Dinosaurs and other extinct mega-fauna are great.
They are big and large and dumb and you can use them as super beasts or dragons without feeling like you are cheating the mythology by just having them being large bastards that eat or step on people.
However they often have long ass hard to say names that can feel out of place amongst the other monster and animal names.
So Now I will Talk About the Merits of Various Nomenclature for Megafauna In Rpgs
This is arguably a redundant point considering the amount of language groups and mythologies involved in the monster manual or even just a regular zoo. Surely one will adapt in time?
Possibly! But there's a certain satisfaction in this (small) aspect of world building .
For example the rareness or familiarity of said dinosaur /mega fauna to the main culture groups is going to be reflected in the name.
So something that a culture talks about a lot is unlikely to have a long name or one with unusual sounds.
If the name used is a loan word from another language it can often becoming shortened or simplified to fit that language.
I.e Tyrannosaurus Rex becomes T-rex, Orang Hutan becomes Orangutan (and not even said like how it's spelt here) .
Names of things very familiar to culture for a very long time tend to be short and simpler (cow , sheep, goat, dog) and sometimes have words created from them (dogged , doggerel)
To mimic this you can retro-fit words for a creature, i.e called a brontosaurs a bridge, the idea being bridges were named after brontosaurs.
When something is discovered or introduced later to culture (and the existing name is unfamiliar or unsuitable) a quick or throw away description often becomes the name.
The name is created by modifying the word for something familiar and/or a closes resemblence to said thing
The familiarity seems to be more important than the actual resemblance (pineapple, sea mouse).
Then a word that references something else it resembles (mole cricket , crab louse)
a differing property from a familiar form (red pine, water melon, sea turtle)
its region or environment (Barbary ape, Canadian goose, Sea snake).
While d&d has a lot of "giant" animals with the giant in the name (giant beaver, giant rat, giant bat etc etc), this doesn't come up a lot in real word naming conventions (obvious exceptions include giant squid, giant clam and a few others).
Probably because its rare that you have a giant animal and the regular animal in the same place , so the resident population would just see the giant animal as regular size.
Even when there is 2 similar animals of different sizes (Rabbit and Hare, Rat and Mouse, Gazelle and like one of those dozens of animals like a gazelle but a different size and horn shape) it's rare that one of them gets called giant.
I think it only gets done when some explorer or discoverer type is trying to impress people back home.
Sometimes when the name is a loan word used, the loan word can just be a common description in that language (orangutan meaning Man of The Woods, though there is possible a touch of reverence here) .
Where a loan word is used and its not particularly simple , its possible because the named creature was particular exotic or impressive and someone was trying to impress everyone back home.
Something particular impressive can then loan its name as new verb or adjective (mammoth ). This can be an excuse to name a beast after an adjective or verb in your world (the Mighty,A Wiggle, Flung)
When new names are created for extinct megafauna in fantasy one awful habit is doing a weird fake tribal "part+ thing the part resembles", i.e Dagger Tail, Hammer head, Whip Tail.
Though the latin name of dinosaur are often this , there's few real world examples of this being used as a naming convention.
To my ear these names tend to be too long for something familiar to culture and too banal if its something unfamiliar and impressive.
Here's my list of megafauna I'm using and the names for them. They are mixture of different language groups, bad puns, descriptors, archaic words , and mashed together combinations of the above.
T-rex: Tyrant , Tyrant King, Tyrant Lizard
(medieval bestiarys had a habit of trying to name one particular animal as the King animal of that type. The basilisk was referred to as the King Of Poison which I always liked)
(assuming namers of it would compare it to tortoise and some wag would have made this joke. The only thing close to a real world name created portmanteau syle like this that I can think of is the old word for giraffe "camelopard". Referring to it having spots like a leopard and a neck like camel)
(armadillo means little armoured one , this means big armoured one. It's an excuse to mix up the language origins without straying too far from the familiar)
Pterodactyl. = skinbird
Medium , ridable : Picador
(these are common enough to even be a steed. Picador refers to the military unit that uses them and has become a name for the animal itself.)
Quetzalcoatlus Emperor Skin Bird
(a geological term meant to be referring to the shape of its back. I won't be able to say this without thinking about the "Because da Jungle is MASSIF" joke but that's not a problem.
(Micheal Raston of Lizardman diaries came up with this and it's fucking gold)
(it's good word and I wasn't using it for a super monster. Doesn't have enough mythological richness for me personally to "waste" on just being a big animal)
Velicoraptor: Raptor (popular culture has done the work here already)
Megatherium: Slothlord (More because it sounds good than applied real world naming conventions)
Paraceratherium: Indrik, Hummock
(Indrik is mythological creature that these were named after at one point. Hummock is type of hill and nice mouth shape word)
Mosasaurs; Devil-whale (The Vikings had a lot of "evil whales" and some of them are described pretty similar to a Mosasaur. I would use one of their names but I can't pronounce them easily)
Plesioaur : snakefish, brinewyrm. tideworm
(I feel I can get away with the slightly inaccurate and unimpressive "snakefish" this as there isn't a lot names like this here and marine animals tended to get named like this , "whale shark", "sea lion", "sun fish". Plus I like the incongruousness of it being called a snakefish?
(I might be overusing the King thing here but Kingpig is good word)
Chalicotherium: goat-ape, knuck-cuu
(as its not as terrifying as some of the others I feel it can have more mundane name like goat-ape. Knuck-cuu ; like a cow but walking on its knuckles