Ediacaran Macro Body Fossils

This paper, Ediacaran Macro Body Fossils, reports a new discovery of well preserved three dimensional macro body fossils of the Ediacaran Period in central YunNan province in the People's Republic of China. These body fossils will enable more detailed and in-depth exploration of the evolution of multi-cellular macro organisms on this planet, whereas in the past, researches could only rely on cast or imprint fossils

Investigating the cores of fossil systems with Chandra

We investigate the cores of fossil galaxy groups and clusters (`fossil systems') using archival Chandra data for a sample of 17 fossil systems. We determined the cool-core fraction for fossils via three observable diagnostics, the central cooling time, cuspiness, and concentration parameter. We quantified the dynamical state of the fossils by the X-ray peak/brightest cluster galaxy (BCG), and the X-ray peak/emission weighted centre separations. We studied the X-ray emission coincident with the BCG to detect the presence of potential thermal coronae. A deprojection analysis was performed for z < 0.05 fossils to obtain cooling time and entropy profiles, and to resolve subtle temperature structures. We investigated the Lx-T relation for fossils from the 400d catalogue to see if the scaling relation deviates from that of other groups. Most fossils are identified as cool-core objects via at least two cool-core diagnostics. All fossils have their dominant elliptical galaxy within 50 kpc of the X-ray peak, and most also have the emission weighted centre within that distance. We do not see clear indications of a X-ray corona associated with the BCG unlike that has been observed for some other objects. Fossils do not have universal temperature profiles, with some low-temperature objects lacking features that are expected for ostensibly relaxed objects with a cool-core. The entropy profiles of the z < 0.05 fossil systems can be well-described by a power law model, albeit with indices smaller than 1. The 400d fossils Lx-T relation shows indications of an elevated normalisation with respect to other groups, which seems to persist even after factoring in selection effects.Comment: Accepted for publication in Astronomy and Astrophysic

Where are the Fossils of the First Galaxies? II. True Fossils, Ghost Halos, and the Missing Bright Satellites

We use a new set of cold dark matter simulations of the local universe to investigate the distribution of fossils of primordial dwarf galaxies within, and around the Milky Way. Throughout, we build upon previous results showing agreement between the observed stellar properties of a subset of the ultra-faint dwarfs and our simulated fossils. Here, we show that fossils of the first galaxies have galactocentric distributions and cumulative luminosity functions consistent with observations. In our model there are ~ 300 luminous satellites orbiting the Milky Way, ~50-70% of which are well preserved fossils, with this fraction decreasing with galactocentric distance. Within the Milky Way virial radius, the majority of these fossils have luminosities L_V<10^5 L_solar. This work produces an overabundance of bright dwarf satellites (L_V > 10^4 L_solar) with respect to observations where observations are nearly complete. The "bright satellite problem" is most evident in the outer parts of the Milky Way. We estimate that, although relatively bright, the primordial stellar populations are very diffuse, producing a population with surface brightnesses below surveys` detection limits and are easily stripped by tidal forces. Although we cannot yet present unmistakable evidence for the existence of the fossils of first galaxies in the Local Group, the results of our studies suggest observational strategies that may demonstrate their existence. Primarily, the detection of "ghost halos" of primordial stars around isolated dwarfs would prove that stars formed in minihalos (M<10^8 M_solar) before reionization, and strongly suggest that at least a fraction of the ultra-faint dwarfs are fossils of the first galaxies.Comment: publishing in ApJ with minor revisions in October 2011 V. 741 article ID. 1

Crossed Tracks: Mesolimulus, Archaeopteryx, and the Nature of Fossils

Organisms leave a variety of traces in the fossil record. Among these traces, vertebrate and invertebrate paleontologists conventionally recognize a distinction between the remains of an organism’s phenotype (body fossils) and the remains of an organism’s life activities (trace fossils). The same convention recognizes body fossils as biological structures and trace fossils as geological objects. This convention explains some curious practices in the classification, as with the distinction between taxa for trace fossils and for tracemakers. I consider the distinction between “parallel taxonomies,” or parataxonomies, which privileges some kinds of fossil taxa as “natural” and others as “artificial.” The motivations for and consequences of this practice are inconsistent. By comparison, I examine an alternative system of classification used by paleobotanists that regards all fossil taxa as “artificially” split. While this system has the potential to inflate the number of taxa with which paleontologists work, the system offers greater consistency than conventional practices. Weighing the strengths and weaknesses of each system, I recommend that paleontologists should adopt the paleobotanical system more broadly

Where are the Fossils of the First Galaxies? I. Local Volume Maps and Properties of the Undetected Dwarfs

We present a new method for generating initial conditions for LCDM N-body simulations which provides the dynamical range necessary to follow the evolution and distribution of the fossils of the first galaxies on Local Volume, 5-10 Mpc, scales. The initial distribution of particles represents the position, velocity and mass distribution of the dark and luminous halos extracted from pre-reionization simulations. We confirm previous results that ultra-faint dwarfs have properties compatible with being well preserved fossils of the first galaxies. However, because the brightest pre-reionization dwarfs form preferentially in biased regions, they most likely merge into non-fossil halos with circular velocities >20-30 km/s. Hence, we find that the maximum luminosity of true-fossils in the Milky Way is L_V<10^5 L_solar, casting doubts on the interpretation that some classical dSphs are true-fossils. In addition, we argue that most ultra-faints at small galactocentric distance, R<50 kpc, had their stellar properties modified by tides, while a large population of fossils is still undetected due to their extremely low surface brightness log(Sigma_V) < -1.4. We estimate that the region outside R_50 (~ 400 kpc) up to 1 Mpc from the Milky Way contains about a hundred true fossils of the first galaxies with V-band luminosities 10^3 - 10^5 L_solar and half-light radii, r_hl ~ 100-1000 pc.Comment: published in ApJ October 2011 with minor revisions V. 741 article ID. 1

Teaching Paleontology

This guide is designed to be used by teachers as an aid for teaching principles of fossils and past life to elementary school students. The activities and labs provided include topics such as fossilization, sedimentation, trace fossils, the importance of fossils, ancient environments, changes in environments, paleontology as a science, biodiversity, food webs, ecosystems, and human influences. The lessons provide pre- and post-questions, procedures, vocabulary, materials, and field trip ideas. This curriculum guide for paleontology was developed by Fossil Butte National Monument as part of its growing environmental education program. Educational levels: Intermediate elementary, Primary elementary

The Mass Assembly of Fossil Groups of Galaxies in the Millennium Simulation

The evolution of present-day fossil galaxy groups is studied in the Millennium Simulation. Using the corresponding Millennium gas simulation and semi-analytic galaxy catalogues, we select fossil groups at redshift zero according to the conventional observational criteria, and trace the haloes corresponding to these groups backwards in time, extracting the associated dark matter, gas and galaxy properties. The space density of the fossils from this study is remarkably close to the observed estimates and various possibilities for the remaining discrepancy are discussed. The fraction of X-ray bright systems which are fossils appears to be in reasonable agreement with observation, and the simulations predict that fossil systems will be found in significant numbers (3-4% of the population) even in quite rich clusters. We find that fossils assemble a higher fraction of their mass at high redshift, compared to non-fossil groups, with the ratio of the currently assembled halo mass to final mass, at any epoch, being about 10 to 20% higher for fossils. This supports the paradigm whereby fossils represent undisturbed, early-forming systems in which large galaxies have merged to form a single dominant elliptical.Comment: 11 pages, 8 figures, submitted to MNRA

The First Galaxies and the Likely Discovery of their Fossils in the Local Group

In cold dark matter cosmologies, small mass halos outnumber larger mass halos at any redshift. However, the lower bound for the mass of a galaxy is unknown, as are the typical luminosity of the smallest galaxies and their numbers in the universe. The answers depend on the extent to which star formation in the first population of small mass halos may be suppressed by radiative feedback loops operating over cosmological distance scales. If early populations of dwarf galaxies did form in significant number, their relics should be found today in the Local Group. These relics have been termed "fossils of the first galaxies". This paper is a review that summarizes our ongoing efforts to simulate and identify these fossils around the Milky Way and Andromeda. It is widely believed that reionization of the intergalactic medium would have stopped star formation in the fossils of the first galaxies. Thus, they should be among the oldest objects in the Universe. However, here we dispute this idea and discuss a physical mechanism whereby relatively recent episodes of gas accretion and star formation would be produced in some fossils of the first galaxies. We argue that fossils may be characterized either by a single old population of stars or by a bimodal star formation history. We also propose that the same mechanism could turn small mass dark halos formed before reionization into gas-rich but starless "dark galaxies". We believe that current observational data support the thesis that a fraction of the new ultra-faint dwarfs recently discovered in the Local Group are in fact fossils of the first galaxies.Comment: Invited review/tutorial paper, 18 pages, 11 figures. Accepted to Advances in Astronomy, special issue on "Dwarf-Galaxy Cosmology

Fossils: Digging Into the Past

Fossils collected in Renaissance collection cabinets were items of wonder and curiosity. Although sometimes mistaken for other pieces of naturalia, they were widely collected by owners of princely cabinets and scholarly collections.Though naturalists and collectors often kept fossils in their collections, they did not have the same understanding as we do today of what they are. Due to their belief in mythological monsters and naturalia with magical properties, there were often misinterpretations or mislabeled objects to something they were not. According to Kenseth’s “A World of Wonders in One Closet Shut,” some collectors believed that fossilized shark’s teeth were “adders’ tongues,” and that they could be used as antidotes to poison. Just as whale ribs were mistaken for “giant bones,” and narwhal tusks were mistaken for “unicorn horns,” fossils were also often misunderstood. [excerpt