Siliceous microfossils from the lower cambrian of northwest Canada: possible source for biogenic chert

Round to oval, scalelike siliceous microstructures from cherts in Cambrian limestones of the western Yukon Territory suggest affinity with chrysophycean algae. At least six morphotypes present include porous forms with single branching processes and nonporous oval, ringlike forms. Partially dissolved specimens may indicate a contribution to contemporaneous or early diagenetic chert formation.     

Early deglaciation of the labrador shelf

Two marine sediment cores from a basin on the southeastern Labrador Shelf penetrate a mud sequence extending back to 21,000 carbon-14 years before the present (B.P.). The benthic foraminifera are dominated by subartic nearshore species indicative of ice-free summer waters. The pollen record indicates the presence of a sedge-shrub tundra in eastern Labrador as early as 21,000 years B.P. Both sources of evidence suggest less extensive continental ice than has previously been reported for this subarctic region.     

The oldest bryozoans: new evidence from the early ordovician

An abundant, previously problematic fossil from the Lower Ordovician (Canadian) Black Rock limestone of the Ozark Uplift area is an undescribed dianulitid bryozoan. It is believed to be the oldest unquestionable bryozoan known. The growth morphology varies widely and is believed to be environmentally influenced.     

Head segmentation in early cambrian fuxianhuia: implications for arthropod evolution

The arthropod Fuxianhuia from the Chengjiang fauna displays primitive aspects of cephalic segmentation and trunk limb morphology that indicate a basal position within Euarthropoda. The cephalon consists of an eye-bearing sclerite that articulates with a head shield bearing antennules and subchelate appendages. Eye stalks, antennules, and subchelate appendages are proto-, deuto-, and tritocerebral limbs and organs, respectovely. The anterior position of the eye-bearing sclerite parallels the embryonic origin of arthropod eye lobes. The head of Fuxianhuia includes the acron and one somite and is regarded as a protocephalon. The definitive head of arthropods may have fused separate eye-bearing and appendage-bearing sclerites.     

Authigenic potassium feldspar in cambrian carbonates: evidence of alleghanian brine migration

The shallow-water limestones and dolostones of the Conococheague Limestone (Upper Cambrian) of western Maryland contain large amounts of authigenic potassium feldspar. The presence of halite daughter crystals in breached fluid inclusions, low whole-rock ratios of chlorine to bromine, and thermochemical data suggest that the potassium feldspar formed at low temperature by the reaction of connate brines with intercalated siliciclastic debris. Analyses of argon age spectra indicate that the authigenic feldspar probably formed during Late Pennsylvanian to Early Permian time. These results may indicate mobilization and migration of connate brines brought about by Alleghanian folding. The widespread occurrence of authigenic potassium feldspar in Cambrian and Ordovician carbonate rocks throughout the Appalachians suggests that this may have occurred throughout the entire basin.     

A fish from the upper cambrian of north america

Phosphatic dermal fragments of Anatolepis, interpreted as a heterostracan fish (class Agnatha), have been discovered in the Deadwood Formation of Late Cambrian age in northeastern Wyoming. This discovery extends back the age of the earliest known vertebrate fossils by approximately 40 million years. Other occurrences of Anatolepis in North America, Greenland, and Spitzbergen show that these fish had a widespread geographic distribution in Late Cambrian and Early Ordovician marine environments.     

Evidence for monophyly and arthropod affinity of cambrian giant predators

The Chinese Early Cambrian Chengjiang fauna includes three different anomalocaridids, a globally spread, extinct marine group including the largest known Cambrian animals. Anomalocaridids were active predators, and their presence implies that a complex ecosystem appeared abruptly in the earliest Phanerozoic. Complete specimens display several sets of characters shared only with some other exclusively Cambrian forms. This evidence indicates that anomalocaridids, Opabinia, and Kerygmachela form a monophyletic clade. Certain features indicate arthropod affinities of the lade, and for this group an unnamed (sub)phylum-level taxon within an arthropod (super)phylum is proposed.     

Modern turtle origins: the oldest known cryptodire

The discovery of a turtle in the Early Jurassic(185 million years before present) Kayenta Formation of northeastern Arizona provides significant evidence about the origin of modern turtles. This new taxon possesses many of the primitive features expected in the hypothetical common ancestor of pleurodires and cryptodires, the two groups of modern turtles. It is identified as the oldest known cryptodire because of the presence of a distinctive cryptodiran jaw mechanism consisting of a trochlea over the otic chamber that redirects the line of action of the adductor muscle. Aquatic habits appear to have developed very early in turtle evolution. Kayentachelys extends the known record of cryptodires back at least 45 million years and documents a very early stage in the evolution of modern turtles.     

A vestige of Earth's oldest ophiolite

A sheeted-dike complex within the approximately 3.8-billion-year-old Isua supracrustal belt (ISB) in southwest Greenland provides the oldest evidence of oceanic crustal accretion by spreading. The geochemistry of the dikes and associated pillow lavas demonstrates an intraoceanic island arc and mid-ocean ridge-like setting, and their oxygen isotopes suggest a hydrothermal ocean-floor-type metamorphism. The pillows and dikes are associated with gabbroic and ultramafic rocks that together make up an ophiolitic association: the Paleoarchean Isua ophiolite complex. These sheeted dikes offer evidence for remnants of oceanic crust formed by sea-floor spreading of the earliest intact rocks on Earth.     

Skeleton of diacodexis, oldest known artiodactyl

A nearly complete skeleton of early Eocene Diacodexis, the oldest known member of the mammalian order Artiodactyla, is described. Its slender, elongate limb elements indicate that Diacodexis was highly cursorial and closer in postcranial adaptations to tragulids and other primitive ruminants than to living or extinct nonruminant artiodactyls. Its skeletal specializations call into question the widespread notion that Diacodexis was the ancestor of all later artiodactyls.     

The works of living social insects as pseudofossils and the age of the oldest known metazoa

Living organisms are known to create structures in ancient rocks that are indigenous but not primary and that have been mistaken for fossils. Examination of burrows recently reported as fossils from 10(9)-year-old sedimentary rocks indicates that they are not the same age as the rocks but were probably made by termites working down after water. The burrows are partially filled with material from a modern lateritic surface from which they descend into steeply dipping, decomposed silt-stones of the Zambian Copperbelt. In fact, no authentic record of Metazoa that are demonstrably coeval with rocks older than 680 million years is known.     

Comment on "A vestige of Earth's oldest ophiolite"

Furnes et al. (Reports, 23 March 2007, p. 1704) reported the identification of an ophiolite sequence within the approximately 3.8-billion-year-old Isua supracrustal belt. However, they did not acknowledge that the belt contains supracrustal rocks and mafic dikes of different ages, nor did they demonstrate that the proposed components of the ophiolite are coeval.