Editorial Type:
Article Category: Research Article
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Online Publication Date: 27 Sept 2021

Diversity and Systematics of Limbless Skinks (Anomalopus) from Eastern Australia and the Skeletal Changes that Accompany the Substrate Swimming Body Form

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Page Range: 361 – 384
DOI: 10.1670/20-137
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ABSTRACT

Limb-reduced and limbless scincid lizards pose problems in untangling their relationships because of a strong tendency toward convergent evolution in which functional characters mask phylogenetic history. Their often small size makes cranial characters difficult to study, and collections of such species are often small and patchy because of their cryptic behavior. One such genus, Anomalopus (Sphenomorphinae), currently includes seven species of reduce-limbed and limbless skinks that occur in tropical and subtropical habitats in eastern Australia. The discovery of previously unreported populations of limbless skinks assignable to Anomalopus has prompted our revision of the morphology and systematics of this genus. We report new DNA sequence data and new morphological data by using X-ray micro-computed tomography scanning that corroborate published molecular data on sphenomorphine phylogeny, leading us to propose a new generic arrangement that recognizes the species of Anomalopus as belonging to three genera. The newly discovered populations represent two new species currently known from only three small and disjunct areas. We review the osteology of the three genera of the former Anomalopus, finding new characters and variable patterns of interspecific and interclade variation. The same morphological characters are modified in every limb-reduced sphenomorphine clade, but to differing degrees and in different combinations in each.

Copyright: Copyright 2021 Society for the Study of Amphibians and Reptiles 2021
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Fig. 1.
Fig. 1.

Phylogenetic relationships of the species formerly assigned to Anomalopus, based on DNA sequence data. The best maximum likelihood tree (RAxML) is presented with clade support indicated; bootstrap values of ≥70 are below the branch and Bayesian posterior probability values of ≥0.95 representing a topologically identical maximum clade credibility (MCC) tree are above the branch. Scale represents average number of substitutions per site.

Fig. 2.
Fig. 2.

Distribution across the Australian Sphenomorphinae of changes in 50 morphological character states that differentiate Anomalopus, Praeteropus, and Sepsiscus from nonsubstrate-swimming sphenomorphines. Character state changes are mapped onto the maximum likelihood tree (RAxML) by using DELTRAN optimizations with unambiguous character changes indicated by black squares. All characters were left as nonadditive. Numbers above the squares refer to the mapped character, and numbers below the squares indicate the character states (see Appendix 1 and Table 2).

Fig. 3.
Fig. 3.

External ear variation. Micro-CT scan images of the osteodermal covering of the head and neck in lateral or posterolateral view, showing the weakly ossified scale patches associated with the position of the stapes. (A) Anomalopus mackayi QM J76802 and (B) A. swansoni SAMA R33732, with moderate-sized patches; (C) Sepsiscus pluto QM J54083 with a deep, dorsoventrally oriented trough of mostly unossified scales; (D) Praeteropus brevicollis QM J91556, showing a small patch with only two or three weakly ossified scales. Scale bar = 5 mm.

Fig. 4.
Fig. 4.

Dorsal view of head scalation redrawn from Greer and Cogger (1985). (A) Anomalopus mackayi, (B) A. swansoni, (C) Sepsiscus pluto, and (D) Praeteropus gowi. Light-gray shading, supraoculars; dark-gray shading, supraciliaries; F, frontal; FN, frontonasal, FP, frontoparietal; IP, interparietal; N, nasal; Nu, transversely enlarged nuchal; P, parietal; PrF, prefrontal; R, rostral; SO, supraoculars. Scale bar = 5 mm.

Fig. 5.
Fig. 5.

Left lateral and ventral views of orbital regions of the skulls of five species currently assigned to Anomalopus, with palatal, jaw, braincase, and temporal arch elements digitally removed, showing modifications to the proportions of the frontal and prefrontals and modifications of the orbitosphenoids and replacement of interorbital cartilages by the frontal and/or prefrontals. (A) Anomalopus verreauxii SAMA R55586; (B) A. swansoni SAMA R33732; (C) Sepsiscus pluto QM J54040; (D) Praeteropus brevicollis QM J74799; (E) P. gowi SAMA R55816. Bones: Epi, epipterygoids; F, frontal; J, jugals; OC, orbital cartilages (calcified portions of interorbital septum and taenia medialis); Os, orbitosphenoids; Par, parietal; Prf, prefrontals. Scale bar = 5 mm.

Fig. 6.
Fig. 6.

(A) Braincase and stapes of a representative pentadactyle Australian sphenomorphine, Concinnia martini SAMA R55602, showing position and orientation of the stapes. Scale bar = 5 mm. (B–G) Proportions and orientation of the left stapes in lateral and ventral views. The ventral views show the angle of the shaft of the stapes with respect to the long axis of the body. Scale bars = 0.5 mm. (B) Glaphyromorphus nigricaudis (tympanic ear) SAMA R55840, (C) Anomalopus mackayi QM J76802, (D) A. swansoni SAMA R33732, (E) Sepsiscus pluto QM J54040, (F) Praeteropus brevicollis QM J74799, (G) P. gowi SAMA R55816.

Fig. 7.
Fig. 7.

Permutations of two characters of the axial skeleton. (A) Anomalopus swansoni, SAMA R33731; and (B) Praeteropus brevicollis, QM J74799. Arrows indicate the separate or fused first and second cervical intercentra and the first vertebra for which the rib articulates with a sternal rib (circled), resulting in eight (A) or seven (B) cervical vertebrae. Scale bar = 5 mm.

Fig. 8.
Fig. 8.

Pectoral girdles and sternal anatomy in ventral view. (A) A. mackayi QM J76802; (B) A. swansoni AMS R122972; (C) Sepsiscus pluto QM J54213; (D) Praeteropus brevicollis QM J74799; (E) P. gowi QM J91774. Scale bar = 5 mm.

Fig. 9.
Fig. 9.

Pelvic region showing sacral vertebrae and pelvic rudiments, in left lateral view. (A) Anomalopus leuckartii SAMA R33564; (B) A. mackayi, QM J87168; (C) A. swansoni , AMS R122972; (D) Sepsiscus pluto, QM J54213; (E) Praeteropus brevicollis, QM J91556; (F) P. gowi, SAMA R55816. Sacral vertebrae and ribs fused in (A) and (D). Arrows indicate individual variations, as follows: in (B), second caudal with an atypical complete hemal arch that is fused ventrally to the hemal arch on the third caudal; in (C), an asymmetric first sacral vertebra (left rib is moveable, right rib fused) and a minute limb remnant. Scale bar = 5 mm.

Fig. 10.
Fig. 10.

Praeteropus auxilliger, holotype female QM J96697, in life, and cephalic scalation in (A) lateral and (B) dorsal views. Labeling as in Fig. 4. Additional abbreviations: IL, infralabials; IP, interparietal; L, loreal; M, mental; PM, postmental; SL, supralabials; 1T, primary temporal; U2T, upper secondary temporal. Scale bar = 5 mm. Photo: P. Horner.

Fig. 11.
Fig. 11.

Cranial features of new species of Praeteropus. (A–D) Orbital regions of the skulls in left lateral and ventral views; (E–F) left stapes in lateral and ventral views; (G and H) transverse section through middle ear showing the relationship of the stapes, ossicle, and quadrate. Left column., P. auxilliger (QM J96698); right column, P. monachus (QM J62995). Scale bars (A–D) = 5 mm; (E–H) = 0.5 mm.

Fig. 12.
Fig. 12.

Postcranial skeletal features of new species of Praeteropus. Pectoral girdles and sternal elements: (A) P. auxilliger QM J96698, (B) P. monachus QM J62995. Sacral region and pelvic remnants: (C) P. auxilliger QM J96697, (D) P. monachus QM J90961. Scale bars = 5 mm.

Fig. 13.
Fig. 13.

Map of central eastern Queensland, Australia, showing the collecting localities for the two new species of Praeteropus.

Fig. 14.
Fig. 14.

Praeteropus monachus, holotype QM J90961, preserved specimen, and cephalic scalation in (A) lateral and (B) dorsal views. Labeling as in Figs. 4 and 10. Scale bar = 5 mm. Photo: A. Amey.

Contributor Notes

5 Corresponding author. E-mail: mark.hutchinson@samuseum.sa.gov.au
Accepted: 25 Apr 2021
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