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Web address:
http://www.sciencedaily.com/releases/2010/07/
100715105951.htm
Remarkable Fossil Cave Shows How Ancient Marsupials Grew
enlarge
Skull of sheep-sized diprotodontid Nimbadon lavarackorum from the middle
Miocene cave deposit, AL90. (Credit: Karen Black, UNSW)
ScienceDaily (July 18, 2010) â" 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.
In an unprecedented find, a team of University of New South Wales [Sydney
Australia] researchers in has unearthed from the cave floor hundreds of
beautifully preserved fossils of the extinct browsing wombat-like marsupial
Nimbadon lavarackorum, along with the remains of galloping kangaroos, primitive
bandicoots, a fox-sized thylacine and forest bats.
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.
"The ceiling and walls of the cave were eroded away millions of years ago, but
the floor of the cave remains at ground level. We have literally only scratched
its surface, with thousands more bones evident at deeper levels in the deposit.'
The site is also scientifically important because it documents a critical time
in the evolution of Australia's flora and fauna when lush greenhouse conditions
were giving way to a long, slow drying out that fundamentally reshaped the
continent's cargo of life as rainforests retreated.
Dr Black notes that the Nimbadon skulls also reveal that early in life, the
emphasis of its growth was on the development of bones at the front of the
face, to help the baby to suckle from its mother. As it grew older and its diet
changed to eating leaves, the rest of the skull developed and grew quite
massive by way of a series of bony chambers surrounding the brain.
Team member Professor Mike Archer says: "Yet we found that its brain was quite
small and stopped growing relatively early in its life. We think it needed a
large surface area of skull to provide attachments for all the muscle power it
required to chew large quantities of leaves, so its skull features empty areas,
or sinus cavities. Roughly translated, this may be the first demonstration of
how a growing mammal 'pays' for the need to eat more greens -- by becoming an
'airhead'.
"The abundance of Nimbadon fossils also suggests that they travelled in family
groups or perhaps even larger gatherings: it's possible that this also reflects
the beginning of mob behaviour in herbivorous marsupials, such as we see today
in grey kangaroos."
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Story Source:
The above story is reprinted (with editorial adaptations by ScienceDaily
staff) from materials provided by University of New South Wales. The original
article was written by Bob Beale.
Journal Reference:
1. Karen H. Black; Michael Archer; Suzanne J. Hand; Henk Godthelp. First
comprehensive analysis of cranial ontogeny in a fossil marsupial -- from a
15-million-year-old cave deposit in northern Australia. Journal of Vertebrate
Paleontology, 2010; DOI: 10.1080/02724634.2010.483567
Need to cite this story in your essay, paper, or report? Use one of the
following formats:
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University of New South Wales (2010, July 18). Remarkable fossil cave shows how
ancient marsupials grew. ScienceDaily. Retrieved July 19, 2010, from
http://www.sciencedaily.com /releases/2010/07/100715105951.htm
Note: If no author is given, the source is cited instead.
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