Dinaelurus crassus was a real extinct pre-historic species that (in the Ratha's novel) was progenitor of the Dinaelurus illumina sapiens.
The species has never appeared nor has been mentioned in the series. It's believed they're lonely hunters, with even less intelligence and organization than the Un-Named. Despite being their progenitors, the Dinaelurus illumina sapiens have distanced from the original species and it's believed that only some less-developed Un-Named could successfully breed with the crassus.
Clare Bell explanation Edit
The existence of the Dinaelurus crassus into Ratha's world has been mentioned by the author Clare Bell.
(quotes from )
"So the Named can't cross with D. crassus; they have become genetically isolated. The UnNamed form a buffer population between the Named and the ancestor species."