2014 Annual Science Report

Massachusetts Institute of Technology Reporting  |  SEP 2013 – DEC 2014

Executive Summary

THEME I: THE EARLIEST HISTORY OF ANIMALS

Members of the MIT Team have been working on some of the oldest chemical and body fossil evidence of animals, and applying studies of genomes and modern animal development to interpret these fossils. The goal is to understand how the interactions between changes in the physical environment, ecological interactions and in developmental mechanisms in evolutionary innovations lead to greater biological complexity.

Post-doctoral fellow David Gold has been investigating the origins and biosynthesis of a steroidal hydrocarbon proposed as a biomarker for sponges, the earliest-branching animals. This molecular record of sponges extends to the Cryogenian period. He has been studying both the distribution of this compound—24-isopropylcholestane—in samples of living and fossil sponges, and the distribution of the genes required for its synthesis in genomes across extant eukaryotes. The results support the conclusion that this compound is a ... Continue reading.

Field Sites
44 Institutions
13 Project Reports
45 Publications
11 Field Sites

Project Reports

  • Paleontological, Sedimentological, and Geochemical Investigations of the Mesoproterozoic-Neoproterozoic Transition

    As we learn more about the earliest evolutionary history of animals and other complex multicellular organisms, it becomes clearer that a satisfactory understanding of these events have to be set within the broader context of late Mesoproterozoic and early Neoproterozoic biological and environmental change. To this end, several labs within our team have focused research effort of Mesoproterozoic and Neoproterozoic sedimentary successions. Over the reporting period, this has included stratigraphic and sedimentological fieldwork on rocks of this age in northwestern Canada, Death Valley, Mongolia, and anaylsis of drill cores from Russia, Congo and Zambia. Progress has also been made in new techniques for the discovery and description of Proterozoic microfossils, the processes forming ooids and wrinkle structures, severalfold improvements in the precision of oxygen-17 measurements, which can record the balance of atmospheric oxygen and carbon dioxide, and in measurements of nitrogen isotopes in ancient pigments, a potential redox tracer for the Proterozoic.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Early Animals: Modeling the Biotic-Abiotic Interface in the Early Evolution of Multicellular Form

    The size of early multicellular organisms was sufficint to modify their local environment. Our initial work modeling of Neoproterozoic frond-like forms in the earliest-known communities of multicellular organisms demonstrates they were of sufficient scale and density to generate a distinctive canopy flow-regime. This modified environment yielded a selective advantage towards large eukaryotic forms that evolved at this time. This result is a function of limits imposed by diffusion at the surface of organisms, and how height and attendant velocity exposure escape these limits. Building on these results, we are now developing additional models of abiotic/biotic interactions at organismal surfaces, which are implicit in the morphology, development and orientation of other Neoproterozoic fossils. Ultimately, this work will help illuminate how forms initialy dependent on passive diffusion became more trophically complex, yielding a transition to the animal radiation.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1
  • Early Animals: The Origins of Biological Complexity

    The focus of the Erwin group remained on the origins of novelty and innovation, particularly associated with the origin and early diversification of animals during the Cryogenian, Ediacaran and early Cambrian. A field campaign in Namibia yielded new specimens, new fossil localities, and a potential new organism from the Ediacaran. Work on the phylogeny of early Cambrian lobopods was carried out to the hypothesis that arthropods evolved from this enigmatic group of organisms.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Taphonomy, Curiosity and Missions to Mars

    Members of our team continue to be involved in both the MER and MSL missions on Mars. On the latter mission, team members have recently documented a long-lived, habitable environment in Gale Crater dominated by rivers and lakes. Research on the mineralogy and geochemistry of rocks at the base of Mt Sharp has improved our understanding of their complex diagenetic history. Progress has also been made in linking orbital observations with those made by the rovers; this has been advanced particularly by field research at Rio Tinto and detailed laboratory experiments that constrain the relationship between mineral combinations and their signatures in infrared reflectance spectroscopy—and their effect on our ability to detect organics.

    ROADMAP OBJECTIVES: 2.1 4.1 4.2 6.1 7.1
  • Early Animals: Taphonomic Controls on the Early Animal Fossil Record

    We have been carrying out a number of studies in support of our objective to investigate the controls on the preservation of complex life on earth, with the ultimate aim of allowing the fossil evidence for the succession of events to be constrained and interpreted. These studies include investigating the connections between taphonomy and ecology of the Ediacara Biota based on the collection of fossil specimens and their careful examination, laboratory experiments designed to better understand how these fossils became preserved in different settings, and investigations of how Proterozoic eukaryotic microfossils are preserved, again from studying both new fossil material through a variety of approaches, and performing analog experiments in the laboratory.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Early Animals: The Genomic Origins of Morphological Complexity

    The Peterson lab has continued its focus on micro-RNAs (miRNA) in order to better understand the relationship between genetic and phenotypic diversity. Toward this goal, they have established a new database of miRNA genes (as opposed to sequences) assembled under strict quality control and an entirely novel nomenclature, bridging the different names previously given to the same gene across taxa. This database allows the evolution of miRNA genes to be studied across the animal kingdom. Such study shows that miRNA evolution is not correlated to the duplication of genetic material, but shaped by periods of intense miRNA innovation.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Molecular Biosignatures of Redox-Sensitive Bacteria and Hyperthermophiles

    The Summons lab has been researching a range of molecular and isotopic phenomena aimed at shedding light on what controls Neoproterozoic ocean redox, evolutionary trends in the abundances of molecular fossils (biomarkers) and the enigmatic natural variability carbon isotopic compositions of organic and inorganic carbon at this time. Our studies of carotenoid pigment biomarkers for green and purple sulfur bacteria have revealed that they are ubiquitous in rock extracts of Proterozoic to Paleozoic age—implying that the shallow oceans became sulfidic more frequently than previously thought. Other projects focused on the biosynthesis of another important biomaker, the hopanoids, vesicles released from marine bacteria for interaction between cells and their environment, and the molecular signatures of microbial communities in hot springs in Yellowstone National Park.

    ROADMAP OBJECTIVES: 4.1 4.2 5.1 5.2 7.1
  • Biosphere-Geosphere Stability and the Evolution of Complex Life

    Both the rise of complex life and the Phanerozoic mass extinctions are accompanied by significant perturbations of the carbon cycle. Attention is usually focused on causality, and environmental change is almost always considered the driver. Yet the co-evolution of life and the environment suggests that the fundamental issue is not causality but rather stability. This project seeks to develop a theory of biosphere-geosphere stability and to test it using the geochemical and fossil records.

    ROADMAP OBJECTIVES: 4.2 4.3 5.2 6.1
  • Early Animals: Lipid Biomarkers as the Earliest Evidence of Metazoans

    A complex hydrocarbon, 24-isopropylcholestane, has been proposed as a biomarker for a particular group of sponges—the earliest-branching animals—and found in Neoproterozoic rocks. However, a particular group of marine algae, the pelagophytes, can also produce the precursor to this compound, and it has not been known whether this ability is more widespread within the eukaryotes. We have used genomic data combined with time-calibrated phylogenies to approach this question and find that pelagophytes did not evolve this ability until the Paleozoic, while in sponges it evolved in the Neoproterozoic. This work supports the conclusion that this sterane is a true sponge biomarker.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Early Animals: Predation, Oxygen and Preservation in Early Animal Evolution

    Research in the Knoll lab has focused on three major issues relevant to early animal evolution. First, Knoll and colleagues developed a hypothesis to explain the mid-Neoproterozoic diversification of eukaryotes by invoking the evolution of eukaryote-eating protists (analogous to the evolution of carnivores driving the Cambrian diversification of animals). Second, work to integrate ecological data from modern oxygen-minimum zones with paleontological and geochemical data has yielded insights on early animal evolution. Finally, collaborations with other groups have focused on a variety of topics including the preservation of tiny animals in phosphate in the earliest Cambrian, a new Neoproterozoic record of vase-shaped protists.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Early Animals: Sensory Systems and Combinatorial Codes

    Understanding the evolution of integrated sensory organs—such as the eyes, ears and nose that develop in concert on our heads—is fundamental to understanding animal complexity. These are the features that permit movement and the environmental responses that characterize animals. We examine understudied early branches of the animal family tree, with a focus on the jellyfish Aurelia, to understand how the genetic regulation of sensory organs is conserved in some cases and evolves in others. Comparison of developmental regulation reveals how similar gene networks can be differentially modified and deployed, permitting the evolution of complex sensory systems. Jellyfish provide an ideal study system for the examination of the evolution of such sensory systems in animal evolution, as they are the most basal branch the animal tree with multiple sensory modes, and these develop at multiple stages in a complex life history. This provides us the ability to compare and contrast within the broader cnidarian group to which jellyfish belong, and to the bilaterians, the broad group containing humans and most other animals. The application of genomic methods greatly enhances our ability to pursue these questions.

    ROADMAP OBJECTIVES: 4.1 4.2
  • Early Animals: The Role of Biosignatures in Illuminating Homonin Diet

    Work conducted by Ainara Sistiaga, a student visitor from the University of La Laguna, Tenerife, Spain, aimed to evaluate the biomarker methodologies we typically apply to modern and ancient sediments to the issues surrounding the evolution of homo sapiens. Gas chromatography-mass spectrometry data on samples from El Salt (Spain), a Middle Palaeolithic site dating to ca. 50,000 yr. BP, represents the oldest positive identification of human faecal matter. We showed that Neanderthals, like anatomically modern humans, have a high rate of conversion of cholesterol to coprostanol related to the presence of specific gut flora. Analysis of five sediment samples from different occupation floors suggests that Neanderthals predominantly consumed meat, as indicated by high coprostanol proportions, but also had significant plant intake, as shown by the presence of 5β-stigmastanol.

    ROADMAP OBJECTIVES: 3.2 4.2
  • Review and Synthesis

    We reviewed aspects of biomarker formation and preservation. In one work, Briggs and Summons (2014), completed a review on Ancient biomolecules: their origin, fossilization and significance in revealing the history of life that was commissioned by the editor of Bioessays. The review was aimed at a general audience and outlined ways in which molecular biosignatures, ranging from the most unstable (DNA) to the most recalcitrant (lipids), could be informative about the evolution of life.

    A second review (Summons, 2014) was prepared for a paleontology short course and dealt with how molecules could be informative about life and the environments in which it lived. This review also touched on the production of highly oxidizing substances through radical chemistry operating in the Martian atmosphere has resulted in environmental conditions that promote the destruction of organic matter.

    ROADMAP OBJECTIVES: 7.2