The Flower Revolution

The rise of angiosperms was accompanied by massive expansion in biodiversity. From Benton et al., 2021

Angiosperms, or flowering plants, represent almost 90% of all living land plants. The group first appeared in the fossil record during the Early Cretaceous and by the Late Cretaceous, angiosperms came to dominate plant diversity. Charles Darwin’s fascination and frustration with the evolutionary events associated with the origin and early radiation of angiosperms are legendary. On 22 July 1879, in a letter to Joseph Dalton Hooker, Darwin refers to the early evolution of flowering plants as an “abominable mystery”. Since Darwin many new fossils have been found and facilitated the calibration of molecular clock age estimates for various angiosperm clades. Before the Aptian, the only convincing angiosperm megafossils are from the Barremian Las Hoyas flora of Spain and the Yixian flora of northeastern China. By contrast, there is an extensive pre-Aptian pollen record of angiosperms.

Model of the ancestral flower (From Sauquet et al., 2017)

The Angiosperm Terrestrial Revolution (Benton et al., 2021) reshaped the entire terrestrial ecosystem. Flowering plants altered climate and water cycles, and drove a massive expansion in biodiversity of numerous key groups of fungi, insects, arachnids, reptiles, mammals and birds. But angiosperm success lies no only in their possesion of flowers. They have smaller genomes on average than other plants, which lead to small cell sizes in angiosperms with tightly-packed internal structures. Other key innovations like high vein density and densely packed stomata are also related to genome size. Stomata are the controlled pores through which plants exchange gases with their environments, and play a key role in regulating the balance between photosynthetic productivity and water loss through transpiration

Atmospheric CO2 concentrations and paleotemperatures were the major drivers of floristic turnover. Multiple climate proxy records, identified the EECO as the warmest interval of the past 65 million years. During EECO (Eocene Climate Optimum), the warmest interval of the past 65 million years, emerged many angiosperm dominated forest. Today, many organisms depend substantially or entirely on angiosperms for their existence, especially in tropical rain forests. Among them are about 15 000 species of lizards, birds and mammals. 

References:

Benton, Michael J., et al. 2021. The Angiosperm Terrestrial Revolution and the Origins of Modern Biodiversity. New Phytologist. Wiley Online Library https://doi.org/10.1111/nph.17822

Sauquet, H., von Balthazar, M., Magallón, S. et al. The ancestral flower of angiosperms and its early diversification. Nat Commun 8, 16047 (2017). https://doi.org/10.1038/ncomms16047

Introducing Dineobellator notohesperus

Life reconstruction of Dineobellator notohesperus. Artwork by Sergey Krasovskiy

 

The iconic Velociraptor mongoliensis, described by Osborn in 1924, belongs to the Dromaeosauridae, a family of highly derived small to mid-sized theropod dinosaurs closely related to birds. Their fossils have been found in North America, Europe, Africa, Asia, South America and Antarctica. They first appeared in the mid-Jurassic Period, but their fossil record in North America is very poor near the time of their extinction prior to the Cretaceous-Paleogene boundary. The group is characterized by the presence of long, three-fingered forelimbs that ended in sharp, trenchant claws and a tail stiffened by the elongated prezygapophyses.

The description of Dineobellator notohesperus, a new specimen discovered in 2008 in New Mexico, offers a glimpse into the biodiversity of Dromaeosaurids at the end of the Cretaceous. The generic name is derived from the Navajo word Diné, in reference to the people of the Navajo Nation, and the Latin suffix bellator, meaning warrior. The specific name is derived from the Greek word noto, meaning southern, or south; and the Greek word hesper, meaning western.

 

Skeletal reconstruction of Dineobellator notohesperus. From Jasinski et al., 2020

 

The holotype (SMP VP-2430), similar in size to Velociraptor and Saurornitholestes, includes elements of the skull, axial, and appendicular skeleton. The nearly complete right humerus measures 185.78 mm, with an estimated total length of 215 mm. The presence of quill knobs in Dineobellator provides further evidence for feathers throughout Dromaeosauridae. This new specimen co-existed with numerous other theropods, including caenagnathids, ornithomimids, troodontids, and tyrannosaurids.

Dineobellator exhibits some features in the forelimbs that suggest greater strength capabilities in flexion, in conjunction with a relatively tighter grip strength in the manual claws, while the possession of opisthocoelous proximal caudal vertebrae may have increased the agility of Dineobellator and thus may have implications for its predatory behavior, particularly with respect to the pursuit of prey.

 

References:

Jasinski, S.E., Sullivan, R.M. & Dodson, P. New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous. Sci Rep 10, 5105 (2020). https://doi.org/10.1038/s41598-020-61480-7

Senter, P., Kirkland, J. I., DeBlieux, D. D., Madsen, S. & Toth, N. New dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous of Utah, and the evolution of the dromaeosaurid tail. PLoS One 7, e36790 (2012). https://doi.org/10.1371/journal.pone.0036790

Osborn, Henry F. (1924a). “Three new Theropoda, Protoceratops zone, central Mongolia”. American Museum Novitates. 144: 1–12. http://hdl.handle.net/2246/3223

 

A Brief Introduction to Conservation Paleobiology

Richard Owen stands next to the largest of all moa, Dinornis maximus (now D. novaezealandiae). From Wikimedia Commons.

Over the past 50 years, the pace and magnitude of human-induced global changes has accelerated dramatically. The term defaunation was created to designate the declining of top predators and herbivores triggered by human activity, that results in a lack of agents that control the components of the ecosystems vegetation. Although anthropogenic climate change is playing a growing role, the primary drivers of modern extinctions seem to be habitat loss, human predation, and introduced species. The same drivers that contributed to ancient megafaunal and island extinctions.

The emerging discipline of conservation paleobiology is supplying necessary information to understand how ecosystems vary naturally through time and space and how they respond to major perturbations. The fossils that have provided such data include phytoplankton, zooplankton, fossil pollen, seeds, leaves, wood, invertebrate animals with hard parts, and vertebrate animals. They are particularly useful because they often show high fidelity to the living communities. Quaternary fossils have proven especially informative for addressing conservation questions, but useful information has also come from much older fossil deposits, reaching back millions of years.

Bison near a hot spring in Yellowstone National Park (From Wikimedia Commons).

The analytical methods that allow comparing present with past fall into two main categories: taxon-based and taxon-free. Taxon-based methods rely on the presence, absence, or abundances of certain taxa and their underlying diversity. Taxon-free methods use metrics that reflect ecosystem function rather than structure. Depending on the availability of fossils and the type of conservation question being asked, one or the other approach may be more appropriate.

Taxon-based paleontological data are critical in deciding if a “natural” landscape represents a historical or a novel ecosystem. Historical ecosystems are those that still have at least 70% of the habitats that were present 500 years ago and that contain fewer than 5 people/km2. In the world’s first national park, Yellowstone National Park, USA, paleontological data influenced critical management decisions by demonstrating that Yellowstone preserves a historical ecosystem. Fossil deposits verified that almost all of the mammal species that had occupied the region for millennia are still present. Also, palynological records show that the current vegetation has persisted with only minor fluctuations in abundance of dominant taxa for at least 8000 years.

Lyuba, the best preserved mammoth mummy in the world, at the Field Museum of Natural History (From Wikimedia Commons).

Taxon-free paleontological can often be related to environmental parameters with statistical significance data, and are critical for understanding whether certain ecosystems are approaching “tipping points,” as demonstrated by analysis of diatoms, pollen, and sediments from lake cores.

Fossils have also figured prominently  with efforts to reconstruct copies of species that humans have driven to extinction either recently (passenger pigeons) or in the deeper past (mammoths). Unfortunately, the ecosystems that supported many extinct species no longer exist, so survival outside of captivity would be difficult. In addition, preventing the extinction of extant species and habitats numbering in the thousands already is challenging, so the prospects of sustaining “de-extincted” species are poor at best. Media reports are presenting de-extinction in an optimistic framework, and conveying the impression that we face a real possibility of bringing mammoth back from extinction in  the near future. Of course, this is far from truth. We will never be able to recreate most extinct species in their purest form. Ultimately,  genetic engineering to simulate extinct life also raises ethical and legal concerns.

 

References:

Anthony D. Barnosky et al. Merging paleobiology with conservation biology to guide the future of terrestrial ecosystems. Science, 2017 DOI: 10.1126/science.aah4787

Rodolfo Dirzo et al., Defaunation in the Anthropocene, Science 345, 401 (2014); DOI: 10.1126/science.1251817

Braje, T.J., Erlandson, J.M., Human acceleration of animal and plant extinctions: A Late Pleistocene, Holocene, and Anthropocene continuum. Anthropocene (2013), http://dx.doi.org/10.1016/j.ancene.2013.08.003

Richmond, D.J., Sinding, M-H.S., Gilbert, M.T.P. (2016). The potential and pitfalls of de-extinction. — Zoologica Scripta, 45, 22–36. DOI: 10.1111/zsc.12212