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PERSPECTIVES

In southeastern Australia, evidence for the contemporaneous presence of permafrost, ice wedges, and hummocky ground in association with dinosaur-bearing deposits during the late Early Cretaceous (105 to 115 million years ago) has Thomas H. Rich, Patricia Vickers-Rich, Roland A. Gangloff been found. This suggests that these animals lived there when n 1960, footprints from Spitzbergen mean annual temperatures showed that nonavian dinosaurs had ranged between −6°C and once lived at polar latitudes (1). Initial+3°C (7). Oxygen isotope ly, this intriguing find remained an essenstudies give a mean annutially isolated discovery, but during the al temperature of −2° ± past 20 years, much information about po5°C for the same deposits lar dinosaurs has (8). For comparison, the been unearthed (2). modern mean annual Enhanced online at temperature of Fairbanks www.sciencemag.org/cgi/ The late development is −2.9°C. However, the content/full/295/5557/979 of knowledge in this f ield was largely a diversity of the late Early 51 matter of logistics: The fossil remains of Cretaceous flora in south50 most polar dinosaurs are to be found today eastern Australia and the 49 at high latitudes and often in remote areas large size of some of its 48 (see the third figure). Their discovery and trees far exceed that 47 collection are, therefore, more costly than found in such cold envi46 is generally the case for comparable lower ronments today. It is diffiCorpse of Leallynasaura amicagraphica on an Early Cretaceous 45 latitude fossils. (110 million years ago) sand bar in southeastern Australia. The sea- cult to imagine how this 44 Despite these drawbacks, the study of son is autumn, and ice has already began to encroach on a stream community functioned if 43 polar dinosaurs provides potentially the temperatures were as that would freeze over during the 3-month-long polar night. 42 unique insights into their physiological low as the physical indi41 adaptations because they may have been Past mean annual temperatures have been cators suggest. No convincing explanation 40 exposed to extreme conditions not experi- estimated in two areas where polar di- exists as yet for this apparent anomaly. 39 enced elsewhere. These conditions cannot nosaurs from the Cretaceous (145 to 65 milHypsilophodontids—rare components of 38 be assumed to have been the same as at lion years ago) have been found: southeast- most dinosaur assemblages—make up half of 37 comparable latitudes today, however. Es- ern Australia and the North Slope of Alaska. the dinosaur taxa in southeastern Australia 36 tablishing just what the climate was like in For the North Slope, Parrish and Spicer (see the first and second figure). Enlarged op35 polar latitudes is critical for the accurate have constructed a mean annual temperature tic lobes on the only brain endocast (a cast of 34 interpretation of polar dinosaur finds. curve spanning the last the inside of the cranium 33 It has been proposed that the inclination 35 million years of the of a fossil skull) available 32 of Earth’s rotational axis may have been sub- Cretaceous based on the in this family from Aus31 stantially different during the Mesozoic Era leaf shapes of flowering tralia suggest that Leaelly30 (248 to 65 million years ago) than it is today, plants (5). They inferred nasaura had more pro29 resulting in warmer climates and more even a maximum temperature nounced visual acuity 28 day length through the year at high latitudes of 13°C and a minimum than lower latitude hyp27 (3). In contrast, theoretical investigations temperature of 2° to 8°C. silophodontids with exist26 suggest that except for the regular and well- For comparison, the ing brain endocasts. Cou25 understood variation by a few degrees that mean annual temperature pled with histological evi24 takes place on the scale of tens of thousands in Portland, Oregon, is dence that their bones 23 of years, the inclination of the Earth axis has 12°C, and that in Calwere constantly growing 22 remained much the same relative to the gary, Alberta, is 4°C. and that they were thus 21 plane of the ecliptic (4). In the latter case, The dinosaurs on the active throughout the 20 polar dinosaurs and their associated biota North Slope closely reyear, this observation sug19 would have had to contend with the same semble contemporanegests that this family of 18 extremes of day length through the year that ous ones farther south in Qantassaurus intrepidus in an Early dinosaurs was well adapt17 characterize comparable latitudes today. Alberta, Montana, and Cretaceous (115 million years ago) sum- ed to polar conditions (7). 16 Mean annual temperature, on the other Wyoming, but there is a mer forest of southeastern Australia. The It has been suggested 15 hand, may have been substantially different profound difference in forest is composed of ginkgoes and that North American po14 at a given polar location during the Meso- the animals associated conifers but lacks the variety of flower- lar dinosaurs may have 13 zoic than at a comparable latitude today. with them. On the North ing plants found here today. occupied high latitudes 12 Slope, the remains of teronly at favorable times of 11 T. H. Rich, Museum Victoria, Post Office Box 666E, restrial, cold-blooded forms such as lizards the year (10). However, such an annual trek 10 Melbourne, Victoria 3001, Australia. E-mail: and crocodilians are conspicuous by their would have been unlikely in southeastern 9 trich@museum.vic.gov.au P. Vickers-Rich, Earth Sciabsence. These missing components consti- Australia, particularly in the case of small, Department, Monash University, Victoria 3800, 8 ences tute a major part of the more southern fau- terrestrial dinosaurs like hypsilophodontids, Australia. E-mail: pat.rich@sci.monash.edu.au R. A. 7 Gangloff, University of Alaska Museum, Fairbanks, AK nas, supporting the idea that at least some because seaways to the north blocked the 6 99775–6960, USA. E-mail: ffrag@uaf.edu nonavian dinosaurs were warm-blooded (6). passage to lower latitudes (7). P E R S P E C T I V E S : PA L E O N T O L O G Y

Polar Dinosaurs

CREDIT: PETER TRUSLER

I

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980

Taloona Station, Queensland, Australia

Sangarskaya Svita, Siberia

Victoria, Australia

Spitzbergen

eK

eJ lJ–eK

Kakanaut, Siberia

?

lK Colville River, Alaska

eK 90°S

Bylot Island, Canada

90°S

lK Mangahouanga Stream, New Zealand

lK

Seymour, Vega, and James Ross Islands, Antarctica

lK

lK

60°S

60°S

J

Black Lake, Alaska

lK

lK

30°S

Beardmore Glacier, Antarctica

Talkeetna Mountains, Alaska

E q u a tor

30°S

Northwest Territories, Canada

lK

Yukon Territory, Canada

E q u a tor

Geological age of site or sites Ankylosauria

Aves

Carnosaur

Small carnosaur or theropod

Ceratopsidae

Crocodilia

Dromaeosauridae

Hadrosauridae

J eJ lJ

Hypsilophontidae

Hypsilophodontidae five different genera

Labyrinthodont amphibian

Marsupialia

Monotreme

Mosasaur

Multituberculata eK lK

Ornithomimosauridae

Ornithopod footprint

Oviraptosauridae

Pachycephalosaur

Placentalia

Plesiosaur

Jurassic, 145 to 208 million years ago Early Jurassic, 178 to 208 million years ago Late Jurassic, 145 to 157 million years ago Early Cretaceous, 97 to 145 million years ago Late Cretaceous, 65 to 97 million years ago

Prosauropod Quantity of fossil material Greater than 1000 bones

Protoceratopsian Pterosaur

Sauropod

Stegosauridae

Tetrapod footprint

Theropod Tritylodontid footprint

Troodontidae

Turtle

100 to 1000 bones Less than 100 bones

Sites of Jurassic (208 million to 145 million years ago) and Cretaceous (145 million to 65 million years ago) polar tetrapod finds. The base map shows the continental configuration in the late Early Cretaceous (100 million years ago). Modified from (7).

During the Early Cretaceous, southeastern Australia was both a nursery and a refugium for terrestrial vertebrates. Early, if not the earliest, records of protoceratopsians, dromaeosaurids, ornithomimosaurs, and oviraptorosaurs have been found there (7). On the other hand, allosaurids, which elsewhere became extinct 30 million years before, survived here along with “labyrinthodont” amphibians. The survival of the labyrinthodonts long after they became extinct elsewhere has been explained by the greater tolerance of amphibians than crocodilians to cold water. Labyrinthodonts were superficially crocodile-like and may have been finally displaced by them when temperatures rose in southeastern Australia in the Early Cretaceous (11). The other chronological anomalies cannot be similarly explained by a polar habitat. These studies in southeastern Australia and the North Slope of Alaska have yielded tantalizing glimpses of polar dinosaurs and their habitat. Elsewhere, studies of po-

lar dinosaurs have focused on establishing what is there: Siberia; Bylot Island, the Yukon, and Northwest Territories, Canada; Talkeetna Mountains, Alaska; Beardmore Glacier, Antarctica; Antarctic Peninsula; New Zealand; and Queensland, Australia (2, 12–15). New genera have been named, but no major groups restricted to high latitudes have been recognized. One location is particularly promising for future investigations (2, 7, 16). A wellexposed sequence of rocks running more than 100 km along the left bank of the Colville River on Alaska’s North Slope spans the last 40 million years that nonavian dinosaurs existed. Exploration of this site will be facilitated when collecting techniques, in particular tunneling (7), are tailored to take advantage of the fact that these fossils are entombed in permafrost. It is there that the greatest known potential exists for recovering the most extensive record of polar dinosaurs, one that is not restricted to a single, brief period of time.

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References 1. A. F. de Lapparent, Norsk Polarinst. Arbok 1960, 14 (1962). 2. T. H. Rich, R. A. Gangloff, W. Hammer, in The Dinosaur Encyclopedia, K. Padian, P. J. Currie, Eds. (Academic Press, San Diego, CA, 1997), pp. 562–573. 3. J. G. Douglas, G. E. Williams, Palaeogeogr. Palaeoclimatol. Palaeoecol. 39, 171 (1982). 4. P. S. Laplace, Traite de Mecanique Celeste (Duprat, Paris, 1798–1827), vol. II. 5. J. T. Parrish, R. A. Spicer, Geology 16, 22 (1988). 6. W. A. Clemens, L. G. Nelms, Geology 21, 503 (1993). 7. T. H. Rich, P. Vickers-Rich, Dinosaurs of Darkness (Univ. of Indiana Press, Bloomington, IN, 2000). 8. R. T. Gregory, C. B. Douthitt, I. R. Duddhy, P. V. Rich, T. H. Rich, Earth Planet. Sci. Lett. 92, 27 (1989). 9. A. Chinsamy, T. H. Rich, P. Vickers-Rich, J. Vertebr. Paleontol. 18, 385 (1998). 10. N. Hotton, III, in A Cold Look at the Warm-Blooded Dinosaurs, R. D. K. Thomas, E. C. Olson, Eds. (Westview Press, Boulder, CO, 1980), pp. 311–350. 11. A. H. Warren, T. H. Rich, P. Vickers-Rich, Palaeontograph. Abt. A 247, 1 (1997). 12. A. Pasch, K. May, in Mesozoic Vertebrate Life , D. Tanke, P. J. Currie, Eds. (Univ. of Indiana Press, Bloomington, IN, 2001), pp. 219–235. 13. W. R. Hammer, W. J. Hickerson, Nat. Sci. Mus. Monogr. (Tokyo) 15, 211 (1999). 14. Z. Gasparini, X. Pereda-Suberbiola, R. E. Molnar, Mem. Queensland Mus. 39, 583 (1996). 15. J. A. Case, J. E. Martin, D. S. Chaney, M. Reguero, J. Vertebr. Paleontol. 18, 32A (1998). 16. R. A. Gangloff, Dakoterra 5, 79 (1998).

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SOURCE: DRAGA GELT

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