Fossils and palaeontological distributions of Macaranga and Mallotus (Euphorbiaceae)

The correct identification of described plant fossils from the sister genera Macaranga and Mallotus (Euphorbiaceae) needs to be confirmed in order to correctly date their phylogeny and map their palaeontological distributions. Previous identifications of fossil specimens often appear to be unreliable since the distinctive features for identification such as leaf details and stamen thecae are usually not preserved in the fossils. Fossil pollen, seeds, wood and leaf (imprints) are so general in appearance that they are only typical either for both genera and their sister group Hancea (pollen), the family Euphorbiaceae (seeds) or even a large group of families (wood, leaf venation). Out of 54 fossils only four could be reliably identified as Macaranga and Mallotus, which is sufficient for dating the phylogeny, but insufficient to provide an insight into palaeontological distributions. All discussed fossils are mapped in order to assess the possibility of ancestral distributions outside the presently known distribution of Macaranga and Mallotus, which otherwise is impossible due to the limitations of the current historical biogeographic techniques that are based on present day distributions. A short overview of best practice to evaluate fossils and their identification is presented.

► Most fossils of Macaranga and Mallotus cannot be reliably identified.
► Fossil leaves do not show enough detail for identification even to family level.
► Only four fossils showed anatomical details enabling identification to a clade.
► Macaranga and Mallotus fossils cannot indicate ancestral distributions.
► Mallotus showed a palaeontological extension of its distribution New Zealand.