Eldonia ludwigi

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A discoidal organism with short tentacles

3D animation of Eldonia ludwigi.

Animation by Phlesch Bubble © Royal Ontario Museum

Eldonia ludwigi (ROM 59550) – Part (top row and bottom left) and counterpart (bottom right). Top row, overall view. Bottom row, close up of the central disk and feeding tentacles. A specimen of the brachiopod Lingulella waptaensis is also present. Specimen diameter = 100 mm. Specimen wet – direct light (top left and bottom row), wet – polarized light (top right). Walcott Quarry.

Eldonia ludwigi (ROM 61137). Top left, slab collected from the Great Eldonia layer of Walcott with several species including of the priapulid worm Ottoia prolifica and the arthropod Marrella splendens. Bottom row detailed of a large Eldonia specimen, and close up of the central disk (top right). Specimen diameter (largest specimen) = 100 mm. Specimen dry – direct light (top left), wet – direct light (bottom left), wet – polarized light (right column). Walcott Quarry.

Eldonia ludwigi (USNM 57540) – Lectotype. Left, plate 8 of Walcott (1911), showing a retouched image of a specimen described as an holothurian (figure 3). Right, images of the counterpart of the same specimen showing the characteristic disk and coiled gut (a smaller specimen preserved on its side is visible on the left). Specimen diameter = 105 mm. Specimen dry – direct light (left), dry – polarized light (right). Walcott Quarry.

Eldonia ludwigi (USNM 57554). Slab with four different specimens (three small, and one large). Specimen diameter (large specimen) = 145 mm. Specimen dry – direct light (left), dry – polarized light (right). Walcott Quarry.

Taxonomy:

Kingdom: Animalia

Phylum: Unknown

Higher Taxonomic assignment: Unranked clade Cambroernida (stem group ambulacrarians)

Species name: Eldonia ludwigi

Remarks:

Eldonia, together with other discoidal or pedunculate fossils such as Herpetogaster, probably belongs in the stem group to a clade known as the Ambulacraria, represented by both echinoderms and hemichordates (Caron et al., 2010).

Described by: Walcott

Description date: 1911

Etymology:

Eldonia – from Eldon, a train stop on the Canadian Pacific Railway 30 km east of Field. Eldon is named after a town in County Durham, England, and means “Aelle’s hill.”

ludwigi – after Hubert Ludwig, a German echinoderm expert who described many fossil holothurians.

Type Specimens: Lectotype –USNM57540 in the National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.

Other species:

Burgess Shale and vicinity: none.

Other deposits: Stellostomites eumorphus (Sun and Hou, 1987), from the Lower Cambrian Chengjiang fauna, was redescribed as Eldonia eumorpha (Chen et al., 1995). However, S. eumorphus is retained in the literature as the only valid species (Zhu et al. 2002); E. berbera was described from the Upper Ordovician of Morocco (Alessandrello and Bracchi, 2003). If confirmed it would be the youngest stratigraphic occurrence for the genus.

Age & Localities:

Age:

Middle Cambrian, Bathyuriscus-Elrathina Zone to Bolaspidella Zone (approximately 505 million years ago).

Principal localities:

Burgess Shale and vicinity: Walcott and Raymond Quarries on Fossil Ridge.

Other deposits: Middle Cambrian Spence Shale and Marjum Formation in Utah (Conway Morris and Robison, 1988).

History of Research:

Brief history of research:

Described by Walcott in 1911, Eldonia was originally interpreted as a holothurian (sea cucumber within the echinoderms), a view that was accepted by some eminent experts at the time (Clark A.H., 1913) and upheld by later re-examination of the material (Durham, 1974). However, this interpretation has always had detractors (Clark H.L., 1912; Dzik, 1991, 1997; Madsen, 1956, 1957, 1962; Paul and Smith, 1984), and the lack of key echinoderm features prohibits a close relationship with that group (Conway Morris, 1993; see also Zhu et al., 2002). Despite their resemblance to jellyfish (scyphozoans) there is a wide consensus that eldoniids do not share any affinities with cnidarians. A connection to “lophophorates” (e.g., brachiopods, phoronids) has been argued in more detail (Chen et al., 1995, Dzik, 1997), but this status remains rather problematic. The description of Eldonia’s close relative Herpetogaster provides a possible link to the Ambulacraria, a group that contains the echinoderms and hemichordates (Caron and Conway Morris, 2010).

Fragments of the reflective gut have been extracted by acid maceration and analyzed for taphonomic studies (Butterfield, 1990).

Description:

Morphology:

Eldonia has a discoidal body with both anus and mouth opening ventrally. Fine rays radiate from a central point within the disc. The gut coils clockwise (viewed from the dorsal surface) around the centre of the organism and is clearly separated into a pharynx, stomach (the darker area), and narrow intestine. There is a pair of relatively stout tentacles around the mouth which probably were used for feeding.

Abundance:

Walcott collected hundreds of specimens of Eldonia in a single fossil layer within the Phyllopod Bed that he called the Great Eldonia Layer. Additional specimens have since been collected from the Walcott Quarry, where they comprise 0.4% of the community (Caron and Jackson, 2008).

Maximum Size:

150 mm

Ecology:

Life habits: Epibenthic, Mobile

Feeding strategies: Deposit feeder

Ecological Interpretations:

Eldonia has conventionally been interpreted as a free-floating filter-feeder. However, based on its morphology, preservational patterns, and its similarity with Herpetogaster, a benthic lifestyle has also been proposed, with its tentacles either collecting food from the water, or sweeping the sea floor for particles of detritus (Caron and Conway Morris, 2010). It is unclear whether the animal could move at least occasionally or was permanently stationary (sessile).

References:

ALESSANDRELLO, A. AND G. BRACCHI. 2003. Eldonia berbera n. sp. a new species of the enigmatic genus Eldonia Walcott, 1911 from the Rawtheyan (Upper Ordovician) of Anti-Atlas (Erfoud, Tafilalt, Morocco). Atti della Società italiana di scienze naturali e del Museo civico di storia naturale in Milano, 144(2): 337-358.

BUTTERFIELD, N. J. 1990. Organic preservation of non-mineralizing organisms and the taphonomy of the Burgess Shale. Paleobiology, 16(3): 272-286.

CARON, J.-B. AND D. A. JACKSON. 2008. Paleoecology of the Greater Phyllopod Bed community, Burgess Shale. Palaeogeography, Palaeoclimatology, Palaeoecology, 258: 222-256.

CARON, J.-B., S. CONWAY MORRIS AND D. SHU. 2010. Tentaculate fossils from the Cambrian of Canada (British Columbia) and China (Yunnan) interpreted as primitive deuterostomes. PLoS ONE, 5(3): e9586.

CHEN, J.-Y., M.-Y. ZHU AND G.-Q. ZHOU. 1995. The early Cambrian medusiform metazoan Eldonia from the Chengjiang Lagerstätte. Acta Palaeontologica Polonica, 40: 213-244.

CLARK, H. L. 1912. Fossil holothurians. Science, 35(894): 274-278.

CLARK, A. H. 1913. Cambrian holothurians. American Naturalist, 48: 488-507.

CONWAY MORRIS, S. AND R. A. ROBISON. 1988. More soft-bodied animals and algae from the Middle Cambrian of Utah and British Columbia. The University of Kansas Paleontological Contributions, 122: 23-84.

CONWAY MORRIS, S. 1993. The fossil record and the early evolution of the Metazoa. Nature, 361(6409): 219-225.

DURHAM, J. W. 1974. Systematic Position of Eldonia ludwigi Walcott. Journal of Paleontology, 48(4): 751-755.

DZIK, J. 1991. Is fossil evidence consistent with traditional views of the early metazoan phylogeny?, p. 47-56. In A. M. Simonetta and S. Conway Morris (eds.), The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge University Press, Cambridge.

DZIK, J. Y., L. ZHAO AND M. Y. ZHU. 1997. Mode of life of the Middle Cambrian eldonioid lophophorate Rotadiscus. Palaeontology, 40(2):385-396.

MADSEN, F. J. 1956. Eldonia, a Cambrian siphonophore-formerly interpreted as a holoturian[sic]. Videnskabelige meddelelser fra Dansk naturhistorisk forening i Københaven, 118: 7-14.

MADSEN, F. J. 1957. On Walcott’s supposed Cambrian holothurians. Journal of Paleontology, 31(1): 281-282.

MADSEN, F. J. 1962. The systematic position of the Middle Cambrian fossil Eldonia. Meddelelser fra Dansk Geologisk Førening, 15: 87-89.

PAUL, C. R. C. AND A. B. SMITH. 1984. The early radiation and phylogeny of echinoderms. Biological Reviews, 59(4): 443-481.

WALCOTT, C. 1911. Cambrian Geology and Paleontology II. Middle Cambrian holothurians and medusae. Smithsonian Miscellaneous Collections, 57(3): 41-68.

ZHU, M. Y., Y. L. ZHAO AND J. Y. CHEN. 2002. Revision of the Cambrian discoidal animals Stellostomites eumorphus and Pararotadiscus guizhouensis from South China. Geobios, 35(2): 165-185.