Starting the car in gear would draw a very large current indeed from the battery, much larger than starting the car normally. The excess current may have damaged the contacts in the starter circuit (the solenoid pushes the starter gear into mesh with the flywheel teeth and when the gear is fully forward this closes some heavy electrical contacts and puts power to the starter motor) or the actual brushes or their leads on the motor may be damaged. The clue is that the headlights don't dim when trying to start the engine - so no extra current is being drawn from battery to try to start the car. Check all the cable contacts in the heavy lead from positive (+) battery terminal and the earth cable to body and heavy braid strap from negative terminal to the engine block this may have been broken by the jerk on the engine. There is no fuse in the actual main cable to starter motor because this can carry over 200 amps when starting the engine.
You should at least hear the solenoid 'clicking' when the key is turned, unless the starter gear is now permanently engaged with the flywheel, but pushing the car back and forward in gear will normally free this up.