Answer

Yes. In Jain cosmology, there is a gradual reduction in human height, lifespan, and physical strength as time moves through the avasarpiṇī era. Because of this, Lord Ṛṣabhanātha, the first Tirthankar of the current cycle, is described as extremely tall, while Lord Mahāvīra is described as much shorter.

Explanation

This reduction is understood as part of the natural decline of the age, not as a difference in spiritual greatness.

• Earlier Tirthankars appeared in a much more expansive and prosperous age.
• Later Tirthankars appeared in a more diminished age.
• So the body size changes according to the era.

In Jain tradition, this is a cosmic rule of time:

• Avasarpiṇī = descending half-cycle
• During this phase, human height, lifespan, memory, and bodily strength gradually decrease

Spiritual Understanding

The important point is that height does not measure spiritual status.

All Tirthankars are:

• equally enlightened,
• equally pure in soul,
• equally worthy of reverence.

Their bodies differ according to the era, but their spiritual realization is the same.

Takeaway

So yes, there is a reduction in height from Ṛṣabhanātha to Mahāvīra according to Jain cosmology, but this reflects the changing age of the world, not any difference in spiritual greatness.