Palaeopascichnus

Not to be confused with the proposed group Palaeopascichnida.

Palaeopascichnus Temporal range: Ediacaran, 580–542  Ma [1] PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	incertae sedis
Informal group:	† Palaeopascichnida
Genus:	† Palaeopascichnus Palij, 1976
Type species
†Palaeopascichnus delicatus Palij, 1976
Species
P. delicatusPalij, 1976 P. linearisFedonkin, 1976 P. gracilisFedonkin, 1985
Synonyms
InritesFedonkin, 1980 YelovichnusFedonkin, 1985 CatellichnusBecker, 1989 IterichnusBecker, 2013 PseudobergaueriaBecker, 2013

Palaeopascichnus is an enigmatic form from the Ediacaran, consisting of a series of lobes. It was originally considered a trace fossil, but further research found it to be a body fossil, being the skeletal remains of an agglutinating organism.

Discovery and naming

The first fossil material of Palaeopascichnus was found in the Studenitsa Formation, Podolia in Ukraine, and named in 1976, ^[2] and has since been found from formations from across the globe. ^[3]

The generic name Palaeopascichnus derives from the Greek word "paleo", to mean "old"; the Latin word "pasco", to mean "graze"; and the Greek word "ichnos", to mean "trace", in line with the naming conventions of other ichnotaxon. Combined, it would translate to "Old grazing trace". ^[2]

Description

Palaeopascichnus is an agglutinating organism, consisting of curved lobe-like modules, which number up to forty in larger specimens. Their are two known module morphologies, "Globular" and "Ellipsoidal". Globular modules can get up to 5 mm (0.2 in) in diameter, whilst ellipsoidal modules can get up to 5 mm (0.2 in) in length, and up to 15 mm (0.6 in) in width, and in either morphology, the modules gradually increase in size from the origin point. The modules are also spaced a part from each other by 0.5–1 mm (0.0–0.0 in), although this has been noted to possibly be a result of post-mortem degradation of organic material. The modules make up a larger body, which is usually linear in structure, with occasional diverging branches, and gets up to 20 cm (7.9 in) in length. ^[4] The modules that make up this body were noted to be loosely connected to each other, due to some fossil specimens showing disarticulation, with the modules being carried away from the main body. ^[5]

Affinities

When described, Palaeopascichnus was originally referred to as an trace fossil of another organism, ^[2] which was upheld by a number of further studies. ^{[6] [7]} One study suggested it to be a macrophyte, due to the fact that in further descriptions of Palaeopascichnus, it was noted that branching was not possible in trace fossils, something that was being found increasingly in new specimens. ^[8]

More studies later put forward the interpretation that Palaeopascichnus may be a protist, with probably affinities with foraminifers. ^{[9] [10]} One study supported the forminiferan affinity of Palaeopascichnus, but noted that it may also be a synonym of Horodyskia . ^[11] Another study done supported the suggestion that fossils of Palaeopascichnus represented an encrusting benthic organism, although did not agree with the foraminiferal affinities, or the agglutinating structure. ^[12]

This all finally came to a head in 2018, when new material was found that showed that Palaeopascichnus was indeed an agglutinating organism, and that all prior fossils found were in fact body fossils, and supports the possibly of a foraminiferan affinity, although may closely related. ^[5]

Taphonomy

Due to the wide range of Palaeopascichnus, it also has a wide range of preservation modes, which are as follows:

• Positive relief: This is where the fossil is protruding from the rock as a cast. This is the original preservation that Palaeopascichnus was found in, and is the most common preservation mode. ^{[2] [8]}

• Negative relief: This is where the fossils are only an impression in the rock. ^[13]

• Full relief: This is where the fossil has both positive and negative relief preservation, resulting in some parts protruding from the rock, and some parts only being impressions in the rock. ^[6]

• Carbonaceous: This is where biogenic markings are left behind on the rock after being buried, with the markings being notably darker than the surrounding matrix. ^[8]

• Calcareous: This is where the fossil material is of the same material as the surrounding matrix, with each module bearing a noticeably darker margin, which sometimes covers the entire module, that is made of a much coarser material. This outer rim may represent the original structure made by the organism before burial, with each chamber being in-filled during and after burial. ^[5]

Distribution

Palaeopascichnus has a very wide distribution, being commonly found across the entire East European Platform (Finnmark, the Baltic Shield, White Sea, Moscow and Mezen Basins, Ural Mountains, Podolia). They can also been found in South China, Siberia, the Adelaide Superbasin in Australia, as well as some parts of Avalonia (Newfoundland and Labrador, and Wales), ^[5] Brazil, ^[14] Oman, ^[15] and Romania. ^[16]

See also

• List of Ediacaran genera
• Palaeopascichnid

References

1. Liu, Alexander G.; Tindal, Benjamin H. (2020). "Ediacaran macrofossils prior to the ~580 Ma Gaskiers glaciation in Newfoundland, Canada". Lethaia. 54 (2): 260–270. doi: 10.1111/let.12401 .
2. Palij, V.M. (1976), Remains of soft-bodied animals and trace fossils from the Upper Precambrian and Lower Cambrian of Podolia, in Palaeontology and Stratigraphy of Upper Precambrian and Lower Cambrian of South-western East European Platform, pp. 63–76
3. Martin, Jean-Paul Saint; Charbonnier, Sylvain; Martin, Simona Saint; Cazes, Lilian; André, Jean-Pierre (9 January 2025). "New records of Palaeopaschichnus Palij, 1976 from the Ediacaran of Romania". Geodiversitas. 47 (1). doi:10.5252/geodiversitas2025v47a1.
4. "Siberian paleontologists discovered the oldest macro-skeleton remains". EurekAlert!. Retrieved 31 December 2025.
5. Kolesnikov, Anton V; Rogov, Vladimir I; Bykova, Natalia V; Danelian, Taniel; Clausen, Sébastien; Maslov, Andrey V; Grazhdankin, Dmitriy V (2018). "The oldest skeletal macroscopic organism Palaeopascichnus linearis". Precambrian Research. 316: 24–37. Bibcode:2018PreR..316...24K. doi:10.1016/j.precamres.2018.07.017. S2CID   134885946.
6. Parcha, S.K.; Pandey, Shivani (November 2011). "Ichnofossils and their significance in the Cambrian successions of the Parahio Valley in the Spiti Basin, Tethys Himalaya, India". Journal of Asian Earth Sciences. 42 (6): 1097–1116. doi:10.1016/j.jseaes.2011.04.028.
7. Becker, Hanka; Pantleon, Wolfgang (August 2013). "Work-hardening stages and deformation mechanism maps during tensile deformation of commercially pure titanium". Computational Materials Science. 76: 52–59. doi:10.1016/j.commatsci.2013.03.028.
8. Haines, Peter W. (March 2000). "Problematic fossils in the late Neoproterozoic Wonoka Formation, South Australia". Precambrian Research. 100 (1–3): 97–108. doi:10.1016/S0301-9268(99)00070-4.
9. Seilacher, Adolf; Grazhdankin, Dmitri; Legouta, Anton (2003). "Ediacaran biota: The dawn of animal life in the shadow of giant protists". Paleontological Research. 7 (1): 43–54. doi:10.2517/prpsj.7.43.
10. Antcliffe, Jonathan B.; Gooday, Andrew J.; Brasier, Martin D. (September 2011). "Testing the protozoan hypothesis for Ediacaran fossils: a developmental analysis of Palaeopascichnus". Palaeontology. 54 (5): 1157–1175. doi:10.1111/j.1475-4983.2011.01058.x.
11. Dong, Lin; Xiao, Shuhai; Shen, Bing; Zhou, Chuanming (January 2008). "Silicified Horodyskia and Palaeopascichnus from upper Ediacaran cherts in South China: tentative phylogenetic interpretation and implications for evolutionary stasis". Journal of the Geological Society. 165 (1): 367–378. doi:10.1144/0016-76492007-074.
12. Gehling, James G.; Droser, Mary L. (October 2009). "Textured organic surfaces associated with the Ediacara biota in South Australia". Earth-Science Reviews. 96 (3): 196–206. doi:10.1016/j.earscirev.2009.03.002.
13. Hawco, Jessica B.; Kenchington, Charlotte G.; McIlroy, Duncan (May 2021). "A quantitative and statistical discrimination of morphotaxa within the Ediacaran genus Palaeopascichnus". Papers in Palaeontology. 7 (2): 657–673. doi:10.1002/spp2.1290.
14. Becker-Kerber, Bruno; Paim, Paulo Sergio Gomes; Chemale Junior, Farid; Girelli, Tiago Jonatan; da Rosa, Ana Lucia Zucatti; Albani, Abderrazak El; Osés, Gabriel Ladeira; Prado, Gustavo M.E.M.; Figueiredo, Milene; Simões, Luiz Sérgio Amarante; Pacheco, Mírian Liza Alves Forancelli (August 2020). "The oldest record of Ediacaran macrofossils in Gondwana (~563 Ma, Itajaí Basin, Brazil)". Gondwana Research. 84: 211–228. doi:10.1016/j.gr.2020.03.007.
15. Pinto, André Jorge; Álvarez-Lloret, Pedro; Callegari, Ivan; Scharf, Andreas (July 2025). "An Ediacaran trace-like body fossil of a Palaeopascichnus specimen from Oman under 3D micro-tomography". Facies. 71 (3). doi:10.1007/s10347-025-00705-5.
16. Martin, Jean-Paul Saint; Charbonnier, Sylvain; Martin, Simona Saint; Cazes, Lilian; André, Jean-Pierre (9 January 2025). "New records of Palaeopaschichnus Palij, 1976 from the Ediacaran of Romania". Geodiversitas. 47 (1). doi:10.5252/geodiversitas2025v47a1.