Upper Cretaceous woods from the Olmos Formation (late Campanian-early Maastrichtian), Coahuila, Mexico

Early Eocene infructescences from Argentine Patagonia expand the biogeography of Malvoideae

PREMISE

Fossil infructescences and isolated fruits with characters of Malvoideae, a subfamily of Malvaceae (mallow family), were collected from early Eocene sediments in Chubut, Argentina. The main goals of this research are to describe and place these fossils systematically, and to explore their biogeographical implications.

METHODS

Fossils were collected at the Laguna del Hunco site, Huitrera Formation, Chubut, Patagonia, Argentina. They were prepared, photographed, and compared with extant and fossil infructescences and fruits of various families using herbarium material and literature.

RESULTS

The infructescences are panicles with alternate arrangement of fruits. They bear the fruits on short pedicels that are subtended by a bract; the fruits display an infracarpelar disk and split to the base into five ovate sections interpreted as mericarps. Each mericarp is characterized by an acute apex and the presence of a longitudinal ridge. The isolated fruits show the same features as those on the infructescences. The fossils share unique features with members of the cosmopolitan family Malvaceae, subfamily Malvoideae.

CONCLUSIONS

The fossils have a unique combination of characters that does not conform to any previously described genus, justifying the erection of a new genus and species, Uiher karuen. This new taxon constitutes the first known Malvoideae reproductive fossils of the Southern Hemisphere, expanding the distribution of Malvoideae during the early Eocene.

First fossil woods and palm stems from the mid-Paleocene of Myanmar and implications for biogeography and wood anatomy

PREMISE

The rise of angiosperm-dominated tropical rainforests has been proposed to have occurred shortly after the Cretaceous-Paleogene transition. Paleocene fossil wood assemblages are rare yet provide important data for understanding these forests and whether their wood anatomical features can be used to document the changes that occurred during this transition.

METHODS

We used standard techniques to section 11 fossil wood specimens of Paleocene-age, described the anatomy using standard terminology, and investigated their affinities to present-day taxa.

RESULTS

We report here the first middle Paleocene fossil wood specimens from Myanmar, which at the time was near the equator and anchored to India. Some fossils share affinities with Arecaceae, Sapindales (Anacardiaceae, Meliaceae) and Moraceae and possibly Fabaceae or Lauraceae. One specimen is described as a new species and genus: Compitoxylon paleocenicum gen. et sp. nov.

CONCLUSIONS

This assemblage reveals the long-lasting presence of these aforementioned groups in South Asia and suggests the early presence of multiple taxa of Laurasian affinity in Myanmar and India. The wood anatomical features of the dicotyledonous specimens reveal that both "modern" and "primitive" features (in a Baileyan scheme) are present with proportions similar to features in specimens from Paleocene Indian localities. Their anatomical diversity corroborates that tropical flora display "modern" features early in the history of angiosperms and that their high diversity remained steady afterward.

Phylogenomic analyses of Sapindales support new family relationships, rapid Mid-Cretaceous Hothouse diversification, and heterogeneous histories of gene duplication

Sapindales is an angiosperm order of high economic and ecological value comprising nine families, c. 479 genera, and c. 6570 species. However, family and subfamily relationships in Sapindales remain unclear, making reconstruction of the order's spatio-temporal and morphological evolution difficult. In this study, we used Angiosperms353 target capture data to generate the most densely sampled phylogenetic trees of Sapindales to date, with 448 samples and c. 85% of genera represented. The percentage of paralogous loci and allele divergence was characterized across the phylogeny, which was time-calibrated using 29 rigorously assessed fossil calibrations. All families were supported as monophyletic. Two core family clades subdivide the order, the first comprising Kirkiaceae, Burseraceae, and Anacardiaceae, the second comprising Simaroubaceae, Meliaceae, and Rutaceae. Kirkiaceae is sister to Burseraceae and Anacardiaceae, and, contrary to current understanding, Simaroubaceae is sister to Meliaceae and Rutaceae. Sapindaceae is placed with Nitrariaceae and Biebersteiniaceae as sister to the core Sapindales families, but the relationships between these families remain unclear, likely due to their rapid and ancient diversification. Sapindales families emerged in rapid succession, coincident with the climatic change of the Mid-Cretaceous Hothouse event. Subfamily and tribal relationships within the major families need revision, particularly in Sapindaceae, Rutaceae and Meliaceae. Much of the difficulty in reconstructing relationships at this level may be caused by the prevalence of paralogous loci, particularly in Meliaceae and Rutaceae, that are likely indicative of ancient gene duplication events such as hybridization and polyploidization playing a role in the evolutionary history of these families. This study provides key insights into factors that may affect phylogenetic reconstructions in Sapindales across multiple scales, and provides a state-of-the-art phylogenetic framework for further research.

A new Oligocene-Miocene tree from Panama and historical Anacardium migration patterns

Migration of Boreotropical megathermal taxa during the Oligocene and Miocene played a key role in assembling diversity in tropical regions. Despite scattered fossil reports, the cashew genus Anacardium offers an excellent example of such migration. The fossil woods described here come from localities in Veraguas, Panama mapped as Oligocene-Miocene. We studied, described, and identified two well-preserved specimens using wood anatomical characteristics and completed extensive comparisons between fossil and extant material. The studied fossil woods share several diagnostic features with the modern Anacardium genus, including large solitary vessels, large intervessel-pitting, a simple vessel-ray pitting pattern, and mostly 1–3 seriate rays with large rhomboidal solitary crystals. We propose a new fossil species named Anacardium gassonii sp. nov., that adds an essential piece to the understanding of the historical biogeography of the genus. In addition, our findings confirm previous interpretations of this species’ migration from Europe to North America and its crossing through Panama, leading to subsequent diversification in South America. This discovery provides an important link to the historical migration patterns of the genus, supporting the notion of an Eocene migration to the Neotropics via Boreotropical bridges, as well as an Oligocene-Miocene crossing of Central America followed by diversification in South America.

Plastome phylogenomics of the East Asian endemic genus Dobinea

Dobinea is a dioecious genus endemic to East Asia that consists of two extant species: Dobinea delavayi and Dobinea vulgaris. Although the genus is morphologically distinct, its phylogenetic position remains controversial. In this study, we investigated the phylogenetic relationships between Dobinea and related taxa by sequencing the whole plastome DNA sequences for both extant species of Dobinea and comparing them to published plastomes within Sapindales. The complete plastomes of D. vulgaris and D. delavayi were 160,683 and 160, 154 base pairs (bp) in length, including a pair of inverted repeat regions (IRs, 26,889 and 26,759 bp) divided by the large single-copy region (LSC, 87,962 and 87,555 bp) and small single-copy region (SSC, 18,943 and 19,081 bp), and identically encoded 113 unique genes (79 protein-coding genes, 30 tRNAs, and 4 rRNA genes). Plastid phylogenomic analyses showed that Dobinea was a well-supported monophyletic unit and sister to the clade including tribes Anacardieae and Rhoideae, which suggests that Dobinea is a member of Anacardiaceae. In addition, molecular dating inferred D. delavayi and D. vulgaris diverged approximately 10.76 Ma, suggesting the divergence between these two species may have been driven by the intensification of the Asian summer monsoon and the establishment of distinct monsoon regimes in East Asia.

Late Campanian fossil of a legume fruit supports Mexico as a center of Fabaceae radiation

Fabaceae is one of the most diverse angiosperm families and is distributed across the globe in a variety of environments. The earliest evidence of the family, previous to this work, was from Paleogene sediments where it was found to be diverse in many fossil assemblages around the world. Here, we describe a fossil legume fruit from the Olmos Formation (upper Campanian) in northern Mexico. We designated the fossil fruit as Leguminocarpum olmensis Centeno-González, Martínez-Cabrera, Porras-Múzquiz et Estrada-Ruiz sp. nov., and related it with the Fabaceae family based on the presence of a dehiscent pod with two valves, an apex bearing stylar base, short stipe, and reticulated veins in the pericarp. We propose a new fossil species of Leguminocarpum for this fossil fruit. This fossil provides critical information on the long geologic history of Leguminosae around the world, significantly extending the record into the Cretaceous of Mexico.

New fossil lizard specimens from a poorly-known squamate assemblage in the Upper Cretaceous (Campanian) San Juan Basin, New Mexico, USA

Recent collection efforts in the upper Campanian (∼76-73.5 Ma) Fruitland and Kirtland formations of northwestern New Mexico have significantly increased the taxonomic diversity of lizards in this historically poorly understood squamate assemblage. New lizard specimens from the “Hunter Wash Local Fauna” of the upper Fruitland and lower Kirtland formations include: (1) new specimens referable to Chamopsiidae; (2) new material belonging to Scincomorpha, (3) new material belonging to Anguidae; and (4) the first reported predatory lizard (Platynota) material from the Campanian of New Mexico. The increase in lizard diversity in the “Hunter Wash Local Fauna” expands our understanding of Late Cretaceous squamate taxonomy, distribution, and diversity in the Western Interior of North America (Laramidia). Collectively, the described specimens represent family-level diversity similar to that seen in other Campanian foreland basin deposits of the Western Interior, such as the mid-paleolatitude Kaiparowits Formation of southern Utah, the higher paleolatitude Dinosaur Park Formation of southern Alberta, and the lower paleolatitude Aguja Formation of southwestern Texas. The lizards of the “Hunter Wash Local Fauna” represent crucial mid-paleolatitude data from a coastal plain depositional setting in Laramidia—allowing for comparisons to more well-studied assemblages at different latitudes and in different depositional settings.

Wood anatomy reveals high theoretical hydraulic conductivity and low resistance to vessel implosion in a Cretaceous fossil forest from northern Mexico

The Olmos Formation (upper Campanian), with over 60 angiosperm leaf morphotypes, is Mexico's richest Cretaceous flora. Paleoclimate leaf physiognomy estimates indicate that the Olmos paleoforest grew under wet and warm conditions, similar to those present in modern tropical rainforests. Leaf surface area, tree size and climate reconstructions suggest that this was a highly productive system. Efficient carbon fixation requires hydraulic efficiency to meet the evaporative demands of the photosynthetic surface, but it comes at the expense of increased risk of drought-induced cavitation. Here we tested the hypothesis that the Olmos paleoforest had high hydraulic efficiency, but was prone to cavitation. We characterized the hydraulic properties of the Olmos paleoforest using theoretical conductivity (K_s), vessel composition (S) and vessel fraction (F), and measured drought resistance using vessel implosion resistance and the water potential at which there is 50% loss of hydraulic conductivity (P₅₀). We found that the Olmos paleoforest had high hydraulic efficiency, similar to that present in several extant tropical-wet or semi-deciduous forest communities. Remarkably, the fossil flora had the lowest , which, together with low median P₅₀ (−1.9 MPa), indicate that the Olmos paleoforest species were extremely vulnerable to drought-induced cavitation. Our findings support paleoclimate inferences from leaf physiognomy and paleoclimatic models suggesting it represented a highly productive wet tropical rainforest. Our results also indicate that the Olmos Formation plants had a large range of water conduction strategies, but more restricted variation in cavitation resistance. These straightforward methods for measuring hydraulic properties, used herein for the first time, can provide useful information on the ecological strategies of paleofloras and on temporal shifts in ecological function of fossil forests chronosequences.

Biogeographic history of Pistacia (Anacardiaceae), emphasizing the evolution of the Madrean-Tethyan and the eastern Asian-Tethyan disjunctions

Pistacia L. exhibits a disjunct distribution in Mediterranean Eurasia and adjacent North Africa, eastern Asia, and North to Central America. The spatio-temporal diversification history of Pistacia was assessed to test hypotheses on the Madrean-Tethyan and the Eurasian Tethyan disjunctions through phylogenetic and biogeographic analyses. Maximum parsimony and Bayesian methods were employed to analyze sequences of multiple nuclear and plastid loci of Pistacia species. Bayesian dating analysis was conducted to estimate the divergence times of clades. The likelihood method LAGRANGE was used to infer ancestral areas. The New World species of Pistacia formed a clade sister to the Old World clade in all phylogenetic analyses. The eastern Asian Pistacia weinmannifolia-P. cucphuongensis clade was sister to a clade of the remaining Old World species, which were further resolved into three subclades. Pistacia was estimated to have originated at 37.60 mya (with 95% highest posterior density interval (HPD): 25.42-48.51 mya). A vicariance event in the early Miocene (19.79 mya with 95% HPD: 10.88-30.36 mya) was inferred to account for the intercontinental disjunction between the New World and the Old World species, which is consistent with the Madrean-Tethyan hypothesis. The two Old World eastern Asian-Tethyan disjunctions are best explained by one vicariance event in the early Miocene (15.87 mya with 95% HPD: 8.36-24.36 mya) and one dispersal event in late Miocene (5.89 mya with 95% HPD: 2.68-9.16 mya). The diversification of the Old World Pistacia species was significantly affected by extensive geological and climatic changes in the Qinghai-Tibetan plateau (QTP) and in the Mediterranean region.