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Home , Columbian Mammoth, Pygmy mammoth, Stegodon

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L a rry D. A g e n b ro a d 1, Don Morr i s 2 & Louise Roth3 1 N o rthern Arizona Unive r s i t y, F l a g s t a f f , A Z 2 Channel Islands National Park,Ve n t u r a , CA 3 D u ke Unive r s i t y, D u r h a m , N C

P y g my Mammuthus exilis f ro m Channel Islands National Pa r k , C a l i fornia (USA)

Agenbroad, L.D., Morris, D. & Roth, L., 1999 – Pygmy mammoths Mammuthus exilis from Channel Islands National Park, (USA) - in: Haynes, G., Klimowicz, J. & Reumer, J.W. F. (eds.) – MA M M O T H S A N D T H E MA M M O T H FA U N A : ST U D I E S O F A N EX T I N C T EC O S Y S T E M – DEINSEA 6: 89-102 [ISSN 0923-9308]. Published 17 May 1999.

A unique skeleton of pygmy (Mammuthus exilis) discovered in a sand dune is described and its significance interpreted. The specimen was exposed on a +30 degree slope, approximately 10 m above a vertical cliff, which dropped ca. 20 m to the surf zone. A recent drainage channel had cut through the dune, and erosion had removed several elements. The specimen is the first virtually com- plete pygmy (dwarf) mammoth individual to be recovered, and is exceptionally intact, including hyoid bones and sternum in life position. The individual represents an adult male that had reached sexual m a t u r i t y, and the skeleton showed signs of arthritis. Stature from field measurements was calculated to 1 be less than 2 m at shoulder height, approximately /2 the height of the mainland mammoth (Mammuthus columbi), its probable ancestor.

D w e rg m a m m o e t e n Mammuthus exilis v a n Channel Islands National Park, California ( U S A ) – In dit artikel wordt een uniek skelet van een dwergmammoet (Mammuthus exilis) beschreven dat werd gevon- den in een zandduin op Santa Rosa Island, California. De betekenis van de vondst wordt geinterpre- teerd. Het exemplaar werd gevonden op een helling van meer dan 30 graden, ongeveer 10 m boven een ca. 20 m hoge verticale afgrond die eindigt bij de zee. Een recent ontstane geul had het duin ingesne- den en een aantal botten was als gevolg van erosie verdwenen. Hier is sprake van de eerste vrijwel com- plete dwergmammoet ooit gevonden. Zelfs de tong- en borstbeenderen zijn in de oorspronkelijke posi- tie. Het dier was een volwassen mannetje dat leed aan arthritis. De schouderhoogte is berekend aan de hand van veldmetingen, en bedroeg minder dan 2 meter. Dit is ongeveer de helft van de schouderhoogte van de mammoet van het Amerikaanse vasteland (Mammuthus columbi), de waarschijnlijke voorouder.

Correspondence: Larry D. Agenbroad, Department of Geology, Northern Arizona University, Flagstaff , AZ 86011, USA; of Hot Springs, Hot Springs, SD 57747, USA; and the Santa Barbara Museum of Natural History, Santa Barbara, CA 93105, USA; Don Morris, Channel Islands National Park, 19001 Spinnaker Drive, Ventura, CA93001, USA; Louise Roth, Department of Zoology, Duke University, Durham, NC 27708-0325, USA.

Keywords: Mammuthus exilis, Channel Islands (California), insular proboscideans

I N T RO D U C T I O N In 1986 the Channel Islands, lying off - s h o r e island terrestrial environment, and even the of Ventura and Santa Barbara, California air above both environments. Beneath the (Fig. 1), were acquired by the National Park waves are historic resources in the form of Service to become one of the newest national shipwrecks. On the islands are both prehisto- parks in the USA. Each island is different and ric and historic human settlements - from has its own particular natural resources. T h e s e Chumash, Spanish, Chinese, and A n g l o resources include the marine environment, the (English-speaking) operations, including

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World War II military bases and radar sta- mon mainland mammoths. He also postulated tions. One resource is unique to the Channel the presence of a land bridge connection, allo- Islands. That is the presence of pygmy wing mainland mammoths access to the (dwarf) mammoth remains. Remains of region that is currently the Channel Islands. pygmy mammoths from the Channel Islands Almost as an aside, he notes that at that date were first reported in the scientific literature (1935) no small mammoth remains had been in 1873 (Stearns 1873). Oliver Hay (1927) found in mainland California deposits, al- also referred to the presence of though large mammoths (M. columbi and i m p e r a t o r, and that of an undetermined spe- M. imperator) had a wide distribution. During cies from the islands. It was not until 1928 the interval 1940 to 1965 Phil Orr, of the (Stock & Furlong 1928) that any paleontolo- Santa Barbara Museum of Natural History, gical attention was paid to the . Stock conducted archaeological investigations of & Furlong proposed the name Elephas exilis, portions of the islands, particularly Santa the exiled mammoth, for the Santa Rosa Rosa. He was convinced the small mammoths Island . The small size suggested and ancient were contempo- insular isolation as a dwarfing mechanism, raries on the island, until the mammoths were similar to the pygmy proboscideans of Malta, hunted to (Orr 1968). Wenner & S i c i l y, and other islands in the Mediterranean Johnson (1980) gave considerable study to Sea (Caloi et al. 1989, Lister & Bahn 1994). the land bridge hypothesis proposed by Stock and others. They concluded that no such dry- Stock (1935) referred to the Santa Rosa land connection existed in the late Island mammoths as E l e p h a s (A rc h i d i s k o d o n ) epoch, therefore, the parent stock of mainland e x i l i s , inferring a closer relationship to the mammoths, as ancestors to the Channel Island Imperial mammoth (referred to as mammoths, had reached the island by swim- A rc h i d i s k o d o n i m p e r a t o r in 1935) than to the ming. That feat is made even more plausible (referred to as by two factors: (1) recorded accounts of Paraelephas columbi in 1935), the two com- modern swimming abilities; and (2)

Figure 1 Location map of the Califo rnia Channel Islands

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AGENBROAD et al.: Santa Rosa pygmy mammoths

Figure 2 The excavation pit with the axial skeleton in the position in which it was discove r e d .

the fact that during the last ice age, water was the island mammoths, but research has been held in storage on the continents as glaciers, limited on the channel island proboscideans. ice sheets, and snow and ice. There was a consequent lowering of eustatic sea level by D I S C OV E RY AND EXCAVATION OF approximately 100 m, that would have expo- THE 1994 M. EXILIS S K E L E TO N sed a very large island - which Orr called On June 29,1994, Tom Rockwell, and one of ‘ S a n t a r o s a e ’ – and which was separated by as his graduate students, Kevin Colson, observed little as 6.5-8 km from the Pleistocene coast strange, white objects protruding through of California. Computer maps based on vegetation on a steep sand slope of an eleva- b a t h y m e t r y, produced by Dr. Tom Rockwell, a ted marine terrace (Figs. 2, 3). The objects structural geologist at San Diego State turned out to be bones of the axial skeleton of U n i v e r s i t y, suggest that as much as 76% of a (Mammuthus exilis). T h e ancient Santarosae is now submerged by the National Park Service contacted Dr. Mead melting of the continental ice sheets and gla- and Dr. Agenbroad, on a field excavation at ciers, which caused a subsequent rise in sea the Mammoth Site of Hot Springs, South level. The modern Channel Islands of Dakota. At the request of the National Park Anacapa, Santa Cruz, Santa Rosa, and San Service, they flew to Ventura, California, and Miguel are the remnant high portions went to Santa Rosa Island to verify the disco- (uplands) of ancient Santarosae. mam- v e r y. Once verified, they urged salvage exca- moth remains are known from the three outer- vation of the specimen prior to the advent of most islands. Roth (1982) conducted a zoolo- winter storms. January, 1995 had more than gical investigation of museum specimens of 76 cm of precipitation; February had an addi-

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Figure 3 Location map of the excavation site (indicated by the arr ow ) , Santa Rosa Island.

tional +50 cm. In our opinion, the skeleton The right front foot was curled back against would have been eroded and lost. the radius and ulna. The rear legs were slight- ly flexed, with the right foot in articulation Excavation took place from August 9-19, and the left partially disarticulated. 1994 by a crew consisting of Agenbroad and Osteoarthritic spurs occurred in several of the his son, Brett, Don Morris, Louise Roth and joints of the feet. Hyoids (stylohyoids) were Tom Rockwell. Dr. Mead was unable to assist in situ in the cranium. The three components in the period of field work. The skeleton was of the sternum were also preserved, in life in an extended position, lying on its left side position (Fig. 6). A slight pelvic rotation, to with the cranium to the east, legs extended to the right, produced a tilt, but it was still in the south (Figs. 4, 5). The bone was in excep- articulation with the sacrum and both femur tionally good shape, except for erosional heads were still in articulation in the acetabu- damage by a post-depositional alluvial chan- la. An encrustation of calcium carbonate nel. The channel had exposed the skeleton, cemented sand was encountered on the upper but had also damaged and removed portions (medial) surface of the left tusk. When wet- of it. Primary damage was done to the right ted with acetone, it flaked off as a sandy tusk, right maxilla and alveolus, the right sca- encrustation, but was much thicker and more pula, dorsal spines of the vertebral column resistant at most of the articular surfaces of (especially in the thoracic region), and the the limb bones. Due to its tenacity and hard- right pelvis. The skeleton had apparently ser- ness, it was referred to as ‘calcrete’ during the ved as a check dam in the channel course, as exposure, disarticulation, and casting of the we exposed a plunge pool which had removed skeletal material. We attempted to remove the the entire left manus. The proximal portion of calcrete from joints, using dental tools, but the right scapula was recovered, ca. 1.7 m ultimately resorted to a ‘tap’ with a cold chisel below the skeleton's position. It was associa- to complete the separation. The recovery was ted with cobbles and stained sand, indicative relatively uneventful until we attempted to cut of a continuation of the channel and its fill. through the central pedestal supporting the ver-

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Figure 4 Photograph of the excavated ske l e t o n , in situ,August 1994.

Figure 5 A bone map of the skeleton by S. M o r ri s .

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tebral column and rib cage. The pedestal, for- were hoisted to a National Park Service boat med of very hard calcrete, was extremely diffi- and transported to Ventura, California. cult to work through. TAPHONOMY OF THE SITE Soil organic matter decomposition and root The remains were nearly horizontal, apparent- respiration generate CO2 gas in the soil ly having come to rest on a flat, smooth sur- column. This gas plus water generates carbonic face near the foreset beds of a sand dune. acid, which can disassociate to hydrogen and From the extended position of the skeleton, bicarbonates. Bicarbonate plus calcium leached lying on its left side, with its back to the sea from bone apatite produce calcium carbonate, it is interpreted as a natural death. Finding the cementing the sand into ‘calcrete’, approxima- sternum and other small bones in articulated ted by the following chemical equations: positions also indicates a natural death, unaf- o rganic material and root respiration-----> CO2 ( g a s ) fected by predators or scavenging of the car- C O2 (g) + H2O <------> H2C O3 + O cass. Bone spurs between the joints in the H2C O3 <------> HCO3 + H hind feet may be arthritic, and argue for H C O3 + Ca <------> CaCO3 + H advanced age. The dental wear confirms this. The skeleton was divided into 10 separate Using Laws' (1966) criteria, the age of the jacketed segments, the largest of which was at the time of death was calculated to the articulated vertebral column including the be 56 +/- 2 A E Y (-equivalent ribs and scapulae. The jacketed casts were air ). Pelvic ratios (Lister & A g e n b r o a d lifted to the Vail Ranch headquarters by a 1994) and the large basal diameter of the left contract helicopter. From that location, they tusk indicate it was a mature male.

Figure 6 A photograph of the sternu m , in situ,August 1994.

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Figure 7 Size - f raction analysis of the dune sand which entombed the ske l e t o n .

As an initial interpretation, an adult male M . P R E L I M I N A RY COMPA R I S O N S e x i l i s lay down on a flat, sandy surface of an The results of the field effort included: (1) the elevated marine terrace on the north coastline recovery of the first nearly complete skeleton of Santa Rosa Island, and expired. The body of a single individual of M. exilis; (2) trans- was covered rather quickly by fine to medium portation of the field casts to the Mammoth size dune sand (Fig. 7). Foreset beds advan- Site of Hot Springs, , for the ced west to east (the dominant wind direc- preparation, preservation, molding and cas- tion) covering the body. The fact that even the ting of pygmy mammoth skeletal elements in smallest bones of the feet are still in articula- f i b e rglass; (3) metric analyses of selected ske- tion attests to a gentle, relatively rapid, post- letal elements of M. exilis and comparison of mortem burial. At 700 + 60 yBP (Beta 76532) those results with similar analyses of M . erosion cut an arroyo (a gully) into the dune c o l u m b i , the large mainland mammoth. As a deposit, removing the left front foot bones in preliminary comparison, selected skeletal ele- the turbulent action of a plunge pool. T h e ments of the August, 1994 skeleton of M. exi - waters rose over the skeleton (which served l i s from Santa Rosa Island were contrasted to as a check dam) and poured over the cranial- the same elements of M. columbi ( Table 1) vertebral column-pelvic areas, doing damage from the Mammoth Site of Hot Springs, to these portions of the skeleton. Major dama- South Dakota (Agenbroad 1994). In each ge was the loss of the right tusk and portions case, the specimens are male . A p l o t of the nuchal crest of the cranium. Most of (Fig. 8) of selected long bones reveals a simi- the dorsal vertebral spines were also broken lar slope when comparing the length of simi- o ff. The proximal right scapula was removed, lar bones in both . An anomaly is but recovered from the arroyo channel, down- noted in the M. exilis humerus length, slope from the skeleton. h o w e v e r, it is ca. 50% shorter than would

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Ta ble 1 Compara t i ve metric attri butes of selected skeletal elements of M . c o l u m b i and M . ex i l i s. Column nu m b e rs indicate d i f ferent measurement locations. For these locations and fusion notations see Agenbroad (1994). HSMS = Hot Spri n g s Mammoth Site; CHIS = Channel Islands, C a l i fo rn i a .

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Figure 8 A plot of the length of selected bones of M . ex i l i s and M . c o l u m b i .

have been predicted from the length of the and coast of California, reveals a deep water other long bones. Since the animal was a channel ca. 6-8 km wide. Mainland mam- mature male, with completed bone fusion, it moths apparently swam this channel to gain suggests that some factor was causing early access to the large island ecosystem. ephyseal fusion in the humerus of the pygmy mammoths. This would have a large effect on Why would mammoths swim to an island shoulder height, profile of the spinal column, they possibly could not even see? We suggest and perhaps even modified gait and locomo- that onshore winds would carry the island's tion, as contrasted to the mainland mam- odor of ripening vegetation to the mainland, moths. This tentative hypothesis, based on a tempting animals in dietary or ecological single individual, will be pursued with addi- stress (during , or perhaps a mainland tional studies. brush fire) to swim the channel. Once on the l a rge island, mammoths would have faced D I S C U S S I O N fewer predators or competitors, compared to Tom Rockwell's reconstruction of the land- the mainland, and the population grew, al- mass of the Pleistocene super- i s l a n d though the ancient island landmass would Santarosae (Fig. 9), showing the Late have provided limited food resources for the Pleistocene sea level (lowered by ca. 100 m) mammoths. As sea level rose at the end of

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Figure 9 A reconstruction of the Pleistocene super-island (by Tom Rockwe l l , San Diego State Unive rs i t y ) .

the Pleistocene, the ancient island landmass Springs, South Dakota, site. As the island was slowly inundated, leaving only the hig- landmass shrank to ca.1/4 its original size, hest portions of Santarosae to remain as the the mammoths which survived had shrunk to four isolated Channel Islands of the present. ca. 46% the size of their mainland contem- The already limited food supply on the poraries, in as little as 9000 years (Fig. 10). islands was made more stressful for the mammoth populations by an approximate Dwarf proboscideans are known from at 76% reduction of available habitat, giving a least nine islands in the Mediterranean Sea selective advantage to smaller body-size. A (Caloi et al. 1989, Lister & Bahn 1994), smaller body-size for mammoths would have several islands of (Hooijer 1970), meant that each individual made less use of two islands of the (Nauman the available resources and reached its maxi- 1890, von Koenigswald 1956, Sondaar mum growth sooner. Measurements of selec- 1976), and one island from the Siberian ted bones and teeth indicate the Santa Rosa Arctic Ocean (Vartanyan et al. 1993, Lister pygmy mammoth skeleton was that of a 1993; see Figure 11 and Table 2). T h e mature male, 56 ± 2 A E Y (African elephant- California Channel Islands have the only equivalent years) old at the time of death. dwarf individuals derived from mammoths Calculations based on the humerus measure- of temperate North American ancestry. ments indicate the animal had a shoulder height of 1.7-1.8 m while living. This con- trasts to a shoulder height of 3.9 m for com- parable age M. columbi from the Hot

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Figure 10 A skeletal comparison of two male mammoths, each lying on its left side.The scale is the same for each animal.T h e l a rge animal is at the Mammoth Site of Hot Spri n g s , South Dako t a ; the smaller individual is the A u g u s t , 1994 skeleton from Santa Rosa Island.

S U M M A RY AND CONCLUSIONS beds from an active sand dune, where it died Discovery and excavation of the first nearly and was covered with sand, swiftly and gent- complete skeleton of Mammuthus exilis w a s l y. A drainage channel dated at 700 yBP c u t undertaken in the interval between June 29 through the dune to the skeleton. The skeleton and August 19, 1994. The remains are of a acted as a check dam in that channel, with a mature male animal, judged to be 56 ± 2 plunge pool forming between the front and A E Y at the time of death. The animal appa- rear legs, then overflowing across the crani- rently lay down on a level surface of foreset um, vertebral column, and pelvis. Damage

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Figure 11 Locations of diminu t i ve insular proboscideans. Mammoths of the Califo rnia Channel Islands,W r angel Island and the elephants of the Mediterranean islands; stegodonts and of the Philippine and Indonesian islands.

was relatively minor, and the erosion exposed Hot Springs, South Dakota. We assume that the axial skeleton, for later discovery. Field M. columbi was the most probable ancestral measurements indicate this mammoth was animal, from which the pygmy forms were approximately 1.7-1.8 m high at the shoulder, derived. This hypothesis was initially propo- in the living animal. That stature equates to sed by C. Madden (1981), and the current ca. 46% of the stature of a similarly aged research clearly supports it. Columbian mammoth in the Mammoth Site of

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Ta ble 2 Diminu t i ve insular proboscideans and their proposed ancestry.

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R E F E R E N C E S Agenbroad, L.D., 1994 - of North A m e r i c a n Maglio, V.J., 1973 - Origin and evolution of the M a m m u t h u s and biometrics of the Hot Springs mam- - Transactions of the A m e r i c a n moths - in: Agenbroad, L.D. & Mead, J.I. (eds.) - The Philosophical Society, New Series 63(3): 149 pp. Hot Springs Mammoth Site: a decade of field Nauman, E., 1890 - mindanensis, eine neue and laboratory research in paleontology, Art von Uebergangs-Mastodonten - Zeitschrift g e o l o g y, and paleoecology – pp. 158-207. Deutsche Geologische Geschichte 42: 166-169 Mammoth Site Inc., Hot Springs O r r, P.C., 1968 - Prehistory of Santa Rosa Island - Santa Caloi, L., Kotsakis, T., Palombo, M.R. & Petronio, Barbara Museum of Natural History, Santa Barbara, C., 1989 - The dwarf elephants of the C a l i f o r n i a Mediterranean islands - Fifth International Roth, V.L., 1982 - Dwarf mammoths from the Santa Theriological Congress, Abstracts of Papers Barbara,California Channel Islands: size, shape, and Posters 1: 141-142 development and evolution - Unpublished Ph.D. H a y, O.P., 1927 - The vertebrated fauna of the western dissertation, Yale University United States - Carnegie Institution, Wa s h i n g t o n , Shoshani, J.H. (ed.), 1992 - Elephants - Weldon Owen Publication 322B: 42-43, 51 Press, McMahons Point, New South Wa l e s , H o o i j e r, D.A., 1970 - Pleistocene south-east A s i a t i c A u s t r a l i a pygmy stegodonts - Nature 225: 474-475 S o n d a a r, P. Y., 1976 - Insularity and its effect on Johnson, D.L., 1981 - More comments on the Northern evolution - in: Hecht, M.K., Goody, P.C. & Hecht, Channel Island mammoths - Research 15: B.M. (eds.) - Major patterns in vertebrate 1 0 4 - 1 0 6 evolution, NATO Advanced Studies Koenigswald, G.H.R. von, 1956 - Fossil from Institute Series 14 – pp. 671-707. Plenum Press, the Philippines - Proceedings Fourth Far- e a s t e r n New Yo r k Prehistory Congress 1: 339-362 Stearns, R.E.C., 1873 - Proceedings of the California Laws, R.M., 1966 - Age criteria for the African elephant Academy of Sciences 5: 152 Loxodonta a. africanus - East African Wi l d l i f e Stock, C., 1935 - Exiled elephants of the Channel Islands, Journal 4: 1-37 California - Scientific Monthly 41: 205-214 L i s t e r, A.M., 1993 - Mammoths in miniature - Nature Stock, C. & Furlong, E.L., 1928 - The Pleistocene 362: 288-289 elephants of Santa Rosa Island, California - L i s t e r, A.M. & Agenbroad, L.D., 1994 - Gender Science 68: 140-141 determination of the Hot Springs mammoths Vartanyan, S.L., Garutt, V.E. & Sher, A . V., 1993 - – in: Agenbroad, L.D. & Mead, J.I. (eds.) dwarf mammoths from - The Mammoth Site: a decade of field in the Siberian arctic - Nature 362: 337-340 and laboratory research in paleontology, geology We n n e r, A.M. & Johnson, D.L., 1980 - Land vertebrates and paleoecology - pp. 208-214. The Mammoth on the California Channel Islands: Sweepstakes Site of Hot Springs, South Dakota, Inc., or Bridges - The California Islands: Proceedings Hot Springs of a multi disciplinary symposium. Santa Barbara L i s t e r, A.M. & Bahn, P., 1994 - Mammoths - Macmillan, Museum of Natural History, Santa Barbara: 497-530 New Yo r k Madden, C.T. 1981 - Origin of mammoth from northern Channel Islands, California - Quaternary Research 15: 101-104

DEINSEA - ANNUAL OF THE NATURAL HISTORY MUSEUM ROTTERDAM P. O . B o x 2 3 4 5 2 , N L - 3 0 0 1 K L R o t t e r d a m T h e N e t h e r l a n d s

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