ScienceDaily (July 18, 2010) — The discovery of a remarkable 15-million-year-old Australian fossil limestone cave packed with even older animal bones has revealed almost the entire life cycle of a large prehistoric marsupial, from suckling young in the pouch still cutting their milk teeth to elderly adults.
Skull of sheep-sized diprotodontid Nimbadon lavarackorum from the middle Miocene cave deposit, AL90. (Credit: Karen Black, UNSW)
By comparing the skulls of 26 different Nimbadon individuals that died in the cave at varying stages of life the team has been able to show that its babies developed in much the same way as marsupials today, probably being born after only a month's gestation and crawling to the mother's pouch to complete their early development.
Details of the find at a site known as AL90 in the famous Riversleigh World Heritage fossil field in Queensland are published in the Journal of Vertebrate Paleontology, by a team led by Dr Karen Black, of the UNSW School of Biological, Earth and Environmental Sciences. The research was supported by the Xstrata Community Partnership Program North Queensland and the Australian Research Council.
"This is a fantastic and incredibly rare site," says Dr Black. "The exceptional preservation of the fossils has allowed us to piece together the growth and development of Nimbadon from baby to adult. So far 26 skulls -- ranging in age from suckling pouch young and juveniles right through to elderly adults -- have been recovered, as well as associated skeletons.
"The animals appear to have plunged to their deaths through a vertical cave entrance that may have been obscured by vegetation and acted as a natural pit-fall trap. These animals -- including mothers with pouch young -- either unwittingly fell to their deaths or survived the fall only to be entombed and unable to escape.
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Journal of Vertebrate Paleontology
First comprehensive analysis of cranial ontogeny in a fossil marsupial—from a 15-million-year-old cave deposit in northern Australia
Authors: Karen H. Black a; Michael Archer a; Suzanne J. Hand a; Henk Godthelp a
Affiliation: a School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW, Australia
DOI: 10.1080/02724634.2010.483567
Published in: Journal of Vertebrate Paleontology, Volume 30, Issue 4 July 2010 , pages 993 - 1011
Subjects: Animal Physiology; Animal Taxonomy; Biogeography; Environmental Anthropology; Palaeobotany; Palaeontology; Palaeozoology; Paleobiology; Plant & Animal Ecology; Plant Morphology; Plant Taxonomy; Sedimentology & Stratigraphy; Vertebrates; Zoology;
We present the first detailed account of cranial ontogeny in a fossil marsupial. An exceptionally well-preserved ontogenetic sample representing 26 individuals of Nimbadon lavarackorum(Diprotodontidae, Zygomaturinae) is described from a 15 million-year-old cave deposit in the Riversleigh World Heritage Area, Queensland. Based on comparison with one of N. lavarackorum's closest living relatives, the common wombat (Vombatus ursinus), the N. lavarackorum sample represents developmental stages spanning suckling pouch young through to elderly adults. In addition to documenting ontogenetic changes, reduced major axis regression analyses of 14 cranial and seven mandibular measurements were used to analyze allometric growth. Early growth patterns in the cranium are comparable to those of other marsupials such that the bones of the facial portion of the cranium develop precociously compared with those of the neurocranium. Most differences between adult and juvenile crania result from reorganization of structures associated with the cranio-mandibular joint and the developing dentition and strengthening of areas for insertion of the muscles of mastication. These changes reflect the transition from a purely suckling function to one focused on mastication of leaves. The sample also provides a unique view into the development of the extraordinarily complex endocranial sinuses characteristic of diprotodontid marsupials.
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