Eastern Moa (Emeus crassus) Dinornithiformes

Biology of the eastern moa

The eastern moa was a short-legged, robust moa of 36 to 79 kg mature body weight found on the eastern lowlands (Marlborough region) of the South Island of New Zealand (Tennyson and Martinson, 2006).  Its diet was probably low fibre material such as fruits and leaves.  It is said to have the longest trachea of any moa and may have made deep or resonant calls to communicate with conspecifics in dense vegetation.

The brain of the eastern moa

The mean endocranial volume (+ SD) of this species is 23.0 + 3.0 ml for an encephalization quotient (EQ) range of 0.268 to 0.419 (Ashwell and Scofield, 2008).  As with many other moas, there is some retroflexion of the forebrain on the brainstem axis compared to extant ratites (emu, ostrich, kiwis).  The forebrain axis for this specimen is at -1.7 degrees with the brainstem axis.  This may be due to structural constraints of the larger and more robust masticatory apparatus in the moa.  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), 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 Legend

Figure 1 below shows images of a 3D reconstruction of a fossil skull of this species.  The specimen (AV8305) 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.