I

PaleoBios 23( 1):20-23, April 15, 2003© 2003 University of California Mu seum of Paleontology

The first Mesozoic mammal from California

GRE GORY P. WILSON!, RI CHARD P. HILTON2, and ERIC S. GO H RE 3IDepartment of Integrative Biology and Museum of Paleontology, University of California, Berkeley, California 94720;

gpwilson@socrates.berkeley.edu. 2Geology Department and Natural History Museum, Sierra Co llege, Rocklin ,California 95677 ; rhilton@sierracollege.edu. 3field paleontologist, Oroville, California 95966

A new specimen from the Upper Cretaceous (Campanian) marine dep osits of the Chico Formation represents the

first Mesozoic mam mal from Californ ia. The specime n adds to the fauna, whi ch inclu des din osaurs, t urtles, ptero­

saurs , and birds, known fro m this nearshore terrestr ial environment . T he specimen, a met acarp al, cannot be confi­

dently iden tified beyond the level o f Mammalia . However, the size o f th e spec ime n suggests that the an imal 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 uras ian hedgehog (Erinaceus europaeus).

I

INTRODUCTION

North America's record of Cretaceous mammals suffersfrom a clear geographic bias-few localities are known out­side those from the fluvial deposits of the Western Interi or.As a result, our view of early mammalian history is skewedtoward the faunas from these ancient coastal lowlands alongthe western margin ofthe Western Interior Seaway. Mamma­lian faunas from other environm ents and areas west of th epresent day Rocky Mountains are sparse. Localities have onlybeen reported from Baja Californ ia del Norte (LiUegraven1976) and Eureka County, Nevada (Clemens et al. 1979 ).Thus far, none have been reported from California.UIUScar, nom: nave oeen reported rrorn Cailtor rua.

Most of Californ ia's Me sozoic sedimentary rocks aremarine deposits, and consequently, Mesozoic terrestrial ver­tebrates from th e state are relatively rare. The only verte ­brate fossils known from terrestrial deposits are dinosa urtracks from the Aztec Sandstone (Lower Jur assic) in theMojave Desert (Reynolds 1989) and dinosaur bone andto oth fragm ents from th e Trail Formation (Jurassic) of thenorthern Sierra Nevada (Christe and Hilton 2001 , Hil tonin press).

All other evidence of California's Mesozoic terrestrial lifehas come from marine deposits. Besides fossils of fish, ple­siosaurs, mosasaurs, and sea turtles (Dupras 1988, Welles1943, Parham and Stidham 1999 ), the marine Great ValleyGroup has yielded information regarding the nearshore ter­restri al fauna . Thi s includes fossils from th e occasional di­no saur carcass th at floated out to sea and sank (Derriere1985 , DeCourten 1997, Hilton and Antuzzi 199 7), as wellas fossils ofterrestrial turtles, flying reptiles, and birds (Downs1968, Hilton et al. 1999, H ilton in press).

Unt il now, the oldest mammalian remains reported fromth e state were from the Paleocene Goler For mation ofsouth­ern California (Mc Kenna 1960) . H ere, we report a metac­arpal from th e Campanian mar ine rocks of the Grea t ValleyGroup in Butte Co unty, California. The specimen repre­sents the first mammal reported from th e Mesozoic of Cali­forni a.

Abbreviations: UCMP, University of California Museumof Paleontology, Berkeley, CA; SC , Sierra Co llege Museum

of Natural History, Rocklin , CA vertebrate locality; VM,vertebrate mammal fossil specimen prefix for Sierra CollegeMuseum of Natural History.

GEOLOGY

During the Late Cretaceous (99-65 million years ago)the shoreline of California was generally just inland fromthe present western base of the Sierra and Klamath Moun­tain Prov inces (Ni lsen , 1986). The present day Sacramentoand San Joa quin Valleys were then an ocean shelf and slopearea receiving sedime nt from rivers along the mo untainousshore (Fig . 1).shore (Fig . 1).

" " " " " " -,

" " " -,-,

" <,-,

" " ",,I

(

J(

\.

_I

Fig . 1. Ap proximate Late C retaceo us shoreline of Californ ia (af­ter Nils en 1986 and othe rs). Dry Creek So ut h locality(SC 1612) is indi cated by th e aste risk.

21 PALEOBIOS, VOL. 23, NUMBER 1, APRIL 2003

The mammalian bone (SC # VM 96) rep orted here wasdiscovered by o ne of us (E ric Gohrc) in the Upper Creta­ceo us (Campanian) rocks of the Chico Formatio n in ButteCounty, California. The Chico Formation is a marine unitin the Great Valley Gro up that is approximately 80 millionyears old. Where the specimen (SC #VM96) was found,the Ch ico Formation strikes nearly due north and dips anaverage of six degrees to the west. Deposition occ urred in afairly nears hore, shelf environment . Here the beds are pre­do min antly shale and siltstone interbedded with meter scalecarbonaceous g lauco nite and shell turbid ites . T he mamma­lian bone (SC #VM96), as well as those of the bird, ptero­saul', plesiosaur, mosasaur, and marine turtles from the ChicoFormation, were found in turbidite matrices (Hilton in press).The specimen probably found its way here after the animal'scarcass floated down a river into the ocean or perhaps aftera predator left its remains in the ocean environment . Fur­thermore, fossil angiosperms, fern s, and redwoods foun d att he site indicate t hat the area was just offshore from a lushlyforested ancestra l Sierra Nevada.

SYSTEMATIC PALEONTOLOGY

Class: MAMMALIA Linnae us 1758incertae sedis

Description-SC #VM96 (F ig. 2) is a left metacar palfrom the Dry Creek Sou th locality, SC 1612. T he articularsurfaces and texture of the bone arc well preserved. Themaximum length is 12.8 mm. The widt hs of the base (proxi ­mal end) and the head (distal end) are 2.8 and 4.0 mm,respectively. At midlength, the maxim um diameter of theshaft (d iaphysis) is 1.9 mm . T he prox imal articular surfaceis flat and slightly sloped in a dorsa-distal direction. I n do r-

sal view (Fig. 2A), the base flares laterally from t he midline.In proximal view (Fig. 20), t his lateral flange is also evi­dent. The proximal aspect of the shaft is somewhat roundin cross -sect ion, but the distal aspect of the shaft is dors­oventrally co mpressed and mediolaterally wide (Fig . 2A). Inlateral view (Fig. 2E-F), t he metacarpal is slightly dorsallyco nvex . T he distal end of the head is ro und (Fig . 2C) ,whereas the medi al and lateral sides have tuberosities thatind icate art iculations and insertions for tendons and liga­ments (Fig. 2E-F). The ventral aspec t of th e head is roundedand has a clear sagittal ridge or keel that subdivides thearticular surface (Fig. 2B).

Discussion-SC #VM96 was co mpared with metapodialsfrom the UCMP collection of mod ern vertebrates. Spec ialattention was given to modern representatives of the smalltet rapo ds that lived in North America during the Campanian,including amph ibians, lizards, and mammals. Examinationof t he complex nat ure of the articular surfaces, especia llyt he sagittal ridge on the palmar aspect of the head, led us to

refer t he fossil specimen to Mammalia.The specimen was identified as a metacarpal rather t han

a met atarsal because t he shaft is both dor soventrally com­pr essed (at mid -length , t he rat io of dorsoventral tomedi olateral width is 1.5 mm/1.9 mm) and med iolaterallywide distally. Based on comparisons with the articulatedmanus of modern mammals, the morphology of the base(proximal end) ofthe metacarpal, partic ularly the asymmetri­cal flaring described above, suggests that it is a left. In t hemodern specimens examined, this flared aspect ofthe proxi­mal end to some exten t overlaps the dorsomedial aspect ofthe laterally adjacent metapodial. Furthermo re, the slendernature of the metacarpal and its weak dorsal convexity sug­gest that it is most likely a metacarpal II, III, or IV, as

°PIV.

all,ID::

meofanfulsutoI ;sli(Cgr#'

Pkpn

t

t

C

F

0.5 mm

D

Fig. 2 . Mammali an left metaca rpal (SC #V1vI96) from t he Chico Formatio n in A . dorsal, B. ventral, C. dista l, 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 o rV

To our knowledge, no rncta pod ial characters exist thatallow further taxono mic distinction between the variousmamma l clades living at this t ime (i.e ., eutherians,metatherians, and multituberculates). Detailed measurementsof the metapodials from a wide array of extant mam malsand from fossil taxa with associated skeleto ns would be help­ful but are beyond the scope of this pape r. However, mea ­surements of the specimen are co nsistent with those fromtoday's Eurasian hedgehog (Erinaceus europaeus Linnaeus1758), which weighs between 400 and 1100 grams, andslightly smaller t han tho se from the water opossum(Chironectes minimus Illiger 1811 ), which weighs up to 800gra ms (Nowak 1999). As for fossil taxa, the length of SC#VM96 is greater t han the metacarpal III length (approxi­mately 7 5 mm) provided by Kiclan-Iaworowska (1978) forthe Late Cretaceous cuthcrian Barunlestes butleri Kielan­Jaworowska 1975 and the metacarpal II length (10.8 mm)provided by Rose (1999) for the Eocene Ieptictid Palaeictopsmulticuspis Granger 1910. Althoug h most of the metacar­pals (II-IV) of the Paleocene multituberculate Ptiloduskummae reported by Krause and Jenkins (1983) are incom­plete, the metatarsal III length (11.8 mm) for their speci ­men suggests that metacarpals of this animal were smallerthan SC #VM96 as well. T hus, based on metacarpal size,the Chico mammal was probably a medium to large-sizedCampanian mammal .

CONCLUSIONS

The discovery ofthe Chico mammal extends the documentedgeographic range ofMesozoic mammals into California. LateCretaceous faunas from areas west of t he Western Interiorare meager, but preliminary findings from faunas, such asthat from Baja California, Mexico, suggest th at these areasmay hold clues to poorly sampled environments or faunalprovinces (Weil and Clemens 1998). Although the metacar­pal from a probable medium to large-sized Mesozoic mam­mal is of limited taxo no mic or biogeographic utility, it doessuggest that further treasures lie in the sediments west ofthe well-sampled Wester n Interior, includ ing those in Cali­fornia.

ACKNOWLEDGMENTS

We wish to thank Dr. David Krause for helpful co m­me nts, Dr. Pat Holroyd and Caroline A.E. Stromberg furhelp with Figure 2, and Dr. William A. C lemens, Dr. J.David Archibald, and one anonymous reviewer for criticallyreviewing the man uscript. However, any mistakes or omis­sions remain those of the authors. Researc h on t his projectwould not have been possible without support from theUCMP and a National Science Foundation Graduate Re­search Fellowship to GPW. This is UCMP ContributionNo. 1087.

LITERATURE CITED

Chrisre, G., and R.P. H ilto n. 20 01. Vertebrate fossils from t heupp er (?) jurassic'Frail Formation, Kettle Rock Sequence: first

recorded evidence of dinosaur rema ins in the Sierra Nevada,

Californ ia. USGS Abs.Clemens, W.A., Jr., J-A. Lillegravcn, E.H. Lindsay, and G.G.

Simpson. 1979. Wh ere, when, and what-a survey of known

Mesozoic mammal dist ribution . pp. 7-58 in J .A. Lillegravcn,Zc Kiclan-jaworowska, and W.A. Cleme ns, Jr. (eds.). Meso­zo ic Manunals- T he first Two-thirds of Mam malian H istory.

University of California Press, Berkeley.DeCourten, FL. 1997. Dinosaurs in California? Pacific Discovery

50(3)26-3LDemcrc, T. 1985. Di nosaurs of Califo rnia. Environment South ­

w«,509,15- IZ

Downs, T. 1968 . Fossil vertebrates ofSouthern California. U niver­

sity of Californ ia Press, Berkeley and Los Angeles. 61 pp.D upras, O . 1988. Ichthyosaurs of California , Nevada, and Or­

egon. CalifiJrnia Geology41(5),99-10ZGranger, W. 1910. Tertiary faunal horizons in the Wind River Ba­

sin, Wyoming, with descri ptions of new Eocene mammals. Bul­letin of the American Museum ofNatural History 28: 235-251.

H ilton, R.P. In press. Dinosaurs and other Mesozoic Reptiles of

California. University oK.:alifurnia Press, Berkeley.H ilton, R.P., and P.J. Antuzzi . 1997. Chico Formation yields clues

to Late Cretaceous paleoenvironment in California. CaliforniaGeology50,135-144.

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. Cali­fornia Geology52,4-10.

IIIiger, C. 1811. Prodromus systematis marnmaliurn et aviurn additis

terminis zoographicis utr iusque classis. C. Salfeld, Ber lin.

Kiclan-Iaworowska, Z. 1975. Preliminary description of two new

eutherian genera from t he Late Cretaceous of Mongol ia.Palaeontologica Polonica 33: 5-16.

Kiclan-Iaworowska, Z. 1978. Evo lution of the t herian mam malsin t he Late Cretaceous ofAsia. Part III. Postcranial skeleton in

Zalambdalestidae. Palaeontologica Polonica 38:3-41.

Krause, D.W., and EA. Je nkins. 1983. The postcranial skeletonof North American multituberculates. Bulktin of the Museum

ofComparative Zoology 150(4),199-246.

Lillegravcn, J .A. 1976. A new genus of therian mam mal fro m theLate Cretaceous "£1 Gallo Formation," Baja California, Mexico.

Journal of Paleontology 50(3)0437-443.Linneus, C. 1758. Systema Naturae. Stockho lm.

McKenna, M.C. 1960. A continental Paleoce ne vertebrate fauna

fro m California. American Museum Novitates 2024: 1- 20 .

Ni lsen, T.H. 1986. Cretaceous paleogeography ofwestern North

America. pp. 1-40 in P.L. Abbott {ed.}. Cretaceous Stratigra­phy ofWestern North America. Pacific Section, Society of Eco­

nomic Paleontologists and Mineralogists, Los Angeles, CA.

Nowak, R.M.1999. Walker's Mammals ofthe World (o" edition).

v.2. Johns Hopkins University Press, Baltimore. 836 pp.

Parham, J.E, and T.A. Stidham. 1999. Late Cretaceous sea turtles

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 JurassicAztec Sandsto ne o f Californ ia. pp. 285-292 ill D.O. Gillette

and M .G . Lockie)' (eds.) . Din osaur T racks and T races. Ca m­

bridge University Press. Cam bridge.Rose, K.D. 1999 . Posrcranial skeleton of Eoce ne Leptictidae (Mam ­

malia ). and its implications for be havior and relationships. [ou rnat of Vet"tebrnte Pa/e01ltology 19(2 ):355-372 .

Weil, A.) and \V.A. Clemens, }r. 1998 . Aliens in Mo ntana; Phylo­

genetically and biogeogra phically diverse lineages contributed

to an earliest Cenozoic commun ity. Geologicn.L Society ofAmeri.ca

Abstracts with Proq rams 30(5 ):69-70.Welles, S. P. 1943. Elasrnosaurid plesiosaurs wid"! description of

new material from Ca lifornia and Co lorado . Memoirs of tbeUni versity ofCaliforni« 13:]25- 254 .