A team of palaeontologists from Flinders University has uncovered fossils of an ancient platypus species, Obdurodon insignis, at Frome Downs Station, approximately 425 km north of Adelaide, South Australia. The fossils date to the late Oligocene period, approximately 25 million years ago.
Discovery and Excavation
The fossils were found in the Namba Formation, also referred to as the Billeroo Creek fossil site. Excavations took place in 2015, 2017, and 2020.
Among millions of fish bones and over 1,000 non-fish vertebrate fossils, researchers identified three fossils belonging to Obdurodon insignis. The species was previously known only from fragments described in 1975.
Fossil Description
The recovered fossils include:
- A lower first molar
- An upper second premolar
- A partial scapulocoracoid (pectoral girdle bone)
Unlike modern adult platypuses, which lose their teeth and use grinding pads, Obdurodon insignis retained well-formed molars and premolars throughout life. The teeth are described as large and pointed.
Physical Characteristics
The scapulocoracoid bone suggests a forelimb structure similar to modern platypuses, indicating comparable swimming capability. Some researchers suggest the ancient species may have had a less specialized rowing motion.
Overall, Obdurodon insignis is described as very similar to modern platypuses, differing mainly by being slightly larger and having teeth.
Diet and Environment
The teeth structure indicates a diet of hard-shelled prey, such as yabbies (crayfish), molluscs, and clams. This contrasts with modern platypuses, which consume soft-bodied prey.
When Obdurodon insignis lived, the landscape contained forests and water bodies, unlike the present-day desert environment. The area was deposited in a tropical, rainforest-like environment with lakes and rivers.
Background and Significance
Platypuses and echidnas are monotremes, a group of egg-laying mammals that split from other mammals over 100 million years ago. The fossil record for monotremes is limited, and platypuses are rare in the fossil record.
The fossils extend the known temporal range of Obdurodon insignis. Researchers note that the overall body plan of platypuses has remained largely unchanged for tens of millions of years, aside from tooth loss.
The study was published in the journal Australian Zoologist by Flinders University palaeontologists Trevor Worthy, Gen Conway, and Aaron Camens.