10 Game fish have ancient history in the South Pacific

Osteichthyes, Scombriformes: Aglyptorhynchus hakataramea

Billfish are large marine bony fish that today include marlin (e.g. Makaira nigricans), sailfish (e.g. Istiophorus platypterus) and swordfish (Xiphias gladius). In addition to their iconic pointed bills, billfish are known for being top predators that feed on other fish as well as squid and crustaceans. Today billfish are found in temperate and tropical waters worldwide but have a fossil record that is mostly restricted to the Northern Hemisphere. Only fragments of skeletons had been reported from Chile, Peru, southern Africa, and Antarctica. This all changed with an incredible discovery made by Brett Black in 1998 in South Canterbury, New Zealand.

Bones from a fossil fish were found in a limestone quarry in the Hakataramea Valley. The limestone in this quarry dates back to the late Oligocene giving the fossil an estimated age of around 25 or 26 million years old. The bones from the fossil were spread out in a broad line across more than three metres, and the limestone containing these fossils was collected as four large blocks for transport back to the Department of Geology. There the fossil was revealed to be a partial skeleton that included the iconic pointed bill of a billfish along with the lower jaw, sections of the back of the skull, 12 vertebrae, bones from the fins, and several ribs. The fossil was described in 2012 by Michael Gottfried, Ewan Fordyce and Seabourne Rust as Aglyptorhynchus hakataramea. Species of Aglyptorhynchus billfish had previously been found in Europe and the USA, and so the discovery of Aglyptorhynchus hakataramea revealed a much broader geographic distribution for this group of fish than had previously been known. Indeed, the latitudinal range of the ancient Aglyptorhynchus billfish now more closely matched the range of living billfish such as swordfish, providing support for the idea that these top predatory fish have ranged across the world’s oceans for tens of millions of years.

Did you know there is a 3D printable model of this fossil for you to view online and download? Follow this link to learn more: 3D model—Game fish have ancient history in South Pacific.

When the researchers described Aglyptorhynchus hakataramea they reflected on an unusual feature of billfish that might have explained this broad geographic range. Billfish and all other ray-finned fish (actinopterygians) are ectothermic which means they mostly rely on external sources of energy for heat (are ‘cold-blooded’). However, living species of billfish have the rare ability to generate their own warmth using a modified eye muscle, so are ‘warm-blooded’ to a limited extent. This allows billfish to hunt and swim in a wide range of sea temperatures. If Aglyptorhynchus billfish also had the ability to generate their own heat then this feature might have allowed them to live in seas with a broader range of temperatures, potentially explaining the wide geographic distribution of these fish in the fossil record.

The discovery of Aglyptorhynchus hakataramea added another large bony fish to the fossil record for New Zealand alongside the previously described giant moonfish Megalampris keyesi which is on display at Tūhura Otago Museum in Ōtepoti Dunedin. Based on the length of the rostrum of Aglyptorhynchus hakataramea (i.e. rostrum is the technical term for the bill), and the position of the eye, the researchers estimated that Aglyptorhynchus hakataramea had a body length of between three and four metres, similar in size to billfish living today. Aglyptorhynchus hakataramea shows a jaw shape that the researchers suspected meant that it primarily hunted squid in the open ocean surrounding Zealandia.

—Written by Daniel B Thomas