Dinocarida (Order: Radiodonta, stem group arthropods)
Laggania is an anomalocaridid. Anomalocaridids have been variously regarded as basal stem-lineage euarthropods (e.g., Daley et al., 2009), basal members of the arthropod group Chelicerata (e.g., Chen et al., 2004), and as a sister group to the arthropods (e.g., Hou et al., 2006).
Laggania – from Laggan, the name given to a now defunct railway station on the Canadian Pacific Railway in Banff National Park, now known as Lake Louise Village. The name Laggan comes from a location of a 1655 battle in the Great Glen of Scotland.
cambria – from the Welsh Cambria meaning Wales.
Holotype –USNM57555 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Burgess Shale and vicinity: A possible new species from the Tulip Beds (S7) on Mount Stephen (Daley and Budd, 2010).
Other deposits: none.
Middle Cambrian, Bathyuriscus-Elrathina Zone (approximately 505 million years ago).
The Walcott Quarry on Fossil Ridge.
Brief history of research:
The anomalocaridids, including Laggania, have a complex history of description, because parts of their bodies were preserved in isolation from each other, resulting in the body part fossils being given their own generic names before they were identified as different parts of the same animal. The name Laggania cambria was first applied to a single specimen of a “sea cucumber” (Walcott, 1911a), which was later re-described as a superimposition of the “jellyfish” Peytoia nathorsti on top of a sponge (Conway Morris, 1978). The frontal appendages of Laggania were first described as “Appendage F”, the feeding appendages of the arthropod Sidneyia (Walcott, 1911b), but they were later removed from that genus and described as the appendage of an unknown arthropod (Briggs, 1979).
A critical revelation was made by Harry Whittington early in the 1980s when he discovered the basic body plan of the anomalocaridids by preparing specimens of Anomalocaris and Laggania. He revealed that the anomalocaridids had the “jellyfish” Peytoia as a mouth part and a pair of large frontal appendages at the front of the head. Whittington and Briggs (1985) first described Laggania under the name Anomalocaris nathorsti. Bergström (1986) re-described some aspects of the morphology of the anomalocaridids.
The discovery of several more complete specimens during Royal Ontario Museum fieldwork in the 1990s allowed Collins (1996) to reconstruct the genus Anomalocaris with greater accuracy. This led to a reversal of names from Anomalocaris nathorsti to Laggania cambria. Laggania has since been the subject of many studies discussing anomalocaridid affinity (e.g., Hou et al., 1995; Chen et al., 2004; Daley et al., 2009).
The body of Laggania consists of a posterior body region with a series of lateral swimming flaps, and a head region with circular mouth parts, a pair of frontal appendages, two large eyes, and a head shield. Full body specimens are no longer than 15 cm in length, but isolated parts suggest that body lengths could be much longer, perhaps up to 50 cm. The frontal appendages have eleven robust segments with short dorsal and lateral spines and five elongated ventral spines.
A pair of these appendages is found on the ventral surface of the head, flanking the mouth parts. They consist of 32 rectangular plates, four large and 28 small, arranged in a circle with sharp spines pointing into a square central opening. The large, oval eyes are located on either side of the head, and a thin carapace shield covers the dorsal head region. The trunk of Laggania has a central region of eleven segments bearing rows of gills, and elongated, wide swimming flaps extending out to either side. The body trunk is tapering, and ends in a blunt tail.
Ten whole-body specimens of Laggania and dozens of isolated frontal appendages are known from the Walcott Quarry on Fossil Ridge.
Laggania was an active swimmer, as indicated by the lack of walking limbs and the presence of numerous gills. It probably propelled itself through the water column by undulating its swimming flaps along the sides of its body. The large eyes, sharp mouth parts and spiny appendages would have made Laggania a formidable predator. It may have used its frontal appendages as a sieve to sift prey out from the sediment or entangle swimming prey and sweep them towards its mouth parts. The mouth parts likely operated by pivoting the plates outwards and contracting them inward to bring prey further into the mouth. Like other anomalocaridids, Laggania probably ingested mostly soft-bodied prey. It swam through the water column just above the sea floor, using its large eyes to seek out prey.