Graptolite Specimen (image) University of Leicester Caption This is the fossil specimen, displaying the change from the interlacing tubes to the hourglass structures. Credit Paul Witney, BGS, (c) NERC 2012 Usage Restrictions Use only with credit. 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.