11 Marine reptile from oceans ancient before Zealandia formed
Sauropsida, Ichthyosauria
Ichthyosaurs, plesiosaurs and mosasaurs are among the most recognisable groups of reptiles that patrolled the oceans during the age of the land-dwelling dinosaurs. Ichthyosaurs were approximately dolphin-shaped animals with the key distinction of having a vertical tail fin.
|
The left image shows a 3D scan of the natural mould of the snout from an unidentified species of ichthyosaur (specimen OU 3859). A natural mould, or trace fossil, shows where the jaws of the marine reptile pressed into the sediment of an ancient sea floor. The light blue region on the left image shows the section of the fossil where a cast was made. The right image shows a 3D scan of the cast made from the natural mould. The shapes of the teeth are clearly visible in the cast. Image credit: DB Thomas. |
A deeply-ancient group, ichthyosaurs first appeared at the beginning of the Triassic about 250 million years ago and survived until the beginning of the Late Cretaceous around 90 million years ago. This means that ichthyosaurs died out before Zealandia had completely separated from the larger southern landmass Gondwana. Ichthyosaurs instead lived in oceans so old that marine rocks containing their fossil remains have been incorporated into the weathered and eroded basement rocks of Zealandia. Ichthyosaurs are thus among the least known marine reptile groups from Aotearoa New Zealand but one remarkable discovery was made by University of Otago paleontologist John Douglas (Doug) Campbell during the summer of 1964 while he was undertaking field work in the Hokonui Hills, Southland.
 |
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—Marine reptile from oceans ancient before Zealandia formed. |
The Hokonui Hills ichthyosaur is a natural fossil mould that formed when the decaying body including jaws and teeth of an ichthyosaur sank onto ancient sea floor sediment more than 217 million years ago during the Triassic. The bones later dissolved, leaving behind a mould of the fossil rather than the remains of the animal itself. The natural mould records a fragment of the skull from close to the tip of the snout. The preservation detail is so fine that delicate impressions of ridges on the teeth are clearly visible.
Doug Campbell sent a cast of the fossil to Dr Alan Jack Charig, Curator of Fossil Amphibians, Reptiles and Birds at the Natural History Museum in London, with a request for help with an identification. The fossil was then described in an article published in the New Zealand Journal of Geology and Geophysics along with Dr Charig’s statement that “…[t]he specimen consists of parts of the jaws and teeth of a medium-sized ichthyosaur, apparently indistinguishable from the corresponding fragment of various forms in the Lower Lias of Dorset…[t]he specimen, like all post-Triassic ichthyosaurs, has teeth of the usual ichthyosaur type set in an open groove and not in separate alveoli…”.
Very little else about the Hokonui Hills ichthyosaur is currently known. Ichthyosaurs are thus another fossil group where a future researcher could make important contributions to the New Zealand fossil record.
—Written by Daniel B Thomas
| Specimen number: OU 3859 | Age: 219 to 217 million years ago (late Triassic, upper Otamitan stage) |
| Locality: Otamita Stream, Southland | Rock Formation: Mandeville Sandstone |
| Collected by: JD Campbell, RM Carter | |
| Citation: Campbell JD. 1965. New Zealand Triassic saurians. New Zealand Journal of Geology and Geophysics 8:505–509. doi:10.1080/00288306.1965.10426420 | |
251.9 to 201.4 million years ago.
100.5 to 66 million years ago. The final epoch of the Cretaceous Period.
The mostly submerged continent of which New Zealand and New Caledonia are a part.
An ancient landmass that existed from the late Precambrian to the Jurassic, which upon fragmenting gave rise to Africa, Antarctica, Australia, India, Madagascar, South America, and Zealandia.
A range of hills that rise to 600 metres above the surrounding Southland Plains. Part of the Southland Syncline geological fold system.
An impression of part of an organism preserved in sediment.
Mesozoic marine sedimentary rocks found in the United Kingdom and elsewhere in western Europe.
Sockets in the mandible and maxilla (i.e. jaw bones) where teeth are set.
