Pelvis. Pl. IX., Figs. 1, 2, and 3.
In my introductory remarks I stated that all search after the pelvis of Harpagornis moorei had been unsuccessful, but that we were fortunate enough to obtain this important bone of the smaller species H. assimilis when excavating the other bones belonging to the latter.
Last year, when visiting the Colonial Museum in Wellington, I observed amongst the specimens of our extinct avi-fauna a perfect pelvis, which, on examination, I assigned to Harpagornis. Dr. Hector, at my request, allowed me to take this fine specimen with me for comparison and description. After placing it near the pelvis of H. assimilis, with which it agreed in all main points except its larger size—bearing the same proportion as the bones of H. moorei do to those of the smaller species—I had no hesitation in assigning it at once to the former.
This compound bone, belonging to a fully-grown but still young individual, has all the characteristics which belong to the pelvis of a diurnal raptorial bird, some of the complex features, owing to its enormous size, being developed in a most remarkable degree. It combines great strength with lightness and
elegance of form, of which the drawings attached to this memoir will convey an accurate conception better than words can do.
In the following pages I shall offer a description of the larger and perfect pelvis, which I assigned to Harpagornis moorei, whilst the references to that of the smaller H. assimilis will prove the close generic, if not specific, relations of both.
In comparing the pelvis of H. moorei with those of Aquila audax, the wedge-tailed Eagle of Australia, and of Circus assimilis, the Harrier, and Hieracidea novŒ zealandiŒ, the Sparrow-Hawk of New Zealand, as shown in the following table, the striking difference in size becomes at once manifest.
|Pelvis of||Greatest Length.||Greatest Breadth.|
|Hieracidea novŒ zealandiŒ||2.00||1.13|
When examining this table of measurements another peculiar feature of the fossil bone will present itself to our attention, namely, its great length when compared with its breadth; whilst in the three recent species the double breadth is more than the length, in Harpagornis it is considerably less. This peculiarity is produced principally by the greater steepness of the pelvic roof and by the comparatively greater length of the ilio-ischial plates; moreover, it is also higher in proportion than any of the recent species of Diurnal Raptores with which I could compare it.
When viewed from below the space formed by the hind part of the neurapophysial crest and the two ilia has an oval shape; whereas in the three recent species previously alluded to it is shorter, more open, and semicircular (a).
Beginning with the first sacral vertebra, we observe that the articular surface of its centrum is broader in a transverse than in a vertical direction, 0.69 inch by 0.58 inch. The neural canal has an oval form, its largest diameter, 0.21 inch, being in the vertical line, in this respect resembling Circus; whilst in Aquila, and still more in Hieracidea, the canal approaches the circular form.
The prezygapophyses (pr.) are of middle size and stand forward, their articular surface of a rounded shape, being almost plane. The neural spine is broad and strong at its base, gradually contracting, and forming only near its coalescence a small neurapophysial expansion lying between the iliac plates (n).
A broad and deep ilio-neural opening is formed on each side of the spinal plate, having a greater vertical than lateral extent, and here again differing from the pelvis of the three recent species previously alluded to, the roof
formed by the iliac plates of Harpagornis being consequently considerably steeper.
The surfaces for the head of the two free sacral ribs are strongly developed, the iliac roof extending, however, a little beyond them.
The under surface of the first sacral centrum in its anterior portion is slightly carinate, whilst the centres of the two succeeding ones are rounded, the edges of their articular surfaces being well raised, the posterior one of the third centre the least; after which they flatten and expand to the beginning of the interacetabular region, contracting again to its termination, and possessing a transversely concave, shallow, inferior surface, being broadest near the anterior articular surface of the seventh vertebra.
From the eleventh to the fourteenth they still diminish in breadth, and now exhibit a low but well marked inferior ridge, running out before the last sacral vertebra is reached.
The parapophyses of the third to the sixth sacral vertebra are anchylosed to the lower border of the ilia, forming four interapophysial vacuities on both sides; of these the last parapophysis is the strongest and thickest, standing at right angles to the direction of the axis of the vertebral column.
There is a short parapophysial process starting from the seventh vertebra (the first of the four next vertebræ forming the interacetabular region), which has a downward direction, and is still attached on the left side of the pelvis to the inner edge of the head of the pubic bone (h).
In the pelvis of Harpagornis assimilis this process does not exist, and it resembles in this respect the recent species previously used for comparison. Of the parapophyses of the last four vertebræ, forming the postacetabular region, the first one belonging to the eleventh sacral centrum is a filamentary bone (m) joining the second round and strongest parapophysis, which abuts against the innominate, and with which the posterior ones are also connected by their distal ends.
Of the interapophysial vacuities the first, second, and fourth are elongate, whilst the third and largest is more circular. In the smaller pelvis of Harpagornis assimilis these vacuities are not relatively, but actually, larger than in that of H. moorei.
The coalesced distal portion of these parapophyses runs in an oblique angle from the inner region of the ilia to the abutment of the twelfth sacral centrum, the space between this distal line and the upper side of the ischiadic foramen, below the pelvic disk, being spanned over by a thin deck of bone (d), perforated by a large oval opening 0.48 inch in its largest diameter, which runs parallel to the main axis of the pelvis, and is situated on each side behind the upper and anterior wall of the ischiadic foramen.
The last sacral vertebra of H. moorei is not yet quite anchylosed to the
foregoing vertebra, thus shewing that it belonged to a not quite adult individual; on the other hand, in the pelvis of H. assimilis the articular surfaces of these two last vertebræ are well anchylosed, and the junction of the parapophyses with the lower border of the ilia in its antacetabular part is also well accomplished, which is not quite the case in the pelvis of the larger species under review, so that we may safely assume that the former belonged to a full-grown mature specimen.
The gluteal ridge is decayed in H. moorei, but is well developed and preserved in the smaller species, the gluteal process forming a rounded knob (g), which rises well above the pelvic disk, whilst in Aquila this process has a convex form, directed downwards, and standing well in advance of the ilia. Of the recent species Circus resembles most, in this respect, the extinct gigantic form.
The pre-acetabular iliac plates unite about one-third from their anterior end above the summit of the sacral ridge, diverging again after having been united for 1.70 inch to form a small interposed neural expansion, anteriorly lying scarcely below the upper border of the iliac plates. In this respect it resembles Aquila, whilst in Hieracidea, and still more in Circus, the neural interposition is continuous all the way, but is narrowest in the region where, as observed, the iliac pre-acetabular plates meet in Harpagornis.
The ischium is very strongly developed at the back part of the acetabulum, as might be expected in a bird of such great strength. The tuberosity of the ischium, a roundish flat process, 0.72 inch from its posterior termination, rises conspicuously above its lamelliform surface (k). The posterior termination of the coalesced ischium and ilium is not rounded off, as in Aquila, but has a rather acute form, which, of recent species, Circus, and still more conspicuously Hieracidea, also possess.
The pubic bone, after forming the lower boundary of the obturator notch, gradually loses its trihedral shape and assumes a vertically flattened form, continuing to run for some distance parallel with the ischium; however, as in both specimens its posterior portion is broken off, I cannot say how far it may have extended. In any case it is longer than in Aquila.
A thin plate of bone, closely connected with the lower border of the ischium and gradually thickening, runs to the termination of that latter bone. At its beginning it forms the posterior boundary of the obturator foramen, and fills up the space between the ischium and the pubic bone.
The subacetabular fossæ (f), which are very shallow in Aquila and the Diurnal Raptores now living in New Zealand, are deeply excavated. The pelvic disk is a strong bone separated on each side by a well-marked line from the hind part of the neurapophysial crest, which rises well above it, the latter showing, like all the rest of the bones of which the pelvis is formed, a
remarkable development of all the principal features to be observed in the pelvis of the smaller recent Diurnal Raptores.
Finally, I wish to observe that the pelvis of Harpagornis moorei, from Otago, has still some of its integuments and ligaments attached, of which the lining membrane on the walls of the acetabulum are best preserved; whereas the more fragmentary bone of H. assimilis is in the semi-fossil condition in which all the bones from the remarkable turbary deposits of Glenmark are usually found.
Since my former paper a second ungual phalanx has been obtained, which, applying the same mode of measurement previously used, is 2.75 inches long, and has a circumference of 2.92 inches at its proximal end. It is the third phalanx, and belongs to the second or inner toe of the right foot.
Amongst the smaller bones lately excavated I found also the second phalanx, with which that latter ungual phalanx articulates.
The pachydermal character, even in these toe-bones, is well sustained, and the form and peculiarities of the articular ends, and the large concavity behind and below the trochlear joints of the distal end, are developed in a striking degree.
Of Harpagornis assimilis we possess, as previously observed, several phalanges.