A new primate from the late Eocene of Vietnam illuminates unexpected strepsirrhine diversity and evolution in Southeast Asia

Abstract

Sivaladapidae is a poorly known Asian strepsirrhine family originally discovered in Miocene sediments of the Indian subcontinent. Subsequent research has considerably increased the diversity, temporal range, and geographical distribution of this group, now documented from China, Thailand, Myanmar, Pakistan, and India and whose earliest representatives date back to the Middle Eocene. We present here a new taxon of sivaladapid from the Na Duong coal mine in the Latest Middle Eocene-Late Eocene of Vietnam. It represents the first Eocene primate from Vietnam and the first medium-sized mammal recovered from this locality, thus documenting a completely new part of the Na Duong paleobiodiversity. This taxon is the largest sivaladapid ever found with an estimated body weight of 5.3 kg and it represents a new subfamily of sivaladapids in exhibiting a very peculiar combination of dental features yet unknown in the fossil record of the family (e.g., retention of four premolars, high-crowned molars with accentuated bunodonty and extreme crest reduction). Besides documenting a complete new part of sivaladapid evolution, its primitive dental formula and derived features shared with the Early Eocene Asiadapidae reinforce the hypothesis of a basal branching of sivaladapids among strepsirrhines.

Exceptionally well-preserved crocodilian coprolites from the Late Eocene of Northern Vietnam: Ichnology and paleoecological significance

“…The age assignments for the Na Duong fauna remain a topic of debate, with recent studies suggesting much younger age of approximately ∼33Ma (for geological reviews on Na Duong Formation, refer to ref. 115 , 118 , 120 , 121 ).…”

Exceptionally well-preserved crocodilian coprolites from the Late Eocene of Northern Vietnam (Na Duong Formation) and their coproecological implications

“…The studied materials for this research were retrieved from the lowest units of the Eocene-Oligocene Na Duong Formation (Vietnam), which is dominated by uvial and peat-forming processes, and are composed of sandstones, siltstones, mudstones with small carbonate concretions, and the claystone layers contain the main lignite-bearing units. The age assignments for the Na Duong fauna are highly debatable, and new studies have suggested much younger ages, which is around ~ 33Ma (see 109,112,114,115 for geological reviews on Na Duong formation).…”

A new specimen of <i>Anthracokeryx naduongensis</i> (Mammalia, Artiodactyla, Anthracotheriidae) from the Eocene Na Duong Formation, northeastern Vietnam

“…Geologic age.̶Later part of the Eocene: late Bartonian to Priabonian (= late middle Eocene to late Eocene) (39-35 Ma) according to Böhme et al (2013); early late to middle late Eocene (= early to middle Priabonian) according to Ducrocq et al (2015); and latest middle to middle late Eocene (= latest Bartonian to middle Priabonian) according to Chavasseau et al (2019).…”

“…1A-B). The formation is an on-shore deposit that yielded many fossils such as mammals, crocodiles, tur-tles, fish, molluscs, and plants (Böhme et al, 2011(Böhme et al, , 2013Ugai et al, 2013;Ducrocq et al, 2015;Chavasseau et al, 2019). It is now dated from the late middle Eocene to late Eocene interval (= late Bartonian to Priabonian interval) on the basis of its fossil mammalian assemblage (Böhme et al, 2013;Ducrocq et al, 2015;Chavasseau et al, 2019).…”

“…The formation is an on-shore deposit that yielded many fossils such as mammals, crocodiles, tur-tles, fish, molluscs, and plants (Böhme et al, 2011(Böhme et al, , 2013Ugai et al, 2013;Ducrocq et al, 2015;Chavasseau et al, 2019). It is now dated from the late middle Eocene to late Eocene interval (= late Bartonian to Priabonian interval) on the basis of its fossil mammalian assemblage (Böhme et al, 2013;Ducrocq et al, 2015;Chavasseau et al, 2019). However, the described mammalian species and specimens are still limited, and only seven species have been reported from the formation: a sivaladapid primate, Anthradapis vietnamensis, described by Chavasseau et al (2019); a ruminant artiodactyl (Tragulidae or Lophiomerycidae) listed by Böhme et al (2011); four anthracotheriid artiodactyls described by Böhme et al (2013) and Ducrocq et al (2015); and a rhinocerotid perissodactyl, Epiaceratherium naduongensis, described by Böhme et al (2013).…”