Inside the elegant 1920s golden marble lobby at the U-M Exhibit Museum, children gather around a folding table to guess how many Brazil nuts are in a jar. A staffer restocks cold apple cider and cookies. A flushed three-year-old in a pink sweater howls; her father grits his teeth and carries her out the door. In the quiet, parents urge children to examine permanent exhibits in the lobby. “Oh, cool!” cries a boy, pointing to eight perfectly formed trilobites caught swarming for eternity in a fossil.

This is the annual Dinosaur Discovery Day at the U-M Exhibit Museum. On the second floor, fifteen kids kneel, shoulder to shoulder, around a shallow sand pit. Their hands and knees embedded in the sand, they dig furiously for fossils. “I got one!” cries a girl, beaming. Another child holds out two fossils. “You can only have one,” says another girl in a bossy tone. In a nearby diorama an endless battle rages between a tiny saber-toothed tiger and even smaller human combatants.

Two towering mastodon skeletons dominate the center of the main hall. The top of a girl’s blue dinosaur paper hat reaches the mastodons’ knees as she roams around the room. Excited volunteers offer information on the layered teeth of one fossil. Adults pick up a black eighteen-inch stegosaurus horn for a closer look.

In the back of the hall, a cheerful helper in a Michigan T-shirt instructs families how to make dinosaur paper hats. Behind the busy crafters, a brown thirty-two-foot-long edmontosaurus skeleton cast rests in a base of white material in an open case. “Look, I have a quadriceratops,” says a laughing mother. She points to her toddler’s four-pointed pastel hat.

On the third floor, two girls and a boy enact a play with “Paleo Puppets.” A T. rex puppet sings his ABCs in tune while a two-year-old girl in a jumper spins in circles. Three glassy-eyed squirrels survey the puppet show from above. The puppeteers cry, “Here, Mommy—watch this show.” The children don’t notice a snarling wolf, body tense, teeth braced, and fur on end, that stands two feet away behind glass.

A disco ball welcomes dancers to the “Dino Dance” on the fourth floor. Music throbs as children whirl in the dark. Colored lights flash on the walls. In another gallery down the hall, silent children stir plaster with water at a fossil-casting table while their parents crash on puffy chairs.

Outside the tall windows, late afternoon shadows darken brick buildings. The moon gleams in a blue, cloudless sky. At five o’clock, children and parents make their way downstairs to greet the icy air. Spiky dinosaur crowns rattle in the wind.

Dinosaur Discovery Day returns to the Exhibit Museum on Saturday, December 6.