Insect Fossils in the Moltino

Insects, which were pre-dated by the spiders, scorpions and crustaceans as well as centipedes and millipedes, appeared during the Carboniferous Period over 300 million years ago. By the Triassic, some 100 million years later (the period in which the fossils in this article were preserved), insects were already well established and on the way to a tremendous expansion in species diversity. An expansion so vast and varied that even now it is not known at all closely how many extant (living) insect species there are on earth. Estimates, which vary greatly, put them at anything between 3 to 8 million species worldwide, of which less than a million have been identified. Due largely to their immense diversity and ability to adapt to their surroundings, insects are considered by far the most successful of all life forms ever to have evolved.

True insects are characterised by having a three segmented body - head, thorax and abdomen - with three pairs of legs attached to the thorax. Most adult insects but not all, have wings which in many species have been adapted, stunted or entirely done away with to suit their particular circumstances. Insect wings represent one of the primary ways in which many insects are classified and identified. Of special importance is the pattern of veins (venation) of the wings which are distinctive for a specific species and act as "finger prints" to identification. Fortunately insect wings (in particular) are also well suited to undergo the process of fossilisation and consequently serve to provide a valuable record of insect life in bygone ages.

The Molteno Formation is situated in the heart of the semi-desert Karoo Basin of South Africa and has the richest known flora and insect fauna at about the time of origin of the mammals, dinosaurs and possibly the flowering plants in the Late Triassic. Birds River, where the fossils illustrated here were found, is close to Dordrecht in the eastern Cape Province. Here together with a large assortment of pteridothytes (ferns and their allies) and gymnosperms (cone bearing , non-flowering seed plants) occurs a rich deposit of insect fossils. Drs. John M. Anderson and Heidi M. Anderson of the South African National Biodiversity Institute in Pretoria have spent a lifetime collecting fossils from the Molteno Formation. Although their primary field of expertise lies in the study of the plants, during the collection of tens of thousands of fossils from 100 sites throughout the Molteno beds they have also assembled a valuable collection of insect fossils consisting of numerous different species. Odonata, (dragonflies) are especially richly represented at the Birds River locality. In spite of the fact that specimens such as dragonfly wings are very thin and fine in structure, many have been preserved in exquisite detail in shale from what was a freshwater lake in the Triassic in the vicinity of Birds River. Wing bases as well as venation are clearly visible.

A cursory study of this table should serve to clarify in your mind the geological time scale relative to the Triassic period.

Millions of years (ago)	Geological Time Scale (Period)	Extinctions evidently due to:
2	Pleistocene
65 to 2	Cenozoic
145 to 65	Cretaceous	Asteroid impact
197 to 145	Jurassic
251 to 197	Triassic	Double asteroid impacts
299 to 251	Permian	Massive CO2 poisoning
359 to 299	Carboniferous
416 to 359	Devonian	Multiple asteroid impacts
444 to 416	Silurian
488 to 444	Ordovician	Climatic change
542 to 488	Cambrian

Extinctions mark the end of the period indicated.

Triassoneura nana. Wing of a dragonfly preserved in shaly slate.

 

 

 

 

The photograph on the right is a closer view of the one above and illustrates how clearly the pattern of the veins can be seen.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Above and left: Triassoneura heidiae, another dragonfly wing shown at three different magnifications . In the last photograph the hair like fringe along the wing edge is mineral, not fossil.

 

 

 

 

Left: An as yet unidentified beetle (Coleoptera).

 

 

 

 

 

 

Right: A closer look at the same specimen.

 

 

 

 

 

 

 

 

Left: Samaroblatta parvula.

Cockroach wing.

 

 

 

 

 

 

The insect fauna of the Molteno.

Below are illustrated 35 of the 350 species so far identified.

Sketches: Dr. John M. Anderson

Rendering: Dr. Heidi M. Anderson

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Acknowledgements

A special thanks to Dr. John M. Anderson, Specialist Scientist, South African National Biodiversity Institute, Pretoria, for supplying the specimens and for checking the accuracy of the information.

 

 

Text and photographs copyright Lambert Smith.

 

© COPYRIGHT Lambert Smith, 2009