Australia: The Land Where Time Began

A biography of the Australian continent 

Lower Cretaceous non-Marine Invertebrates

The substantial Australian record of macroinvertebrates from the Lower Cretaceous comes mostly from a few known sites that are highly productive. The Trinity Well Sandstone Member of the Cadna-owie Formation, a deposit of Valanginian age in South Australia and the Wallumbilla Formation, from the Aptian at White Cliffs, New South Wales. In these deposits have been found freshwater unionoid bivalves (Alathyria coatsi, Hyridella whitecliffensis) and the viviparid Notopala alboscopularis, the oldest known non-marine gastropod, a species which is common in freshwater-estuarine habitats of the present.

The Koonwarra Fossil Beds of southern Victoria, from the Barremian-Aptian, are the richest known deposits from the Lower Cretaceous of non-marine invertebrates. More than 80 species have been found in the Koonwarra Fossil Beds that include:

bivalves Alathyria coatsi and Mesohydridella ipsviciensis, that have also been found in other nearby localities;

freshwater bryozoans;

a possible earthworm;

harvestman spiders;

crustaceans (Koonaspides indistinctus, a syncarid), a shrimp or anostracan, an ostracod and a cladoceran;  

more then 70 insect species.

The insect assemblage, that includes a number of extant species, in the Koonwarra Fossil Beds is the best documented insect assemblage in the Southern Hemisphere. The dominant taxa in the assemblage are the larvae of dragonflies, scorpionflies, caddisflies and mayfly (Australurus plexus), all of which live in water, as well as hydrophilid beetles and mayflies that inhabit streams (Promirara cephalota and Dulcimanna sculptor) that are suggested to have washed in from nearby watercourses. Also in the deposits are dragonflies, scorpionflies and parasitic wasps, all flying insects. Of terrestrial insects that have been assumed to have blown into the water there are beetles and pucilid fleas, the presence of which suggests the presence of mammals. Shallow cool-water conditions that have been suggested to have undergone periodic mass mortality, possibly as a result of the lake freezing over in winter, are indicated by the Koonwarra assemblage.

The Toolebuc Formation, of upper Albian age, marine deposits, a single impression of a wing of a dragonfly Aeschnidopsis flindersiensis and an unknown mecopteroan or scorpion fly have been found. At Lightning Ridge, the Griman Creek Formation from the lower-middle Albian, contains decapod crustaceans that are known only from gastroliths, and a number of unionoid bivalves and gastropods that are non-marine. Included among the bivalves are Alathyria jaqueti, Palaeohyridella godthelpi, Megalovirgus wintonensis and Hyridella macmichaeli, all of which were living throughout the Cretaceous of Australia. Among the gastropods are both freshwater forms such as the viviparids Notopala, Albianopalin benkeari, A. lizsmithae, Fretacaeles gautae, and taxa from brackish water such as the thiarid Melanoides godthelpi, which suggests the sediments were deposited in a complex estuarine habitat. There are also terrestrial pulmonates (camaenids and possible succineids). It has been suggested that they either fell from overhanging vegetation or were washed into the aquatic deposits.

Sources & Further reading

1. Kear, B.P. & Hamilton-Bruce, R.J., 2011, Dinosaurs in Australia, Mesozoic life from the southern continent, CSIRO Publishing.