924
Journal of Paleontology 92(5):920–937
Figure 3. Micro-CT scan images; (1–4, 9, 10, 13–16) Arcius fuscus Russell et al., 1967; (5–8, 11, 12, 17–19) Arcius lapparenti Russell et al., 1967. (1)CB 2560, left P4, occlusal view; (2) MU 6458, right M1, occlusal view; (3) AV 422-L, left M2, occlusal view; (4) MU 6507, holotype, left M3, occlusal view; (5)CB 4162, left P4, occlusal view; (6) AV 7716, right M1, occlusal view; (7) AV 7707, right M2, occlusal view; (8) AV 5849, left M3, holotype, occlusal view; (9, 10) AV 6838, left I1,(9) lingual view, (10) mesial view; (11, 12) AV 7714, right I1,(11) lingual view, (12) mesial view; (13) CB 1914-L, left P4, occlusal view; (14) UCMP 71976, left M1, occlusal view; (15) AV 610-BN, left M2, occlusal view; (16) UCMP 71982, left M3, occlusal view; (17) CB 232-BN, left P4, occlusal view; (18) AV 1306-Ph, rightM1, occlusal view; (19) AV 1092-BN, right M2, occlusal view. Scale bar=1mm.
Materials.—PAT2, mandible with right I1–M1; PAT3, left M3; PAT5, right M2.
Remarks.—In this paper, all diagnoses for the six species of Arcius include diagnostic features of the referred material along with the holotype. The reason behind this decision is that the holotypes for A. fuscus and A. lapparenti are M3 specimens (Russell et al., 1967), and this tooth position is probably the most variable in paromomyids, in particular with respect to the relative proportions of the hypoconulid lobe with the rest of the tooth. This would make the diagnosis for these species solely based on M3 morphology very limited and not very diagnostic. The holotype of Arcius rougieri, along with PAT1 bis and
PAT2, represent the first described gnathic fossils with associated teeth in a European paromomyid. The I1 of
A. rougieri differs greatly from those of A. fuscus and A. lapparenti (Rose et al., 1993) and is more similar to the deciduous I1 of A. fuscus and A. lapparenti (Fig. 6) in that the anterocone is the tallest cusp rather than the mediocone (tallest in adult specimens attributed to A. fuscus and A. lapparenti). In addition, the laterocone is more proximally located to the mediocone in juveniles of A. fuscus and A. lapparenti than in adult representatives of the tooth, as is observed in the adult form of A. rougieri. There are some differences, however, between the I1 of A. rougieri and the deciduous I1 of A. fuscus and A. lapparenti in that the mediocone is better developed in juveniles of A. fuscus and A. lapparenti while the posterocone is less so, although the posterocone is still poorly expressed in A. rougieri compared to the condition in most adult paromo- myid I1s. PAT1 is inferred to pertain to an adult because all of its
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