Marine fossils are known in New Zealand from 13 of the 15 major divisions of geologic time. Fossils belonging to the Silurian and Carboniferous periods have not been definitely recognised in the New Zealand succession.
The New Zealand fossil record is predominantly marine and most phyla of marine animals are represented; the record of terrestrial or freshwater life is extremely poor. As Phyla vary widely in their structure for preservation as fossils (hard-shelled creatures are more likely to be preserved than those with soft bodies), the fossil record at best only provides glimpses of the history of life in the past.
Of the marine Protozoa, Foraminifera are particularly well represented in the Upper Cretaceous and Tertiary of New Zealand, but older records are rare, owing to the hardness of the enclosing rocks. Scattered Lower Cretaceous faunas are known, and rare Jurassic and Permian faunas. The study of fossil Coccolithophorida and Radiolaria from New Zealand is yet in its infancy, but Coccoliths occur in the Upper Cretaceous and Tertiary, and Radiolaria in the Tertiary and Triassic (radiolarian cherts). Sponge remains (Porifera), mainly isolated spicules, are preserved in the Cambrian, Ordovician, Upper Cretaceous, Lower Tertiary, and Pleistocene, but they have been little studied. Receptaculites, a spongelike fossil, but of uncertain systematic position, is recorded from the Devonian of New Zealand. The fossil record of the Coelenterata in New Zealand starts in the Devonian, when Rugose and Tabulate corals flourished. Two types of coral assemblage characterise the New Zealand Permian: solitary, cool-water types in the Lower Permian, and reef-building, warm-water types in the Upper Permian. Apart from a conularid found in the Upper Triassic, the post-Permian records of coelenterates are from the Cretaceous and Tertiary rocks – a few Hydrozoa and Anthozoa and abundant Zoantharia (Scleractinia). Marine tube-forming Annelida are represented by tubes and shells. Not much work has been done on New Zealand fossil annelids, but two species have been described from the undifferentiated Triassic-Jurassic rocks of the main ranges of the North and South Island, and these may be of Triassic age. Other worm tubes are known from the Jurassic, Cretaceous, and Tertiary. Marine Arthropoda are well represented in New Zealand by Ostracoda and Cirripedia and by rarer Decapoda and Trilobita, but other Arthropoda have extremely poor fossil records and terrestrial groups are hardly represented at all apart from insects in late Quaternary deposits. The oldest New Zealand Ostracods are from the Cretaceous, and the group ranges throughout the Tertiary. Fossil Cirripedes occur in the Tertiary, and fossil Decapoda in the Lower and Upper Jurassic, Upper Cretaceous, and Tertiary. Phyllocarids (Leptostraca) are preserved in the Ordovician, and Trilobites in the Cambrian, Ordovician, and Devonian. Shelled Mollusca have the most complete record of all larger invertebrates, but land shells are not recorded as fossils in New Zealand before the Pleistocene, and freshwater groups are little known. Gastropoda range back to the Cambrian, but it is not until the Devonian that the first Pelecypoda appear.
From the Permian to the present day, each of the geologic periods in New Zealand is characterised by important pelecypod and gastropod faunas. About 240 genera of pelecypods and 570 gastropod genera have been described from the New Zealand Tertiary and Quaternary. The Scaphopoda, appearing first in the Triassic of New Zealand, are a minor element in the fossil invertebrate fauna, but become locally abundant in the Middle Tertiary. Because of their usefulness for dating and correlation, Cephalopoda are important Mesozoic fossils, but they are, on the whole, sparsely distributed in New Zealand. Rare Dibranchiata are known from the Upper Triassic, but none from the Lower Jurassic. The record improves in the Middle and Upper Jurassic, when belemnites are abundant and useful fossils. The Lower Cretaceous lacks belemnites, but distinctive belemnites characterise the Upper Cretaceous. Ammonoids occur in the Triassic and ammonites in most of the Jurassic stages and from some of those of the Cretaceous. Nautiloids are a minor element in the New Zealand fossil fauna and occur in the Mesozoic and Tertiary. Polyzoa are known from Devonian, Triassic, and Tertiary rocks. Brachiopoda are found in all of the geologic periods present in New Zealand. Primitive types (Atremata) are recorded from the Cambrian and Ordovician and more advanced forms from the Devonian. The Middle and Upper Jurassic and Cretaceous brachiopods are little known. Tertiary brachiopod faunas are of importance and rich faunas characterise the Oligocene. Echinodermata are rare in the Palaeozoic and Mesozoic of New Zealand. A carpoid is known from the Devonian, a cidarid (Echinoidea) from the Upper Triassic, an ophiuroid from the Upper Cretaceous, and asteroids from the Upper Jurassic and Upper Cretaceous. Good echinoid faunas are known from the Tertiary. New Zealand crinoids are not well known, but fragments occur in the Permian, Triassic, Upper Jurassic, and Tertiary. Primitive Chordata are represented in New Zealand by the graptolites (Stomochorda), found in the Ordovician.
Vertebrata have a sparse record in New Zealand and those that are preserved are mainly marine forms. Sharks and saw-sharks are represented by teeth, found in the Upper Cretaceous and Tertiary. Elephant Fish and Chimaerids have left some bone fragments in an Upper Cretaceous deposit. Rays have left rare grinding teeth and spines. Bones and scales of Teleost fish are occasionally preserved, but their commonest remains are otoliths. There is a single Pliocene record of a freshwater fish (Galaxias). Reptilia are known from Middle Triassic, Jurassic, and Cretaceous. In the late Cretaceous, large marine Mosasaurs and Elasmosaurs were not uncommon. No terrestrial dinosaurs (known in Australia and Patagonia) have been reported from New Zealand and the Tuatara (Sphenodon) of the present day has no fossil record before the Holocene. Birds have a poor fossil record, except for the penguins. The oldest moa bones (Dinornithi-formes) are Upper Miocene, and footprints, perhaps Apteryx, are about the same age. Extinct subfamilies of penguins (Sphenisciformes) are well represented from Lower Eocene to Oligocene, and there is a single Pliocene skeleton, but the living Spheniscinae are unknown before the late Pleistocene. A possible albatross bone is known from the Oligocene, but other flying birds have no record in New Zealand before the Pleistocene. Two groups of marine mammals are represented by scanty fossils: Cretacea in the Oligocene, Pliocene, and Pleistocene; Pinnipedia by a few bones from the Pliocene and Pleistocene.
Abundant coals, lignites, and peats, ranging in age from Jurassic to Recent, yield pollen grains and spores of land plants and provide a good basis for study of past plant life. Leaf, seed, and wood fossils, still not adequately studied, are a valuable supplement to the pollen record. The oldest recognisable plants in the New Zealand succession are fernlike fossils from the Permian of Southland. Middle Jurassic vegetation is represented by the well-known Curio Bay fossil forest of Waikawa, Southland; and Upper Jurassic vegetation by the Port Waikato plant fossils. Angiosperms arose and spread throughout the world at the end of the Lower Cretaceous, and angiosperm pollen grains of this age are known in New Zealand. Many good Tertiary floras are known, and in the Miocene they include fossil coconuts in Northland. Late Pliocene and Pleistocene floras reflect the gradual world-wide cooling in the Late Pliocene, followed by the oscillating climate of the Pleistocene. Marine and freshwater Algae have left no record, except for some marine calcareous forms and marine and freshwater diatoms.