1086th General Monthly Meeting
Talks by Winnners of the Society's Studentships
Date: November 1999Venue: Australian Museum
ABSTRACTS
Early Devonian Micro and Macro Fish Faunas from Southeastern Australia
Alison BasdenDepartment of Geology, Macquarie University
During the Early Devonian (approximately 410-390 million years ago), the shallow marine environments of the present southeastern Australia contained diverse fish faunas of both cosmopolitan and endemic taxa. Fish fossils recovered from these horizons range in size from microvertebrates (microscopic scales, platelets, teeth, spines and bone fragments) to large bones and plates. The present study is concentrating on three aspects of this fauna.
Currently, the established zonation system for the Devonian of Australia is based on conodonts, phosphatic tooth-like microfossils. The marine conodont animals evolved and changed rapidly, with different forms characterising short time periods. Precise ages can be applied to microvertebrates by using conodonts found in the same sediments. Since some fish are euryhaline (tolerate different salinities), it is hoped that establishing a biozonation for southeastern Australia based on microvertebrate taxa may extend stratigraphic alignments from marine into brackish and non-marine environments.
Extensive collections of Devonian fish fossils made in recent decades from the Burrinjuck area of NSW are held in Canberra and London. The microfossils recovered from the rock matrix surrounding the large specimens are being investigated to determine which macro and micro fossils originated from the same groups of fish.
Documentation of previously undescribed forms includes both microfossils and, more significantly, a primitive braincase from Wee Jasper. Comparison of this specimen with other early forms is likely to shed new light on early vertebrate evolution.
Sedentary snakes and gullible geckos: predator-prey coevolution in nocturnal rock-dwelling reptiles
Sharon J. DownesSchool of Biological Sciences, University of Sydney
I investigated (1) the importance of chemical cues for predator detection by the nocturnal rock-dwelling velvet gecko (Oedura lesueurii), and (2) the ways in which the lizards' responses to snake odour may have exerted selection on the foraging behaviours of a nocturnal elapid snake. This snake species (broad-headed snake, Hoplocephalus bungaroides) feeds primarily on velvet geckos, and does so by means of a distinctive foraging behaviour: the snakes remain sedentary in rock crevices for days or weeks, waiting to ambush geckos. Behavioural assays showed that geckos which are sympatric with this sedentary "ambush" predator can detect and respond to the scent of the snake. Retreat-site selection experiments showed that geckos are less likely to enter crevices if the snake's scent is distributed over the entire rock surface, rather than localized to a central portion.
Together, these data support the notion that the "ambush" predator benefits by remaining sedentary within a retreat-site for long periods, because it thereby minimizes the extent to which it spreads its scent over the rocks forming the crevice. Geckos from populations sympatric with the "ambush" predator responded strongly to the snake scent, but those from allopatric populations did not. Additionally, geckos from sympatric populations were able to detect the scent of a nocturnal snake that does not eat geckos (small-eyed snake, Rhinoplocephalus nigrescens), but did not modify their retreat-site selection or locomotory behaviours in response to this cue. Lizards from allopatric populations apparently did not detect the scent of small-eyed snakes.
Quantitative genetic tests revealed that antipredator behaviours of geckos are at least partially inherited. Collectively, these findings support an interpretation of predator-prey coevolution in the present system, and emphasize the importance of chemosensory cues to these rock-dwelling reptiles.
Enquiries: A/Prof. Tony Baker
Phone: 9514 1764
email: Tony.Baker@uts.edu.au
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