RESUMO
Evolutionary origins of novel forms are often obscure because early and transitional fossils tend to be rare, poorly preserved, or lack proper phylogenetic contexts. We describe a new, exceptionally preserved enigmatic crab from the mid-Cretaceous of Colombia and the United States, whose completeness illuminates the early disparity of the group and the origins of novel forms. Its large and unprotected compound eyes, small fusiform body, and leg-like mouthparts suggest larval trait retention into adulthood via heterochronic development (pedomorphosis), while its large oar-like legs represent the earliest known adaptations in crabs for active swimming. Our phylogenetic analyses, including representatives of all major lineages of fossil and extant crabs, challenge conventional views of their evolution by revealing multiple convergent losses of a typical "crab-like" body plan since the Early Cretaceous. These parallel morphological transformations may be associated with repeated invasions of novel environments, including the pelagic/necto-benthic zone in this pedomorphic chimera crab.
Assuntos
Artrópodes/anatomia & histologia , Artrópodes/classificação , Evolução Biológica , Fósseis , Adaptação Fisiológica , Animais , Linhagem da Célula , Colômbia , Larva , Filogenia , Natação , Estados UnidosRESUMO
A new species of carcineretid crab, Carcineretes planetarius, is described from the Upper Cretaceous (lower Maastrichtian) Barton Creek Dolomite at Albion Island, Belize. The age is based on the stratigraphic range of associated nerineid gastropods and correlation with nannoplankton, benthic foraminifera, and the other known congeneric species of crab found in Jamaica. Confirmation of this age aids in constraining the timing of ejecta deposits of the Chicxulub impact found at the top of Barton Creek Dolomite exposed on Albion Island. Paleoenvironmental and paleoecological analyses suggest that these crabs were swimmers in lagoonal settings, capable of burrowing a few centimeters into the mud for protection.
Assuntos
Braquiúros/classificação , Fósseis , Paleontologia , Animais , Belize , Evolução Biológica , Braquiúros/anatomia & histologia , Fenômenos Geológicos , GeologiaRESUMO
In an attempt to find better animal models for percutaneous penetration studies relevant to man, urinary excretion of 14C-labeled compounds was studied in the Mexican hairless dog and in man. With benzoic acid, progesterone and testosterone, the total absorption and maximum absorption rate were greater in man than in the hairless dog. As urinary excretion lasted days longer in the dog than in man, it is possible that the thin dog skin held the chemicals longer than man. Surface-counting experiments with a Geiger counter with a thin mica window protected by a special screen of fine stainless steel wires showed that benzoic acid and progesterone did persist on the dog skin far longer than on human skin. We conclude that the Mexican hairless dog has permeability characteristics significantly different from those of human skin.