Every one says there only in the railway caves,but in reality they can be found across the blue zone. The problem is they often get killed, or they are in places you cannot reach since they can cling to walls like the megalania. Of course the railway cave is the most recommended place to tame one becaue that cave is actually safer than the blue zone. Also for some reason, despite having the narcotic mushroom being their favorite, they can knock themselves out if you put it in their inventory when tamed, and while I found have seen some having from ceilings of the railway cave, they don't appear to climb anymore when you tame them. Otherwise their an interesting light pet. By the way, there's almost always a carnotaurus inside the railway cave, and while I was able to kill it the first time, it respawed on my way out, and chased me until I got to the point where you have to crawl. By the way, it's not worth bringing a mount to the railway cave. You need a cryopod to bring anything that won't sit on your shoulder, and many of the passage ways are too small, plus this cave forces you to use the climbing pick or a grappling hook. There's a few scorpions, raptors, and ravagers, and don't fall into any pits, because there's a beefy crab down there. Also you can cheese your way through by getting creatures to walk off ledges. I highly recommend plant species z fruit and bolas.
Throw down some sleeping bags in the cave and catch a low level anything and us them as a vault for glow sticks and climbing pick,then c carrying nothing run through and have all the bad things chase you and the glowtail will stay there, then come back after revive and tame yourself glowtail
To help you get through the cave listed above just bring a metal shield climbing picks chitin armor a sword and a cross bow to get through the first clearing just climb over all of the dinos using the climbing pick then lead them off of the cliff if you have to come face to face with anything just cut it down with the sword