Elizabeth J. Hermsen

Oldest Known Eucalyptus Macrofossils Are from South America

The evolutionary history of Eucalyptus and the eucalypts, the larger clade of seven genera including Eucalyptus that today have a natural distribution almost exclusively in Australasia, is poorly documented from the fossil record. Little physical evidence exists bearing on the ancient geographical distributions or morphologies of plants within the clade. Herein, we introduce fossil material of Eucalyptus from the early Eocene (ca. 51.9 Ma) Laguna del Hunco paleoflora of Chubut Province, Argentina; specimens include multiple leaves, infructescences, and dispersed capsules, several flower buds, and a single flower. Morphological similarities that relate the fossils to extant eucalypts include leaf shape, venation, and epidermal oil glands; infructescence structure; valvate capsulate fruits; and operculate flower buds. The presence of a staminophore scar on the fruits links them to Eucalyptus, and the presence of a transverse scar on the flower buds indicates a relationship to Eucalyptus subgenus Symphyomyrtus. Phylogenetic analyses of morphological data alone and combined with aligned sequence data from a prior study including 16 extant eucalypts, one outgroup, and a terminal representing the fossils indicate that the fossils are nested within Eucalyptus. These are the only illustrated Eucalyptus fossils that are definitively Eocene in age, and the only conclusively identified extant or fossil eucalypts naturally occurring outside of Australasia and adjacent Mindanao. Thus, these fossils indicate that the evolution of the eucalypt group is not constrained to a single region. Moreover, they strengthen the taxonomic connections between the Laguna del Hunco paleoflora and extant subtropical and tropical Australasia, one of the three major ecologic-geographic elements of the Laguna del Hunco paleoflora. The age and affinities of the fossils also indicate that Eucalyptus subgenus Symphyomyrtus is older than previously supposed. Paleoecological data indicate that the Patagonian Eucalyptus dominated volcanically disturbed areas adjacent to standing rainforest surrounding an Eocene caldera lake.

W(h)ither Fossils? Studying Morphological Character Evolution in the Age of Molecular Sequences

Abstract A major challenge in the post-genomics era will be to integrate molecular sequence data from extant organisms with morphological data from fossil and extant taxa into a single, coherent picture of phylogenetic relationships; only then will these phylogenetic hypotheses be effectively applied to the study of morphological character evolution. At least two analytical approaches to solving this problem have been utilized: (1) simultaneous analysis of molecular sequence and morphological data with fossil taxa included as terminals in the analysis, and (2) the molecular scaffold approach, in which morphological data are analyzed over a molecular backbone (with constraints that force extant taxa into positions suggested by sequence data). The perceived obstacles to including fossil taxa directly in simultaneous analyses of morphological and molecular sequence data with extant taxa include: (1) that fossil taxa are missing the molecular sequence portion of the character data; (2) that morphological characters might be misleading due to convergence; and (3) character weighting, specifically how and whether to weight characters in the morphological partition relative to characters in the molecular sequence data partition. The molecular scaffold has been put forward as a potential solution to at least some of these problems. Using examples of simultaneous analyses from the literature, as well as new analyses of previously published morphological and molecular sequence data matrices for extant and fossil Chiroptera (bats), we argue that the simultaneous analysis approach is superior to the molecular scaffold approach, specifically addressing the problems to which the molecular scaffold has been suggested as a solution. Finally, the application of phylogenetic hypotheses including fossil taxa (whatever their derivation) to the study of morphological character evolution is discussed, with special emphasis on scenarios in which fossil taxa are likely to be most enlightening: (1) in determining the sequence of character evolution; (2) in determining the timing of character evolution; and (3) in making inferences about the presence or absence of characteristics in fossil taxa that may not be directly observable in the fossil record.

Divisestylus gen. nov. (aff. Iteaceae), a fossil saxifrage from the Late Cretaceous of New Jersey, USA.

Fossilized flowers and fruits from the Upper Cretaceous (Turonian, ca. 90 million years [my] before present) Raritan Formation of New Jersey are described as the new genus Divisestylus with two species, D. brevistamineus and D. longistamineus. The fossils are fusainized and three-dimensionally preserved. Morphological characteristics suggest affinities with extant Saxifragaceae and Iteaceae, two closely related families in Saxifragales. Similarities include a pentamerous perianth, calyx fused below into a hypanthium with free sepal lobes above, haplostemonous androecium with stamens situated opposite the calyx lobes, inferior ovary, bicarpellate gynoecium, numerous ovules on axile placentas, conspicuous intrastaminal nectary ring, and capsulate fruit opening apically. The unique fusion of the gynoecium, with carpels and stigmas fused but styles free, indicates closer affinities with extant Iteaceae, whereas other characters, such as basifixed anthers in D. brevistamineus, tricolpate and striate pollen grains, and anomocytic stomata, indicate closer affinities to Saxifragaceae. Cladistic analyses utilizing molecular data from a previously published analysis and morphological data as well as morphological data alone demonstrate the fossils share a more recent common ancestor with Iteaceae than Saxifragaceae, thereby making Divisestylus the oldest fossils known with clear affinities to Iteaceae.

The Generification of the Fossil Record

Abstract Many modern paleobiological analyses are conducted at the generic level, a practice predicated on the validity of genera as meaningful proxies for species. Uncritical application of genera in such analyses, however, has led—perhaps inadvertently—to the unjustified reification of genera in an evolutionary context. While the utility of genera as proxies for species in evolutionary studies should be evaluated as an empirical issue, in practice it is increasingly assumed (rather than demonstrated) that genera are suitable proxies for species. This is problematic on both ontological and epistemological grounds. Genera are arbitrarily circumscribed, non-equivalent, often paraphyletic, and sometimes polyphyletic collections of species. They are useful tools for communication but have no theoretical or biological reality of their own and, whether monophyletic or not, cannot themselves operate in the evolutionary process. Attributes considered important for understanding macroevolution—e.g., geographic ranges, niche breadths, and taxon durations—are frequently variable among species within genera and will be inflated at the generic level, especially in species-rich genera. Consequently, the meaning(s) of results attained at the generic level may not “trickle down” in any obvious way that elucidates our understanding of evolution at the species level. Ideally, then, evolutionary studies that are actually about species should be pursued using species-level data rather than proxy data tabulated using genera. Where genera are used, greater critical attention should be focused on the degree to which attributes tabulated at the generic level reflect biological properties and processes at the species level.

The fossil record of Eucalyptus in Patagonia.

PREMISE OF THE STUDY Herein, we name, describe, and illustrate new macrofossil material representing Eucalyptus (Myrtaceae: Myrtoideae, Eucalypteae) from the diverse early Eocene Laguna del Hunco (LH) flora of Chubut Province, Patagonia, Argentina. We explore the significance of these fossils in light of understanding the fossil record of eucalypts and the biogeography of the Eucalypteae. METHODS Fossils representing vegetative and reproductive organs were collected from multiple LH localities over several field seasons. These specimens were prepared, photographed, and compared to extant Eucalyptus. Additional historical collections of Patagonian fossil Eucalyptus were also examined. KEY RESULTS Vegetative and reproductive organs representing five different Eucalyptus taxa were identified in the LH paleoflora. One new taxon each representing leaves, flower buds, and infructescences with co-occurring, isolated capsules are described and named as new Eucalyptus species. Additionally, two flower types cf. Eucalyptus, represented by one specimen each, are illustrated and briefly described. The fossil species have unique characteristics that independently suggest each belongs within the Eucalypteae. The reproductive material is most similar morphologically to extant Eucalyptus, although it also shares many similarities to the closely related genus Corymbia. CONCLUSIONS The LH fossil Eucalyptus material is among the few eucalypt macrofossils that have recently been named and described and are the oldest macrofossils that can presently be definitively ascribed to the Eucalypteae. They also represent the only credible description of Eucalyptus fossils occurring outside of Australasia and suggest a once broader geographic distribution for this group.

Synthesizing and databasing fossil calibrations: Divergence dating and beyond

Divergence dating studies, which combine temporal data from the fossil record with branch length data from molecular phylogenetic trees, represent a rapidly expanding approach to understanding the history of life. National Evolutionary Synthesis Center hosted the first Fossil Calibrations Working Group (3–6 March, 2011, Durham, NC, USA), bringing together palaeontologists, molecular evolutionists and bioinformatics experts to present perspectives from disciplines that generate, model and use fossil calibration data. Presentations and discussions focused on channels for interdisciplinary collaboration, best practices for justifying, reporting and using fossil calibrations and roadblocks to synthesis of palaeontological and molecular data. Bioinformatics solutions were proposed, with the primary objective being a new database for vetted fossil calibrations with linkages to existing resources, targeted for a 2012 launch.

The Fossil Calibration Database-A New Resource for Divergence Dating

Fossils provide the principal basis for temporal calibrations, which are critical to the accuracy of divergence dating analyses. Translating fossil data into minimum and maximum bounds for calibrations is the most important-often least appreciated-step of divergence dating. Properly justified calibrations require the synthesis of phylogenetic, paleontological, and geological evidence and can be difficult for nonspecialists to formulate. The dynamic nature of the fossil record (e.g., new discoveries, taxonomic revisions, updates of global or local stratigraphy) requires that calibration data be updated continually lest they become obsolete. Here, we announce the Fossil Calibration Database (http://fossilcalibrations.org), a new open-access resource providing vetted fossil calibrations to the scientific community. Calibrations accessioned into this database are based on individual fossil specimens and follow best practices for phylogenetic justification and geochronological constraint. The associated Fossil Calibration Series, a calibration-themed publication series at Palaeontologia Electronica, will serve as a key pipeline for peer-reviewed calibrations to enter the database.

First record of Todea (Osmundaceae) in South America, from the early Eocene paleorainforests of Laguna del Hunco (Patagonia, Argentina)

UNLABELLED PREMISE OF THE STUDY The early Eocene Laguna del Hunco caldera-lake paleoflora (ca. 52 Ma) from Chubut Province, Argentina, is notably diverse and includes many conifer and angiosperm lineages that are extinct in South America but extant in Australasian rainforests. No ferns have been previously described from Laguna del Hunco. We describe and interpret a new species of fossil Osmundaceae based on fertile and sterile pinnae. • METHODS The fossil specimens were compared with other extant and fossil Osmundaceae based on living and herbarium material and published descriptions. A morphological matrix based on 29 characters was constructed for 17 living species in Osmundaceae, four species assigned to the fossil genus Todites, and the new fossil species. Phylogenetic analyses were conducted under parsimony using morphology and total evidence matrices. • KEY RESULTS Both the new fossil and the Todites species were consistently resolved within the leptopteroid clade of Osmundaceae, and the new species resolved in a clade with the two living Todea species, which are now restricted to Australia, New Guinea, New Zealand, and southern Africa. • CONCLUSIONS Todea amissa sp. nov. is the first record of Todea, living or fossil, in South America and only the second fossil record worldwide. The distribution of extant Todea on Gondwanan continents other than South America is broadly shared with other taxa from Laguna del Hunco, further indicating that a large component of this flora represents a Gondwanic biome that is no longer found on the South American continent.

REGNELLIDIUM(SALVINIALES, MARSILEACEAE) MACROFOSSILS AND ASSOCIATED SPORES FROM THE LATE CRETACEOUS OF SOUTH AMERICA

Premise of research. Fossils representing aquatic ferns with clear affinities to extant Regnellidium (Salviniales, Marsileaceae) are reported for the first time from Upper Cretaceous sediments of the La Colonia Formation, Chubut Province, Argentina. Methodology. Preserved organs including rhizomes bearing roots, compound leaves, and associated putative sporocarps were collected from the Cerro Bosta and Quebrada del Helecho localities of the La Colonia Formation. Spores were macerated for the macrofossil-bearing sediments of the Cerro Bosta locality and examined with SEM. Pivotal results. The macrofossils are morphologically similar to extant Regnellidium diphyllum. The fossil plants are rhizomatous, with the rhizomes bearing roots and leaves with two leaflets. The leaflets have dichotomizing venation and a marginal vein. Associated megaspores attributed to Molaspora lobata and microspores of the Crybeloporites type are also comparable to those of extant Regnellidium. Conclusions. These fossils represent the first report of Regnellidium-like macrofossils and the widespread Cretaceous megaspore taxon Molaspora from South America. Their presence in the La Colonia Formation suggests that Regnellidium may have been present on the continent continuously for more than 65 million years, although Cenozoic reports are necessary to confirm this hypothesis.

New marsileaceous fossils from the Late Cretaceous of South America and a reevaluation of Marsileaceaephyllum

Herein we report new macrofossils and associated microfossils representing the aquatic fern family Marsileaceae from the Campanian to Maastrichtian Cañadón del Irupé locality, La Colonia Formation, Chubut Province, Argentina. The macrofossils include compound leaves, detached leaflets, and sporocarps. The venation of the leaflets is consistent with the diagnosis of Marsileaceaephyllum, which we argue is poorly defined. Consequently, the circumscription and diagnosis of Marsileaceaephyllum are emended in order to limit the taxon to include only leaves or rhizomes bearing leaves with four leaflets that most resemble those of Marsilea among extant genera of Marsileaceae. The Cañadón del Irupé leaves and leaflets are assigned to the new genus Mirasolita, erected to encompass compound leaves bearing two petiolulate leaflets, each leaflet having a reniform lamina and reticulate venation. The architecture of Mirasolita leaves and leaflets is distinct from that of leaves of any of the living marsileaceous genera. The stalked sporocarps are assigned to the new genus Lugiomarsiglia. They are attributed to Marsileaceae because each has a sclerenchymatous wall surrounding circular bodies interpreted as sporangia. Associated megaspores are assigned to Molaspora lobata, a geographically widespread, primarily Late Cretaceous dispersed spore taxon. The co-occurrence of Molaspora lobata with an extinct marsileaceous leaf form fits a pattern wherein Cretaceous Regnellidium-like megaspores are associated with or found in situ within marsileaceous macrofossils that display a variety of morphologies.