Final answer:
The statement regarding Late Triassic understory is false; gymnosperms were likely more dominant. Ferns, however, did thrive after the mass extinction due to their ability as early colonizers and rapid reproducers.
Step-by-step explanation:
The statement that ferns and seed ferns dominated the Late Triassic understory is false. During the Late Triassic, it is likely that gymnosperms, such as cycads and conifers, were more dominant in the understory. Ferns did become more abundant after the Cretaceous-Paleogene (K-Pg) mass extinction, taking advantage of their capacity as early colonizers to grow quickly on poor soil and reproduce rapidly.
Fossil records indicate that by the end of the Devonian period, ferns and horsetails populated the landscape. The fossilized leaf from Glossopteris, a seed fern that thrived during the Permian age, exemplifies such plants. Furthermore, it is observed that fern spores were more abundant below the Cretaceous-Paleogene boundary than above it, suggesting their significant presence before the mass extinction event.