Ooedigera

Ooedigera peeli is an extinct vetulicolian from the Early Cambrian of North Greenland. The front body was flattened horizontally, oval-shaped, likely bearing a reticulated or anastomosing pattern, and had 5 evenly-spaced gill pouches along the midline. The tail was also bulbous and flattened horizontally, but was divided into 7 plates connected by flexible membranes, allowing movement. Ooedigera likely swam by moving side-to-side like a fish. It may have lived in an oxygen minimum zone alongside several predators in an ecosystem based on chemosynthetic microbial mats, and was possibly a deposit or filter feeder living near the seafloor.

Ooedigera Temporal range: Cambrian Stage 3, 519–516.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type specimen
Artist's restoration
Scientific classification
Kingdom:	Animalia
Phylum:	†Vetulicolia
Class:	†Vetulicolida
Order:	†Vetulicolata
Family:	†Vetulicolidae
Genus:	†Ooedigera
Species:	†O. peeli
Binomial name
†Ooedigera peeli Vinther et al. 2011

Etymology

The genus name Ooedigera derives from Ancient Greek ooedis "egg-shaped/oval" and geros "old". The species name peeli is in honour of Professor John S. Peel from the Geological Survey of Greenland, who especially researched the locality Ooedigera was discovered in.[1]

Taxonomy

Sirius Passet in the Early Cambrian

The type specimen MGUH 29279 was discovered in the Early Cambrian Sirius Passet Lagerstätte of the North Greenlandic Buen Formation. The area corresponds to the early Cambrian Stage 3 about 519–516.5 million years ago. The specimen is a flat compression fossil preserved in fissile mudstone, with an odd, thin lamination, and several small splotches which represent the remains of various other creatures, such as sponges and trilobites.[1]

Ooedigera is classified in the extinct Cambrian subphylum Vetulicolia in the family Vetulicolidae along with Vetulicola. Ooedigera is the third vetulicolid found outside the Chinese Maotianshan Shales (the others an undescribed specimen from Mural Formation, Canada[1] and Nesonektris from Emu Bay Shale, Australia[2]).

Vetulicolia is a subphylum of primitive Deuterostomia, a large group of animals whose first opening in fetal development becomes the anus as opposed to the mouth as in protostomes.[3] The subphylum was originally classified in Arthropoda, but had been reassigned several times. It was suggested to represent primitive chordates[4] or an invalid grouping of primitive tunicates.[5] The subphylum was also suggested to more closely related to protostomes,[6] as an ecdysozoan (which includes arthropods, nematodes, and related taxa), specifically kinorhynchans (segmented worm-like creatures).[7]

Anatomy

The type specimen is 41.3 mm (1.63 in) long in total, and the body plan is divided into an ovoid front body and a segmented tail. The type specimen seems to have been compressed on its side during fossilization, and due to the irregular folding of the outline, the skin may have been softer than other vetulicolians.[1]

The front body was oval-shaped, measuring 22.5 mm (0.9 in) in length and 14 mm (0.55 in) in height, and flattened horizontally. It had a straight front edge, and the back edge came to a point, intersecting at the midline of the front body. Unlike Chinese vetulicolians, the type specimen shows no indication of a ridge running along the midline, and a lack of such in Ooedigera would be significant in terms of its taxonomy, but more specimens are required to confirm this. Like other vetulicolians, the midline had 5 more or less evenly spaced openings, 3.3 mm (0.13 in) from the front edge and 2.4 mm (0.094 in) from the back edge, corresponding to gill pouches. The front body seems to have had a reticulated or anastomosing pattern.[1] It could possibly indicate the specimen was a juvenile, as such ornamentation is seen in what are thought to be juvenile specimens of the vetulicolian Beidazoon.[8]

Like other vetulicolians, the tail was asymmetrical, flattened horizontally, and divided into 7 segments which were connected by flexible membranes, the latter allowing movement. It is 18.8 mm (0.74 in) long and 8.7 mm (0.34 in) high. Each segment had concave edges, which gave each one an hourglass shape in side-view. Segments 2–7 were flat on the underside, and segments 5–7 were also flat on the top. The last segment was shorter than other vetulicolians. Given the asymmetrical flattening, the tail likely propelled by flexing side-side like a fish rather than up-and-down.[1]

Palaeocology

It is largely unknown what vetulicolians fed upon. Lacking mouths adapted for chewing or grasping, they were probably not predators or scavengers. Lacking limbs, it is unlikely they were burrowers or lived on the seafloor, rather inhabiting the water column (nektonic) but perhaps staying near the seafloor (nektobenthic). They may have been passive floaters, but it is possible that the gills were used for jet propulsion like thaliaceans.[9] The gills may have also been used in filter feeding, actively swallowing and expelling water using the mouth and gills respectively.[10][9] However, Vetulicola, Banffia, and Pomatrum have remains of sediments in the gut, which is either evidence of deposit feeding on the seafloor[6][9] or a result of fossilization. It is possible vetulicolians used both feeding methods like the modern acorn worm Balanoglossus.[9]

About 45 species have been discovered in Sirius Passet, mostly endemic fauna, including trilobites, sponges, worms, and the extinct halkieriids and lobopodians.[11] Another indeterminate vetulicolian was found here.[1] The area may have been an oxygen minimum zone, and, like the preceding Ediacaran, the ecosystem may have been primarily based on chemosynthetic microbial mats which fed grazers and filter feeders. Arthropods and sponges are the most common fossils, and members of the former and lobopodians may have been major predators. Predators appear to have been the most common animals.[11]

References

1. Vinther, J.; Smith, M. P.; Harper, D. A. T. (2011). "Vetulicolians from the Lower Cambrian Sirius Passet Lagerstätte, North Greenland, and the polarity of morphological characters in basal deuterostomes". Palaeontology. 54 (3): 711–719. doi:10.1111/j.1475-4983.2011.01034.x.
2. García-Bellido, D. C.; Lee, M. S. Y.; Edgecombe, G. D.; Jago, J. B.; Gehling, J. G.; Paterson, G. R. (2014). "A new vetulicolian from Australia and its bearing on the chordate affinities of an enigmatic Cambrian group". BMC Evolutionary Biology. 14 (214). doi:10.1186/s12862-014-0214-z. PMC 4203957. PMID 25273382.
3. Shu, D. G.; Morris, S. C.; Zhang, Z. F.; Han, J. (2010). "The earliest history of the deuterostomes: the importance of the Chengjiang Fossil‐Lagerstätte". Proceedings of the Royal Society B. 277 (1679): 165–174. doi:10.1098/rspb.2009.0646. PMC 2842668. PMID 19439437.
4. Gee, H. (2001). "On being vetulicolian". Nature. 414 (6862): 407–409. doi:10.1038/35106680. PMID 11719790.
5. Lacalli, L. C. (2002). "Vetulicolians--are they deuterostomes? chordates?". BioEssays. 24 (3): 208–211. doi:10.1002/bies.10064. PMID 11891757.
6. Caron, J.-B. (2006). "Banffia constricta, a putative vetulicolid from the Middle Cambrian Burgess Shale". Transactions of the Royal Society of Edinburgh: Earth Sciences. 96 (2): 95–111. doi:10.1017/S0263593300001255.
7. Briggs, D. E. G.; Lieberman, B. S.; Halgedahl, S. L.; Jarrard, R. D. (2005). "A new metazoan from the Middle Cambrian of Utah and the nature of the Vetulicolia". Palaeontology. 48 (4): 681–686. doi:10.1111/j.1475-4983.2005.00489.x.
8. McMenamin, M. C. (2019). "Cambrian Chordates and Vetulicolians". Geosciences. 9 (8): 354. doi:10.3390/geosciences9080354.
9. Aldridge, R. J.; Xian-Guang, H.; Siveter, D. J.; Gabbot, S. E. (2007). "The systematics and phylogenetic relationships of vetulicolians". Palaeontology. 50 (1): 162–163. doi:10.1111/j.1475-4983.2006.00606.x.
10. Ou, Q.; Morris, S. C.; Han, J.; Zhang, Z.; Liu, J.; Chen, A.; Zhang, X.; Shu, D. (2012). "Evidence for gill slits and a pharynx in Cambrian vetulicolians: implications for the early evolution of deuterostomes". BMC Biology. 10 (81): 81. doi:10.1186/1741-7007-10-81. PMC 3517509. PMID 23031545.
11. Harper, D. A. T.; Hammarlund, E. U.; Topper, T. P.; Nielsen, A. T.; Rasmussen, J. A.; Park, T.-Y. S.; Smith, M. P. (2019). "The Sirius Passet Lagerstätte of North Greenland: a remote window on the Cambrian Explosion" (PDF). Journal of the Geological Society. 176 (6): 1023–1037. doi:10.1144/jgs2019-043.