... I would have waited an eternity for these...

[Hursticon]

I might be wrong but isn't sludge a diplodocus?

No, you're dead right actually.
When Sludge was originally designed, he was modelled after a Brontosaurus but the Brontosaurus has been found to be a non-existent Dinosaur since (Whether it was misnamed, mis-identified or both I'm not sure), which is why he is now, at least by me, referred to as a Diplodocus.

*EDIT: Brontosaurus = Apatosaurus
From Wikipedia:

In 1877, Othniel Charles Marsh published the name of the type species Apatosaurus ajax. He followed this in 1879 with a description of another, more complete specimen, which he thought represented a new genus and species, which he named Brontosaurus excelsus. In 1903, Elmer Riggs re-examined the fossils. While he agreed with Marsh that Brontosaurus excelsus was likely a distinct species, he also noted many similarities between B. excelsus and A. ajax, and decided that both should be placed in the same genus. Riggs re-classified the species as Apatosaurus excelsus.[15] Almost all paleontologists since Riggs published his opinions have agreed that the two species should be classified together in a single genus. According to the rules of the ICZN (which governs the scientific names of animals), the name Apatosaurus, having been published first, had priority as the official name; Brontosaurus is considered a junior synonym and has therefore been discarded from formal use.