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 (50 miles) left before the two big climbs in Stage 12, prompting Bahrain-Merida to open an investigation. According to the French TV station broadcasting the race, Dennis had an argument with officials in the team car.

Stangelj said Dennis’ condition was good enough to perform, adding he was not aware of any kind of argument that could have triggered the rider’s decision.

Dennis’ withdrawal was even more surprising as it came a day before Friday’s short time trial in Pau, where he would have been an obvious favorite alongside defending Tour champion Geraint Thomas given his pedigree in the race against the clock.

Stangelj said he was not aware of any complaint from Dennis in regards to his time trial equipment and also dismissed suppositions that Dennis could have been frustrated with his role in the team. Bahrain-Merida’s main goal at the Tour this year was to fulfill former Tour champion Vincenzo Nibali’s ambition to fight for a podium finish.

“I never asked him to bring the water bottles in the race,” Stangelj said. “Actually, I even told him yesterday and today that he should save energy for the time trial.”

When asked if Dennis had been difficult to work with before, Stangelj said “it’s difficult to answer this question.”

“But I never have hard discussions with him,” he insisted. “We always found a solution when it was needed.”

Stangelj explained that after Dennis stopped at the feed zone, he was not immediately able to reach out to him because he had already passed that point on the route and could not turn back with his car. He finally managed to get his rider on the phone after another car from the team arrived next to him.

Dennis’ extraordinary withdrawal was the talk of the day but did not eclipse Yates’ maiden win at the Tour.