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. 2014 Oct 7;9(10):e109717.
doi: 10.1371/journal.pone.0109717. eCollection 2014.

Redescription and phylogenetic analysis of the mandible of an enigmatic Pennsylvanian (Late Carboniferous) tetrapod from Nova Scotia, and the lability of Meckelian jaw ossification

Roland B Sookias  1 , Christine Böhmer  2 , Jennifer A Clack  3
Affiliations

Redescription and phylogenetic analysis of the mandible of an enigmatic Pennsylvanian (Late Carboniferous) tetrapod from Nova Scotia, and the lability of Meckelian jaw ossification

Roland B Sookias et al. PLoS One. .

Abstract

The lower jaw of an unidentified Pennsylvanian (Late Carboniferous) tetrapod from Nova Scotia--the "Parrsboro jaw"--is redescribed in the light of recent tetrapod discoveries and work on evolution of tetrapod mandibular morphology and placed for the first time in a numerical cladistics analysis. All phylogenetic analyses place the jaw in a crownward polytomy of baphetids, temnospondyls, and embolomeres. Several features resemble baphetids and temnospondyls including dermal ornamentation, absence of coronoid teeth, and presence of coronoid shagreen. Dentary dentition is most similar to Baphetes. An adsymphysial toothplate may not preclude temnospondyl affinity. An apparent large exomeckelian fenestra, with the dorsal foraminal margins formed by an unossified element, echoes the morphology of the stem tetrapod Sigournea and is unusually primitive given the other features of the jaw. The jaw may thus provide an example of an intermediate stage in Meckelian element evolution.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Anterior portion of the Parrsboro jaw, NSM 987GH65.1, in medial view.
A, photograph of anterior part of jaw natural mould peel loaned to JAC in medial view; B, interpretative line drawing of anterior part of jaw in medial view; C, alternative interpretative line drawing of anterior jaw in medial view, with denticulated element below anterior coronoid interpreted as splenial rather than prearticular. adsym, adsymphyseal toothplate; adsym fang, adsymphyseal fang; ant cor, anterior coronoid; dent, dentary; dent fang, dentary fang; meck for, Meckelian foramina; meck, unossified Meckelian element; mid cor, middle coronoid; ?mid-post cor s., possible suture between middle and posterior coronoids; pospl, postsplenial; ?post cor, possible posterior coronoid; preart, prearticular; spl, splenial. Hollow circular stippling indicates denticulation.
Figure 2
Figure 2. Anterior portion of the Parrsboro jaw, NSM 987GH65.1, in dorsal view.
A, photograph of peel of anterior of natural mould of jaw loaned to JAC in dorsal view; B, interpretative line drawing of anterior of jaw in dorsal view; C, alternative interpretative line drawing of anterior jaw in dorsal view, with denticulated element below anterior coronoid interpreted as splenial rather than prearticular. adsym, adsymphyseal toothplate; adsym fang, adsymphyseal fang; ant cor, anterior coronoid; dent, dentary; dent fang, dentary fang; mid cor, middle coronoid; ?mid-post cor s., possible suture between middle and posterior coronoids; orn, ornamentation; ?post cor, possible posterior coronoid; preart, prearticular; spl, splenial. Hollow circular stippling indicates denticulation.
Figure 3
Figure 3. Interpretive line drawings of the anterior of the Parrsboro jaw, NSM 987GH65.1, modified from fig. 1 of Godfrey and Holmes (1989).
A, dorsal view; B, medial view. adsym, adsymphyseal tooth plate; ang, angular; cor, coronoid; dent, dentary; pospl, postsplenial; preart, prearticular.
Figure 4
Figure 4. Close up of prearticular of the Parrsboro jaw, NSM 987GH65.1.
The dorsal section of prearticular can be seen to have been displaced so that its medial surface faces ventromedially. mid cor, middle coronoid; ?post cor, possible posterior coronoid; preart, prearticular.
Figure 5
Figure 5. Phylogenetic position of the Parrsboro jaw, NSM 987GH65.1.
The matrix used was based on the matrix of Clack et al. (2012). The analyses show correspond to Analysis 1.1 in Table 1, with the denticulated element below the anterior coronoid interpreted as a continuation of the prearticular (Figs. 1B, 2B), all characters unordered and no taxa excluded. A, strict consensus tree; B, 50 percent majority rule consensus tree. Numbers next to nodes are standard bootstrap values.
See this image and copyright information in PMC

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