Late Cretaceous bioconnections between Indo-Madagascar and Antarctica: refutation of the Gunnerus Ridge causeway hypothesis

Abstract

Aim To evaluate the Gunnerus Ridge land‐bridge hypothesis, which postulates a Late Cretaceous causeway between eastern Antarctica and southern Madagascar allowing the passage of terrestrial vertebrates. Location Eastern Antarctica, southern Indian Ocean, Madagascar. Methods The review involves palaeogeographical modelling, which draws upon geological and geophysical data, bathymetric charts, and plate tectonic reconstructions, and the evaluation of stratigraphically calibrated phylogenetic analyses to document ghost lineages of select taxa. Results The available geological and geophysical evidence indicates that eastern Antarctica’s Gunnerus Ridge and southern Madagascar were separated for the entire Late Cretaceous by a vast marine expanse. In the mid–Late Cretaceous, the gap was probably punctuated by land on two intervening physiographical highs, the northern Madagascar Plateau and Conrad Rise, the latter of which, although probably large, was still separated from Antarctica’s Riiser‐Larsen Peninsula by c. 1600 km. Recent, stratigraphically calibrated phylogenies including large, terrestrial end‐Cretaceous vertebrate taxa of Madagascar and the Indian subcontinent reveal long ghost lineages that extended into the Early Cretaceous. Main conclusions The view that Antarctica and Madagascar were connected by a long causeway between the Gunnerus Ridge and southern Madagascar in the Late Cretaceous, and that terrestrial vertebrates were able to colonize new frontiers using this physiographical feature, is almost certainly incorrect, as was previously demonstrated for the purported causeway between Antarctica and the Indian subcontinent across the Kerguelen Plateau. Connection across mainland Africa to account for the close relationships of several fossil and extant vertebrate taxa of Indo‐Madagascar and South America is another option, although this too lacks credibility. We conclude that (1) throughout the Late Cretaceous there was no intervening, continuous causeway through Antarctica and associated land bridges between South America to the west and Indo‐Madagascar to the east; and (2) mid‐ to large‐sized, obligate terrestrial forms (e.g. abelisauroid theropod and titanosaurian sauropod dinosaurs and notosuchian crocodyliforms) gained broad distribution across Gondwanan land masses prior to fragmentation and were isolated on Indo‐Madagascar before the end of the Early Cretaceous.

Sokatra, a New Side-Necked Turtle (Late Cretaceous, Madagascar) and the Diversification of the Main Groups of Pelomedusoides

“…Madagascar was, prior to the Coniacian, still sutured to the Indian subcontinent and together they formed the Indo-Madagascar landmass, along with the Seychelles (Storey et al, 1995(Storey et al, , 1997Torsvik et al, 2000). Assuming a restricted capacity for dispersal across marine barriers, the presence of Sokatra and Kurmademydini (Bothremydidae) in the latest Cretaceous of Madagascar may represent the legacy of ancient lineages that persisted after isolation of Indo-Madagascar from other Gondwanan landmasses in the Early Cretaceous (Ali and Aitchison, 2009;Ali and Krause, 2011).…”

A Middle Jurassic abelisaurid from Patagonia and the early diversification of theropod dinosaurs

“…Based on the previously available fossil record, abelisaurids were thought to have originated after the separation of Gondwana from the continents of the Northern Hemisphere [1,33], and recent discussions have focused on the possible effects (or lack thereof) of Gondwanan fragmentation on abelisaurid biogeography during the Cretaceous [1,3,4,33 -35]. The discovery of Eoabelisaurus demonstrates that there was ample time for a dispersal of abelisaurids over the Gondwanan continents prior to their separation in the course of the 'middle' to Late Cretaceous, as it has been argued recently on the basis of geological palaeogeographic evidence [33].…”

“…Based on the previously available fossil record, abelisaurids were thought to have originated after the separation of Gondwana from the continents of the Northern Hemisphere [1,33], and recent discussions have focused on the possible effects (or lack thereof) of Gondwanan fragmentation on abelisaurid biogeography during the Cretaceous [1,3,4,33 -35]. The discovery of Eoabelisaurus demonstrates that there was ample time for a dispersal of abelisaurids over the Gondwanan continents prior to their separation in the course of the 'middle' to Late Cretaceous, as it has been argued recently on the basis of geological palaeogeographic evidence [33]. However, the finding of an abelisaurid some 10 -15 Myr before the effective separation of the continents of the Northern and Southern Hemispheres begs the question why no abelisauroid remains have been recorded from the Jurassic of Laurasia (a recent record of an abelisauroid from the Middle Jurassic of England [17] cannot be substantiated; see the electronic supplementary material).…”

A radiation of arboreal basal eutherian mammals beginning in the Late Cretaceous of India

“…Character order follows Wible et al (2), with the addition of the seven characters detailed below. These changes result primarily from three factors: (i ) the new specimens are better preserved than the relatively worn and pitted Naskal specimens originally described, and demonstrate that some of the apparent morphology observed in those original specimens was inaccurate because of weathering/erosion and did not reflect original features of this taxon; (ii ) new specimens demonstrate that many features are polymorphic, as with incisor shape (character 5), metacone to paracone size (character 77), metacone and paracone base relationship (character 79), metaconule shape and position (character 89), protocone position and height (characters 95 and 96), paraconid crest shape (character 109), and protoconid height (character 112); or (iii ) new specimens represent elements that were not previously preserved, including mandibular fragments (characters 130-135), molar series (character 62), ultimate upper premolars (characters [40][41][42][43][44][45][46], and humeri (characters 359-363). None of these changes are unexpected with increases in available fossil data, but the polymorphic characters are of particular interest for evaluating taxonomic affiliations of new discoveries and for comparing the amount of variation observed in fossil taxa to that of modern taxa (50).…”