Bollettino SPI Vol. 55 (2)
Published in September 2016
- Westall F. (2016)
Microbial palaeontology and the origin of life: a personal approach
Palaeontology is an essential tool for tracing the history of life in the geological record. However, access to the origin of life is blocked because of the lack of preservation of suitable rocks dating from the first billion years of Earth’s history. Nevertheless, study of Early Archaean rocks (~4-3.3 Ga) indicates that the environmental conditions of the early Earth, upon which life emerged, were very different to those of today and provides essential information for guiding investigations into the origin of life in terms of realistic environmental scenarios and possible timing of the appearance of life. Microbial palaeontology investigations of well-preserved, Early Archaean rocks ~3.5 to 3.3 Ga show that the earliest preserved life was diverse and widespread and suggest that it probably appeared in the Hadean, as soon as the Earth’s surface was habitable. The extreme, anaerobic conditions characterising the early Earth, together with the ingredients of life, i.e. carbon molecules, liquid water and energy, were common on other planets and satellites in the early Solar System. Considering carbon and water-based life forms to be a cosmically frequent phenomenon, it is hypothesised that life could have emerged on some of these bodies and that traces of its appearance may still be preserved, for instance on Mars, Europa or Enceladus. Microbial palaeontology as well as information gleaned from extant extremophiles and experimental data provides us with essential information about what kinds of extant or fossilised life forms to look for on another planet or satellite. Moreover, the methods evolved to study and understand the remains of fossil traces of primitive microbial life will aid the search for life and its origins on Mars or other satellites. The perspective of returning to Earth rocks from Mars (or other samples from Europa or Enceladus?) containing potential traces of extraterrestrial life, most likely primitive anaerobic chemotrophs, will be a challenge for microbial palaeontology that we need to start addressing now. Most importantly, it will open up the possibility of establishing the universality of life.
- Rosso A., Sanfilippo R., Di Geronimo I. & Bonfiglio L. (2016)
Pleistocene occurrence of recently discovered cryptic vermetid species from the Mediterranean
Significant genetic differences between populations previously assigned to Dendropoma petraeum (Monterosato, 1884) from diverse Mediterranean localities have been recently highlighted. Molecular analyses disclosed a complex of at least four cryptic species with highly diverging sequences coupled to a low degree of morphological differentiation or stasis in the adult stages. Differences were found in the early development of intracapsular larval shells. In the present paper the use of morphology and size of intracapsular larval shells preserved in the fossil record is proposed in order to trace genetic divergence in the geological past. The application of this research method in the study of Upper Pleistocene representatives of Dendropoma from Eastern Sicily, allowed documentation of the persistence of the expected clade for the area, at least since the Tyrrhenian Stage. This time interval, of the order of one hundred thousand years, is very short, when compared to the 4.5-17 Myr period indicated as a possible time frame for divergence utilizing the molecular clock. It is suggested that examination of protoconchs of Dendropoma specimens from selected older outcrops within the Mediterranean area could in this case provide more precise information with respect to the extremely broad interval obtained utilizing the molecular clock.
- Crippa G., Ye F., Malinverno C. & Rizzi A. (2016)
Which is the best method to prepare invertebrate shells for SEM analysis? Testing different techniques on recent and fossil brachiopods
The analysis of invertebrate shell microstructures by Scanning Electron Microscope (SEM) is a method easily available to most palaeontologists and geochemists; sample preparation does not require specialised techniques or instruments but it requires attention to detail in order to capture microstructural information invaluable to researchers in different fields of palaeontology. Herein, several tests were performed on recent and fossil brachiopod shells, excellent archives of ecological/palaeoecological and climatological/palaeoclimatological information, experimenting new and old methodologies in order to identify a general protocol to better highlight and analyse the shell biocomposite. The results of these tests are documented by SEM images. For recent brachiopod shells, we analysed seven specimens belonging to the species Liothyrella uva and Liothyrella neozelanica, respectively collected from Antarctica and New Zealand. We carried out several tests to check the response of the shell fabric to the resin used to embed the valves before cutting (Procedures 1b and 2c) and to different times of exposure to hydrochloric acid (Procedure 1a); as the presence of the organic matrix in recent shells represents the main obstacle to obtaining high quality images at the SEM, to remove it we used bleach (Procedure 2a) and hydrogen peroxide (Procedure 2b) with different concentrations and times of exposure. We then analysed two fossil specimens of Terebratula scillae collected from a lower Pleistocene succession in Northern Italy; here, we mainly checked the degree of penetration of the resin into the shell substance, embedding (Procedure 3a) vs not embedding (Procedure 3b) the specimens before cutting them. We show that Procedures 2a and 2b (embedding in the resin, bleach and hydrogen peroxide at the highest time of exposure, hydrochloric acid for 3 seconds) are the best methods to use when preparing recent brachiopods, whereas fossil shells should be subject to Procedure 3b (embedding in the resin, hydrochloric acid for 15 seconds).
- Kaminski M.A., Ferretti A., Messori F., Papazzoni C.A. & Sevastopulo G. (2016)
Silurian agglutinated foraminifera from the Dingle Peninsula, Ireland
In assemblage of primitive agglutinated foraminifera is reported for the first time from Silurian limestones from the Dingle Peninsula, Ireland. The assemblage is dominated by tubothalamids (Rectoammodiscus and rare Sansabaina), with less abundant monothalamids (Psammosiphonella and Psammosphaera). At the species level, the agglutinated foraminiferal assemblage is identical to those described previously from the Silurian of North America but is of lower diversity. The foraminiferal assemblage has limited potential for stratigraphic correlation as long-ranging taxa are present. The co-occurring conodont fauna enables an assignment to the early Ludlow.
- Marramà G., Garbelli C. & Carnevale G. (2016)
A clade-level morphospace for the Eocene fishes of Bolca: Patterns and relationships with modern tropical shallow marine assemblages
The world-famous Eocene Konservat-Lagerstätte of Bolca, northern Italy, has been celebrated since the 16th century for its exquisitely preserved fishes, which provide the earliest evidence of a modern tropical shallow marine fish assemblage. Due to the presence of many of the earliest representatives of several modern families of reef-associated fishes, the remarkable taxonomic and morphological richness of this fish assemblage has traditionally been attributed to the presence of a coral reef system. Several studies have suggested that the broad morphological diversification of modern fish lineages may be due to the availability of greater ecological opportunity for the survivors of the end-Cretaceous mass extinction. This hypothesis was supported by a major expansion of the morphospace occupied by the fish lineages that crossed the Cretaceous-Paleogene transition, occupying regions previously inhabited by extinct Cretaceous groups. In this context, we used a geometric morphometric approach in order to describe the clade-level structure of the morphospace of the Bolca fish assemblage, and to compare the patterns of morphospace occupation and morphological diversification between the Eocene and modern tropical shallow marine fish assemblages. Although the similarity in morphospace area and the overlapping of the different convex hulls seem to indicate a relative stasis in the overall morphospace occupation from the Eocene to Recent, some differences at the clade level can be detected. In particular, the representatives of several lineages, including anguilliforms, “perciforms”, syngnathiforms and tetraodontiforms, seem to have undergone significant changes in terms of morphospace occupation, body shape variation and contribution to the overall disparity from the Eocene to today.