PREQUEL TO EXTINCTION: MORPHOMETRIC ANALYSIS OF THE NORIAN – RHAETIAN (LATE TRIASSIC) CONODONT SPECIES MOCKINA ENGLANDI AND MOCKINA CARINATA ACROSS WESTERN CANADA

The final extinction of class Conodonta occurred during the end-Triassic to earliest Jurassic interval. Leading up to this, Tethyan conodont pectiniform morphology underwent an overall shift near the Norian – Rhaetian boundary from the prominent platform denticulation typical of the Mockina genus to smaller elements with reduced or absent platforms exemplified by the genus Misikella. This shift may have occurred in response to elevated environmental pressure that has been proposed to persist throughout the entire Rhaetian stage, stressing marine biotic communities on a multi-million-year timescale and elevating the impact of the terminal extinction event. Within the Upper Triassic strata of the Panthalassan realm (western North America), this morphological trend is comparatively more ambiguous, as occurrences of Misikella are rare. Morphometric analysis of Mockina species that persist into the Rhaetian can determine with quantitative rigor if morphological shifts comparable and coeval with those of Tethys occur in Panthalassa.

The species Mockina englandi and Mockina carinata are abundant in extensive Norian and Rhaetian conodont collections from the Canadian Cordillera, particularly from the Pardonet Formation in northeastern B.C., the Sinwa and Aksala formations in northwestern B.C. and southern Yukon, the Parson Bay Formation on northern Vancouver Island, and the Peril Formation on Haida Gwaii. The present study utilizes landmark-based geometric morphometrics with eigen analyses to investigate shape variation within the P₁ elements of these species. Principal component analyses are used to determine factors representing the most significant morphological variation, after which canonical variate analyses are used to determine how these forms vary with age and paleogeographic position. The factor most consistently representing the greatest amount of morphological variance appears to be the number and displacement of both carinal and platformal denticles together, differentiating elongate elements with more denticles and stout elements with fewer. This may suggest that intraspecific variation in these conodonts favour carinal compression and expansion in response to abiotic conditions, contrary to the stress-induced intergeneric platform reduction observed in Tethys at this time.