Go to National Library of New Zealand Te Puna Mātauranga o Aotearoa
Volume 84, 1956-57
Previous Article | Table of Contents | Next Article
This text is also available in PDF
(1 MB) Opens in new window
– 342 –

The Skull

(Figs. 1 and 2.)

Of the median dorsal skull elements, the nasals and parietals remain separate throughout life in both Naultinus and Hoplodactylus. The premaxillae are more or less fused in the adults and contribute to a wedge-shaped prenasal process which extends up between the two nasals. The frontals also are fused, but the degree of fusion, as with the premaxillae, is less in Naultinus than in Hoplodactylus. Similarly, the occipital elements (supraoccipital, exoccipitals and basioccipital) are separate from one another in Naultinus but indistinguishably fused to form a more solid ring of bone in Hoplodactylus.

As is characteristic of recent geckos (Camp, 1923), there is no pineal foramen in either genus. In Naultinus the parietal roof is largely membranous towards the middle line, and a large membranous area may also occur medially in the floor of the cranium, between the basioccipital and the basisphenoid. In a general comparison of Naultinus and Hoplodactylus it is noted that adults of the former genus show a lack of ossification in many regions of the skeleton and less tendency towards the fusion of paired elements. Such features might well be interpreted as being neotenic.

The geckonid tendency towards reduction of membrane bones, which has resulted in the loss of skull arches, is the most striking feature of the skulls. The consequent incompleteness of the temporal region in geckos has prevented these otherwise primitive lizards from throwing valuable light on the much debated question of modified parapsid or diapsid origin of the lacertilian skull (Watson, 1914; Williston, 1914; Broom, 1925; Versluys, 1936). The temporal space is neither divided into upper and lower temporal fossae nor demarcated from the orbit.

Distinct bones, shaped like arrow-heads, are situated at the sides of the parietals and frontals, at their sutures with one another. These, by their relationships in geckos and by comparison with the elements present in other lizards, are normally regarded as postfrontals, though possibly they represent a fused postfrontal and postorbital on each side. Elements similar to the postfrontals of the New Zealand geckos are noted in alizarin transparencies of Phyllurus platurus, Aristelliger praesignis, Sphaero-

– 343 –

dactylus parkeri and Gonatodes fuscus (Sphaerodactylidae). Postfrontals have also been described in Gekko gecko (Boulenger, 1912). Hemidactylus flaviviridis (Mahendra, 1949); Aristelliger lar and Coleonyx variegatus (Eublepharidae) (McDowell & Bogert, 1954). However, they are not universally present for Brock (1932) notes that postfrontals are present in Pachydactylus maculosa and Pachydactylus bibroni but absent in Lygodactylus capensis.

Brock states that in Pachydactylus bibront only a small strip of the postfrontal lies along the margin of the frontal, but that the part of it in contact with the

Picture icon

Text-fig. 1—A, Skull of Naultinus elegans, dorsal view B, Skull of Hoplodactylus duva [ unclear: ] celii, dorsal view C, Skull of Hoplodactylus duvauceli, lateral view ept, epipterygoid; exoc, exoccipital; fr, fused frontals; [ unclear: ] jugal; mx, maxilla; na, nasal; pa, parietal; pal, palatine; pinx, premaxilla; poc, paroccipital process; poj, postfrontal; prf, pre-frontal; pro, prootic; pt, pterygoid; q, quadrate; [ unclear: ] ; supraoccipital; stm, supratemporal; tr, transpalatine.

– 344 –

parietal is expanded into a broad plate of bone. This feature, which is particularly accentuated in Aristelliger lar, indicates a reasonable possibility that the broad plate of bone bordering the parietal on each side represents a postorbital fused with the postfrontal but not yet greatly reduced.

In none of the above mentioned species is there a prefrontal-postfrontal junction above the orbit. Boulenger (1885) used this feature as one of two points distinguishing the skull of a gecko from that of a pygopod, but, as McDowell and Bogert (1954) point out, this distinction will not hold.

Postorbitals, at least as separate elements, are lacking in the adults of both Naultinus and Hoplodactylus, as also are the squamosals. Closely applied to the postero-lateral border of the supratemporal process of the parietal (parietal process) on each side, there is present in both genera a fairly distinct, splint-like element, the supratemporal or tabular. Against the inner side of this supratemporal the head of the paroccipital process abuts, while the dorsal head of the quadrate is directed towards both of them from below.

Brock (1932) notes in Lygodactylus a bony splint on the outer surface of the quadrate which is present in embryos as a definite membrane bone. This element, present also in Pachydactylus, is regarded by her as being a vestigial quadratojugal. Examination of detached quadrates of adults of Naultinus and Hoplodactylus reveals no trace of a quadratojugal, but in this respect no information is available regarding developmental stages in the two genera.

On the other hand, Brock states that a jugal is altogether lacking in Lygodactylus and merely a microscopic vestige in Pachydactylus where it is seen in adult transverse sections. In Naultinus and Hoplodactylus, however, although the jugal is a slender bone, it is a definite macroscopic element between the maxilla and the transpalatine. This is also the case in Hemidactylus flaviviridis (Mahendra, 1949); Aristelliger lar and Coleonyx variegatus (McDowell & Bogert, 1954): and Gekko gecko (Lakjer, 1927). From our own observations also, a jugal was noted in Sphaerodactylus parkei and Aristelliger praesignis, but could not be distinguished in an alizarin transparency of Gonatodes fuscus. Where it occurs in geckos, the jugal is reduced to a horizontal splint and does not exhibit a more vertical bony extension towards the postfrontal. In this position a ligament extends upwards and slightly backwards from the jugal to the postfrontal in the New Zealand genera and represents a remnant of the postorbital arch which is normally lost in geckos. Lakjer (1927) has noted a similar ligament in Gecko gecko.

In Naultinus and Hoplodactylus, the orbit is bounded anteriorly by a conspicuous prefrontal. No lachrymal is visible in the adult skulls, and this is also the case in Hemidactylus flaviviridis (Mahendra, 1949). Brock (1932), however, identifies a small lachrymal in sections of a newly hatched Lygodactylus. Where it occurs in geckos, this bone is crowded within the orbit and, according to Camp (1923), lost to view externally.

According to Walls (1942), most lizards usually have fourteen scleral ossicles surrounding the eyeball, although in Sphenodon the scleral bones number sixteen or seventeen. Until more recent years, the highest known number in living animals has been in birds which may have as many as eighteen. An examination of scleral ossicles in the New Zealand geckos reveals that Naultinus has twenty, while Hoplodactylus has twenty-five. The number in this latter genus was first noted by Underwood (1951) to whom specimens of Hoplodactylus pacificus were sent in connexion with his work on reptilian retinas. This count has subsequently been confirmed by us in other specimens of H. pacificus, and also in H. duvaucelii. Underwood's (1954) count for Naultinus is eighteen and twenty-two. Furthermore, he notes that in the case of the Australian gecko Oedura lesueurii there are thirty scleral ossicles. This number is not exceptional for the Australian representatives, for we have counted the same number in Phyllurus platurus.

– 345 –

The greater number of scleral ossicles has been regarded as the more primitive condition on the grounds that Stegocephalians usually had twenty to thirty-two scleral ossicles set in several rows Underwood (1954) indicates that there may be individual variation in the number of scleral ossicles, but at the moment there seems inadequate evidence to support his contention that there has been a multiplication of ossicles to account for the “supernumerary” condition in geckos.

The floor of the orbit is formed partly by the jugal, palatine, transpalatine (ectopterygoid) and pterygoid bones. Like the palatines, the pterygoids are very widely separated from one another. Between them in the middle line, the basisphenoid and

Picture icon

Text-fig. 2.—A, Skull of Naultinus elegans, ventral view B, Skull of Hoplodactylus duvaucelii, ventral view. C, Lower jaw of Hoplodactylus duvaucelii, left side. ang, angular; art, articular; boc, basioccipital; bs, basisphenoid; bpt, basipterygoid process; c, occipital condyle; cor, coronoid; d, dentary; ec, extra-columella; ept, epipterygoid; h, hyoid; j, jugal; mx, maxilla; pal, palatine; pmx, premaxilla; poc, paroccipital process, ps, parasphenoid, pt; pterygoid; pv, prevomer; q, quadrate; sa, surangular; st, columella auris; tr, transpalatine.

– 346 –

parasphenoid extend forwards. Each pterygoid is connected to the parietal (anterior superior) process of the prootic by an upwardly extending rod, the epipterygoid (columella cranii). The quadrate process of the pterygoid extends back to articulate with the quadrate proper.

Supporting the floor of the nasal capsules are the prevomers. These are separate bones lying side by side in the middle line of the palate. Between each prevomer and the more lateral maxilla of its side lie both the choana and, more anteriorly, the foramen of Jacobson's organ. The septomaxillae lie inside the olfactory capsules and are exposed only by the removal of the nasals. Each septomaxilla forms a roof over Jacobson's organ of its side and rests on the prevomer.

The relationship of bones in the region of the auditory capsules is best seen in Naultinus, where there is less fusion of skull bones and where, except for the exoccipital and opisthotic on each side, the various auditory and occipital elements are separate. The prootic, forming the anterior part of the auditory capsule is large and irregularly tri-radiate. Dorsally, it meets the supraoccipital behind and extends up as the parietal process in front; at a mid-lateral level its posterior process reaches back almost to the level of the paroccipital process; ventrally it extends down to flank both the basioccipital and the basisphenoid.

The opisthotic is much smaller and although distinct in Naultinus from the adjacent supraoccipital, prootic and basioccipital bones, it is indistinguishably fused with the exoccipital. It is close to this region of fusion that the stout paroccipital process arises and extends out laterally.

Below the paroccipital process, and just in front of it, is the fenestra ovalis, which is bounded partly by the prootic and partly by the opisthotic. Fitting into the fenestra ovalis is the expanded foot plate of the stapes. In the main the stapes consists of a narrow rod, the columella auris, bearing distally the extra-columella.

Slightly below the fenestra ovalis and bounded largely by the opisthotic, though bordered partly by the basioccipital, is the fenestra rotunda.

Previous Article | Table of Contents | Next Article