An 25-year-old fossil of an eagle was found on a remote South Australian cattle station. It has been identified as the oldest known raptor species.
In 2016, Palaeontologists found the eagle fossil along the shore of Lake Pinpa, a dry lake. They have since identified it to be Archaehierax, a new species, in a study published by the journal Historical Biology.
Ellen Mather, a PhD student at Flinders University, was the first author of the study. She stated that the ancient bird was slightly smaller and more compact than a wedge-tailed Eagle, with a footspan 15cm.
Based on what we know, it would have been one of the largest eagles at that time. Although Lake Pinpa now exists in a sandy desert habitat it was 25m years ago a temperate rainforest that had permanent water bodies.
Mather stated that the bird would have preyed on all small-to medium birds and mammals at the time. This includes ancestors of modern Koalas and possums that lived in the forest.
The wings of the eagle were small for their size but they had long legs. Mather stated that this is quite common among forest eagles. This is because they have to navigate through more densely populated areas than eagles who live in open spaces such as grasslands and woodlands.
It would have been an ambush-hunter, according to our estimation. Although it was not fast, it would have been agile and able to make quick turns. It would also have waited on a perch to allow prey to come within striking distance.
Mather stated that the discovery revealed that Australia had an endemic eagle lineage early in the evolution of the animal. This ancient bird was not an ancestor of any living species, but belonged to a distinct branch.
It is clear that this family, the Accipitridae, was widespread worldwide 25m years ago. However, it also showed that they were already diversifying. Australia appears to have been an area of exceptional diversity back then.
The features of the ancient eagle were different from modern hawks or eagles. They had a larger foot-span to capture prey.
Mather stated that some of the muscle insertion points on Mather's leg were deeper than those of most living accipitrids (the family of birds, including hawks or eagles). This could indicate a very strong grip given Mather's slim build.
The ancient eagle's bones were found in more than 60 pieces. This makes it one of the most preserved fossils at Lake Pinpa. The site also contains the remains of many Australian species' ancestors, such as wombats and platypus.
The eagle was probably washed into the lake after it died. Mather stated that the bones would have been buried in sediment at the time. This is what preserved them.