94 Proceedings of the South Dakota Academy of Science, Vol. 96 (2017)
A RARE OCCURRENCE OF THE FOSSIL WATER MOLE GAILLARDIA (DESMANINI, TALPIDAE) FROM THE NEOGENE IN NORTH AMERICA
James E. Martin University of Louisiana Geology Museum School of Geosciences Lafayette, LA 70505
ABSTRACT
One of the rarest fossil mammals of the Neogene of North America is the desman, which dispersed to North America from Eurasia. The desmans, notably the genus, Gaillardia, did not persist in North America but were able to widely disperse, with occurrences known from New Mexico, Oregon, and Nebraska. Only three North American localities had previously been known to produce water moles, but a new discovery from southern Oregon, Lake County, adds to the known distribution. A tephra associated with the fossil specimens produced an 40Ar/39Ar date of 5.74 ± 0.01 Ma. Therefore, the Fort Rock Formation, which produced the specimens, was deposited during the latest Hemphillian North American Land Mammal Age (NALMA). The Gaillardia specimens are associ- ated with fish, anurans, shrews, beavers (Dipoides), rabbits, and arvicolin rodents (Cosomys) indicating a riparian environment of deposition.
Keywords
Gaillardia, Talpidae, Oregon Hemphillian, semiaquatic specialization
INTRODUCTION
The Desmanini includes small semiaquatic mammals classified within the typi- cally fossorial family of moles, the Talpidae. Only two extant desman species are recognized, Desmana moschata, the Russian desman, and the smaller Galemys pyrenaicus, the Pyrenean desman. These small mammals are well adapted to a semiaquatic manner of existence as evinced by a laterally flattened long tail, webbed feet, small eyes, chemoreception, absence of an external ear, acute hear- ing, and dense hair for buoyancy. They are also characterized by musk produc- tion from glands lying under the tail and a long, narrow, mobile proboscis with many vibrissae utilized in prey apprehension and tactile sensory functions. The Pyrenean water mole inhabits turbulent creeks and rivers, whereas the Russian water mole occurs in slower moving water of the Ural, Don, Dnieper, and Volga basins (Queiroz et al. 1996). Proceedings of the South Dakota Academy of Science, Vol. 96 (2017) 95
In the past, desmans were more widely dispersed; they are first known from the Oligocene of Europe and became widely dispersed across Eurasia during the Miocene. During the Barstovian NALMA (~14-16 Ma, middle Miocene), desmans appear in North America but are only known to persist through the late Hemphillian NALMA (~4.9-10 Ma, latest Miocene). They first appear in North America in the Barstovian Jacona Quarry in the Pojoaque Member of the Tesuque Formation in northern New Mexico (Chaney 1985; Tedford and Barghoorn 1993). Additional specimens occur in Hemphillian NALMA deposits at the McKay Reservoir Locality in the McKay Formation of the Dalles Group in northern Oregon (Shotwell 1956) and at the the ZX Bar Locality of the Upper Snake Creek beds in northwestern Nebraska (Matthew 1932). Gaillardia thomsoni was named by Matthew (1932) based upon a dentary with three teeth from the Hemphillian Nebraska locality. Later, Shotwell (1956) named the desman, Hydroscapheus americanus, from a late Hemphillian northern Oregon site, based initially on postcranial elements, particularly humeri. This taxon was later synonymized with Gaillardia when dental material was discovered at McKay Reservoir (Hutchison 1968). Most recently, Chaney (1985) docu- mented Gaillardia from late Barstovian deposits in northern New Mexico, based principally on isolated teeth. These specimens represent the earliest occurrence of a desman in North American, and no others have been found to occur until the late Hemphillian in North America, a significant amount of the late Miocene time with no desman representatives. As part of paleontological surveys conducted through the Bonneville Power Administration for power line construction/renovation across southern Oregon, a fourth occurrence of a desman was discovered. The water mole was found in late Hemphillian rocks assignable to the Fort Rock Formation (Hampton 1964) associated with fossil fish, anurans, beavers (including Dipooides), shrews, and rodents (including Cosomys). These genera are indicative of the late Hemphillian NALMA (e.g. Martin, 2008). Moreover, an 40Ar/39Ar radiometric date of 5.74 ± 0.01 Ma (New Mexico Geochronology Laboratory) was derived from a tephra associated with the specimens.
EULIPOTYPHLA TALPIDAE Fisher, 1814 DESMANINI Thomas, 1912 GAILLARDIA Matthew, 1932 GAILLARDIA sp. indet. cf. G. THOMSONI Matthew, 1932
Referred Specimens: University of Louisiana Geology Museum (ULGM) V12201, distal left humerus, and ULGM V12358, distal right tibiofibula, from ULGM Locality V-13, BPA Pole Locality 183/5, Lake County, OR.
Description: ULGM V12201 is the distal portion of a left humerus (Figure 1), characterized by a distinct teres tubercule that is oriented obliquely to the humeral shaft, by lack of a fossa for the M. flexor digitorum ligament, and by a very wide distal transverse expansion (10.73 mm transversely) characteristic of desmans and 96 Proceedings of the South Dakota Academy of Science, Vol. 96 (2017) unlike typical fossorial talpines. The entepicondylar and ectepicondylar processes are expanded, the entepicondylar foramen is distinct, and the trochlea is wide without a deep notch distinctly separating the trochlea from the ventral margin medially. Overall, the Lake County specimen is identical to humeral specimens of Gaillardia thomsoni collected from McKay Reservoir.
Figure 1. ULGM V12201, anterior view, distal left humerus, Gaillardia sp. indet. cf. G. thomsoni, from Lake County, OR. Scale graduated in half millimeters.
From the same locality, the distal portion of a right tibiofibula (Figure 2) of a desman was recovered. This specimen also resembles the tibiofibula of Gaillardia thomsoni. As is typical of desmans, the tibia and fibula are well fused distally (5.25 mm transversely), and the lateral malleolus is robust. The groove on the distal fibular portion of the element and the medial process above the tibial por- tion are not as distinct as those illustrated for Gaillardia thomsoni from McKay Reservoir in northern Oregon (Hutchison 1968 Fig. 36). Whether these charac- ters are significant at a specific taxonomic level will await a greater sample size. Proceedings of the South Dakota Academy of Science, Vol. 96 (2017) 97
Figure 2. ULGM V12358, anterior view, distal right tibiofibula, Gaillardia sp. indet. cf. G. thomsoni, from Lake County, OR. Scale graduated in half millimeters.
DISCUSSION
A newly discovered desman (water mole) was recently collected from Hemphillian deposits in southern Oregon. Only three areas had previously produced specimens of fossil water moles in North America. The newly found desman is based upon a distal humerus and distal tibiofibula that occurred in tuffaceous deposits of the Fort Rock Formation dated at 5.74 ± 0.01 Ma in Lake County. The discovery was the result of paleontological salvage resulting from surveys required for Bonneville Power Administration construction and renova- tion on federal land. In most regards, the specimens from southern Oregon are similar to those of Gaillardia thomsoni, also known from late Hemphillian deposits. The humerus appears identical to Gaillardia thomsoni from McKay Reservoir in northern Oregon, and only minor differences appear between known specimens of the tibiofibulae. Until additional specimens are recovered to assess the significance of these differences, the specimens from southern Oregon are provisionally assigned to Gaillardia thomsoni. Desman moles are extremely rare in North America, whereas they were a rela- tively common component of Neogene assemblages in Eurasia. Extant desmans occur in riparian habitats, and most fossil occurrences likewise have been found in such paleoenvironments. The new discovery was found in fluvial sediments in conjunction with other creatures adapted to a riparian habitat such as fish, frogs, shrews, beavers, and arviolin rodents. Therefore, this desman occurrence in southern Oregon occurs at an appropriate time in the North American fossil record and from an appropriate paleoenvironment for an insectivore adapted to a riparian habitat. 98 Proceedings of the South Dakota Academy of Science, Vol. 96 (2017)
ACKNOWLEDGMENTS
I sincerely thank Mr. William Cannon, Bureau of Land Management, and Mr. John Wiley, Bonneville Power Administration, for making possible the surveys that resulted in this discovery. Their vision concerning the paleontology of Oregon resulted in extremely important specimens preserved for our scien- tific heritage. This contribution was greatly enhanced by the reviews of Dan S. Chaney from the US National Museum, Washington, DC, David C. Parris, New Jersey State Museum, Trenton, NJ, and Proceedings editor, Dr. Robert Tatina.
LITERATURE CITED
Chaney, D.S. 1985. The Jacona microfauna (late Barstovian), Pojoaque Member, Tesuque Formation; north central New Mexico, geology, taphonomy, paleoecology, Insectivora. Unpubl. M.S. Thesis, University of California., Riverside, CA. 172 p. Hampton, E.R. 1964. Geologic Factors that control the occurrence and avail- ability of ground water in the Fort Rock Basin Lake County, Oregon. U.S. Geological Survey Prof. Paper 383-B:BN1-B29. Hutchison, J.H. 1968. Fossil Talpidae (Insectivora, Mammalia) from the later Tertiary of Oregon. Mus. Nat. Hist., University Oregon Bulletin 11:1-117. Martin, J.E. 2008. Hemphillian rodents from northern Oregon and their bio- stratigraphic implications. Paludicola 6(4):155-190. Matthew, W.D. 1932. New fossil mammals from the Snake Creek quarries. American Museum Novitates 540:1-8. Queiroz, A.I., A. Bertrand, and G. Khakhin. 1996. Status and conservation of Desmaninae in Europe. Council Europe Publ., Nature and Environment, no. 76:1-81. Shotwell, J.A. 1956. Hemphillian mammalian assemblage from northeastern Oregon. Bulletin of the Geological. Society of America 67:717-738. Tedford, R.H., and S.F. Barghoorn. 1993. Neogene stratigraphy and mammalian biochronology of the Espanola Basin, northern New Mexico. Vertebrate Paleontology in New Mexico, New Mexico Museum Natural History Science Bulletin 2:159-168.