Oldest Fossil Sea Turtle Discovered
The discovery of the oldest known fossil sea turtle was announced earlier this month (September 2015) by researchers from the Senckenberg Research Institute and Natural History Museum in Frankfurt. This new fossil pushes back the earliest date for true sea turtles by 25 million years, displacing the previous title holder discovered back in 1998. At 2 metres long the new species; Desmatochelys padillai, would have been an impressive animal in life, in death its well preserved fossil remains are now helping scientists calculate the age of the entire turtle lineage.
The new discovery comes from fossil beds around Villa de Layva in Columbia and altogether total one nearly complete skeleton plus four additional skulls and two partial shells. This level of detail allowed the researchers studying it to compare this new discovery to other known fossils and modern species, and the researchers placed Desmatochelys in a group called the Cheloniodiea. This is a large collection of species which includes all modern sea turtles. Dates for the age of the rocks surrounding the specimens returned a minimum ago of ~120 million years which makes it substantially older then the previous record holder, Santanachelys gaffneyi.
The origins and evolution of the turtles and tortoises (properly known as the Testudines) is still controversial. The earliest animals that could be classified as testudines probably arose during the Late Triassic but their fossil record is scarce. Sea turtles themselves are a highly specialised group and are thought to have evolved much later, possibly from a fresh water dwelling ancestor. Modern sea turtles have several special adaptations to their ocean habitat including paddle-like limbs and enlarged salt glands to deal with the increased salinity, but when these adaptations arose is not always clear from the fossil record which doesn’t preserve soft tissue well. Therefore definitively saying whether a fossil turtle was marine or not is difficult but Desmatochelys shows almost all the features of a modern sea turtle, in contrast to Santanachelys, despite its far earlier age. This is not only very important for shedding light on this ancient split between the marine and non-marine turtles but it also helps researchers refine their search for specimens which are older still.
Reference: Cadena, E.A., & Parham, J.F., et al. 2015. Oldest known marine turtle? A new protostegid from the Lower Cretaceous of Columbia. PaleoBios. 32, pp.1-42. Available online here.
Featured Image: Modern Green Sea Turtle, NOAA