scholarly journals Discovery of the oldest bilaterian from the Ediacaran of South Australia

2020 ◽  
Vol 117 (14) ◽  
pp. 7845-7850 ◽  
Author(s):  
Scott D. Evans ◽  
Ian V. Hughes ◽  
James G. Gehling ◽  
Mary L. Droser
Keyword(s):  
Fossil Record ◽  
Common Ancestor ◽  
South Australia ◽  
Trace Fossils ◽  
Last Common Ancestor ◽  
Ediacara Biota ◽  
Size And Morphology ◽  
Animal Communities ◽  
Critical Link ◽  
Anterior Posterior

Analysis of modern animals and Ediacaran trace fossils predicts that the oldest bilaterians were simple and small. Such organisms would be difficult to recognize in the fossil record, but should have been part of the Ediacara Biota, the earliest preserved macroscopic, complex animal communities. Here, we describeIkaria wariootiagen. et sp. nov. from the Ediacara Member, South Australia, a small, simple organism with anterior/posterior differentiation. We find that the size and morphology ofIkariamatch predictions for the progenitor of the trace fossilHelminthoidichnites—indicative of mobility and sediment displacement. In the Ediacara Member,Helminthoidichnitesoccurs stratigraphically below classic Ediacara body fossils. Together, these suggest thatIkariarepresents one of the oldest total group bilaterians identified from South Australia, with little deviation from the characters predicted for their last common ancestor. Further, these trace fossils persist into the Phanerozoic, providing a critical link between Ediacaran and Cambrian animals.

scholarly journals Spinopelvic pathways to bipedality: why no hominids ever relied on a bent-hip–bent-knee gait

2010 ◽  
Vol 365 (1556) ◽  
pp. 3289-3299 ◽  
Author(s):  
C. Owen Lovejoy ◽  
Melanie A. McCollum
Keyword(s):  
Fossil Record ◽  
Vertebral Column ◽  
Common Ancestor ◽  
Last Common Ancestor ◽  
Early Hominid ◽  
African Apes ◽  
Locomotor Pattern

Until recently, the last common ancestor of African apes and humans was presumed to resemble living chimpanzees and bonobos. This was frequently extended to their locomotor pattern leading to the presumption that knuckle-walking was a likely ancestral pattern, requiring bipedality to have emerged as a modification of their bent-hip-bent-knee gait used during erect walking. Research on the development and anatomy of the vertebral column, coupled with new revelations from the fossil record (in particular, Ardipithecus ramidus ), now demonstrate that these presumptions have been in error. Reassessment of the potential pathway to early hominid bipedality now reveals an entirely novel sequence of likely morphological events leading to the emergence of upright walking.

scholarly journals An early Cambrian polyp reveals an anemone-like ancestor for medusozoan cnidarians

2021 ◽  
Author(s):  
Yang Zhao ◽  
Luke Parry ◽  
Jakob Vinther ◽  
Frances S. Dunn ◽  
Yujing Li ◽  
...  
Keyword(s):  
Phylogenetic Analysis ◽  
Fossil Record ◽  
Soft Tissues ◽  
Common Ancestor ◽  
Last Common Ancestor ◽  
Early Cambrian ◽  
Crown Group ◽  
Sessile Polyp ◽  
Animal Evolution ◽  
Chengjiang Biota

Extant cnidarians are a disparate phylum of non-bilaterians and their diploblastic body plan represents a key step in animal evolution. Anthozoans (anemones, corals) are benthic polyps, while adult medusozoans (jellyfishes) are dominantly pelagic medusae. A sessile polyp is present in both groups and is widely conceived as the ancestral form of their last common ancestor. However, the nature and anatomy of this ancestral polyp, particularly of medusozoans, are controversial, owing to the divergent body plans of both groups in the extant lineages and the rarity of medusozoan soft tissues in the fossil record. Here we redescribe the enigmatic Conicula striata Luo et Hu from the early Cambrian Chengjiang biota, south China, which has previously been interpreted as a polyp, lophophorate or deuterostome. We show that C. striata possessed features of both anthozoans and medusozoans. Its stalked polyp and fully encasing conical, annulated organic skeleton (periderm) are features of medusozoans. However, the gut is partitioned by ~28 mesenteries, and has a tubular pharynx, resembling anthozoans. Our phylogenetic analysis recovers C. striata as a stem medusozoan, indicating that the enormously diverse medusozoans were derived from an anemone-like ancestor, with the pharynx lost and number of mesenteries reduced prior to the origin of crown group Medusozoa.

Problematica, trace fossils, and tubes within the Ediacara Member (South Australia): redefining the ediacaran trace fossil record one tube at a time

2011 ◽  
Vol 85 (2) ◽  
pp. 256-265 ◽  
Author(s):  
Aaron Sappenfield ◽  
Mary L. Droser ◽  
James G. Gehling
Keyword(s):  
Fossil Record ◽  
South Australia ◽  
Trace Fossils ◽  
Information Structures ◽  
Common Component ◽  
The Past ◽  
Morphological Criteria ◽  
New Perspective ◽  
Body Fossil ◽  
Hand Sample

Ediacaran trace fossils are becoming an increasingly less common component of the total Precambrian fossil record as structures previously interpreted as trace fossils are reinterpreted as body fossils by utilizing qualitative criteria. Two morphotypes, Form E and Form F of Glaessner (1969), interpreted as trace fossils from the Ediacara Member of the Rawnsley Quartzite in South Australia are shown here to be body fossils of a single, previously unidentified tubular constructional morphology formally described herein as Somatohelix sinuosus n. gen. n. sp. S. sinuosus is 2-7 mm wide and 3-14 cm long and is preserved as sinusoidal casts and molds on the base of beds. Well-preserved examples of this fossil preserve distinct body fossil traits such as folding, current alignment, and potential attachment to holdfasts. Nearly 200 specimens of this fossil have been documented from reconstructed bedding surfaces within the Ediacara Member. When viewed in isolated hand sample, many of these specimens resemble ichnofossils. However, the ability to view large quantities of reassembled and successive bedding surfaces within specific outcrops of the Ediacara Member provides a new perspective, revealing that isolated specimens of rectilinear grooves on bed bases are not trace fossils but are poorly preserved specimens of S. sinuosus. Variation in the quality and style of preservation of S. sinuosus on a single surface and the few distinct characteristics preserved within this relatively indistinct fossil also provides the necessary data required to define a taphonomic gradient for this fossil. Armed with this information, structures which have been problematic in the past can now be confidently identified as S. sinuosus based on morphological criteria. This suggests that the original organism that produced this fossil was a widespread and abundant component of the Ediacaran ecosystem.

Ediacara growing pains: modular addition and development in Dickinsonia costata

Paleobiology ◽  
2021 ◽  
pp. 1-16
Author(s):  
Scott D. Evans ◽  
James G. Gehling ◽  
Douglas H. Erwin ◽  
Mary L. Droser
Keyword(s):  
Body Size ◽  
Fossil Record ◽  
South Australia ◽  
Growth Stages ◽  
Genetic Pathways ◽  
Morphogen Gradients ◽  
Ediacara Biota ◽  
Growing Pains ◽  
Competing Hypotheses ◽  
The Relationship

Abstract Constraining patterns of growth using directly observable and quantifiable characteristics can reveal a wealth of information regarding the biology of the Ediacara biota—the oldest macroscopic, complex community-forming organisms in the fossil record. However, these rely on individuals captured at an instant in time at various growth stages, and so different interpretations can be derived from the same material. Here we leverage newly discovered and well-preserved Dickinsonia costata Sprigg, 1947 from South Australia, combined with hundreds of previously described specimens, to test competing hypotheses for the location of module addition. We find considerable variation in the relationship between the total number of modules and body size that cannot be explained solely by expansion and contraction of individuals. Patterns derived assuming new modules differentiated at the anterior result in numerous examples in which the oldest module(s) must decrease in size with overall growth, potentially falsifying this hypothesis. Observed polarity as well as the consistent posterior location of defects and indentations support module formation at this end in D. costata. Regardless, changes in repeated units with growth share similarities with those regulated by morphogen gradients in metazoans today, suggesting that these genetic pathways were operating in Ediacaran animals.

scholarly journals Biostratinomy of the Ediacara Member (Rawnsley Quartzite, South Australia): implications for depositional environments, ecology and biology of Ediacara organisms

2020 ◽  
Vol 10 (4) ◽  
pp. 20190100 ◽  
Author(s):  
Mary L. Droser ◽  
Lidya G. Tarhan ◽  
Scott D. Evans ◽  
Rachel L. Surprenant ◽  
James G. Gehling
Keyword(s):  
Fossil Record ◽  
South Australia ◽  
Depositional Environments ◽  
Bedding Planes ◽  
Ediacara Biota ◽  
National Heritage ◽  
Fossil Site ◽  
Fossil Assemblages ◽  
Multicellular Organisms

The Precambrian Ediacara Biota—Earth's earliest fossil record of communities of macroscopic, multicellular organisms—provides critical insights into the emergence of complex life on our planet. Excavation and reconstruction of nearly 300 m 2 of fossiliferous bedding planes in the Ediacara Member of the Rawnsley Quartzite, at the National Heritage Ediacara fossil site Nilpena in South Australia, have permitted detailed study of the sedimentology, taphonomy and palaeoecology of Ediacara fossil assemblages. Characterization of Ediacara macrofossils and textured organic surfaces at the scale of facies, bedding planes and individual specimens has yielded unprecedented insight into the manner in which the palaeoenvironmental settings inhabited by Ediacara communities—particularly hydrodynamic conditions—influenced the aut- and synecology of Ediacara organisms, as well as the morphology and assemblage composition of Ediacara fossils. Here, we describe the manner in which environmental processes mediated the development of taphofacies hosting Ediacara fossil assemblages. Using two of the most common Ediacara Member fossils, Arborea and Dickinsonia , as examples, we delineate criteria that can be used to distinguish between ecological, environmental and biostratinomic signals and reconstruct how interactions between these processes have distinctively shaped the Ediacara fossil record.

Stretched, mangled, and torn: Responses of the Ediacaran fossil Dickinsonia to variable forces

Geology ◽  
2019 ◽  
Vol 47 (11) ◽  
pp. 1049-1053 ◽  
Author(s):  
Scott D. Evans ◽  
Wei Huang ◽  
Jim G. Gehling ◽  
David Kisailus ◽  
Mary L. Droser
Keyword(s):  
Plastic Deformation ◽  
Fossil Record ◽  
South Australia ◽  
Ediacara Biota ◽  
Evolution Of Life ◽  
Biomechanical Responses ◽  
Biological Characters ◽  
Oxygen Requirements ◽  
Elastic And Plastic Deformation ◽  
Extinct Taxon

Abstract Dickinsonia is one of the oldest macroscopic metazoans in the fossil record. Determining the biological characters of this extinct taxon is critical to our understanding of the early evolution of life. Preservation of abundant specimens from the Ediacara Member (Rawnsley Quartzite), South Australia, in a variety of taphonomic states allows the unparalleled opportunity to compare the biomechanical responses of Dickinsonia tissue to various forces with those typical of modern organisms. Dickinsonia are found as lifted, transported, folded, rolled, ripped, and expanded or contracted individuals, while maintaining diagnostic morphology. This suite of characters indicates that Dickinsonia was composed of material that was flexible, difficult to rip, and capable of elastic and plastic deformation. While none of these traits are diagnostic of a single biomaterial component, we find many similarities with modern biopolymers, particularly collagen, keratin, and elastin. Maintenance of significant relief following complete tearing suggests that Dickinsonia was composed of relatively thick tissues, signifying higher oxygen requirements than previously hypothesized. The ability to be transported and still be preserved as recognizable fossils is unique amongst the Ediacara Biota and demonstrates that Dickinsonia was a taphonomic elite. Combined with discovery in multiple environmental settings, this indicates that the absence of Dickinsonia represents the likely extinction of this organism prior to the Nama assemblage, possibly due to a decrease in the global availability of oxygen in the latest Ediacaran.

Using the fossil record to estimate the age of the last common ancestor of extant primates

Nature ◽  
2002 ◽  
Vol 416 (6882) ◽  
pp. 726-729 ◽  
Author(s):  
Simon Tavaré ◽  
Charles R. Marshall ◽  
Oliver Will ◽  
Christophe Soligo ◽  
Robert D. Martin
Keyword(s):  
Fossil Record ◽  
Common Ancestor ◽  
Last Common Ancestor

Scratch Traces of Large Ediacara Bilaterian Animals

2014 ◽  
Vol 88 (2) ◽  
pp. 284-298 ◽  
Author(s):  
James G. Gehling ◽  
Bruce N. Runnegar ◽  
Mary L. Droser
Keyword(s):  
Fossil Record ◽  
Microbial Mats ◽  
White Sea ◽  
South Australia ◽  
Trace Fossil ◽  
Cambrian Explosion ◽  
The White Sea ◽  
Feeding Patterns ◽  
Fossil Evidence ◽  
Ediacara Biota

Ediacara fan-shaped sets of paired scratchesKimberichnus teruzziifrom the Ediacara Member of the Rawnsley Quartzite, South Australia, and the White Sea region of Russia, represent the earliest known evidence in the fossil record of feeding traces associated with the responsible bilaterian organism. These feeding patterns exclude arthropod makers and point to the systematic feeding excavation of seafloor microbial mats by large bilaterians of molluscan grade. Since the scratch traces were made into microbial mats, animals could crawl over previous traces without disturbing them. The trace maker is identified asKimberella quadrata, whose death masks co-occur with the mat excavation traces in both Russia and South Australia. The co-occurrence of animals and their systematic feeding traces in the record of the Ediacara biota supports previous trace fossil evidence that bilaterians existed globally before the Cambrian explosion of life in the ocean.

scholarly journals Experimental evidence for yawn contagion in orangutans (Pongo pygmaeus)

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Evy van Berlo ◽  
Alejandra P. Díaz-Loyo ◽  
Oscar E. Juárez-Mora ◽  
Mariska E. Kret ◽  
Jorg J. M. Massen
Keyword(s):  
Experimental Evidence ◽  
Common Ancestor ◽  
Great Apes ◽  
Pongo Pygmaeus ◽  
Last Common Ancestor ◽  
Contagious Yawning ◽  
Proximate Mechanism ◽  
Social Species ◽  
Ultimate Causation

AbstractYawning is highly contagious, yet both its proximate mechanism(s) and its ultimate causation remain poorly understood. Scholars have suggested a link between contagious yawning (CY) and sociality due to its appearance in mostly social species. Nevertheless, as findings are inconsistent, CY’s function and evolution remains heavily debated. One way to understand the evolution of CY is by studying it in hominids. Although CY has been found in chimpanzees and bonobos, but is absent in gorillas, data on orangutans are missing despite them being the least social hominid. Orangutans are thus interesting for understanding CY’s phylogeny. Here, we experimentally tested whether orangutans yawn contagiously in response to videos of conspecifics yawning. Furthermore, we investigated whether CY was affected by familiarity with the yawning individual (i.e. a familiar or unfamiliar conspecific and a 3D orangutan avatar). In 700 trials across 8 individuals, we found that orangutans are more likely to yawn in response to yawn videos compared to control videos of conspecifics, but not to yawn videos of the avatar. Interestingly, CY occurred regardless of whether a conspecific was familiar or unfamiliar. We conclude that CY was likely already present in the last common ancestor of humans and great apes, though more converging evidence is needed.

scholarly journals Recombinant transfer in the basic genome ofEscherichia coli

2015 ◽  
Vol 112 (29) ◽  
pp. 9070-9075 ◽  
Author(s):  
Purushottam D. Dixit ◽  
Tin Yau Pang ◽  
F. William Studier ◽  
Sergei Maslov
Keyword(s):  
Common Ancestor ◽  
Recipient Cell ◽  
Gene Clusters ◽  
Selective Advantage ◽  
Last Common Ancestor ◽  
Genome Sequences ◽  
Bacterial Genomes ◽  
Basic Genome ◽  
Single Base Pair ◽  
Generalized Transduction

An approximation to the ∼4-Mbp basic genome shared by 32 strains ofEscherichia colirepresenting six evolutionary groups has been derived and analyzed computationally. A multiple alignment of the 32 complete genome sequences was filtered to remove mobile elements and identify the most reliable ∼90% of the aligned length of each of the resulting 496 basic-genome pairs. Patterns of single base-pair mutations (SNPs) in aligned pairs distinguish clonally inherited regions from regions where either genome has acquired DNA fragments from diverged genomes by homologous recombination since their last common ancestor. Such recombinant transfer is pervasive across the basic genome, mostly between genomes in the same evolutionary group, and generates many unique mosaic patterns. The six least-diverged genome pairs have one or two recombinant transfers of length ∼40–115 kbp (and few if any other transfers), each containing one or more gene clusters known to confer strong selective advantage in some environments. Moderately diverged genome pairs (0.4–1% SNPs) show mosaic patterns of interspersed clonal and recombinant regions of varying lengths throughout the basic genome, whereas more highly diverged pairs within an evolutionary group or pairs between evolutionary groups having >1.3% SNPs have few clonal matches longer than a few kilobase pairs. Many recombinant transfers appear to incorporate fragments of the entering DNA produced by restriction systems of the recipient cell. A simple computational model can closely fit the data. Most recombinant transfers seem likely to be due to generalized transduction by coevolving populations of phages, which could efficiently distribute variability throughout bacterial genomes.

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