Megalobrachidae (lit. "big arms") are a clade of Synischia.
Megalobrachids first evolved around the year 4205ma, driving many large Placostracans to extinction in the process. Following the emergence of the steppe, the Titanopoda clade diverged from the main branch, although the earlier species remained in the forests.
Megalobrachids are herbivorous, with the majority of species serving as browsers. Their pedipalps are equipped with hooked claws used to reach for vegetation, and an expanded foregut used for aiding digestion, resulting in a larger cephalothorax compared to other Osteopoda. The Megalobrachid branch boasts the largest terrestrial animals yet seen, with the smallest species measuring 1.5m in height and the largest at 4m.
- Archemegalobrachidae: The earliest branch, found in the forests and equatorial swamps
- Titanopoda: A later branch, found along the steppe