Fabiany Herrera

Sensitivity of leaf size and shape to climate: global patterns and paleoclimatic applications

• Paleobotanists have long used models based on leaf size and shape to reconstruct paleoclimate. However, most models incorporate a single variable or use traits that are not physiologically or functionally linked to climate, limiting their predictive power. Further, they often underestimate paleotemperature relative to other proxies. • Here we quantify leaf-climate correlations from 92 globally distributed, climatically diverse sites, and explore potential confounding factors. Multiple linear regression models for mean annual temperature (MAT) and mean annual precipitation (MAP) are developed and applied to nine well-studied fossil floras. • We find that leaves in cold climates typically have larger, more numerous teeth, and are more highly dissected. Leaf habit (deciduous vs evergreen), local water availability, and phylogenetic history all affect these relationships. Leaves in wet climates are larger and have fewer, smaller teeth. Our multivariate MAT and MAP models offer moderate improvements in precision over univariate approaches (± 4.0 vs 4.8°C for MAT) and strong improvements in accuracy. For example, our provisional MAT estimates for most North American fossil floras are considerably warmer and in better agreement with independent paleoclimate evidence. • Our study demonstrates that the inclusion of additional leaf traits that are functionally linked to climate improves paleoclimate reconstructions. This work also illustrates the need for better understanding of the impact of phylogeny and leaf habit on leaf-climate relationships.

Giant boid snake from the Palaeocene neotropics reveals hotter past equatorial temperatures

The largest extant snakes live in the tropics of South America and southeast Asia where high temperatures facilitate the evolution of large body sizes among air-breathing animals whose body temperatures are dependant on ambient environmental temperatures (poikilothermy). Very little is known about ancient tropical terrestrial ecosystems, limiting our understanding of the evolution of giant snakes and their relationship to climate in the past. Here we describe a boid snake from the oldest known neotropical rainforest fauna from the Cerrejón Formation (58–60 Myr ago) in northeastern Colombia. We estimate a body length of 13 m and a mass of 1,135 kg, making it the largest known snake. The maximum size of poikilothermic animals at a given temperature is limited by metabolic rate, and a snake of this size would require a minimum mean annual temperature of 30–34 °C to survive. This estimate is consistent with hypotheses of hot Palaeocene neotropics with high concentrations of atmospheric CO2 based on climate models. Comparison of palaeotemperature estimates from the equator to those from South American mid-latitudes indicates a relatively steep temperature gradient during the early Palaeogene greenhouse, similar to that of today. Depositional environments and faunal composition of the Cerrejón Formation indicate an anaconda-like ecology for the giant snake, and an earliest Cenozoic origin of neotropical vertebrate faunas.

Late Paleocene fossils from the Cerrejón Formation, Colombia, are the earliest record of Neotropical rainforest

Neotropical rainforests have a very poor fossil record, making hypotheses concerning their origins difficult to evaluate. Nevertheless, some of their most important characteristics can be preserved in the fossil record: high plant diversity, dominance by a distinctive combination of angiosperm families, a preponderance of plant species with large, smooth-margined leaves, and evidence for a high diversity of herbivorous insects. Here, we report on an ≈58-my-old flora from the Cerrejón Formation of Colombia (paleolatitude ≈5 °N) that is the earliest megafossil record of Neotropical rainforest. The flora has abundant, diverse palms and legumes and similar family composition to extant Neotropical rainforest. Three-quarters of the leaf types are large and entire-margined, indicating rainfall >2,500 mm/year and mean annual temperature >25 °C. Despite modern family composition and tropical paleoclimate, the diversity of fossil pollen and leaf samples is 60–80% that of comparable samples from extant and Quaternary Neotropical rainforest from similar climates. Insect feeding damage on Cerrejón fossil leaves, representing primary consumers, is abundant, but also of low diversity, and overwhelmingly made by generalist feeders rather than specialized herbivores. Cerrejón megafossils provide strong evidence that the same Neotropical rainforest families have characterized the biome since the Paleocene, maintaining their importance through climatic phases warmer and cooler than present. The low diversity of both plants and herbivorous insects in this Paleocene Neotropical rainforest may reflect an early stage in the diversification of the lineages that inhabit this biome, and/or a long recovery period from the terminal Cretaceous extinction.

Palms (Arecaceae) from a Paleocene rainforest of northern Colombia

Palms are a monophyletic group with a dominantly tropical distribution; however, their fossil record in low latitudes is strikingly scarce. In this paper, we describe fossil leaves, inflorescences, and fruits of palms from the middle to late Paleocene Cerrejón Formation, outcropping in the Ranchería River Valley, northern Colombia. The fossils demonstrate the presence of at least five palm morphospecies in the basin ca. 60 Ma. We compare the morphology of the fossils with extant palms and conclude that they belong to at least three palm lineages: the pantropical Cocoseae of the subfamily Arecoideae, the monotypic genus Nypa, and either Calamoideae or Coryphoideae. The fossil fruits and inflorescences are among the oldest megafossil records of these groups and demonstrate that the divergence of the Cocoseae was more than 60 Ma, earlier than has previously been thought. These fossils are useful in tracing the range expansion or contraction of historical or current neotropical elements and also have profound implications for the understanding of the evolution of neotropical rainforests.

Fossil Araceae from a Paleocene neotropical rainforest in Colombia

Both the fossil record and molecular data support a long evolutionary history for the Araceae. Although the family is diverse in tropical America today, most araceous fossils, however, have been recorded from middle and high latitudes. Here, we report fossil leaves of Araceae from the middle-late Paleocene of northern Colombia, and review fossil araceous pollen grains from the same interval. Two of the fossil leaf species are placed in the new fossil morphogenus Petrocardium Herrera, Jaramillo, Dilcher, Wing et Gomez-N gen. nov.; these fossils are very similar in leaf morphology to extant Anthurium; however, their relationship to the genus is still unresolved. A third fossil leaf type from Cerrejón is recognized as a species of the extant genus Montrichardia, the first fossil record for this genus. These fossils inhabited a coastal rainforest ∼60-58 million years ago with broadly similar habitat preferences to modern Araceae.

Phytogeographic implications of fossil endocarps of Menispermaceae from the Paleocene of Colombia

PREMISE OF THE STUDY Fossil leaves of Menispermaceae were previously described from the Paleocene of Colombia. Because of strong homoplasy of leaf characters, the fossils could not be placed more specifically within recognized clades, and additional data were needed to specify intrafamilial and paleogeographic relationships during the Paleocene. METHODS Fossil endocarps of Menispermaceae were collected from the Cerrejón Formation, the recently discovered Bogotá flora, and Wyoming (∼60 Ma). We surveyed the endocarp morphology of almost all extant genera, conducted character optimization, a molecular scaffold analysis, and critically reviewed the related fossil genera. KEY RESULTS Parallel syndromes of fruit characters have appeared in unrelated clades of the family according to current phylogenetic reconstructions. However, mapping selected endocarp characters across those clades that contain horseshoe-shaped endocarps facilitates identification and phylogenetic assessment of the fossils. Three fossil species are recognized. One of them belongs to the extant genus Stephania, which today grows only in Africa and Australasia. Palaeoluna gen. nov. is placed within the pantropical clade composed of extant Stephania, Cissampelos, and Cyclea; this morphogenus is also recognized from the Paleocene of Wyoming. Menispina gen. nov. shows similarity with several unrelated clades. CONCLUSIONS The new fossils from Colombia reveal a complex paleobiogeographic history of the recognized clades within Menispermaceae, suggesting a more active exchange among neotropical, paleotropical, North American, and European paleoforests than previously recognized. In addition, the new fossils indicate that neotropical forests were an important biome for the radiation and dispersal of derived lineages in Menispermaceae after the Cretaceous-Paleogene boundary.

PHYTOGEOGRAPHIC HISTORY AND PHYLOGENY OF THE HUMIRIACEAE

To place a new fossil occurrence of Sacoglottis in a broader context, we surveyed the fruit morphology of all extant genera of the Humiriaceae, conducted a cladistic analysis, and critically reviewed the fossil record for this family. Living and fossil fruits of Humiriaceae are recognized by a woody endocarp, germination valves, and, in some genera, wall cavities. The phylogenetic analysis based on 40 morphological characters yielded two most parsimonious trees indicating Vantanea as sister taxon to all genera among Humiriaceae. Schistostemon is indistinguishable from Sacoglottis in fruit morphology and is recovered as sister to Sacoglottis in the topology; we recommend restoring Schistostemon to the rank of subgenus within Sacoglottis. A review of prior published reports of fossil fruits attributed to Humiriaceae led to the rejection and/or reattribution of some records but supports recognition of Vantanea, Humiria, Humiriastrum, and Sacoglottis. The available characters do not support recognition of multiple fossil species of Sacoglottis. We recognize the occurrence of Sacoglottis tertiaria Berry emend. Herrera from Peru, Ecuador, Colombia, and a newly collected Miocene site from Panama. The Cenozoic fossil record of Humiriaceae in South and Central America, together with discreditation of former reports from Europe, strongly supports a Neotropical origin for this family.

Fruits of an “Old World” tribe (Phytocreneae; Icacinaceae) from the Paleogene of North and South America

Abstract The Phytocreneae (Icacinaceae) are a tribe of scrambling shrubs and lianas presently distributed in tropical Africa, Madagascar, and Indo-Malesia. We describe the oldest known fossils of this tribe and provide the first recognition of this group in the Neotropical fossil record based on distinctive fruit remains. Palaeophytocrene piggae sp. nov., from the late Paleocene of western North America, and Palaeophytocrene hammenii sp. nov. and cf. Phytocrene sp., from the middle-late Paleocene of Colombia, constitute the oldest confirmed records of this tribe. Pyrenacantha austroamericana sp. nov., from the Oligocene of Peru, represents an extant Old World genus known also from the Eocene fossil record of North America and Europe. Collectively, these fossils indicate that the Phytocreneae were previously established in the Neotropics, despite their current absence from the region, and may provide evidence for Paleogene floristic exchange between North and South America.

A New Voltzian Seed Cone from the Early Cretaceous of Mongolia and Its Implications for the Evolution of Ancient Conifers

Premise of research. Abundant fossil and molecular evidence suggests that all extant conifer families were established by the Early Cretaceous. However, the recognition and understanding of the lineages that lead to the evolution of these extant families remain incomplete. Late Paleozoic to Early Mesozoic Voltziales conifers—also known as transitional conifers, usually with multilobed ovuliferous scales—have been hypothesized to be among the stem lineages of modern crown conifers. This article describes an exquisitely preserved voltzian seed cone from the Aptian-Albian of Mongolia that introduces new taxonomic diversity and morphological data into the complex pattern of conifer evolution. Methodology. Bulk lignite samples collected from the Tevshiin Govi locality were disaggregated in water, cleaned with hydrochloric and hydrofluoric acids, washed, and dried in air. Fossils were examined using LM, SEM, and X-ray microtomography. Pivotal results. Krassilovia mongolica gen. et sp. nov. has seed cones with helically arranged, imbricated, and tightly interlocked bract-scale complexes. Each mature bract-scale complex consists of an inconspicuous bract partially fused to the stalk of a five-lobed scale. Three of the lobes are distal (always pointing away from the cone base), while the other two are proximal (always pointing toward the cone base). Up to five inverted winged seeds are present on the adaxial side of the ovuliferous scales. A systematic review of Late Paleozoic to Early Cretaceous multilobed ovuliferous scales—together with a morphological cladistic analysis—supports the placement of the Mongolian material in a new genus within the voltzian clade of the Voltziales. Conclusions. Krassilovia mongolica provides evidence of the additional diversity of extinct voltzian conifers and shows that some persisted to inhabit forest-moor swamp environments in eastern Asia during the Early Cretaceous. The new fossil taxon also shows novel morphological adaptations of the bract-scale complexes and the cone (i.e., imbrication and interlocking) for the protection of the ovules/seeds that are broadly concurrent with the appearance of new insect and other animal feeding strategies.

Oligocene Age of the Classic Belén Fruit and Seed Assemblage of North Coastal Peru based on Diatom Biostratigraphy

The Belén flora, in north coastal Peru, is the most diverse fruit and seed assemblage yet known from the Paleogene of South America. Little original paleobotanical work has been performed on this assemblage since the pioneering treatments published by E. W. Berry in the 1920s, and the precise age has not been determined. Nevertheless, the flora has been regarded as a focal point in understanding the vegetational, orogenic, and climatic history of northern South America, and in recent literature it has been assumed to be early Eocene. In order to tighten this age assignment, which has varied from early Eocene to early Oligocene in the opinions of different authors, we revisited the Belén site, measured the stratigraphic section, and processed the fruit- and seed-containing sediment for age-diagnostic microfossils. Although pollen and foraminifera were not recovered, the sediment is rich in diatoms. The diatom assemblage includes Lisitzinia ornata and Rocella vigilans, among others, indicating a latest early Oligocene age (∼30–28.5 Ma) for these deeper marine sediments, which we infer to have been subsequently reworked into the Belén environment. We also reevaluate the botanical identifications, which are based on the original museum specimens supplemented by more recently collected specimens. The Belén flora provides a window into extinct forests in South America that were present before the rising of the Andes in western Peru.