Apteryx littoralis sp. nov. (1 Viewer)

[Fred Ruhe]

Alan James Drummond Tennyson & Barbara Mizuma Tomotani, 2021

A new fossil species of kiwi (Aves: Apterygidae) from the mid-Pleistocene of New Zealand

Historical Biology: An International Journal of Paleobiology. in press.
doi:10.1080/08912963.2021.1916011

Abstract: https://www.tandfonline.com/doi/full/10.1080/08912963.2021.1916011?src=

We describe Apteryx littoralis sp. nov., a new species of kiwi based on a 1-million-year-old tarsometatarsus from shallow marine sediment in the North Island of New Zealand. The fossil is very similar to the tarsometatarsi of living kiwi species, most closely resembling Apteryx rowi and A. mantelli in size and shape, but differs in being stouter, with proportionally narrower proximal and distal ends. The new fossil is the second oldest known record of kiwi. It demonstrates a relatively conservative kiwi morphology since the mid-Pleistocene.

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Fred

 

[Fred Ruhe]

Systematic palaeontology

Class Aves Linnaeus, 1758
Order Apterygiformes Haeckel, 1866
Family Apterygidae Gray, 1840
Genus Apteryx Shaw, 1813

Apteryx littoralis sp. nov.

http://zoobank.org/urn:lsid:zoobank.org:act:

Holotype
NMNZ S.36731.a complete left tarsometatarsus

Etymology

The fossil was found on an ancient marine shore (= littoral); additionally, the species was probably restricted to a coastal region due to volcanic activity in the central North Island.

Description

A largely complete left tarsometartarsus with a small amount of damage on the extremities, particularly to the hypotarsus (see Figure 1). Mineralisation has turned the bone light brown, as are previous bones recovered at this locality (Worthy 1997a). It partly broke when found in the field so required minor reconstruction and hardening with polyvinyl butyral.

Differential Diagnosis

The fossil is a typical Apteryx tarsometatarsus, differing from the tarsometatarsus of other kiwi species by being stouter, with proportionally narrower proximal and distal ends. The relatively narrow width across the trochleas suggests that the toes were less splayed than those of modern kiwi taxa. In modern kiwi the narrowest distal tarsometatarsus width is found in A. owenii (see Table 1). Apart from these broad differences in shape, the bone also shows a larger, deeper sulcus extensorius (Figure 1) in comparison to all other taxa. A. owenii have the deepest sulcus extensorius of extant taxa.
A. littoralis sp. nov. was probably about the size of A. mantelli and A. rowi because its tarsometatarsus was similar in length to the tarsometatarsi of these taxa (see Table 1). The fossil was shorter than the tarsometatarsi of A. haastii, A. a. australis and A. a. lawryi and longer than that of A. owenii.

Type locality

‘Morrison’s Farm Gully’, north of Marton, North Island, New Zealand, (40°0ʹ16.8"S 175°21ʹ54.2"E).

Geological context, stratum and age

The fossil was found in a c.1 m deep coarse sand layer, within a series of unconsolidated cobble, sandstone and mudstone layers, many with abundant intertidal and subtidal marine molluscs and pumice pebbles. The fossil was found c. 15 m above the present-day stream, c.5 m above the farm road and 20 cm above the base of the 1 m deep fossiliferous layer. It was in the Kaimatira Pumice Sand (part of the Potaka tephra) of the Kai-Iwi Group, Lower Castlecliffian, mid-Pleistocene (about 1 million years old) (see New Zealand Fossil Record Number S22/f162; (Worthy 1997a). At the time of deposition of the kiwi bone, the site was coastal shoreline, being either an exposed beach or a more sheltered environment (Worthy 1997a). The fact that the bones at this site have been found as isolated elements with their extremities worn (Worthy 1997a), indicates that they were washed around in water before final deposition.

Fred


Figure 1. Dorsal view (above) and ventral view (below) of the tarsometatarsus of all kiwi taxa analysed in this study (all specimens in NMNZ). The differential diagnosis characters are marked on the figure: a) narrower proximal end, b) narrower distal end and narrow width across the trochlea, c) deeper sulcus extensorius.