High-resolution X-ray computed tomography of an Early Cretaceous gekkonomorph (Squamata) from Öösh (Övörkhangai; Mongolia)

The enormous variation of the orbit in lepidosaurs is better conceptualized in terms of composition and configuration. Broadly, the orbit varies from having totally closed rim to being open posteriorly. Two processes are responsible for changes in the components of the circumorbital series, element loss and fusion. The resulting contacts among elements are the main factors determining orbital configuration. Here, we present a revision of the gekkotan circumorbital bones in the general context of the Lepidosauria. From observations of a sample of 105 species of gekkotans prepared using different techniques, we describe the main changes in the orbit and corroborate the presence or absence of some of the ambiguous elements such as the lacrimal and the jugal. The supraorbital bones of squamates are reviewed and some problems of homology are evaluated using recent phylogenenetic hypothesis. Anat Rec, 293:402-413, 2010. V V C 2009 Wiley-Liss, Inc.

Section: The Circumorbital Bones Of the Gekkotamentioning

confidence: 99%

The Circumorbital Bones of the Gekkota (Reptilia: Squamata)

Daza

Bauer

2010

“…3). This element lies more anterior than the location of the primitive gekkotan position for the postfrontal (see illustrations in Conrad and Norell, 2006), and lacks the lateral process of that element, but still separates the rostral portion of the postorbital from contact with the frontal. We advocate that it is more parsimonious to propose an anterior shift of an existing element than the appearance of a de novo structure and the loss of another.…”

Section: Discussionmentioning

confidence: 99%

“…2) and, thus, can be hypothesized to exhibit a condition characteristic of this cluster, especially as it appears to represent a situation somewhat similar to that of basal lepidosauromorphs (Daza and Bauer, 2010: Figs. 1A,2) and some primitive gekkonomorphs (Conrad and Norell, 2006), with the exception that the anterior element is fused to the frontal rather than being free, a condition also noted to occur in some iguanids (Norell, 1989). Eublepharids retain many primitive features among gekkotans (Kluge, 1962;Daza, personal communication); thus the dorsal circumorbital bones could represent another example of such expression.…”

Section: Discussionmentioning

confidence: 99%

“…This is partly borne out. The element regarded as the postfrontal by Evans (2008) appears and develops as a single center, but actually has all of the morphological characteristics of the primitive gekkotan postorbital (Conrad and Norell, 2006) (Fig. 2) but lying in a more dorsomedial position, bounding the frontoparietal suture.…”

Section: Discussionmentioning

confidence: 99%

“…They identified this putatively combined element as the postorbitofrontal, adopting the most conservative interpretation because it does not necessitate the loss of either element. Their interpretation was guided primarily by the observation that basal members of the Gekkonomorpha posses both elements (Conrad and Norell, 2006), and additionally on statements such as that of Siebenrock (1895) that the postorbital is absorbed by the postfrontal. Empirical evidence for such fusion is, however, rather slender.…”

mentioning

confidence: 99%

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Development of the Dorsal Circumorbital Bones in the Leopard Gecko (Eublepharis macularius) and Its Bearing on the Homology of These Elements in the Gekkota

Wise

Russell

2010

Five nominal elements comprise the circumorbital series of bones in gekkotans: prefrontal, postfrontal, postorbital, jugal, and lacrimal. Determination of the homology of two of these, the postfrontal and postorbital, has been particularly problematic. Two conflicting hypothesis exist relating to these: either the postorbital is lost and the postfrontal remains or they fuse during development to form a combined element, the postorbitofrontal. Such a combined element apparently occurs in at least some members of all lizard clades. There is, however, no direct developmental evidence that supports either theory. To overcome that, we investigate the sequence and pattern of ossification in the circumorbital region in a developmental series of the Leopard gecko. We posit that both the postfrontal and postorbital appear during development. Contrary to previous predictions they neither fuses to each other, nor do either degenerate. Instead, the postfrontal shifts anteriorly and fuses with the frontal to become indistinguishable from it by the time of hatching, and the postorbital persists as a robust independent element bounding the frontoparietal suture. These observations accord, in part, with both hypotheses of homology of these elements and result in the recognition of a new pattern, placing in doubt the existence of the composite postorbitofrontal. The phylogenetic implications of these findings may prove to be far reaching if similar and conserved patterns of development are encountered in other clades.

On the Fossil Record of the Gekkota

Daza

Bauer

Snively

2014

Gekkota is often interpreted as sister to all remaining squamates, exclusive of dibamids, or as sister to Autarchoglossa. It is the only diverse lineage of primarily nocturnal lizards and includes some of the smallest amniotes. The skeleton of geckos has often been interpreted as paedomorphic and/or “primitive” but these lizards also display a wide range of structural specializations of the postcranium, including modifications associated with both scansorial locomotion and limb reduction. Although the concept of “Gekkota” has been variously applied by different authors, we here apply a rigorous apomorphy based definition, recent advances in gekkotan morphology and phylogenetics, and diverse comparative material to provide a comprehensive assessment of 28 known pre‐Quaternary geckos, updating the last such review, published three decades ago. Fossils evaluated include both sedimentary fossils and amber‐embedded specimens. Known Cretaceous geckos are exclusively Asian and exhibit character combinations not seen in any living forms. Cenozoic gekkotans derive from sites around the world, although Europe is especially well represented. Paleogene geckos are largely known from disarticulated remains and show similarities to Sphaerodactylidae and Diplodactylidae, although resemblances may be plesiomorphic in some cases. Many Neogene gekkotans are referable to living families or even genera, but their geographic occurrences are often extralimital to those of modern groups, as is consistent with paleoclimatic conditions. The phylogenetic placement of fossil gekkotans has important repercusions for timetree calibration, but at present only a small number of fossils can be confidently assigned to even family level groupings, limiting their utility in this regard. Anat Rec, 297:433–462, 2014. © 2014 Wiley Periodicals, Inc.