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A description of the gill skeleton of a very early fossil shark-like fish shows that it bears more resemblance to gill skeletons from bony fishes rather than to those from modern cartilaginous fishes, suggesting that modern sharks are not anatomically primitive, as previously thought. Today's sharks are no living fossils The cartilaginous fishes -- including the sharks, rays and skates -- are so-called because their skeleton is made primarily of cartilage rather than the much harder bone. The fact that many sharks alive today look generally similar to fossil sharks creates the impression that they are 'living fossils', preserving in their anatomy some deeply primitive state. This study adds to a growing body of evidence that this is far from the case. The authors describe the gill skeleton of a very early fossil shark that bears a marked resemblance to the gill skeletons in osteichthyans (bony fish), suggesting that the arrangement in modern sharks reflects evolutionary innovation rather than morphological stasis. The evolution of serially arranged, jointed endoskeletal supports internal to the gills--the visceral branchial arches--represents one of the key events in early jawed vertebrate (gnathostome) history, because it provided the morphological basis for the subsequent evolution of jaws.sup.1,2,3,4,5. However, until now little was known about visceral arches in early gnathostomes.sup.6,7,8,9,10,11,12,13,14,15,16,17, and theories about gill arch evolution were driven by information gleaned mostly from both modern cartilaginous (chondrichthyan) and bony (osteichthyan) fishes. New fossil discoveries can profoundly affect our understanding of evolutionary history, by revealing hitherto unseen combinations of primitive and derived characters.sup.18,19. Here we describe a 325 million year (Myr)-old Palaeozoic shark-like fossil that represents, to our knowledge, the earliest identified chondrichthyan in which the complete gill skeleton is three-dimensionally preserved in its natural position. Its visceral arch arrangement is remarkably osteichthyan-like, suggesting that this may represent the common ancestral condition for crown gnathostomes. Our findings thus reinterpret the polarity of some arch features of the crown jawed vertebrates and invert the classic hypothesis, in which modern sharks retain the ancestral condition.sup.3,20. This study underscores the importance of early chondrichthyans in resolving the evolutionary history of jawed vertebrates., Author(s): Alan Pradel [sup.1] , John G. Maisey [sup.1] , Paul Tafforeau [sup.2] , Royal H. Mapes [sup.3] , Jon Mallatt [sup.4] Author Affiliations: (1) Department of Vertebrate Paleontology, American [...]

New fossils from Australia reveal that the Cambrian apex predator Anomalocaris possessed compound eyes more powerful than those of most living arthropods. A sharp-eyed Cambrian predator The metre-long swimming invertebrate Anomalocaris was the top predator in the Cambrian ocean more than 500 million years ago. Recent discoveries of fly-like compound eyes attributable to this creature confirm suggestions that it is related to the arthropods -- jointed-limbed creatures such as insects, crustaceans and trilobites -- and show that compound eyes evolved before hardened exoskeletons. The superbly preserved fossils from South Australia show that Anomalocaris had exceptional vision. Its compound eyes are among the largest and most acute to have ever existed; each eye is up to 3 centimetres long and contains more than 16,000 lenses. The existence of highly visual hunters during the Cambrian would have accelerated the pace of the predator-prey 'arms race' then under way. Until recently.sup.1, 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-Lagerstätten.sup.2,3. 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.sup.4, 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.sup.5,6. 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.sup.7,8., Author(s): John R. Paterson [sup.1] , Diego C. García-Bellido [sup.2] , Michael S. Y. Lee [sup.3] [sup.4] , Glenn A. Brock [sup.5] , James B. Jago [sup.3] [sup.6] , Gregory [...]

Molecules used to preen feathers identified in 48-million-year-old fossil. Molecules used to preen feathers identified in 48-million-year-old fossil., Author Affiliations: Ancient bird gland gives up its chemical secrets Organic molecules extracted from a 48-million-year-old fossilized bird are the remains of lipids produced by a gland involved in feather [...]

The first whales probably could not communicate underwater over long distances. The first whales probably could not communicate underwater over long distances., Author Affiliations: A reconstructed image of a cochlea (red), part of the inner ear, from a fossil of an ancient whale relative. The inner ear structure is more similar to [...]