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Home , Madagascar Plate, Maevarano Formation, Mahajangasuchus, Rahonavis

Vol. 9, No. 8 August 1999 INSIDE • Mentor Opportunities, p. 3 • New CEO, p. 9 GSA TODAY • Fellows, Members, Student A Publication of the Geological Society of America Associates, p. 22 The Late Fauna of : Implications for Gondwanan Paleobiogeography

David W. Krause, Department of Anatomical Sciences, State University of New York, Stony Brook, NY 11794, [email protected] Raymond R. Rogers, Department of Geology, Macalester Figure 1. Reconstruction of College, 1600 Grand Avenue, St. Paul, MN 55105, ostromi, a primitive from the of Madagascar. [email protected] Only the bones shown in yellow Catherine A. Forster, Department of Anatomical Sciences, were found. Photo is of the State University of New York, Stony Brook, NY 11794, left hind foot skeleton in [email protected] dorsal view. Joseph H. Hartman, Energy and Environmental Research Center, University of North Dakota, Grand Forks, ND 58202, [email protected] Gregory A. Buckley, Roosevelt University, Evelyn T. Stone University College, Chicago, IL 60605, [email protected] Scott D. Sampson, Utah Museum of Natural History and Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, [email protected]

ABSTRACT A rich, newly discovered assemblage of to the Late Cretaceous. The discovery of mam- exquisitely preserved vertebrate from the Late mals, , and crocodiles in the latest Creta- Cretaceous of Madagascar provides an unparalleled ceous () of Madagascar that are closely opportunity to investigate the paleobiogeography of related to forms in and South America reveals a Gondwanan landmasses. Most current plate tectonic cosmopolitanism at or near the close of the Cretaceous models depict widespread fragmentation of prior that is paradoxical in the context of these models.

INTRODUCTION The southern of Gondwana fragmented into isolated landmasses during the Late and Cretaceous, with dramatic consequences for the associated terrestrial and fresh- water vertebrate faunas. Reconstructions of the timing and sequence of this fragmentation are based almost entirely on geo- physical evidence and remain poorly tested paleontologically, primarily due to a sparse record. The Mahajanga Basin Pro- ject, initiated in 1993 and conducted jointly by the State Univer- sity of New York at Stony Brook and the University of Antana- narivo (Madagascar), has recovered a diverse assemblage of , including the primitive bird Rahonavis ostromi (Fig. 1), from the Upper Cretaceous , Mahajanga Basin, northwestern Madagascar (Fig. 2). This assemblage is one of the richest and best preserved yet known from the Mesozoic of Gondwana. It provides a new opportunity to elucidate distribu- tion patterns among Cretaceous vertebrates from Gondwana and, thereby, to test competing plate tectonic and biogeographic hypotheses.

MALAGASY VERTEBRATE FOSSIL RECORD The Malagasy record of terrestrial and freshwater vertebrates Figure 2. Upper Cretaceous stratigraphy of the Mahajanga Basin. Inset: prior to the Late Cretaceous is sparse but improving, consisting of base map of Madagascar from Satellite Atlas of the World, 1998, National a diversity of primitive fishes, (including the -like Geographic Society, Washington, D.C., 222 p. Madagascar continued on p. 2 IN THIS ISSUE GSA TODAY August Vol. 9, No. 8 1999 The Late Cretaceous Vertebrate Fauna Rock Stars— Preston Cloud ...... 16 of Madagascar: Implications for Letters ...... 18 GSA TODAY (ISSN 1052-5173) is published monthly Gondwanan Paleobiogeography ...... 1 by The Geological Society of America, Inc., with offices at 3300 Penrose Place, Boulder, Colorado. Mailing address: P.O. Box In Memoriam ...... 2 Birdsall-Dreiss Distinguished 9140, Boulder, CO 80301-9140, U.S.A. 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Opinions presented in this publication do not reflect official positions of the Society. Louis C. Conant Francis J. Pettijohn SUBSCRIPTIONS for 1999 calendar year: Society Cupertino, California Glen Arm, Maryland Members: GSA Today is provided as part of membership June 2, 1999 April 23, 1999 dues. Contact Membership Services at (800) 472-1988, (303) 447-2020 or [email protected] for member- ship information. Nonmembers & Institutions: Free with paid subscription to both GSA Bulletin and Geology, Please contact the GSA Foundation for information on contributing to the Memorial Fund. otherwise $50 for U.S., Canada, and Mexico; $60 else- where. Contact Subscription Services. Single copies may be requested from Publication Sales. Also available on an annual CD-ROM, (together with GSA Bulletin, Geology, GSA Data Repository, and an Electronic Retrospective Index to Madagascar continued from p. 1 a result, the biogeographic origins of the journal articles from 1972); $89 to GSA Members, others call GSA Subscription Services for prices and details. Claims: highly endemic and imbalanced extant For nonreceipt or for damaged copies, members contact Triadobatrachus), and , as well as fauna, perhaps best represented by lemurs, Membership Services; all others contact Subscription Ser- spotty occurrences of dinosaurs, therap- remains shrouded in mystery. The late vices. Claims are honored for one year; please allow suffi- cient delivery time for overseas copies, up to six months. sids, and crocodiles (Fig. 3; Flynn et al., Pleistocene and Holocene record only 1998; Krause, 1999). Depéret (1896) was increases the level of endemism, as it STAFF: Prepared from contributions from the GSA staff and membership. the first to record Late Cretaceous verte- includes several giant lemurs, pygmy Executive Director: Sara S. Foland brates from the island. He described iso- hippopotami, the aardvark-like Plesioryc- Science Editors: Suzanne M. Kay, Department of lated remains and, on the basis of teropus, and several other taxa unique to Geological Sciences, Cornell University, Ithaca, NY 14853; Molly F. Miller, Department of Geology, Box 117-B, Vanderbilt fragmentary bones and teeth, named two the island. University, Nashville, TN 37235 from the Maevarano For- Forum Editor: Bruce F. Molnia, U.S. Geological Survey, mation—the meat-eating theropod Mega- MAHAJANGA BASIN PROJECT MS 917, National Center, Reston, VA 22092 losaurus crenatissimus and the plant-eating Director of Publications: Peggy S. Lehr The Mahajanga Basin Project has Managing Editor: Faith Rogers sauropod madagascariensis. focused on the same small set of Mae- Assistant Editor: Vanessa Carney Intermittent collecting over the course of Production Manager: Jon Olsen varano Formation badlands around the nearly a century in the same field area by Production Editor and Coordinator: Gaynor Bloom village of Berivotra that served as the set- Graphics Production: Gaynor BLoom expeditions from France, Madagascar, and ting for prior paleontological field efforts. Japan yielded additional fragmentary spec- ADVERTISING: Classifieds and display: contact Ann The primary objectives of our four expedi- Crawford, (303) 447-2020; fax 303-447-1133; acrawford@ imens of and dinosaurs, as well as tions (1993, 1995, 1996, 1998) have been geosociety.org. isolated elements of a fish, a , two to discover terrestrial and freshwater verte- Issues of this publication are available as electronic Acrobat crocodiles, and a purported (see files for free download from GSA’s Web Site, http://www. brate fossils and to place them in a sound summary in Krause et al., 1997a). geosociety.org. They can be viewed and printed on various phylogenetic, stratigraphic, paleoenviron- personal computer operating systems: MSDOS, MSWin- There are no undisputed records of mental, taphonomic, and paleobiogeo- dows, Macintosh, and Unix, using the appropriate Acrobat Cenozoic terrestrial and freshwater verte- reader. Readers are available, free, from Adobe Corporation: graphic context. http://www.adobe.com/acrobat/readstep.html. brates from Madagascar prior to the late Pleistocene, primarily owing to the over- This publication is included on GSA’s annual Maevarano Formation CD-ROM, GSA Journals on Compact Disc. whelming predominance of marine rocks Call GSA Publication Sales for details. 50% Total The Maevarano Formation is well Recoverd Fiber during the era (Krause et al., 1997a). As Printed in U.S.A. using pure soy inks. 10% Postconsumer exposed in the Berivotra region, where

2 GSA TODAY, August 1999 Institute for Earth Science & J. John Sepkoski ENVIRONMENT MATTERS the Environment 1948–1999

Paleontologist J. John (Jack) Make a Difference— Sepkoski Jr., University of Chicago, Become a Mentor died May 1, 1999, of heart failure. He was 50. Did you receive career advice or guid- The Mann Mentor Program is an Sepkoski’s research and activity ance as an undergraduate student? Did opportunity for a mentor team (a junior in played a major role you benefit from the opportunity to learn and senior mentor) to spend 4–8 hours at in reshaping the discipline during the about different careers in the geosciences? two or three universities in your area. The past 25 . His major contribu- Undergraduate and graduate students are team will candidly discuss what it is like to tions included documenting and hungry for career mentoring in the be a hydrogeologist—how to get a job, analyzing large-scale patterns of applied geosciences. Many have not had challenges in the field, case histories, and origination and , major the opportunity to learn about what lies billable hours. The team will also be pre- changes in the diversity of life over beyond graduation outside of academia. sent to meet with students individually to time, and the environmental and Your wisdom is priceless to students! offer invaluable career advice. IEE is cur- ecological context of biotic diversifi- Please consider sharing your experience rently seeking two mentor teams for the cation. He had taught at the Univer- and advice with students as they prepare spring of 2000. sity of Chicago since 1978. He was a to venture into the real world. At recent workshops, students openly member of the Geological Society of The Institute for Earth Science and expressed their gratitude to mentors for America. the Environment is currently seeking spending time and energy to share career Sepkoski served as president of mentors for the Roy J. Shlemon Mentor information. One young woman was so the Paleontological Society, co-editor Program in Applied Geology and the impressed by what she gained that she and associate editor of Paleobiology, John F. Mann Mentor Program in Applied talked about how she might be a mentor and associate editor of Acta Palaeonto- Hydrogeology. The Shlemon Mentor Pro- to younger undergraduate women. Please logica Polonica. He founded the Pale- gram presents an opportunity for a panel consider this not only an opportunity to ontological Society International of applied geoscientists to engage students discuss your job highlights and challenges, Research Program (PalSIRP), to assist in a discussion of careers in the applied but also an opportunity to truly be a valu- paleontologists in Eastern Europe and geosciences. We are seeking mentors from able role model and mentor in the bud- in the former Soviet Union. Dona- all disciplines in the applied geosciences to ding career of a future geoscientist. For tions in his honor may be made to spend 4–6 hours with students during the more information, please contact Stacey PalSIRP, c/o Thomas W. Kammer, GSA Section meeting of your availability. Ginsburg at 303-447-2020, ext. 194 or Treasurer, Paleontological Society, Mentors are needed for GSA Section meet- [email protected]. Dept. of Geology and Geography, ings in the spring of 2000. West Virginia University, P.O. Box 6300, Morgantown, WV 26506-6300.

~100 m of the unit is accessible in surface rock units, oversimplified the geological extant, from the island (Krause et al., exposures (Fig. 2). The formation is history of the Mahajanga Basin and hin- 1994; Forster et al., 1996; Asher and entirely nonmarine and consists of strata dered accurate comparisons between Krause, 1998; Gottfried and Krause, 1998; that accumulated on a semiarid, low-relief Madagascar’s record of Late Cretaceous Gottfried et al., 1998). Despite varied col- that was bounded to the vertebrates and those from other Gond- lecting methods and intensive effort, the southeast by crystalline highlands and to wanan localities. Our work reveals instead purported presence of (Russell et the northwest by the Mozambique Chan- that the Maastrichtian marine transgres- al., 1976) has not been confirmed and is nel. The predominant lithology is coarse- sion that led to deposition of the Berivotra suspect. grained, poorly sorted , which Formation was demonstrably diachronous, Fishes, , turtles, and are ranges from pervasively cross-stratified to and that the Maevarano Formation accu- now represented in some considerable massive. Massive beds tend to show con- mulated, at least in part, during this same diversity in the Maevarano assemblage, spicuous evidence of pedogenesis, includ- transgressive event (Rogers and Hartman, but their diversity pales in comparison to ing well-preserved root traces and caliche. 1998). Vertebrate-bearing facies of the that of crocodiles, which are represented A distinctive 15–20-m–thick interval of upper Maevarano Formation are accord- by as many as seven different species. The extremely fossiliferous sandstone facies ingly reinterpreted as Maastrichtian, and crocodiles range in size from the small and caps the formation in the vicinity of perhaps late Maastrichtian. gracile to the large and pon- Berivotra. Virtually all of the vertebrate derous (Fig. 4; Buckley fossils known from the Maevarano Forma- Vertebrate Assemblage and Brochu, 1999). The 1998 field cam- tion have been recovered from these upper We have now established the pres- paign resulted in the discovery of a bizarre beds, which accumulated in a shallow ence of at least 32 species of terrestrial and new pug-nosed form with mitten-shaped channel-belt system. freshwater vertebrates in the Maevarano teeth. The nonmarine Maevarano Forma- Formation, thus quadrupling the previ- Two species of sauropod dinosaurs tion and the marine Berivotra Formation ously known species diversity from the have been discovered, both of which were previously considered to be stacked Late Cretaceous of Madagascar. These belong to the enigmatic Titanosauridae. in layer-cake fashion, the - efforts have provided the first pre–late Each is represented by skeletal material Maastrichtian boundary being at their Pleistocene records of Malagasy frogs, that is among the most complete known contact (e.g., Besairie, 1972). This interpre- , and , and the first records tation, and similar interpretations of lower of several groups of vertebrates, fossil or Madagascar continued on p. 4

GSA TODAY, August 1999 3 Cretaceous (130–125 Ma). Madagascar remained in contact with the Indian subcontinent (through the intervening Seychelles island group) until approxi- mately 88 Ma, at which time the Indian subcontinent and Seychelles block sepa- rated from Madagascar and began moving rapidly northeastward toward Eurasia (Storey et al., 1995; Plummer, 1996). The timing of separation between the Indian subcontinent and Antarctica- Australia, and thus intervening physical connections between Madagascar and South America, is more controversial (Fig. 6). Traditional geophysical interpre- tations posit a plate reorganization event at about 135–120 Ma that resulted in ces- sation of movement between Africa and Madagascar-India-Antarctica-Australia and the initiation of separation between India- Madagascar and Antarctica-Australia. Roeser et al. (1996, p. 262), for instance, found evidence for a seaway “along most if not all of the coast of East Antarctica” shortly after chron M0 (124 Ma). Lawver et al. (1992, p. 18) stated that by 110 Ma, “Madagascar, India, and the southern had cleared Antarctica, and a wide, open seaway existed along that part of the present-day East Antarctic margin.” Hay et al. (1999), however, have Figure 3. Temporal distribution of the terrestrial and freshwater vertebrates of Madagascar. Late Cretaceous occurrences are from the Maevarano Formation (upper red rectangles) and the hypothesized a much longer-lived connec- Ankazomihaboka beds (lower red rectangles). tion between the Indian subcontinent and Antarctica-Australia across the Kerguelen Plateau, perhaps as late as 80 Ma. The Madagascar continued from p. 3 tuberculate, and a new species of suda- discrepancy in interpretation has crucial mericid gondwanathere (Krause et al., implications concerning the biogeo- for titanosaurids. Perhaps the most spec- 1994, 1997b; Krause and Grine, 1996). graphic history of Late Cretaceous ter- tacular fossil discovery of the Mahajanga restrial and freshwater Gondwanan ver- Basin Project to date is an exquisitely pre- MADAGASCAR tebrates (Krause et al., 1997a, 1997b; served and virtually complete skull of the AND BIOGEOGRAPHY Sampson et al., 1998). mid-sized theropod dinosaur Majungatho- lus atopus, the name now assigned to Plate Tectonic Models Biogeographic Scenarios Depéret’s crenatissimus (Fig. There is now general consensus that, Madagascar is of unusually high pale- 5; Sampson et al., 1998). The skull is com- prior to rifting, Madagascar lay adjacent to obiogeographic interest and intrigue plemented by a second specimen consist- present-day Somalia, Kenya, and Tanzania because: (1) it occupies a somewhat cen- ing of a nearly complete axial skeleton of a (see Coffin and Rabinowitz, 1992; Storey, tral geographic position within Gondwana juvenile individual. At least one other 1995). Sea-floor spreading between the and was among the first, and last, land- smaller and as yet unidentified theropod is conjugate rifted margins of east Africa and masses to be involved in fragmentation of present in the Maevarano Formation. No northern Madagascar began in the Late the supercontinent; (2) it has been isolated ornithischian dinosaurs are represented in Jurassic. Madagascar moved south-south- from all other Gondwanan landmasses for the fauna. eastward along the transform known more than 85 m.y.; (3) it has a highly Birds are represented by at least five as the Davie Fracture Zone until endemic and imbalanced modern biota; taxa (Forster et al., 1996, 1998). The most reaching its current significant specimen is a partial skeleton position some 400 of Rahonavis ostromi (Fig. 1), a close rela- km off the east tive of the Late Jurassic . coast of Mozam- Rahonavis provides strong confirmatory bique in the evidence for the dinosaurian origin of Early birds in that its hind foot bore a robust, hyperextendable killing claw on the sec- ond digit, just as in its theropod predeces- sors. Multiple, independent analyses of fibrous material adhering to the claw of the second digit has revealed that it is ker- atin from the claw sheath (Schweitzer et al., 1999). This represents by far the oldest documented record of keratin. Mammals are represented by four Figure 4. Postcranial skeleton and lower jaws of the broad-mouthed metasuchian crocodile species: two possible therians, a multi- Mahajangasuchus insignis in dorsal view.

4 GSA TODAY, August 1999 Figure 5. Skull and lower jaws of the abelisaurid theropod dinosaur and (4) its fossil record of terrestrial and agreement. While Dietz Majungatholus freshwater vertebrates is spotty at best and Holden (1970) atopus in left lateral (Fig. 3). maintained that the view. Late Cretaceous vertebrate fossils Indian subcontinent from Madagascar historically have been was an isolated land- most frequently compared to those from mass in the Indian the Indian subcontinent, Africa, and for the South America. The sauropod Titanosaurus entire Jurassic madagascariensis, for instance, was trans- and Cretaceous, ferred to the South American Smith and Hal- Laplatasaurus and also identified in the lam (1970, p. Late Cretaceous of India. The theropod 960), on the crenatissimus (now Majun- basis of fossil gatholus atopus) was identified in the Late marine inverte- Cretaceous of both Egypt and India, and brates, envi- a fragmentary dentary from the Early sioned a terrestrial Cretaceous (?) of Morocco was connection identified as that of cf. Majungasaurus sp. between Africa, Similar patterns have been noted for non- Madagascar, and dinosaurian vertebrates (e.g., crocodiles, the Indian subcon- snakes) as well. tinent until “at least Many of these identifications, based the close of the Creta- 10 cm on fragmentary, isolated specimens, are ceous.” Similarly, Colbert (1973, 1984), suspect, and were made before the para- Sues (1980), Taquet (1982), Briggs (1989), digm of plate tectonics held sway. The Russell (1993), and others postulated land many workers have speculated that the reigning stabilist paradigm prompted bridges that allowed dispersal of Creta- ancestral stocks were present on the island workers in the late 19th and early 20th ceous dinosaurs from Madagascar and/or since the Paleogene, the Late Cretaceous, centuries to invoke ephemeral land India to South America through Africa, or even earlier, prior to its rifting from bridges between South America and Africa, rather than through Antarctica as pro- Africa (see review in Krause et al., 1997a). Africa and Madagascar, and Madagascar posed by Huene and Matley (1933). In Although it appears that certain taxa (e.g., and the Indian subcontinent to explain support of this assessment, Le Loeuff some birds, , and frogs) may be of these distributions (e.g., Blanford, 1890). (1991) performed a biogeographic analysis Indian-Malaysian origin, the consensus Alternatively, Huene and Matley (1933), of Late Cretaceous Gondwanan verte- is that most taxa arrived by random dis- who viewed Laplatasaurus madagascariensis brates, which showed closer affinity of the persal (rafting, swimming, and/or island as showing affinities between India and then poorly known Maevarano Formation hopping) across the 400 km span of the South America, speculated upon a polar vertebrate assemblage (Fig. 2) to that of Mozambique Channel from Africa. McCall route including Antarctica. Africa than to that of any other landmass. (1997, p. 664) recently suggested that Even later, under a mobilist paradigm, With regard to the biogeographic “large areas of the Mozambique Channel land bridge scenarios were used to explain origins of the extant terrestrial and fresh- such distributions, but not without dis- water vertebrate fauna of Madagascar, Madagascar continued on p. 6

Figure 6. Paleogeographic reconstructions of major Gondwanan landmasses at 120, 100, and 80 Ma modified from authors shown. Land areas in green, except Madagascar, which is indicated in red.

GSA TODAY, August 1999 5 Madagascar continued from p. 5 firmed, are otherwise known with cer- other Gondwanan landmasses, including tainty only from the Late Cretaceous Madagascar (Fig. 3), remain as well. (Senonian) of South America (Price, 1955; The Mahajanga Basin Project will were dry land” during the Paleogene as a Gasparini et al., 1991). continue to exploit the fossil riches of the result of uplift along the Davie Ridge and The presence of closely related terres- Maevarano Formation and to test biogeo- that these large areas served as a land trial and freshwater in Madagas- graphic hypotheses on the basis of new bridge for mammalian colonization of car, the Indian subcontinent, and South finds. The number of new taxa discovered Madagascar from Africa. Rage (1996) envi- America near the end of the Cretaceous is in our most recent field demon- sioned a Late Cretaceous land bridge to seemingly incompatible with paleogeo- strates that many more await discovery. the east, extending from Madagascar to graphic reconstructions (e.g., Smith et al., Our efforts will also extend explorations the Seychelles to the Indian subcontinent 1994; Scotese, 1998) in which India-Mada- into other horizons in the basin, most to Laurasia, to explain the modern-day gascar is viewed as having been isolated notably the underlying Ankazomihaboka presence of iguanid lizards, boine snakes, from all other Gondwanan landmasses by beds (Fig. 2), which have already demon- and perhaps even lemurs on the island. 120 Ma (Fig. 6). Rather, this distribution strated their potential through reconnais- accords with the reconstruction by Hay et sance forays in 1996 (Curry, 1997) and Biogeographic Significance of the al. (1999), which posits a subaerial link 1998. The Ankazomihaboka beds overlie Maevarano Formation Vertebrate between India-Madagascar and Antarctica Coniacian basalts, which have been dated Assemblage across the Kerguelen Plateau that persisted to 87.6 ± 0.6 Ma and purportedly signal The exquisite and relatively complete well into the Late Cretaceous (Fig. 6). the time of separation between Madagas- preservation of skeletal material of Late The Maevarano Formation assem- car and the Indian subcontinent (Storey et Cretaceous vertebrates from the Maeva- blage also yields substantial, though nega- al., 1995). rano Formation allows the opportunity to tive, evidence with regard to the biogeo- Finally, the results of the Mahajanga make much better phylogenetic determi- graphic origins of the highly endemic and Basin Project provide focus for future geo- nations of many taxa that were previously imbalanced modern fauna. We have found physical research. In particular, the paleo- represented only by fragmentary, isolated no evidence in the Maevarano Formation biogeographic hypotheses outlined in this specimens. This, plus the discovery of sev- to support the hypothesis that the basal report underscore the need for more eral new taxa, has obvious and important stocks of extant Malagasy vertebrate taxa research in the southern Indian Ocean, consequences for testing paleobiogeo- were present on the island in the Late Cre- with attention being directed toward graphic hypotheses. Two taxa from the taceous (Krause et al., 1997a, 1998). None resolving the time of separation between Maevarano Formation in particular, gond- of the fish, frog, turtle, snake, crocodilian, India-Madagascar and Antarctica and the wanatherian mammals and abelisaurid bird, or taxa now known from role that the Kerguelen Plateau may have theropods (and possibly a third, peiro- the Maevarano Formation appears closely played in connecting those two land- saurid crocodiles), reveal an interesting related to the higher taxa of vertebrates on masses in the Late Cretaceous. Paleontolo- biogeographic pattern. the island today. The basal stocks of the gists and geophysicists have much to gain Sudamericid gondwanatheres are a modern taxa must have arrived sometime by working synergistically to provide highly distinctive but phylogenetically in the Cenozoic, presumably by crossing a reciprocal illumination on the sequence enigmatic group of mammals first known significant marine barrier, a possibility and timing of Gondwanan fragmentation. from the Late Cretaceous and Paleocene of made even more feasible by the recent Argentina (Krause and Bonaparte, 1993). observation of Caribbean iguanas travers- ACKNOWLEDGMENTS Their recent discovery in both the Mae- ing a distance roughly equivalent to the varano Formation of Madagascar and the We thank L. Jacobs and L. Lawver for minimum width of the Mozambique Deccan volcanic-sedimentary sequence of their careful reviews of the manuscript, all Channel on floating logs (Censky et al., India revealed a previously unknown expedition members for their efforts in the 1998). McCall’s (1997) contention that degree of cosmopolitanism among Gond- field, Luci Betti-Nash for help with the fig- there is geological evidence for a Cenozoic wanan mammals at the end of the Creta- ures, and A. Wyss and J. Flynn for proof- land bridge between Africa and Madagas- ceous (Krause et al., 1997b). A similar ing pre-Cretaceous records in Figure 3. car along the Davie Ridge is unfounded geographic distribution was recently Field work for the Mahajanga Basin Pro- (see Krause et al., 1997a). Although demonstrated among theropod dinosaurs ject could not have been conducted with- seamounts that may have been emergent with the discovery of the skull of the out the logistical assistance of B. Rakoto- do exist, they would have been but small abelisaurid Majungatholus atopus (Sampson samimanana (University of Antananarivo); dots of land in a vast seaway some 400 to et al., 1998). The skull provides strong evi- P. Wright, B. Andriamihaja, and staff 1000 km wide. dence that Majungatholus is closely related (Institute for the Conservation of Tropical to taxa in both Argentina (Carnotaurus) Environments); and the ever-helpful vil- PROSPECTUS and India (Indosuchus). Interestingly, prior lagers of Berivotra. Supported by grants to discovery of the skull, M. atopus was A densely sampled fossil record from the National Science Foundation and only known from an isolated skull frag- coupled with well-supported phylogenetic The Dinosaur Society. ment that had been referred to the Pachy- hypotheses and sound paleogeographic cephalosauridae (Sues and Taquet, 1979; models are the fundamental building REFERENCES CITED Sues, 1980), a group of ornithischian blocks of paleobiogeographic analysis. Asher, R. A., and Krause, D. W., 1998, The first pre- dinosaurs known as “bone-heads” previ- Although the record of terrestrial and Holocene (Cretaceous) record of Anura from Mada- ously reported only from Laurasia. The freshwater vertebrates from the Mesozoic gascar: Journal of Vertebrate Paleontology, v. 18, p. 696–699. new, complete skull demonstrates that the of Gondwana has improved dramatically Besairie, H., 1972, Géologie de Madagascar. I. Les ter- fragment of M. atopus is that of a theropod in the last two decades, it is still sparse. rains sédimentaires: Annales Géologique de Madagas- and not a pachycephalosaurid. The bio- One of the key stumbling blocks for test- car, v. 35, p. 1–463. geographic enigma of pachycephalo- ing the paleobiogeographic hypotheses Blanford, W. T., 1890, The permanence of ocean basins: saurids in the Late Cretaceous of southern outlined here is the virtual lack of terres- Geological Society of London Proceedings, 1889–1890, Gondwana is thus resolved (Sampson et trial and freshwater vertebrates from the p. 59–109. al., 1998). Finally, peirosaurid crocodiles, post- Late Cretaceous of Briggs, J. 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