Field explorations in the San Pedro Valley and Sulfur Springs Valley of southern Arizona] Explorations and Field-Work of the Smithsonian Institution in 1921, pp. Preliminary Report on Fossil Vertebrates of the San Pedro Valley, Arizona, vpith Descriptions of New Species of Rodentia and Lagomorpha.
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484 PROCEEDINGS OF THE
SYSTEMATIC DESCRIPTION OF THE BENSON MAMMALIAN FAUNA
Gidley (1922, p. 120) in his list of San Pedro Valley faunas indicated the presence of mustelid material in the Benson as well as in the Curtisranch collections. Citellus hensoni is a little smaller than G. {Ofospermophilus) heecheyi, and the teeth are not of the true Citellus type, in which there is a development of tall, compressed transverse lophs, but correspond more closely to those of the forms belonging to Ofosperen. - mophilus group, where a certain character of the individual tips is preserved.
486 PROCEEDINGS OF THE
FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY — GAZIN 487
On the lower cheek teeth the enamel is distributed as in Geomys and Gratogeomys, but they are slightly narrower than in the recent forms, and the reentrant teeth separating the columns of P4 are more open than in Geomys, although in the type the reentrant teeth are not separate from each other so effectively. the columns as in Recent Gratogeomys. The jaw and teeth are slightly smaller than Baiomys taylorior or the Curtis ranch Baiomys hrachygnathus.
FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY — GAZIN" 489
Tnorgan has a deeper jaw, more brachydon teeth, denser incisors, a distinctly better developed notch on the anterior lobe of the first cheek tooth, the third cheek tooth slightly less reduced and somewhat more many mental foramen located dorsally, which is closer to the emphasis on the anterior edge of the masseteric ridge. The shortness of the symphysis shown by Gidley cannot be determined with certainty, as none of the jaws is sufficiently complete in front, and the cut seems to have slipped backwards. 10509, with all teeth but missing part of the coronoid and angle, is the type and sole specimen of Benson Onychomys.
As mentioned in the description of the Bensonomys arizonae material above, Gidley's figure of Onychomys hensoni is labeled Elig^nodontia aHzonxie^ so that O. It shows the same cusp tooth structure seen in modern Onychomys^ with the then narrow, single cusp anterior loph of the first. The third lower cheek tooth is markedly^ less reduced and has a low but much less shortened talonid part than in O .
FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY GAZIN 491
Furthermore, this tooth lacks the reentrant from the anterior wall seen in Sylvilagus, Lepus and some other genera.
494 PROCEEDINGS OF THE NATIONAL MUSEUM
FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY — GAZIN 495
In those cases where the mandibular symphysis is known at this stage, the lower third incisor is persistent as indicated in the Hagerman and Coso Mountain material. Camels are represented in Benson's collection by portions of the maxillae of one individual, no. The presence or absence of P- cannot be determined, but it may be assumed that the tooth was absent at this stage, as appears to have been the case in Megatylopus^ CameJops^ and several other forms named from upper Pliocene and Pleistocene horizons. .
The teeth in the upper jaw are much worn, so that only a small part of an inch remains at the depth of the crown of M% and perhaps a little more than an inch of the rather poorly preserved M^. The shape may not have been noticeably larger than some of the material assigned to the genus Camelops. Lie Benson's teeth compare favorably in size with certain larger teeth from these localities, but are noticeably larger than the average.
Cope's measurements of the lower teeth do not indicate an animal significantly larger in size than the Benson camel.
FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY — GAZIIST 497
SYSTEMATIC DESCRIPTION OF THE CURTIS RANCH MAMMALIAN FAUNA
10536, the type, consists of mandibles, complete limbs and lateral legs, part of vertebral column, parts of carapace and tail rings. A composite skeleton has been assembled for display in the National Museum, consisting of the lower jaws and legs of the type, region carapace no. outer figures that overlap with those of adjacent figures.
Along the anterolateral apron-like portions, the four outer rows of setae are closer in serial order, with the posteriorly directed bosses reaching greatest development in the marginal row. The marginal row continues around the nuchal margin, while the knob-shaped segments clearly depart from the main mass of the carapace. Posteriorly, the marginal series becomes a row of downward and backward-directed almost horn-shaped processes, increasing in size to the posterior extent of the carapace and extending over the nearly conical, backward-directed tail armor and outside.
The tail armor apparently consists of eight movable, biserial rings and a terminal piece consisting of the equivalent of about three rings. The posterior series of each annulus exhibits an almost conical elevation, placed posterior to each annulus, and from about the fifth annulus to the tip of the tail, the two adjacent dorsal elements are developed to a greater extent than the others. FOSSIL VERTEBRATES FROM THE SAN PEDRO GAZIN VALLEY 499 The carapace of Glyptotheriuin arizonae closely resembles the notice-.
FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY GAZIN 499 The carapace of Glyptotheriuin arizonae resembles rather notice-
500 PROCEEDINGS OF THE NATIONAL MUSEUM
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502 PROCEEDINGS OF THE NATIONAL MUSEUM
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The form is close in size to such species as Citellus columbianus in the Northwest and Citellus evers77iannii in Siberia, larger than forms belonging to the subgenus Ictidomys^ common in Cochise County, Ariz., toda}'. The protocone of the upper molars is not as compressed anteriorly as in recent material belonging to the subgenus Citellus^ but moderately so, as in material of Citellus inexicanus^ although the teeth are larger and relatively much wider than in this species. Furthermore, as noted by Gidley, the valley between the protoloph and metalophene does not appear to extend as far lingually as in Recent Citellus, suggesting Cynomys, but with less development of the valley behind the metalophene; The teeth are also more brachydone than in the Recentprairie dog.
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508 PROCEEDINGS
FOSSIL VERTEBRATES FROM SAN PEDRO VALLEY — GAZIN" 509
Gidley noted that the cheek teeth were less hypsodont than in the living species, that the valleys of the recurved folds were wider open and the lophs more compressed. The upper dentition added to the collection in 1936 is in an early stage of wear, and the teeth appear markedly more hypsodont than the upper teeth belonging to type jS. In this respect they approach the teeth in modern species, although the re-entrant valleys appear more widely open than in these.
The anterior lobe of the first upper cheek tooth, unlike that in the lower dentition of S.curtisi, is pillar than observed in modern material, and closer to the relative proportions seen in jS. A small species of Slgmodon is represented in the Pleistocene collection by no fewer than ten mandibles and a maxillary portion. 16611, has slightly larger teeth than the smallest of the Benson lot; however, the average of the teeth is clearly less and all S.
The degree of hypodontia and the pattern of the lower tooth of S.?ni do not nearly correspond to those of S.medium, and both forms differ in almost the same respect from the living species.
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10556 and includes the basal part of the skull with the cheek teeth and tusks, as well as the mandibles and other parts of the skeleton. The form is clearly of the stegomastodon type, and from the lower molars appears, as stated by Gidley and Osborn, to be more progressive than the Stegomastodon rnhnfous species. Osborn further notes that the lower third molar, with its seven and one ridges, is also slightly more progressive than that of Stegomastodon texanus from the Blanco strata, but less progressive than S .
The Curtis ranch collection includes a number of isolated upper and lower molars, parts of jaws, foot bones, and fragments of limb bones of Equus. I hesitate to refer the Curtis ranch material to one of the many species of Pleistocene horses because of the great need for revision in this group, and also because I regard the scene represented at the Curtis ranch as somewhat earlier than the Pleistocene horizons represented at Eock Creek, Tex. and Hay Springs, Neb.
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Anita's large camel type, the greater part of the upper molar is much worn, and, in addition to being a little smaller than the teeth of the larger camels of the San Pedro Valley, shows much sharper external forms, especially those on the outer wall of the anterior lobe. between the Parastyle and the Mesostyle. In addition to the giant line of camels, the Curtis Ranch fauna includes a representative of the llama group, the Tanupolama Stock.'** There are also fragments of the mandible and right maxilla of a second and immature individual.
Pj and P3 are missing from the formula, but the canine Pi with its backward-facing hook was found intact in the jaw. There is a shallow fold on the posterior part of the outer wall, giving the tooth a somewhat bilobed appearance, with sharp enamel returning to the anterior part of the lingual wall, but disappearing downwards; and in the stage of wear shown, a prominent enamel fold extends forward from the pos. From his description and examination of the material it is clear that this is a species of Tanupolama.
Although the anteroposterior length of the occlusal surface of the teeth would change significantly with wear, possibly not enough to explain the difference in tooth size between the Curtis ranch form and that of McKittrick tar pits. Another feature noted, but possibly not important, is the superior position of the angle process on the posterior margin of the Curtis ranch ramus. The type Tanupolamaamericana (Wortman) from the Pleistocene at Hay Springs, Nebr., a stage also later than that at the Curtis ranch, has an apparently shorter set of cheek teeth and the portion of the jaw anterior to P4 appears considerably longer than in the Curtis ranch jaw, although these differences could be. partly explained by the difference in maturity between the two individuals.
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