The finding upends what many archaeologists thought they knew about when our ancestors arrived in the New World.
The Nebraska man said he initially believed the underwater find was the skeleton of a catfish or deer.
The eggs and fossilized bones are the oldest known evidence of "complex social behavior" among dinosaurs, according to scientists.
Researchers named the now-extinct creature "Phiomectus anubis" after Anubis, the Egyptian god of death.
Researchers also found burned bones and carved stones.
Llukalkan aliocranianus appears to have been a top predator in its time, with hearing capabilities potentially exceeding those of similar dinosaurs.
With 45 tentacles, the Sollasina cthulhu could snatch food and creep along the ocean floor.
“I will probably spend the rest of my career working on this site," said paleontologist Robert Gay.