Originally distinguished by Haast from the _Dinornithidae_ as an ancient
form of the _Apterygidae_, but afterwards united by Lydekker with the
_Dinornithidae_. Mr. Lydekker's diagnosis of the genus is as follows:--
"Distinguished from _Dinornis_ by the extreme slenderness and length of the
femur and tibio-tarsus, and the relatively shorter tarso-metatarsus, of
which latter the length is considerably shorter than that of the femur. The
pelvis is much narrower than in Dinornis, with the ventral surface of the
postacetabular sacrals ridged and narrower, and a more developed pectineal
process to the pubis. The femur is markedly curved forwards, with the
distal extremity moderately expanded, the popliteal depression larger and
less defined, the linea aspera narrower and sharper, and a more distinct
anterior intermuscular ridge."
The following additional diagnostic characters are taken from Mr. Charles
W. Andrews' description of the complete skeleton of _Megalapteryx tenuipes_
in the Tring Museum (Nov. Zool. IV, pp. 188-194, fig. 1-2 in text and pl.
VI):--
Width of cranium at paroccipital processes less than half the length of the
basis cranii. Length of premaxilla less than two-and-a-half times that of
the basis cranii. Body of the premaxilla pointed and slightly decurved; its
length and breadth less than the basis cranii. The occipital plane slightly
declined backwards. Occipital condyle projecting slightly beyond the
paroccipital processes. Anterior and posterior lambdoidal ridges separated
by a very narrow interval in their middle region only. Width at squamosals
slightly more than double the length of the basis cranii. Mammillary
tuberosities not very prominent. Margin of tympanic cavity evenly curved.
Temporal fossae very large. The distance between the temporal ridges about
four-fifths the width of the cranium at the fossae. The posterior temporal
ridge confluent with the lambdoidal ridge. Post-temporal fossae very large.
The inferior temporal ridge is strongly marked, and there is a pretympanic
process. The zygomatic process is well developed. Rostrum dilated towards
its anterior end, compressed and carinate beneath the large presphenoid
fossae. Mandible very slender. Posterior angular process small. Sternum
very convex, and with a very nearly straight anterior border between the
tuberosities for the coracoscapular ligaments. Costal processes short but
large, with distinct {196} coracoidal facets. The lateral processes are
long and distally expanded. The sternum is just as wide as it is long.
There are three costal articulations. The most notable character is the
enormous length of the toes, the middle one being longer than the
tarso-metatarsus. The ungual phalanges are peculiarly long, narrow and
curved, instead of being comparatively short and broad, as in most other
Moas.
Type of the genus _Megalapteryx hectori_, Haast.