Fossil Forelimbs (image) Field Museum Share Print E-Mail Caption Photographs of the upper arm bones from seven kinds of early mammal relatives. The three bones on the left are from an early group called pelycosaurs, and the bones are all roughly the same shape. The four bones on the right are from therapsids, the group that includes today's mammals, and they show the greater variety of shapes and sizes that characterize therapsid limbs. The black scale bars represent 2cm. Credit (c) Jacqueline Lungmus, Field Museum Usage Restrictions Please include credit: (c) Jacqueline Lungmus, Field Museum. Share Print E-Mail 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.