Else Marie Friis

A reevaluation of seed plant phylogeny

Seed plant phylogeny is evaluated using a data set of 46 terminals (taxa) and 103 morphological and anatomical characters. Cladistic analyses using the criterion of parsimony were performed on the complete data set as well as on subsets of the data, e.g., excluding fossils and/or combining various complex taxa into single terminals. The results support the placement of the cycads as the sister group of a monophyletic group that includes several fossil «seed ferns» as well as extant Ginkgo, conifers, gnetopsids, and angiosperms. When fossils were included, Bennettitales (cycadeoids) were part of an «anthophyte» clade that included gnetopsids and angiosperms. Pentoxylon was a sister taxon to the core anthophyte clade, in some, but not all, of the most parsimonious trees

The Origins of angiosperms and their biological consequences

List of contributors Preface 1. Introduction to angiosperms E. M. Friis, W. G. Chaloner and P. R. Crane 2. The origin of angiosperms J. A. Doyle and M. J. Donoghue 3. Global palaeogeography and palaeoclimate of the Late Cretaceous and Early Tertiary Judith Totman Parrish 4. Mid-Cretaceous to Early Tertiary vegetation and climate: evidence from fossil leaves and woods G. R. Upchurch, Jr and J. A. Wolfe 5. Vegetational consequences of angiosperm diversification P. R. Crane 6. Time of appearance of floral features E. M. Friis and W. L. Crepet 7. The evolution of insect pollination in angiosperms W. L. Crepet and E. M. Friis 8. Interactions of angiosperms and herbivorous tetrapods through time S. L. Wing and B. H. Tiffney 9. Dinosaurs and land plants M. J. Coe, D. L. Dilcher, J. O. Farlow, D. M. Jarzen and D. A. Russell 10. Vegetational and mammalian faunal changes in the Early Tertiary of southern England M. E. Collinson and J. J. Hooker Classification of plants and animals Stratigraphic table Glossary Index.

Fossil evidence of water lilies (Nymphaeales) in the Early Cretaceous

Phylogenetic analyses have identified the water lilies (Nymphaeales: Cabombaceae and Nymphaeaceae), together with four other small groups of flowering plants (the ‘ANITA clades’: Amborellaceae, Illiciales, Trimeniaceae, Austrobaileyaceae), as the first diverging lineages from the main branch of the angiosperm phylogenetic tree, but evidence of these groups in the earliest phases of the angiosperm fossil record has remained elusive. Here we report the earliest unequivocal evidence, based on fossil floral structures and associated pollen, of fossil plants related to members of the ANITA clades. This extends the history of the water lilies (Nymphaeales) back to the Early Cretaceous (125–115 million years) and into the oldest fossil assemblages that contain unequivocal angiosperm stamens and carpels. This discovery adds to the growing congruence between results from molecular-based analyses of relationships among angiosperms and the palaeobotanical record. It is also consistent with previous observations that the flowers of early angiosperms were generally very small compared with those of their living relatives.

Dating phylogenetically basal eudicots using rbcL sequences and multiple fossil reference points

A molecular dating of the phylogenetically basal eudicots (Ranunculales, Proteales, Sabiales, Buxales and Trochodendrales sensu Angiosperm Phylogeny Group II) has been performed using several fossils as minimum age constraints. All rbcL sequences available in GenBank were sampled for the taxa in focus. Dating was performed using penalized likelihood, and results were compared with nonparametric rate smoothing. Fourteen eudicot fossils, all with a Cretaceous record, were included in this study for age constraints. Nine of these are assigned to basal eudicots and the remaining five taxa represent core eudicots. Our study shows that the choice of methods and fossil constraints has a great impact on the age estimates, and that removing one single fossil change the results in the magnitude of tens of million years. The use of several fossil constraints increase the probability of approaching the true ages. Our results suggest a rapid diversification during the late Early Cretaceous, with all the lineages of basal eudicots emerging during the latest part of the Early Cretaceous. The age of Ranunculales was estimated to 120 my, Proteales to 119 my, Sabiales to 118 my, Buxales to 117 my, and Trochodendrales to 116 my.

SEED PLANT RELATIONSHIPS AND THE SYSTEMATIC POSITION OF GNETALES BASED ON NUCLEAR AND CHLOROPLAST DNA: CONFLICTING DATA, ROOTING PROBLEMS, AND THE MONOPHYLY OF CONIFERS

We investigated the systematic position of Gnetales and other seed plant groups using molecular data from 119 land plant species. More than 100 new sequences of rbcL, atpB, 26S, and 18S ribosomal DNA were analyzed together with available GenBank sequences. To evaluate thoroughly the phylogenetic information of each gene, the four data sets were analyzed both separately and combined using different character coding. We found no supported conflict between codon positions in the plastid sequences, but we found a more complex pattern, indicating conflict between transitions and transversions, within each position. Including all information, plastid data results in a “Gnetales basal” phylogeny, whereas nuclear data weakly supports anthophytes. When transitions are excluded, Gnetales associate with conifers. Our study does not answer all questions on seed plant phylogeny, but it does show conifers as monophyletic with high support, rejecting a close relationship between Gnetales and the conifer family Pinaceae. Nuclear and chloroplast data produced essentially identical phylogenies except for the position of the seed plant root, and a sister relationship between Gnetales and angiosperms could not be fully ruled out. These results strongly conflict with previously published analyses of mitochondrial data.

Phase-contrast X-ray microtomography links Cretaceous seeds with Gnetales and Bennettitales

Over the past 25 years the discovery and study of Cretaceous plant mesofossils has yielded diverse and exquisitely preserved fossil flowers that have revolutionized our knowledge of early angiosperms, but remains of other seed plants in the same mesofossil assemblages have so far received little attention. These fossils, typically only a few millimetres long, have often been charred in natural fires and preserve both three-dimensional morphology and cellular detail. Here we use phase-contrast-enhanced synchrotron-radiation X-ray tomographic microscopy to clarify the structure of small charcoalified gymnosperm seeds from the Early Cretaceous of Portugal and North America. The new information links these seeds to Gnetales (including Erdtmanithecales, a putatively closely related fossil group), and to Bennettitales—important extinct Mesozoic seed plants with cycad-like leaves and flower-like reproductive structures. The results suggest that the distinctive seed architecture of Gnetales, Erdtmanithecales and Bennettitales defines a clade containing these taxa. This has significant consequences for hypotheses of seed plant phylogeny by providing support for key elements of the controversial anthophyte hypothesis, which links angiosperms, Bennettitales and Gnetales.

Seed Size, Fruit Size, and Dispersal Systems in Angiosperms from the Early Cretaceous to the Late Tertiary

Fossil data from 25 angiosperm floras from the Early Cretaceous (∼124 million years ago) to the Pliocene (∼2 million years ago) were compiled to estimate sizes of seeds and fruits and the relative proportion of two different seed‐dispersal systems by animals and by wind. The results suggest that, first, seed and fruit sizes were generally small during most of the Cretaceous, in agreement with previous suggestions, but the trend of increasing sizes started before the Cretaceous‐Tertiary boundary; second, there was a decrease in both seed and fruit sizes during late Eocene and Oligocene, reaching a level that has continued to the Late Tertiary; third, the fraction of animal dispersal was, in contrast to previous suggestions, rather high also during the Cretaceous but increased drastically in the Early Tertiary and declined congruently with the declining seed and fruit sizes from the late Eocene; and fourth, the fraction of wind dispersal showed a bimodal pattern, being high in the Late Cretaceous and in the Oligocene‐Miocene but with a drop in between. We find that the observed trends are only weakly related to the availability of animal fruit dispersers. Instead, the trends are congruent with a climate‐driven change in environmental conditions for recruitment, where larger seeds are favored by closed forest vegetation. The prevalence of semiopen, dry, and probably herbivore‐disturbed vegetation during the Cretaceous, the development of closed multistratal forests in the Eocene, and the later development of a more open vegetation and grasslands starting in the Oligocene‐Miocene, are reflected in the distribution of angiosperm seed and fruit sizes and in the dispersal systems.

Archaefructus – angiosperm precursor or specialized early angiosperm?

With molecular analyses indicating that angiosperms are not closely related to any other extant seed plant group, information from fossils might provide the only basis for reconstructing their origin. Therefore the description of a new Early Cretaceous angiosperm, Archaefructus, placed as the sister of all extant angiosperms, has created much debate and optimism. However, we question both the interpretation and the analysis of Archaefructus, concluding that it might be a crown-group angiosperm specialized for aquatic habit rather than a more primitive relative.

Reproductive Structure and Organization of Basal Angiosperms from the Early Cretaceous (Barremian or Aptian) of Western Portugal

A survey of five mesofossil floras from the Early Cretaceous (Barremian or Aptian) of Portugal documents considerable taxonomic and structural diversity among early angiosperms. Currently ca. 140–150 different angiosperm taxa have been identified in these floras, of which ca. 85% are taxa at the magnoliid grade—perhaps also with some basal monocots. Evidence is beginning to emerge that those lineages identified as basal among angiosperms in phylogenetic analyses (recently referred to as the ANITA grade of basal magnoliids, including Amborellaceae, Nymphaeales, Illiciales, Trimeniaceae, and Austrobaileyaceae) were already well represented in the Early Cretaceous, at which time they were probably more diverse than they are today. Many of the fossil angiosperms from the Portuguese floras cannot be assigned to any existing group, and there is clear evidence of significant extinction.

Fossils and plant phylogeny

Developing a detailed estimate of plant phylogeny is the key first step toward a more sophisticated and particularized understanding of plant evolution. At many levels in the hierarchy of plant life, it will be impossible to develop an adequate understanding of plant phylogeny without taking into account the additional diversity provided by fossil plants. This is especially the case for relatively deep divergences among extant lineages that have a long evolutionary history and in which much of the relevant diversity has been lost by extinction. In such circumstances, attempts to integrate data and interpretations from extant and fossil plants stand the best chance of success. For this to be possible, what will be required is meticulous and thorough descriptions of fossil material, thoughtful and rigorous analysis of characters, and careful comparison of extant and fossil taxa, as a basis for determining their systematic relationships.