Eocene turtles and whales from New Zealand

• Main Author: Kohler, Richard
• Other Authors: Fordyce, R. Ewan
• Format: Thesis
• Language: English
• Published: University of Otago 2018
• Subjects: Antarctic; Antarctic Peninsula; New Zealand; Seymour; Seymour Island; Antarc*
• Online Access: http://hdl.handle.net/10523/8576

This thesis documents eleven specimens of Eocene turtles (Reptilia: Testudines: Dermochelyidae, Cheloniidae) and seven specimens of archaeocete whales (Mammalia: Cetacea: Basilosauridae) from New Zealand. All taxa derive from marine sediments from the New Zealand Bortonian, Kaiatan and Runangan Stages (late middle to late Eocene). The first fossil record of the family Dermochelyidae (genus Psephophorus) from the Southern Hemisphere is based on five specimens from the Waihao Greensand near Waimate in South Canterbury, and a dermochelyid humerus from the Burnside Mudstone near Dunedin. One large specimen from the Waihao Greensand is the holotype of the new species Psephophorus terrypratchetti Kohler, 1995b; other specimens are referred to this species. Comparisons with specimens from overseas show that the New Zealand Psephophorus fossils are distinctive in that keels are lacking on their secondary carapace, and primary carapace elements are more pronounced than in geologically younger species elsewhere. A cladistic analysis of dermochelyids, together with a new interpretation of the evolution of their secondary carapace, supports an early Tertiary origin for this group of marine turtles. Changes in the secondary armour during the late Pliocene to earliest Pleistocene are probably linked to a cooling world climate. The New Zealand Psephophorus fossils represent one of the earliest records of this genus worldwide. Elsewhere in the Southern Hemisphere, Eocene dermochelyids (undescribed) have been reported from Seymour Island, Antarctic Peninsula. Other fossil turtles from New Zealand include sparse non-dermochelyid material from the West Coast of the South Island and one specimen from the North Island (Kaipara Harbour, Northland). These fragments also indicate marine animals, which could not, however, be identified beyond family level. The New Zealand record of fossil turtles differs from the Australian record in that there are no terrestrial turtles reported from New Zealand, and no Tertiary marine turtles from Australia. This discrepancy may be explained by differences in preservation and accessibility of marine facies, but may also be due to insufficient prospecting work. Cetacean fossils (archaeocetes) are known from two formations, the Waihao Greensand in South Canterbury and the Mangatu Mudstone near Gisborne in the North Island. The six specimens from the Waihao Greensand are Bortonian to Kaiatan in age; they represent animals related to the dorudontine genus Zygorhiza, and an animal more than twice as large which could not be placed within a known archaeocete group. The age for the single specimen from the North Island, which is also referred to the dorudontine genus Zygorhiza, can only be given as middle to late Eocene. The La Meseta Formation of Seymour Island represents the nearest location from which archaeocetes and Eocene dermochelyids are reported. Large, nondorudontine cetacean fossils from Seymour Island may represent the same taxon as the large archaeocete fossil from New Zealand. The New Zealand archaeocetes form, apart from an isolated find from early Lutetian strata in Senegal, the second oldest record for Dorudontinae worldwide, and one of very few substantiated records of archaeocetes in the Southern Hemisphere; they are seen as an indicator for an early colonisation of southern seas by archaic whales. Because most of the archaeocete specimens and all but one dermochelyid derived from Bortonian to Kaiatan greensands in the Waihao River Basin, this area was mapped in detail. A fine-stratigraphy is established for the Waihao Greensand in the study area, based on two widespread index horizons, which are used to link outcrops and to establish the relative age of the different units of Waihao Greensand as exposed in different parts of this area. A depositional model for the Waihao Greensand is given, showing that the sediment was deposited during a steady rise in sea-level under tropical to subtropical conditions; it can be correlated approximately to a middle Lutetian to middle Bartonian age.