What dynamic languages run on the jvm? To my knowledge it doesn't support dynamic types at all.
https://en.wikipedia.org/wiki/List_of_JVM_languages
> To my knowledge it doesn't support dynamic types at all.
Not sure where you've got that from or what that's supposed to mean.
Perhaps he meant no dynamic languages have become popular enough on the JVM that it becomes common knowledge that the JVM can support popular types. None of those 4 languages you mentioned (Clojure, Apache Groovy, JRuby, Jython) are popular, whereas alternative JVM languages built from the ground up as static languages (i.e. Kotlin and Scala) are the ones people are adopting.
Reflection used to be used to implement dynamic types, but since Java 7 (2011) there's been a JVM instruction, invokedynamic, to explicit support dynamic types.