Okay, so imagine you're outside playing with your toys in a big park. Now, imagine there are lots of different animals living in that park, like dogs, cats, birds, and even some weird-looking creatures you've never seen before.
Now, a long, long time ago, before you were even born, there was a time when the Earth looked very different than it does today. This was a time called the Triassic period, and there were lots of different animals living on land during this time too.
Scientists have studied the bones and fossils of these Triassic animals, and they've organized them into groups based on what they looked like and how they lived. They call these groups "faunachrons."
Basically, a faunachron is just a fancy word that means "a group of animals that lived in the same time and place, and had similar features." So, just like how there are different types of animals in the park today, there were different types of animals living during the Triassic period, and scientists group them together based on their similarities.
Some of the faunachrons that lived during the Triassic period include things like archosaurs (an ancestor of modern-day crocodiles and birds), therapsids (an ancestor of modern-day mammals), and many others.
So, if you ever hear someone talking about Triassic land vertebrate faunachrons, just remember that they're talking about all the different types of animals that lived on land during that time period, and how scientists group them together based on their similarities.