Apeomyoides savagei, Smith & Cifelli & Czaplewski, 2006
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publication ID |
https://doi.org/ 10.5281/zenodo.13644208 |
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publication LSID |
lsid:zoobank.org:pub:795AFE23-E400-4264-813C-697154BD3946 |
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persistent identifier |
https://treatment.plazi.org/id/03A287F3-2E7B-FF8A-BF69-FECEAFCEFEB9 |
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treatment provided by |
Felipe |
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scientific name |
Apeomyoides savagei |
| status |
gen. et sp. nov. |
Apeomyoides savagei gen. et sp. nov.
Figs. 2 View Fig , 3 View Fig .
Etymology: Species named in honor of Donald E. Savage, for his contributions to the study of Tertiary mammals and for helping the senior author with the loan of important material and innumerable other courtesies.
Holotype: UCMP 109300 View Materials , right dentary with p4–m3 ( Figs. 2A View Fig , 3A View Fig ).
Hypodigm.— Holotype, UCMP 109300 View Materials , right dentary with p4–m3 ( Figs. 2A View Fig , 3A View Fig ); OMNH 54618 View Materials , right p4; OMNH 54619 View Materials , left m1 or m2; OMNH 54620 View Materials , left m3; and OMNH 54621 View Materials , right dentary fragment with p4–m2.
Referred material.—OMNH 54746, left m1 or m2; OMNH 54747, left m1 or m2; UCMP 109301, left dentary fragment with m3; UCMP 141564, left dentary fragment with p4–m2; UCMP 141774−01, left M1 or M2 ( Figs. 2B View Fig , 3C View Fig ); UCMP 141774−02, left M1 or M2; UCMP 141774−03, left m1 or m2; UCMP 141774−04, right p4; UCMP 141774−06, right m1 or m2; UCMP 141774−07, left p4; UCMP 141774−08, left DP4 ( Figs. 2C View Fig , 3B View Fig ); UCMP 141818−02, left p4; UCMP 141818−03, right m1 or m2.
Locality and age.—UCMP V70139, V70140, and V70147, Monarch Mill Formation, Eastgate local fauna, Churchill County, Nevada; early Barstovian.
Diagnosis.—A large eomyid that is bigger than Apeomys and Megapeomys lavocati Fejfar, Rummel, and Tomida, 1998 from Eurasia, smaller than Megapeomys lindsayi Fejfar, Rummel, and Tomida, 1998 and Megapeomys sp. from Eurasia, and Megapeomys bobwilsoni from North America. Differs from all known Neogene eomyids in North America and Eurasia in having a very long diastema and a procumbent incisor (except Megapeomys ). A mental foramen is anterior to p4 near the level of the ventral shelf of the masseteric scar, whereas in Apeomys and Megapeomys it occurs near the level of the dorsal shelf. Both shelves are weak, but strong in Apeomys . A rounded masseteric scar terminates below the anterior roots of the m1, but in Apeomys and Megapeomys it ends below the anterior root of p4. All cheekteeth are bilobed and higher crowned than Apeomys , Megapeomys , and Arikareeomys . An entoloph is incomplete on M1 and M2, but is complete in M. bobwilsoni , and reduced but more prominent in Arikareeomys . The transverse valley (syncline IV) between the hypolophid and posterolophid is closed labiolingually on the m1–3, whereas in M. bobwilsoni it is open. The posteriormost valley (syncline IV) opens into the central transverse valley (syncline III), whereas they are closed in Arikareeomys . An ectolophid is absent from all lower cheekteeth, but present in Arikareeomys . The cheekteeth are rectangular in occlusal outline, not barrel−shaped as in other apeomyines (e.g., M. bobwilsoni ). The lophids of unworn cheekteeth are very rugose. Two roots occur on the p4 and three roots occur on the m1–m3; in M. bowilsoni , however, the p4 has three roots and the m1–m3 possess four roots. The p4 is the largest of the lower cheekteeth, whereas the p4–m2 are subequal in size for Apeomys .
Description
Upper premolars.—P3 is absent and the P4 is not known at present. The DP4 possesses four major cusps (protocone,
paracone, hypocone, and metacone) and four lophs (protoloph, mesoloph, metaloph, and posteroloph) with three transverse valleys (synclines II, III, IV). The anteriormost valley forms an isolated lake (syncline II). The protoloph extends labially from the anterolabial margin of the protocone but does not reach the paracone. The protocone and paracone are not joined directly by the mesoloph; instead, the mesoloph joins the protoloph lingual to the protocone. Absent are the anteroloph, mesocone and mesostyle. Unlike the mesoloph, the metaloph is complete and joins the hypocone to the metacone. The posteroloph arises along the posteromedial margin of the hypocone and joins the metacone. The posteroloph is anteroposteriorly narrow and closed labially, forming a D−shaped enamel lake (syncline IV).
Upper molars.—The M1 and M2 are subquadrate, trigon and talon equal, high crowned, and similar in size to the DP4. The protoloph arises high on the anterolabial margin of the protocone and traverses the anteriormost edge of the tooth but does not join the paracone. The protoloph and mesoloph do not join at the paracone; thus, the anterior transverse valley (syncline II) is open lingually (lacks a D−shaped enamel lake). A prominent mesocone is present. The posterior arm of the entoloph (spur or endoloph; see Korth 1992; Morea and Korth 2002) is distinct and arises from the labial part of the metaloph. A mesostyle is absent. The hypocone and metacone are joined by a metaloph. A posteroloph arises along the posterolabial margin of the hypocone and does not reach the metacone; thus, the posterior valley does not form a D−shaped enamel lake and is open lingually. However, after heavy wear to the occlusal surface, a D−shaped enamel lake may appear.
Dentary.—The dentary has a very long diastema. A very small, anteriorly open mental foramen occurs along the dorsoventral midline of the dentary in the diastema, anterior to the p4, and near the level of the ventral shelf of the masseteric scar. The masseteric scar is rounded anteriorly, ends below the anterior margin of m1, and has weak ventral and dorsal shelves. A fossa occurs anterior to the distal end of the masseteric scar, below the p4, and may house a foramen. On the lingual surface of the dentary there are many foramina below the cheekteeth.
Lower cheekteeth.—The p4–m3 are high crowned, possess four cusps (metaconid, protoconid, entoconid, and hypoconid), four lophids (metalophid, mesolophid, hypolophid, and posterolophid), and three transverse valleys (synclines II, III, IV). The four lophids and their completeness (labial and lingual arms present) for the p4–m3 are as follows: metalophid complete, mesolophid variably complete (labial and lingual arms may not unite centrally), hypolophid variably complete (labial and lingual arms may not unite), and posterolophid complete. Based on specimens with a complete dentary (UCMP 109300 and OMNH 54621), it appears that the completeness of lophids (mesolophid and hypolophid) changes with wear to the occlusal surface from incomplete to complete, respectively. The metalophid and mesolophid of unworn cheekteeth are very rugose. Thus, heavily worn lower molars have complete lophids. There are three roots on all lower cheekteeth except p4, which has two large roots. The m1–m3 have two small anterior roots and a single, large, posteromedial root that occurs along the posterior part of the tooth.
The p4 is molariform and larger than the molars, is longer than wide, and has a metalophid that runs from the anteromedial margin of the protoconid and extends lingually to join the anterolingual margin of the metaconid. The protoconid and metaconid are joined centrally by a mesolophid. The ectolophid is absent. An anterolophid, mesoconid, and mesostylid are absent. A hypolophid arises along the labial margin of the entoconid and joins the posterolophid posterior to the hypoconid. A posterolophid arises along the posterolingual margin of the hypoconid and ends along the posteromedial margin of the entoconid; no hypolophulid is present. The posterolophid is anteroposteriorly narrow and closed labially forming a D−shaped enamel lake.
The m1 is slightly wider than long; on the anterolingual surface of this tooth, the metalophid arises high on the anterolabial margin of the protoconid and traverses the anterior margin of the tooth to join the anteromedial margin of the metaconid. The protoconid and metaconid are joined centrally by a mesolophid after late stages of wear. The ectolophid, mesoconid, and mesostylid are absent. The hypolophid is incomplete (it is incised mesiodistally along its midline), and therefore does not join the hypoconid and entoconid until very late stages of wear. The posterolophid arises along the posterolingual margin of the hypoconid and ends along the posteromedial margin of the entoconid. The posterolophid forms a D−shaped enamel lake. The m2 does not differ significantly in any characters or size from m1. The m3 is distinguished from the preceding molars only by its smaller size and a more rounded, narrower posterior margin that is triangular in shape.
Discussion
A combination of defining features for Apeomyoides savagei gen. et sp. nov. clearly distinguishes it from other Neogene eomyids. These characters include large size; high crowned cheekteeth with thick enamel; very long diastema; p4 largest of lower cheekteeth; and arrangements of lophs, transverse valleys, and submerged cusps. In addition to size, Apemyoides is unlike any other genus of Neogene eomyid from North America in that it lacks an anteroloph on all cheekteeth, has four lophs and three transverse valleys, and is bilophed (except Megapeomys ). Most North American eomyid genera possess an anteroloph, entoloph and ectolophid (both may vary from complete to incomplete), and have five lophs and four transverse valleys. The absence of an ectoloph or entolophid is also evident in Pseudotheridomys hesperus Wilson, 1960 from the Miocene of Colorado ( Wilson 1960; Korth 1992) and Apeomys from the Oligocene of Europe (Fahlbusch 1968; Korth 1992; Engesser 1999). Apeomyoides savagei gen. et sp. nov. also lacks an ectolophid but is larger than P. hesperus or Apeomys . However, A. savagei gen. et sp. nov. is smaller than Megapeomys bobwilsoni and slightly larger than Arikareeomys . This arrangment of characters clearly separates A. savagei from other described genera of eomyids.
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