Conodonts are an extinct group of marine chordates with a feeding apparatus composed of microscopic “tooth-like” elements. Detailed size measurements of 441 conodont elements of the closely related genera Neospathodus, Triassospathodus, and Novispathodus from south China show for the first time that these clades suffered a temporary, but significant, size reduction during the Smithian-Spathian Boundary crisis. Size reduction of conodonts was caused by an episode of global warming, further strengthening the link between morphological and climatic changes recorded in the fossil record. Systematic sampling of five sections in the IdrijaŽiri area, Slovenia, has resulted in the discovery of new species: Platyvillosus corniger sp. nov. and Neospathodus planus sp. nov. Nine discrete conodont Unitary Association zones are proposed for this area. However, the Lilliput effect recorded here is in younger strata than in south China and demonstrates that further research is needed to better understand this phenomenon. The first study of morphological variation in Triassic segminiplanate conodonts using geometric morphometrics demonstrates strong allometric growth patterns for the species Paragondolella bifurcata Budurov & Stefanov, 1972. We suggest using only larger sized conodonts in the population of a rock sample for the definition of new species in future studies. A review of the literature on all Middle and early Late Triassic conodonts is presented. The evolutionary lineages, stratigraphic distributions as well as their taxonomic systems have been re-evaluated, and synonymous species have been identified. Conodont provincialism and diversity have been briefly discussed.