Around 00:53:25, when the helicopters are flying over Downtown LA, the moment before the camera perspective changes from in the sky to in the helicopter, the helicopter towards the bottom of the screen inexplicably vanishes into thin air. This error was fixed in later releases of the film however.
Before setting off to the marker it is emphasized that everyone must travel in pairs side-by-side; however, every time the party is seen on the move, they are in single file.
At 1:04:20 the black Hummer passes the four characters running in the street. At 1:04:22, or two seconds later, the black Hummer passes the same four characters running in the street, again.
Bud comes up with a plan to lure and trap Big Red in the Third Street Tunnel. But the tunnel they go to is actually the Second Street Tunnel.
Big Red constantly changes size throughout the film.
When Lt. Commander Ellis briefs Lieutenant Peet on why his team has been chosen for the mission, he tells him that his Seal team is the best Search & Rescue team in the Navy. The "best Navy Seal team" would not have non-regulation haircuts (such as long hair and long sideburns), use hair gel to "spike" their hair, have goatees and beards.
When the Navy helicopter attacks the dinosaur it shows muzzle flashes coming from the helicopter's nose which indicate the gun is mounted in its nose. The helicopter is an SH-60 Seahawk and no version used by the Navy has any weapons mounted in the nose.
When Dr. Frank is informing the team of what they will encounter, he tells them that the cretaceous period had less oxygen making it harder for them to breathe, when in fact it had 3 times more than what we have now.
Empty ammo cartridges are never seen being ejected from any automatic weapons.
Commander Dorn asks; "Where did that tank come from?" He is looking at a half track, not a tank. Unlike today, where many armored vehicles have turrets and a passing resemblance to tanks, a half track and a tank are not even vaguely similar.
They went back in time 60 years ago they said that BIG RED was tough skin and that a M-60 would not kill him. If they went back in time when the movie was made that put them from 1948. The M-60 came out 1957. However, the statement was made by a modern SEAL team member while in the present, so the statement is, time-wise, consistent.
When the surviving crew are attempting to get the attention of 'Big Red' while staying in the 3rd street tunnel, an SUV can be seen driving through the tunnel which just finished being barricaded by the military. The SUV is driving backwards.
The shot of the T-rex turning and roaring at Chief is immediately re-used twice, in close-up to remove Chief from the shot. However, both times the sight of Chief's automatic weapon is still visible in the lower left corner.
When the soldiers first travel back in time, they encounter a Brachiosaurus. On the hillside behind it is a very noticeable road that runs all the way from one side of the screen to the other.
When Lt. Commander Ellis briefs Lieuenant Peet on why his team has been chosen for the mission, he tells him that his Seal team is the best Search & Rescue team in the Navy. The "best Navy Seal team" would not have non-regulation haircuts (such as long hair and long sideburns), use hair gel to "spike" their hair, have goatees and beards.
When the rescue team finds the survivors they are dressed in "stone age" gear, including quite a lot of fur hides. Which would have been difficult considering the lack of furry animals larger than very small mice during that era.
Throughout the film, sound effects of gunfire are not accompanied by images of anyone shooting, or the muzzle flash special effect was forgotten.
Before the man and woman rappel down the side of the mountain to go looking for caves, she starts talking about Land-sat photos. During her dialog, the camera crew (about five people) and all their camera equipment is plainly seen in the reflection on her black safety helmet.
At the 31 minute mark the camera pans across a lake with mountains in the background. There is clearly a blue luxury home in the upper left on top of the mountain.
The very title of this film is wrong. The "100 Million BC" isn't actually mentioned in the movie but instead they say they go something like between 60 and 80 million years back in time.
After the briefing the commander tells the men they will be leaving in the time machine at "0300 hours" which is 3:00 AM. However, when they meet at the time machine you can see it is obviously daylight outside.
Dr. Reno says; "We're going to attempt to bend light using electromagnetic radiation", which is patent nonsense. Light *is* electromagnetic radiation, along with ultra-violet, x-rays, microwaves, infra-red and radio waves - none of which will bend light.
LCDR Dorn is wearing a miniature SEAL pin. Miniature devices are only worn on formal Dinner Dress uniforms. Also his belt isn't khaki. Pretty unsat for a SEAL officer.