Oligoryctes cameronensis Hough, 1956

ASHER, ROBERT J., McKENNA, MALCOLM C., EMRY, ROBERT J., TABRUM, ALAN R. & KRON, DONALD G., 2002, Morphology And Relationships Of Apternodus And Other Extinct, Zalambdodont, Placental Mammals, Bulletin of the American Museum of Natural History 2002 (273), pp. 1-117 : 58-69

Oligoryctes cameronensis Hough, 1956

TYPE SPECIMEN: USNM 19909 , rostrum (38) with right P2­P4, broken M1, M2­M3, left P3­M3, preserving pterygoid region, associated left dentary with p3­m3 (fig. 39) ; original lost, known only from illustrations.

REFERRED MATERIAL: USNM 516840, undistorted cranium (fig. 40), missing premaxillae and mandibles, preserving left?C, P2, dP3, erupting P3, P4­M3, right P2, dP3, erupting P3, P4­M3; USNM 516846, left dentary with p3­m3; UCM 52446, rostrum (fig. 41) with left broken I2, I3­M3, right I2, P2­M3, orbitotemporal region, articulated left dentary with complete dentition except for missing crown of i3, associated right dentary with p3­m3 (fig. 42); MPUM 6677, left dentary with heavily worn i1­m3; MPUM 6859, right?M1, left maxillary fragments with P3­M3, associated left petromastoid fragment preserving superior semicircular canal and stapedius fossa, missing bulk of pars cochlearis; CM 17193, rostrum with right and left P3­M3 plus anterior alveoli (fig. 43; original lost, known only from photos); CM 73977, associated right and left dentaries, each with p4­m3.

TEMPORAL AND GEOGRAPHIC DISTRIBUTION: Chadronian (late Eocene) of central Wyoming (Cameron Spring 5, Flagstaff Rim 18) and western Montana (Pipestone Springs 29, Eureka Valley Rd. 16), probably also northwestern Nebraska (33; see Ostrander, 1987) .

DIAGNOSIS: The small maxillary rudiment of the zygoma is located lateral to the posterior edge of M1. The type skull shows a foramen in the alisphenoid posterior to the enlarged foramen ovale, similar in position to the alisphenoid foramen transmitting the inferior stapedial ramus in some tenrecs ( Asher, 2001). A small foramen is evident on the rostrum near the nasal­frontal suture, as are foramina laterally along the path of the sinus canal, above the external auditory meatus and jaw joint. The dental formula is 3.1.3.3/3.1.3.3, differing from that of Apternodus in having one more upper incisor. The crown of P3 is longer than that of P4; both show a prominent, anteriorly projecting parastyle. The trigonids of the lower molars decrease progressively in width, with that of m1 the largest and m3 the smallest. The talonid of the m3 is elongate, making this tooth the longest in the molar series. As in O. altitalonidus , the m3 talonid cusp is slightly greater in height than the m3 paraconid; the medial aspect of the coronoid process is pocketed; and the coronoid process is externally convex.

REMARKS: USNM 516840, collected by one of us (RJE) from Flagstaff Rim, is by far the best specimen yet known of this taxon (fig. 40). It is one of the few small ‘‘apternodontid’’ specimens known that preserves petrosals and elements of the deciduous dentition; and its pristine state of preservation is also quite remarkable. The undistorted rostrum shows sutures between the nasals and maxilla; the nasal­frontal suture is faint, but appears to delimit a posteriorly narrow nasal. A small foramen is present in the rostrum at the posterior margin of the nasal. Premaxillae are missing. The lacrimal foramen is large, laterally directed, and situated on the anterior aspect of the infraorbital canal. The frontalmaxillary suture is also visible and appears to extend well into the orbit, accompanied by the roots of the maxillary teeth (fig. 40). The maxilla anterior to the infraorbital canal is also perforate and shows roots of the erupting permanent P3. The posterior ethmoid region is broad and contributes to a slight postorbital constriction.

The braincase is well preserved and shows no sign of sutures within the frontal or between the frontal, parietal, and occipital, although numerous hairline cracks, some bilateral, may represent such sutures. In contrast, the petromastoid shows well­defined sutures with the occipital, parietal, and squamosal, and is well­exposed laterally. The petromastoid­squamosal suture extends ventrally onto the basicranium and defines the lateral boundary of the tympanic cavity. The squamosal also shows fairly well­defined sutures with the parietal and alisphenoid. On the squamosal side of the squamosal­parietal suture are three foramina, two located adjacent to the petromastoid, and one dorsal to the jaw joint.

USNM 516840 shows four foramina anterior to the sphenorbital fissure. The anteriormost is a large ethmoid foramen, providing a conduit into the anterior cranial fossa and posterior ethmoid region. Immediately posterior and ventral is a much smaller foramen which may also connect the orbit with the anterior cranial fossa. Continuing posteriorly, the next large foramen is the anterior exit point of the sinus canal; slightly medial to that is a small optic foramen. Both the sinus canal and the optic foramen are located immediately anterior to the large sphenorbital fissure, the ventral boundary of which is continuous with the pterygoid. Posterior to the palate, sutures are evident between the Vshaped vomer and pterygoids.

The most conspicuous openings on the basicranium of USNM 516840 are the large piriform fenestra and foramen ovale. The latter is slightly larger than the sphenorbital fissure, and the piriform fenestra is as large as the bony promontory itself. Posterior to foramen ovale, and within the base of the entoglenoid process, is a foramen that served as a conduit for the inferior ramus of the stapedial artery (mentioned above as similar in position to that of tenrecs such as Geogale ; see Asher, 2001). Subtle grooves on the promontory bone indicate that the internal carotid artery entered the tympanic cavity at the ventral apex of the pars cochlearis, just medial to the prominent caudal tympanic process of the promontory. It immediately bifurcated into a proximal stapedial ramus, which traversed laterally toward the fenestra vestibuli, and a transpromontorial internal carotid (sensu Wible, 1986), which ran anteromedially, entering the braincase via the piriform fenestra. A foramen in the basisphenoid at the dorsomedial margin of the tympanic cavity is smaller in caliber than the groove for the internal carotid on the pars cochlearis. Hence, we believe this foramen provided a conduit for a small vidian artery, branching from the internal carotid immediately proximal to the latter’s path through the piriform fenestra.

Zygomatic arches are completely lacking, and both maxillary and squamosal rudiments of the zygoma are reduced. As in Apternodus , the jaw joint is defined posteriorly by the entoglenoid, not postglenoid, process. This is located medial to the postglenoid foramen and anterior to the middle ear.

The upper molars of USNM 516840 are fully erupted and show minimal wear. P4 is almost fully erupted; P3 is still in its crypt, but some cusps are evident dorsal to dP3. P2 is fully erupted and minute in size. The right upper canine is missing; on the left side it is intact but not yet fully erupted and is displaced posteriorly.

Also noteworthy among the new specimens of O. cameronensis is UCM 52446, a well­preserved rostrum (fig. 41) and associated, largely complete mandible (fig. 42). Its dentition is fully erupted and shows a permanent P3 that is larger than the dP3 of USNM 516480, particularly the paracrista running posterior to the paracone. The dentary shows trigonids of m1­m3 becoming progressively smaller posteriorly, as well as multicuspid incisors. Otherwise, UCM 52446 conforms with the morphology evident in USNM 516840.

Some of Hough’s (1956) original descrip­ tion of Oligoryctes does not accord with the material that we now have available. Unfortunately, the type specimen designated by her ( USNM 19909 ) now appears to be lost ; however, one of us (MCM) previously had an opportunity to examine it. Her diagnosis stat­ ed (1956: 538) that the basicranial region differs from that of Apternodus ‘‘in having lateral descending processes of the basisphenoid, which embrace medially the small anterior bullae.’’ The features in question are actually the medial walls of the sphenorbital fissures; and the contents of the ‘‘anterior bullae’’ consist principally of matrix fillings of the trigeminal nerve tracts. If the lower teeth are placed in occlusion with the uppers, this area may be seen to lie well in front of the jaw suspensorium. The medially excavated coronoid process of the mandible was not seen by Hough because the specimen was incompletely prepared at the time it was described.

McDowell (1958: 171, 172) also mistakenly regarded Oligoryctes as possessing an ossified auditory bulla, going even farther than Hough by arguing (p. 171) that Apternodus also possessed an ossified bulla, based on a presumed close relationship between the two genera. However, elsewhere in his paper ( McDowell, 1958: 167–168), he seems to have recognized Hough’s mistake: ‘‘ Hough (1956) claims that the basisphenoid tympanic wing is present in Oligoryctes , a genus probably closely related to Apternodus . However, this is not clear from the specimen and appears rather to be but a slight selvage of basisphenoid against the ear chamber and does not have the characteristic position of the lipotyphlan basisphenoid, abutting against the Eustacian cartilage.’’ In any event, new material described here of both Apternodus and Oligoryctes clearly demonstrates that the middle ear of both taxa is similar to that of soricids and Solenodon , with neither taxon showing an ossified auditory bulla, and both showing a piriform fenestra (polymorphic within A. brevirostris and A. mediaevus ).

Oligoryctes altitalonidus Clark, 1937 (new combination, formerly ‘‘ Apternodus ’’

altitalonidus )

TYPE SPECIMEN: YPM PU13774 , left dentary with p4­m3 ; original lost but casts remain (fig. 44).

(top), dorsal (middle), and lateral (bottom) views.

REFERRED MATERIAL: USNM 516843, nearly complete skull (fig. 45), slightly compressed dorsoventrally, missing petrosals, with associated mandibles with left i1­m3 and right p3­m3 (fig. 42); USNM 22816, associated right maxillary fragments with P2­ M3 (fig. 46); USNM 516841, left dentary with m1­m3; USNM 516842, rostrum with nearly complete dentition including dP3 and dP4 and erupting left P3­P 4 in crypts, plus associated mandibles with complete dentition; USNM 516847, left dentary with p3­ m3; USNM 516848, left dentary with p4­ m3; USNM 516849, left dentary with p4­ m3; USNM 516850, right dentary with p3­ m3; USNM 516851, right dentary with p4­m3; USNM 516852 left dentary with m1; USNM 516853, left dentary with p3­m3; USNM 516854, rostrum with right and left P3­M3; USNM 516855, rostrum with heavily worn left C­M3 and right P3­M3; USNM 516856, rostrum with right C­M3 and left C­ P4; USNM 516857, rostrum with right P3­ M3 and left P3­P4; USNM 516858, right dentary with m2­m3; USNM 516862, left maxilla with P3­M2; USNM 516863, right maxilla with P3, M1­M3; USNM 516864, right maxilla with M1­M3; USNM 516865, left dentary with m1­m3; USNM 516866 left maxilla with M1­M2; USNM 516867, anterior braincase and rostrum with right P3­M3 and left P4­M3; USNM 516868, left dentary with m1­m3; USNM 516869, left dentary with p3­m3; USNM 516870, left dentary with m2; AMNH 105310, right dentary with p4­m3; MPUM 0414, left dentary with p3­ m3; MPUM 2592, left dentary with m2­m3; MPUM 6797, left dentary with p4­m2; MPUM 6857, left dentary with p4­m3; MPUM 6858, rostrum with right and left P3s; CM 9260, right dentary with p3–4, m2– 3; CM 71571, left dentary with p4­m2; CM 71572, left dentary with m1­m2; CM 71573, left dentary with m2–3; and CM 73976, right maxilla with P4­M2.

TEMPORAL AND GEOGRAPHIC DISTRIBUTION:

Uintan (middle Eocene) through Orellan (early Oligocene) of Wyoming (Flagstaff Rim 18, East Fork Basin 12), Montana (Pipestone Springs 29, Diamond O Ranch 9, Little Pipestone Creek 25, Cook Ranch 7), South Dakota (Big Badlands 4), and North Dakota (Fitterer Ranch 17). Geographic distribution probably also includes Saskatchewan (8; see Storer, 1996) and California (34; see Walsh, 1996).

DIAGNOSIS: Unlike Apternodus , and like most other mammals including Oligoryctes cameronensis , O. altitalonidus lacks the extensive, box­shaped structures of the posterior braincase. Instead, its braincase is round­ ed and gracile, as in Microgale . O. altitalonidus possesses a maxillary rudiment of the zygoma lateral to M2, slightly posterior to that of O. cameronensis . O. altitalonidus is smaller than all other Tertiary zalambdodonts except for the unnamed Tabernacle Butte taxon ( McKenna et al., 1962; Bloch et al. in prep.). Perhaps the most conspicuous similarity with O. cameronensis is the large size of foramen ovale, which is greater in diameter than the jugular foramen (fig. 45). The squamosal is posteriorly elongate, forming the lateral border of the large piriform fenestra. The stylar crests of P3 are elongate, as in O. cameronensis . In contrast to Apternodus and O. cameronensis , this species possesses a p1, one of eight teeth anterior to the three lower molars; hence, its dental formula is 3.1.3.3/3.1.4.3. The p3 shows a cingulid buccally. As in O. cameronensis , the m3 is longer than more anterior cheek teeth, and the posterior two incisors are tricuspid. The tall trigonid cusp on m3, for which this species was named, is also present in the larger O. cameronensis and the Tabernacle Butte taxon. Unlike O. cameronensis , the molar trigonids of O. altitalonidus are similar in size and do not decrease markedly from m1 to m3. The medial side of the coronoid process is pocketed, as in modern soricids. Unlike soricids, the coronoid process is bowed in shape, or externally convex.

REMARKS: USNM 516843 (figs. 42, 45) is the best specimen of O. altitalonidus yet known. Several additional specimens from Pipestone Springs (USNM 22816; fig. 46) and Flagstaff Rim (e.g., USNM 516842, 516854, and 516857) confirm details of cra­ nial anatomy of this genus evident from USNM 516843. USNM specimens from Fitterer Ranch (516868–516870) document the previously unknown presence of this species in the Orellan of North Dakota. In addition to fully erupted M1­M3, USNM 516842 shows an erupting P3 and P 4 in the process of replacing their deciduous precursors, demonstrating that unlike shrews, O. altitalonidus had functional deciduous teeth. As in O. cameronensis , P4 erupts prior to P3.

Oligoryctes altitalonidus resembles O. cameronensis more than it does any species of Apternodus . It shares a zalambdodont dentition with both Apternodus and O. cameronensis , but lacks the derived shape of the Apternodus posterior braincase. O. altitalonidus shares with O. cameronensis an enlarged foramen ovale, an elongate P3, and multicuspid lower incisors. For these reasons, many previous authors (e.g.,. Emry, 1979; Tabrum et al., 1996; Robinson and Kron, 1998) have referred to this species using the name Oligoryctes altitalonidus , a combination that we support.

UNNAMED TAXON FROM TABERNACLE BUTTE AND ELSEWHERE (formerly ‘‘ Eoryctes ’’ Romer, 1966 nomen nudum)

TYPE SPECIMEN: To be determined by Bloch et al. (manuscript in progress).

REFERRED MATERIAL: USNM 417465, left maxillary fragment with M1­M3; USNM 417464, distorted left dentary with p3­m3; CM 13627, left dentary with m1­m3, original lost but casts remain (see fig. 47); CM 13859, left dentary with m2; DMNH 8776, right dentary fragment with broken m1, talonid of m2, and partial alveolus for m3; probably also AMNH 55689, edentulous mandibular fragment mentioned by Simpson in McGrew et al. (1959).

TEMPORAL AND GEOGRAPHIC DISTRIBUTION: Bridgerian (early middle Eocene) of eastern Nevada (Elderberry Canyon 14), southwestern Wyoming (Tabernacle Butte 37), northeastern Utah (Powder Wash 31), and Uintan (middle Eocene) of northwestern Colorado (Sand Wash 35).

REMARKS: Among taxa that lack a talonid basin and metacone, the Tabernacle Butte

species is unique by virtue of its deep anterior cingulum and large protocones of the upper molars, medially deep but not fully pocketed coronoid process, and extreme small size.

Several authors, including McKenna et al. (1962) and Emry (1990), have acknowledged the presence of this as yet unnamed, diminutive, early­middle Eocene ‘‘apternodontid’’. In fact, based on previously circulated, unpublished versions of this paper, Romer (1966) prematurely called this taxon ‘‘ Eoryctes ’’, a name now unavailable as it was used by Thewissen and Gingerich (1989) for a genus of palaeoryctid. As of early 2002, J. Bloch et al. have a manuscript in progress that will name this taxon, including additional material from southwestern Wyoming in the University of Michigan collections. We defer to them for nomenclature, but will use available material of this species as an informally named terminal taxon (i.e., ‘‘Tabernacle Butte taxon’’) in our phylogenetic analyses.

PARAPTERNODONTIDAE , NEW FAMILY

INCLUDED GENERA: Parapternodus Bown and Schankler, 1982 ; Koniaryctes Robinson and Kron, 1998 .

TEMPORAL AND GEOGRAPHIC DISTRIBUTION: Wasatchian (early Eocene) of northern Wy­

oming (Clark’s Fork, Bighorn, and Powder River basins).

DIAGNOSIS: Known only from fragmentary teeth and jaws, the members of this small, shrew­sized family have zalambdodont molars with a reduced, unbasined talonid and lack buccal cingulids and an m3 posterior cusp. The m3 is anteroposteriorly shorter than m1 or m2. The anterior incisor is enlarged, leaving a large alveolus that extends posteriorly along the base of the jaw at least as far posteriorly as p3 (figs. 48, 49).