Transformation of the pectoral girdle in the evolutionary origin of frogs: insights from the primitive anuran Discoglossus

Using cleared-and-stained whole mounts and computer-aided three-dimensional reconstructions made from serial histological sections, we studied the development of the pectoral girdle in Discoglossus pictus, an extant member of an ancient frog lineage, represented for example by Eodiscoglossus from the Middle Jurassic to Early Cretaceous periods in Europe. Basic developmental features were compared with those of extinct Temnospondyli, considered to be the most probable anuran ancestors, and with Triadobatrachus, an early Triassic proanuran. In the endochondral girdle, the separate scapula and coracoid of Discoglossus and other anurans (completed by suprascapular and procoracoid cartilages) evolved from the compact scapulocoracoid of temnospondyls by paedomorphosis. In parallel, the dermal ossifications of the girdle were reduced to a small clavicle and cleithrum. The overall reduction in ossification of the anuran pectoral girdle supports the hypothesis of a paedomorphic origin for Anura. The almost simultaneous appearance of dermal and endochondral ossifications may be explained by the accumulation of developmental events during a short, distinct metamorphosis (which did not occur in neotenic temnospondyls living permanently in water). The sternal elements seem to be neomorphs for the most part, which help to cushion the shock of landing in jumping anurans but which also evolved as functional substitutes (insertion area for the pectoralis muscles) of the temnospondyl interclavicle

Is the prefrontal bone in Alpine newt (Triturus alpestris Laurenti, 1768) of dual origin?

According to current knowledge, only the prefrontal bone (os prefrontale) of the circumorbital series is preserved in the family Salamandridae. However, the exact origin and number of ossification centres creating this bone is unknown. Detailed examination of the prefrontal bone during ontogeny of juvenile and adult specimens of the Alpine Newt (Triturus alpestris) indicates its dual origin (prefrontal and lacrimal). We found that the prefrontal bone originates from four ossification centres, i.e. three prefrontal centres and one posterior lacrimal centre. The anterior lacrimal centre participates in the maxillar ossification. The development of these ossification centres occurs very late in ontogeny (at stage 54), and starts after differentiation of the nasal capsules. The total fusion of the lacrimal ossification centre with the prefrontal bone of T. alpestris is distinct from the fully differentiated lacrimal bone attached to the prefrontal bone of the fossil family Branchiosauridae (Temnospondyly). We propose that heterochrony, observed in the recent species, is a delayed development followed by accelerated ossification that resulted in the fusion of the anterior lacrimal centre with the maxilla and the posterior lacrimal centre with the prefrontal bone

Salamandra salamandra (Amphibia: Caudata: Salamandridae) in Portugal: not all black and yellow

The fire salamander complex is quite diverse in the Iberian Peninsula where nine subspecies of Salamandra salamandra are currently recognized. Here, we analysed the geographical distribution of the subspecies S. s. gallaica and S. s. crespoi using partial sequences of the mitochondrial cytochrome b gene of 168 individuals from 12 locations in Portugal. Our results support the existence of a deep lineage divergence between the two subspecies, with non-overlapping geographical distributions except in two contact zones: one in Sesimbra on the western coast, and another in Alcoutim on the southeastern border with Spain. Moreover, S. s. crespoi displays signs of gene flow among the sampled locations whereas S. s. gallaica shows evidence of some restriction to gene flow. Present-day genetic make-up of S. s. gallaica and S. s. crespoi is a result of past historical events, fine-tuned by contemporary Iberian geoclimate. Humid mountain areas were found to harbour increased genetic diversity possibly acting as past refugia during drier interglacial periods. To analyse wider geographical patterns and lineage splitting events within S. salamandra we performed a Bayesian dating analysis completing our data set with previously published sequences. The observed divergences were associated to successive biogeographic scenarios, and to other Iberian species showing similar trends