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Figure 1. Example of how the selected Micro-CT scanned specimens were virtually sectioned at several heights parallel to a plane approximating the occlusal surface.

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Figure 2. Virtual sections of the ontogenetic development of the p3 of "Amphilagus" antiquus. (1) Occlusal surface. The hypoconulid shallows up (2) and a central connection interrupts the hypoflexid forming a mesofossettid (3). Both hypoflexid and mesofossettid progressively disappear in further stages of wear (4, 5). White arrow: hypoflexid; grey arrow: hypoconulid; dotted white arrow: lingual flexid; dotted white arrow: mesofossettid.

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Figure 3. Virtual sections of the ontogenetic development of the p3 of Desmatolagus cf. youngi. (1) Occlusal surface. The hypoflexid (white arrow) progressively shallows up (2, 3).

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Figure 4. Virtual sections of the ontogenetic development of the p3 of Palaeolagus sp. (a) Occlusal surface. Beginning with an hourglass shape (1, 2), an additional lingual connection between trigonid and talonid forms a mesofossettid (3); the hypoflexid does not substantially shallow up (4). White arrow: mesoflexid; grey arrow: hypoflexid; dotted white arrow: mesofossettid.

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Figure 5. Left lower jaw of Piezodus branssatensis virtually sliced along the mesiodistal midline. In the younger specimen (1) we can observe dp3 and dp4 lying upon p3 and p4 (white arrow), and the lack of the anteroconid along the shaft (grey dotted line); the roots are not present. In the older specimen (2) we see the incipient roots (white dotted arrow).

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Figure 6. Virtual sections of the ontogenetic development of the p3 of Piezodus branssatensis. (1, 4) Occlusal surfaces. In the younger specimen the dp3 covers the p3 (1); the unworn p3 has the shape of an hourglass (2) which remains even at maximum stages of wear. The anteroconid (3) does not appear. In the older specimen of Piezodus the anteroconid is already present at the level of the occlusal surface (4), and eventually merges lingually with the trigonid (5) (white arrow); trigonid and talonid merge lingually (6) (dotted white arrow) and the hypoflexid (grey arrow) progressively shallows up (7).

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Figure 7. Virtual sections of the ontogenetic sequence of the trigonid-talonid connection in Palaeolagus sp. From unconnected trigonids and talonids on the occlusal surface (1) progressive wear produces connections (indicated by the white arrow) in m1 (2) then in m2 (3) and at last in p4 (4).

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Figure 8. Virtual sections of the ontogenetic sequence of the trigonid-talonid connection in Desmatolagus cf. youngi. From unconnected trigonids and talonids on the occlusal surface (1) progressive wear produces connections (indicated by the white arrow) in m2 (2) then in m1 (3) and at last in p4 (4).

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Figure 9. Virtual sections of the ontogenetic sequence of the trigonid-talonid connection in "Amphilagus" antiquus. From unconnected trigonids and talonids in the occlusal surface (1) progressive wear starts an incipient connection (indicated by the white arrow) in m2 (2) then in m1 (3) and at last in p4 (4).

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Figure 10. Virtual sections of the ontogenetic sequence of the trigonid-talonid connection in Piezodus branssatensis. In the younger specimen trigonid and talonid remain separated even with maximum wear. In the occlusal surface of the older specimen (1) wear starts an incipient connection (white arrow) between trigonids and talonids in m2 (2) then in m1 (3) and at last in p4 (4).

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Figure 11. Virtual sections of the ontogenetic sequence of hypoconulid/fossettes development in "Amphilagus" antiquus. From lingually directed hypoconulids in the occlusal surface (1) progressive wear develops a fossette (white arrow) in m1 (2) then in m2 (3) and at last in p4 (4).

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Figure 12. Virtual sections of the ontogenetic sequence of hypoconulid/fossettes development in Piezodus branssatensis. In the original occlusal surface only m1 and m2 are visible (1); the hypoconulid in m1 forms a fossette in very early stages of wear (2) that rapidly disappears (3); eventually a fossette is formed in p4 (4) and in m2 (5).

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