Canis dirus Leidy, 1858

TEDFORD R. H., WANG X. & TAYLOR B. E., 2009, Phylogenetic Systematics Of The North American Fossil Caninae (Carnivora: Canidae), Bulletin of the American Museum of Natural History 2009 (325), pp. 1-218 : 144-148

Canis dirus Leidy, 1858 Figures 40, 43, 44, 56A–F; appendices 2, 3

Canis primaevus Leidy, 1854: 200 (preoccupied by

C. primaevus, Hodgson, 1833 ). Canis dirus Leidy, 1858: 21 . Canis indianensis Leidy, 1869: 368 . Canis mississippiensis Allen, 1876: 49 . Canis ayers Sellards, 1916: 152 . Aenocyon dirus Merriam, 1918: 533 . Aenocyon dirus nebrascensis Frick, 1930: 7 (nomen

nudum). Canis armbrusteri Nowak, 1979: 93 (in part).

Late Irvingtonian Material: Hay Springs Area, ‘‘Sheridan beds’’ (late Irvingtonian), Sheridan County, Nebraska: F:AM 25511, anterior part of skull with I1–I3 alveoli and C–M2 (P1 alveolus) (fig. 56B, E); F:AM 25511M, right isolated P4 (fig. 56A); F:AM 25511L, left isolated and broken M1; F:AM 25509, right partial ramus with p3–m2 (m2 broken) (fig. 56F); F:AM 25510, left partial ramus with m1 (broken)–m3 (alveolus); F:AM 95306 and 95308, two metacarpals II; F:AM 95309, partial metacarpal II; F:AM 95310, astragalus; F:AM 95311, calcaneum; and F:AM 95312, first phalanx. Hay Springs Quarry 2, UNSM locality Sh-2, UNSM 2912, right ramus with partial c alveolus, p1–p4, m1–m2, m3 alveolus; Rushville Quarry 3, UNSM locality Sh-3, UNSM 15486-38, left M1; Rushville Quarry 4, UNSM locality Sh- 4, unnumbered right M1; UNSM 4026-71, right and left M1; UNSM 4062-71*, left p3; Gordon Quarry 5, UNSM locality Sh-5, UNSM 25691, left maxillary fragment with P4 and M1 (identified as ‘‘ C. armbrusteri ’’ by Nowak, 1979: 93); UNSM 21431, right ramus with c, p1–p2 alveoli, p3–p4, m1 alveolus; UNSM 21432, right p4; UNSM 8137-41*, unerupted left p4; UNSM 21436*, premaxillary fragment with I2–I3; UNSM 21439*, right p4; and UNSM 10337-39, right femur.

Albert Ahrens site, UNSM locality No- 104, site in ponded sediments between two bodies of red (‘‘Loveland’’) loess incised into Lava Creek B tephra (0.61 Ma), late Irvingtonian, Nickolls County, Nebraska: UNSM 3269-94, left maxillary fragment with P4, M1–M2, and base of zygoma; UNSM 2223- 90, talonid of right m1; and UNSM 2233-90, little worn left m2.

Mullen, Pit 1, UNSM locality Cr-10, middle Loup River, latest Irvingtonian, Cherry County, Nebraska: UNSM 26117, left ramus with p2–p4, m1–m2, m3 alveolus, and ascending ramus; UNSM locality Cr-10, Pit 3, UNSM 39337, right maxillary fragment with well-worn M1–M2 (‘‘ C. dirus ’’ in Martin, 1972: 174; ‘‘ C. lupus ’’ in Nowak, 1979: 101); UNSM 6.31.8.31 NP, left femur.

Irvington site 2, UCMP locality V3604 (late Irvingtonian), 1.3 km southeast of Irvington, Alameda County, California: UCMP 38749, left ramal fragment with m1 broken–m3 alveolus; UCMP 41779*, trigonid of right m1; UCMP 58032*, a mandible in a concretion, right and left m2–m3, roots of other cheek teeth; UCMP 38784, anterior part of a skeleton lacking skull and mandible, but with fragments of most limbs and some vertebrae; UCMP 38806, distal end of right humerus; UCMP 67930, proximal end of baculum; and UCMP 58033, inion of skull.

Fairmead Landfill locality, UCMP locality V93128 , upper part of Turlock Lake Formation (late Irvingtonian), Madera County, California: UCMP 140265, partial right ramus of mid-aged adult (probable female) with p1–m2 ( Dundas et al., 1996: pl. 1, fig. A); UCMP 156047, mandible of old adult (probable male) lacking right i1, left i1–2, left and right m3, and left ascending ramus with m1–m2; UCMP 156048, fragments of a skull including right maxillary with C alveolus, p1– p4, paracone of M1, left maxillary with M1 paracone broken, complete M2, and fragment of P4 and part of right ear region.

Distribution: Late Irvingtonian of California and Nebraska; Rancholabrean of Canada, United States, Mexico, Venezuela, Ecuador, Bolivia, and Peru.

Revised Diagnosis: Canis dirus is distinguished by a number of autapomorphies related to hypercarnivory: loss of m2 anterolabial cingulum; wide palate; greatly reduced m1–m2 metaconids and entoconids; greatly reduced M1–M2 hypocones; very weak or discontinuous anterolingual cingulum across M1 protocone. It shares with C. armbrusteri two synapomorphies: short and little recurved canine, and a reduced P4 protocone. With C. lupus it shares four additional synapomorphies: paroccipital process strongly expanded posteriorly; frontal sinus reaching the frontoparietal suture; long incisive foramina that extend to or behind canine alveoli; M1 parastyle very weak, preparacrista directed anteriorly, not to parastyle.

Description and Comparison: We agree with Frick (1930) that the late Irvingtonian wolf from the Hay Springs area in Sheridan County, Nebraska, may represent the earliest record of the largely Rancholabrean C. dirus . Unfortunately, the cranial evidence is limited to the preorbital part of a skull (F:AM 25511, fig. 56B, E) with a toothrow length falling within that of C. armbrusteri . However, two of the skull measurements (the palatal width at P1 of 41.5 mm, and the height of the maxillary between the M1 alveolar border and the ventral border of the orbit of 42.3 mm) are larger than in C. armbrusteri and equivalent in size to those of C. dirus (see appendix 2).

The dentition of the Hay Springs individual is smaller than that of C. dirus and within the size range of C. armbrusteri (fig. 40), but it shares a number of derived characters with C. dirus . In F:AM 25511, the incisors are missing and the canine is robust and shortcrowned. The first upper premolar is missing. The second (length X width, 14.8 X 6.9 mm) and third (length X width, 17.2 X 7.5 mm) upper premolars both have posterior cusps as in C. dirus and are likewise more robust than in C. armbrusteri . The P4 (F:AM 25511M, length X width, 30.5 X 12.5; F:AM 25511, 27.5 X 11.4 mm) is slightly smaller than Rancholabrean C. dirus but within the size range of C. armbrusteri . Unlike the latter, the anterolabial surface of the paracone is more rounded and the protocone is reduced as in C. dirus and C. lupus . Like P4, the morphological features of M1 are also very similar to those of C. dirus . The M1 (length X width, 17.8 X 20.2 mm) is small relative to the size of the P4, more as in C. dirus than in C. armbrusteri . The labial cingulum is also much weaker than in C. armbrusteri and, like C. dirus , it is nearly absent across the paracone. After an allowance is made for wear, the heights of the paracone and metacone seem to be about as in C. armbrusteri , and the paracone is not quite as enlarged as in C. dirus . As in C. dirus , the hypocone is smaller, the conules poorly developed, and the anterolingual cingulum is weaker and not continuous with the hypocone across the protocone. Additional examples of some of these teeth in the UNSM collection from Hay Springs agree in the stated features. Some variability in these characters is expected, but Martin (1974: 72) stated that ‘‘in C. dirus the anterolingual cingulum [of M1] does not reach the hypocone, but ends at the protocone. In samples of living wolves that approximate the average size of C. dirus ( C. lupus pambasileus and C. lupus occidentalis ), the cingulum fails to reach the hypocone on only 4 out of 75 individuals.’’ Gidley and Gazin (1938: 17) also observed some variability in the size of the M1 hypocone in C. armbrusteri and stated, ‘‘this character is variable and in some dentitions where the heel of M1 is narrower the hypocone is not so prominent. However, the reduction of the hypocone in these cases does not reach the stage common in C. dirus of Rancho La Brea.’’ The M2 is significantly more reduced relative to M1 than in C. armbrusteri (fig. 44) and in accord with the degree of reduction seen in Rancholabrean C. dirus . Reduction of the labial cingulum and hypocone account for most of the change in proportions of this tooth. The metaconule seems to be lacking but not the postprotocrista.

Characters of the lower dentition are seen in two incomplete and probably associated rami (F:AM 25509 and 25510), with p3–m2 represented, and in other material from the Hay Springs area in the UNSM collection, and they show that the lower teeth lie within lower range of values given for C. dirus by Kurtén (1984). The p3 and p4 (F:AM 25509: length p3, about 15.0 mm; p4 length X width, 19.0 X 10.0 mm) are no longer than in C. armbrusteri but tend to be wider in relationship to their length. The p3, however, has a posterior cusp, which is characteristic of C. dirus and not usually present in C. armbrusteri , although Gidley and Gazin (1938: fig. 20) figured a ramus of C. armbrusteri from the type locality with a well-developed posterior cusp on p3. The p4 of F:AM 25509 has a second posterior cusp that lies on the cingulum as described for some individuals of C. dirus by Merriam (1912: 230). It also has a wide posterolingual shelf as in C. dirus . The M1 (F:AM 25509; length, about 32.0 mm; width trigonid, 12.1 mm; width talonid, 12.9 mm) has the paraconid broken away, the metaconid is very small, the entoconid is barely differentiated from the posterolingual ridge of the talonid, and the hypoconid, although the dominant talonid cusp, is still laterally located with a short hypoconulid shelf lying medial to it. The worn m2 (F:AM 25509, length X width, 12.0 X 9.3 mm; F:AM 25510, 12.0 X 9.8 mm) tends to be smaller relative to M1 than that of C. armbrusteri , but larger than in C. dirus . The anterolabial cingulum is lacking, the metaconid is greatly reduced, and the talonid narrows posteriorly, implying the loss of the entoconid although the tooth is too worn for confirmation.

University of Nebraska State Museum 2912 is the smallest individual in the Hay Springs sample. It has a shallow ramus (depth beneath m1–m2, 29.5 mm; compared to F:AM 25510, 36.4 mm) and uncrowded premolars. The p1–p3 lack posterior cusps, as in C. armbrusteri . The second posterior cusp of p4 is not clearly differentiated from the cingulum, and it has a posterolingual shelf. However, the m1 shows typical C. dirus -like morphology in which the metaconid and entoconid are reduced, the hypoconid is connected to the entoconid by a cristid, and a hypoconulid shelf occurs behind the transverse cristid. The m2 likewise has the metaconid reduced relative to the protoconid, but a small entoconid remains on the narrow talonid; there is a well-formed anterolabial cingulum. The premolars and m1 of this specimen lie just outside the range for length of the samples of C. dirus measured by Kurtén (1984: table 4) and Nowak (1979: appendix C) but inside for the width. The m2 dimensions are within the lower range for C. dirus , and although the depth of the ramus falls within the range of C. lupus , the teeth are absolutely larger. This specimen forms a morphological link between C. armbrusteri (premolar morphology) and C. dirus (dental proportions and molar morphology).

The Hay Springs material was the basis for Frick’s undescribed taxon Aenocyon dirus nebrascensis , a name that appeared in a faunal list of extinct forms from Nebraska. Nowak (1979: 93) referred the same material to C. armbrusteri , but we find that it has more characters in common with C. dirus and differs from C. lupus in its wider muzzle, greater distance between the M1 alveolar border and the ventral border of the orbit, smaller P4 protocone, reduced M1 hypocone and lingual cingulum, weaker M1 labial cingulum, and great reduction of metaconid of m1–m2. Because of these derived characters shared with C. dirus , and the general agreement in dental size, we refer these specimens to that taxon.

In her review of the large Quaternary canids of South America, Berta (1988) redescribed Canis gezi L. Kraglievich, 1928 , from Argentine deposits of Ensenadan age (early to medial Pleistocene, correlated with the Matuyama and early Brunhes chrons, Tonni et al., 1992, 1999) that correspond with the late Blancan and Irvingtonian of North America. Berta (1988: 55) compared C. gezi with late Irvingtonian C. dirus (referred to as ‘‘ C. cf. dirus ’’) and found these taxa ‘‘most similar’’ among North American large canids. In a cladogram, Berta (1988: fig. 28) placed C. gezi and the Irvingtonian C. dirus as sister taxa, but relegated Rancholabrean C. dirus to a closer relationship with C. nehringi F. Ameghino, 1902 , from deposits of Lujanian age (late Pleistocene, Brunhes Chron, Tonni et al., 1992, 1999).

The reevaluation of the late Irvingtonian material in this work provides a link between C. armbrusteri and Rancholabrean C. dirus , suggesting that the South American forms may form a collateral lineage with C. dirus during the medial and late Pleistocene. However, the Argentine and North American lineages are united by many dental similarities related to developing hypercarnivory as well as cranial similarities (some related to size increase) including such peculiarities as the union of the optic and anterior lacerate foramina in a common pit. This latter feature is apparently also shared with C. armbrusteri , further suggesting a common source for the two clades.

Despite suggestions of the ‘‘origin’’ of C. dirus in South America ( Kurtén and Anderson, 1980; Dundas, 1999), a case can be made for a collateral South American lineage ( C. gezi and C. nehringi ) that would be united by such synapomorphies as elongate jaws and exceptionally small, low-crowned, and simple premolars with prominent premolar diastemata. As in C. armbrusteri , p2 and p3 are nearly the same length (in C. gezi the p4 is only a little longer) with the p3 strongly set below p2 and p4 and its posterior cingulum completely below the base of the crown of p4. The m2 primitively retains an anterolabial cingulum in both species. This lineage does not show a striking increase in size with time, but it does acquire somewhat more complex premolars, and the cranium of C. nehringi shows a more C. dirus -like conformation (both holotypes appear to be male individuals based on relative canine dimensions). This lineage was the only large Canis in South America until the appearance of C. dirus in the later Pleistocene. The dire wolf seems to have been restricted to the north and west coasts of South America. Its remains have not been found in the very fossiliferous Pampean Pleistocene deposits of Argentina that produced C. gezi and C. nehringi , nor have remains of these species been found elsewhere in South America.