In science education, epistemic vigilance plays a key role in the development of students' critical thinking by supporting students' abilities to evaluate the expertise level of the source and to evaluate the claim itself, using rigorous scientific standards and appropriate argumentation heuristics. Based on previous studies, which suggested two aspects of epistemic vigilance--reflecting the source of information and the claim that is made--we developed the Extended Epistemic Vigilance Framework (EEVF) that includes an additional aspect of evaluating the receiver. In an empirical exploratory pilot study, we evaluated the reliability and validity of an EEVF-based category system and investigated to what extent the EEVF can be used to characterize changes in biology graduate students' epistemic vigilance after participating in a critical thinking course. Results show that the EEVF-based category system includes reliable and valid categories for identifying students' epistemic vigilance. A statistically significant increase with a small effect size was found in students' epistemic vigilance regarding the reliability of the source and the references used to support the claim following their participation in the critical thinking course. However, a statistically significant decrease with a small effect size was found regarding the awareness of the aspects of the one-sidedness of the claim, the context of the claim, and cognitive biases and socioemotional influences on the receiver. In general, these findings indicate that the EEVF offers an improved framework to analyze students' epistemic vigilance more comprehensively.