Research ArticlePALEONTOLOGY

A Triassic plesiosaurian skeleton and bone histology inform on evolution of a unique body plan

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Science Advances  13 Dec 2017:
Vol. 3, no. 12, e1701144
DOI: 10.1126/sciadv.1701144
  • Fig. 1 Locality and horizon of the new species.

    (A) Location of Bonenburg clay pit in eastern North Rhine-Westphalia, Germany. (B) Measured section of the Norian to Hettangian deposits with the discovery horizon (indicated by plesiosaurian silhouette and red arrows) of Rhaeticosaurus mertensi and the bonebeds with the Triassic vertebrate fauna. Horizons of lowermost Jurassic ammonites indicated by silhouettes. Colors of the rock types in the main stratigraphic column approximate colors in fresh outcrop. Cly, claystone; Fss, fine-grained sandstone; Het., Hettangian; L. J., Lower Jurassic; Md, mudstone; Slt, siltstone.

  • Fig. 2 The holotype of Rhaeticosaurus mertensi gen. et sp. nov.

    (A) Photograph. (B) Color overlay. (C) Cervical vertebrae 10 to 15 in right lateral view showing medially inclined zygapophyses (black arrow) and the autapomorphic ventrally concave V-shaped neurocentral sutures (white arrow). (D) Left radius, a phalanx, and a carpal element. (E) Left femur, tibia, and fibula. The proximal femur is a cast because the original was sectioned for histology. ca, caudal vertebra; ce, cervical vertebra; cr, carpal bone; d, dorsal vertebra; f, femur; fi, fibula; l., left; ph, phalange; r., right; ra, radius; s, sacral vertebra; ti, tibia; ?, unidentified bone. Scale bars, 20 cm (A) and 1 cm (C to E).

  • Fig. 3 Calibrated phylogenetic tree of Middle Triassic to Early Jurassic Eosauropterygia and evolution of key features of Plesiosauria.

    (A) Major features of the tree resemble topologies from previous analyses (4, 11) and uses the same clade names. Rhaeticosaurus mertensi is a sister to the main radiation of Pliosauridae. (B) Evolution of key features of plesiosaurians plotted on the phylogeny of Sauropterygia. Note that these key features were not necessarily recovered as synapomorphies in the phylogenetic analysis and that their arrangement on a specific branch does not imply the order of appearance. Asterisk indicates latest possible appearance of the feature. Lad., Ladinian; He., Hettangian; Pliens., Pliensbachian; Sinem., Sinemurian; Toarc., Toarcian. Geologic time is from Walker et al. (62). The horizontal gray bands indicate that stratigraphic position of the major plesiosaurian faunas in the Lower Jurassic. LR, Lyme Regis; H, Holzmaden; S, Street; Y, Yorkshire.

  • Fig. 4 Bone histology of the holotype of Rhaeticosaurus mertensi gen. et sp. nov.

    (A) Midshaft cross section of the femur in normal light. Note the large nutrient canal and the single growth mark (arrow). Box marks enlargement in (B). (B) Close-up of outer part of first growth cycle and of second growth cycle. Note the abrupt directional change of the vascular canals at the growth mark (arrow). (C) Close-up of (B) in polarized light with lambda filter. (D) Radial FLB of the first growth cycle in polarized light with lambda filter. (E) Close-up of (D). Note the woven bone scaffold (magenta) surrounded by primary osteons (light blue). In addition, note the plump and densely spaced osteocyte lacunae in the woven bone and the lenticular ones in the primary osteons. c, nutrient canal. Scale bars, 10 mm (A), 500 μm (B and C), 100 μm (D), and 20 μm (E).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/12/e1701144/DC1

    Supplementary Anatomical Descriptions

    fig. S1. The holotype of R. mertensi gen. et sp. nov.

    fig. S2. The holotype of R. mertensi gen. et sp. nov., anterior cervical vertebral column.

    fig. S3. The holotype of R. mertensi gen. et sp. nov.

    fig. S4. The holotype of R. mertensi gen. et sp. nov.

    fig. S5. Reconstruction of the skeleton of R. mertensi gen. et sp. nov. based on the available measurements and proportions.

    fig. S6. Selected skeletal proportions in Eosauropterygia.

    fig. S7. Principal component analysis of trunk and limb measurements in Eosauropterygia.

    fig. S8. Examples of CT scans of plesiosaurian long bones used in locating the nutrient canal before sectioning.

    fig. S9. Evolution of long bone histology in Triassic Eosauropterygia.

    fig. S10. Long bone histology of Jurassic and Cretaceous Plesiosauria.

    fig. S11. Long bone histology of a mature Middle Jurassic plesiosaurian.

    fig. S12. Long bone histology of the holotype of R. mertensi gen. et sp. nov. in longitudinal section.

    table S1. Faunal list of bonebed above plesiosaurian discovery horizon.

    table S2. Unambiguous but not unique synapomorphies diagnosing R. mertensi gen. et sp. nov. in addition to the two autapomorphies.

    table S3. List of synapomorphies from phylogenetic analysis.

    table S4. Measurements and proportions in the trunk and limbs of Eosauropterygia.

    table S5. List of histological samples.

    table S6. Local bone apposition rate to the end of the first year and relative body size at the end of the first year in selected sauropterygians.

    table S7. Comparison of local bone apposition rates in the femur of selected amniotes compared to local bone apposition rates in the humeri and femora of plesiosaurians.

    data file S1. Character matrix in NEXUS format for phylogenetic analysis described in Materials and Methods.

    References (6375)

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Anatomical Descriptions
    • fig. S1. The holotype of Rhaeticosaurus mertensi gen. et sp. nov.
    • fig. S2. The holotype of Rhaeticosaurus mertensi gen. et sp. nov., anterior cervical vertebral column.
    • fig. S3. The holotype of Rhaeticosaurus mertensi gen. et sp. nov.
    • fig. S4. The holotype of Rhaeticosaurus mertensi gen. et sp. nov.
    • fig. S5. Reconstruction of the skeleton of Rhaeticosaurus mertensi gen. et sp. nov. based on the available measurements and proportions.
    • fig. S6. Selected skeletal proportions in Eosauropterygia.
    • fig. S7. Principal component analysis of trunk and limb measurements in Eosauropterygia.
    • fig. S8. Examples of CT scans of plesiosaurian long bones used in locating the nutrient canal before sectioning.
    • fig. S9. Evolution of long bone histology in Triassic Eosauropterygia.
    • fig. S10. Long bone histology of Jurassic and Cretaceous Plesiosauria.
    • fig. S11. Long bone histology of a mature Middle Jurassic plesiosaurian.
    • fig. S12. Long bone histology of the holotype of Rhaeticosaurus mertensi gen. et sp. nov. in longitudinal section.
    • table S1. Faunal list of bonebed above plesiosaurian discovery horizon.
    • table S2. Unambiguous but not unique synapomorphies diagnosing Rhaeticosaurus mertensi gen. et sp. nov. in addition to the two autapomorphies.
    • table S3. List of synapomorphies from phylogenetic analysis.
    • table S4. Measurements and proportions in the trunk and limbs of Eosauropterygia.
    • table S5. List of histological samples.
    • table S6. Local bone apposition rate to the end of the first year and relative body size at the end of the first year in selected sauropterygians.
    • table S7. Comparison of local bone apposition rates in the femur of selected amniotes compared to local bone apposition rates in the humeri and femora of plesiosaurians.
    • Legend for data file S1
    • References (63–75)

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    Other Supplementary Material for this manuscript includes the following:

    • data file S1 (.txt format). Character matrix in NEXUS format for phylogenetic analysis described in Materials and Methods.

    Files in this Data Supplement: