Thrinaxodon (IMAGE) Field Museum Caption Life reconstruction of the ancient mammal relative Thrinaxodon from the Triassic Period of Earth history. Similar in size and shape to a modern mink, Thrinaxodon is close to the inferred size of the ancestor of the group of ancient mammal relatives called cynodonts, and it shared that ancestor’s likely preference for animal food. Image by April Neander. Credit Image by April Neander. Usage Restrictions Please include credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.