Little bush moa (Anomalopteryx didiformis) Dinornithiformes
Biology of the little bush moa
The little bush moa was the most widespread moa species in the North Island of New Zealand. Its small stature and short legs may have been an adaptation to moving quickly though dense vegetation. It is thought to have had a diet high in fibrous material and its sharp-edged beak was adapted to cutting woody parts of trees and shrubs (Tennyson and Martinson, 2006).
Brain of the little bush moa
The mean endocranial volume of this species (+ SD) is 24.4 + 1.6 (Ashwell and Scofield, 2008), with an adult body weight of 19 to 73 kg (Tennyson and Martinson, 2006). This gives an encephalization quotient (EQ) range of 0.338 to 0.725 for this specimen. The forebrain is not as retroflexed as other moa: the angle between the forebrain and brainstem axes is + 16.1 degrees for this specimen, comparable to the emu. The features of the telencephalic surface (olfactory bulb, parts of the pallium) have left impressions on the skull interior (see Figure 1). The maxillomandibular foramen transmits the maxillary and mandibular divisions of the trigeminal nerve (5max, 5mand). The optic foramen transmits the optic nerve (2n). The optic lobe is composed of the soft tissue optic tectum, a part of the midbrain which projects ventrolaterally caudal to the telencephalon in birds. The wulst is a dorsal projection of the telencephalon which is made up of the dorsal pallium (or hyperpallium) and the parahippocampal area. The wulst is separated from the rest of the pallial surface by a groove (vallecula). A substantial proportion of the wulst is concerned with vision, so the large wulst but small olfactory bulbs in moa suggest a greater reliance on vision relative to olfaction.
Figure Legend
Figure 1 shows images of a 3D reconstruction of a fossil skull of this species. The specimen (AV8548) is from the collection of the Canterbury Museum, Christchurch (with thanks to RP Scofield). The fossil was scanned at Christchurch Radiology Group, St George’s Hospital (Siemens Somatom Definition, 120 kV, 400 mA, 0.6 mm slice thickness). Impressions on the skull interior from soft tissue structures have been labelled.
References
Ashwell KWS, Scofield RP (2008) Big birds and their brains: Paleoneurology of the New Zealand Moa. Brain Behavior and Evolution 71, 151-166.
Tennyson A, Martinson P (2006) Extinct Birds of New Zealand. Wellington, NZ: Te Papa Press.
Figure 1: 3D reconstruction of a fossil skull of this species. The specimen (AV8548) is from the collection of the Canterbury Museum, Christchurch (with thanks to RP Scofield). The fossil was scanned at Christchurch Radiology Group, St George’s Hospital (Siemens Somatom Definition, 120 kV, 400 mA, 0.6 mm slice thickness). Impressions on the skull interior from soft tissue structures have been labelled. a) Interior of left side of skull; b) Interior of right side of skull; c) Interior of dorsum of skull; d) Interior of base of skull. Scale bar is 10mm.