Abstract Detail

Macroevolution

Flores, Jorge R [1], Bippus, Alexander [2].

Total-Evidence dating analysis yields a Late Devonian origin of the complex thalloid liverworts (Marchantiopsida, Marchantiophyta) and suggests that current morphological diversity was reached by the Late Mesozoic.

Integrating fossils into phylogenetic analyses has been shown to improve the accuracy of tree inference and estimates of divergence times. However, fossils have rarely been employed in bryophyte phylogenetics and dating has relied upon arbitrarily fixed calibration points in molecular-clock analyses. The goals of this study are: 1) to estimate divergence times of the complex thalloid liverworts (Marchantiopsida, Marchantiophyta) using a total-evidence (TE) approach that incorporates molecular, morphological, and palaeontological data, and 2) to assess the evolutionary trends in morphological "diversity" (disparity) and evolutionary rate changes in the group. Our combined dataset consists of 111 discrete morphological characters and 11 molecular markers (sampled from the nuclear, plastid and mitochondrial genomes). Taxon sampling included 56 extant species - representing all the recognised orders within Marchantiophyta and extant genera within Marchantiales - and six fossils: Metzgeriothallus sharonae, Pallaviciniites sandaolingensis, Marchantites cyathodoides, M. huolinhensis, Ricciopsis ferganica and R. sandaolingensis. Non-clock analyses resulted in topologies that were consistent with previous parsimony analyses under equal weighting and implied weighting. Conversely, except for P. sandaolingensis, the TE analysis recovered fossils as sister to more inclusive nodes after excluding the most unstable taxa. Divergence times inferred from the TE analysis were consistent with the fossil record and older than those from previous molecular-clock studies. The initial Marchantiopsida radiation, for instance, was inferred as Late Devonian (median 370.9 Mya) instead of Early Permian (295.4 Mya). Similarly, genera within Ricciaceae were inferred to have diverged during the Early Jurassic (190.1 Mya) rather than the Early Cretaceous (115.9 Mya). Optimising discrete and continuous morphological characters onto the TE post-burn-in topologies retrieved branches with high change rates during the Late Carboniferous - Early Triassic period and after the Late Mesozoic alternating with low-rate branches. Disparity-through-time analyses performed with these same TE topologies further revealed three discernible stages in the evolution of "morphological diversity": a fast increase in disparity until Early Mesozoic, a plateau until Late Mesozoic and a slow increase after the Late Mesozoic. Overall, these outcomes suggest that much of the current morphological diversity was reached by the Late Mesozoic after episodes of accelerated change rates in pre-Mesozoic branches. Although the sampling of extinct taxa is still limited in the present study, our results highlight the utility of incorporating fossils into phylogenetic analyses and macroevolutionary assessments of bryophytes.

1 - Finnish Museum of Natural History - University of Helsinki, Helsinki, 00014, Finland
2 - Oregon State University, Department of Botany and Plant Pathology, 2701 SW Campus Way, Corvallis, 97331, USA

Keywords:
Bryophytes
fossils
macroevolution
morphology
Total-evidence dating.

Presentation Type: Oral Paper
Session: MACROI, Macroevolution I
Location: Virtual/Virtual
Date: Tuesday, July 20th, 2021
Time: 1:45 PM(EDT)
Number: MACROI006
Abstract ID:288
Candidate for Awards:None