Figure 1.
Volume rendering of the µCT data of the holotype of Eocaecilia micropodia (MNA V8066).
A, dorsal view. B, ventral view.
Figure 2.
The braincase and middle ear ossicle of Eocaecilia micropodia as revealed by µCT.
A–C, three-dimensional digitally segmented braincase of the holotype (MNA V8066) in dorsal, left lateral and ventral views, respectively, with the sphenethmoid (orange) and the os basale (blue). D–E, surface renderings of an isolated braincase referred to E. micropodia (MNA V8063) in dorsal and ventral views, respectively. The alternative hypotheses of foramen identity are depicted in blue and green. F–H, three-dimensional digitally segmented middle ear ossicle of E. micropodia (MNA V8066) in dorsal, left lateral, and ventral views respectively. This element is termed the stapes-quadrate by Jenkins et al. [14] because of the hypothesized fusion of these two elements. Abbreviations: ant., antotic region; ant.w., antotic wall; a.l.p., anterolateral process; d.s., dorsal surface of the otic capsule; f.c.a., foramen for the carotid artery; f.d.v., foramen for a dorsal vein; f.j., jugular foramen; f.s., stapedial foramen; f.v., fenestra vestibuli; f.1, foramen 1 (see text for interpretation); f.2, foramen 2 (see text for interpretation), f.Vmx,md, foramen for the maxillary plus mandibular trunk of the trigeminal nerve; f.Vop, foramen for the ophthalmic branch of the trigeminal nerve; n.s., nasal septum; oto., otic-occipital complex; o.ca., otic capsule.
Figure 3.
Identification of paired dorsal and ventral foramina, serving the likely transmission of the paired trunks of the olfactory nerve, similar to the condition seen in extant caecilians.
A, µCT image of a transverse section through the level of the anterior sphenethmoid in E. micropodia (MNA V8066), showing the location of dorsal and ventral foramina in the anterior wall of the sphenethmoid. B, posterior view of the three-dimensionally segmented sphenethmoid of E. micropodia, further showing the locations of the anterior foramina interpreted here as those serving the dorsal and ventral trunks of the olfactory nerve. C, posterior view of the three-dimensionally segmented sphenethmoid of the extant caecilian Dermophis mexicanus (UMMZ 219030), showing the location of comparable foramina known to transmit the trunks of the olfactory nerve [14]. Abbreviation: f.ID, foramen for the dorsal branch of the olfactory nerve; f.IV, foramen for the ventral branch of the olfactory nerve.
Figure 4.
The 50% majority-rule consensus tree of the 34 most parsimonious trees obtained in the parsimony analysis (1450 steps).
Numbers above nodes represent bootstrap values greater than 50% (values below 50% not shown). Within the temnospondyl lineage a monophyletic Lissamphibia was obtained. Eocaecilia micropodia was recovered on the stem of extant caecilians (Apoda) and together this clade (Gymnophiona) formed the sister taxon to the clade of Batrachia plus Gerobatrachus. The sister taxon to Lissamphibia in this hypothesis is Doleserpeton.
Table 1.
Ancestral character state reconstructions of the 34 braincase characters from Maddin et al. [28] for the condition at the base of extant caecilians and a comparison with the condition seen in Eocaecilia micropodia.
Figure 5.
Alternative hypotheses for the evolution of the open temporal region in extant lissamphibians.
A, Scenario in which the open condition is homologous for lissamphibians, and Eocaecilia micropodia is a homoplastic reversal to the condition present in Doleserpeton. B, Scenario in which the open condition is a homoplastic convergence between extant caecilians and batrachians plus Gerobatrachus. This hypothesis is favoured here given the occurrence of a similar condition in lysorophian lepospondyls. Illustrations modified from: Amphibamus [51]; Doleserpeton [42]; Eocaecilia [14]; caecilians [52]; Gerobatrachus [18]; frogs [21]; Triadobatrachus [53]; salamanders [21]; Karaurus [54].