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An amphisbaenian skull from the European miocene and the evolution of Mediterranean worm lizards.

Bolet A, Delfino M, Fortuny J, Almécija S, Robles JM, Alba DM - PLoS ONE (2014)

Bottom Line: This specimen, from the Middle Miocene of Abocador de Can Mata (11.6 Ma, MN7+8) in the Vallès-Penedès Basin (Catalonia, NE Iberian Peninsula), unambiguously asserts the presence of Blanus in the Miocene of Europe.This reinforces the referral to this genus of the previously-known, much more incomplete and poorly-diagnostic material from other localities of the European Neogene.This supports previous paleobiogeographic scenarios for blanid evolution and provides a significant minimum divergence time for calibrating molecular analyses of blanid phylogeny.

View Article: PubMed Central - PubMed

Affiliation: Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Barcelona, Spain.

ABSTRACT
The evolution of blanid amphisbaenians (Mediterranean worm lizards) is mainly inferred based on molecular studies, despite their fossils are common in Cenozoic European localities. This is because the fossil record exclusively consists in isolated elements of limited taxonomic value. We describe the only known fossil amphisbaenian skull from Europe - attributed to Blanus mendezi sp. nov. (Amphisbaenia, Blanidae) - which represents the most informative fossil blanid material ever described. This specimen, from the Middle Miocene of Abocador de Can Mata (11.6 Ma, MN7+8) in the Vallès-Penedès Basin (Catalonia, NE Iberian Peninsula), unambiguously asserts the presence of Blanus in the Miocene of Europe. This reinforces the referral to this genus of the previously-known, much more incomplete and poorly-diagnostic material from other localities of the European Neogene. Our analysis - integrating the available molecular, paleontological and biogeographic data - suggests that the new species postdates the divergence between the two main (Eastern and Western Mediterranean) extant clades of blanids, and probably precedes the split between the Iberian and North-Western African subclades. This supports previous paleobiogeographic scenarios for blanid evolution and provides a significant minimum divergence time for calibrating molecular analyses of blanid phylogeny.

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Related in: MedlinePlus

Selected material of extant Blanus cinereus (MDHC 156) and Blanus strauchi (MDHC 286) for comparison purposes.(A–H) Cervical vertebrae of B. cinereus (A–D) and B. strauchi (E–H), in left lateral view. (I–J) Dorsal vertebrae of B. cinereus (I) and B. strauchi (J), in dorsal view. (K–N) Left maxillae of B. cinereus (K) and B. strauchi (M), in lingual view; right maxillae of B. cinereus (L) and B. strauchi (N), in labial view. (O–P) Left dentary of B. strauchi, in lingual (O) and labial (P) views. (Q), Articulated parietal and frontals of B. strauchi, in dorsal view. (R–S) Frontals of B. strauchi; right frontal in dorsal view (R), and left frontal in ventral view (S). (T–U) Premaxillae of B. cinereus (T) and B. strauchi (U), in left lateral view. (V) Left quadrate, in lateral view. Scale bar equals 2 mm.
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pone-0098082-g005: Selected material of extant Blanus cinereus (MDHC 156) and Blanus strauchi (MDHC 286) for comparison purposes.(A–H) Cervical vertebrae of B. cinereus (A–D) and B. strauchi (E–H), in left lateral view. (I–J) Dorsal vertebrae of B. cinereus (I) and B. strauchi (J), in dorsal view. (K–N) Left maxillae of B. cinereus (K) and B. strauchi (M), in lingual view; right maxillae of B. cinereus (L) and B. strauchi (N), in labial view. (O–P) Left dentary of B. strauchi, in lingual (O) and labial (P) views. (Q), Articulated parietal and frontals of B. strauchi, in dorsal view. (R–S) Frontals of B. strauchi; right frontal in dorsal view (R), and left frontal in ventral view (S). (T–U) Premaxillae of B. cinereus (T) and B. strauchi (U), in left lateral view. (V) Left quadrate, in lateral view. Scale bar equals 2 mm.

Mentions: IPS60464 bears seven premaxillary (Fig. 3C), five maxillary (Fig. 3D) and eight dentary (Fig. 2 and 4A) pleurodont teeth; the first dentary tooth is smaller than the third one, as in other species of Blanus. The teeth are robust (comparable to B. cinereus, B. antiquus and P. tobieni), contrasting with the much more slender dentition of B. gracilis and B. strauchi (Figs. 5 and 6). The premaxilla bears a very long, apically truncated nasal process (Fig. 3A–C), and the snout is only weakly protruding – similar to that of B. cinereus (Fig. 5T) and fossil forms, but contrasting with the more clearly protruding snout with a ventrally-directed premaxilla of B. strauchi (Fig. 5U). The frontals are relatively long (3.1 mm) and roughly rectangular (Fig. 3R–U), with an almost straight suture between them and a strong interdigitation with the parietal (Fig. 2A). The nasals are short relative to the frontals (Fig. 2A). The maxilla has a medially directed rostral process (Figs. 2B and 3F) and an unusually long and pointed orbital process (figure 3D–G). The prefrontal is present and well developed (Figs. 2A and B, and 3V and W), precluding the contact between the maxilla and frontal except in the anterior lateral margin of the latter (Fig. 2A). Elements of the palate (Fig. 3J–Q) are observable, but at present provide little taxonomic information because their morphology in other taxa is barely known. The parietal (Figs. 2A–C and 3X–Z) is by far the largest bone of the skull; although its limits with the otic-occipital complex (Figs. 2B and 3Y and Z) are clear in some regions, we were unable to completely separate them due to partial fusion or, more likely, limitations in the resolution of the CT-scan. The cranial proportions of IPS60464 roughly fit those reported for extant species – only described for B. cinereus and B. strauchi[46], [47], [48], [49] – except for the relatively shorter preorbital region displayed by the fossil specimen (ca. 25%, in front of 30% in the two morphotypes of B. cinereus, see Fig. S2). The quadrate (Figs. 2, and 3AA and AB) is rather robust. The cranium of the new species (length, 11.3 mm; width, 5.8 mm) is larger (ca. 25% longer) than that of all extant blanids [48]. The comparison of the dimensions of isolated tooth-bearing bones also indicate for B. mendezi a slightly larger size than for B. antiquus and P. tobieni, and a much larger size than for B. gracilis (Fig. 6).


An amphisbaenian skull from the European miocene and the evolution of Mediterranean worm lizards.

Bolet A, Delfino M, Fortuny J, Almécija S, Robles JM, Alba DM - PLoS ONE (2014)

Selected material of extant Blanus cinereus (MDHC 156) and Blanus strauchi (MDHC 286) for comparison purposes.(A–H) Cervical vertebrae of B. cinereus (A–D) and B. strauchi (E–H), in left lateral view. (I–J) Dorsal vertebrae of B. cinereus (I) and B. strauchi (J), in dorsal view. (K–N) Left maxillae of B. cinereus (K) and B. strauchi (M), in lingual view; right maxillae of B. cinereus (L) and B. strauchi (N), in labial view. (O–P) Left dentary of B. strauchi, in lingual (O) and labial (P) views. (Q), Articulated parietal and frontals of B. strauchi, in dorsal view. (R–S) Frontals of B. strauchi; right frontal in dorsal view (R), and left frontal in ventral view (S). (T–U) Premaxillae of B. cinereus (T) and B. strauchi (U), in left lateral view. (V) Left quadrate, in lateral view. Scale bar equals 2 mm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4045672&req=5

pone-0098082-g005: Selected material of extant Blanus cinereus (MDHC 156) and Blanus strauchi (MDHC 286) for comparison purposes.(A–H) Cervical vertebrae of B. cinereus (A–D) and B. strauchi (E–H), in left lateral view. (I–J) Dorsal vertebrae of B. cinereus (I) and B. strauchi (J), in dorsal view. (K–N) Left maxillae of B. cinereus (K) and B. strauchi (M), in lingual view; right maxillae of B. cinereus (L) and B. strauchi (N), in labial view. (O–P) Left dentary of B. strauchi, in lingual (O) and labial (P) views. (Q), Articulated parietal and frontals of B. strauchi, in dorsal view. (R–S) Frontals of B. strauchi; right frontal in dorsal view (R), and left frontal in ventral view (S). (T–U) Premaxillae of B. cinereus (T) and B. strauchi (U), in left lateral view. (V) Left quadrate, in lateral view. Scale bar equals 2 mm.
Mentions: IPS60464 bears seven premaxillary (Fig. 3C), five maxillary (Fig. 3D) and eight dentary (Fig. 2 and 4A) pleurodont teeth; the first dentary tooth is smaller than the third one, as in other species of Blanus. The teeth are robust (comparable to B. cinereus, B. antiquus and P. tobieni), contrasting with the much more slender dentition of B. gracilis and B. strauchi (Figs. 5 and 6). The premaxilla bears a very long, apically truncated nasal process (Fig. 3A–C), and the snout is only weakly protruding – similar to that of B. cinereus (Fig. 5T) and fossil forms, but contrasting with the more clearly protruding snout with a ventrally-directed premaxilla of B. strauchi (Fig. 5U). The frontals are relatively long (3.1 mm) and roughly rectangular (Fig. 3R–U), with an almost straight suture between them and a strong interdigitation with the parietal (Fig. 2A). The nasals are short relative to the frontals (Fig. 2A). The maxilla has a medially directed rostral process (Figs. 2B and 3F) and an unusually long and pointed orbital process (figure 3D–G). The prefrontal is present and well developed (Figs. 2A and B, and 3V and W), precluding the contact between the maxilla and frontal except in the anterior lateral margin of the latter (Fig. 2A). Elements of the palate (Fig. 3J–Q) are observable, but at present provide little taxonomic information because their morphology in other taxa is barely known. The parietal (Figs. 2A–C and 3X–Z) is by far the largest bone of the skull; although its limits with the otic-occipital complex (Figs. 2B and 3Y and Z) are clear in some regions, we were unable to completely separate them due to partial fusion or, more likely, limitations in the resolution of the CT-scan. The cranial proportions of IPS60464 roughly fit those reported for extant species – only described for B. cinereus and B. strauchi[46], [47], [48], [49] – except for the relatively shorter preorbital region displayed by the fossil specimen (ca. 25%, in front of 30% in the two morphotypes of B. cinereus, see Fig. S2). The quadrate (Figs. 2, and 3AA and AB) is rather robust. The cranium of the new species (length, 11.3 mm; width, 5.8 mm) is larger (ca. 25% longer) than that of all extant blanids [48]. The comparison of the dimensions of isolated tooth-bearing bones also indicate for B. mendezi a slightly larger size than for B. antiquus and P. tobieni, and a much larger size than for B. gracilis (Fig. 6).

Bottom Line: This specimen, from the Middle Miocene of Abocador de Can Mata (11.6 Ma, MN7+8) in the Vallès-Penedès Basin (Catalonia, NE Iberian Peninsula), unambiguously asserts the presence of Blanus in the Miocene of Europe.This reinforces the referral to this genus of the previously-known, much more incomplete and poorly-diagnostic material from other localities of the European Neogene.This supports previous paleobiogeographic scenarios for blanid evolution and provides a significant minimum divergence time for calibrating molecular analyses of blanid phylogeny.

View Article: PubMed Central - PubMed

Affiliation: Institut Català de Paleontologia Miquel Crusafont, Universitat Autònoma de Barcelona, Cerdanyola del Vallès, Barcelona, Spain.

ABSTRACT
The evolution of blanid amphisbaenians (Mediterranean worm lizards) is mainly inferred based on molecular studies, despite their fossils are common in Cenozoic European localities. This is because the fossil record exclusively consists in isolated elements of limited taxonomic value. We describe the only known fossil amphisbaenian skull from Europe - attributed to Blanus mendezi sp. nov. (Amphisbaenia, Blanidae) - which represents the most informative fossil blanid material ever described. This specimen, from the Middle Miocene of Abocador de Can Mata (11.6 Ma, MN7+8) in the Vallès-Penedès Basin (Catalonia, NE Iberian Peninsula), unambiguously asserts the presence of Blanus in the Miocene of Europe. This reinforces the referral to this genus of the previously-known, much more incomplete and poorly-diagnostic material from other localities of the European Neogene. Our analysis - integrating the available molecular, paleontological and biogeographic data - suggests that the new species postdates the divergence between the two main (Eastern and Western Mediterranean) extant clades of blanids, and probably precedes the split between the Iberian and North-Western African subclades. This supports previous paleobiogeographic scenarios for blanid evolution and provides a significant minimum divergence time for calibrating molecular analyses of blanid phylogeny.

Show MeSH
Related in: MedlinePlus