Greater broad-billed/stout-legged moa (Euryapteryx gravis/curtus) Dinornithiformes

Biology of the greater broad-billed moa

One of the most widespread moa in the North Island of New Zealand.  The species had short legs and a short blunt beak, giving rise to the alternate names.  This trachea was as long as 1 m and would have allowed these moa to emit loud calls to communicate with conspecifics.  The stout-legged moa was originally considered to be two species, because of its highly variable morphology.  The species had pronounced reverse sexual dimorphism, with females weighing as much as an ostrich and males not much larger than a turkey (Tennyson and Martinson, 2006).  It was heavily hunted by humans and its eggs have been found frequently in archaeological sites.

 Brain of the greater broad-billed moa

The endocranial volume of this specimen (AV9285) is 23.5 ml, with a body weight of 142.9 kg, giving a very low encephalization quotient of 0.205.  The forebrain is retroverted on the brainstem axis with an angle of -9.4 degrees.

 The features of the telencephalic surface (olfactory bulb, parts of the pallium) have left impressions on the skull interior (see Figure 1a to d).  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), which may be divided into medial and lateral divisions in some avian species, but these divisions are not visible on the moa endocranium.  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 legends

Figure 1 shows images of a 3D reconstruction of the skull of a greater broad-billed moa (AV9285) from Christchurch Museum (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 (Figure 1a to d) 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.