The First Mesozoic Mammal from California """ "

Home , Chico Formation

GRE GORYP. WILSON!, RI CHARD P. HILTON2, and ERIC S. GOH RE 3 IDepartment of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720; I [email protected]. 2Geology Department and Natural History Museum,Sierra Co llege, Rocklin, California 95677 ; [email protected]. 3field paleontologist, Oroville, California 95966

A new specimen from the Upper Cretaceous (Campanian) marine dep osits of the Chico Formation represents the first Mesozoic mammal from California. The specime n adds to the fauna, whi ch inclu des din osaurs, turtles, ptero saurs, and birds, known fro m this nearshore terrestr ial environment.T he specimen, a metacarp al, cannot be confi dently identified beyond the level of Mammalia . However, the size of th e specime n suggests that the animal was a medium to large-sized Mesozoic mammal, larger tha n the Late Cret aceo us eut herian Baru nlestes butleri and com para ble to the modern day E urasian hedgehog (Erinaceus europaeus).

INTRODUCTION of Natural History, Rocklin, CA vertebrate locality; VM, North America's record of Cretaceous mammals suffers vertebrate mammal fossil specimen prefix for Sierra College from a clear geographic bias-few localities are known out Museum of Natural History. side those from the fluvial deposits of the Western Interi or. As a result, our view of early mammalian history is skewed GEOLOGY toward the faunas from these ancient coastal lowlands along During the Late Cretaceous (99-65 million years ago) the western margin ofthe Western Interior Seaway. Mamma the shoreline of California was generally just inland from lian faunas from other environm ents and areas west of th e the present western base of the Sierra and Klamath Moun present day Rocky Mountains are sparse. Localities have only tain Provinces (Ni lsen, 1986). The present day Sacramento been reported from Baja California del Norte (LiUegraven and San Joaquin Valleys were then an ocean shelf and slope 1976) and Eureka County, Nevada (Clemens et al. 1979). area receiving sedime nt from rivers along the mo untainous Thus far, none have been reported from California. shore (Fig. 1). UIUScar, nom: nave oeen reported rrorn Cailtorrua. shore (Fig . 1). Most of California's Me sozoic sedimentary rocks are marine deposits, and consequently, Mesozoic terrestrial ver tebrates from th e state are relatively rare. The only verte brate fossils known from terrestrial deposits are dinosa ur tracks from the Aztec Sandstone (Lower Jur assic) in the Mojave Desert (Reynolds 1989) and dinosaur bone and to oth fragm ents from th e Trail Formation (Jurassic) of the northern Sierra Nevada (Christe and Hilton 2001 , Hil ton in press). All other evidence ofCalifornia's Mesozoic terrestrial life " has come from marine deposits. Besides fossils of fish, ple " " siosaurs, mosasaurs, and sea turtles (Dupras 1988, Welles " " 1943, Parham and Stidham 1999), the marine Great Valley " -, Group has yielded information regarding the nearshore ter " " restrial fauna . Thi s includes fossils from th e occasional di " -, nosaur carcass th at floated out to sea and sank (Derriere -, " <, 1985 , DeCourten 1997, Hilton and Antuzzi 199 7), as well -, as fossils ofterrestrial turtles, flying reptiles, and birds (Downs " 1968, Hilton et al. 1999, H ilton in press). " ", Until now, the oldest mammalian remains reported from , I th e state were from the Paleocene Goler Formation ofsouth ( ern California (Mc Kenna 1960). H ere, we report a metac J arpal from th e Campanian marine rocks ofthe Great Valley ( \. Group in Butte Co unty, California. The specimen repre _I I sents the first mammal reported from th e Mesozoic of Cali forni a. Fig. 1. Ap proximate Late C retaceo us shoreline of Californ ia (af Abbreviations: UCMP, University ofCalifornia Museum ter Nils en 1986 and othe rs). Dry Creek So ut h locality ofPaleontology, Berkeley, CA; SC , Sierra College Museum (SC 1612) is indi cated by th e asterisk. 21 PALEOBIOS, VOL. 23, NUMBER 1, APRIL 2003

The mammalian bone (SC # VM 96) rep orted here was sal view (Fig. 2A), the base flares laterally from t he midline. °PI discovered by one of us (Eric Gohrc) in the Upper Creta In proximal view (Fig. 20), t his lateral flange is also evi V. ceo us (Campanian) rocks of the Chico Formatio n in Butte dent. The proximal aspect of the shaft is somewhat round County, California. The Chico Formation is a marine unit in cross-section, but the distal aspect of the shaft is dors all, in the Great Valley Gro up that is approximately 80 million oventrally co mpressed and mediolaterally wide (Fig . 2A). In ID:: years old. Where the specimen (SC #VM96) was found, lateral view (Fig. 2E-F), t he metacarpal is slightly dorsally me co nvex. T he distal end of the head is ro und (Fig . 2C), the Ch ico Formation strikes nearly due north and dips an of average ofsix degrees to the west. Deposition occ urred in a whereas the medi al and lateral sides have tuberosities that an ind icate art iculations and insertions for tendons and liga fairly nears hore, shelf environment . Here the beds are pre ful domin antly shale and siltstone interbedded with meter scale ments (Fig. 2E-F). The ventral aspect ofth e head is rounded su carbonaceous glauco nite and shell turbidites. T he mamma and has a clear sagittal ridge or keel that subdivides the to articular surface (Fig. 2B). lian bone (SC #VM96), as well as those of the bird, ptero I ; Discussion-SC #VM96 was co mpared with metapodials saul', plesiosaur, mosasaur, and marine turtles from the Chico sli Formation, were found in turbidite matrices (Hilton in press). from the UCMP collection of mod ern vertebrates. Spec ial (C The specimen probably found its way here after the animal's attention was given to modern representatives of the small gr carcass floated down a river into the ocean or perhaps after tet rapods that lived in North America during the Campanian, #' a predator left its remains in the ocean environment . Fur including amph ibians, lizards, and mammals. Examination thermore, fossil angiosperms, fern s, and redwoods found at of t he complex nat ure of the articular surfaces, especially t he site indicate t hat the area was just offshore from a lushly t he sagittal ridge on the palmar aspect ofthe head, led us to forested ancestral Sierra Nevada. refer t he fossil specimen to Mammalia. The specimen was identified as a metacarpal rather t han SYSTEMATIC PALEONTOLOGY a met atarsal because t he shaft is both dor soventrally com pr essed (at mid-length, t he ratio of dorsoventral to P Class: MAMMALIA Linnae us 1758 medi olateral width is 1.5 mm/1.9 mm) and med iolaterally k incertae sedis wide distally. Based on comparisons with the articulated p Description-SC #VM96 (Fig. 2) is a left metacar pal manus of modern mammals, the morphology of the base n from the Dry Creek Sou th locality, SC 1612. T he articular (proximal end) ofthe metacarpal, partic ularly the asymmetri t surfaces and texture of the bone arc well preserved. The cal flaring described above, suggests that it is a left. In t he t maximum length is 12.8 mm. The widths ofthe base (proxi modern specimens examined, this flared aspect ofthe proxi C mal end) and the head (distal end) are 2.8 and 4.0 mm, mal end to some exten t overlaps the dorsomedial aspect of respectively. At midlength, the maxim um diameter of the the laterally adjacent metapodial. Furthermo re, the slender shaft (diaphysis) is 1.9 mm .T he proximal articular surface nature ofthe metacarpal and its weak dorsal convexity sug is flat and slightly sloped in a dorsa-distal direction. I n do r- gest that it is most likely a metacarpal II, III, or IV, as

0.5 mm

Fig. 2.Mammali an left metaca rpal (SC #V1vI96) from t he Chico Formatio n in A . dorsal, B. ventral, C. distal, D. proximal, E. medial, and F. lateral views. WILSON, H ILTON & GOHRE-FIRST CA MESOZOIC MAMMAL 22

opposed to the more sto ut proportions of metacarpal I or LITERATURE CITED V Chrisre, G., and R.P. H ilto n. 2001. Vertebrate fossils from t he To our knowledge, no rnctapod ial characters exist that upp er (?) jurassic'Frail Formation, Kettle Rock Sequence: first allow further taxono mic distinction between the various recorded evidence of dinosaur remains in the Sierra Nevada, mamma l clades living at this t ime (i.e., eutherians, California. USGS Abs. metatherians, and multituberculates). Detailed measurements Clemens, W.A., Jr., J-A. Lillegravcn, E.H. Lindsay, and G.G. of the metapodials from a wide array of extant mam mals Simpson. 1979. Wh ere, when, and what-a survey of known and from fossil taxa with associated skeleto ns would be help Mesozoic mammal distribution. pp. 7-58 in J.A. Lillegravcn, ful but are beyond the scope of this pape r. However, mea Zc Kiclan-jaworowska, and W.A. Cleme ns, Jr. (eds.). Meso surements of the specimen are consistent with those from zo ic Manunals- T he first Two-thirds of Mam malian H istory. today's Eurasian hedgehog (Erinaceus europaeus Linnaeus University of California Press, Berkeley. 1758), which weighs between 400 and 1100 grams, and DeCourten, FL. 1997. Dinosaurs in California? Pacific Discovery slightly smaller t han tho se from the water opossum 50(3)26-3L (Chironectes minimusIlliger 1811 ), which weighs up to 800 Demcrc, T. 1985. Di nosaurs of Califo rnia. Environment South gra ms (Nowak 1999). As for fossil taxa, the length of SC w«,509,15- IZ #VM96 is greater t han the metacarpal III length (approxi Downs, T. 1968. Fossil vertebrates ofSouthern California. U niver mately 7 5 mm) provided by Kiclan-Iaworowska (1978) for sity ofCalifornia Press, Berkeley and Los Angeles. 61 pp. the Late Cretaceous cuthcrian Barunlestes butleri Kielan D upras, O . 1988. Ichthyosaurs of California, Nevada, and Or Jaworowska 1975 and the metacarpal II length (10.8 mm) egon. CalifiJrnia Geology41(5),99-10Z provided by Rose (1999) for the Eocene Ieptictid Palaeictops Granger, W. 1910. Tertiary faunal horizons in the Wind River Ba multicuspis Granger 1910. Althoug h most of the metacar sin, Wyoming, with descri ptions ofnew Eocene mammals. Bul pals (II-IV) of the Paleocene multituberculate Ptilodus letin of the American Museum ofNatural History 28: 235-251. kummae reported by Krause and Jenkins (1983) are incom H ilton, R.P. In press. Dinosaurs and other Mesozoic Reptiles of plete, the metatarsal III length (11.8 mm) for their speci California. University oK.:alifurnia Press, Berkeley. men suggests that metacarpals of this animal were smaller H ilton, R.P., and P.J. Antuzzi. 1997. Chico Formation yields clues than SC #VM96 as well. T hus, based on metacarpal size, to Late Cretaceous paleoenvironment in California. California the Chico mammal was probably a medium to large-sized Geology50,135-144. Campanian mammal. H ilto n, R.P., E.S. Gohre, P.G. Emb ree, and T.A. Stidham. 1999. first flying vertebrates from the Mesozoic of California. Cali CONCLUSIONS fornia Geology52,4-10. IIIiger, C. 1811. Prodromus systematis marnmaliurn et aviurn additis The discovery ofthe Chico mammal extends the documented terminis zoographicis utr iusque classis. C. Salfeld, Berlin. geographic range ofMesozoic mammals into California. Late Kiclan-Iaworowska, Z. 1975. Preliminary description oftwo new Cretaceous faunas from areas west of t he Western Interior eutherian genera from t he Late Cretaceous of Mongolia. are meager, but preliminary findings from faunas, such as Palaeontologica Polonica 33: 5-16. that from Baja California, Mexico, suggest th at these areas Kiclan-Iaworowska, Z. 1978. Evo lution of the t herian mam mals may hold clues to poorly sampled environments or faunal in t he Late Cretaceous ofAsia. Part III. Postcranial skeleton in provinces (Weil and Clemens 1998). Although the metacar Zalambdalestidae. Palaeontologica Polonica 38:3-41. pal from a probable medium to large-sized Mesozoic mam Krause, D.W., and EA. Je nkins. 1983. The postcranial skeleton mal is oflimited taxo no mic or biogeographic utility, it does ofNorth American multituberculates. Bulktin ofthe Museum suggest that further treasures lie in the sediments west of ofComparative Zoology 150(4),199-246. the well-sampled Western Interior, including those in Cali Lillegravcn, J .A. 1976. A new genus of therian mam mal fro m the fornia. Late Cretaceous "£1 Gallo Formation," Baja California, Mexico. Journal ofPaleontology50(3)0437-443. ACKNOWLEDGMENTS Linneus, C. 1758. Systema Naturae. Stockholm. We wish to thank Dr. David Krause for helpful co m McKenna, M.C. 1960. A continental Paleoce ne vertebrate fauna me nts, Dr. Pat Holroyd and Caroline A.E. Stromberg fur from California. American Museum Novitates 2024:1- 20. help with Figure 2, and Dr. William A. C lemens, Dr. J. Nilsen, T.H. 1986. Cretaceous paleogeography ofwestern North David Archibald, and one anonymous reviewer for critically America. pp. 1-40 in P.L. Abbott {ed.}. Cretaceous Stratigra reviewing the man uscript. However, any mistakes or omis phy ofWestern North America. Pacific Section, Society ofEco sions remain those ofthe authors. Researc h on t his project nomic Paleontologists and Mineralogists, Los Angeles, CA. would not have been possible without support from the Nowak, R.M.1999. Walker's Mammals ofthe World (o" edition). UCMP and a National Science Foundation Graduate Re v.2. Johns Hopkins University Press, Baltimore. 836 pp. search Fellowship to GPW. This is UCMP Contribution Parham, J.E, and T.A. Stidham. 1999. Late Cretaceous sea turtles No. 1087. from t he Chico Formation of Califo rnia. PaleoBios 19(3):1-7. 23 PA LEOBIOS, VOL. 23, N UMBER 1, A PR iL 2003

Reynolds, R.E. 1989 . Dinosaur rrackways in the Lower Jurassic Weil, A.) and \V.A. Clemens, }r. 1998. Aliens in Mo ntana; Phylo Aztec Sandsto ne of California. pp. 285-292 ill D.O. Gillette genetically and biogeogra phically diverse lineages contributed and M .G. Lockie)' (eds.). Din osaur T racks and T races. Ca m to an earliest Cenozoic commun ity. Geologicn.L Society ofAmeri.ca bridge University Press. Cam bridge. Abstracts with Proqrams 30(5 ):69-70. Rose, K.D. 1999 . Posrcranial skeleton ofEoce ne Leptictidae (Mam Welles, S.P. 1943. Elasrnosaurid plesiosaurs wid"! description of malia). and its implications for be havior and relationships. [ou r new material from Ca lifornia and Co lorado . Memoirs of tbe nat of Vet"tebrnte Pa/e01ltology 19(2 ):355-372 . Uni versity ofCaliforni« 13:]25- 254 .