Redescription and phylogenetic relationships of Megachirella wachtleri Renesto et Posenato, 2003 (Reptilia, Diapsida)

Abstract

Megachirella wachtleri Renesto et Posenato, 2003, a well preserved partial reptile skeleton from the Middle Triassic of the Dolomites (N. Italy), was originally considered a lepidosauromorph, but no phylogenetic analysis was carried out. Consequently, the taxon was overlooked in later phylogenetic analyses of the Diapsida. Here, the holotype and only known specimen of M. wachtleri is redescribed, allowing an investigation of its phylogenetic relationships. Phylogenetic analyses confirm that Megachirella is a lepidosauromorph close to the crown group lepidosaurs (Squamata + Rhynchocephalia). Megachirella enhances our knowledge of the series of morphological modifications that led to the origin of the Lepidosauria, the most diverse clade of extant reptiles.

Kurzfassung

Megachirella wachtleri Renesto et Posenato, 2003, ein gut erhaltenes Teilskelett aus der mittleren Trias der Dolomiten (Nord-Italien) wurde ursprünglich den Lepidosauromorphen zugeordnet, auch wenn keine phylogentische Analyse durchgeführt wurde. In späteren phylogenetischen Studien wurde M. wachtleri daher völlig außer Acht gelassen. Eine Neubearbeitung des Holotypus und einzigen Exemplars von M. wachtleri ermöglicht es, die phylogenetische Position der Art neu zu analysieren. Die phylogenetische Studie bestätigt, dass die Art zu den Lepidosauromorpha gehört und nah an der Krongruppe der Lepidosauren (Squamata + Rhynchocephalia) steht. Megachirella erweitert unsere Kenntnisse über den Ablauf der morphologischen Veränderungen, die zum Ursprung der Lepidosaurier geführt hat, der variabelsten Gruppe rezenter Reptilien.

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Acknowledgments

Our sincere thanks to E. Kustatscher (Museo di Scienze Naturali dell’Alto Adige/Naturmuseum Südtirol, Italy) for access to the specimen and for translation into German of the summary (together with K. Bauer, same Institution), and to S.E. Evans (University College of London, UK) for access to unpublished data and permission to reproduce it. We also thank M.J. Benton (University of Bristol, UK) for useful comments on an earlier version of the manuscript and linguistic revision. M. Caldwell (University of Alberta, Canada) and M. Laurin (Muséum National d’Histoire Naturelle, Paris, France) are thanked for their constructive reviews, and the Editor O.W.M. Rauhut (Bayerische Staatssammlung für Paläontologie und Geologie, Munich) for useful comments and corrections. This study was supported by the Promotion of Educational Policies, University and Research Department of the Autonomous Province of Bolzano-South Tyrol as part of the project “The Permian–Triassic ecological crisis in the Dolomites: extinction and recovery dynamics in Terrestrial Ecosystems”.

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Correspondence to Silvio Renesto.

Appendices

Appendix 1

Character coding for Megachirella wachtleri within the different matrices:

In Laurin (1991): 11?11 11?11 11??0 0??11 1?111 ??11? 111?? ??100 00??? ?000? 0000? ?0000 01?11 111??

In Dilkes (1998), after Renesto et al. (2010): 0001? ????? ????? 0???0 00010 1?011 ?1022 12??? ????? ????? 1?1?0 ?000? ???0? ????0 ??020 00000 10100 1???? ?11?? ??00? ????? ?000? ????? ????? ????? ????? 0??0? 0???0 ??0?

In Müller (2004), after Evans and Borsuk-Bialynicka (2009): ????? ???10 0?0?1 0221? ?1??? 11?1? ????1 ??3?1 01?10 0?0?? 1110? ???00 00020 0???? ????? ????? 10??? ???0? 2???? ????? 0001? ???0? ????? ??00? 000?? ????? 1???? ????? ????0 10??? ????0 11??? ????? ????? ???0? 100?? ????

In Evans and Borsuk-Białynicka (2009): ??0?? 10010 1??11 ?1??? ????? 100?0 ?100? 01110 10??1 101?? 10100 ????? ????? ????? ????? 0?

Appendix 2

List of characters and their character states used by Evans and Borsuk-Bialynicka (2009), which was not originally published and is reported here with permission from the author (courtesy Evans).

  1. 1.

    Lacrimal large with extensive exposure on cheek, 0; small, confined to orbital rim, 1; absent, 2.

  2. 2.

    Greatest width of nasals exceeds greatest width of both nares, 0; is less then the latter, 1.

  3. 3.

    Frontoparietal suture more or less W shaped, subequal to or narrower then the nasofrontal suture in width, 0; suture more or less straight broader then naso-frontal suture, 1.

  4. 4.

    Parietal foramen within parietal, 0; on frontoparietal border or within frontal, 1; absent, 2.

  5. 5.

    Postparietals present, 0; absent, 1.

  6. 6.

    Tabulars present, 0; absent, 1.

  7. 7.

    Postorbital overlain by postfrontal, 0; postfrontal overlain by postorbital, 1.

  8. 8.

    Squamosal extends anteriorly halfway or less over lower temporal fenestra and is widely separated from jugal by postorbital, 0; extends more than halfway over lower temporal fenestra and comes close to or contacts jugal below postorbital, 1.

  9. 9.

    Anterior process of quadratojugal present, 0; absent, 1.

  10. 10.

    Posterior process of jugal extends about halfway back or less below lower temporal fenestra, 0; extends more than halfway back below lower temporal fenestra, 1.

  11. 11.

    Quadratojugal always present as a separate element at some point in ontogeny, 0; never present as a separate element, 1.

  12. 12.

    Supratemporal present, 0; fused or lost, 1.

  13. 13.

    Supratemporal lies superficially, 0; lies deep association with ventral face of postparietal process, 1.

  14. 14.

    Ventral process of squamosal present, 0; absent, 1.

  15. 15.

    Adductor chamber small, quadrate does not extend well below level of occipital condyle, 0; enlarged adductor fossa and quadrate extends well below adductor fossa, 1.

  16. 16.

    Nares paired, 0; nares confluent, 1.

  17. 17.

    Quadrate narrow in posterior view, 0; wide in posterior view forming lateral conch, 1.

  18. 18.

    Quadrate foramen present, 0; absent, 1.

  19. 19.

    Vomerine teeth numerous, 0; few or absent, 1.

  20. 20.

    Teeth or transverse flange of pterygoid present, 0; absent, 1.

  21. 21.

    Abducens canal absent or incomplete, 0; present and complete, 1.

  22. 22.

    Parasphenoid teeth present, 0; absent 1.

  23. 23.

    Paroccipital process does not extend laterally to contact quadrate, 0; process contacts quadrate, 1.

  24. 24.

    Paroccipital process not expanded distally, 0; expanded distally, 1.

  25. 25.

    Stapes thick and perforated for passage of stapedial artery in adults, 0; stapes thinner and imperforate in adults, 1; stapes columelliform and usually imperforate in adults, 2.

  26. 26.

    Quadrate straight in lateral view, 0; bowed, 1.

  27. 27.

    Postorbital contacts parietal, 0; separated from parietal, 1.

  28. 28.

    Posterior process of postorbital does not reach to posterior end of upper temporal fenestra, 0; process extends beyond posterior margin of upper temporal fenestra, 1.

  29. 29.

    Choanal fossa on palatine absent, 0; present, 1.

  30. 30.

    Snout comparatively shorter and broader, 0; longer and narrower, 1.

  31. 31.

    Premaxillae paired in full grown adults, 0; fused prior to hatching, 1.

  32. 32.

    Parietals paired in full grown adults, 0; fused prior to hatching, 1.

  33. 33.

    Exoccipitals sutured to opisthotic above and below metotic fissure, 0; fused only above metotic fissure with metotic fissure extended ventrally into basioccipital, 1; metotic fissure subdivided to create a dorsal vagus foramen and a ventral opening for the glossopharyngeal nerve and perilymphatic sac, 2.

  34. 34.

    Frontals paired, 0; fused, 1.

  35. 35.

    Splenial present, 0; absent, 1.

  36. 36.

    Angular extends posteriorly to articular condyle, 0; does not, 1.

  37. 37.

    Angular extends more than one-third up lateral face of mandible, 0; less than one-third, 1.

  38. 38.

    Retroarticular process relatively small or absent, 0; large, 1.

  39. 39.

    Outer one-third of articular condyle formed by surangular, 0; formed entirely by articular, surangular forming only outer rim, 1.

  40. 40.

    Teeth set in shallow sockets or depressions, 0; superficially attached to medial side of jaw with labial wall higher than lingual one, but only slightly, 1; labial wall significantly higher than lingual wall (pleurodont), 2.

  41. 41.

    Neural arches fuse to their respective centra in postembryonic development, 0; in embryo, 1.

  42. 42.

    Zygosphenes and zygantra, absent, 0; present, 1.

  43. 43.

    Caudal autotomy absent, 0; present, 1.

  44. 44.

    Trunk vertebrae without accessory articulations between neural spines, 0; accessory articulations present, 1.

  45. 45.

    Intercentra present in trunk, 0; absent, 1.

  46. 46.

    Vertebrae amphicoelous notocordal, 0; amphicoelous solid, 1; procoelous, 2.

  47. 47.

    Transverse processes not elongated, 0; short transverse processes, 1; long transverse processes, 2.

  48. 48.

    One or more cervical ribs bear two distinct heads, 0; all ribs single headed, 1; one or more ribs with three heads, 2.

  49. 49.

    No trunk vertebrae without free ribs, 0; one or more postsacrals without free ribs (lumbar), 1.

  50. 50.

    Sacral and caudal ribs fuse to their respective centra in postembryonic development, 0; fuse in embryo, 1.

  51. 51.

    Rib-bearing portion of sternum a single rod, 0; this region of sternum enlarged and formed from two plates; they remain paired until nearly maximum size, 1; paired sternal plates fuse in embryo, 2.

  52. 52.

    Anterior margin of scapulocoracoid without fenestrae, 0; fenestrate, 1.

  53. 53.

    Interclavicle robust, 0; gracile, 1.

  54. 54.

    Entepicondylar foramen of humerus, present, 0; absent, 1.

  55. 55.

    Prominent posteromedial process of distal epiphyses of radius absent, 0; present, 1.

  56. 56.

    Fourth metacarpal longer than third, 0; third and fourth metacarpal subequal, 1; fourth metacarpal shorter than third, 2.

  57. 57.

    Ilium includes 80–85 % of acetabulum, 0; 60–65 % acetabulum, 1.

  58. 58.

    Pubic flange on ilium absent, 0; present, 1.

  59. 59.

    Iliac blade long, 0; short, 1.

  60. 60.

    Anteromedial portion of pubis not out-turned dorsally, 0; out-turned dorsally, 1.

  61. 61.

    Dorsal edge of ilium essentially horizontal, 0; more steeply inclined, 1.

  62. 62.

    Pelvis a solid plate, 0; small thyroid fenestra with broad pubic symphysis, 1; large fenestra with small pubic symphysis, 2.

  63. 63.

    Ischial tubera short, 0; long, 1.

  64. 64.

    In fully grown individuals, pelvic elements separate, 0; fused, 1.

  65. 65.

    Fibula and femur articulate end to end, distal femoral condyles symmetrical, 0; fibula sits in a recess on lateral margin of distal end of femur, distal femoral condyles markedly asymmetrical, 1.

  66. 66.

    Articular surface of fibula for astragalocalcaneum restricted to a small portion of the distal end, 0; covers most of distal end of fibula, 1.

  67. 67.

    Astragalus and calcaneum separate throughout ontogeny, 0; fused prior to fusion of scapulocoracoid, 1.

  68. 68.

    Lateral centrale of pes discrete throughout ontogeny, 0; fused to astragalus in embryo, 1.

  69. 69.

    Distal tarsal 1 present, 0; absent 1.

  70. 70.

    Distal tarsal 2 present, 0; absent 1.

  71. 71.

    Distal tarsal 5 present at some point in postembryonic ontogeny, 0; absent or fused in embryo, 1.

  72. 72.

    Metatarsal 5 straight, 0; inflected, somewhat hooked but without enlarged plantar tubercles, 1; hooked, inflected angulated proximally and with enlarged medial and lateral plantar tubercles, 2.

  73. 73.

    Ridge on distal extremity of tibia for astragalar articulation, 0; no ridge present, 1.

  74. 74.

    No tongue and groove articulation between distal tarsal 4 and astragalocalcaneum, 0; process on distal tarsal 4 extends under astragalocalcaneum to form partial tongue and groove articulation, 1; full tongue and groove articulation, 2.

  75. 75.

    Premaxilla without posterolateral process excluding maxilla form narial rim, 0; with posterolateral process, 1.

  76. 76.

    Cervical vertebrae not elongated, 0; elongated, 1.

  77. 77.

    Astragalus and calcaneums without specialised joint between them, 0; with specialised joint, 1.

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Renesto, S., Bernardi, M. Redescription and phylogenetic relationships of Megachirella wachtleri Renesto et Posenato, 2003 (Reptilia, Diapsida). Paläontol Z 88, 197–210 (2014). https://doi.org/10.1007/s12542-013-0194-0

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Keywords

  • Megachirella wachtleri
  • Triassic
  • Diapsida
  • Lepidosauromorpha
  • Phylogeny

Schlüsserwörter

  • Megachirella wachtleri
  • Triassic
  • Diapsida
  • Lepidosauromorpha
  • Phylogenie