Dinaelurus crassus was a real extinct pre-historic species that (in the Ratha's novel) was progenitor of the Dinaelurus illumina sapiens.
Appearances[]
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.
(c)viergacht. An art of a D.crassus.
Clare Bell explanation[]
The existence of the Dinaelurus crassus into Ratha's world has been mentioned by the author Clare Bell.
(quotes from [1])
"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."