Dark Emu - Description

Description

The King Island Emu was the smallest Emu taxon, and was about half the size of the mainland birds. It was about 87 cm (34 in) tall. According to François Péron's interview with a local sealer, the largest specimens were up to 137 cm (4.5 ft) in length, and the heaviest weighed 20 (40 lb) to 23 kg (51 lb). It had a darker plumage, with extensive black feathers on the neck and head, and blackish feathers on the body, where it was also mixed with brown. The bill and feet were blackish, and the naked skin on the side of the neck was blue. The 2011 genetic study did not find genes commonly associated with melanism in birds, but proposed the dark colouration could be due to alternate genetic or non-genetic factors. Péron stated there was little difference between the sexes, but that the male was perhaps brighter in colouration and slightly larger. The juveniles were grey, while the chicks were striped like other Emus. There were no seasonal variations in plumage. Since the female mainland Emus are averagely larger than the males, and can turn brighter during the mating season, unlike the norm in other bird species, some of these observation may have been based on erroneous conventional wisdom.

Subfossil remains of the King Island Emu show that the tibia was about 330 mm. (13 in) long, and the femur was 180 mm (7 in) long. The pelvis was 280 mm. (11 in) long, 64 mm (2.5 in) wide at the front, and 86 mm (3 in) wide at the back. The tarsometatarsus averaged 232 mm (9 in) in length. In males, the tibiotarsus averaged 261 mm (10 in), whereas it averaged 301 mm (12 in) in females. In contrast, the same bones measured 269 mm (10.5 in) and 305 mm (12 in) in the Kangaroo Island Emu. Apart from being smaller, the King Island Emu differed osteologically from the Kangaroo Island Emu in the intertrochlear foramen of the tarsometatarsus usually being fully or partially abridged. The outer trochlea was more incurved towards the middle trochlea in the Kangaroo Island bird, whereas they were parallel in the King Island Emu.

The King Island Emu and the modern Emu show few morphological differences other than their significant difference in size. Mathews stated that the legs and bill were shorter than those of the mainland Emu, yet the toes were nearly of equal length, and therefore proportionally longer. The tarsus of the King Island Emu was also three times longer than the culmen, whereas it was four times longer in the mainland Emu. Additional traits that supposedly distinguish this bird from the mainland Emu have previously been suggested to be the distal foramen of the tarsometatarsus, and the contour of the cranium. However, the distal foramen is known to be variable in the modern Emu showing particular diversity between juvenile and adult forms and is therefore taxonomically insignificant. The same is true of the contour of the cranium, which is more dome-shaped in the King Island Emu, a feature which is in fact also seen in juvenile modern Emus.