User blog comment:Kogath/Monster Hunter: World Discussion/@comment-6050823-20190412000015

This information comes from the Dive to Monster Hunter World, pages 334 and 335.

Bird Wyverns: Bird Wyverns have astonishing characteristics that are reminiscent of birds. Some species like the Kulu-Ya-Ku have slender, wingless bodies while others like Pukei-Pukei have wings that allow flight. The wingless ones often have crests, or other special organs, on their head. Many of them are medium-sized monsters that walk bipedally with their developed legs, allowing them to leap great distances.

Fanged Wyverns: Fanged Wyverns are quadrupedal monsters that have forelimbs that are larger than their hindlimbs. Despite walking on all fours, Fanged Wyverns share the same ancestors as Bird Wyverns and Flying Wyverns, and are considered to be a relatively new monster class in the Old World. Interestingly, various kinds of Fanged Wyverns like Jagras and Great Jagras have been seen living in the New World, and investigations on this class continue on.

Piscine Wyverns: Instead of wings or arms, Piscine Wyverns possess fins and specialize in swimming in certain environments. Species similar to Jyuratodus support their bulk with their hind legs, though their basic movements tend to be slow while walking on land.

The Existence of Subspecies: The Guild defines Subspecies as a monster species whose population has changed from environmental factors or one that evolved differently to adapt. The Pink Rathian found in the New World, for example, is thought to have grown under the influence of the land's rich energy. There are some exceptions that are differentiated by their gender alone like Black Diablos for example. Most Subspecies sport different colors from their cousins and are usually more aggressive than them as well.

Flying Wyverns: Many species of Flying Wyverns have excellent flying abilities like Rathalos for example. This monster class often has winged forelimbs and strong hindlimbs. The biggest feature for this class is their wings which is quite similar to a bat's. Though none have been confirmed in the New World so far, there are some quadrupedal Flying Wyverns, species with forelimbs that have developed into arms which allow them to walk and run on all fours.

Brute Wyverns: Bipedal monsters that perfectly adapted for life on land, Brute Wyverns use their muscular legs to dominate their competition. Though most of them have small front limbs only used for supporting their body, some exceptions have been found in the Old World. As seen in the New World with Anjanath, Brute Wyverns and Flying Wyverns can often cross paths with one another.

Elder Dragons: Elder Dragons aren't really a classification, they're just monsters that can't be classified or grouped with other known species. If the monster can't be classified, it is made an Elder Dragon, and many of them have special abilities that can be considered natural disasters. Some have horns on their head, wings on their back, and walk on all fours, but there are many that don't possess those features like Zorah Magdaros. It is said that these monsters have an energy in their blood known as the Dragon Element, however, that has yet to be confirmed.

Other Classes Identified by the Guild: Small monsters of various classes have been confirmed living on the New World; Herbivores (Aptonoth), Neopterons (Vespoid and Hornetaur), Fish (Gajau), Wingdrakes (Mernos, Noios, Raphinos, and Barnos), and Lynians. Since there is no confirmation about the following classes living within the New World, details about them have been omitted; Carapaceons, Fanged Beasts, Leviathans, Temnocerans, Snake Wyverns, and Amphibians. Though they were excluded, it is illogical to deny the possibility of discovering these classes in the New World in the future.