Toweius was among the most widespread and important calcareous nannoplankton groups in the oceans 53 million years ago, playing a key role in the evolutionary transition to another prominent group during the Cenozoic (Reticulofenestra). Using detailed biometric measurements with high-resolution imaging, we describe a distinctive, smaller morphotype of Toweius. Our results indicate that this form evolved gradually through speciation, shedding light on the complex evolutionary dynamics of Toweius.