Florivory of Early Cretaceous flowers by functionally diverse insects: implications for early angiosperm pollination

Florivory (flower consumption) occurs worldwide in modern angiosperms, associated with pollen and nectar consumption. However, florivory remains unrecorded from fossil flowers since their Early Cretaceous appearance. We test hypotheses that earliest angiosperms were pollinated by a diverse insect fauna by evaluating 7858 plants from eight localities of the latest Albian Dakota Formation from midcontinental North America, in which 645 specimens (8.2%) were flowers or inflorescences. Well-preserved specimens were categorized into 32 morphotypes, nine of which displayed 207 instances of damage from 11 insect damage types (DTs) by four functional-feeding groups of hole feeding, margin feeding, surface feeding and piercing-and-sucking. We assessed the same DTs inflicted by known florivores on modern flowers that also are their pollinators, and associated insect mouthpart types causing such damage. The diverse, Dakota florivore–pollinator community showed a local pattern at Braun's Ranch of flower morphotypes 4 and 5 having piercing-and-sucking as dominant and margin feeding as minor interactions, whereas Dakotanthus cordiformis at Rose Creek I and II had an opposite pattern. We found no evidence for nectar robbing. These data support the rapid emergence of early angiosperms of florivore and associated pollinator guilds expressed at both the local and regional community levels.

Cretaceous fire-resistant angiosperms

Background: Flowering plants (angiosperms) dominate most global ecosystems today, but their rapid Cretaceous diversification has remained poorly understood ever since Darwin referred to it as an ‘abominable mystery’. Although numerous Cretaceous fossil flowers have been discovered in recent years, most are represented by incomplete charcoalified fragments that do not preserve delicate structures such as complete petals and surface textures, which means that their similarity to living forms is often difficult to discern. The scarcity of information about the ecology of early angiosperms makes it difficult to test hypotheses about the drivers of their diversification. Among other factors, frequent fires in the Cretaceous have been postulated as having possibly facilitated the rise of angiosperms. However, to date no early fossil angiosperms displaying fire-adapted traits have been known, making the role of fire in shaping Cretaceous floras uncertain.Results: We report the discovery of two exquisitely preserved fossil flower species, one identical to the inflorescences of the extant crown eudicot genus Phylica and the other recovered as a sister group to Phylica, both preserved as inclusions in Cretaceous amber from northern Myanmar (~99 Ma). These specialized flower structures, named Phylica piloburmensis sp. nov. and Eophylica priscastellata gen. et sp. nov., were adapted to surviving frequent wildfires, providing the earliest evidence of fire-resistance in angiosperms. The fossils suggest that fire was a significant selective force in Cretaceous angiosperm floras and that adaptations to fire resistance in some eudicot clades have been conserved for at least 99 Ma. This morphological stasis encompasses a range of floral characters, including the production of ‘pseudo-flowers’, and characteristic fruit and pollen architecture. Given its morphological distinctiveness, the Eophylica-Phylica clade represents one of the first well-documented angiosperm ‘living fossil’ genera from the Cretaceous. Conclusion: Our study suggests that core eudicots with specialised flower morphology displaying hallmarks of fire resistance and identical to those of the extant south African genus Phylica, had originated by the mid-Cretaceous (~99 Ma). Palaeoenvironmental reconstructions indicate that these plants lived in conditions similar to those of present-day southern Africa where 70% of taxa survive frequent burning, and that fire resistance was probably widespread in the fire-prone Cretaceous. The results also provide new insights into the biogeographic origin of at least one element of the highly endemic Greater Cape Region biodiversity hotspot flora biota.

Early flowers of primuloid Ericales from the Late Cretaceous of Portugal and their ecological and phytogeographic implications

A distinctive feature of the major eudicot diversification that occurred through the Late Cretaceous is the unequivocal presence of Cornales and diverse Ericales. Here we describe well-preserved fossil flowers from the Mira locality in western Portugal, of Campanian-Maastrichtian age, that we assign to a new extinct genus of Ericales with two new species; Miranthus elegans gen. et sp. nov. and Miranthus kvacekii sp. nov. The fossil flowers are pedicellate, structurally bisexual, actinomorphic, pentamerous and isomerous, with five narrowly triangular persistent calyx lobes, a five-lobed corolla, five antepetalous stamens, five staminodes alternating with the petals and a semi-inferior, unilocular ovary. The ovary consists of five carpels and has a raised nectariferous ring with stomata-like openings above the insertion of the perianth, and a long five-angled style. A key feature, which confirms a relationship with Primulaceae s. l., is the free, central dome-shaped placenta that bears numerous, densely spaced ovules. The ovary matures into a capsule containing many, minute, reticulate seeds. Flowers of Miranthus are especially similar to those of extant Samolus, a genus of about twelve species that is sister group to other genera of subfamily Theophrastoideae and that has a disjunct distribution mainly in the Southern Hemisphere. Miranthus also appears to have grown in environments influenced by marine conditions, an ecological preference also seen in Samolus. Miranthus expands the diversity of Ericales known from the Late Cretaceous, and together with previously described fossils provides further evidence that the diversification of Ericales was already underway by the Campanian-Maastrichtian stages of the Late Cretaceous.

Fossil flowers of Lachnociona camptostylus sp. nov., a second record for the genus in mid-Cretaceous Myanmar Amber

Two flowers embedded in a single block of amber from Myanmar are here proposed as a second species of the previously described fossil genus Lachnociona. The mid-Cretaceous age of the fossils was earlier established through paleontological and U-Pb isotope dating methods. Because they lie within millimeters of each other in the amber, the flowers are assumed to have come from the same parent plant. One flower is hermaphrodite while the other is functionally pistillate. They differ by the number of styles—4 in the perfect flower and 5 in the unisexual one—and most notably by the presence, in the perfect flower, of 10 conspicuous nectar glands forming a disc above the whorl of stamens. The pistillate flower has no such glands. In the new species, the arched styles are widely divergent and the ovary is fully inferior, while in the earlier-described Lachnociona terriae, the flower is functionally pistillate, with styles that are erect and connivent or connate. It could not be determined whether the ovary is superior or half-inferior. The best-preserved anther in the perfect flower of L. camptostylus resembles, in its dorsal filament attachment and hooked filament tip, a vestigial anther present in the flower of L. terriae. Pollen of the new species is tri- or tetracolpate. As proposed in the previous paper, the genus may have participated in the early diversification of the rosid clade of eudicots.

Endobeuthos paleosum gen. et sp. nov., fossil flowers of uncertain affinity from mid-Cretaceous Myanmar amber

Endobeuthos paleosum gen. et sp. nov. is based on 6 flowers preserved together in a single block of mid-Cretaceous amber from Myanmar (Burma). The calyx is composed of ca. 50+ small, helically arranged sepals. The corolla consists of 5 imbricate petals forming a sheath-like structure that is usually concealed within the calyx. The petal tips are often spreading and exserted from the calyx. There are numerous stamens, each of which consists of a filament and an enlarged anther connective with a single lateral, bisporangiate theca. Dehiscence is extrorse. The tips of 3 or 4 styles are visible, indicating that the flowers are bisexual. The fossils possess unique features that prevent assignment to any modern family. However, the numerous sepals and stamens and a thickened anther connective may suggest an association of E. paleosum with the family Dilleniaceae.