Trilobita (Order: Corynexochida?)
Trilobites are extinct euarthropods, probably stem lineage representatives of the Mandibulata, which includes crustaceans, myriapods, and hexapods (Scholtz and Edgecombe, 2006).
Hanburia – unspecified, but probably after Hanbury Peak or Hanbury Glacier in the Canadian Rockies, in turn named for David T. Hanbury (1864-1910), a British explorer of the Canadian Northwest Territories.
gloriosa – from the Latin gloriosus, meaning “glorious” or “boastful,” perhaps in allusion to the unusual cephalic morphology of this rare species.
Lectotype – USNM 61724, in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
Burgess Shale and vicinity: none.
Other deposits: none.
Middle Cambrian, Glossopleura to Bathyuriscus-Elrathina Zones (approximately 505 million years ago).
The Walcott Quarry on Fossil Ridge. The Tulip Beds (S7) and smaller localities on Mount Stephen.
Brief history of research:
Walcott’s three original specimens of Hanburia gloriosa were found over the course of five years of quarrying the Phyllopod Bed on Fossil Ridge (Walcott, 1916); two more from this locality are also in theUSNM collections. A singleUSNM specimen was later found by Charles Resser, supposedly from the “Ogygopsis shale” on Mount Stephen (Rasetti, 1951), but this is almost certainly an error. Harry Whittington reassessed this odd trilobite in 1998.
Hard parts: the few known specimens of Hanburia gloriosa range in length from 4 mm (for a juvenile stage) to 35 mm. Dorsal shields are broadly ovate to subcircular in outline and all specimens are considerably flattened by compression of the thin exoskeleton. The cephalon is semicircular with a weak, shallow border furrow along the posterior and lateral margins, fading out towards the anterior corners of the glabella. The glabella in small specimens expands forwards and shows two pairs of faint bulbous lateral lobes; in larger specimens, the glabella is parallel-sided and the lobes are subdued. There are no apparent eyes located laterally on the cephalon, and there is no sign of dorsal facial suture. In these two features, Hanburia is unique among the non-agnostoid trilobites of the Burgess Shale.
Whittington (1998) has suggested that the facial suture might run along the outside edge of the cephalon, or ventrally, crossing to the dorsal side only at the genal angles, which in all specimens appear to be rounded. Larger individuals show six or seven segments in the comparatively short thorax, and a single known (presumed) juvenile stage shows four; the distal tips of the pleurae are rounded. The semicircular pygidium lacks a defined border, and is approximately the same width and length as the cephalon. Seven or eight axial rings and a terminal piece make up the pygidial axis, which ends short of the posterior margin. Eight or nine pairs of well-marked pygidial pleurae radiate out and back from the axis.
Unmineralized anatomy: not known
Very rare in all the Burgess Shale localities.
Due to its unusual cephalic morphology (i.e., no dorsal sutures or lateral compound eyes), rarity, and unique occurrence only in the Burgess Shale, Hanburia gloriosa remains an ecological enigma. Other “blind” Cambrian trilobites with somewhat similar morphologies have been interpreted as inhabiting deeper waters, perhaps below the photic zone (Whittington, 1998).