all other taxa except the eutherian outgroup. It is indeed excluded from placentals, and should be considered as a stem eutherian as for the Zhelestidae [71]. However, it should be noted that Todralestes variabilis remains poorly known (45% of characters unknown in matrix), being documented only by cheek teeth.

Zhelestidae, Protungulatum, and Arctocyonidae have a basal position in the trees that is not fixed relative to each other. However, the Zhelestidae is generally the most basal clade.

Ocepeia has a basal position in the trees, outside the Paenungulata, “Altungulata” (lophodont ungulates) and “Taxeopoda”. It most frequently belongs to a basal afrotherian clade together with Potamogale, Ptolemaia, Orycteropus, corresponding to the molecular-based clade Afroinsectiphilia minus Macroscelidea, although in some case (e.g., unordered analysis) it is a more derived branch (sister group of all other taxa). Relationships with Afroinsectiphilia afrotherians result from the analysis of the whole matrix and from partitioned analysis restricted to dental features, which indicates that the phylogenetic signal is mostly dental. Bremer support for this node (Afroinsectiphilia and Ocepeia) is rather low. Within Afroinsectiphilia, Ocepeia joins preferentially Potamogale (e.g., 148-1, postorbital process reduced), and Ptolemaia groups with Orycteropus in many of our analyses (ordered, unordered, and step matrix; Text S1, part III). The clade (Ptolemaia, Orycteropus), that is well supported by 3 exclusive synapomorphies (*27-2, *50-2, *116-2; ordered analysis), agrees with the conclusions of Simons & Gingerich [72] and Seiffert [73].

In the higher part of the MPTs obtained in this work, the main clades are stable and robust; in nearly all trees, we recover the following clades: (Phenacodonta (Teilhardimys, Macroscelidea, (Perissodactyla, Paenungulata))). This node is supported by 3 exclusive synapomorphies of which the most noticeable are the upper molars with lingual root enlarged and bearing a sulcus, and with developed interloph. Upper molar with incipient lophodonty (89-1) appears at this node or at the next node (Teilhardimys, Macroscelidea, (Perissodactyla, Paenungulata)).

The relative position of Teilhardimys and Macroscelidea to each other (i.e., same clade or not) changes in several trees. In the partitioned analysis restricted to skull features (Text S1, part III, Cladograms 7-8), the Macroscelidea groups with basal afrotherians, as in the molecular-based Afroinsectiphilia hypothesis.

Following Gheerbrant et al. [37] and Gheerbrant [69], we recover the sister-group relationships of Perissodactyla (usually allied to Radinskya) and Paenungulata, that corresponds to the taxon “Altungulata”. This is a very robust node in our analysis (ordered analysis: 5 exclusive synapomorphies: *25-2, *35-1, *42-2, *49-2; 4 homoplastic synapomorphies: 11-0, 16-1, 52-1, 90-2). Consequently, it would refute the monophyly of the clades Afrotheria and Laurasiatheria. It is supported especially by the lophodonty (*25-2, *35-1, *42-2) and the enlarged M₃ (*49-2). However, the latter feature implies unlikely reversal in Eritherium, and the lophodonty is most likely convergent in Perissodactyla and Paenungulata, as indicated by detailed structural traits (see below).We suggest, following Gheerbrant [69], that our cladistic analysis remains unable to detect convergence of lophodonty in Laurasian and African “ungulates” because of fossil gaps, i.e. because of unknown early structural steps in its evolution. We lack data especially on the dental ancestral morphotype of perissodactyls, but also on some questionable paenungulates such as Phenacolophus, Minchenella, and anthracobunids. Phenacodonts are plesiomorphic with a low stem position and do not help to solve this question in the analysis. Only the partitioned analysis restricted to cranial features (ordered analysis; Text S1, part III, Cladograms 7-8) does not recover sister-group relationships of Perissodactyla and Paenungulata. This confirms that the signal for “Altungulata” here is mostly dental (e.g., lophodonty).

The node Paenungulata occurs in all our trees with identical taxonomic content. However, 1) Bremer supports are generally low, except in unordered analysis (Fig. 21; Text S1, III, Cladogram 1), 2) internal (inter-ordinal) topology varies strongly. In the ordered analysis (Fig. 21), the clade is supported by three exclusive synapomorphies (*61-1: coronoid foramen present; *115-1: M³ with one hypocone root; *135-2: orbit above P4-M1) and 9 homoplastic synapomorphies of which the best ones (RI>75) are lower molars with loph transverse (26-2) and with large lingual cusps (28-1), and amastoidy (161-1). The presence of a coronoid foramen, unknown in Ocepeia, was recently evidenced in macroscelideans [74]. The amastoidy is known in Ocepeia, as well as the selenodont ectoloph (101-2).

The clade Tethytheria is generally recovered at least for the crown groups Sirenia and Proboscidea, but the position of stem taxa such as Embrithopoda, Anthracobunia, Desmostylia is variable, and the Bremer supports are low. Tethytheria is not recovered only in partitioned analysis with step matrix restricted to dental features (Text S1, part III, Cladogram 11), in which Proboscidea joins the Hyracoidea.

The clade Proboscidea is one of the most stable in all our analyses. It is supported by a strong Bremer Index.

Embrithopoda. A clade (Minchenella (Phenacolophus (Embrithopoda))) is very stable (several analyses, see Text S1). It is supported by 10 homoplastic features in the ordered analysis (Fig. 22). However, it should be noted that a recent analysis of dental enamel microstructure argues against close relationships of Phenacolophus and Embrithopoda [77]. We concur, and suggest that the cladistic relationships of Phenacolophus recovered here results from unresolved significant dental convergences, in the same way as between perissodactyls and paenungulates. This is probably related to our poor knowledge of Phenacolophus (59% of its characters unknown in matrix) and Minchenella (50% of its characters unknown in matrix) which are known only by dental specimens and are among the less known analysed taxa. Actually, it should be emphasized that even the described dental material of Phenacolophus [78] is very poorly preserved – a point which is widely underestimated in current phylogenetic discussions; for instance the structural dental homology remains widely to check. Embrithopods are usually sister-group of Sirenia as recovered by Seiffert [73], except in partitioned analysis (ordered) restricted to dental traits in which they are stem tethytheres (Text S1, part III, Cladograms 5-6).

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Figure 22. Relationships of Ocepeia.

Cladogram resulting from parsimony analysis with TNT version 1.1 program of modified matrix of Gheerbrant [68] (Text S1, parts I-II). 152 features are processed as ordered in contrast to Figure 21 (Text S1, part I). Strict consensus of 2 trees resulting from the “traditional search” command (Text S1, part III, Cladogram 3). Tree lengths: 665. Retention index: 54.6. Consistency Index: 37. In Figure 22b, the black and open white circles represent respectively strict and homoplasic synapomorphies. This is our reference topology for our discussion of the relationships of Ocepeia. In this analysis Ocepeia is also strongly autapomorphic.

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The different topologies obtained.

• Unordered analysis (Fig. 21; Text S1, part III, Cladograms 1-2). The analysis of the matrix with all features unordered provides a single resolved tree, which is the shortest tree (length 596, RI 53.6, CI 40.8) obtained in all our analyses. It differs from most other analyses in the interchanged position of Hyopsodus and Ocepeia: the former joins the primitive afrotherian clade (afroinsectiphilians), and the latter is more derived as sister group of all other taxa that are characterized by incipient lophodonty. The implied weighting analysis does not change the topology. In this analysis, Ocepeia is by far the most autapomorphic with 6 exclusive autapomorphies and 35 homoplastic traits.
• Ordered analysis (Fig. 22; Text S1, part III, Cladogram 3). The analysis of the matrix with 152 ordered features provides only 2 trees which differ in the relative position of Protungulatum and Arctocyonidae. The consensus tree (Length 665, RI 54.6, CI 37) illustrated Figure 22 is our reference topology for our discussion of the relationships of Ocepeia. Ocepeia is the sister group of Potamogale, and both are sister group of the clade (Ptolemaia, Orycteropus), corresponding to the clade Afroinsectiphilia (minus Macroscelidea). Analysis with standard “implied weighting” command provides a single tree that fixes relative position of Protungulatum and Arctocyonidae (Text S1, part III, Cladogram 4). In this analysis Ocepeia is strongly autapomorphic, as it is in the unordered analysis (36 homoplastic states, 5 exclusive autapomorphies).
• The partitioned ordered analysis (Text S1, part III, Cladogram 5) restricted to dental features recovers similar topology than in the unpartitioned analysis (Fig. 22; e.g. Ocepeia  =  basal afrotherian) except in the derived position of Orycteropus that clusters with Proboscidea, probably as the result of the optimization of many features (50% of unknown data in Orycteropus; see Table S1). The partitioned ordered analysis restricted to skull features and to taxa only documented by skull features (Text S1, III, Cladogram 8) recovers two main clades: basal afrotherians (Potamogale, Orycteropus and Macroscelidea, i.e. clade Afroinsectiphilia) and Paenungulates (but including Zhelestidae). The position of Ocepeia is surprisingly not resolved in the partitioned ordered analysis restricted to the skull. Similar results are obtained with the TNT “implied weighting” command.
• Ordered analysis with step matrix (Table S4 and Text S1, part III, Cladograms 9-12). In this analysis we ordered the state transformation according to the most likely successive structural steps, and we excluded unlikely reversals (e.g., reappearance of teeth; see Table S3). The analysis recovers 8 trees of which the consensus agrees (Text S1, part III, Cladogram 9) with the ordered analysis (Fig. 22; Text S1, part III, Cladogram 3). Length, retention and consistency indices of trees from step matrix analysis (Text S1, part III, Cladogram 9) are very close to the ordered analysis. In this analysis, Proboscidea are supported by a strong Bremer Index, and Ocepeia clusters with basal afrotherians. “Implied weighting” command provides a single tree (Text S1, part III, Cladogram 10) which differs in the interchanged position of Hyopsodus and Ocepeia, the latter which is excluded from basal afrotherians. In this analysis Ocepeia is much less autapomorphic, with 28 autapomophic traits.
• The partitioned analysis including ordered features and step matrix (Text S1, part III, Cladograms 11-12) shows that dental features yield the most significant phylogenetic signal: 1) dental features provide one single tree very similar to the ordered analysis, except for the position of Orycteropus that surprisingly joins Proboscidea (as in analysis without step matrix); 2) skull features provide an unresolved basal polytomy (Text S1, part III, Cladogram 12).
• Constrained analysis for paenungulates relationships of Ocepeia (Fig. 23; Text S1, part III, Cladogram 13). We constrained the analysis to cluster Ocepeia with Paenungulata by increasing the weight of features shared with paenungulates (Tables 6, 7, 12). The most important shared characters with paenungulates that impacts topology in the cladistic analysis are characters related to the selenodont pattern of upper molars (ectoloph dilambdodont and joined to a developed mesostyle: characters 98, 99, 101). Other shared features (see Table 12), such as the occurrence of an entolophid (34-1), do not support cladistic relationships with paenungulates at similar weight cost. Constrained analysis with weighted upper molar selenodonty results in only two trees, the consensus of which is well resolved (Fig. 23; Text S1, part III, Cladogram 13) and significantly longer than in other (unweighted) analyses (RI = 53.2, CI = 37.5, Length = 767). Bremer supports in resulting trees are higher than in other analyses, including for nodes among Paenungulata (e.g., Proboscidea, Tethytheria). In this topology the node Paenungulata (node 23) is supported by 5 exclusive synapomorphies (*40-3, *42-3, *61-1, *126-1, *161-1 and 4 homoplastic features (28-1, 37-0, 130-1, 152-1). However, the node is paradoxically not supported by features related to the selenodonty, following our hypothesis; these features support in fact the more internal paeungulate node 31 ((Phenacolophus, Embrithopoda) (Hyracoidea (Ocepeia, Orycteropus))). In these trees Ocepeia is noticeably less autapomophic (16 homoplasies; 2 exclusive states, including: 118-2, extensive pneumatization; 122-1, palatine posterior to M¹). Within Paenungulata, Ocepeia has a nested derived position rather than a stem position; it clusters with Orycteropus, both as sister group of Hyracoidea (with good Bremer support). We reject this hypothesis of the derived position of Ocepeia within Paenungulata because it admits unlikely reversal of the hypocone that is typically absent in Ocepeia. This topology implies other noticeable reversals in Ocepeia. A stem position of Ocepeia to Paenungulata would be actually more parsimonious for several features at the node of crown Paenungulata (e.g. coronoid foramen, frontal-maxilla contact, lower molars without entoconulid, and with hypoconulid low and distal).
• Finally, we analyzed the position of Ocepeia in the exclusive context of the afrotherian relationships (i.e., relationships within the monophyletic clade Afrotheria); in this way we excluded from the analysis putative laurasiatherian ungulates such as Perissodactyla, Radinskya, Phenacodonta, and even Hyopsodus. In all obtained trees, Ocepeia keeps the same outgroup position with respect to Macroscelidea and Paenungulata, in the same clade with Potamogale and Orycteropus (Afroinsectiphilia). This is especially related to the absence of hypocone and lophodonty in Ocepeia.

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Figure 23. Relationships of Ocepeia.

Cladogram resulting from parsimony analysis with TNT version 1.1 program of modified matrix of Gheerbrant [68] (Text S1, parts I-II). This tree results from an analysis in which Ocepeia is constrained to cluster with paenungulates by increasing the weight of characters shared with paenungulates (Tables 6, 7, 12), i.e., characters 98, 99, 101 that are directly related to the selenodonty. Consensus of two trees (Text S1, part III, Cladogram 13). This tree is well resolved but significantly longer than trees resulting from other analyses (Figs. 21, 22). Tree length: 767; retention index: 53.2; consistency index: 37.5. The black and open white circles represent respectively strict and homoplasic synapomorphies; see Text S1, part III, for description of characters. In this tree Ocepeia is noticeably less autapomophic. See text for further comments.

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Table 12. Cladistic interpretation of shared characters of Ocepeia with ungulates and paenungulates (ordered analysis, Fig. 21).

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Relationships with Placentalia.

Whereas Todralestes is a stem eutherian, several features indicate unequivocal relationships of Ocepeia with crown placentals. This is especially true of the inner ear morphology (e.g., cochlear canal with two full turns), as identified from the CT scan study.

Relationships with Afrotheria.

The most striking result of the cladistic analysis of Ocepeia is its relationships with Afrotheria, and especially its basal position within Afrotheria. The primitive morphology of the skull of Ocepeia agrees with its basal position in Afrotheria, and also with the basal position of Afrotheria among placentals.

However, the relationship with an exclusive clade of basal afrotherians such as Potamogale, Ptolemaia and Orycteropus, i.e. the clade Afroinsectiphilia minus Macroscelidea, remains poorly supported morphologically. The single identified exclusive synapomorphy with afroinsectiphilian implies an unlikely character transformation in Ocepeia (120-1>3: rostrum very narrow to very wide). Six homoplastic synapomorphies (ordered analysis) also support the node, most with low RI (40-60), and of which the best is the loss of P¹₁ (11-3 RI = 41; 72-1 RI = 75). Within basal afrotherians, the reduced postorbital process (148-1) is interpreted as an unambiguous synapomorphy of Ocepeia and Potamogale.

A peculiar relationship of Ocepeia with basal afrotherian taxa such as Potamogale is questionable in regard to its many remarkable ungulate-like features, for instance. We interpret the basal afrotherian placement of Ocepeia in our trees as a rather more general phylogenetic signal for its afrotherian relationships. However, our analysis does not recognize a monophyletic clade Afrotheria and, hence, any exclusive afrotherian synapomorphy in the Moroccan genus. This is related to the more general problem that the monophyly of the supercohort Afrotheria remains poorly characterized morphologically on the basis of available fossil and neontological morphological data (but see [73], [76], [79]). In this regard, Ocepeia should help to characterize the ancestral morphotype of the afrotherians.

The sister- or stem-group position of Ocepeia to the whole Afrotheria cannot be indeed rejected, especially if we agree with the hypothesis of an ungulate-like ancestral afrotherian morphotype, instead of an insectivore-like ancestral afrotherian morphotype, as raised by Seiffert [73], [75], [76]. However, this does not fit well with 1) the early diversity of the insectivorous-grade mammals from the Paleocene of Morocco [32], [33], [34], and 2) several striking paenungulate-like traits of Ocepeia, such as the selenodonty (see below) that remain unknown in extant and fossil insectivoran-like afrotherians (Afroinsectiphilia). Moreover, the synapomorphies that support in our cladistic analysis a relationship of Ocepeia to insectivoran-like afrotherians (Afroinsectiphilia) are weak (see above).

Relationships with Paenungulata.

Within Afrotheria, our cladistic analysis places Ocepeia outside of the Paenungulata. Even the constrained analysis that clusters Ocepeia with paenungulates results in a hypothesis of nested paenungulate position that is refuted by unlikely implied characters transformations such as a secondary loss of the hypocone.

Whatever the cladistic results, the new material of Ocepeia described here evidences a combination of primitive eutherian features, placental traits and ungulate-like traits. The ungulate-grade traits include proto-ungulate-like and paenungulate-like features that are summarized in Tables 6, 7 and 12. These traits have a noticeable heterogeneous distribution in our trees. The generalized ungulate-grade traits of Ocepeia are the low and bunodont teeth (e.g., 25-1, 88-1), and the posteriorly projecting broad angular process of the dentary (62-1). The most remarkable paenungulate-like features of Ocepeia are dental traits such as especially the presence of an incipient entolophid (34-1, see also [26]), and the ectololoph selenodont (W-shaped centrocrista, 101-2) and linked to an inflated mesostyle (98-1, 99-2 or 99-1), and lower molars with large inflated lingual cusps (28-1). The ectoloph is secondarily lost within paenungulates (e.g., Proboscidea), and the entolophid is known in perissodactyls. Some noticeable paenungulate features of the skull such as the periotic amastoidy (161-1), the developed zygomatic process of the maxilla, and lower molars with enlarged lingual cusps are known in Ocepeia. Amastoidy in the only trait restricted to paenungulates in our analysis. Several other traits of Ocepeia are known in paenungulates (Table 12), but not in all of them for several reasons such as reversals, convergences, or poor knowledge. The most remarkable ones are the high (deep) zygomatic arch with ventral process below the orbit (145-1), the short process of the maxilla in the orbit rim (136-1), presence of a coronoid fossa (63-1), and wide nasal cavity (126-1). Some paenungulate-like traits of Ocepeia seem even restricted to proboscideans (Table 12: 7-1, vestigial I₃; 67-1, enlarged I²; 162-1, large pars mastoidea). The ancestral condition of several of these traits remains poorly known in several paenungulate orders such as hyracoids (e.g., features 126, 145), sirenians (63, 98, 99, 101, 136) and embrithopods (63, 136).

Table 12 summarizes the interpretations of the paenungulate-like traits of Ocepeia in the trees (ordered analysis). The shortest trees (unconstrained parsimonious analyses, Figs. 21-22) admit noticeable parallelisms of Ocepeia and Paenungulata in their ungulate-like traits (Table 12), which instead are autapomorphic in both taxa. Resemblances with Proboscidea are also interpreted as convergences in the cladistic analysis. As a result Ocepeia is strongly autapomorphic in our trees (31 autapomorphies in ordered analysis, 41 in unordered analysis).

In fact, the shared traits of Ocepeia and Paenungulata conflict with the shared lophodonty of Paenungulata and Perissodactyla which is interpreted in our parsimony analyses as a synapomorphy for a questionable clade “Altungulata”, and which challenges the monophyly of Afrotheria in our trees. The morphotypic bunodont incipiently lophodont pattern of primitive proboscideans and paenungulates (89-1, also shared by Teilhardimys and primitive macroscelideans) is well distinct from the advanced lophodont pattern (89-2) of primitive perissodactyls, supporting the probable convergence of Laurasian and African ungulate-like mammals [69]. Together with remarkable shared features of Ocepeia and paenungulates such as the selenodont ectoloph, that is unknown in primitive perissodactyls, this challenges such a clade “Altungulata”, and agrees with the alternative hypothesis of the relationships of Ocepeia and Paenungulata.

In this hypothesis, the proto-ungulate features of Ocepeia best fit with its primitive stem position with respect to Paenungulata. The most noticeable plesiomorphic features that exclude Ocepeia from the crown group of extant paenungulate orders are the presence of paraconid, the absence of hypocone and related absence of bilophodonty, and the large canines. Crown paenungulates also depart by the M³ with two lingual roots (115-1), the molar trigonid compressed with reduced paracristid (29-1), presence of coronoid foramen (61-1), orbit more anterior (above P⁴-M¹, 135-2) and possibly relatedly the tuber maxillae more posterior to orbit (143-1), and a more developed posttympanic process (158-1). Such hypothesis of a stem paenungulate position of Ocepeia would actually be more parsimonious for several features at the nodes of stem and crown Paenungulata.

In our view, the selenodont morphology of the molar ectoloph is a structural landmark of the monophyly of the paenungulates including stem taxa such as Ocepeia, i.e. as a key feature of their ancestral morphotype. The incipient entolophid is another, but more derived, significant shared derived trait. Together with the relationships of Ocepeia with basal afrotherians (afroinsectiphilians) obtained in the parsimony study, this would make it the first known fossil link between insectivore-like and ungulate-like afrotherians.

Recent Eocene discoveries evidenced intriguing paenungulate dental and postcranial affinities of the European louisinid Teilhardimys and some primitive afrotherians such as early macroscelideans (e.g., [79]). In contrast to Ocepeia, these taxa share with paenungulates especially a large hypocone and the primitive bunodont-bilophodont pattern. However, they lack the selenodont ectoloph linked to a well-developed mesostyle and other paenungulate features seen in Ocepeia such as the incipient entolophid, implying unsuspected noticeable convergent evolution of ungulate-like features within Afrotheria (see Table 12).

The autapomorphic and endemic nature of Ocepeia.

Our cladistic analysis emphasizes the autapomorphic nature of Ocepeia, that is here distinguished at least at familial level in the new family Ocepeiidae (see diagnosis). The ordered analysis (Fig. 22) records 31 autapomorphies; 5 are exclusive autapomorphies (68-1, 118-2, 120-3, 122-1, 154-1) and others are mostly homoplastic convergences with paenungulates (see above and Table 12). In this topology, Ocepeia is by far as the most autapomorphic taxon compared in this work. The constrained analysis however shows that Ocepeia is much less autapomorphic when it clusters with paenungulates; in this topology Ocepeia has only 18 autapomorphies (including 2 exclusive states), and Orycteropus is consistently much more autapomorphic.

The most remarkable specialized features of Ocepeia are the anthropoid-like traits of the skull face and dentition (Tables 6, 7), such as the rostrum short and robust and the shortened anterior dentition. Other important specialized features of Ocepeia are the skull with elongated meso- and postero-cranial region as illustrated especially by the very long parietal and related short frontal. The noticeable pneumatization of the skull bones (a feature that evolves parallely in large proboscideans) is also remarkable; its adaptive significance remains unknown (structural pattern specialized for enhanced sound transmitting?).

These autapomorphic traits are evidences of the strong endemic nature of Ocepeia, and the long evolutionary history of its lineage in Africa.