Fig 1.
Abdounodus hamdii, Selandian (Phosphate level IIa) of the Ouled Abdoun Basin, Morocco.
MHNM.KHG.154 (collections of the Natural History Museum of Marrakech), left maxillary of preserving P3-4, M1-3; (A) strereophotographic pair of P3-4, M1-3 in occlusal view; (B) occlusal sketch; (C) strereophotographic pair of 3D models reconstructed from CT scans in occlusal view. The 3D models of MHNM.KHG.154 were reconstructed by F. Goussard (MNHN) from the CT scans using the computer programs Materialise Mimics Innovation Suite 18.0 Research Edition (x64), and Maxon Cinema 4D R15. Scale bar = 10 mm.
Fig 2.
Abdounodus hamdii, Selandian (Phosphate level IIa) of the Ouled Abdoun Basin, Morocco.
MHNM.KHG.154 (collections of the Natural History Museum of Marrakech), right maxillary of Abdounodus hamdii preserving P3-4, M1-3; (A) strereophotographic pair of P3-4, M1-3 in occlusal view; B, s.e.m. photograph of occlusal view; (C) occlusal sketch. Scale bar = 10 mm.
Table 1.
Measurements of the upper teeth of Abdounodus hamdii, specimen MHNM.KHG.154 (in millimeters; L: length; W: Width; r: right; l: left).
Fig 3.
Abdounodus hamdii, Selandian (Phosphate level IIa) of the Ouled Abdoun Basin, Morocco.
MNHN.F PM92, left dentary bearing roots of M3 and M2, crown of M1, P4, P3 (damaged) and root of P2 or P1 or C1. (A) stereophotographic pair in occlusal view and 3D model of the isolated teeth in occlusal view reconstructed from the CT scans; (B) Labial view; (C) Transparent 3D model in labial view reconstructed from the CT scans and showing the roots of the teeth; (D) 3D model of the isolated teeth in labial view, reconstructed from CT scans. (E-F) Same in lingual view. Scale bar = 10 mm.
Fig 4.
Abdounodus hamdii, Selandian (Phosphate level IIa) of the Ouled Abdoun Basin, Morocco.
Transverse horizontal CT scan section of the partial lower jaw PM67 preserving M2 and M3 and showing the vertical root furrow and infilling crest of bone (arrows). A: anterior; P: posterior. Scale bar = 1 mm.
Table 2.
Measurements of the dentary MNHN.F PM92 of Abdounodus hamdii (in millimeters; L: length, H: height, W: width).
Table 3.
Measurements of the lower teeth of Abdounodus hamdii, specimen MNHN.F PM92 (in millimeters).
Fig 5.
Occlusal sketch of the molars of Abdounodus hamdii reconstructed with the maxillary dentition of specimen MHNM.KHG.154.
(A) occlusal sketch of MHNM.KHG.154 with M2-3 of specimen PM68; (B) cclusal sketch of MHNM.KHG.154 with M1, M2, M3 of specimen OCP DEK/GE 310; (C) occlusal sketch of MHNM.KHG.154 with M2-3 of specimen PM67. The occlusion of opposed molars is reconstructed here in sub-centric position.
Fig 6.
Wear facets of upper (MHNM.KHG.154) and lower molars of Abdounodus hamdii, and mastication compass following Koenigswald et al.
[30]. (A) Right lower molars M2 and M3; (B) left upper molars M1, M2, M3. C1-C10: Crompton [31] wear facets of tribosphenic molars (in red); B1-10, Butler [32] wear facets of lophodont molars (in blue). (C) Mastication compass of Abdounodus hamdii, indicating the inclination and direction of the lower jaw motion during power stroke of mastication. Note that the lower jaw motion is mostly labio-lingual (transverse) and horizontal, and is restricted to phase I of mastication.
Table 4.
Occlusal shearing contacts between the opposite molars of Abdounodus hamdii during the power stroke of mastication as identified from occlusal sketches (Fig 5) and from 3D simulation of occlusion with the OFA software.
Table 5.
Wear pattern of the upper and lower molars of Abdounodus hamdii: attritional wear facets and related occluding structures.
C1-6 primitive shearing facets of tribosphenic molars following the nomenclature of Crompton [31], B1-B10 shearing facets of lophodont molars described by Butler [32].
Table 6.
Angle of the wear striae of the upper and lower molars of Abdounodus hamdii with respect to the horizontal plan (= relative inclination of the motion of the lower jaw during phase I); wear facets number of Crompton [31].
Fig 7.
Comparison of the upper molar pattern (occlusal view) of early paenungulatomorphans (Afrotheria) with respect to the tribosphenic-tritubercular pattern of Todralestes, with indication of significant homologous structures.
(A) Todralestes variabilis (Eutheria, Pantolesta?), M2-1; (B) Ocepeia grandis (left), M3, and O. daouiensis (right), M2-1 (Paenungulatomorpha); (C) Abdounodus hamdii (Paenungulatomorpha), M3-1; (D) Eritherium azzouzorum (Paenungulata, Proboscidea), M3-1; (E) Phosphatherium escuilliei (Paenungulata, Proboscidea), M3-1. Not to scale. All teeth figured as right teeth. Abbreviations: centr: centrocrista; hyp: hypocone; interl: interloph; ling c: lingual cinglum (pre- and postcingulum); crest metal and crest protol: full crest-like protoloph and metaloph (true lophodonty); mle: metaconule; mesost: mesostyle; pal: paraconule; pseudohyp: pseudohypocone; postprot: postprotocrista.
Fig 8.
Origin and evolution of the bilophodont pattern in paenungulates: a new structural scenario for upper molars including the stem taxa Ocepeia and Abdounodus which documents two intermediate stages between the tribosphenic-tritubercular pattern and the quadritubercular-bilophodont pattern.
Photography and occlusal sketch of teeth, all figured as right teeth. Symbols of dental structures: Black circles: paracone and metacone, green circle: metaconule; red circle: protocone; blue circle: hypocone; transverse lines: proto- and metaloph; double arrow: interloph.
Fig 9.
Convergence of lophodonty in Paenungulata (Afrotheria) and Perissodactyla (Euungulata, Laurasiatheria).
The fourth upper molar cusp (postero-lingual cusp bearing the metaloph) is not homologous in Paenungulata and Perissodactyla: it is issued from a modified metaconule (pseudohypocone) in Paenungulata (Phosphatherium here) and from the true cingular hypocone in the Perissodactyla (Cymbalophus here) and early lophodont euungulates such as the Anthracobunidae (not shown here). Stem groups illustrating early stages of the evolution of the lophodonty remain poorly known in Euungulata, being represented mainly by phenacodontids such as Ectocion and Phenacodus that have a large hypocone. The stem paenungulates Ocepeia (not shown here) and Abdounodus are the first fossil taxa documenting intermediate morphological stages between the primitive tritubercular molar pattern and the derived quadritubercular and bilophodont molar pattern of the crown Paenungulata (here represented by Phosphatherium). Symbols of dental structures: Black circles: paracone and metacone, green circle: metaconule; blue circle: hypocone; red circle: protocone; transverse lines: proto- and metaloph. Occlusal sketch of teeth, all figured as right teeth.
Table 7.
Cladistic analyses of Abdounodus relationships performed in this work.
Analysis 2 (S2 Text, part III.2) is our reference analysis and tree in this work. All parsimony analyses were made with the “traditional search” command of TNT. Matrix with 27 taxa, 184 characters (S2 Text), 16 uninformative characters (inactived), 44 additive (ordered) characters (S6 Table). “Altungulata”: former grouping of lophodont ungulates including the Paenungulata and the crown and stem Perissodactyla; stem Perissodactyla: Phenacolophus, Minchenella, Cambaytherium, Anthracobunia, Radinskya.
Fig 10.
Relationships of Abdounodus and paenungulates.
Most parsimonious tree resulting from the unweigheted analysis with ordered features. Details, Bremer index and distribution of synapomorphies are provided in S2 Text (part III.1). Tree length: 735. Retention index: 53. Consistency Index: 37.
Fig 11.
Relationships of Abdounodus and paenungulates.
Most parsimonious tree resulting from analysis with implied weighting and ordered features. This tree is in this work our reference topology for the discussion of the relationships of Abdounodus and Ocepeia and of the distribution of the characters. Main upper molar patterns are outlined at the node of lophodont taxa (incl. early stages) to show the convergent development of the pseudohypocone in the Paenungulatomorpha and the hypocone in the Perissodactyla and other lophodont euungulates such as Anthracobunidae. See Fig 9 for caption of symbols of dental structures. Details, Bremer index and distribution of synapomorphies of this tree are provided in S2 Fig and S2 Text (part III.2). The clades numbers are reported above the nodes. Tree length: 746. Retention index: 52. Consistency Index: 33.