Miocene Mammal Reveals a Mesozoic Ghost Lineage on Insular New Zealand, Southwest Pacific
Total Page:16
File Type:pdf, Size:1020Kb
Miocene mammal reveals a Mesozoic ghost lineage on insular New Zealand, southwest Pacific Trevor H. Worthy*†, Alan J. D. Tennyson‡, Michael Archer§, Anne M. Musser¶, Suzanne J. Hand§, Craig Jonesʈ, Barry J. Douglas**, James A. McNamara††, and Robin M. D. Beck§ *School of Earth and Environmental Sciences, Darling Building DP 418, Adelaide University, North Terrace, Adelaide 5005, South Australia, Australia; ‡Museum of New Zealand Te Papa Tongarewa, P.O. Box 467, Wellington 6015, New Zealand; §School of Biological, Earth and Environmental Sciences, University of New South Wales, New South Wales 2052, Australia; ¶Australian Museum, 6-8 College Street, Sydney, New South Wales 2010, Australia; ʈInstitute of Geological and Nuclear Sciences, P.O. Box 30368, Lower Hutt 5040, New Zealand; **Douglas Geological Consultants, 14 Jubilee Street, Dunedin 9011, New Zealand; and ††South Australian Museum, Adelaide, South Australia 5000, Australia Edited by James P. Kennett, University of California, Santa Barbara, CA, and approved October 11, 2006 (sent for review July 8, 2006) New Zealand (NZ) has long been upheld as the archetypical Ma) dinosaur material (13) and isolated moa bones from marine example of a land where the biota evolved without nonvolant sediments up to 2.5 Ma (1, 14), the terrestrial record older than terrestrial mammals. Their absence before human arrival is mys- 1 Ma is extremely limited. Until now, there has been no direct terious, because NZ was still attached to East Antarctica in the Early evidence for the pre-Pleistocene presence in NZ of any of its Cretaceous when a variety of terrestrial mammals occupied the endemic vertebrate lineages, particularly any group of terrestrial adjacent Australian portion of Gondwana. Here we report discov- nonvolant mammals, let alone the latter’s survival into the ery of a nonvolant mammal from Miocene (19–16 Ma) sediments Miocene. of the Manuherikia Group near St Bathans (SB) in Central Otago, In 1978, a previously unknown fauna was discovered near SB, South Island, NZ. A partial relatively plesiomorphic femur and two Central Otago, South Island, NZ, in the Early Miocene sedi- autapomorphically specialized partial mandibles represent at least ments of the Manuherikia Group, containing, anatids and fish (8, one mouse-sized mammal of unknown relationships. The material 15). Recent excavations from three locations in the SB district implies the existence of one or more ghost lineages, at least one of have recovered a sphenodontid, a crocodilian, geckos, skinks, which (based on the relatively plesiomorphic partial femur) bats, a minimum of 24 avian taxa (16, 17), and a terrestrial spanned the Middle Miocene to at least the Early Cretaceous, mammal described below. probably before the time of divergence of marsupials and placen- tals >125 Ma. Its presence in NZ in the Middle Miocene and An Early to earliest Middle Miocene age (19–16 Ma) for apparent absence from Australia and other adjacent landmasses at sediments in the Manuherikia River section has been deter- this time appear to reflect a Gondwanan vicariant event and imply mined by comprehensive palynology studies, placing the verte- persistence of emergent land during the Oligocene marine trans- brates within the Casuarinaceae biozone of the regional palynos- gression of NZ. Nonvolant terrestrial mammals disappeared from tratigraphic scheme (18–20). Globally, this was a period of NZ some time since the Middle Miocene, possibly because of late habitat change where warm perpetually wet forests became drier EVOLUTION Neogene climatic cooling. and cooler, with more seasonal definition (21). Lake Manuher- ikia was surrounded by an extensive fluvial plain with grasslands, Gondwana ͉ Miocene ͉ nontherian mammal ͉ vicariant event herbfields, and peat-forming swamp-woodland, with relatively dry Casuarinaceae woodland nearby (18, 22). ew Zealand (NZ), the emergent part of a continental Results Nfragment Ϸ1,400 km east of Australia, is a land of birds, where the only known terrestrial mammals in the Recent fauna Palaeontology: First Nonvolant Terrestrial Mammal from NZ. At least are three species of bats (1) whose ancestors may have dispersed one species of nonflying terrestrial mammal is represented by from Australia sometime in the mid to late Cenozoic (2). Lack three specimens from the HH1a site, two almost-identical of evidence for nonflying mammals before the arrival of humans mandibular fragments and one femoral fragment. Because all has been enigmatic, because NZ was still attached to East three could represent the same mouse-sized animal and are the Antarctica in the Early Cretaceous, a time when a variety of first remains of a terrestrial mammal known from NZ, we have terrestrial mammals occupied the adjacent Australian portion of tentatively presumed they represent a single phylogenetically Gondwana (3, 4). NZ separated from Gondwana Ϸ82 Ma (5, 6), enigmatic taxon. An alternative hypothesis would be that the and much of its endemic biota (e.g., southern beeches, onych- femoral fragment represents a relatively archaic mammal, ophorans, leiopelmatid frogs, tuatara, and acanthisittid wrens) is whereas the mandibles represent a second relatively more de- generally thought to reflect this last continental attachment (1, rived mammal. Discovery of further material will be required 5). Such a view assumes that land was continuously present before these alternative hypotheses can be adequately tested. In during the Tertiary, but that eustatic submergence of most of NZ the meantime, we provide here a description and comparison of in the Oligocene (30–25 Ma) reduced the land area of this all of the terrestrial mammal material discovered to date. archipelago to Ϸ20% of current size (5, 7) and may have led to the extinction of some Gondwanan groups (7, 8). In contrast to the prevailing view that some land and hence biota existed Author contributions: T.H.W., A.J.D.T., C.J., B.J.D., and J.A.M. designed research; T.H.W., throughout the Tertiary, some geologists and biogeographers A.J.D.T., C.J., B.J.D., and J.A.M. performed research; T.H.W., M.A., A.M.M., S.J.H., and have recently argued that during the Oligocene transgression, R.M.D.B. analyzed data; and T.H.W., M.A., A.M.M., S.J.H., and R.M.D.B. wrote the paper. there was possibly no emergent land (9), and the entire modern This article is a PNAS direct submission. biota of NZ may be the result of dispersal from nearby land- Freely available online through the PNAS open access option. masses (e.g., refs. 10–12). Abbreviations: NZ, New Zealand; SB, St Bathans. The NZ terrestrial fossil faunal record has been silent in this †To whom correspondence should be addressed. E-mail: [email protected]. regard; although NZ has a rich late Quaternary terrestrial fossil This article contains supporting information (SI) online at www.pnas.org/cgi/content/full/ vertebrate record, it has one of the world’s poorest preQuater- 0605684103/DC1. nary records. Except for fragmentary Late Cretaceous (80–71 © 2006 by The National Academy of Sciences of the USA www.pnas.org͞cgi͞doi͞10.1073͞pnas.0605684103 PNAS ͉ December 19, 2006 ͉ vol. 103 ͉ no. 51 ͉ 19419–19423 Downloaded by guest on September 24, 2021 Fig. 2. First pre-Pleistocene mammal from NZ. MNZ S.42214, proximal section of a right femur. (A) Dorsal view. (B) Ventral view. (C) Medial view. (D) Proximal view. agt, apex of greater trochanter; fc, fovea capita for acetabular ligament; h, head; itf, intertrochanteric fossa; n, notch between greater trochanter and head; olt, origin of lesser trochanter. (Scale bar, 2 mm.) about the orientation of the glenoid fossa of the pelvis. That the Fig. 1. First pre-Pleistocene mammal from NZ. MNZ S.40958, edentulous mandibular fragment. (A) Left lateral view. (B) Right lateral view. (C) Anterior fovea capita is positioned near the top of the head, which lacked view. (D) Dorsal view. (E and F) Stereopair occlusal view. fs, fused symphysis; a well developed neck, suggests the animal had an abducted or i, c, p1, and p2, alveoli for incisor, canine, and two premolars (the homology somewhat sprawling femoral posture. But, if we are correct in of premolars is uncertain); mf, mental foramen; MNZ S, prefix for catalog interpreting that the femoral head projects slightly dorsomedi- numbers of the Vertebrate Fossil Collection, Museum of New Zealand Te Papa ally with respect to the shaft of the femur, and that the lesser Tongarewa, Wellington. (Scale bar, 2 mm.) trochanter had its origin ventrally, then the femur did not project out to the side in the extreme abducted posture of monotremes. Mandibles. MNZ S.40958 (Fig. 1) is an edentulous mandibular Comparisons: Evidence for an Archaic Mammalian Lineage. For rea- fragment consisting of fused left and right anterior ends of the sons noted below, we have made the assumption on the basis of dentaries with six alveoli preserved on the left side and five on parsimony that the mandibular and femoral remains represent a the right. MNZ S.41866 is a second smaller nearly identical single taxon. Because these comparisons involve all of the edentulous mandibular fragment preserving the same but fewer material, if our single-species assumption is subsequently falsi- features, reflecting its more incomplete nature. Key features fied, comparisons presented below will still stand. In terms of include the long fused symphysis; evidently procumbent medial which specific groups of mammals would be most appropriately incisor; and five additional alveoli that suggest a dental formula compared with the SB taxon, whether the SB mammal occurs in of one incisor, one canine, and two double-rooted premolars [see NZ as the result of a vicariant event relating to the 82-Ma supporting information (SI)]. separation of NZ from Antarctica or as the result of a dispersal Femur. MNZ S.42214 (Fig.