Fig 1.
Definition of morphometric parameters used to evaluate the size and shape of the primary aperture in specimens with different morphologies (three- and four-chambered), exemplified for the morphospecies “G.” primordius (A), “G.”. immaturus (B), and G. subquadratus (C).
Primary aperture diameter ratio (PADR) that describes the relative width of the aperture is defined as the ratio between aperture width and height (measured perpendicular to width), i.e. as a/b, c/d, f/e. The symmetry index (SI) indicates the degree of symmetry of the primary aperture and is expressed as the ratio between the larger and smaller angle at the opposite sides of the primary aperture, i.e. as β/α, β1/α1, β2/α2.
Table 1.
Details of SSU rDNA sequences used to generate the molecular phylogeny for extant Globigerinoides.
Fig 2.
Chronology of the appearance of specimens with supplementary apertures on the spiral side showing the origin of the “G.” trilobus and G. ruber lineages from different Globoturborotalita ancestors at the Oligocene-Miocene transition.
The “G.” trilobus lineage starts in the late Oligocene with the ancestor “G.” primordius and diversifies in the lower Miocene at the base of Zone M1. The G. ruber lineage starts at the base of Zone M1. A = “Globigerinoides” primordius, Sample K3-F10-76, Trinidad; B = “Globigerinoides” primordius, Sample DSDP Hole 538A-2CC, Gulf of Mexico; C = “G.” praeimmaturus, DSDP Hole 94-10-2, 22–24 cm, Gulf of Mexico; D = early form of “G.” trilobus, Sample Bolli 407, Trinidad; E = Globoturborotalita woodi, Sample DSDP Hole 94-10-2, 22–24 cm, Gulf of Mexico; F = Globigerinoides parawoodi, Sample DSDP Hole 94-10-2, 22–24 cm, Gulf of Mexico; G = Globigerinoides subquadratus, Sample DSDP Hole 94-10-2, 22–24 cm, Gulf of Mexico; H = Globigerinoides sp. 1, Sample Bolli 407, Trinidad; I = wall texture of modern G. ruber pink, Sample boxcore top BC3441, Alboran Sea; J = wall texture of modern G. ruber white, Sample boxcore top BC3441, Alboran Sea; K = wall texture of modern “G.” sacculifer, Sample boxcore top BC3441, Alboran Sea. Scale bars of all specimens = 100 μm; Scale bars of all wall textures = 10 μm. Zonation from [13].
Fig 3.
A morphometric analysis of the primary aperture among different morphologies of “Globigerinoides”.
The Symmetry Index (SI) and the Primary Aperture Diameter Ratio (PADR) are defined in Fig 1. Dashed line indicates the best discrimination between specimens attributed to the trilobus (blue) and ruber (red) lineages, determined by linear discriminant analysis between the two groups in Zone M3. The line is perpendicular to the linear discriminant function at the position of the optimum discrimination score (z = 0). Specimens on each side of the line would be classified as belonging to either one of the groups in Zone M3.
Fig 4.
Maximum likelihood phylogeny of representative SSU rDNA sequences of extant species of the genus “Globigerinoides” and related taxa.
The lower panels show the topology for trees rooted on different outgroups (Table 1). Branches with bootstrap support > 95% (1000 replicates) are marked with grey circles.
Fig 5.
Simplified stratophenetic phylogeny based solely on fossil data (and thus not necessarily congruent with DNA-based phylogenies) showing the relationships between living species of Sphaeroidinella, Trilobatus n. gen., Orbulina, Globigerinoides, and Globoturborotalita (open circles) and their common ancestors (filled circles).
Stratigraphic ranges are shown as vertical grey bars and evolutionary relationships by horizontal dashed grey lines. The reconstruction is based on the new observations of the PPFWG for the Eocene to lower Miocene and [14] for the rest. This is not the complete clade: many fossil species (side-branches that are not ancestral to the modern species) in the genera Globoturborotalita, Trilobatus, and Globigerinoides have been omitted for clarity. The modern species Globigerinoides elongatus is omitted because most paleontologists lumped it (wrongly) with G. ruber prior to genetic studies. Also omitted is the modern Globigerinoides tenellus which has often been considered as closely related with G. rubescens but that relationship is uncertain. The modern species Trilobatus trilobus encompasses T. sacculifer which has a shorter stratigraphic range, are shown. Genera are shown as dashed panels; paraphyletic genera are shown encompassing their descendant genera. The evolution of supplementary apertures is shown as stars; this occurred independently three times in the origin of Trilobatus, Globigerinoides, and Sphaeroidinella. Fossil morphospecies are given as numbered circles: (1) Globoturborotalita bassriverensis; (2, 3) Globoturborotalita cancellata group; (4) Trilobatus primordius; (5) Trilobatus trilobus; (6) Trilobatus sacculifer; (7) Globigerinoidesella fistulosa; (8) Trilobatus bisphericus; (9) Trilobatus sicanus; (10) Praeorbulina glomerosa; (11) Orbulina universa; (12) Globoturborotalita brazieri; (13) Globoturborotalita woodi; (14) Sphaeroidinellopsis disjunctus; (15) Sphaeroidinellopsis seminulinus; (16) Sphaeroidinellopsis paenedehiscens; (17) Sphaeroidinella dehiscens; (18) Globoturborotalita decoraperta; (19) Globoturborotalita rubescens; (20) Globigerinoides subquadratus; (21) Globigerinoides altiaperturus; (22) Globigerinoides obliquus / extremus; (23) Globigerinoides conglobatus; (24) Globigerinoides ruber. PL = Pliocene, PT = Pleistocene, e = early, m = middle, l = late. Timescale of [13] and [30].
Table 2.
Similarities and differences between the Genera Globoturborotalita (ancestor), Globigerinoides, the new genus Trilobatus and its descendant Globigerinoidesella.