New fossil discoveries illustrate the diversity of past terrestrial ecosystems in New Caledonia

Abstract

New Caledonia was, until recently, considered an old continental island harbouring a rich biota with outstanding Gondwanan relicts. However, deep marine sedimentation and tectonic evidence suggest complete submergence of the island during the latest Cretaceous to the Paleocene. Molecular phylogenies provide evidence for some deeply-diverging clades that may predate the Eocene and abundant post-Oligocene colonisation events. Extinction and colonization biases, as well as survival of some groups in refuges on neighbouring paleo-islands, may have obscured biogeographic trends over long time scales. Fossil data are therefore crucial for understanding the history of the New Caledonian biota, but occurrences are sparse and have received only limited attention. Here we describe five exceptional fossil assemblages that provide important new insights into New Caledonia’s terrestrial paleobiota from three key time intervals: prior to the submersion of the island, following re-emergence, and prior to Pleistocene climatic shifts. These will be of major importance for elucidating changes in New Caledonia’s floristic composition over time.

The evolution of insular woodiness

“…Among continental islands, the flora of Madagascar stands out (78 IWS and 13 transitions). New Caledonia, in contrast, harbors surprisingly few IWS and evolutionary transitions (3 IWS and 0 transitions), despite its tropical climate and the total submergence of the island during the Late Cretaceous and Early Paleogene ( 29 ) (resulting in the chance of herbaceous populations to colonize the island after reemergence and evolve IW as a response to competition). The occurrence of 395 IWS on continental islands, as well as 808 derived woody island species that evolved their woodiness on nearby continents prior to island colonization, invokes the question of how common evolutionary transitions toward woodiness occurred on continents.…”

Origin and evolution of the Micronesian biota: Insights from molecular phylogenies and biogeography reveal long‐distance dispersal scenarios and founder‐event speciation

“…While New Caledonia, a Gondwanan Island, was completely submerged during the last Cretaceous to Paleocene period, recent fossil data illustrate the diversity of the past terrestrial ecosystems, which is crucial to understand the link with refuges of neighboring paleo-islands and taxa that colonized the island after its re-emersion ca. 37 Ma (Garrouste et al, 2021).…”

Leaves in Iron Oxide: Remarkable Preservation of a Neogene Flora From New Caledonia

“…Samples of fossil dicotyledonous angiosperm leaves (Fig. 2) were collected from a ~2 cm thick duricrust of ferruginous silt and claystone within uplifted fluvio-lacustrine deposits in the Rivière des Lacs Basin (Garrouste et al 2021, Supplementary Figure 7) toward the southern end of the Massif du Sud (Fig. 1).…”

“…1). Abundant dicotyledonous angiosperm leaves dominate the flora, which also includes flowers, seeds, and wood (Garrouste et al 2021). The samples are the property of the government of New Caledonia, Service Géologique de la Nouvelle-Calédonie (SGNC) and are held by the Direction de l'Industrie, des mines et de l'énergie de la Nouvelle-Calédonie (DIMENC).…”

“…Here we describe the taphonomy of an exceptionally preserved fossil flora from New Caledonia which includes angiosperm leaves, seeds and flowers, gymnosperm leaves, with rare associated insects, in Neogene fluvial and lacustrine deposits developed on ultramafic basement (Bourdon and Podwojewski 1988;Locatelli 2013;Garrouste et al 2021). The leaves preserve cellular detail in three-dimensions in primary iron oxides precipitated externally, at least initially, on a microbially mediated iron-rich clay template.…”