Scales of thelodont and shark-like fishes from the Ordovician of Colorado

Article Abstract:

The scales of the thelodont and shark-like fishes obtained from the Harding Sandstone, Colorado, are of the Ordovician period. The majority of the scales belong to loganiid thelodonts. The scales are conical and the point of the cone occurs at a shallow angle to the rounded and flared base. Other fossil scales are similar to chondrichthyan placoid scales. They have a cyclomorial growth pattern with a large, tear-drop shaped primordial odontode. The presence of the fossils shows that the lower vertebrates diversified during the Ordovician period rather than the Silurian period.

Observations, Colorado, Animals, Fossil, Fossil animals, Paleontology, Scales (Fishes), Scales (Anatomy), Ordovician period

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George D. Snell (1903-96)

Article Abstract:

The medical biologist George D. Snell died on Jun. 6, 1996. Snell made important contributions to the field of genetics and immunology. He demonstrated that X-Rays cause chromosomal aberrations and translocation strains in mammals, establishing the basis for mammalian cytogenetics. His work on mouse embryology provided the foundation for mammalian developmental biology. Together with Peter A. Gorer, he identified a major locus of genetic histocompatibility. Snell, along with Jean Dausset and Baruj Benacerraf, was awarded the Nobel Prize for Medicine in 1980.

Obituary, Biologists, Personalities, Snell, George Davis

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Extensive MHC variability in cichlid fishes of Lake Malawi

Article Abstract:

The fish population that founded the 500 to 1,000 species in Lake Malawi some two to three million years ago was highly polymorphic at its major histocompatibility complex (MHC) loci. MHC genes seem to do for fish what they do for mammals: aid the immune response by telling self from non-self peptides Extant cichlid species exhibit large variation at their MHC loci. During adaptive species radiation different species kept different MHC alleles, perhaps helping us estimate the size of the initial population.

Physiological aspects, Major histocompatibility complex, Varieties, Cichlidae, Cichlids, Lake Nyasa

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