Nocturnal behavior may have evolved Many Times in Synapsids: Study
A research paper titled, Nocturnality in Synapsids Predates the Origin of Mammals by 100 Million Years, unveiled that change to nocturnal behavior happened at almost the same time as mammals evolved, 200 years ago.
Mammals’ features including large brain and light-sensitive chemicals present in mammals’ eyes among other features add to the above-mentioned belief. Researchers said these factors give a hint that nocturnal activity had much older origin in synapsids, ancient mammal relatives.
Kenneth Angielczyk, a curator at The Field Museum, lead researcher, said that it was considered that synapsids are day animals, but they do not have hard evidence for the same. Researchers have based their findings on the analysis of small bones called scleral ossicles.
These tiny bones are found in the eyes of many backboned animals and also, in birds and lizards. Living mammals do not have these bones, but they were present in many of their ancient synapsid relatives. Lars Schmitz, a professor of biology at Claremont McKenna, Pitzer, said that the information helped them to know more about the light sensitivity feature of the eye. It is that component that reflects the time when animal is active.
It was not at all easy to test these scleral ossicles, as they are quite delicate in nature. But Angielczyk and Schmitz visited many museum collections in the United States and South Africa and took help from other paleontologists.
All these efforts helped them to collect data on scleral ossicles from 24 species. The data was then used to compare with another dataset of living lizards and birds. The comparison was done using a statistical technique developed by Schmitz.
Major findings included, ancient synapsids’ eyes covered the full spectrum of light sensitivities found in living animals; the common ancestor of all synapsids and even living mammals may be nocturnal. Plant eating synapsids are considered to be active during the day. One of the important findings was nocturnality has evolved many times in synapsids.
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