Some species I would pick for a Triassic species pack, assuming I could only pick four; please note that I was not sure for some of them which is why there is another option listed with the word or above their name:
Caelestiventus, A pterosaur species from the late Triassic period found in Saints & Sinners Quarry of northeastern Utah in United States. It's name means heavenly winds. It is important because it is the sole example of a desert-dwelling non-pterodactyloid pterosaur and is 65 million years older than other known desert-dwelling pterosaurs. Caelestiventus is one of the largest known Triassic pterosaurs, with a wingspan of at least 1.5 meters (4.9 ft) and a skull 17.8 cm (7.0 in) long.
Either Moschorhinus, An extinct genus of therocephalian, it was a carnivorous Synapsid found in the Late Permian to Early Triassic of the South African Karoo Supergroup. It is believed to have hunted like a big cat. Moschorhinus were the only large therocephalians. During the Triassic period, they were the largest therocephalians of their time.
or
Cynognathus, An extinct genus of large-bodied cynodontian therapsids that lived in the Middle Triassic. Cynognathus was a 1.2-metre (3 ft 11 in) long predator closely related to mammals and had a southern hemispheric distribution. Fossils have so far been recovered from South Africa, Argentina, Antarctica, and Namibia. The generic name Cynognathus is derived from Greek kyon and gnathos, meaning "dog jaw".
Lisowicia, An extinct genus of giant dicynodont synapsid that lived in what is now Poland during the late Triassic period. Lisowicia is the largest known dicynodont, as well as the largest non-mammalian synapsid, and is estimated to have weighed between 5–6 tons, comparable in size to modern elephants. It was also one of the last dicynodonts, living shortly before their extinction at the end of the Triassic period. Lisowicia is unique amongst dicynodonts for its erect posture, with all four limbs held upright directly under its body. This is similar to the limbs of living mammals and dinosaurs, but unlike the sprawling and semi-erect postures typical of all other dicynodonts (and indeed all other non-mammalian synapsids), and shares many independently evolved features of its limbs with large mammals.
Either Panphagia, It was a sauropodomorph dinosaur described in 2009. It lived around 231 million years ago, during the Carnian age of the Late Triassic period in what is now northwestern Argentina. The name Panphagia comes from the Greek words pan, meaning "all", and phagein, meaning "to eat", in reference to its inferred omnivorous diet. It is believed to have been an omnivore and is one of the earliest known dinosaurs.
or
Ingentia, a genus of early sauropod dinosaur from the Late Triassic (late Norian-Rhaetian) of Argentina. The type specimen of Ingentia, PVSJ 1086, was discovered in the Quebrada del Barro Formation of northwestern Argentina. Its name means first huge one, a reference to one of the first very large sauropodomorphs to evolve.
or
Macrocollum, A species of unaysaurid sauropodomorph dinosaur that lived during the Late Triassic period in what is now Brazil. It is one of the oldest dinosaurs known. The generic name combines the Greek word μακρός (long) and the Latin word collum (neck), referring to the animal's elongated neck.
