BAGNERES-DE-BIGORRE, France — In 116 years of racing at the Tour de France, riders have done all sorts of bizarre things, from jumping on trains to fighting with fans at mountain stops.

Rarely have they just vanished in the middle of a stage like Rohan Dennis did on Thursday during the first Pyrenean stage.

For a couple of hours on an otherwise uneventful day in the mountains, nobody was able to say where the time trial world champion had gone. His Bahrain-Merida team even sent an alarming message out on social networks, saying all it cared about was “the welfare” of Dennis after Tour organizers announced he had pulled out of the race.

The Australian ultimately resurfaced at the finish line in Bagneres-de-Bigorre, where British rider Simon Yates, the reigning Spanish Vuelta champion, posted his first stage win after a long breakaway that did not shuffle the overall standings.

Dennis was spotted near the Bahrain-Merida team bus after the stage, but did not make any comment about his decision to pull out.

“We are also confused,” Bahrain-Merida team director Gorazd Stangelj said. “It was his decision today to stop at the feed zone. We tried to speak with him, he said `I just don’t want to talk,’ and abandoned the race.”

Dennis quit with about 80 kilometers left before the two big climbs in Stage 12, prompting Bahrain-Merida to open an investigation.