Litomylus grandaletes, S.Scott & C.Fox & P.Youzwyshyn, 2002

S. Scott, Craig, C. Fox, Richard & P. Youzwyshyn, Gordon, 2002, New earliest Tiffanian (late Paleocene) mammals from Cochrane 2, southwestern Alberta, Canada, Acta Palaeontologica Polonica 47 (4), pp. 691-704 : 695-697

Litomylus grandaletes sp. nov.

Fig. 2; Table 3.

Holotype: UALVP 25000 , incomplete right maxilla containing M2 and alveoli for M1 and M3, Fig. 2C.

Type horizon and locality: Cochrane 2, Paskapoo Formation, southwestern Alberta.

Age and distribution: Earliest Tiffanian of Alberta (type locality) .

Etymology: Grandis, Latin, meaning “large, great, grandparent”, aletes, Greek, meaning “grinder”, in reference to the large size of the species, primitive dental morphology, and possible ancestry to Aletodon .

Material.—UALVP 18405, P4; UALVP 340, 25003, 25005, M1s; UALVP 45119, 45122, M1s or M2s; UALVP 25001– 25002, M2s; UALVP 45092, 45120, M3s; UALVP 25010, 25015, 45113, 45115, 45121, 45124, 45125, m1s (total: 7); UALVP 25008, 25009, 25012, 25013, 45093, 45116–45118, 45123, m2s (total: 9); UALVP 25014, 45114, m3s.

Diagnosis.—Differs from other Litomylus species except? Litomylusishami Gazin, 1956b in size (molar teeth approximately 25 percent larger than those of Litomylus orthronepius Johnston and Fox, 1984 , Litomylus dissentaneus Simpson, 1935a , or Litomylus scaphicus Gazin, 1956a , and 13 percent larger than those of Litomylusosceolae Van Valen, 1978); differs further from Litomylusosceolae in having less inflated molar cusps and a better developed, more lingual paraconid on m1.Differs from? Litomylusishami Winterfeld, 1982 in possessing stronger crests and taller, less−inflated molar cusps, and better−developed paraconids and cingulids on the lower molars.

Description.—P4: UALVP 18405 is similar to P4, L. dissentaneus , in its overall structure, but the crown is more inflated. It is rounded in occlusal view and displays two cusps, a paracone and protocone, both of which are bulbous.The parastylar and metastylar areas, and the ectocingulum are greatly reduced.The parastylar lobe is bluntly rounded.A short crest extends posteriorly from the paracone; the tip of the paracone and the summit of the crest are heavily worn. The paracone crest ends at a tiny metastyle, which is more posterolingual in position than in L. dissentaneus .No evi − dence of a metacone is present.The ectocingulum is very weakly developed labial to the paracone, but is conspicuous more posteriorly.The preprotocrista is weak, while the post − protocrista is robust and runs labially to the metastyle. A short, poorly developed crest connects the bases of the paracone and protocone; neither pre− nor postcingulum is developed.

M1: The crown is slightly wider than long and subrectangular in occlusal view, with stout cusps.The antero − labial corner of the crown is rounded and no separate parastylar lobe is developed; the metastylar corner is more acute, projecting further labially, and has a flat posterior side.The ectocingulum is robust and the ectoflexus fairly deep.The paracone and metacone are low, stout, subconical, and subequal in height.The postmetacrista bends abruptly labially and meets the ectocingulum at the acute posterolabial corner of the crown; the postmetaconule crista turns labially as well, meeting the postmetacrista posterolabial to the metacone. The protocone and hypocone are robust and swollen.The precingulum, and especially the postcingulum, are prominent; on UALVP 25005, a weak “accessory” cingulum arises posterobasal to the postcingulum.Small cuspules are present on the ectocingulum and precingulum.

M2: Compared to M1, M2 is substantially wider and its cusps are more massive in construction.The anterolabial margins of the crown protrude labially and anteriorly.The posterolabial corner is flattened labially and less strongly developed than the comparable parts on M1.The paraconule is nearer to the apex of the protocone than on M1, and the postmetaconule crista terminates labial to the postmetacrista. The bases of the hypocone and protocone are more swollen, and these cusps are larger overall than on M1.The post − cingulum is deeply notched between the protocone and hypocone, especially on UALVP 340, in which a small cuspule arises from the posterolingual side of the protocone.

M3: The M3 of L. grandaletes is more transverse than that of L. dissentaneus , but is otherwise similar; in both, the conules are weak, the conule cristae are absent, and there is no hypocone.The pre− and postcingulum are conspicuous on all M3s of the species from Cochrane 2.On UALVP 25004 and 25006, a crest extends between the postprotocrista and postcingulum, slightly lingual to the metaconule.

m1: In occlusal view, the crown of m1 is hourglassshaped, with stout trigonid and talonid cusps.The trigonid and talonid are nearly equal in width.The paraconid is ro − bust, with a distinct apex that projects anteriorly.The para − cristid extends labially and then swings sharply posteriorad to the apex of the protoconid.The metaconid and protoconid are inflated at their bases, but these cusps are acute apically. The cusps of the talonid are swollen as well, but have high, sharp apices and well−defined crests.On UALVP 25010 and 25015, a small mesoconid arises from the cristid obliqua.The talonid basin and notch are deep; the basin is deepest at the apex of the notch.The pre− and postcingulid are well devel − oped.A weak labial cingulid crosses the hypoflexid; its enamel is wrinkled on the surfaces of the protoconid and hypoconid.

m2: The m2 of L. grandaletes is substantially wider than m1, and its paraconid is more labial and closer to the metaconid than on the more anterior molar.On UALVP 25008, a crest between the apex of the metaconid and the posterolingual corner of the paraconid encloses the trigonid basin.A broad labial cingulid joins the pre− and postcingulid to each other.A lingual cingulid sometimes extends from the para − conid past the metaconid and talonid notch; it is best developed on UALVP 25009 and 25013.The talonid resembles that of m1, except that it is larger and has a prominent mesoconid on the cristid obliqua.

m3: The m3 of L. grandaletes is less transverse than m2, with a low trigonid and short, broad talonid.The paraconid and metaconid are as closely appressed as on m2, and a crest from the paraconid extends to the metaconid, joining it anteromedially.The precingulid is robust and curves labially around the base of the trigonid to the hypoflexid.The hypo − conulid projects posteriorly but is not as large overall as the entoconid.A short postcingulid extends between the hypo − conid and hypoconulid.

Remarks.—Although comparable parts of the dentition of L. grandaletes sp.nov., and the genotypic species, L. dissentaneus , are similar, they differ significantly in several features.For example, the trigonid is higher in L. grandaletes , and the paraconid more cuspidate and more lingual in position, the trigonid and talonid cusps are not as swollen, the talonid cusps are higher, and the labial cingulid is prominent, especially on m2.The lower molars of L.grandaletes closely approximate those of L.orthronepius from the Puercan Medicine Hat Brick and Tile Quarry (Rav W−1 horizon) of southwestern Saskatchewan ( Johnston and Fox 1984), but differ in their larger size, more swollen cusps, and medial paraconid, especially on m2.In regards upper molar morphology, L. grandaletes most closely resembles L. orthronepius , but the upper molars of L.grandaletes are more transverse, and have a stronger ectocingulum and wider stylar shelf; both species possess a prominent parastylar area on M2.The molar struc − ture of L. grandaletes is also similar to that of Aletodon Gingerich, 1977 , from the middle Tiffanian to the late Clarkforkian of Colorado, Wyoming, and North Dakota ( Gingerich 1977; Rose 1981a; Gingerich 1983).A transition from L. grandaletes to A. quadravus , the earliest species of the genus, would require further inflation of the molar cusps, reduction of the molar crests, slight reduction of the paraconid, and a decrease in crown height.