Geometric morphometric assessment of Guanshan trilobites (Yunnan Province, China) reveals a limited diversity of palaeolenid taxa

The Guanshan Biota is a typical Burgess Shale-type Cambrian-aged Lagerstätte with diverse trilobites. As such, the taxonomy of trilobites from the Guanshan Biota, especially the palaeolenid group, has been the focus of research over the last decade. To develop this research, we present a geometric morphometric analysis of cranidial shape in 60 specimens from three sections of the Guanshan Biota from the Wulongqing Formation (Cambrian Series 2, Stage 4), Yunnan Province, South China. We show that cranidia of Megapalaeolenus deprati and Palaeolenus douvillei occupy distinct regions of morphospaces and that P. douvillei and P. "lantenoisi" occupy the same region of morphospace. Combined with qualitative observation on the thorax, P. "lantenoisi" is here considered a junior synonym of P. douvillei. Megapalaeolenus deprati is still considered valid and is distinguished from P. douvillei by its rounded glabella, longer palpebral lobes, shorter ocular ridges, and more developed posterolateral projections. Its pleural spines are more curved, and pleural lobes are markedly wider than P. douvillei. These results highlight that the supposed diversity of palaeolenid taxa in lower Cambrian deposits need reconsideration, potentially using similar morphometric methods.