Acute vision in the giant Cambrian predator Anomalocaris and the origin of compound eyes

Until recently, intricate details of the optical design of non-biomineralized arthropod eyes remained elusive in Cambrian Burgess-Shale-type deposits, despite exceptional preservation of soft-part anatomy in such Konservat-Lagerst?tten. The structure and development of ommatidia in arthropod compound eyes support a single origin some time before the latest common ancestor of crown-group arthropods, but the appearance of compound eyes in the arthropod stem group has been poorly constrained in the absence of adequate fossils. Here we report 2-3-cm paired eyes from the early Cambrian (approximately 515 million years old) Emu Bay Shale of South Australia, assigned to the Cambrian apex predator Anomalocaris. Their preserved visual surfaces are composed of at least 16,000 hexagonally packed ommatidial lenses (in a single eye), rivalling the most acute compound eyes in modern arthropods. The specimens show two distinct taphonomic modes, preserved as iron oxide (after pyrite) and calcium phosphate, demonstrating that disparate styles of early diagenetic mineralization can replicate the same type of extracellular tissue (that is, cuticle) within a single Burgess-Shale-type deposit. These fossils also provide compelling evidence for the arthropod affinities of anomalocaridids, push the origin of compound eyes deeper down the arthropod stem lineage, and indicate that the compound eye evolved before such features as a hardened exoskeleton. The inferred acuity of the anomalocaridid eye is consistent with other evidence that these animals were highly mobile visual predators in the water column. The existence of large, macrophagous nektonic predators possessing sharp vision--such as Anomalocaris--within the early Cambrian ecosystem probably helped to accelerate the escalatory 'arms race' that began over half a billion years ago.     

Structure and toxicity of the alkaloids of Russian comfrey (Symphytum x uplandicum Nyman), a medicinal herb and item of human diet

Summary Eight pyrrolizidine alkaloids of hepatotoxic type have been indentified in leaves ofSymphytum × uplandicum The combined alkaloids exhibit chronic hepatotoxicity in rats.The authors thank N. Anderton and P. Stewart for skilled assistance and V. Lord for statistical analyses.     

Santa Catharina and the origin of cloudy taenite in meteorites

CLOUDY taenite appears as a dark-etching rim that occurs at the high nickel border of taenite fields in iron meteorites and mesosiderites. Transmission electron microscopy (TEM) shows it to consist of a foam-like association of interpenetrating single crystals of taenite and kamacite when well developed(1) with an orientation relationship between those of the Kurdjumow-Sachs and the Nishiyama(2). It occurs between compositional limits that have been reported as approximately 25-40% Ni(1) and 30-40% Ni(3). Observed taenite particle sizes range from 0.4 microm in the Estherville mesosiderite(1) to considerably less than 0.1 microm for many iron meteorites (unpublished data). The mechanism of cloudy taenite formation has not been previously explained, although it is believed(2) to be a phenomenon related to the Invar effect, which occurs in Fe-35% Ni (Invar) and several other alloy systems. Santa Catharina is a wholly taenitic anomalous iron meteorite that contains 35% Ni and 0.6% Co (ref. 4). This composition, which is very similar to that of Invar, places it well inside the range where cloudy taenite is known to form. The optical microstructure of Santa Catharina suggested that the matrix phase of the entire meteorite may consist of cloudy taenite, so I have now examined it by TEM and the results are reported here.     

Modern optics in exceptionally preserved eyes of Early Cambrian arthropods from Australia

Despite the status of the eye as an "organ of extreme perfection", theory suggests that complex eyes can evolve very rapidly. The fossil record has, until now, been inadequate in providing insight into the early evolution of eyes during the initial radiation of many animal groups known as the Cambrian explosion. This is surprising because Cambrian Burgess-Shale-type deposits are replete with exquisitely preserved animals, especially arthropods, that possess eyes. However, with the exception of biomineralized trilobite eyes, virtually nothing is known about the details of their optical design. Here we report exceptionally preserved fossil eyes from the Early Cambrian (～ 515 million years ago) Emu Bay Shale of South Australia, revealing that some of the earliest arthropods possessed highly advanced compound eyes, each with over 3,000 large ommatidial lenses and a specialized 'bright zone'. These are the oldest non-biomineralized eyes known in such detail, with preservation quality exceeding that found in the Burgess Shale and Chengjiang deposits. Non-biomineralized eyes of similar complexity are otherwise unknown until about 85 million years later. The arrangement and size of the lenses indicate that these eyes belonged to an active predator that was capable of seeing in low light. The eyes are more complex than those known from contemporaneous trilobites and are as advanced as those of many living forms. They provide further evidence that the Cambrian explosion involved rapid innovation in fine-scale anatomy as well as gross morphology, and are consistent with the concept that the development of advanced vision helped to drive this great evolutionary event.