In Your Face: Geology and Vertebrate Natural History of Australia

John Merck

Geology Basics

Rock types:

Bubble in basalt flow - Santiago, Galapagos Islands
  • Igneous: Rocks that form from the cooling and solidification of magma. Igneous rocks are generally have interlocking crystals that show no preferred orientation. E. G.:

    Ortega Quartzite, Picuris, NM
  • Metamorphic: Rocks that form from the recrystallization of preexisting rocks under extreme heat and/or pressure. These often show crystals that are aligned with the direction of compression. E.g.:

    Supai Group sandstone, Bright Angel Trail, Grand Canyon
  • Sedimentary: Rocks that form from transported fragments of preexisting rocks. E.g.:

    In Australia, we will mostly be concerned with sedimentary and igneous rocks. Some highlights:

    Northern Territory: The Arnhemland Escarpment dominates the landscape. It is made entirely of one rock unit - the sedimentary Kombolgie Formation, representing ancient continental river and alluvial fan deposits. Why is it special? 1.7 billion years old and an extremely hard topography dominator.

    Queensland: The mainland of northern Queensland is igneous, representing:

    Ironically, Australia is the only continent with no active volcanoes today.

    But the real geologic standout is the Great Barrier Reef - the worlds primer factory for carbonate rocks. But why is this region such a great site for reef building?

    Carbonate chemistry:

    Equilibrium constants An equilibrium constant is equal to the concentration of products over reactants. In the case of carbonate system we see the following equilibrium constants:

    CO2 + H2O -> H2CO3 (K3 = 1*10-1.43)
    H2CO3 -> H+ + HCO3- (K3 = 1*10-6.40)
    >HCO3- -> H+ + CO32- (K3 = 1*10-10.33)
    Ca2+ + CO32- -> CaCO3 (K3 = 1*10-8.33 for aragonite and 1*10-8.48 for calcite)

    Looking at this reaction series, you would think that adding more CO2 would drive the reactions toward the right and increase CaCO3 precipitation, but this is not the case:

    Because they proceed in the same environment, reactants can "leak" from one reaction to the other. K3 is much greater for reaction 2 than reaction 3. Thus, H+ from 2 is able to leak into reaction 3, driving it to the left. paradoxically, precipitation of CaCO3 is facilitated by the reduction of CO2.

    Thus, CaCO3 is deposited where there is the least CO2 in the water:

    Incredible Vertebrate Diversity

    On the right is a cladogram of all of the major vertebrate groups. The wonder and glory of the Australia travel study is that it is possible that we could see representatives of each one. That could possibly even include the Australian lungfish (albeit unlikely.)

    That's far more vertebrate diversity than I we address here. For this half hour, I want to consider the critters in red that include some of the most conspicuous animals we will see. Dr. Thompson has discussed Australian mammals. Please feel free to examine my notes from the 2015 trip as well. I focus on the other two groups:


    Australia has been called "the land of lizards," both because it is home to an interesting endemic radiation of squamates and because they are fantastically diverse, with over three times as many species as live in North America.

    There are hundreds of living squamate species. All of their diversity falls into two major groups:

    These groups appear in the Early Jurassic, with essentially modern looking forms occurring in the Cretaceous.

    Gilbert's dragon Amphibolurus gilberti


    Contains a great diversity of smaller groups. In North America we are familiar with: Iguania has many synapomorphies (shared derived characters). We'll be content with one - The use of the tongue in prey capture.

    Australian iguanians are represented by the taxon Agamidae, whose members are referred to as "dragons." Common examples include:

    I especially look forward to seeing: Iguanians have two important plesiomorphies (ancestral characters), also:

    Yellow-spotted monitor Varanus panoptes


    Contains familiar North American groups including: In Australia, add: And with the aid of a time-machine:

    Varanus panoplies senses its environment
    Our only synapomorphy of Scleroglossa is also the etymology of the name:

    Oxyuranus microlepidotus the fierce snake - world's most poisonous

    Dreadful Snakes

    Snakes are scleroglossans. In Australia one group predominates: Elapidae. Familiar as coral snakes and cobras.


    Calyptorhynchus banksii the Red-tailed black cockatoo - loveliest of birds


    The birds of Australia are like the animals of Australia in microcosm:

    Our trip should enable us to get close to some of the world's most charismatic bird species (right) including creatures that you would pay thousands of dollars to own as an exotic pet.


    We can reasonably hope to see examples of the three major monophyletic groups of birds:

    Dromaeus novaehollandae - Emu


    The Emu - Dromaeus novaehollandae: A large flightless bird inhabiting most of the continent with:

    Mating: Emus are polyandrous, with females mating with a number of males and distributing her eggs among their nests. Males care for the offspring, who may be either full or half siblings. Because males are the limiting gender in this system, females develop garish display coloration and display to attract males.

    Casuarius casuarius - Southern cassowary father and juvenile
    The Southern Cassowary - Casuarius casuarius: A large flightless bird of northern Queensland similar to the emu in general proportions but:

    Ecology: Critically endangered by the encroachment of humans into their habitat. Cassowaries have a bad reputation, being the only bird ever known to kill humans. That was over a century ago, but they can be aggressive.

    Cassowary reproduction is similar to that of emus. Indeed, this pattern of polyandry and paternal care may be a hold-over from the mating behavior of non-avian theropod dinosaurs.

    Alectura lathami - Australian Brush Turkey

    Galloanserae 1: Galliformes

    Megapodes, incuding the Australian Brush Turkey - Alectura lathami: Australia boasts an odd group of galliform birds, the megapodes. We are likely to see:

    Nesting: All birds incubate their eggs. Megapodes, however, don't use their bodies. Rather, the males heap mounds of rotting vegetation over them, and use the heat they give off for incubation. Males carefully monitor the nests, adding and subtracting material as necessary to maintain the right temperature. Upon hatching, the extremely precocial chicks emerge and fend for themselves.

    Anseranas semipalmata - Magpie goose

    Galloanserae 2: Anseriformes

    Magpie geese, Anseranas semipalmata: Australia has many ducks and geese, but also one common species that is neither duck nor goose, the magpie goose:

    And with luck we will see the Australian swan.


    The phylogenetic patterns we saw above was recovered in the early days of cladistics. But Neoaves, the majority of birds, was utterly intractable until about ten years ago when combined molecular/morphological analyses began yielding consistent results. As a result we saw that Neoaves contains Inopinaves, a large clade containing the majority of land birds. This has recently been confirmed by Prum et al., 2015. It presents a very interesting pattern:

    Focus, for a moment on the geographic distribution of Passeriformes (perching-birds) and Psittaciformes (parrots) It presents a very interesting pattern:

    Their last common ancestor seems to have lived in the lands around southwest Pacific around 50 million years ago.

    When we visit Australia, we will be seeing the place where this radiation happened, and observing members of the most basal branches.

    Some superlatives:

    Blue-faced honeyeater Entomyzon cyanotis


    A speciose group of nectar-fruit specialists. We will see these at every stop on the trip. First encounter, the noisy miners of Sydney.

    Australian magpie Gymnorhina tibicen


    Closely related to, but distinct from the corvids (crows, magpies, jays), Artamidae contains crow-sized passerines that ecologically converge on birds of prey. Some like the pied butcher bird have heavy hooked beaks.

    Little Corella Cacatua sanguinea


    An Australia-New Guinea radiation of parrots that make up some of Australia's most common and charismatic birds:

    Cockatoos encompass a range of morphology and color. Some groups are:

    All, however, have: They tend to feed in flocks on fruit, seeds, roots, and insects.

    Collared lorikeet Trichoglossus rubritorquis


    An Australasian-southeast Asian radiation of specialized nectar eating birds:

    Red-winged parrot Aprosmictus erythropterus

    Psittacoidea - Proper parrots:

    Australia is home to 35 species of other parrots. We are likely to see the Red-winged parrot (right). Maybe, if the wind blows from the desert, we might see:

    Good hunting!