Morphological Criteria for Staging Near-Hatching Embryos of the Domesticated Mallard (Anas platyrhynchos) and Swan Goose (Anser cygnoides).

Studying avian embryology necessitates reliable and precise staging tables-descriptions of embryonic features appearing during development that are used to approximate the extent of embryonic development from fertilisation to hatching. Staging tables for waterfowl (Anseriformes) have previously been established based on morphological features from fertilisation to approximately 10 days before hatching. Embryonic changes over the final 10 days of pre-hatching development have also been documented and proposed as useful staging criteria.

The histology of sutures in chicken skulls: Types, conservation, and ontogeny.

Sutures are fibrous joints that occur between bone elements in vertebrate skulls, where they play a variety of roles including facilitating skull growth and function. In addition, a variety of studies examining sutures from diverse perspectives in many taxa have enabled the determination of anatomical homologs. Surprisingly, one important aspect of sutures-histology-remains unknown in the key model organism of the chicken.

Development of the chicken skull: A complement to the external staging table of Hamburger and Hamilton.

Embryonic staging tables provide a standard of developmental stages that can be used by individual investigators and provide approximate time points for the study of developmental phenomena. Surprisingly, despite the presence of a plethora of studies on the chicken skull and its role as a model species in developmental research, a staging table of the development of the chicken skull remains lacking. A detailed photographic staging table of the osseous portion of the chicken skull is thus presented here based on cleared and stained HH stages spanning HH 35 (first appearance of skull ossification) to the final stage before hatching (HH 45).

The evolution of the avian bill as a thermoregulatory organ.

The avian bill is a textbook example of how evolution shapes morphology in response to changing environments. Bills of seed-specialist finches in particular have been the focus of intense study demonstrating how climatic fluctuations acting on food availability drive bill size and shape. The avian bill also plays an important but under-appreciated role in body temperature regulation, and therefore in energetics.