Taphonomic Artifact Research Articles

Reassessment of Archaeooides based on new material from the Fortunian (early Cambrian) of China infers algal affinity

Archaeooides originally refers to a group of early Cambrian globular microfossils with regularly arranged nodular surface ornaments, and of a diameter ranging from less than 400 μm to more than 2 mm. The traditional taxonomy assigns all Archaeooides-like microfossils to a single morphotaxon, Archaeooides granulatus, irrespective of their differences in size and surface ornamentation. Archaeooides has been interpreted as a possible diapause embryo because of its inferred palintomical cell division and thick wall with vesicular structures. However, this interpretation needs further testing based on an updated taxonomy and differentiation of taphonomic artifacts from biological structures. Here, we report new, three-dimensionally phosphatized, Archaeooides-like microfossils from the Fortunian of China. In addition to A. granulatus with nodular ornaments, we recognized three new taxa, i.e., Shaanisphaera spinosa gen. et sp. nov. with spine-like ornaments, Qinlingisphaera conica gen. et sp. nov. with cone-like ornaments, and Dahisphaera plana gen. et sp. nov. with oblate ornaments. Each taxon has a wide size interval, ranging continuously from several hundred micrometers to one or two millimeters, which is different from animal eggs that generally have a narrow and conservative size interval. Micro-CT analyses and thin sections reveal that the vesicular structures may be taphonomic in nature, and that the wall thickness is specimen-dependent. Collectively, the evidence at hand does not support an embryo interpretation for Archaeooides. Instead, the wide size interval probably represents ontogenetic variations that are common in many fossil and modern algae, and thus further suggests an algal affinity for Archaeooides as well as the other Archaeooides-like microfossils.

The early animal radiation: insights from interpreting the Cambrian problematic fossils

Genic and genomic data have been reshaping our understanding of the earliest radiation event of metazoans, the well-known Cambrian Evolutionary Radiation, not only from the respects of reshuffling the phylogenetic topologies of some animal phyla but by deciphering the deep homologies of many morphological features. These advances, together with the continuing discoveries of the Ediacaran-Cambrian fossils, are unveiling the cladogenetic process of the early metazoans and the patterns of morphologic evolution during this biological radiation event. In this review, I focus on a small but challenging field, the problematic fossils from the early Cambrian fossil Lagerstätten, such as the Chengjiang biota, mainly on the controversies concerning their interpretation and the consequent impacts on understanding the early evolution of animals. The bizarre body plans of the early Cambrian problematica alone do not account for the difficulties in studying their biology and affinity. Instead, it is the combined action of the taphonomic artifacts and the uncertainty in homologizing the preserved characters that impede generating plausible interpretations. Despite all these issues, a testable and repeatable method for interpreting fossils has emerged and is becoming more practicable. The integration of an evolutionary-grade conceptual frame is beneficial to the interpretation of the Cambrian problematic fossils. Together with the focus on taphonomic alternation and homologic assessment, the Cambrian problematic fossils are becoming more informative nodes in the “parsing tree” of early animal evolution.

Unusual pubic bone morphology in A.L. 288‐1 (Australopithecus afarensis) and MH2 (Australopithecus sediba)

AbstractObjectivesWe describe a novel pelvic feature, the “ventral sulcus,” located on the pubic bone ventrolateral to the pubic symphysis, which is present in A.L. 288‐1 (Australopithecus afarensis) and MH2 (Australopithecus sediba). We determine how widespread the appearance of the ventral sulcus is in fossil hominins, modern humans, and other extant hominoids.Materials and MethodsWe examine all known hominin fossils that preserve the medial portion of the pubic bone, including A.L. 288‐1 and MH2. We also study 217 humans derived from global osteological collections and all genera of extant apes.ResultsWe illustrate, describe, and define the ventral sulcus and distinguish it from age‐ and sex‐related morphologies that are sometimes present in extant humans. We do not find evidence for the ventral sulcus in our comparative human and ape samples, but find equivocal evidence for its presence in the fossils Sts 14 (Australopithecus africanus) and StW 573 (A. africanus/Australopithecus prometheus).DiscussionVentral sulci are potentially present in all four known adult Australopithecus fossils that preserve the medial portion of the pubic bone, but not present in MH1, a subadult Australopithecus sediba. This raises questions about whether ventral sulci are widespread in Australopithecus, confined to adults, or, as A.L. 288‐1, MH2, StW 573, and Sts 14 have all been estimated as female, whether it is a sex‐associated trait. Alternatively, ventral sulci could be taphonomic artifacts or idiosyncratic pathologies. Further research is needed to determine if ventral sulci are functional in origin and how widespread they are in the genus Australopithecus.

A microfossil assemblage from the Ediacaran Doushantuo Formation in the Shennongjia area (Hubei Province, South China): Filling critical paleoenvironmental and biostratigraphic gaps

Microfossils of the Ediacaran Doushantuo Formation in South China provide an important window onto the rapid diversification of marine eukaryotes after the terminal Cryogenian global glaciation. They also offer key data in the biostratigraphic subdivision and correlation of the lower–middle Ediacaran System. Previously published Doushantuo microfossils in South China were mostly from intra-shelf facies in the Yangtze Gorges area, shelf margin facies in the Weng’an area, and upper slope facies in the Zhangjiajie area, whereas paleontological data from shallow-water inner shelf facies have been rarely documented. In addition, previous data from South China leave a “barren zone” associated with the negative δ13Ccarb excursion EN2 that impedes biostratigraphic correlation. To address these environmental and stratigraphic gaps, we conducted an integrated chemostratigraphic and biostratigraphic analysis of the Doushantuo Formation at the inner shelf Lianhuacun section in the eastern Shennongjia area of Hubei Provence, South China. The Lianhuacun fossils are preserved in chert nodules/bands of the lower Doushantuo Formation, precisely in a chemostratigraphic interval identified as EN2, indicating that the so-called “barren zone” is likely a taphonomic artifact. A total of 33 genera and 82 species are identified, including a new genus (Duospinosphaera gen. nov.) and seven new species (Duospinosphaera shennongjiaensis sp. nov., D. biformis sp. nov., Jixiania retorta sp. nov., Mengeosphaera mamma sp. nov., Sinosphaera exilis sp. nov., Tanarium columnatum sp. nov., and Weissiella concentrica sp. nov.). The Lianhuacun acanthomorphic acritarchs can be broadly assigned to the third microfossil assemblage zone (i.e., the Tanarium conoideum – Cavaspina basiconica Assemblage Zone) recognized on the basis of the Weng’an biota that is correlated with upper Member II of Doushantuo Formation in the Yangtze Gorges area, consistent with chemostratigraphic correlation between the Shennongjia and Yangtze Gorges areas. Thus, the so-called “barren zone” may be a poorly preserved part of the third microfossil assemblage zone. Alternatively, it may represent a new and yet unnamed microfossil assemblage zone between the third and the overlying Tanarium pycnacanthum – Ceratosphaeridium glaberosum Assemblage Zone. Regardless, the new data presented here fill important gaps in the geographical, paleoenvironmental, and stratigraphic distributions of Ediacaran acanthomorphic acritarchs in South China. As such, they facilitate integrative chemostratigraphic and biostratigraphic correlation of Ediacaran strata at regional and global scales.

An unusual preservation of a new species of Cicadomorpha (Auchenorrhyncha) from the Crato formation, Lower Cretaceous of Brazil

ABSTRACT The Crato Formation boasts an extremely high diversity and abundance of fossil insects with many families preserved in the limestone beds, and several yet unnamed taxa. Here, we present a new insect species found in the Crato Formation limestone associated with branches and leaves of Ruffordia goeppertii, a small creeping plant of Leptosporangiate ferns. The insect is assigned as a member of the Cicadellidae family and is named Hallex martinsnetoi sp. nov. based on morphological description based also on SEM images. The new specimen is articulated and preserved in three-dimensionality, suggesting a relatively fast burial preventing the contact with decomposers or preservation in local anoxic conditions. This fossil shows a rare example of preservation involving Ruffordia goepertii leaves and the Cicadellidae (leafhopper) specimen. The fact that Hallex martinsnetoi sp. nov. was preserved in one leaf, and could be interpreted as some type of insect-plant interaction, but it could also be a taphonomic artefact. The occurrence of Cicadomorpha is consistent with the present interpretation that the limestone of the Crato Formation was formed in lacustrine conditions, and ideal habitat for this group of insects that might be more diverse in this deposit than previously thought.

Significance of the suture line in cephalopod taxonomy revealed by 3D morphometrics in the modern nautilids Nautilus and Allonautilus

Assessing the taxonomic importance of the suture line in shelled cephalopods is a key to better understanding the diversity of this group in Earth history. Because fossils are subject to taphonomic artifacts, an in-depth knowledge of well-preserved modern organisms is needed as an important reference. Here, we examine the suture line morphology of all known species of the modern cephalopods Nautilus and Allonautilus. We applied computed tomography and geometric morphometrics to quantify the suture line morphology as well as the conch geometry and septal spacing. Results reveal that the suture line and conch geometry are useful in distinguishing species, while septal spacing is less useful. We also constructed cluster trees to illustrate the similarity among species. The tree based on conch geometry in middle ontogeny is nearly congruent with those previously reconstructed based on molecular data. In addition, different geographical populations of the same species of Nautilus separate out in this tree. This suggests that genetically distinct (i.e., geographically isolated) populations of Nautilus can also be distinguished using conch geometry. Our results are applicable to closely related fossil cephalopods (nautilids), but may not apply to more distantly related forms (ammonoids).

A tiny ornithodiran archosaur from the Triassic of Madagascar and the role of miniaturization in dinosaur and pterosaur ancestry

Early members of the dinosaur-pterosaur clade Ornithodira are very rare in the fossil record, obscuring our understanding of the origins of this important group. Here, we describe an early ornithodiran (Kongonaphon kely gen. et sp. nov.) from the Mid-to-Upper Triassic of Madagascar that represents one of the smallest nonavian ornithodirans. Although dinosaurs and gigantism are practically synonymous, an analysis of body size evolution in dinosaurs and other archosaurs in the context of this taxon and related forms demonstrates that the earliest-diverging members of the group may have been smaller than previously thought, and that a profound miniaturization event occurred near the base of the avian stem lineage. In phylogenetic analysis, Kongonaphon is recovered as a member of the Triassic ornithodiran clade Lagerpetidae, expanding the range of this group into Africa and providing data on the craniodental morphology of lagerpetids. The conical teeth of Kongonaphon exhibit pitted microwear consistent with a diet of hard-shelled insects, indicating a shift in trophic ecology to insectivory associated with diminutive body size. Small ancestral body size suggests that the extreme rarity of early ornithodirans in the fossil record owes more to taphonomic artifact than true reflection of the group's evolutionary history.

Effects of size-dependent sediment mixing on deep-sea records of the Paleocene-Eocene Thermal Maximum

Abstract Stratigraphic features of the carbon isotope excursion (CIE) marking the Paleocene-Eocene Thermal Maximum (PETM; ca. 55.8 Ma) are used to study ocean-climate change and carbon cycling during this ancient global warming event. Yet discrepancies in its timing and amplitude exist between bulk-carbonate and planktic-foraminifera δ13C records. Here we examine these disparities through the lens of δ13C compositions of size-segregated planktic shells across the pre-CIE to CIE transition in the iconic PETM section of Ocean Drilling Program Site 690 in the Weddell Sea. Our results show that the stratigraphic position of the CIE onset is dependent upon shell size, which we attribute to preferential mixing of smaller shells with pre-CIE δ13C values up into the overlying CIE interval. Hence, the transitory loss of size-dependent δ13C signatures in photosymbiotic planktic foraminifera is a taphonomic artifact, not a geochemical signal of symbiont “bleaching” during the PETM. Our results also indicate that many salient features of the Site 690 bulk-carbonate δ13C record are aberrations caused by size-dependent sediment mixing, and as such, should not be viewed as primary signals of ocean-climate change during what is arguably one of the best ancient analogs for future ocean-climate change.

A new faveoloolithid oogenus from the Wido Volcanics (Upper Cretaceous), South Korea and a new insight into the oofamily Faveoloolithidae

The Cretaceous oofamily Faveoloolithidae has a unique shell unit and pore canal system that clearly differs from most of the extant and fossil eggshells. Despite its distinctiveness, morphological (micro- and ultrastructural) and crystallographic features of the Faveoloolithidae are poorly known. Here we report a new faveoloolithid nesting ground from the Upper Cretaceous siltstones within the Daeri Andesite of the Wido Volcanics (Coniacian–Santonian), South Korea. Forty-one of the same kind of dinosaur eggs distributed in at least eight clutches occur in seven different stratigraphic horizons, suggesting a colonial nesting ground and paleontological site fidelity (reuse of a site over geological time scale). These eggs were assigned to a new ootaxon, Propagoolithus widoensis oogen. et oosp. nov., based on a unique shell unit morphology which is branching towards the external part of eggshell, unlike other faveoloolithid eggs. New morphological and crystallographic features of P. widoensis provide a new insight into the oofamily Faveoloolithidae: (1) superimposed shell units, which are widely used as diagnoses of the Faveoloolithidae and Dictyoolithidae, are in fact taphonomic artifacts and (2) round and crystallographically upright shell units partially connected by inclined crystals (bridges) at the inner portion in the tangential section is proposed as an additional synapomorphy of the oofamily Faveoloolithidae. Furthermore, elemental analysis combined with light microscopy, EBSD, and CL analyses provide a successful reconstruction of the complex pore canal infilling process, and suggest that magnesium concentration can be used as a proxy for calcite overgrowth.

Invertebrate borings from the Eocene of Seven Rivers, parish of St. James, western Jamaica

The fossil biota of the Eocene Yellow Limestone Group of Jamaica is diverse in vertebrates and, particularly, invertebrates. However, its invertebrate trace fossils remain understudied. Herein, we document the borings of the Seven Rivers vertebrate site in western Jamaica. This is in the Litchfield Formation, high in the Lutetian (about mid-Middle Eocene). The suite of borings identified from this site comprises Apectoichnus longissimus (Kelly and Bromley); Entobia isp.; Oichnus simplex Bromley; and Oichnus paraboloides Bromley. Substrates infested by Entobia isp. include both molluscs and sirenian ribs. Oichnus ispp. occur only in bivalves and are mainly non-penetrative, which may be a taphonomic artifact. Tubes of the common A. longissimus are preserved free from any woody substrates, which have presumably rotted away; however, one specimen has a dark, carbonaceous external film and others have carbonized wood inclusions. The occurrence of A. longissimus in the Jamaican rock record coincides with periods of sub-aerial exposure.

Dinosaur egg colour had a single evolutionary origin

Birds are the only living amniotes with coloured eggs1-4, which have long been considered to be an avian innovation1,3. A recent study has demonstrated the presence of both red-brown protoporphyrin IX and blue-green biliverdin5-the pigments responsible for all the variation in avian egg colour-in fossilized eggshell of a nonavian dinosaur6. This raises the fundamental question of whether modern birds inherited egg colour from their nonavian dinosaur ancestors, or whether egg colour evolved independently multiple times. Here we present a phylogenetic assessment of egg colour in nonavian dinosaurs. We applied high-resolution Raman microspectroscopy to eggshells that represent all of the major clades of dinosaurs, and found that egg colour pigments were preserved in all eumaniraptorans: egg colour had a single evolutionary origin in nonavian theropod dinosaurs. The absence of colour in ornithischian and sauropod eggs represents a true signal rather than a taphonomic artefact. Pigment surface maps revealed that nonavian eumaniraptoran eggs were spotted and speckled, and colour pattern diversity in these eggs approaches that in extant birds, which indicates that reproductive behaviours in nonavian dinosaurs were far more complex than previously known3. Depth profiles demonstrated identical mechanisms of pigment deposition in nonavian and avian dinosaur eggs. Birds were not the first amniotes to produce coloured eggs: as with many other characteristics7,8 this is an attribute that evolved deep within the dinosaur tree and long before the spectacular radiation of modern birds.

A Zoophycos carnival in Devonian beds: Paleoecological, paleobiological, sedimentological, and paleobiogeographic insights

Devonian occurrences of Zoophycos are often observed in successions representing shelfal deposits and have been interpreted as the first expansion of this trace fossil during the Paleozoic. Dense Zoophycos occurrences in storm-generated Paleozoic beds have been interpreted as the result of ecological opportunist strategy when the tracemaker exploited quiet, nutrient garden substrates after storms. In the Devonian Ponta Grossa Formation (Pragian to Frasnian) of the Paraná Basin (Brazil), Zoophycos is both preserved in storm-generated strata indicating oxyc substrates, and in association with Chondrites and Phycosiphon suggesting dysoxic offshore deposition. This study focuses on the analysis of Zoophycos observed in the Devonian strata to understand the depositional context reflected by paleoecologic strategies and taphonomic signatures. We analyzed the ichnofabrics and sedimentary facies of Devonian sections from the Paraná Basin, focusing on the occurrences of Zoophycos. The tiering structure involving dense Zoophycos ichnofabrics demonstrated that shallower burrows (e.g., Asterosoma, Palaeophycus, Cylindrichnus, Schaubcylindrichnus, Skolithos) reworked deep-tier burrows (Chondrites, Phycosiphon, and Zoophycos), indicating erosion of surficial levels. The dense Zoophycos ichnofabric representing the fair-weather suite obliterated primary sedimentary structures of storm deposits, which favored the visibility of deep-tier structures in a lam-scram pattern. In this sense, dense Zoophycos ichnofabric from Paraná Basin cannot be linked to an opportunistic behavior, but to an over-represented occurrence in space and time, being a taphonomic artifact related to low accommodation space in prograding context. The association with other trace fossils allowed the attribution of Zoophycos as a component of distal and archetypal expressions of Cruziana Ichnofacies rather than Zoophycos Ichnofacies. Concerning the vertical distribution of Zoophycos in the Paraná Basin, this trace appears in strata related to the first occurrence of land plants, being common in the Pragian–Eifelian interval, and declining in upper strata. This decline might be related to a potential structural change of the Paraná Basin during Middle Devonian.

EXPERIMENTAL TAPHONOMY OF KERATIN: A STRUCTURAL ANALYSIS OF EARLY TAPHONOMIC CHANGES

Research Article| October 10, 2017 EXPERIMENTAL TAPHONOMY OF KERATIN: A STRUCTURAL ANALYSIS OF EARLY TAPHONOMIC CHANGES EVAN T. SAITTA; EVAN T. SAITTA 1School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar CHRISTOPHER S. ROGERS; CHRISTOPHER S. ROGERS 2School of Biological, Earth and Environmental Sciences, University College Cork, Distillery Field, N Mall, Cork, T23 XA50, Ireland Search for other works by this author on: GSW Google Scholar RICHARD A. BROOKER; RICHARD A. BROOKER 1School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK Search for other works by this author on: GSW Google Scholar JAKOB VINTHER JAKOB VINTHER 1School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 1RJ, UK 3School of Biological Sciences, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol, BS8 1TQ, UK Search for other works by this author on: GSW Google Scholar PALAIOS (2017) 32 (10): 647–657. https://doi.org/10.2110/palo.2017.051 Article history first online: 16 Oct 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation EVAN T. SAITTA, CHRISTOPHER S. ROGERS, RICHARD A. BROOKER, JAKOB VINTHER; EXPERIMENTAL TAPHONOMY OF KERATIN: A STRUCTURAL ANALYSIS OF EARLY TAPHONOMIC CHANGES. PALAIOS 2017;; 32 (10): 647–657. doi: https://doi.org/10.2110/palo.2017.051 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyPALAIOS Search Advanced Search Abstract: The evolution of integumentary structures, particularly in relation to feathers in dinosaurs, has become an area of intense research. Our understanding of the molecular evolution of keratin protein is greatly restricted by the fact that such information is lost during diagenesis and cannot be derived from fossils. In this study, decay and maturation experiments are used to determine if different keratin types or integumentary structures show different patterns of degradation early in their taphonomic histories and if such simulations might advance our understanding of different fossilization pathways. Although different distortion patterns were observed in different filamentous structures during moderate maturation and ultrastructural textures unique to certain types of scales persisted in moderate maturation, neither of these have been observed in fossils. It remains uncertain whether these degradation patterns would ever occur in natural sediment matrix, where microbial and chemical decay happens well before significant diagenesis. It takes some time for remains to be buried, meaning that keratin may not be left for moderate maturation to produce such patterns. Higher, more realistic maturation conditions produce a thick, and water soluble fluid that lacks all morphological and ultrastructural details of the original keratin, suggesting that such textural or distortion patterns are unlikely to be preserved in fossils. Although different degradation patterns among keratinous structures are intriguing, it is unlikely that such information could be recorded in the fossil record. Calcium phosphates and pigments are the surviving components of integumentary structures. Thus, the results here are likely of more relation to the archaeological record than fossil record. Other noteworthy results of these experiments are that melanin may not be the leading factor in determining the rate of microbial decay in feathers but may reduce the rate of degradation from maturation, that the existence of rachis filamentous subunits similar to plumulaceous barbules is supported, and that previously reported dinosaur ‵erythrocytes' may be taphonomic artifacts of degraded organic material. You do not currently have access to this article.

Stable isotopes, niche partitioning and the paucity of elasmosaur remains in the Maastrichtian type area

AbstractRemains of elasmosaurid plesiosaurs are exceedingly rare in the type-Maastrichtian strata (Late Cretaceous, southeast Netherlands and northeast Belgium), in stark contrast to relatively common skeletal remains of mosasaurs. Here, we present an analysis of δ13C stable isotope values for tooth enamel of two elasmosaur teeth from the type Maastrichtian. The δ13C signal is a proxy for foraging area, trophic level and diving behaviour, the net value of which in these rare elasmosaurs turns out to be not noticeably different from that for the much commoner mosasaurs in the type Maastrichtian. Therefore, the rarity of elasmosaurs in the area probably reflects a primary near-absence of such reptiles during the latest Cretaceous, rather than a taphonomic artefact.

A large abelisaurid (Dinosauria, Theropoda) from Morocco and comments on the Cenomanian theropods from North Africa.

We describe the partially preserved femur of a large-bodied theropod dinosaur from the Cenomanian “Kem Kem Compound Assemblage” (KKCA) of Morocco. The fossil is housed in the Museo Geologico e Paleontologico “Gaetano Giorgio Gemmellaro” in Palermo (Italy). The specimen is compared with the theropod fossil record from the KKCA and coeval assemblages from North Africa. The combination of a distally reclined head, a not prominent trochanteric shelf, distally placed lesser trochanter of stout, alariform shape, a stocky shaft with the fourth trochanter placed proximally, and rugose muscular insertion areas in the specimen distinguishes it from Carcharodontosaurus, Deltadromeus and Spinosaurus and supports referral to an abelisaurid. The estimated body size for the individual from which this femur was derived is comparable to Carnotaurus and Ekrixinatosaurus (up to 9 meters in length and 2 tons in body mass). This find confirms that abelisaurids had reached their largest body size in the “middle Cretaceous,” and that large abelisaurids coexisted with other giant theropods in Africa. We review the taxonomic status of the theropods from the Cenomanian of North Africa, and provisionally restrict the Linnean binomina Carcharodontosaurus iguidensis and Spinosaurus aegyptiacus to the type specimens. Based on comparisons among the theropod records from the Aptian-Cenomanian of South America and Africa, a partial explanation for the so-called “Stromer’s riddle” (namely, the coexistence of many large predatory dinosaurs in the “middle Cretaceous” record from North Africa) is offered in term of taphonomic artifacts among lineage records that were ecologically and environmentally non-overlapping. Although morphofunctional and stratigraphic evidence supports an ecological segregation between spinosaurids and the other lineages, the co-occurrence of abelisaurids and carcharodontosaurids, two groups showing several craniodental convergences that suggest direct resource competition, remains to be explained.

Digit-only sauropod pes trackways from China--evidence of swimming or a preservational phenomenon?

For more than 70 years unusual sauropod trackways have played a pivotal role in debates about the swimming ability of sauropods. Most claims that sauropods could swim have been based on manus-only or manus-dominated trackways. However none of these incomplete trackways has been entirely convincing, and most have proved to be taphonomic artifacts, either undertracks or the result of differential depth of penetration of manus and pes tracks, but otherwise showed the typical pattern of normal walking trackways. Here we report an assemblage of unusual sauropod tracks from the Lower Cretaceous Hekou Group of Gansu Province, northern China, characterized by the preservation of only the pes claw traces, that we interpret as having been left by walking, not buoyant or swimming, individuals. They are interpreted as the result of animals moving on a soft mud-silt substrate, projecting their claws deeply to register their traces on an underlying sand layer where they gained more grip during progression. Other sauropod walking trackways on the same surface with both pes and manus traces preserved, were probably left earlier on relatively firm substrates that predated the deposition of soft mud and silt . Presently, there is no convincing evidence of swimming sauropods from their trackways, which is not to say that sauropods did not swim at all.

Biotic replacement and mass extinction of the Ediacara biota.

The latest Neoproterozoic extinction of the Ediacara biota has been variously attributed to catastrophic removal by perturbations to global geochemical cycles, 'biotic replacement' by Cambrian-type ecosystem engineers, and a taphonomic artefact. We perform the first critical test of the 'biotic replacement' hypothesis using combined palaeoecological and geochemical data collected from the youngest Ediacaran strata in southern Namibia. We find that, even after accounting for a variety of potential sampling and taphonomic biases, the Ediacaran assemblage preserved at Farm Swartpunt has significantly lower genus richness than older assemblages. Geochemical and sedimentological analyses confirm an oxygenated and non-restricted palaeoenvironment for fossil-bearing sediments, thus suggesting that oxygen stress and/or hypersalinity are unlikely to be responsible for the low diversity of communities preserved at Swartpunt. These combined analyses suggest depauperate communities characterized the latest Ediacaran and provide the first quantitative support for the biotic replacement model for the end of the Ediacara biota. Although more sites (especially those recording different palaeoenvironments) are undoubtedly needed, this study provides the first quantitative palaeoecological evidence to suggest that evolutionary innovation, ecosystem engineering and biological interactions may have ultimately caused the first mass extinction of complex life.

Sphaerapus, A Poorly Known Invertebrate Trace Fossil From Nonmarine Permian and Jurassic Strata of North America

In 1858, Edward Hitchcock named Sphaerapus larvalis and S. magnus for burrows from the nonmarine Lower Jurassic Turners Falls Formation in Massachusetts. Walpia hermitensis White, 1929, from the Lower Permian Hermit Shale, Arizona, is also a little known ichnotaxon. Examination of the type material indicates that Sphaerapus is a senior subjective synonym of Walpia. Sphaerapus is also a nomen oblitum, but Walpia has not been sufficiently used to replace its senior synonym as a conserved name; thus, we use the senior synonym Sphaerapus as the valid name of this ichnogenus, which is monospecific (S. larvalis = S. magnus = W. hermitensis). Numerous specimens of Sphaerapus from the Lower Permian of New Mexico and Texas, and a new record from the Lower Jurassic of Massachusetts show that it is a horizontal endichnion or exichnion having an unpacked tunnel with a cylindrical to ellipsoidal cross section, in some specimens branching, and lined with flattened, lenticular, non-coprolitic sediment pellets that are irregularly arranged and in some specimens imbricated. The pellets distinguish Sphaerapus from other endichnia. Sphaerapus resembles burrows of recent variegated mud-loving beetles and mole crickets, so Sphaerapus was likely produced by a hexapod similarly adapted for subsurface, compaction burrowing. Variation in pellet shape and arrangement in Sphaerapus reflects fluidity of the sediment burrowed, so this variation is a taphonomic artifact of no ichnotaxonomic significance. The latest Wolfcampian first appearance of Sphaerapus is not facies related, as similar facies lacking Sphaerapus are present in middle-late Wolfcampian strata. Therefore, the first appearance of Sphaerapus may reflect the evolutionary first appearance of a hexapod that moved through the sediment by compaction tunneling. However, the stratigraphically disjunct distribution of Sphaerapus may indicate that its preservation and fossilization were sensitive to paleoenvironmental and/or taphonomic factors that may also be involved in its first appearance.

Longevity and growth rate estimates for a polar dinosaur: a Pachyrhinosaurus (Dinosauria: Neoceratopsia) specimen from the North Slope of Alaska showing a complete developmental record

Our knowledge of growth dynamics in large ceratopsian dinosaurs is very poor, in part, due to the paucity of quantifiable age markers such as growth lines in their bones. We sought marker-based, osteohistological evidence for ceratopsid age structure from high Arctic paleolatitudes based on the observations that: (1) extant mammals from high latitudes better express growth lines in their hard tissues than those from lower latitudes, and (2) the occurrence of accentuated growth banding in teeth from Arctic dinosaurs. We examined the long bones in the specimens of Pachyrhinosaurus sp. from the early Maastrichtian of northern Alaska, and found conspicuous osseous banding. Histological analysis of the spacing, structure, pattern and numbers of these bands in the femur of a very large specimen suggests that they are not a taphonomic artefact, rather they appear to reflect annual growth cycling. Counts and measurements of the growth zones suggest that the animal showed rapid linear growth early in ontogeny, sexual maturity in perhaps the 9th year of life, and that it died in the 19th year of life. Our data adds to a growing body of evidence that a genetically distinct northern dinosaurian fauna existed at high paleolatitudes in Alaska during the Late Cretaceous.

Life and death of Saccocoma tenella (Goldfuss)

The morphology of the small stalkless Saccocoma tenella is unique among crinoids. It is characterized by an extremely light skeleton with dish-like lateral wings on the proximal brachials and peculiar paired vertical processes flanking the food grooves of more distal brachials. The arms are heavily branched. The lateral wings obviously were involved in vertical movement. For the vertical processes a “baffle rail” function for arm curling and “snap swimming” has been postulated, with muscles between the processes. However, there is no evidence that the processes were connected by muscles. For food collection a “pulsating funnel” model in the water column is advocated, with the processes serving to collect plankton during upward movement of the arms. The resulting mouth-up position is supported by the biostratinomy. Saccocoma tenella is considered to have been pelagic, a benthic lifestyle is rejected on ecologic and taphonomic grounds. Adorally-curled arms are considered a reaction to hostile environment before death, not a taphonomic artefact.