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2015-11-29. By Kelly.
Fig. 1. Chicken picture provided by Matt Davis, flickr Creative Commons.
You may wonder why I ask this question and to be honest it is because of statements such as, "You know that the chicken is the most closely related animal to dinosaurs.", that I hear from my students. My response is "I am not sure" or "I will have to look that up". I like to investigate questions/statements that my students have and I use Patrick as my go to source. This time I started by reading through Science News articles. I noticed an article called the "Missing link between dinosaur nests and bird nests" by Sid Perkins (November 25, 2015). Yes! This was exactly the nudge I needed to begin my search.
In Perkins' Science News article, he highlights the work done by Zelenitsky at the University of Calgary in Canada. Zelenistky and her colleagues found that dinosaur nests had eggs with porous shells similar to crocodile or turtle eggs. The pores allow for the exchange of oxygen and carbon dioxide to support the growing embryo. The larger number of pores indicates that the eggs were buried and incubated by decaying organic matter. However in her study, Zelenistky and her colleagues also found a subgroup of theropod eggs that had fewer pores. This suggests that some dinosaurs were warm blooded and able to incubate their own eggs with body heat in an open nest.
My search to answer the question, "Are dinosaurs and chicken closely related?" continued. I had to look for the skeletal and the DNA link between dinosaurs and birds. I used a Berkley University article titled, "Are Birds Really Dinosaurs?". In the article, Dr. Kevin Padian's research at Berkeley was highlighted. Padlian's work supported the theory that birds are theropod dinosaurs. The article also discussed how scientists throughout the 16th to 19th centuries noticed similarities between the fossil records of reptiles and birds. Birds and reptiles both have scales and feathers are produced by structures that are similar to the tissue that produce scales. The comparison of the skeletons done by Gauthier and others also provide strong evidence for the close evolutionary relationship between birds and dinosaurs. In fact birds are considered coelurosaurs, closely related to theropods.
Further work on evolutionary development of the beak also indicates the close relationship between birds and dinosaurs. Bhart-Anjan Bhullar, at Yale University in New Haven, decided to understand the evolutionary mechanism that triggered the development of the modern bird beak from the early snouts found in fossils. Bhullar's team looked at the DNA of several organisms including "mice, emus, alligators, lizards and turtles, representing many of the major animal groups." (http://www.bbc.com/earth/story/20150512-bird-grows-face-of-dinosaur) The Bhullar group found that chicken had unique genes that are similar to those that determine the development of the snout in dinosaurs. After Bhullar's group isolated the protein that develops the beak and altered its expression, they were able to cause the formation of a snout in chicken embryo. Bhullar's finding demonstrates that the beak developed as an adaption.
Birds are closely related to dinosaurs and the students focus on the chicken was probably due to news articles based on the recent article published by Bhullar and his team in Evolution, International Journal of Organic Evolution, 30 JUN 2015 DOI: 10.1111/evo.12684.
Fig. 2. http://www.ucmp.berkeley.edu/diapsids/saurischia/theropoda.html Used on the Berkeley webpage about the theropods. Tarbosaurus skeletal mount at the Mesa Southwest Museum. Photo (c) Geb Bennett.
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