Origin of the phrase
The word missing is from Old English ‘missan’ of Germanic origin to describe something that is not present, while link is from the early 15th century, likely from Old Norse, to describe a series of rings or loops in a chain. The phrase missing link is first attested in 1851 in Lyell.
Missing link refers to an omitted or unknown detail that is necessary in order to fully comprehend an issue or subject. The missing link is also used as a non-scientific term to describe a transitional fossil or species connected to the process of evolution. It is used to represent a hypothetical intermediate evolutionary form connecting animal species and its presumed ancestors.
A bizarre dinosaur discovered in southern Chile could provide the missing link to a mystery that has puzzled scientists. The Chilesaurus has been described as a kind of ‘Frankenstein’ dinosaur, as its physical characteristics seem to borrow elements emerging from different species. While the creature appears to be vegetarian due to the fact that its teeth are flat and designed for grinding plants, its head looks like a carnivore’s. Scientists have determined that the Chilesaurus belongs to its own group, the Ornithischia, and was related to the Stegosaurus and Iguanodon. The strange blending of features places the species in an important position in dinosaur evolution as the missing link between major groups.
A fact or piece of information that you need in order to have complete knowledge of something.