A review of terrestrial mammalian and reptilian carnivore ecology in Australian fossil faunas, and factors influencing their diversity: the myth of reptilian domination and its broader ramifications
Authors: Wroe S. 
Published: August 2002

The notion that Australia’s large, terrestrial carnivore faunas of the
middle Tertiary to Pleistocene were dominated by reptiles has gained wide
acceptance in recent decades. Simple but sweeping hypotheses have been
developed seeking to explain this perceived ecological phenomenon. However, a
review of the literature does not support these interpretations, which are
based on largely speculative and, in many cases, clearly erroneous
assumptions. Few size estimates of fossil reptilian taxa are based on
quantitative methodology and, regardless of method, most are restricted to
maximum dimensions. For species of indeterminate growth, this practice
generates misleading perceptions of biological significance. In addition to
misconceptions with respect to size, much speculation concerning the
lifestyles of large extinct reptiles has been represented as fact. In reality,
it has yet to be demonstrated that the majority of fossil reptiles
underpinning the story of reptilian domination were actually terrestrial. No
postcranial evidence suggests that any Australian mekosuchine crocodylian was
less aquatic than extant species, while a semi-aquatic habitus has been
posited for madtsoiid snakes and even the giant varanid,
Megalania. Taphonomic data equivocally supports the
hypothesis that some Australian mekosuchines were better adapted to life on
land than are most extant crocodylians, but still semi-aquatic and restricted
to the near vicinity of major watercourses. On the other hand, the
accelerating pace of discovery of new large mammalian carnivore species has
undermined any prima facie case for reptilian supremacy
regarding pre-Pleistocene Australia (that is, if species richness is to be
used as a gauge of overall impact). However, species abundance and
consumption, not richness, are the real measures. On this basis, even in
Pleistocene Australia, where species richness of large mammalian carnivores
was relatively low, available data expose the uncommon and geographically
restricted large contemporaneous reptiles as bit players. In short, the
parable of a continent subject to a Mesozoic rerun, wherein diminutive mammals
trembled under the footfalls of a menagerie of gigantic ectotherms, appears to
be a castle in the air. However, there may be substance to some assertions.
Traditionally, erratic climate and soil-nutrient deficiency have been invoked
to explain the perception of low numbers or relatively small sizes of fossil
mammalian carnivore taxa in Australia. But these arguments assume a simple and
positive relationship between productivity, species richness and maximum body
mass and either fail to recognise, or inappropriately exclude, other factors.
Productivity has undoubtedly played a role, but mono-factorial paradigms
cannot account for varying species richness and body mass among
Australia’s fossil faunas. Nor can they explain differences between
Australian fossil faunas and those of other landmasses. Other factors that
have contributed include sampling bias, a lack of internal geographic
barriers, competition with large terrestrial birds and aspects of island
biogeography unique to Australia, such as landmass area and isolation, both
temporal and geographic.