Temnocyon altigenis Cope, 1878

Hunt, Robert M., 2011, Evolution Of Large Carnivores During The Mid-Cenozoic Of North America: The Temnocyonine Radiation (Mammalia, Amphicyonidae), Bulletin of the American Museum of Natural History 2011 (358), pp. 1-153 : 24-32

Temnocyon altigenis Cope, 1878 Figures 4–8 , 65

Temnocyon altigenis Cope, 1878 (December 3): 6– 8; 1879a: 68–70; 1879b: 55–69; 1881: 179; 1883: 238, figs. 2–3; 1884: 903–905, pl. 68, fig. 9, pl. 70, fig. 11.

Temnocyon altigenis: Merriam, 1906: 21–28 , text figs. 7–11, pl. 3 (fig. 2).

non Temnocyon altigenis: Thorpe, 1922: 167–168 ; Hough, 1948: 100–101 (YPM 10065 is removed from T. altigenis ).

TYPE: AMNH 6855, right mandible with p2–m2 and alveoli of the canine and p1, from the John Day beds, Oregon.

DISTRIBUTION: Early Arikareean, John Day Formation, Oregon.

DIAGNOSIS: Smallest and most plesiomorphic North American temnocyonine species distinguished from all other species of Temnocyon by small size and range of m1 lengths, 17.4–19.5 mm (table 2), and from T. subferox , T. fingeruti , and T. percussor by either M1 or P4 proportions (dental ratios A/B, C/D, table 6); from T. ferox and the huge T. macrogenys by much smaller size. Ratio of m1/m2 lengths, 1.67–1.83, indicating a short m2 relative to m1, thus distinct from species of Mammacyon (1.57, 1.61) but not from other Temnocyon species (ratios of 1.62–1.79) or Delotrochanter (1.64–1.69). Basilar length of skull,, 16–18 cm relative to 21–30 cm for other Temnocyon species (table 7); frontal sinuses moderately inflated.

REFERRED SPECIMENS: (1) AMNH 6856, left lower jaw with c, p2, p4–m2, alveoli of p1, p3, and m3, from the John Day beds, Turtle Cove, Grant County, Oregon; (2) AMNH 6857, right lower jaw with p2–m1, roots or alveoli of c, p1, m2–3, partial rostrum anterior to the orbits, with attached left lower jaw fragment, right C, P2–M2, alveolus of P1, left I3–C, P1–3, left c, p1–4, the entire left dentition highly fragmented, and a partial postcranial skeleton, from the John Day beds, Turtle Cove, Grant County, Oregon; (3) USNM 7940, left lower jaw with m1, m2 erupting, and damaged deciduous teeth; right maxilla with C, P1, P2–3 erupting, M1 fully erupted, P4 and M2 erupting, DP2–3, DC, from the John Day beds, Turtle Cove, Grant County, Oregon; (4) UCMP 1549, nearly complete uncrushed skull without basicranium, with right I1–2, alveolus for I3, C, P1–M2 (P4–M2 with parts missing); left I1–P1, P2 roots, P3–M2 (P4–M1 damaged), partial endocast of temporal lobes exposed and undistorted, from John Day beds, Morgan’s Place, UCMP loc. 874, Grant County, Oregon, collected by UCMP party, 1899; (5) UCMP 9999, skull with wellpreserved basicranium, associated lower jaws, and much of the postcranial skeleton; teeth present include right C–M2, left C–P4, M2 (damaged M1); right C–M2 (broken M3); left C–M3; from the John Day beds, Logan Butte, Crook County, Oregon, collected by Davis and Osmont, 1900.

DESCRIPTION: The lower jaws of the hypodigm are very similar in dental morphology and size and can be described as a group (AMNH 6855, 6856, 6857, USNM 7940, UCMP 9999). In 1884 Cope described and figured AMNH 6855 and the rostrum of AMNH 6857; he briefly mentioned AMNH 6856 and the jaws of AMNH 6857. Although Merriam (1906) mentioned UCMP 1549, it has never been described or figured, but in this same paper considerable attention was given

to the associated skull, jaws, and skeleton from Logan Butte (UCMP 9999), which is arguably the most plesiomorphic North American temnocyonine, based upon its dental traits.

The premolars of these lower jaws from the John Day beds are exceedingly similar in form and size: there is a progressive increase in size from p1–4, with p1 a rather small single-rooted tooth relative to p2–4. There are no accessory cusps with the exception of a prominent laterally placed posterior accessory cusp on p4, the plesiomorphic state for the subfamily. The premolars are not crowded except in young animals with newly erupting premolars. In adults the premolars are ranked in a linear series and are narrow with anterior and posterior slopes each traversed by a fine enamel ridge, running down each slope from the tip of the principal cusp to the base of the tooth. Only p4 shows any posterior expansion in width at the base of the tooth, and this is very slight (6.8 mm vs. 5.4 mm anterior width, AMNH 6855).

The molars are also similar in form and size within the hypodigm, with the exception of AMNH 6856, which has a short m2 relative to m1 length (table 6, ratio E/F, 1.83). All lower carnassials conform to a common pattern: the trigonid is high, the three principal cusps present but unequally developed—the tall protoconid is the main cusp, the paraconid and metaconid lower and at about the same height. The metaconid is somewhat reduced and is located both internal to and posterior to the protoconid. The paraconid forms a robust bladelike cusp anterointernally directed. The m1 talonid is short relative to the trigonid: it is much lower relative to the trigonid than in younger, larger species of temnocyonines in which the height inequity is resolved. The m1 talonid is dominated by a large, prominent, centrally placed hypoconid; there is no entoconid. The m2 is characterized by a trigonid somewhat longer than the talonid; there are two main cusps, the protoconid and hypoconid, situated one behind the other toward the labial edge of the tooth. The paraconid is small, occupying the anterointernal corner of m2. The m2 metaconid is absent or in USNM 7940, a juvenile with unworn teeth, a small vestigial metaconid is discernible; a low ridge extends from protoconid to the lingual edge of m2, and in all other specimens except USNM 7940 the ridge is uninterrupted by a metaconid cusp. The anterolabial corner of m2 is slightly protruded in some individuals (AMNH 6856).

The m3 is preserved only in UCMP 9999, where it is a very reduced version of m2. It is rectangular in occlusal outline, not circular. The protoconid and hypoconid are labially placed; there is a small paraconid.

Depth of the lower jaw below the m1 hypoconid (in mm) is: AMNH 6855, 30.7; AMNH 6856, 26.8; AMNH 6857,,25.4; USNM 7940, 20.6 (juvenile); UCMP 9999, 23.3.

The rostrum described by Cope (1884: 904–905, pl. 70, fig. 11) is much less well preserved than his description implies. The left upper and lower jaws are still in matrix and the teeth badly shattered so that preparation is unwarranted. The right upper dentition, which Cope figured, is so badly damaged that it would be useless for diagnosis were it not for the associated lower jaws. The only undamaged tooth is M2.

However, the intact upper teeth of UCMP 9999, described by Merriam (1906), can be used to supplement the description of Cope’s rostrum. UCMP 9999 from Logan Butte has a gracile dentition relative to the Turtle Cove material, which forms the greater part of the T. altigenis hypodigm. UCMP 9999 may prove eventually to represent a somewhat older and more primitive species but is here considered a gracile female morph of T. altigenis .

The upper premolars of UCMP 9999 are without accessory cusps and were not as crowded nor as tall as the lower premolars. They are triangular, narrow teeth with a slight widening at the posterior base of P3. P4 is a shearing carnassial, although the protocone is enlarged, anticipating the marked change in P4 form that occurs in the younger, more derived temnocyonines. There is little to distinguish the T. altigenis P4 from that of Daphoenus , other than the more prominent protocone in the former. P4 is surrounded by a distinct basal cingulum, more defined lingually.

M1 is intact only in UCMP 9999 and USNM 7940 where it demonstrates the plesiomorphic temnocyonine pattern. Portions of M1 occur in UCMP 1549 and AMNH 6857 where they indicate a tooth of the same type. The protocone is low and anteriorly placed as in Daphoenus , not yet completely isolated on a broad enamel flat as in younger, more derived temnocyonines. The cingulum anterior to the protocone was not swollen as it is in more derived species, an indication that this carnivore retained a highly sectorial carnassial. However, temnocyonine hallmarks have already appeared: the lingual cingulum is slightly swollen, and the paracone and metacone are prominent with a developed parastylar region. Consequently, both the labial and lingual parts of M1 are enlarged, creating the impression that the tooth is somewhat constricted in its middle part in occlusal view. The protocone of M1 is connected by a preprotocrista to the anterior cingulum, a feature retained in most larger, derived species of the genus. A small paraconule is present on the preprotocrista. The postprotocrista is absent and there is no metaconule. The configuration of M 1 in UCMP 9999 is the most plesiomorphic of any North American temnocyonine. From this pattern evolved the enormous crushing M1s of the more dentally derived Arikareean species of the subfamily.

M2 is much smaller than M1. Its metacone is more reduced, and its protocone is isolated on an enamel shelf surrounded by a thickened lingual cingulum. Length of the upper toothrow of AMNH 6857 from the anterior alveolar border of P1 to the posterior edge of M2 is 67.2 mm: crushing has to some extent altered the actual distance, but in UCMP 9999 where distortion is less, the same measurement is 67.3 mm. The only significant difference warranting mention between the rostrum of AMNH 6857 and UCMP 9999 is that the upper canine is larger and more robust in AMNH 6857, suggesting it is a male, and more slender and gracile in UCMP 9999, presumably a female.

The Logan Butte skull (UCMP 9999) preserves the basicranium in which the auditory region shows a deeply embayed basioccipital bone containing an enlarged inferior petrosal venous sinus that conforms to the amphicyonid pattern (see Basicranial Anatomy).

I refer to T. altigenis a well-preserved, undistorted skull (figs. 7, 8, UCMP 1549), lacking the basicranium, mentioned by Merriam (1906: 22–24, 29) but not figured. The skull was collected near the town of Monument during the 1899 University of California– Berkeley expedition to the John Day beds. Merriam considered this skull merely an uncrushed version of UCMP 9999 from Logan Butte; its large canines, broad rostrum, and inflated frontal region suggest that it represents an intact male cranium of the species.

In dorsal view UCMP 1549 is a robust skull, similar in overall form to the much larger skull of Mammacyon ferocior (F:AM 54134). The inflated frontals and expanded rostrum swollen around the large canines are believed to be male traits. The braincase of UCMP 1549, measuring 55 mm in greatest width, is surmounted by a low sagittal crest whose height is undetermined (the occiput is missing). Skull width decreases to 35 mm at the postorbital constriction, its narrowest point, and the width of the expanded frontal sinuses at the level of the postorbital processes is 46 mm. Anterior to the frontal region and the orbits, the maxillae are shallowly depressed, but in front of these depressions the snout expands due to the swelling of the maxillary region around the large canine roots: width of rostrum at the base of the canine roots is 40.7 mm. Both zygomatic arches are lost as is the occipital region and basicranium posterior to the basisphenoid. The distance between the infraorbital foramen and the posterior opening of the alisphenoid canal measures 83.4 mm.

I1–3 are preserved on the left side. I2 is somewhat larger than I1, but I3 is considerably larger than I2. I1 and I2 are worn flat at their tips but I3 is grooved obliquely on the posteroexternal face by the lower canine. There is a diastema of 4–5 mm between I3 and the upper canine. Width at the base of I3 (6.1 mm) relative to the more gracile I3 (4.6 mm) of UCMP 9999 reflects the malefemale dichotomy.

The canine is robust, its root causing inflation of the maxilla and consequently a widening of the rostrum. Only the canine root and a small segment of the base of each tooth is preserved, so wear grooves cannot be identified. The left canine measures 14.6 mm in anteroposterior length by 9.7 mm in width at the alveolar margin.

About 2 mm posterior to the canine is a small peglike unicuspid P1, measuring 5.8 in length, 4.0 mm in width at the base of the crown.

P2 measures 10.9 mm in length, 4.6 mm in greatest width. It is heavily worn on its posterior surface, is wider behind the main cusp than in front, and has no accessory cusps. The posterior slope is slightly more inclined than the anterior, and a fine enamel ridge runs down each slope.

P3 measures 12.8 mm in length, 5.9 mm in greatest width. It is expanded at its posterior base, has a posterior slope somewhat longer than the anterior, but because of wear it is not possible to decide if accessory cusps were present.

P4 measures 17.8 mm in length of the labial margin, 13.2 mm in greatest width. Although both upper carnassials are damaged, the form of the tooth is discernible, much like P4 of UCMP 9999, although the protocone is somewhat more enlarged than in UCMP 9999. Also, the P4 protocone of UCMP 1549 was somewhat more posteriorly situated relative to the protocone of UCMP 9999, although the difference is quite small. P4 remains a shearing tooth but its height and enlarged protocone foreshadow the change in P4 form that occurs in the more derived temnocyonines from younger rocks.

M1 is 13.5 mm in length, 18.7 mm in width, and is best preserved on the left side. Although the left M1 has a broken metacone, the tooth is nearly intact, whereas most of the right M1 is missing. M1 is worn, the tips of paracone and protocone beveled to flat surfaces. The paracone was larger than the metacone, and the labial portion of M1 bearing the paracone-metacone was elevated, with a developed parastylar region. As in UCMP 9999, the lingual faces of paracone and metacone form a shear surface that descends to an enamel platform forming the lingual half of the tooth. On this enamel flat is situated an apically worn protocone. A distinct ridge (preprotocrista) leads from the protocone to the anterior cingulum; there is no postprotocrista. The protocone region is widened but no more than in UCMP 9999; this expansion is the result of the swollen or thickened posterior and medial parts of the lingual cingulum surrounding the protocone region: there is no expansion of the tooth anterior to the protocone and an anterior cingulum of normal width is developed. Thus a tricuspid m1 trigonid with developed metaconid would be expected in the lower jaw and such a tooth occurs in UCMP 9999. Cope’s holotype lower jaw (AMNH 6855) and AMNH 6856, both with an m1 metaconid, occlude well with this skull. A small cuspule on the posterior border of M1 may represent a vestigial metaconule.

M2 measures 8.4 mm in length, 12.0 mm in greatest width. M2 is a small replica of M1 except that the protocone is more centrally located within the enamel flat forming the lingual half of the tooth. The paracone is slightly larger than the metacone. No conules seem to be present but the tooth is well worn. The protocone was apparently a prominent knoblike cusp, which has been worn to a flat surface; it was surrounded by a slightly swollen lingual cingulum. As in UCMP 9999, the M2 is situated on a plane slightly above M 1 in order to occlude with the m2, which was elevated and tilted forward on the ascending ramus of the mandible.

No M3 was present. M2 is the most posterior tooth in the maxilla and there is no space available for an M3.

The orbital region of the skull is intact and is characterized by a deeply excavated trough, which in its posterior part contains the sphenorbital fissure and the anterior foramen for the alisphenoid canal (the foramen rotundum in the beardog opens internally into the alisphenoid canal as in Ursus and Canis , hence cannot be seen). They are placed almost side-by-side where they perforate the sidewall of the skull, similar to their location in Ursus . Dorsal and anterior to this is a smaller optic foramen that also lies within the elliptical depression that includes the sphenorbital fissure and foramen for the alisphenoid canal. Leading directly forward beneath the optic foramen is a low horizontal ridge which extends craniad, 35 mm to end directly above the sphenopalatine foramina. This ridge probably marks the dorsal extent of the pterygoid musculature and corresponds closely to the palatine-orbitosphenoid suture. A second ridge runs upward at a 45 ° angle to the first, beginning above the sphenorbital fissure and coursing anterodorsad above the optic foramen. It forms the dorsal border of the elliptical depression housing these orbital foramina and terminates, 18 mm below the postorbital process. This same arrangement of ridges and foramina occurs throughout the Temnocyoninae and is evident in F:AM 54134 ( Mammacyon ferocior ) and YPM 10065 ( Temnocyon subferox ), and is suggested in YPM-PU 10787 ( T. ferox ) in which the orbital region is badly crushed.

Structure in the vicinity of the foramen ovale is similar in other members of the subfamily. The foramen ovale and posterior opening of the alisphenoid canal are contained in a deep common fossa. Anterior to this fossa is a shallow depression for pterygoid musculature, which is even more pronounced in T. subferox (YPM 10065) and Mammacyon (ACM 34–41, F:AM 54134). Medial to the common fossa for the foramen ovale and alisphenoid canal is an oval percussion fracture in the sphenoid bone, evidence that the missing basicranium may have been lost to a scavenger. Lateral to the foramen ovale is a remnant of the glenoid fossa. Little can be inferred about the middle ear cavity and surrounding basicranial structures other than that the anterointernal corner of the auditory region was deep, suggesting the presence of an auditory bulla similar to that known in Temnocyon (YPM 10065) and Mammacyon (ACM 34–41).

The skull of UCMP 1549 measures 146.5 mm in length from a point between the first incisors to the posterior border of the foramen ovale. The approximate distance between the same points on UCMP 9999 is, 130 mm. Basilar skull length of UCMP 9999 is, 167 mm. Assuming similar proportions for UCMP 1549, basilar length would be, 180 mm.

The rostrum of a juvenile animal (USNM 7940) from the John Day beds collected by William Day in 1883 includes part of the deciduous (DP2–3, DC) and permanent (P1, P4–M2 erupted) dentition. This animal agrees most closely with UCMP 1549 in the form of its P4–M1. P4–M1 are somewhat less sectorial than these teeth in UCMP 9999. This is evident in the more expanded protocone region of M1 and in the larger P4 protocone of USNM 7940. The unworn condition of these newly erupted teeth shows that initially the upper carnassial of T. altigenis had a modest cingulum entirely surrounding the tooth that was only weakly developed on the lingual face of the protocone. M1 is encircled by a cingulum as well, which is most pronounced posterolingual to the protocone and on the posterior face of the tooth but remains thin on the anterior face (as in UCMP 9999 and 1549). This condition of the cingulum clearly represents the plesiomorphic state prior to massive enlargement of the lingual cingulum in younger, larger temnocyonines.

DISCUSSION: Temnocyon altigenis Cope is the most dentally plesiomorphic species of North American temnocyonines, and also the smallest in body size. The hypodigm was collected from the John Day beds of Oregon; none are known from the Great Plains or elsewhere in North America. Skulls attributable to the hypodigm indicate carnivorans with basilar lengths of, 16 to 18 cm (table 7).

The dentition of T. altigenis shares similarities with the teeth of the late EoceneOligocene amphicyonid Daphoenus . The principal differences are: (a) T. altigenis has all teeth larger than those of Daphoenus vetus of Orellan age despite similar skull size; (b) T. altigenis has taller premolars than Daphoenus (excluding P1/p1); (c) the T. altigenis P4 is larger and has a more robust lingually extended protocone relative to Orellan Daphoenus ; (d) M1–2 of T. altigenis have expanded or swollen lingual cingula not found in Daphoenus ; (e) T. altigenis has lost M3 which Daphoenus retains; (f) lower molars of T. altigenis lack entoconids, and have an enlarged m1 hypoconid and only an m2 protoconid and hypoconid relative to Daphoenus , which has a plesiomorphic amphicyonid m1–2; (g) T. altigenis has lost the m2 metaconid that Daphoenus retains.

Merriam’s (1906) associated skull, mandibles, and partial postcranial skeleton from Logan Butte (UCMP 9999), is here interpreted as a small female of the T. altigenis hypodigm. The gracile canines, less swollen snout, less expanded frontal region, and smaller overall skull size are believed to indicate the female morph. Logan Butte is an isolated John Day outlier far distant southwest of Turtle Cove where most other T. altigenis fossils were found. Eventually UCMP 9999 may prove a distinct speciesthe most plesiomorphic North American temnocyonine—but for the present it is placed within T. altigenis as its teeth and dental measurements do not merit separation.

Temnocyon altigenis from the John Day beds shares some dental characteristics with European haplocyonine amphicyonids from the Aquitanian Allier Basin localities of StGérand, France. A holotype mandible of Haplocyon elegans (MNHN-SG 395: Bonis, 1966: pl. 3, fig. 4; Viret, 1929: pl. 8, fig. 1) displays teeth and dental measurements much like those of the Logan Butte jaw of T. altigenis (UCMP 9999). The holotype of Haplocyon crucians (MNHN-SG 404: Viret, 1929: pl. 8, fig. 2), a partial ramus with p2–4, and an m1 (MNHN-SG 403) are comparable to Cope’s holotype of T. altigenis (AMNH 6855). This similarity between haplocyonine and temnocyonine dentitions had been previously noted by Viret (1929) and Bonis (1973).

In 1992 I was able to study Aquitanian haplocyonines in Paris through the courtesy of L. de Bonis and L. Ginsburg. Of all haplocyonines, Haplocyon elegans and H. crucians from St-Gérand are dentally closest to John Day T. altigenis , which is the most plesiomorphic North American species. However, subtle yet evident dental differences distinguish the St-Gérand forms from John Day T. altigenis —although similar in mandibular length, depth and tooth size, H. elegans (MNHN-SG 395) is dentally more plesiomorphic than UCMP 9999: (1) its m1 metaconid is not as reduced as in UCMP 9999; (2) the more plesiomorphic m2 trigonid is taller and wider, with fully developed metaconid, a low talonid with labially placed hypoconid, and an internal talonid shelf. In UCMP 9999 there is no m2 metaconid, the talonid is nearly equal in height to the trigonid, and the hypoconid nearly fills the talonid, which is not the case in MNHN-SG 395. In all the dental features where UCMP 9999 is more derived than MNHN-SG 395, the small Logan Butte carnivore closely approaches Cope’s larger holotype of T. altigenis (AMNH 6855), suggesting a plausible male-female relationship between the two John Day fossils.

Finally, the age of the derived Logan Butte Temnocyon altigenis , found in proximity to tuffs dating from,28.8–29.3 Ma, seems in conflict with the probable younger age (within MP29-MN2:,26–20.5 Ma) of the more plesiomorphic Haplocyon elegans jaw from the St-Gérand basin.

Figures

Fig. 4. Temnocyon altigenis (UCMP 9999) from Logan Butte, Crook Co., Oregon: A, palate with right C, P1–M2; B, C, right mandible with c, p1–m2 in labial and lingual views. Its skull, dentition, and small size establish UCMP 9999 as the most plesiomorphic temnocyonine.

Fig. 5. Temnocyon altigenis (UCMP 9999), John Day Formation, Logan Butte, Crook Co., Oregon.

Fig. 6. Holotype of Temnocyon altigenis Cope (AMNH 6855), John Day Formation, Oregon. Right mandible with p2–4, m1–2 in (A) labial and (B) lingual views.

Fig. 7. Temnocyon altigenis (UCMP 1549), John Day Formation, Morgan’s Place, UCMP loc. 874, near the town of Monument, Grant Co., Oregon. (A) lateral and (B) dorsal views of uncrushed cranium.

Fig. 8. Palate with I1–3, C, P1–4, M1–2 of Temnocyon altigenis (UCMP 1549), John Day Formation, Morgan’s Place, UCMP loc. 874, near the town of Monument, Grant Co., Oregon.

Fig. 65. Basicranium of the Logan Butte Temnocyon altigenis (UCMP 9999): the basioccipital has been opened to show sediment [C(IPS)] filling the deep embayment in the bone for the inferior petrosal venous sinus characteristic of temnocyonines. For abbreviations, see page 5.