Part of the Breakthrough secret project. ;)

The semi-transparents are the smallest average height and the full opacity is the largest average height. The former is usually young adults and the latter is elders and ancients. Since Sparkwings vary so damn much, they're an exception. Young adults vary between the sizes of young adult Sparkclaws and young adult Sparkwings and elders can be the size of elder Sparkclaws and elder Longwings.

Sparkwing:
Min: 1.68m (5'6")
Max: 3.66m (12')

Longwing:
Min: 2.29m (7'6")
Max: 3.66m (12')

Sparkclaw:
Min: 1.68m (5'6")
Max: 2.67m (8'9")

Night Wyvern
Min: 2.74m (9')
Max: 4.27m (14')

Forest Wyvern
Min: 1.68m (5'6")
Max: 2.29m (7'6")

Desert Wyvern
Min: 1.07m (3'6")
Max: 1.52m (5')

Sea Wyvern
Min: 1.83m (6')
Max: 1.22m (4')

Tundra Wyvern
Min: 83cm (2'9")
Max: 1m (3'3")