Three-dimensional Preservation Research Articles

A confuciusornithiform (Aves, Pygostylia)-like tarsometatarsus from the Early Cretaceous of Siberia and a discussion of the evolution of avian hind limb musculature

ABSTRACTWe describe a new isolated tarsometatarsus from the Early Cretaceous (Barremian-Aptian) Ilek Formation Shestakovo-3 locality in western Siberia. The new specimen represents a new taxon, Evgenavis nobilis, gen. et sp. nov., significantly increasing the Mesozoic avifauna from Russia. The specimen shares morphologies with a number of basal ornithothoracine taxa, but shows most similarity to the basal pygostylian Confuciusornis sanctus, the oldest known beaked bird and most common taxon from the Yixian Formation. Evgenavis may represent the first record of Confuciusornithiformes outside of the Jehol Group and its equivalent deposits. However, this is not supported by cladistic analysis, which weakly resolves the new species and Mystiornis both within the diverse Enantiornithes, indicating that additional material is required to assess the systematic position of Evgenavis nobilis (Aves incertae sedis). The three-dimensional preservation of the specimen allows for a partial reconstruction of the pedal musculature, revealing a primitive stage in the evolution of the neornithine condition.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at http://www.tandfonline.com/UJVP.

Plant inclusions from the Cenomanian flints of Archingeay, Les Nouillers, western France

Here, we report flint nodules bearing fossil plant inclusions from the early Cenomanian of the Font-de-Benon sand quarry, between the villages of Archingeay and Les Nouillers, Charente-Maritime, western France. The broken-open surfaces of these dense siliceous rocks only partly show the whole diversity, which is established using a non-destructive, multi-scale approach based on propagation phase-contrast X-ray synchrotron microtomography. The conifer genera Brachyphyllum, Frenelopsis, Geinitzia, and Glenrosa have three-dimensional preservation, and vegetative and reproductive organs are in connection in some cases. The flint nodules formed by silicification of Cenomanian sediments, probably as a result of an intensive period of soil alteration and leaching under warm and wet climate during the Eocene. Although the time was long between the Cenomanian sedimentation and the Eocene silicification, the fossil plants show three-dimensional external morphology. These mineralizations are interpreted as fine silica microcrystallization over the cell walls and thus are examples of late silica permineralization. The association of foraminifers, echinoids, sponge spicules, and conifers suggests that the Cenomanian sediments were deposited in a coastal and open to the sea palaeoenvironment, near a conifer-dominated mangrove.

A snapshot into the terrestrial ecosystem of an exceptionally well-preserved dinosaur (Hadrosauridae) from the Upper Cretaceous of North Dakota, USA

A palynological investigation of sedimentary rocks enclosing an exceptionally well-preserved fossil dinosaur (Hadrosauridae) discovered in the upper part of the Hell Creek Formation in south western North Dakota was conducted in order to document the immediate paleoenvironment of this dinosaur. The specimen, an Edmontosaurus annectens is remarkable in having exceptional three-dimensional preservation of soft tissue around the skeleton, indicating rapid burial. A well-preserved palynological assemblage dominated by fern and bryophyte spores, with lesser gymnosperm and angiosperm pollen was recovered. Sparse fresh-water algae and marine dinoflagellate cysts were also recorded. The palynofacies is dominated by wood fragments, including charcoal, with little amorphous organic matter. The presence of some typical pollen taxa of the Wodehouseia spinata Assemblage Zone including Striatellipollis striatellus, Tricolpites microreticulatus, Leptopecopites pocockii as well as a diverse suite of Aquilapollenites, is fully consistent with a Late Cretaceous (late Maastrichtian) age. The palynoflora indicates a local vegetation composed of a canopy of conifers dominated by Pinaceae and a minor sub-canopy of Taxodium and cycads, as well as an understory of hydrophilous ferns, mosses and herbaceous angiosperms, indicative of a warm and humid climate – an environment where this specific hadrosaur roamed over 66 million years ago.

Aspects of clavate borings in the type Maastrichtian (Upper Cretaceous) of the Netherlands and Belgium

We describe a collection of borings in carbonate and xylic substrates (Gastrochaenolites ispp., Teredolites longissimus Kelly & Bromley), some of them containing their producers, from the Maastricht and Houthem formations (late Maastrichtian and early Danian) in the type area of the Maastrichtian Stage, but mainly from the ENCI-HeidelbergCement Group quarry, St. Pietersberg (southern Limburg, the Netherlands). Included are specimens of Gastrochaenolites dijugus Kelly & Bromley, showing different modes of formation of the figure-of-eight aperture, either as part of the lining, incorporating the substrate or both. Gastrochaenolites lapidicus Kelly & Bromley was produced by the gastrochaenid bivalve Gastrochaena, whereas G. orbicularis Kelly & Bromley is the trace of Jouannetia supracretacea (De Ryckholt). Bioglyph-like infills of G. orbicularis and G. torpedo Kelly & Bromley rather represent external moulds of the producing bivalves; they are termed pseudobioglyphs herein. Teredolites longissimus is preserved as clusters of in situ, parallel to sub-parallel tubes, although the woody substrate has decayed, and disarticulated fragments of calcareous tubes have been released from rotten wood. The latter include some specimens filled by flint and show good three-dimensional preservation. Some notes on the taxonomy of the producing bivalve taxa are added.

Characterization of the stem anatomy of the Eocene fern Dennstaedtiopsis aerenchymata (Dennstaedtiaceae) by use of confocal laser scanning microscopy

Permineralization provides the most faithful known mode of three-dimensional preservation of the morphology and cellular anatomy of fossil plants. Standard optical microscopic documentation of such structures can provide only an approximation of their true three-dimensional form and is incapable of revealing fine-structural (<300 nm) details, deficiencies that can be addressed by the use of confocal laser scanning microscopy (CLSM). To demonstrate the usefulness of CLSM in such studies, we compare confocal laser scanning micrographs and optical photomicrographs of the permineralized tissues of rhizomes and petioles of the Eocene fern Dennstaedtiopsis aerenchymata preserved in cherts of the Clarno Formation of Oregon, USA, and the Allenby Formation (Princeton chert) of British Columbia, Canada. The laser-induced fluorescence detected by CLSM produces crisp high-resolution images of the three-dimensionally permineralized tissues of Dennstaedtiopsis aerenchymata. Tissues analyzed include the epidermis and epidermal hairs, cortex, aerenchyma, endodermis, vascular tissue, and pith-for each of which, CLSM yields results superior to those of standard optical microscopy. CLSM and previous Raman spectroscopic analyses of the same specimens provide evidence consistent with original biochemistry. Use of CLSM to characterize the morphology and cellular anatomy of permineralized fossil plants can provide accurate data in two and three dimensions at high spatial resolution, information that can be critically important to taxonomic, taphonomic, and developmental interpretations. Results presented here from this first detailed CLSM-based study of permineralized plant axes indicate that this nonintrusive, nondestructive technique should be widely applicable in paleobotany.

Osteological redescription of the skull ofMicrocleidus homalospondylus(Sauropterygia, Plesiosauria) from the Lower Jurassic of England

The plesiosaur specimen NHMUK 36184 from the Lower Jurassic of Whitby, Yorkshire and kept in the Natural History Museum of London, comprises an almost entire skeleton with nearly complete skull. It was described as one of two syntypes ofPlesiosaurus homalospondylusby Owen, and selected as the lectotype by Lydekker. Extensive preparation of the skull has revealed it as one of the most complete and best-preserved Jurassic plesiosaurian skulls known, and its description adds much-needed data to our knowledge of the cranial osteology of the Plesiosauria. The three-dimensional preservation permits a relatively reliable reconstruction of its form.Microcleidus homalospondylusdisplays an interesting combination of cranial characters present in Jurassic plesiosauroids and Cretaceous Elasmosauridea. Its snout presents a very distinctive sculpture; the first pair of premaxillae teeth are extremely reduced; the frontal is partially overlain by the premaxillae, contacts the pineal foramen but does not contact the temporal fenestra; the jugal does not contact the orbit nor the temporal fenestra; the squamosal contacts the postorbital but not the maxilla and presents a bulb; the postfrontal contacts the posterolateral orbit margin; the anterior interpterygoid vacuity is absent; the pterygoids meet posterior to the posterior interpterygoid vacuities and are pierced by a foramen at this level; the quadrate ramus of the pterygoid presents a ventromedial flange; the parasphenoid is crested; the epipterygoid contacts the parietal; the paroccipital process is spatulate distally; the prootic presents an anteroventral process; the mandibular symphysis is keeled and bears four pairs of teeth.Microcleidusappears very similar toHydrorionandOccitanosaurus, and the three taxa share a great number of plesiomorphic characters with basal plesiosaurians and pliosauroids.

Exceptional three-dimensional preservation and coloration of an originally iridescent fossil feather from the Middle Eocene Messel Oil Shale

A feather from the Eocene Messel Formation, Germany, has been demonstrated to have been originally structurally colored by densely packed sheets of melanosomes similar to modern iridescent feathers exhibiting thin-film diffraction. The fossil itself currently exhibits a silvery sheen, but the mechanism for generating this optical effect was not fully understood. Here we use scanning electron microscopy, electron probe microanalysis, and dual-beam focused ion beam scanning electron microscopy to investigate the source of the silvery sheen that occurs in the apical feather barbules. Focused ion beam scanning electron microscopy provides a powerful tool for studying three-dimensionality of nanostructures in fossils. Use of the method reveals that the flattened apical barbules are preserved almost perfectly, including smooth structural melanosome sheets on the obverse surface of the fossil feather that are identical to those that cause iridescence in modern bird feathers. Most of each apical barbule is preserved beneath a thin layer of sediment. The silvery sheen is generated by incoherent light diffraction between this sediment layer and melanosomes and, although related to the original iridescence of the feather, is not a feature of the feather itself. The reddish and greenish hues frequently exhibited by fossil feathers from the Messel Formation appear to be due to precipitates on the surface of individual melanosomes.

Controls on Gut Phosphatisation: The Trilobites from the Weeks Formation Lagerstätte (Cambrian; Utah)

Despite being internal organs, digestive structures are frequently preserved in Cambrian Lagerstätten. However, the reasons for their fossilisation and their biological implications remain to be thoroughly explored. This is particularly true with arthropods – typically the most diverse fossilised organisms in Cambrian ecosystems – where digestive structures represent an as-yet underexploited alternative to appendage morphology for inferences on their biology. Here we describe the phosphatised digestive structures of three trilobite species from the Cambrian Weeks Formation Lagerstätte (Utah). Their exquisite, three-dimensional preservation reveals unique details on trilobite internal anatomy, such as the position of the mouth and the absence of a differentiated crop. In addition, the presence of paired pygidial organs of an unknown function is reported for the first time. This exceptional material enables exploration of the relationships between gut phosphatisation and the biology of organisms. Indeed, soft-tissue preservation is unusual in these fossils as it is restricted to the digestive structures, which indicates that the gut played a central role in its own phosphatisation. We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus. The fact that gut phosphatization has almost exclusively been observed in arthropods could be explained by their uncommon ability to store ions (including phosphorous) in their digestive tissues. However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods. We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace.

Preservational modes in the Ediacaran Gaojiashan Lagerstätte: Pyritization, aluminosilicification, and carbonaceous compression

Burgess Shale-type (BST) fossils often are preserved as two-dimensional carbonaceous compressions, sometimes aided by two mineralization processes: pyritization and aluminosilicification, defined by a thin and sometimes localized coating of authigenic pyrite or aluminosilicate minerals on the carbonaceous materials. Here we report similar mineralization modes within the late Ediacaran Gaojiashan Lagerstätte of southern Shaanxi Province, South China. Examination of two common Gaojiashan fossils, Conotubus hemiannulatus and Gaojiashania cyclus (hereafter referred by generic names only), indicates that pervasive pyritization is the primary taphonomic pathway in this deposit, responsible for the preservation of ~80% of the collected fossils. Pervasive pyritization of Gaojiashan fossils results in their three-dimensional preservation, as opposed to two-dimensional carbonaceous compression with thin pyrite coatings seen in some BST Lagerstätte. However, microscale investigation using environmental scanning electron microscopy (ESEM) and energy dispersive X-ray spectroscopy (EDS) shows that some flattened specimens of Conotubus and Gaojiashania are preserved as carbonaceous compressions, which are in some cases associated with aluminosilicate minerals. Rare compressed specimens of Conotubus are replicated by greenish clay minerals, which are interpreted as diagenetic products of aluminosilicate precursors. Our taphonomic analysis shows that pervasive authigenic pyritization tends to replicate more labile tissues than aluminosilicate-aided carbonaceous compression, but both pyritization and aluminosilicification processes can facilitate the replication and preservation of soft-bodied organisms in siliciclastic sediments. Building upon this conclusion, we propose that multiple taphonomic processes, including kerogenization (or polymerization of organic molecules), pyritization, and aluminosilicification, can contribute to the mode of BST preservation. Viewed in this light, various siliciclastic-hosted Lagerstätten that are facilitated by kerogenization, pyritization, and aluminosilicification can be plotted on a ternary diagram based on the relative importance of these taphonomic processes.

From tree to shining sea: taphonomy of the arboreal lizard Geiseltaliellus maarius from Messel, Germany

Much has been written about the palaeoenvironment of the middle Eocene fossil Lagerstatte of Messel, Germany, and of the taphonomy of the vertebrates found in it, but taphonomic phenomena among the reptiles in this locality are virtually unstudied. The iguanid Geiseltaliellus maarius is the most common lizard species in Messel. We present taphonomic data for this species and analyse it. Specimens of G. maarius can be divided into three preservation classes, one of which is distinguished purely by decompositional phenomena. Most specimens sank quickly to the bottom of Lake Messel after entering it, but one floated for some time prior to emplacement. In theory, overlying pressure should not preclude the accumulation of gases of decay in submerged carcasses. In one specimen, such gases appear to have built up intracoelomically for many weeks, but did not cause the carcass to rise because of overlying water pressure. Eruption of the gases through the oral and cloacal openings, possibly initiated by a coincident turbidity current, scattered the bones of the skull, the pelvic region, and the proximal part of the tail. G. maarius had evolved a form of intervertebral urotomy (pseudoautotomy), which is indicative of arboreal habits. The waxy substance adipocere, formed after breakdown of fat, has been neglected in discussions of taphonomy, but may constitute an important factor in stabilising carcasses and enabling three-dimensional preservation before diagensis.

A diverse terrestrial fauna in the Pleistocene of Jamaica: the treasures of the Red Hills Road Cave

The thick and widespread limestones of Jamaica include many hundreds of caves of all shapes and sizes. The Red Hills Road Cave, near Kingston, is unusual for the richness of its included tetrapods and gastropods, and the exceptional, three-dimensional preservation of terrestrial arthropods such as millipedes. This diverse assemblage consists mainly of a forest fauna that was washed into a bottle-shaped cave, either alive or as carcasses, during tropical storms and hurricanes about 30 000 years ago.

Microorganism-mediated preservation of Planolites, a common trace fossil from the Harkless Formation, Cambrian of Nevada, USA

Specimens of Planolites, a tubular ichnofossil, from the Harkless Formation (Cambrian of Nevada) are commonly rimmed by thin layers of limonite, a probable pseudomorph after pyrite, suggesting that bacterially induced biomineralization played a key role in the preservation of the burrows. Organic material secreted by a vermiform, infaunal tracemaker is inferred to have formed the substrate for a biofilm that facilitated iron sulfide biomineralization by bacteria under localized anaerobic or dysaerobic conditions. Rapid, microbially mediated biomineralization of mucus-lined burrow walls is inferred to have promoted three-dimensional preservation of burrows by strengthening them against sediment compaction, and possibly providing sufficient support for burrows to allow time for sediment infill. Decomposition of organic materials in Planolites also left evidence in sediment layers immediately above the burrows: undulose sediment surfaces and small, round, pimpleform gas escape structures.

A new, three-dimensionally preserved enantiornithine bird (Aves: Ornithothoraces) from Gansu Province, north-western China

In recent years, the Lower Cretaceous (Aptian) Xiagou Formation has yielded approximately 100 avian partial skeletons, many with soft-tissue traces, from sites in the Changma Basin of Gansu Province, north-western China. The most abundant taxon amongst these is the ornithuromorph Gansus yumenensis, but enantiornithines have also been identified in the sample. Here we describe two incomplete, semi-articulated appendicular skeletons, the first consisting of a partial left pelvic girdle and complete pelvic limb, and the second comprised of a nearly complete right pelvic limb. Both specimens bear characteristics diagnostic of Enantiornithes, and are referred to a new taxon, Qiliania graffinigen. et sp. nov. The exceptional, three-dimensional preservation of these specimens (compared to the crushed, nearly two-dimensional condition of most other Early Cretaceous avian fossils) reveals new information regarding enantiornithine anatomy, evolution, and diversity. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162, 201–219.

Earth’s earliest non-marine eukaryotes

The existence of a terrestrial Precambrian (more than 542 Myr ago) biota has been largely inferred from indirect chemical and geological evidence associated with palaeosols, the weathering of clay minerals and microbially induced sedimentary structures in siliciclastic sediments. Direct evidence of fossils within rocks of non-marine origin in the Precambrian is exceedingly rare. The most widely cited example comprises a single report of morphologically simple mineralized tubes and spheres interpreted as cyanobacteria, obtained from 1,200-Myr-old palaeokarst in Arizona. Organic-walled microfossils were first described from the non-marine Torridonian (1.2-1.0 Gyr ago) sequence of northwest Scotland in 1907. Subsequent studies found few distinctive taxa-a century later, the Torridonian microflora is still being characterized as primarily nondescript "leiospheres". We have comprehensively sampled grey shales and phosphatic nodules throughout the Torridonian sequence. Here we report the recovery of large populations of diverse organic-walled microfossils extracted by acid maceration, complemented by studies using thin sections of phosphatic nodules that yield exceptionally detailed three-dimensional preservation. These assemblages contain multicellular structures, complex-walled cysts, asymmetric organic structures, and dorsiventral, compressed organic thalli, some approaching one millimetre in diameter. They offer direct evidence of eukaryotes living in freshwater aquatic and subaerially exposed habitats during the Proterozoic era. The apparent dominance of eukaryotes in non-marine settings by 1 Gyr ago indicates that eukaryotic evolution on land may have commenced far earlier than previously thought.

CAMBRIAN ORSTEN LAGERSTATTE FROM THE ALUM SHALE FORMATION: FECAL PELLETS AS A PROBABLE SOURCE OF PHOSPHORUS PRESERVATION

The Furongian Orsten-type fossil Lagerstatte in the Alum Shale Formation of Sweden is an extraordinary deposit known for its detailed, three-dimensional preservation of the soft parts of small animal carcasses which have been replaced by calcium phosphate and occur in organic-rich nodular limestone. The exact cause and mechanism of this unusual fossil preservation, however, particularly the source of phosphorus, which plays a key role, remains unknown. Detailed observation in the Agnostus pisiformis Zone in the Backeborg section (Kinnekulle district) reveals that the phosphatocopine crustaceans showing soft-part preservation occur only in a few thin (<3 cm) layers containing abundant fecal pellets (pellet beds). Development of cross lamination suggests that the pellet beds were formed by low density sediment-gravity flow. Orsten-type preservation has been attributed to high phosphate levels in global marine waters during the Cambrian period; however, wavelength-dispersive X-ray and X-ray diffractometry analyses reveal that the Orsten limestones and surrounding shale were generally poor in phosphorus, which was mostly concentrated in the fecal pellets. The small animal carcasses preserved in such deposits were phosphatized during early diagenesis owing to the high local phosphorus levels of the accumulated fecal pellets. Searches for such cesspool-type preservation may yield further discoveries of Orsten-type fossil Lagerstatten in other strata of various ages.

NEW PTEROSAUR SPECIMENS FROM THE KEM KEM BEDS (UPPER CRETACEOUS, CENOMANIAN) OF MOROCCO

Although pterosaurs from Africa are still rare, in recent years several specimens have been described from the Kem Kem beds (Upper Cretaceous, Cenomanian) of Morocco. Here we describe four additional specimens from this informal lithostratigraphic unit: a jaw fragment, two mid-cervical vertebrae, and a humerus. All these specimens show three-dimensional preservation, differing much from the flat condition found in most pterosaur material. The vertebrae are particularly well preserved, and allow accurate observations on the pneumatization of the neural arch. Based on comparable material, we show that at least two edentulous pterosaur species were present in this informal lithostratigraphic unit, thus adding to the growing evidence of considerable pterosaur diversity in northwestern Africa during the middle Cretaceous. So far, the Kem Kem beds have the most diverse pterosaur fauna in this continent, with the presence of anhanguerids, azhdarchids, pteranodontids, and tapejarids.

Possible link connecting reptilian scales with avian feathers from the early Late Jurassic of Kazakstan

Organic tissue of a recently found second specimen of feather-like Praeornis from the Karabastau Formation of the Great Karatau Range in southern Kazakstan, has a stable carbon isotope composition indicative of its animal affinity. Three-dimensional preservation of its robust carbonised shaft indicates original high contents of sclerotic organic matter, which makes the originally proposed interpretation of Praeornis as a keratinous integumental structure likely. The new specimen is similar to the holotype of Praeornis in the presence of three ‘vanes’ on a massive shaft not decreasing in width up to near its tip. Unlike it, the vanes are not subdivided into barbs and the pennate structure is expressed only in the distribution of organic-matter-rich rays. Similar continuous blades border the ‘barbs’ in the holotype, but the organic matter was removed from them by weathering. It is proposed that the three-vaned structure is a remnant of the ancestral location of scales along the dorsum and their original function in sexual display, similar to that proposed for the Late Triassic probable megalancosaurid Longisquama. Perhaps subsequent rotation around the shaft, in the course of evolution from an ancestral status similar to Praeornis towards the present aerodynamic and protective function of feathers, resulted in the tubular appearance of their buds.

The Late Devonian Gogo Formation Lägerstatte of Western Australia: Exceptional Early Vertebrate Preservation and Diversity

The Gogo Formation of Western Australia preserves a unique Late Devonian (Frasnian) reef fauna. The exceptional three-dimensional preservation of macrofossils combined with unprecedented soft-tissue preservation (including muscle bundles, nerve cells, and umbilical structures) has yielded a particularly rich assemblage with almost 50 species of fishes described. The most significant discoveries have contributed to resolving placoderm phylogeny and elucidating their reproductive physiology. Specifically, these discoveries have produced data on the oldest known vertebrate embryos; the anatomy of the primitive actinopterygian neurocranium and phylogeny of the earliest actinopterygians; the histology, radiation, and plasticity of dipnoan (lungfish) dental and cranial structures; the anatomy and functional morphology of the extinct onychodonts; and the anatomy of the primitive tetrapodomorph head and pectoral fin.

SILICIFICATION OF HIGHER PLANTS IN GEOTHERMALLY INFLUENCED WETLANDS: YELLOWSTONE AS A LOWER DEVONIAN RHYNIE ANALOG

Silicification of higher plants associated with active, alkali-chloride hot springs in Yellowstone National Park, Wyoming, USA, occurs dominantly in areas of geothermally influenced wetlands. Plants grow in an environment with many of the characteristics of an oligosaline marsh and are subjected to brackish salinity and high pH, temperature, silica, and heavy metal concentrations. As such, the plants undergoing silicification at Yellowstone are predominantly those more typically found colonizing widespread evaporation-driven inland waters and coastal salt marshes (e.g., Eleocharis rostellata, Triglochin maritimum) and are in some ways preadapted to hot-spring settings. This paper documents hydrochemistry and physical parameters in a typical geothermally influenced wetland at Big Blue Hot Spring, Elk Park in Yellowstone and records the taphonomic processes involved in silicification of the most common wetland plant Eleocharis rostellata. Silicification of plants in situ results in the three-dimensional preservation of tissues and cells characteristic of plants preserved around the Lower Devonian Rhynie chert hot-spring system. Sinter deposition at active and fossil hot-spring areas is typically associated with alkali-chloride springs above low-sulfidation epithermal systems. As mineralogical and geological evidence indicates that such a system was responsible for preservation of the Rhynie plants, it is hypothesized that they too, at least periodically, withstood comparable physiological stresses to the modern analogs.

Reconstructing a lost world: Ediacaran rangeomorphs from Spaniard's Bay, Newfoundland

Ediacaran fronds at Spaniard's Bay on the Avalon Peninsula of Newfoundland exhibit exquisite, three-dimensional preservation with morphological features less than 0.05 mm in width visible on the best preserved specimens. Most of the nearly 100 specimens are juvenile rangeomorphs, an extinct Ediacaran clade that numerically dominated the early evolution of complex multicellular life. Spaniard's Bay rangeomorphs are characterized by cm-scale architectural elements exhibiting self-similar branching over several fractal scales that were used as modules in construction of larger structures. Four taxa of rangeomorph fronds are present – Avalofractus abaculus n. gen. et sp., Beothukis mistakensis Brasier and Antcliffe, Trepassia wardae (Narbonne and Gehling), and Charnia cf. C. masoni Ford. All of these taxa exhibit an alternate array of primary rangeomorph branches that pass off a central stalk or furrow that marks the midline of the petalodium. Avalofractus is remarkably self similar over at least four fractal scales, with each scale represented by double-sided rangeomorph elements that were constrained only at their attachment point with the higher-order branch and thus were free to rotate and pivot relative to other branches. Beothukis is similar in organization, but its primary branches show only one side of a typical rangeomorph element, probably due to longitudinal branch folding, and the position of the individual branches was moderately constrained. Trepassia shows only single-sided branches with both primary and secondary branches emanating from a central stalk or furrow; primary branches were capable of minor pivoting as reflected in bundles of secondary branches. Charnia shows only single-sided primary branches that branch from a zigzag central furrow and that were firmly constrained relative to each. This sequence provides a developmental linkage between Rangea-type and Charnia-type rangeomorphs. Avalonian assemblages show a wide array of rangeomorph constructions, but later Ediacaran assemblages contain a lower diversity of rangeomorphs represented mainly by well-constrained forms.