What we think of as new has probably been done before if you take time to search for it. Google patents is the easiest way to search the USPTO content. We use patents as a time stamped proof of design activity which is of course traceable and a legal document. 

Some Backhoe History

The agricultural tractor was an ideal base machine for early construction equipment with its robust transmission and frame strength. The tractor first had a front loader attachment added to it sometime in the 1920's. There are references to Clifford Hamilton inventing the first tractor mounted loader in 1926 at Iowa State University for example and also to a Hough designed loader from 1922 manufactured by Blair. The usefulness of these front loaders increased as time went by as they were initially cable operated until they became more effective and popular in the 1940's and had moved to be hydraulically operated.

The development of a tractor mounted rear grading and trenching hoe (hence the "backhoe" name) seem to happen concurrently and independently in the US and in Scotland (we also know that in 1952 Mr. JCB visited Norway on a promotional tour where he viewed and probably purchased a hydraulic hoe attachment but I cannot find a reference to the inventor of the Norwegian backhoe attachment).