Morpho‐anatomical differences of the Early Cambrian Chengjiang and Recent lingulids and their implications

Abstract

Since the publication of Darwin's theory of evolution in 1859, lingulids have probably been the most widely quoted examples of arrested evolution. This, to some degree, may be because few anatomical features are impressed either on or inside valves so these may not adequately reflect the extent of change incurred during lingulid evolution. Two lingulid brachiopods, Lingulella chengjiangensis and Lingulellotreta malongensis, from the Early Cambrian Chengjiang Lagerstätte (Yunnan, South China) show preservation of a series of soft parts, notably the lophophores, setae mantle canals and perfectly impressed visceral region, which are vital to understanding the evolution and lifestyle of brachiopods. Analysis of the valve interiors favours the claim that an epifaunal mode of life could be a plesiomorphic state in contrast to the infaunal one of modern lingulids. Based on these fossils, the three‐pseudosiphon formation of setae found in Recent lingulids is proposed to be an apomorphy derived as an adaptation to an infaunal lifestyle. Comparison between the interior of the fossils with that of modern lingulids does little to support the widespread notion that the morphology of this lineage has remained remarkably constant since at least the early Palaeozoic.

Oldest glosselline linguliform brachiopod with soft parts from the Lower Cambrian of Yunnan, Southern China

“…In the middle of anterior tongue-shaped area, there is a rounded scar possible indicating the mouth of Eoglossa chengjiangensis (Fig.2I, J). A U-shaped digestive canal extends from the mouth and ends with a black print of anus at the left anterior body wall, as was described by Zhang et al (2004Zhang et al ( , 2005. The exquisite preserved digestive canal structures were also observed in our specimens, but in nearly all specimens, the trace of the intestine is suddenly lost in the central of dorsal visceral areas (Fig.2H).…”

Rhynchonelliformean Brachiopods With Soft‐tissue Preservation From the Early Cambrian Chengjiang Lagerstätte of South China

“…The alimentary canals are also preserved as reddish‐brown impressions on the internal moulds of dorsal valves (Text‐figs 2C, F–I, 3C–E, 5B). The preservation of the setal fringe (Text‐figs 3F–G, 5E) is weaker than those seen in Cambrian lingulid taxa (Zhang, Z. F. et al . 2005, 2006).…”

“…2005). Information regarding these clades has been obtained recently from the fossil record, notably from those deposits with exceptional preservation of soft parts (Zhang, Z. F. et al . 2003, 2004 a , b , 2005, 2006, 2007 a , b ; Zhang X. G. et al .…”

“…It appears to be much more robust than that of the Chengjiang lingulids (Jin et al . 1993; Zhang, Z. F. et al . 2005, 2006, 2007 a , b ).…”

Lingulide Response to Severe Storms Recorded in Middle Triassic Strata of Northeastern British Columbia

“…Infaunal colonization also provides shelter from physical reworking and wave stress in such dynamic depositional settings as the shoreface (Thayer and Steele-Petrovic, 1975). Lingulides are the sole group of brachiopods that have achieved a fully infaunal lifestyle and have occupied this niche since the Cambrian (Thayer and Steele-Petrovic, 1975;Zhang et al, 2005;Chen et al, 2007).…”