It is thought the remains belong to a child from the Roman period.
Archaeologists also found two bangles made of jet.
The coffin was opened with ease, as the lid was made of beaten lead folded over a box. The corners were sealed with molten lead.
Tests will, over the coming weeks, be carried out on a soil sample taken from the coffin.
Investigators at the University of York will look for biological and chemical signatures, as well as evidence of any organic remains such as oil or flowers that may have been buried with the deceased.
It may also be possible to find evidence for Roman medicines or drugs.
Meanwhile experts will, over the next few days, remove the clay and silt that has filled the coffin. Archaeologists hope to be able to submit a bone sample for a radiocarbon dating, which would help narrow down the possible date range for the burial.
Scientists hope the findings will shed new light on the culture of Roman Britain.
Stuart Palmer from Archaeology Warwickshire told historyextra: “This is an aspect of Roman British burial that is virtually unknown. It is very unusual to find a Roman child buried in this way.
“We suspect the child came from a wealthy family. The two jet bangles rather suggest that the child was female, although we cannot say with certainty if they were worn as bracelets, clothing adornments or were woven into long hair.
“What we really want to find is teeth, as they can tell us about diet. We may even be able to undertake isotope analysis to find out whether the child was born in the local area.”
Chris Wright, a Digging Up the Past metal detectorist who stumbled across the coffin while searching for historical ‘casual loss items’ such as coins and brooches, told historyextra: “It has been absolutely fascinating. It will be very interesting to see what these tests tell us.
“I am just someone who enjoys history, so if I can find something that contributes towards our understanding of the Roman period, I feel very proud.”