Thai amber: insights into early diatom history?

Abstract

The origin of the diatom still remains enigmatic. Their fossil record is scarce until the Late Cretaceous and great divergences exist between molecular data and the early fossil evidences. While molecular data indicate an origin during the Triassic or Lower Jurassic, early fossil evidences are only from the Late Jurassic-Early Cretaceous. The discovery of diatoms in French mid-Cretaceous amber by the end of the 2000’s already questioned a potential bias in diatom fossil record as it made older many diatom lineages known before by the end of the Cretaceous only. Thai amber allows the discovery of a new diatom specimen that has been attributed to the genus Hemiaulus. This material is difficult to date, but fossil assemblages and sedimentological data indicate that Thai amber and its Hemiaulus specimen are Late Jurassic-Early Cretaceous in age. This discovery extended the fossil record of the bipolar diatoms and of the genus Hemiaulus of several dozens of millions years and brings closer the fossil evidences and molecular data (that estimated an origin of the bipolar diatoms at around 150 Ma ago). It reinforces the hypothesis of a pre-Cretaceous fossil diatom record and also supports an origin of the diatoms in shallow coastal environments.

First occurrence of brachyopid temnospondyls in Southeast Asia and review of the Mesozoic amphibians from Thailand

“…However, a pair of otic notches and a pineal foramen are preserved. The pattern of the ornamentation and the shallow interotic embayment of this skull allow an assignment to Cyclotosaurus (Fraas, 1913;Ingavat and Janvier, 1981;Damiani, 2001) and are similar to those of the holotype of Cyclotosaurus posthumus Fraas, 1913 from the Upper Middle Keuper, Bavaria (Germany).…”

“…Hitherto, the Upper Triassic Indochina block of Thailand revealed at least two taxa of temnospondyls consisting of Cyclotosaurus (Ingavat and Janvier, 1981) and the plagiosaurids (Suteethorn et al, 1988). Moreover, the newly discovered specimens from the Huai Hin Lat Formation, i.e., dermal bones 365,368,and 377) and an intercentrum (CY-HN 378), are of uncertain affinities.…”

“…It is considered Upper Triassic based on palynomorphs, plant macro-remains, conchostracans, and vertebrate remains (Kobayashi, 1975;Racey et al, 1996;Buffetaut and Suteethorn, 1998;Department of Mineral Resources, 2014). The vertebrate assemblages from the Huai Hin Lat Formation consist of actinopterygian fishes (Martin, 1984), lungfish (Martin and Ingavat, 1982), temnospondyls (Ingavat and Janvier, 1981;Suteethorn et al, 1988), and phytosaurs (Buffetaut and Ingavat, 1982).…”

“…However, fossils of Thai amphibians (i.e., Cyclotosaurus cf. posthumus, Plagiosauridae, Temnospondyli indet., and Anura) were discovered only from three formations of the Indochina block (Ingavat and Janvier, 1981;Suteethorn et al, 1988;Buffetaut et al, 1994a;Srisuk, 2002Srisuk, , 2005 which are as follows.…”

Amber, from deposit to inclusions: new data

“…The presence of marine diatoms was therefore first reported in Cretaceous amber from Vendée and Charente-Maritime in France (Girard et al, 2008;2009;Saint Martin et al, 2015). Another exceptional case of inclusion of a marine diatom attributed to the genus Hemiaulus is described in Late Jurassic amber from Thailand (Girard et al, 2020), thus significantly going back in time the known fossil record of this genus. Among the micro-inclusions, the detection of spermatozoa constitutes an unexpected exceptional case of the preservation of organic structures rarely observed in the fossil record (Breton and Poinar, 2020).…”