Help me rediscover an old short story.

I probably read this 30ish years ago, most likely in OMNI or a similar mag. It involved a group of explorers who land on a lush jungle planet to chart it. They encounter several weird animals who hide within the jungle, emerging only to retrieve bones (maybe some of the explorers were killed or maybe they killed other animals)?

Far off in the distance is a giant white spire. The big payoff at the end comes when the explorers reach the spire and discover that it's made up of all the bones that the animals had taken for years.

Couple other details I remember:

* One member was a mapmaker, and he repeatedly would stop and sight back down the way they came to better remember/write down the way they came.

* I think the main protagonist was the typical square-jawed captain. But in the end, when confronted with the spire of bone, he looses his nerve or otherwise becomes less heroic?

* Certain local animals travelled along the top of the jungle canopy, almost like it was a solid level above the ground. At one point I believe one or more of the explorers climbs a tree to get to this upper level.

Sound familiar to anyone? Thanks!