Limits...
Reacquisition of the lower temporal bar in sexually dimorphic fossil lizards provides a rare case of convergent evolution.

Simões TR, Funston GF, Vafaeian B, Nydam RL, Doschak MR, Caldwell MW - Sci Rep (2016)

Bottom Line: An analysis of the functional significance of the LTB using proxies indicates that, unlike for T. zhengi, this structure had no apparent functional advantage in P. sternbergi, and it is better explained as the result of structural constraint release.The observed canalization against a LTB in squamates was broken at some point in the evolution of borioteiioids, whereas never re-occuring in other squamate lineages.This case of convergent evolution involves a mix of both adaptationist and structuralist causes, which is unusual for both living and extinct vertebrates.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.

ABSTRACT
Temporal fenestration has long been considered a key character to understand relationships amongst reptiles. In particular, the absence of the lower temporal bar (LTB) is considered one of the defining features of squamates (lizards and snakes). In a re-assessment of the borioteiioid lizard Polyglyphanodon sternbergi (Cretaceous, North America), we detected a heretofore unrecognized ontogenetic series, sexual dimorphism (a rare instance for Mesozoic reptiles), and a complete LTB, a feature only recently recognized for another borioteiioid, Tianyusaurus zhengi (Cretaceous, China). A new phylogenetic analysis (with updates on a quarter of the scorings for P. sternbergi) indicates not only that the LTB was reacquired in squamates, but it happened independently at least twice. An analysis of the functional significance of the LTB using proxies indicates that, unlike for T. zhengi, this structure had no apparent functional advantage in P. sternbergi, and it is better explained as the result of structural constraint release. The observed canalization against a LTB in squamates was broken at some point in the evolution of borioteiioids, whereas never re-occuring in other squamate lineages. This case of convergent evolution involves a mix of both adaptationist and structuralist causes, which is unusual for both living and extinct vertebrates.

No MeSH data available.


Related in: MedlinePlus

Polyglyphanodon sternbergi, from the Late Cretaceous of Utah (USA).(a) CM 9188 in dorsal view (image credits to Amy Henrici); (b–f) anatomy of the skull, reconstructed from all the specimens used in this study (image credits to Arthur Brum); (g–i) ontogeny of the temporal region, illustrating the relative increase in length of the LTB in P. sternbergi, from juvenile (g), NMNH 427672 and (h), NMNH 16586) to adult (i), NMNH 15816); (j) NMNH 16587, representing the sexual morphotype (a,k) CM 9188, sexual morphotype (b). Abbreviations: Art-Pra, articular + prearticular; AdCr, adductor crest of surangular; Ang, angular; AnSFr, anterior surangular foramen; Boc, basioccipital; Bsp, basipterygoid; C, coronoid; D, dentary; Ect, ectopterygoid; F, frontal; HyFr, hypoglossal foramina; J, jugal, JFr; jugular foramen; L, lacrimal; M, maxilla; Me, Meckelian canal; N, nasal; P, parietal; OcR, occipital recess; Oto, otoccipital; Pal, palatine; PM, premaxilla; Po, postorbital; PoF, postfrontal; PoSFr, posterior surangular foramen; PraCr, prearticular crest; PrF; prefrontal; Ptg, pterygoid; Q, quadrate; QFr, quadrate foramen; San, surangular; Smx, septomaxilla; Soc, supraoccipital; Spl, splenial; Sq, squamosal; Sym, dentary symphysis; V, vomer. Scale bars equal to 10 mm (g–k).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4829860&req=5

f1: Polyglyphanodon sternbergi, from the Late Cretaceous of Utah (USA).(a) CM 9188 in dorsal view (image credits to Amy Henrici); (b–f) anatomy of the skull, reconstructed from all the specimens used in this study (image credits to Arthur Brum); (g–i) ontogeny of the temporal region, illustrating the relative increase in length of the LTB in P. sternbergi, from juvenile (g), NMNH 427672 and (h), NMNH 16586) to adult (i), NMNH 15816); (j) NMNH 16587, representing the sexual morphotype (a,k) CM 9188, sexual morphotype (b). Abbreviations: Art-Pra, articular + prearticular; AdCr, adductor crest of surangular; Ang, angular; AnSFr, anterior surangular foramen; Boc, basioccipital; Bsp, basipterygoid; C, coronoid; D, dentary; Ect, ectopterygoid; F, frontal; HyFr, hypoglossal foramina; J, jugal, JFr; jugular foramen; L, lacrimal; M, maxilla; Me, Meckelian canal; N, nasal; P, parietal; OcR, occipital recess; Oto, otoccipital; Pal, palatine; PM, premaxilla; Po, postorbital; PoF, postfrontal; PoSFr, posterior surangular foramen; PraCr, prearticular crest; PrF; prefrontal; Ptg, pterygoid; Q, quadrate; QFr, quadrate foramen; San, surangular; Smx, septomaxilla; Soc, supraoccipital; Spl, splenial; Sq, squamosal; Sym, dentary symphysis; V, vomer. Scale bars equal to 10 mm (g–k).

Mentions: From the examination of almost 30 specimens of Polyglyphanodon sternbergi, including almost complete skeletons, we obtained new information on the morphology of that species, especially regarding the skull (Fig. 1a–f). Individuals of different size classes present variation that is concentrated on the shape of the frontoparietal suture and the length of the posteroventral process of the jugal (Fig. 1g–i). Great variation in the shape of the frontoparietal suture has been reported during the post-embryonic ontogeny of extant lizards2223 and variation on the length of the jugal process has also been reported during the ontogeny of fossil sphenodontian reptiles131424 (see also Table 1 and Supplementary Discussion). To our knowledge, neither have ever been detected before in fossil lizards. Furthermore, specimens of similar sizes present variations in skull shape. Overall, some individuals possess relatively taller skulls (morphotype A—Fig. j) while others have more depressed skulls (morphotype B—Fig. 1k). Such variation happens across individuals of all size classes (Table 1) and thus cannot be related to ontogeny. Sexual dimorphism in lizards commonly affects body proportions, with male lizards tending to have proportionally bigger heads—either taller, longer, or wider, or a combination of these252627—for male-male combat or holding females during copulation (see also Supplementary Discussion). Therefore, the variation in relative skull height between both morphotypes is suggestive of sexual dimorphism, with morphotype A (proportionally taller skulls) being more likely to represent the male morphotype. All Polyglyphanodon individuals come from the same mudstone horizon, in what is considered as the flood basin of a fluvial system (RN, personal observation), being totally or partially articulated. This is indicative that they represent a local population that was caught in a flood, or another similarly catastrophic event, and thus finding individuals of different age and sex classes should be expected.


Reacquisition of the lower temporal bar in sexually dimorphic fossil lizards provides a rare case of convergent evolution.

Simões TR, Funston GF, Vafaeian B, Nydam RL, Doschak MR, Caldwell MW - Sci Rep (2016)

Polyglyphanodon sternbergi, from the Late Cretaceous of Utah (USA).(a) CM 9188 in dorsal view (image credits to Amy Henrici); (b–f) anatomy of the skull, reconstructed from all the specimens used in this study (image credits to Arthur Brum); (g–i) ontogeny of the temporal region, illustrating the relative increase in length of the LTB in P. sternbergi, from juvenile (g), NMNH 427672 and (h), NMNH 16586) to adult (i), NMNH 15816); (j) NMNH 16587, representing the sexual morphotype (a,k) CM 9188, sexual morphotype (b). Abbreviations: Art-Pra, articular + prearticular; AdCr, adductor crest of surangular; Ang, angular; AnSFr, anterior surangular foramen; Boc, basioccipital; Bsp, basipterygoid; C, coronoid; D, dentary; Ect, ectopterygoid; F, frontal; HyFr, hypoglossal foramina; J, jugal, JFr; jugular foramen; L, lacrimal; M, maxilla; Me, Meckelian canal; N, nasal; P, parietal; OcR, occipital recess; Oto, otoccipital; Pal, palatine; PM, premaxilla; Po, postorbital; PoF, postfrontal; PoSFr, posterior surangular foramen; PraCr, prearticular crest; PrF; prefrontal; Ptg, pterygoid; Q, quadrate; QFr, quadrate foramen; San, surangular; Smx, septomaxilla; Soc, supraoccipital; Spl, splenial; Sq, squamosal; Sym, dentary symphysis; V, vomer. Scale bars equal to 10 mm (g–k).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4829860&req=5

f1: Polyglyphanodon sternbergi, from the Late Cretaceous of Utah (USA).(a) CM 9188 in dorsal view (image credits to Amy Henrici); (b–f) anatomy of the skull, reconstructed from all the specimens used in this study (image credits to Arthur Brum); (g–i) ontogeny of the temporal region, illustrating the relative increase in length of the LTB in P. sternbergi, from juvenile (g), NMNH 427672 and (h), NMNH 16586) to adult (i), NMNH 15816); (j) NMNH 16587, representing the sexual morphotype (a,k) CM 9188, sexual morphotype (b). Abbreviations: Art-Pra, articular + prearticular; AdCr, adductor crest of surangular; Ang, angular; AnSFr, anterior surangular foramen; Boc, basioccipital; Bsp, basipterygoid; C, coronoid; D, dentary; Ect, ectopterygoid; F, frontal; HyFr, hypoglossal foramina; J, jugal, JFr; jugular foramen; L, lacrimal; M, maxilla; Me, Meckelian canal; N, nasal; P, parietal; OcR, occipital recess; Oto, otoccipital; Pal, palatine; PM, premaxilla; Po, postorbital; PoF, postfrontal; PoSFr, posterior surangular foramen; PraCr, prearticular crest; PrF; prefrontal; Ptg, pterygoid; Q, quadrate; QFr, quadrate foramen; San, surangular; Smx, septomaxilla; Soc, supraoccipital; Spl, splenial; Sq, squamosal; Sym, dentary symphysis; V, vomer. Scale bars equal to 10 mm (g–k).
Mentions: From the examination of almost 30 specimens of Polyglyphanodon sternbergi, including almost complete skeletons, we obtained new information on the morphology of that species, especially regarding the skull (Fig. 1a–f). Individuals of different size classes present variation that is concentrated on the shape of the frontoparietal suture and the length of the posteroventral process of the jugal (Fig. 1g–i). Great variation in the shape of the frontoparietal suture has been reported during the post-embryonic ontogeny of extant lizards2223 and variation on the length of the jugal process has also been reported during the ontogeny of fossil sphenodontian reptiles131424 (see also Table 1 and Supplementary Discussion). To our knowledge, neither have ever been detected before in fossil lizards. Furthermore, specimens of similar sizes present variations in skull shape. Overall, some individuals possess relatively taller skulls (morphotype A—Fig. j) while others have more depressed skulls (morphotype B—Fig. 1k). Such variation happens across individuals of all size classes (Table 1) and thus cannot be related to ontogeny. Sexual dimorphism in lizards commonly affects body proportions, with male lizards tending to have proportionally bigger heads—either taller, longer, or wider, or a combination of these252627—for male-male combat or holding females during copulation (see also Supplementary Discussion). Therefore, the variation in relative skull height between both morphotypes is suggestive of sexual dimorphism, with morphotype A (proportionally taller skulls) being more likely to represent the male morphotype. All Polyglyphanodon individuals come from the same mudstone horizon, in what is considered as the flood basin of a fluvial system (RN, personal observation), being totally or partially articulated. This is indicative that they represent a local population that was caught in a flood, or another similarly catastrophic event, and thus finding individuals of different age and sex classes should be expected.

Bottom Line: An analysis of the functional significance of the LTB using proxies indicates that, unlike for T. zhengi, this structure had no apparent functional advantage in P. sternbergi, and it is better explained as the result of structural constraint release.The observed canalization against a LTB in squamates was broken at some point in the evolution of borioteiioids, whereas never re-occuring in other squamate lineages.This case of convergent evolution involves a mix of both adaptationist and structuralist causes, which is unusual for both living and extinct vertebrates.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.

ABSTRACT
Temporal fenestration has long been considered a key character to understand relationships amongst reptiles. In particular, the absence of the lower temporal bar (LTB) is considered one of the defining features of squamates (lizards and snakes). In a re-assessment of the borioteiioid lizard Polyglyphanodon sternbergi (Cretaceous, North America), we detected a heretofore unrecognized ontogenetic series, sexual dimorphism (a rare instance for Mesozoic reptiles), and a complete LTB, a feature only recently recognized for another borioteiioid, Tianyusaurus zhengi (Cretaceous, China). A new phylogenetic analysis (with updates on a quarter of the scorings for P. sternbergi) indicates not only that the LTB was reacquired in squamates, but it happened independently at least twice. An analysis of the functional significance of the LTB using proxies indicates that, unlike for T. zhengi, this structure had no apparent functional advantage in P. sternbergi, and it is better explained as the result of structural constraint release. The observed canalization against a LTB in squamates was broken at some point in the evolution of borioteiioids, whereas never re-occuring in other squamate lineages. This case of convergent evolution involves a mix of both adaptationist and structuralist causes, which is unusual for both living and extinct vertebrates.

No MeSH data available.


Related in: MedlinePlus