Fossil Embryos Research Articles

Terrestrial Origin of Viviparity in Mesozoic Marine Reptiles Indicated by Early Triassic Embryonic Fossils

Viviparity in Mesozoic marine reptiles has traditionally been considered an aquatic adaptation. We report a new fossil specimen that strongly contradicts this traditional interpretation. The new specimen contains the oldest fossil embryos of Mesozoic marine reptile that are about 10 million years older than previous such records. The fossil belongs to Chaohusaurus (Reptilia, Ichthyopterygia), which is the oldest of Mesozoic marine reptiles (ca. 248 million years ago, Early Triassic). This exceptional specimen captures an articulated embryo in birth position, with its skull just emerged from the maternal pelvis. Its headfirst birth posture, which is unlikely to be a breech condition, strongly indicates a terrestrial origin of viviparity, in contrast to the traditional view. The tail-first birth posture in derived ichthyopterygians, convergent with the conditions in whales and sea cows, therefore is a secondary feature. The unequivocally marine origin of viviparity is so far not known among amniotes, a subset of vertebrate animals comprising mammals and reptiles, including birds. Therefore, obligate marine amniotes appear to have evolved almost exclusively from viviparous land ancestors. Viviparous land reptiles most likely appeared much earlier than currently thought, at least as early as the recovery phase from the end-Permian mass extinction.

Two new theropod egg sites from the Late Jurassic Lourinhã Formation, Portugal

Two new Late Jurassic (uppermost Late Kimmeridgian) dinosaur eggshell sites are described, Casal da Rola and Porto das Barcas, both near Lourinhã, central-west Portugal. Casal da Rola yields eggshells with an obliquiprismatic morphotype comparable to those from a nest with the associated fossil embryos from Paimogo, tentatively assigned to the theropod Lourinhanosaurus antunesi. The Porto das Barcas eggshells have a dendrospherulitic morphotype with a prolatocanaliculate pore system. This morphotype was also recognised in eggshells from a clutch with associated Torvosaurus embryos at the Porto das Barcas locality. A preliminary cladistic analysis of eggshell morphology suggests theropod affinities for the Casal da Rola eggs, but is unable to resolve the phylogenetic position of the Porto das Barcas eggs. The eggshells at both sites are preserved in distal flood plain mudstones and siltstones. Carbonate concretions within the deposits indicate paleosol development.

Story one: Fossil embryos offer glimpse at dinosaur growth: Hundreds of bones found in southwestern China reveal rapid development

Story one: Fossil embryos offer glimpse at dinosaur growth: Hundreds of bones found in southwestern China reveal rapid development

Oldest dinosaur embryo fossils discovered in China

Oldest dinosaur embryo fossils discovered in China

Biological and taphonomic implications of Ediacaran fossil embryos undergoing cytokinesis

A collective of three-dimensionally (3D) phosphatized animal embryos with elongated olive shapes was discovered from the fossiliferous Ediacaran Doushantuo Formation (635–551Myr) in Weng'an, Guizhou, southwest China. In order to reconstruct 3D architectures of the specimens without destroying them, a non-destructive imaging technique termed propagation phase contrast synchrotron X-ray microtomography (PPC-SR-μCT) was applied in concert with scanning electron microscopy (SEM). The results show that the embryos were enclosed in a thin capsule with an ornament of cell-like polygons on the surface. Moreover, each elongated specimen consists of two blastomeres inside the sculptured capsule, and the geometric relationship of the two blastomeres in each specimen suggests that these specimens probably represent cleaving embryos during different phases of cytokinesis. This is the first detailed description of Doushantuo fossil embryos undergoing cytokinesis, and this new discovery supports the view that not all of the ornamented Doushantuo embryos are at diapause stage. Additionally, the rare phenomenon that the dynamic cytokinesis process was captured and fixed in fossils yields valuable insights into the taphonomic process of animal embryos before early diagenesis.

Phase Contrast Synchrotron Microtomography: Improving Noninvasive Investigations of Fossil Embryos In Ovo

Fossil embryos are paramount for our understanding of the development of extinct species. However, although thousands of fossil amniote eggs are known, very few embryos in ovo have been described. First reports of fossil embryos were based on broken eggs, where the embryonic remains were already exposed, because destructive methods on complete eggs were avoided. Investigations of complete eggs therefore required nondestructive approaches, such as X-ray microtomography (μCT). However, due to the general low density contrast between fossilized bones and infilling matrix, only a few specimens have been reported using these techniques. Using propagation phase contrast X-ray synchrotron microtomography (PPC-SR-μCT), we report here the discovery of three well-preserved embryos in Early Cretaceous eggs from Thailand. By scanning these eggs using different imaging techniques, we show that vastly different interpretations can be made regarding the preservation state and/or the developmental stage of these embryos. PPC-SR-μCT also revealed differential contrast between bone categories, presumably reflecting the ossification pattern of these embryos. Applying such an approach to large-scale studies of fossil eggs could lead to more discoveries and detailed studies of fossil embryos, providing important developmental and phylogenetic information on extinct and extant amniotes.

Organization, anatomy, and fungal endophytes of a Triassic conifer embryo

Much is known about the Paleozoic conifers and the conifers assignable to extant families that appear in the Jurassic; however, relatively little is known about the transitional conifers of the early Mesozoic, especially the Voltziales. To better understand the evolution of this group, we aim to increase knowledge of voltzialean anatomy and morphology. A fossil embryo of the group is described in this study. • Several permineralized seeds, one containing a well-preserved embryo, were collected from the early Middle Triassic Fremouw Peak locality in the Central Transantarctic Mountains. Samples were prepared using the standard acetate peel technique and studied in transmitted light. • The embryo belongs to Parasciadopitys aequata, a member of the Voltziales. The embryo and megagametophyte tissues are exquisitely preserved. The embryo is colonized by two distinct fungi. Sporocarps of the fungi are found in the megagametophyte and in the space between the megagametophyte and nucellus. The additions of embryo and megagametophyte characters to the description of P. aequata have made it one of the most completely known fossil taxa reproductively. • Preservation of fossil embryos, although rare, can expand the array of characters available in tracing the evolutionary history of plants. The embryo of P. aequata shares similarities with embryos of other extinct and extant conifer families. The association of the embryo with Combresomyces cornifer and Mycocarpon asterineum increases our understanding of the roles of microorganisms in Triassic ecosystems.

The anatomy, taphonomy, taxonomy and systematic affinity of Markuelia: Early Cambrian to Early Ordovician scalidophorans

Abstract: Markuelia is a vermiform, annulated introvertan animal known as embryonic fossils from the Lower Cambrian to Lower Ordovician. Analysis of an expanded and revised dataset for Introverta shows that the precise position of Markuelia within this clade is dependent on the taxa included. As a result, Markuelia is assigned to the scalidophoran total group to reflect uncertainty as to whether it is a stem-scalidophoran or a stem-priapulid. The taxonomy of the genus is revised to provide an improved taxonomic framework for material assigned to Markuelia. Five species are recognized: M. secunda Val’kov, M. hunanensis Dong and Donoghue, M. lauriei Haug et al., M. spinulifera sp. nov. and M. waloszeki sp. nov. Finally, the preservation of Markuelia is evaluated in the light of both the taphonomy of the fossil embryos themselves and the experimental taphonomy of the priapulid Priapulus caudatus, which has been proposed as both a close relative and an anatomical analogue of Markuelia.

Mineralogical constraints on the paleoenvironments of the Ediacaran Doushantuo Formation

Assemblages of clay minerals are routinely used as proxies for paleoclimatic change and paleoenvironmental conditions in Phanerozoic rocks. However, this tool is rarely applied in older sedimentary units. In this paper, the clay mineralogy of the Doushantuo Formation in South China is documented, providing constraints on depositional conditions of the Ediacaran Yangtze platform that host the earliest animal fossils in the geological record. In multiple sections from the Yangtze Gorges area, trioctahedral smectite (saponite) and its diagenetic products (mixed-layer chlorite/smectite, corrensite, and chlorite) are the dominant clays through the lower 80 m of the formation and constitute up to 30 wt% of the bulk rock. Saponite is interpreted as an in situ early diagenetic phase that formed in alkaline conditions (pH > or = 9). The absence of saponite in stratigraphically equivalent basin sections, 200-400 km to the south, indicates that alkaline conditions were localized in a nonmarine basin near the Yangtze Gorges region. This interpretation is consistent with crustal abundances of redox-sensitive trace elements in saponitic mudstones deposited under anoxic conditions, as well as a 10 per thousand difference in the carbon isotope record between Yangtze Gorges and basin sections. Our findings suggest that nonmarine environments may have been hospitable for the fauna preserved in the Yangtze Gorges, which includes the oldest examples of animal embryo fossils and acanthomorphic acritarchs.

Exceptional preservation of embryos in the actinopterygian Saurichthys from the Middle Triassic of Monte San Giorgio, Switzerland

New excavations in the famous Monte San Giorgio area, close to the historical sites where the Cassina beds crop out (Lower Meride Limestone, Early Ladinian), revealed an interesting vertebrate fauna, including several specimens of the actinopterygian fish Saurichthys. Among the prepared specimens, three specimens of Saurichthys contain embryos, and in one example the embryos are preserved with traces of the soft parts, most probably phosphatized musculature. This discovery is of particular relevance because fossil embryos with preserved soft parts are extremely rare. In addition, although viviparity had previously been described for Saurichthys, the new specimens are rather better evidence and add further support to this reproductive mode.

Fossil embryos and adult Viviparidae from the Early–Middle Pleistocene of Gesher Benot Ya’aqov, Israel: ecology, longevity and fecundity

Ashkenazi, S., Klass, K., Mienis, H.K., Spiro, B. & Abel, R. 2010: Fossil embryos and adult Viviparidae from the Early–Middle Pleistocene of Gesher Benot Ya’aqov, Israel: ecology, longevity and fecundity. Lethaia, Vol. 43, pp. 116–127. A unique fossil assemblage of the extinct freshwater viviparids Viviparus apameae galileae and Bellamya sp. with intact embryos enabled the assessment of population ecology parameters applied so far only to recent living populations. The assemblage, from the Early Middle Pleistocene site of Gesher Benot Ya’aqov, occurs in the sedimentary sequence above the Matuyama Brunhes Boundary (MB boundary) at 0.78 Ma. This fossil assemblage is related to a shoreline habitat that was affected by desiccation during a sudden drop in water level. In both species, the youngest females with embryos had five or more whorls, with heights of >24.8 and >16.1 mm in Viviparus and Bellamya respectively. Comparison of shell height and width, aperture height and width and the ratio of shell height/width indicated that females are significantly longer and larger than the shells without embryos. Longevity was estimated as at least 9 years for Viviparus and 8 years for Bellamya and lifetime fecundity of female viviparids was estimated based on longevity and reproductive period. The high number of reproducing females and high number of embryos indicate favourable habitat and climate conditions for both Viviparidae. The fossil Viviparidae from GBY have the characteristics of organisms that are K-selected by natural selection forces. □Fecundity, fossil embryos, longevity, molluscs, Pleistocene, reproductive output, sexual dimorphism, viviparids.

Cambrian Fossil Embryos from Western Hunan, South China

Abstract:The exquisitely preserved fossil embryos of Markuelia recovered from the limestones of the Middle Cambrian Haoqiao Formation and Upper Cambrian Bitiao formation in western Hunan, South China are described and illustrated in detail for the first time. A new species Markuelia elegans sp. nov. is established based mainly on embryos from the Upper Cambrian. A few of animal's resting eggs, which are comparable with those of the Ediacaran Doushantuo Formation, have been also found in the Upper Cambrian of western Hunan. The membrane of one egg from the uppermost Cambrian has been replaced by pyrite and the overgrowth of the pyrite crystals exhibits a unique inorganic pattern termed herein ‘Pseudoembryo’. The taphonomic setting in deeper water with possible strong reducing conditions promoted the excellent preservation for the Markuelia specimens. The study of Markuelia provides not only constraint on the anatomy, affinity, embryonic development and phylogenetic significance of this wormlike animal and but also opens a new window onto the evolution and development of the earliest animals.

Embryo fossilization is a biological process mediated by microbial biofilms

Fossilized embryos with extraordinary cellular preservation appear in the Late Neoproterozoic and Cambrian, coincident with the appearance of animal body fossils. It has been hypothesized that microbial processes are responsible for preservation and mineralization of organic tissues. However, the actions of microbes in preservation of embryos have not been demonstrated experimentally. Here, we show that bacterial biofilms assemble rapidly in dead marine embryos and form remarkable pseudomorphs in which the bacterial biofilm replaces and exquisitely models details of cellular organization and structure. The experimental model was the decay of cleavage stage embryos similar in size and morphology to fossil embryos. The data show that embryo preservation takes place in 3 distinct steps: (i) blockage of autolysis by reducing or anaerobic conditions, (ii) rapid formation of microbial biofilms that consume the embryo but form a replica that retains cell organization and morphology, and (iii) bacterially catalyzed mineralization. Major bacterial taxa in embryo decay biofilms were identified by using 16S rDNA sequencing. Decay processes were similar in different taphonomic conditions, but the composition of bacterial populations depended on specific conditions. Experimental taphonomy generates preservation states similar to those in fossil embryos. The data show how fossilization of soft tissues in sediments can be mediated by bacterial replacement and mineralization, providing a foundation for experimentally creating biofilms from defined microbial species to model fossilization as a biological process.

The internal structure of Early Cambrian fossil embryo Olivooides revealed in the light of Synchrotron X-ray Tomographic Microscopy

Countless fossil embryo Olivooides and the hatched larvae, juveniles and adults (the latter two kinds are Punctatus) are recovered by means of acid maceration from the fine-crystalline to medium-crystalline phosphatic limestone and phosphatic micrite of Early Cambrian Kuanchuanpu Formation at the Shizhonggou section, near Kuanchuanpu Village, Ningqiang County, Shaanxi Province, China. Using the technique of Synchrotron X-ray Tomographic Microscopy, the 3D internal structure of Olivooides and Punctatus is reconstructed. The morphological and statistic analyses are also given to the stellae structure of Olivooides and Punctatus, which indicates that this structure is a result of adaptive evolution to a lifestyle of fast-attaching after hatching, probably with the function of mucilage secretion. The internal structure of Punctatus is described and discussed. The ovum-like structure, a common internal feature of Punctatus, is considered as the taphonomic structure, rather than eggs or other biological structure. This structure is thought to be formed after the burial of the animal and before or during the mineralization. The original internal structure of Punctatus is assumed to be tabulae-filled, with soft body grown on them.

Deciphering the fossil record of early bilaterian embryonic development in light of experimental taphonomy

Experimental analyses of decay in a tunicate deuterostome and three lophotrochozoans indicate that the controls on decay and preservation of embryos, identified previously based on echinoids, are more generally applicable. Four stages of decay are identified regardless of the environment of death and decay. Embryos decay rapidly in oxic and anoxic conditions, although the gross morphology of embryos is maintained for longer under anoxic conditions. Under anoxic reducing conditions, the gross morphology of the embryos is maintained for the longest period of time, compatible with the timescale required for bacterially mediated mineralization of soft tissues. All four stages of decay were encountered under all environmental conditions, matching the spectrum of preservational qualities encountered in all fossil embryo assemblages. The preservation potential of embryos of deuterostomes and lophotrochozoans is at odds with the lack of such embryos in the fossil record. Rather, the fossil record of embryos, as sparse as it is, is dominated by forms interpreted as ecdysozoans, cnidarians, and stem-metazoans. The dearth of deuterostome and lophotrochozoan embryos may be explained by the fact that ecdysozoans, at least, tend to deposit their eggs in the sediment rather than through broadcast spawning. However, fossil embryos remain very rare and the main controlling factor on their fossilization may be the unique conspiracy of environmental conditions at a couple of sites. The preponderance of fossilized embryos of direct developers should not be used in evidence against the existence of indirect development at this time in animal evolutionary history.

Yolk

Yolk

Earliest Cambrian fossil embryos and their fossilization processes and paleoceanographic background

Earliest Cambrian fossil embryos and their fossilization processes and paleoceanographic background

Ca isotopic compositions of dolomite, phosphorite and the oldest animal embryo fossils from the Neoproterozoic in Weng'an, South China

Deciphering the drastic changes of surface environment and the emergence of animals after the Neoproterozoic Snowball Earth event are important for understanding the changes of surface environment and its influence on the evolution of life through geologic time. Especially, the emergence of two types of Metazoan animals such as animal embryo fossils, cnidarians or sponges, and Ediacaran fauna in the late Neoproterozoic was one of the critical turning points in the biological evolution. Calcium is one of the essential elements for the growth of most animals. In this study, in order to evaluate the Ca cycles in the Neoproterozoic, we have measured Ca isotopic ratios ( 44Ca/ 42Ca and 43Ca/ 42Ca) for phosphorite, dolostone and phosphatic animal embryo fossils with a multiple collector, inductively coupled plasma-mass spectrometer (MC-ICP-MS). The resulting 44Ca/ 42Ca ratio defined by the relative deviation from the ratio of NIST SRM915a ( δ 44/42Ca NIST915) for phosphorite and dolostone ranges from 0.83 to 0.95‰, demonstrating that the fractionation between phosphorite/dolostone and seawater was very small. This evidence indicates that at the emergence of the Weng'an biota seawater was deficient in Ca probably due to mass deposition of phosphorite/dolostone and to the beginning of Ca-biomineralization. Three phosphatic animal embryo fossils have lower δ 44/42Ca values than the phosphorite and dolomite, implying that the precursor of the phosphatic embryo fossils was able to fractionate Ca isotopes through Ca-biomineralization, consistent with marine gastropods.

The earliest fossil embryos begin to mature

Evolution & DevelopmentVolume 9, Issue 3 p. 206-207 The earliest fossil embryos begin to mature Neil J. Gostling, Corresponding Author Neil J. Gostling Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK*Author for correspondence (email: [email protected])Search for more papers by this authorPhilip C. J. Donoghue, Philip C. J. Donoghue Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UKSearch for more papers by this authorStefan Bengtson, Stefan Bengtson Department of Palaeozoology, Swedish Museum of Natural History, Stockholm SE 104 05, SwedenSearch for more papers by this author Neil J. Gostling, Corresponding Author Neil J. Gostling Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK*Author for correspondence (email: [email protected])Search for more papers by this authorPhilip C. J. Donoghue, Philip C. J. Donoghue Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UKSearch for more papers by this authorStefan Bengtson, Stefan Bengtson Department of Palaeozoology, Swedish Museum of Natural History, Stockholm SE 104 05, SwedenSearch for more papers by this author First published: 09 May 2007 https://doi.org/10.1111/j.1525-142X.2007.00152.xCitations: 5Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article.Citing Literature Volume9, Issue3May/June 2007Pages 206-207 RelatedInformation

Application of Atomic Force Microscopy on Observing the Ultra‐Fine Structure of the Neoproterozoic Microfossils from China

Phosphatic microfossils from the Doushantuo Formation, Guizhou, China, have been reported with preserved cellular structure or even sub-cellular structure in micron scale. However, more details in sub-micro scale have not been reported as having been found. The Fossil embryos from the acid residue of the phosphorite rocks of the Neoproterozoic Doushantuo Formation in south China have been studied with a scanning electron microscope (SEM) and an atomic force microscope (AFM). Some ultra-structures in sub-micro scale have been found by AFM on the surface of the fossil embryos. There are four types of structures found on the surface of the selected fossil embryos, the sizes of which vary from 30 to 645 nm in diameter under our AFM. One of the structures is composed of several big sub-units integrated with each other, and the size of the big sub-units is from 250 to 645 nm. Meanwhile, we also found an ultra-layer structure on the surface of the big sub-units, the thickness of which was about 10 nm. Thus we speculate that it could most probably be of biological origin. Therefore, AFM provides a new method for direct observation of the ultra-structure of the Doushantuo fossils in the sub-micro scale.