Daouitherium rebouli Gheerbrant and Sudre, 2002

Gheerbrant, Emmanuel, Sudre, Jean, Cappetta, Henri, Iarochène, Mohamed, Amaghzaz, Mbarek & Bouya, Baâdi, 2002, A new large mammal from the Ypresian of Morocco: Evidence of surprising diversity of early proboscideans, Acta Palaeontologica Polonica 47 (3), pp. 493-506 : 494-504

publication ID	https://doi.org/ 10.5281/zenodo.13286142
persistent identifier	https://treatment.plazi.org/id/B560F638-5C3D-FFB4-FFED-F88EFF38863B
treatment provided by	Felipe
scientific name	Daouitherium rebouli Gheerbrant and Sudre
status	gen. et sp. nov.

Treatment

Daouitherium rebouli Gheerbrant and Sudre , gen. et sp. nov.

Figs. 1–8 View Fig View Fig View Fig View Fig View Fig View Fig View Fig View Fig , 10A View Fig .

Etymology: Species dedicated to Roland Reboul who donated specimens MNHN PM3 and CPSGM MA4 for study and preservation in a scientific public institution.

Holotype: CPSGM MA4 , left dentary bearing p2–4, m1–3 ( Figs. 1–5 View Fig View Fig View Fig View Fig View Fig , 10A View Fig ), Paleontological Collections of the Office Chérifien des Phosphates ( OCP) and the Geological Survey of Morocco, Rabat.

Hypodigm ( lower dentition).— Holotype CPSGM MA4 , left dentary (corpus) bearing p2–4, m1–3 ( Figs. 1–5 View Fig View Fig View Fig View Fig View Fig , 10A View Fig ); MNHN PM3 , right dentary bearing p3, m1–3 and preserving most part of the ascending ramus ( Figs. 6 View Fig , 7 View Fig ); MNHN PM3 and CPSGM MA4 have both an erupting m3 and a similar wear degree, which suggests they belong to the same individual.

Referred material.—Lowerdentition:CPSGMMA5,strongly worn isolated right m1. Upper dentition: CPSGM MA6, left P3 or more probably P4 ( Figs. 8 View Fig , 11 View Fig ).

Locality and age.—Ouled Abdoun, area of Grand Daoui, exact site unknown, possibly site “TS”; level 1 of the local phosphatic series, “intercalaire couches I/II” of earliest Ypresian age, which is the same local fossiliferous level which has yielded Phosphatherium escuilliei (work in preparation).

Study by H. Cappetta of the selachian fauna preserved in the matrix of MNHN PM3 supports a probable earliest Ypresian age of the species. The taxa recovered and identified are as follows: Striatolamia macrota striata (Winkler, 1874) (sensu Arambourg 1952) ; Carcharias atlasi (Arambourg, 1952) ; Abdounia beaugei (Arambourg, 1935) ; Casieria sp. ; Rhinobatos sp. ; Myliobatis sp. ; and Archaeomanta sp.

ThemostsignificanttaxonforanYpresianageis Abdounia beaugei ; this is in accordance with the rarity of the micro−selachians in the recovered fauna, in contrast with Thanetian phosphatic levels. Abasal Ypresian age is indicated by the frequency of Casiera sp., which is rarer in higher Ypresian phosphatic levels. The Thanetian age previously referred to Phosphatherium escuilliei on the basis of associated selachians in the matrix of the holotype ( Gheerbrant et al. 1996, 1998) was based on taxa which are now considered as being reworked from the underlying phosphatic level 2 (Thanetian). This will be discussed with more detail in a paper devoted to the geology and stratigraphy of the mammals sites from Ouled Abdoun Basin (work in preparation)

Diagnosis (lower jaw and lower dentition).—Primitive proboscidean with true lophodont and bilophodont molars similar to those of Phosphatherium , Numidotherium , and Barytherium . It is closer to Numidotherium and Barytherium and more advanced than Phosphatherium in the molarization of the premolars, the semi−bilophodont p4 with incipient entolophid, the articular condyle of the mandible very high above the dental row, the deep dentary, the entocristid slightly curved or labially oblique in the molars, and its large size close to that of N. koholense (80–90% smaller than N. koholense ).

It differs from Numidotherium and Barytherium and is closer to Phosphatherium in the more primitive anterior dentition which lacks a lower diastema, indicating a distinctive brevirostrine large−sized proboscidean, and which preserves four dental alveoli in front of p2 (retention of one or two additional anterior teeth). It is also distinct from Numidotherium koholense by the greater molarization of its lower premolars,thedistincttraceofentolophidinp3,andtheoverall less bunodont jugal teeth. It is characterized by a very large, probably autapomorphic, hypoconid on p3 and p2, and bytheoriginalextensionoftheenamelonthelabialsideofits premolars anterior roots.

Description

Lower molars.—Molar size increases strongly from m1 to m3 (area ratio of m2/m1: 189.5%; area ratio of m3/m1: 268.4%). They are characterized by a typical true lophodont and bilophodont pattern close to that of Phosphatherium , Numidotherium and Barytherium . The protolophid and entolophid (= hypolophid) are long, parallel, sharp, anteriorly concave and continuous (no sulci or notch). Their strictly transverse orientation is due to the transversal alignment of labial and lingual cusps. The entolophid is longer than the protolophid.

The cusps are crestiform. The lingual cusps are slightly higher than the labial ones. The trigonid is higher than the talonid,whereasthetalonidisslightlywider(m1–2)andmuch longer. The occlusal outline is extended longitudinally and concave on the labial flank at the level of the wide and deep hypoflexid.Awelldevelopeddistalcingulidoccursonm1and m2 and it is distally extended as a third small lobe on m3. It is most likely homologous with the postcristid of tribosphenic molars. The basins (pre− and postfossid) are shallow.

Aslight mesial precingulid occurs. It is upwardly concave in m1, but more horizontal in m2 and m3. The trigonid is compressed mesio−distally. The paraconid is absent and the paracristid is distinct only as a vestigial oblique ridge on the mesial flank of protoconid. There is also trace of a premetacristid on the mesial flank of the metaconid which is convergent downward with the paracristid. The metaconid is larger than the protoconid. The hypoconid is the most voluminous cusp of the tooth. The cristid obliqua is well developed and the entocristid is weaker and slightly curved labially. The cristid obliqua ends mesially on the trigonid slightly labially with respect to its mid−width, and it does not rise onto it significantly. The postfossid is noticeably extended mesio−distally. The distal cingulid is enlarged and inflated labially, especially in m2, as a small hypoconulid located behind the hypoconid; however there is no trace of postentoconulid. The hypoconulid is not linked by any crest to the hypoconid and entoconid. There is a weak trace of mesoconid on m3. On m3 the distal lobe bears an extended but shallow basin. It is surrounded by a low distal ridge, without inflated cusps. There are two labio−lingually expanded roots. The enamel is slightly wrinkled, especially at the apex of crests.

m1 differs from m2 by its smaller size (see area ratio above) and its talonid which is wider with respect to the trigonid. With wear a crescentiform facet is formed along the distal apex of the transverse lophs.

Lower premolars.—A notably increasing molariform morphology typifies the premolar series from p2 to p4: p4 is

20 mm

molariform and semi−bilophodont, p3 and p2 are sub− or premolariform. p4 and p3 have a well developed and basined talonid, a paraconid and a metaconid. p2 is more simple (cusps reduced, crests mesio−distally aligned) and is triangular in occlusal outline, but it is nearly as large as p3–4 and it retains molariform features such as a large talonid, a large hypoconid linked to the protoconid by a strong crest, the distinct cingulids, and a paracristid linked to a small paraconid. p4 has a rectangular occlusal outline similar to the molar ones, whereas p2–3 are more triangular with a trigonid compressed transversally (much narrower than the talonid) and extended mesio−distally. In p4, the two transverse lophs are differentiated (though the entolophid is incipient: morphology semi−bilophodont) and parallel, whereas in p3 only the small entolophid is differentiated (metaconid reduced and more distal with respect to protoconid), and p2 lacks transverse crests. p4 differs from the molars by the more reduced entolophid (incipient), the higher and mesio−distally less compressed trigonid, and the narrower talonid.

With respect to molars, the enamel extends at a lower level onthelabialsideoftheanteriorrootofp2–4,astrikingfeature. p2–4 are biradicular. The tooth anterior to p2 (canine or p1?) was small and monoradicular, judging from its alveolus.

Anterior lower teeth ( Figs. 4 View Fig , 10A View Fig ).—The holotype CPSGM MA4 preserves the anterior part of the dentary, although it is damaged. It exhibits four more or less distinct dental alveoli mesial to p2, and it is characterized by the complete absence ofdiastema,astrikingfeatureofthespecies.Thepoorpreservation of this anterior area makes only tentative the identification of the tooth rank of these alveoli. The two most anterior alveoli are well distinct, rather proclive, and can be interpreted as incisors, either i1 and i2 or i2 and I3; the anteriormost one (i1 or i2) is rather enlarged and compressed labio−lingually; the posterior one (i2 or i3) is smaller and more circular. More posteriorly, two small alveoli seem to occur: the posteriormost one is close to p2 and may account for a small and monoradicular c1, or possibly p1 or i3; the more anterior one is very small and may be that of i3 or of c1. The identification of the central incisor as an i2, as possibly in Numidotherium (Mahboubi et al. 1986) , would lead to the anterior dental formula i2, i3, c1?, p1?. However, our prefered interpretation of the anterior dental formula is i1, i2, i3?, c1?, mirroring the upper dentition of Numidotherium Jaeger, 1986 and agreement with the identified lower incisors of Barytherium Andrews, 1901a and Moeritherium Andrews, 1901b (i1, i2). In other word we favour the loss of p1.

Dimensions.—Measurements of teeth: see Table 1; length of p2–m3 (CPSGM MA4): 138 mm; length of m1–m3 (CPSGM MA4): 88 mm.

An estimation of the body mass based on size/mass regression equation of m1 and m2 (e.g., Damuth 1990), of the material described here, and especially based on their length, gives surprisingly very variable results, from about 170 Kg (MNHN PM3) to about 80 Kg (CPSGM MA5).

Fig. 9 View Fig illustrates the relative size of the jugal dentition of Daouitherium with respect to Numidotherium .

Dental formula.—i3?–1?, c1?, p2–4, m1–3; however, the retention of p1 and loss of one incisor cannot be excluded on this basis of this material.

Dentary.—The horizontal ramus (= mandibular corpus) is dorso−ventrally deep. It shows one anterior mental foramina in front of the first alveolus anterior to p2 (= canine or p1?). MNHN PM3 preserves the ascending ramus ( Fig. 7 View Fig ). The apex of its anterior part (coronoid process) lies 65 mm above the m3. It is vertical or slightly inclined mesially and labially shifted, resulting in the labial position of its mesial flank with respect to m3. Its anterior margin is located at the level of m3 talonid. The articular condyle is much higher than the dental row.Themassetericfossaisratherdeepabovethedentalrow. The symphysis is not preserved.

Height of the horizontal ramus below m1 (CPSGM MA4): 58 mm; estimated height of the vertical ramus, from the coronoid apex: 120 mm (MNHN PM3); estimated height of the articular condyle 105 mm (MNHN PM3).

Upper dentition.—A single isolated left P3 or probably P4,

10 mm

specimen CPSGM MA6, is referable to the upper dentition of this species. It is bicuspid and bears one loph, the paraloph, which is extended between the paracone and the protocone. The distal cingulum is strong but the mesial cingulum is weak or absent. A small parastyle occurs; it is not linked by a crest to the paracone. The metacone is absent or very reduced. The paracone has a well developed distal crest. The postprotocrista is absent. An extensive wear facet is developed along the mesial flank of the paracone and the paralophid. The tooth bears three roots and two additional small mesial and distal root processes.

Comparisons and polarity of the main features of Daouitherium rebouli gen. et sp. nov.

The most important features of Daouitherium rebouli gen. et sp. nov. and their polarity with respect to primitive lophodont proboscideans such as Phosphatherium escuilliei Gheerbrant, Sudre, and Cappetta, 1996 , Numidotherium koholense Jaeger, 1986 (in Mahboubi et al. 1986), Numidotherium savagei Court, 1995 , and Barytherium grave Andrews, 1901b , are listed below. (0), (1), (2), (3) are successive, additive states of the examined features.

Feature1.Anteriordentition:numberofalveolianteriortop2.

(0) 4 alveoli (2 or 3 i, c1 and/or p1): Daouitherium rebouli .

(1) 3 alveoli (2 i, c1): Phosphatherium escuilliei .

(2) 2 alveoli (2 i; loss of p1 and c1): Numidotherium koholense , N. savagei ? (probably 2 alveoli, but feature unknown in available material), Barytherium grave .

Comments: 1(0) and the primitive eutherian anterior dental formula (i1–3, c1, p1) characterize outgroups such as phenacodontid “condylarths”, and also anthracobunids ( Pilgrimella Dehm and Oettingen−Spielberg, 1958 ). Moeritherium is 1(2).

Feature 2. Diastema between lower incisors and p2.

(0) absent (brevirostrine morphology): Phosphatherium escuilliei , Daouitherium rebouli .

(1) present and large (longirostrine morphology): Numidotherium koholense , Barytherium grave ; probably also Numidotherium savagei , though the feature is unknown in the species.

Comments: The outgroup condition known in many “condylarths” (e.g., phenacodontids) is 2(0), as for anthracobunids and phenacolophids ( Minchenella Zhang, 1980 ). Moeritherium is 2(1).

Feature 3. Central lower incisor (i1?). (0) small: primitive generalized eutherian condition.

(1) moderately enlarged: Phosphatherium escuilliei , Daouitherium rebouli ? (feature poorly preserved).

(2) very enlarged (tusk−like): Numidotherium koholense , Numidotherium savagei , Barytherium grave .

Comments: The primitive outgroup condition is 3(0). Moeritherium has a very enlarged lower incisor (as in state 3(2)), but it may not be homologous (lateral incisor).

Feature 4. Premolars.

(0) all unmolarized (premolariform): Phosphatherium escuilliei .

(1) only p4 molariform: Numidotherium koholense . (2) p3–4 molariform: Daouitherium rebouli .

(3) p2–4 molariform: Numidotherium savagei , Barytherium grave .

Comments: Unmolarized premolars characterize the primitive eutherian condition and especially many “condylarths”. However, an early trend for p4 molarization is known in phenacodontids and pantomesaxonians. Anthracobunids and Moeritherium are 4(2).

Feature 5. p4 morphology.

(0) premolariform: protocristid reduced and oblique with respect to the transversal axis, no entolophid: Phosphatherium escuilliei .

(1) semi−bilophodont: protocristid transversal, entolophid incipient but distinct: Daouitherium rebouli , Numidotherium koholense , Numidotherium savagei , Barytherium grave .

Comments: p3 has also an incipient trace of an entolophid in Daouitherium , Numidotherium savagei and possibly Barytherium ; this is absent in N. koholense and Phosphatherium . The primitive outgroup condition is 5(0). Primitive pantomesaxonians, anthracobunids and Moeritherium have a molariform p4 with a transversal protolophid, but it is not bilophodont (no trace of an entolophid).

Feature 6. Paraconid of p3–4.

(0) small but clearly distinct: Daouitherium rebouli .

(1) reduced to absent: Phosphatherium escuilliei , Numidotherium koholense , Numidotherium savagei , Barytherium grave .

Comments: The polarity of the states of this feature may be questionable. However, primitive pantomesaxonians and phenacodontids show a differentiated paraconid (6(0)). Anthracobunids have a large paraconid in p3–4 (larger and higher in p3) (6(0)). Moeritherium has also a well developed paraconid especially on p2–3 (6(0)).

Feature 7. Occlusal outline of the premolars (especially p2–3). (0) mesio−distally extended: Phosphatherium escuilliei , Daouitherium rebouli , Numidotherium koholense .

(1) more compressed mesio−distally (trigonid shortened) and rounded: Numidotherium savagei , Barytherium grave .

Comments: The outgroup condition may be 7(0) as in many “condylarths”. Anthracobunids are rather 7(0) for p2–3. Moeritherium is variable for this feature, but it seems to have a shorter p3–4 and with a more rounded occlusal outline resulting especially from a more inflated labial flank; p2 is labio−lingually compressed as in Daouitherium .

Feature 8. Relative size of p3 and p2.

(0) Length of p3> p2: Phosphatherium escuilliei , Daouitherium rebouli Numidotherium savagei , Barytherium grave . (1) Length of p3 <p2: Numidotherium koholense .

Comments: The primitive outgroup condition is 8(0). It is also generalized in tethytherians (e.g., anthracobunids and Moeritherium ).

Feature 9. Enamel development in the premolars.

(0) restricted to above the cervix (crown): Phosphatherium escuilliei , Numidotherium koholense ?, Numidotherium savagei ?, Barytherium grave ?

(1) extended basally (below the cervix) on the labial flank of the mesial root: Daouitherium rebouli .

Comments: The outgroup very generalized eutherian condition is 9(0). Numidotherium koholense may have a construction related to 9(1) in the wear pattern of the labial flank of mesial root of p2; in the parsimony analysis it is processed as unknown for this feature until more data is available; N. savagei and B. grave are probably primitive in this feature. Anthracobunids and Moeritherium are 9(0).

Feature10. Roots of premolars p3–4.

(0) 2 roots, generally expanded transversally: Phosphatherium escuilliei , Daouitherium rebouli , Numidotherium koholense , Numidotherium savagei .

(1) the two roots of p3–4 are subdivided (four alveoli for each tooth): Barytherium grave .

Comments: The primitive outgroup condition known in “condylarths” such as phenacodontids is 10(0) or 2 roots not significantly expanded transversally (primitive eutherian condition). Anthracobunids and Moeritherium are 10(0).

Feature 11. Roots of premolar p2.

(0) 2 roots in all premolars: Daouitherium rebouli,Numido − therium koholense , Barytherium grave .

(1) one root for p2: N. savagei ( Court 1995: roots fused), Phosphatherium escuilliei (loss of one root or roots fused).

Comments: 11(0) is the primitive eutherian condition. Anthracobunids and Moeritherium are 11(0). Desmostylians are 11(1).

Feature 12. Molar cristid obliqua.

(0) weakly oblique: weak angle with respect to the longitudinal axis, and joining the trigonid significantly labially: Phosphatherium escuilliei .

(1) moderately oblique lingually but more than Phosphatherium and less than Numidotherium : Daouitherium rebouli . (2) well oblique lingually, ending mesially against the trigonid mid−width: Numidotherium koholense , N. savagei , Barytherium grave .

Comments: The polarity of the states of this feature may be equivocal. The primitive eutherian condition is a cristid obliqua strongly oblique joining the metaconid (many “protheutherians” and “condylarths”), or an oblique cristid obliqua joining the trigonid in its mid−width between metaconid and protoconid (many “condylarths” including phenacodontids).Thelabialdriftofthecristidobliquaisaderived trend in tethytherians ( Tassy and Shoshani 1988; Fischer and Tassy 1993), and the cristid obliqua “entirely labial” is described as a probable synapomorphy of proboscideans s.s. ( Tassy 1994). The weakly oblique (rather labial) cristid obliqua of Phosphatherium is indeed obviously derived with respect to the primitive eutherian (outgroup) condition. However other lophodont proboscideans seem to be characterized by a secondary lingual (more oblique) migration of the cristid obliqua (12(1) and 12(2)) with respect to Phosphatherium . Anthracobunids are probably primitive (or secondary derived?) in their cristid obliqua strongly oblique lingually, joining the metaconid. Moeritherium is like Numidotherium and Barytherium . The alternative hypothesis would be that Phosphatherium is precociously specialized and that the later lophodont proboscideans ( Numidotherium and Barytherium ) remained more primitive in this respect.

Feature 13. Molar cristid obliqua.

(1) mesial part reduced (vanished), in relation with the development of the interlophid: N. savagei .

Comments: 13(0) corresponds to the primitive eutherian condition. Anthracobunids and Moeritherium have well developed cristid obliqua (13(0)), with some specializations (long and sharp in the former and inflated as a protoconulid and a mesoconid in the latter).

Feature 14. Molar entocristid.

(0) more or less longitudinal and straight: Phosphatherium escuilliei .

(1) concave labially or oblique mesio−labially: Daouitherium rebouli .

(2) very oblique mesio−labially and significantly convergent mesially with the cristid obliqua: Numidotherium koholense , N. savagei , Barytherium grave .

Comments: 14(0) corresponds to the generalized eutherian condition known in many “condylarths”. Anthracobunids are derived in the reduction of the entocristid (large talonid notch), as are several phenacodontids. Moeritherium also has a reduced entocristid.

Feature 15. Cusps developed in the distal cingulid of lower molars (postentoconulid).

(0) hypoconulid distinct, postentoconulid variably distinct: Phosphatherium escuilliei .

(1) hypoconulid distinct, postentoconulid absent: Daouitherium rebouli , Numidotherium koholense , N. savagei , Barytherium grave .

Comments: The primitive eutherian (outgroup) condition known in many “condylarths” such as phenacodontids is the absence of a postentoconulid. A variable, incipient or small postentoconulid is known at least in the m3 of primitive tethytheres, phenacolophids such as Minchenella (small entoconulid close to hypoconulid which remains central), desmostyles, and sirenians. Anthracobunids such as Pilgrimella have a well developed postentoconulid on m3. Moeritherium has a variable more or less distinct postentoconulid. True lophodont bilophodont proboscideans seem to have reduced secondarily the postentoconulid: the reduction of the postentoconulid in Daouitherium , Numidotherium and Barytherium may be derived with respectto Phosphatherium .Trilophodontproboscideanshavea postentoconulid.

Feature 16. Horizontal ramus (mandibular corpus) of the dentary.

(0) not high: Phosphatherium escuilliei .

(1) high (deep): Daouitherium rebouli , Numidotherium koholense , Numidotherium savagei , Barytherium grave .

Comments: 16(0) is the generalized outgroup eutherian condition from which many ungulates including anthracobunids, sirenians, Moeritherium and other proboscideans have departed.

Feature 17. Ascending ramus of the dentary. (0) its mesial flank arises at the level of m3 or more posteriorly: Phosphatherium escuilliei , Numidotherium koholense , Daouitherium rebouli .

(1) its mesial flank arises more anteriorly than m3: Numidotherium savagei (m2–3), Barytherium grave (m2).

Comments: The mesial flank of the ascending ramus of the dentary arises posterior to m3 (17(0)) in anthracobunids and primitive eutherians (outgroup condition), with respect to Moeritherium and derived proboscideans (17(1)). 17(1) is generally associated with a mesial inclination (and labial shift) of the ascending ramus in proboscideans, a feature which is only incipient in Daouitherium .

Feature 18. Articular condyle of the dentary.

(0) relatively low above the dental row: Phosphatherium escuilliei .

(1) very high above the dental row: Daouitherium rebouli , Numidotherium koholense , Barytherium grave .

Comments: 18(0) corresponds to the primitive outgroup eutherian condition, from which many ungulates have departed, including most proboscideans (incl. Moeritherium ). This feature is unknown in Numidotherium savagei .

Feature 19. Body size.

(0) small: Phosphatherium escuilliei .

(1) large (up to the tapir size): Daouitherium rebouli , Numidotherium koholense , Numidotherium savagei . (2) very large: Barytherium grave .

Comments:Outgroupgeneralizedeutherianconditionis19(0).

Discussion

The Ouled Abdoun material described here illustrates a new, well characterized genus and species (see diagnosis above) of primitive proboscidean (traditional concept) which is named Daouitherium rebouli .

Some proboscidean features of Daouitherium , which should be noted are the development of a probable enlarged lower incisor (as exemplified by the most anteriorly preserved alveolus of the holotype), the true lophodont molar morphology, which is distinctive with respect to anthracobunids and sirenians ( Gheerbrant et al. 1996, 1998), the molar cristid obliqua located labially, and the large body size. Striking features of Daouitherium previously unknown (primitive) in proboscideans are the absence of diastema in theanteriordentitionandtheretentionoftwoadditionalanterior teeth, i3 and/or c1, c1 and/or p1.

Thelowerjugaldentitionof Daouitherium rebouli andespecially the molar series is strikingly similar to Numidotherium koholense Jaeger, 1986 from the early/middle Eocene of El Kohol ( Mahboubi et al. 1984, 1986), N. savagei Court, 1995 from the late Eocene of Dor El Talha, and Barytherium grave Andrews, 1901b from the late Eocene and early Oligocene of Dor El Talha and Fayoum, suggesting close relationships at least within the same proboscidean suborder Barytherioidea . It is also similar to that of Phosphatherium escuilliei Gheerbrant, Sudre, and Cappetta, 1996 , as isshownbythenewmaterialofthisspecies,andespeciallyin the molar morphology. Actually, the morphology of the lower molars of Daouitherium is virtually identical to that of Numidotherium and their size is close to that of N. koholense ( Fig. 10 View Fig ). The morphology of the upper premolar CSGPM MA6 referred to Daouitherium rebouli is also similar to that of Numidotherium and Barytherium ( Fig. 11 View Fig ).

Daouitherium also shares with Numidotherium and Barytherium the very high position of the articular condyle of the dentary, the deep horizontal ramus of the dentary, molarization of the lower premolars (but simplified in N. koholense ), the p4 semi−bilophodont (entolophid weak but differentiated), and the entocristid concave labially or oblique mesio−labially. These features are probably derived, especially with respect to Phosphatherium which is also a much smaller form.

Daouitherium , however, differs strongly from Numidotherium and Barytherium in its anterior lower dentition: it is short mesio−distally, without any distinct diastema, and it preserves several additional teeth as exemplified by the occurrence of four dental alveoli in front of p2 (see the description for their interpretation). In contrast, Numidotherium and Barytherium show the occurrence of only two incisors (i1 and i2) separated from p2 by a large diastema. The short anterior lower dentition of Daouitherium , lacking a diastema, indicates a rather brevirostrine morphology of the head as opposed to the derived longirostrine morphology of Numidotherium and Barytherium .

This primitive construction of the anterior lower dentition

I/1

I/2

of Daouitherium reminds that of Phosphatherium . It may be even more primitive than that of Phosphatherium in some features such as the retention of an additional dental alveolus in front of p2 (however, this difference needs to be confirmed in better preserved material), and the p2 which has two roots as in Numidotherium koholense and Barytherium . The p2 of Phosphatherium has most probably one root, which is by contrast a derived feature. The p2 of N. savagei has also only one root, probably as the result of parallelism. It should be noticed that the loss of c1 and p1 was once considered as a synapomorphic feature of proboscideans (e.g., Tassy 1981; Domningetal.1986; Tassy1994; Court1995;Shoshanietal. 1996). These teeth are now known in Daouitherium (retention of two teeth among i3, c1 and p1) and Phosphatherium (retention of c1).

Other primitive features of Daouitherium with respect to Numidotherium and Barytherium are the distal location of the anterior margin of the coronoid process (ascending ramus; feature 17), which rises from the horizontal ramus at the level of m3, and its weak mesial inclination. Daouitherium is also characterized by premolars retaining a small paraconid (especially p3–4; feature 6). In addition, the premolars of Daouitherium show an elongated occlusal outline, which resembles that of Phosphatherium and Numidotherium koholense and which clearly differs from the shorter (trigonid very compressed mesio−distally) and more rounded occlusal outline of N. savagei and Barytherium grave (feature 7). This latter condition indicates a relative shortening of the jugal dental series in N. savagei and Barytherium grave (which contrasts strikingly with the long diastema in these species). In addition, the most anterior alveolus (i1 or less possiblyi2)preservedinCPSGMMA4ismuchlessenlarged with respect to the central lower incisor of Numidotherium (here interpreted as a possible i1), and probably even with respect to that of Phosphatherium (i1?) (feature 3).

Comparison with other primitive proboscideans suggests that the occurrence of a very large and very labial hypoconid in the p3 and p2 of Daouitherium , and that the resulting characteristic triangular occlusal outline, may be autapomorphic. This might be also true for the basal extension of the enamel on the labial side of the anterior root of lower premolars (feature 9), which appears to be distinctive with respect to Phosphatherium , N. savagei , and Barytherium species. Instead, this feature is reminiscent of the peculiar mode of wear evidenced by Court (1993) on the labial side of the anterior root of p2 of N. koholense . These features seem to be more or less functionally related, although in N. koholense the peculiar mode of wear of p2 appears to be linked to the development of a large diastema. The condition seen in N. koholense could be a more derived expression of a same specialized functional trend of the premolar series already initiated in Daouitherium .

Some other features of Daouitherium are of uncertain polarity with respect to Numidotherium and Barytherium , such as the cristid obliqua being less oblique lingually (feature 12; primitive?) and the precingulid which is small (thin and not extended laterally), but distinct and curved upward in m1.

Daouitherium is closer to Numidotherium koholense than to N. savagei and Barytherium grave in size (smaller), the elongatedocclusaloutlineofitspremolars,thetwo−rootedpremolars (p2: roots fused in N. savagei ; p3–4: four roots in Barytherium resulting from the subdivision of the two transverse roots), and the unreduced anterior part of entocristid and cristid obliqua (interlophid poorly differentiated). However these resemblances may be symplesiomorphic and Numidotherium koholense differs by its more simplified p2–3 (primitive), the jugal teeth broader and significantly more bunodont (probably primitive), the absence of entolophid in p3 (primitive), and the p2 slightly longer than p3 (derived, possibly autapomorphic).

Phylogenetic and systematic conclusions ( Fig. 12 View Fig )

Daouitherium rebouli gen. et sp. nov. is a new, primitive large lophodont African proboscidean of basal Eocene age. A parsimony analysis (Hennig 86) of its most important features (features 1–19) produced the cladogram of Fig. 12 View Fig . It shows that the phylogenetic position of Daouitherium with respect to other lophodont primitive proboscideans is intermediate between the primitive Phosphatherium and the more derived Numidotherium and Barytherium . This is supported by important features such as large body size (feature 19), the very high position of the articular dentary (feature 18), the deep horizontal ramus of the dentary (feature 16), molarization of the premolars (feature 4) and the semi−bilophodont p4 with an incipient entolophid (feature 5), among others (features 12–14).

It should be emphasized that this resulting cladogram is unrooted. The significance of Daouitherium for the ancestral dental morphotype of proboscideans (out of the true lophodont molars), as well as for the basal relationships of these primitive lophodont taxa with respect to other proboscideans (e.g., Moeritherium ), to tethytherians (anthracobunids, sirenians, desmostyles) and to higher inclusive taxa such as pantomesaxonians, will be investigated together with the study of the new informative material of Phosphatherium (skull and lower dentition: work in preparation).

The problem of the relationships with the deinotheres will be also investigated separately in the light of the new data on Phosphatherium and of the extended comparisons with Moeritherium and Elephantiformes Tassy, 1988. Daouitherium itself does not add significant data to the question of the origin of deinotheres, except it shares the true lophodonty and supports that this is the probable ancestral morphotype of theProboscidea. Numidotherium andespecially Barytherium are clearly closer to deinotheres in their more derived anterior dentition (e.g., diastema, loss of several anterior teeth).

The family referral of Daouitherium remains difficult to establish confidently in the present state of data. Daouitherium is especially close to Numidotherium , but no special synapomorphy excluding Barytherium can be identified. Here, we emphasize this phenetic special resemblance of Daouitherium with Numidotherium with its provisional inclusion in the Numidotheriidae . This, however, makes this family probably paraphyletic, as with the inclusion of Phosphatherium in this family ( Gheerbrant et al. 1996, 1998). Referral of Daouitherium to the Numidotheriidae would be more legitimate than for Phosphatherium , which is much more primitive as evidenced by new material in the course of study. As for Phosphatherium , there are indeed some striking primitive features of Daouitherium which raise questions about their familial numidotheriid allocation. This is especially true for the anterior dentition which has no developed diastema (brevirostrine form) and which retains several teeth (i3 or c1, c1 or p1) which are lost in Numidotherium , i.e. corresponding to a more primitive dental formula.

Daouitherium and Numidotherium seem to exemplify an early radiation of basal Barytherioidea . Daouitherium is indeed included in Barytherioidea , following the initial systematic position adopted for Numidotherium (Mahboubi et al. 1986) . However, formally such a concept of the Barytherioidea is paraphyletic. Phosphatherium , Daouitherium , Numidotherium , Barytherium and the Deinotheriidae correspond actually to successive plesions belonging to the stemgroup Proboscidea .

The antiquity (early Ypresian) and primitive morphology of Daouitherium with respect to N. koholense would be in accordance with their hypothesized ancestral−descendant relationship. Clearly, this is a better supported hypothesis than the possible filiation of Phosphatherium and N. koholense discussed by Gheerbrant et al. (1996, 1998): the mandibular and dental anatomy of Daouitherium is much closer to those of N. koholense . However, there are no special synapomorphies of Daouitherium and N. koholense supporting a peculiar lineage of primitive lophodont proboscideans. In addition Daouitherium has some derived features with respect to N. koholense : the p3–4 more molarized, the enamel extended basally on the anterior root of premolar (feature 9; however the peculiar mode of wear of p 3 in N. koholense may be reminiscent of this feature in Daouitherium : see above), and the jugal teeth less bunodont. These specializations seem, conversely, to exclude Daouitherium from the direct ancestry of N. koholense .