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Figure 3 | BMC Evolutionary Biology

Figure 3

From: Identification of the notothenioid sister lineage illuminates the biogeographic history of an Antarctic adaptive radiation

Figure 3

Pectoral girdle morphology in Percophis brasiliensis and five species of Notothenioidea. These are left lateral views of alizarin-stained girdles of (A) Percophis brasiliensis (SL = 115 mm, UW 21233, the specimen illustrated in [31]); (B) Bovichtus variegatus (SL = 130 mm); (C) Cottoperca trigloides (SL = 217 mm); (D) Pseudaphritis urvillii (SL = 180 mm); (E) Eleginops maclovinus (SL = 260 mm); and (F) Dissostichus mawsoni (SL = 271 mm). Bones are identified in panel C as follows: cl, cleithrum; co, coracoid; r, radials 1–4; sc, scapula; scf, scapular foramen. In Percophis (A) the dorsal-most radial 1 is relatively small and the suture between it and the scapula is evident in both small (A) and large (243 mm SL) specimens [63]. In notothenioids (B–F), radial 1 is present in larvae but, after incorporation into the scapula during development and obliteration of the sutures, it is no longer discrete in adults. The R1 label in (B–D) does not indicate the presence of this radial in adults, but rather the approximate location of the anlage of radial 1. Percophis (A) plus Bovichtus (B), Cottoperca (C) and Pseudaphritis (D) differ from Eleginops (E) and Dissostichus (Cryonotothenioidea) (F) in several respects. In the latter, radials 2–4 are expanded and plate-like (E & F). The maximum anteroposterior length of the pectoral girdle therefore shifts from the posterior margin radial 2 (A–D) to the posterior margin of enlarged radial 3 (E & F). This shift changes the articulation pattern among the bones. In Percophis (A), Bovichtus (B), Cottoperca (C) and Pseudaphritis (D), radial 2 articulates with the scapula whereas in Eleginops and Cryonotothenioidea (E & F), it meets both the scapula and the posterior margin of the coracoid [23]. The apparent gaps between individual bones in Dissostichus mawsoni (F) are filled in life by cartilage. The reduced intensity of the alizarin staining of the coracoid (F) of D. mawsoni is attributable to the spongy composition of the bone covering the cartilaginous core [71]. In this and other paedomorphic lineages, the pectoral girdle contains considerable persistent cartilage as ossification is delayed and, in some species, is never completed.

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