NEW EVIDENCE FROM THE NORTHERN INDIAN MARGIN DOES NOT SUPPORT A CONODONT LILLIPUT EFFECT AT THE SMITHIAN-SPATHIAN BOUNDARY EXTINCTION EVENT

The pattern and timing of the biotic recovery of marine ecosystems after the end-Permian mass extinction is still a matter of debate. It has been suggested that the size of individuals was reduced in several marine clades during this recovery interval, a phenomenon coined the ‘Lilliput effect’ (Schubert and Bottjer 1995, Twitchett 1999). Yet, Brayard et al (2010, 2011) showed that previous conclusions drawn from the iconic gastropod case are not supported and a recent study (Schaal et al 2016) showed that several clades have responded contrastingly.

Owing to their high evolutionary rates and widespread, abundant distribution, conodonts are a tool of choice for these studies because of their high temporal resolution. The largest intra-Triassic crisis for nektonic organisms (ammonoids and conodonts) occurred at the Smithian-Spathian boundary (SSB) and it was overall the largest crisis for conodonts in the Triassic (Orchard 2007, Goudemand et al, 2008). Chen et al (2013) measured the temporal evolution of the size of conodont P1 elements from the Nanpanjiang Basin, China and concluded that their size shrunked at the SSB, when seawater temperature became extremely high.

We performed a similar study using conodont material from three other localities of the Northern Indian Margin (Tulong, South Tibet; Guryul Ravine, Kashmir, India; Nammal Gorge, Salt Range, Pakistan). Our material comprised more than 6000 measured conodont P1 elements. Furthermore it included not only specimens of segminate (Neospathodus, Novispathodus, Triassospathodus) but also segminiplanate (Neogondolella, Borinella, Scythogondolella) conodont elements.

We observe that conodont genera with segminate resp. segminiplanate P1 elements show opposite trends of temporal size evolution around the SSB, contrasting with the previous conclusions of Chen et al. 2013. Moreover, the material from Nammal shows that between the middle Smithian and the late Smithian, both segminate and segminiplanate conodonts experienced a size reduction. Overall our results indicate that a simplistic link between hot seawater temperature and decreasing conodont size is not supported.