Taxonomy

Phylum: Arthropoda

Class: Dinocaridida

Order: uncertain

Family: uncertain

Genus: Kerygmachela

Specie: K.kierkegaardi

Description: 

The ancient creature measured between one to ten inches and is flanked by 11 wrinkly flaps on both sides of the body. The spiny frontal appendages suggests that Kerygmachela may have been a predator; however, fossils indicate a total size of approximately 175 mm and, with a relatively small mouth, suggest that it would have been restricted to very small prey. The predator also sported a round head and an elongated tail spine. The head forms a rounded anterior lobe extending between the frontal appendages. The head of Kerygmachela possess a pair of well-developed frontal appendages which correspond to those of other dinocaridids and siberiid lobopodians. Each of them terminated with a series of long spines. A pair of sessile, slit-like compound eyes were located slightly behind the base of these appendages. At the base of the frontal appendages are structures interpreted as eyes, based on both their position and preservation, with distinctive relief and high reflectivity similar to the preservation of eyes in arthropods from the Burgess Shale. Their outline is reminiscent of the kidney- or sickle-shaped eye lobes of trilobites. The eyes are situated ventrolaterally, because they are best delineated in ventral specimens where mouth structures and rostral spines are most visible. In dorsal specimens, the epidermal annulations continue over the eye lobes. The anterior half of the eye is located under the posterior part of the frontal appendages. The visual structures seen in K.kierkegaardi represent primitive compound eyes. A small anterior-facing mouth was located below its head and bore a pair of stylet-like structures. The head also possesses a median lobe-like projection that carries a pair of small, possible ocular structures. The body compose of 11 segments indicated by 4 dorsal turberculates on each of them, associated with 11 pairs of lateral flaps with dorsal gill-like structure, along with 11 pairs of small legs (lobopods) located just below the flaps. The body ends with a single, unsegmented tail spine which was formerly thought to be a pair of cerci. Internally, Kerygmachela possesses a well-developed pharynx and a midgut with 8 pairs of arthropod-like digestive glands. The brain compose of only protocerebrum (the frontalmost cerebral ganglion) with ramified nerves extended to the median lobe, frontal appendages and eyes. Eleven rows of tubercles are present in the axial region, corresponding to each set of lateral flaps, with four tubercles present in each row. The tubercles become more prominent posteriorly. The central two tubercles are larger than the outer ones and become more widely spaced posteriorly, eventually becoming almost superimposed on the lateral ones in the distal region. The lateral flaps appear successively smaller rearward in the holotype. In the new material, the fourth and fifth pair of lateral flaps appear to be largest, rendering an oval outline in dorsal view. All new specimens show a single, long, medially attached, and unsegmented tail spine, when preserved. The tail spine is almost as long as the body, excluding the frontal appendages. Each segment of the main body is composed with an axial region and a pair of lateral, imbricated lobes that bear wrinkled structures interpreted as gills on the dorsal surface. Specimens exhibit sub-triangular bulges projecting later-ally from the axial region. These bulges are interpreted as stout, lobopod-like limbs. In the complete specimen, the bulges connect to the tubercled units of the axial region,a characteristic of other Cambrian lobopods.

Although Kerygmachela shows a unique combination of morphological features, several of its characters are also possessed in varying degrees by lobopod-like Cambrian animals such as Luolishania, Xenusion, Microdictyon, Onychodictyon, Hallucigenia as well as the Recent Peripatus. These characters include the possession of (1) unsegmented, lobopod limbs; (2) circular body musculature ; (3) appendages with spines; and (4) alternating axial units of transverse wrinkling and rows of tubercles. Kerygmachela, however, provides morphological evidence that the biramous arthropods may be derived from a lobopodous ancestor, giving rise to a taxon like Marrella that lacks dorsal pleurae and occupies a primitive position in cladistic analyses of biramous arthropods. In this case, the gill-lobe and the lobopod would be united during arthropodization to form the biramous limb. The homology of the lobopod and biramous arthropod limbs implied by Kerygmachela suggests that lobopod animals constitute a paraphyletic stem-group assemblage from which arthropodized taxa arose.

Age & Localities

Age: Cambrian Series 2, Stage 3, Nevadella trilobite Biozone

Principal localities: The Sirius Passet fauna (Mudstone-dominated Member of Buen Formation), in the southern margin of the Franklinian Basin, North of Greenland