  Ultrahigh energy cosmic ray air showers probe particle physics at energies
beyond the reach of accelerators. Here we introduce a new method to test
hadronic interaction models without relying on the absolute energy calibration,
and apply it to events with primary energy 6-16 EeV (E_CM = 110-170 TeV), whose
longitudinal development and lateral distribution were simultaneously measured
by the Pierre Auger Observatory. The average hadronic shower is 1.33 +- 0.16
(1.61 +- 0.21) times larger than predicted using the leading LHC-tuned models
EPOS-LHC (QGSJetII-04), with a corresponding excess of muons.
