Ancient crocodilian ancestors that abandoned land for water nearly 200 million years ago supposedly got larger because they were released from the constraints of gravity, territory and diet. But a new study suggests that the upper bounds of size in aquatic vs. landlocked crocs were similar — and that smaller aquatic species got larger mostly to avoid freezing in the frigid, heat-stealing depths.

Water might inflict more pressure in the pounds-per-square-inch sense, the thinking went, but it also probably relieved some — especially the sort that kept crocs from going up a size or 10. If they wanted to enjoy the considerable spoils of considerable size, water seemed the easy way.

A recent study from the University of Nebraska-Lincoln’s Will Gearty, who compiled a database of 264 species stretching back to the Triassic Period, says that freedom was actually compulsion in disguise.

After analyzing the database of crocodyliforms — a lineage of crocodile-like species that share a common ancestor — Gearty found that the average weights of aquatic crocodyliforms did easily surpass their semi-aquatic and landlocked counterparts, sometimes by a factor of 100.

But the study suggests that this disparity represented a response to, not a release from, the pressures of natural selection. Rather than expanding the range of crocodyliform body sizes, as some longstanding theories would predict, taking to the water instead seemed to compress that range by raising the minimum size threshold needed to survive its depths. The maximum size of those aquatic species, by contrast, barely budged over time.

And when Gearty derived a set of equations to estimate the largest feasible body sizes under aquatic, semi-aquatic and terrestrial conditions?

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Materials provided by University of Nebraska-Lincoln. Original written by Scott Schrage. Note: Content may be edited for style and length.