◄ Carnets Geol. 25 (8) ►
Outline:
[1. Introduction]
[2. Geological background]
[3. Geological background]
[4. Systematic paleontology]
[5. Discussion]
and ...
[Bibliographic references]
Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu (Estonia)
Geology Department, Faculty of Science, Alexandria University (Egypt)
College of Science, King Saud University (Kingdom of Saudi Arabia)
College of Science, King Saud University (Kingdom of Saudi Arabia)
Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, Tallinn (Estonia)
Published online in final form (pdf) on June 2, 2025
DOI 10.2110/carnets.2025.2508
[Editor:
José Noel Pérez Asensio; technical editor: Bruno R.C. Granier]
The Yunnanpriapulus? sp. can be divided into three distinct parts: an anterior introvert, a slightly constricted elongated neck, and a slightly bulbous elongated posterior trunk. The fossil is preserved as a three-dimensional cast in the fine-grained sandstone and is oriented parallel to the bedding plane. Rapid burial helped protect the organism from scavengers and decay and provided the opportunity for fossilization via pyritization. The preservation of the specimen on a bedding plane resulted from the post-mortem transportation of the dead animal, likely due to a storm event. The priapulid likely hunted other worms for food. The similarity of the Estonian specimen to the Chinese species suggests that there may have been some faunal exchange between the remote continents of Baltica and South China in the early Cambrian.
• lower Cambrian;
• exceptional preservation;
• priapulid worms;
• sandstones;
• Baltica
Vinn O., El Hedeny M., Almansour M.I., Alfarraj S. & Toom U. (2025).- The first record of a possible 'priapulid' from the lower Cambrian (Series 2) of Estonia.- Carnets Geol., Madrid, vol. 25, no. 8, p. 169-175. DOI: 10.2110/carnets.2025.2508
Le premier signalement d'un possible 'priapulien' du Cambrien inférieur (Série 2) d'Estonie.- Le Yunnanpriapulus ? sp. peut ętre divisé en trois parties distinctes : un introvert antérieur, un cou allongé légčrement rétréci et un tronc postérieur allongé légčrement bulbeux. Le fossile est préservé sous forme de moulage tridimensionnel dans un grčs fin. Il e orienté parallčlement au plan de stratification. Un enfouissement rapide a contribué ŕ protéger l'organisme des charognards et de la décomposition, permettant ainsi une fossilisation par pyritisation. La préservation du spécimen sur un plan de stratification résulte d'un transport post-mortem du cadavre, probablement ŕ l'occasion d'un événement de type tempęte. Le priapulien chassait probablement d'autres vers pour se nourrir. La similitude du spécimen estonien avec les espčces chinoises suggčre qu'il pourrait avoir existé un échange faunique entre les continents éloignés de la Baltica et de la Chine du Sud au Cambrien inférieur.
• Cambrien inférieur ;
• préservation exceptionnelle ;
•
vers priapuliens ;
• grčs ;
• Baltica
Priapulid worms today consist of a small group of cycloneuralians, with approximately 20 species (Schmidt-Rhaesa, 2013). Most of them are small and live within the sediment (Shirley & Storch, 1999). While the geological record of priapulids is somewhat limited due to low preservation potential. The archaeopriapulids (Conway Morris, 1977), some of which may be part of the early evolutionary lineage of modern priapulids, are notably diverse in lower and middle Cambrian Lagerstätten (Peel, 2017). Most Cambrian worms are scalidophorans that closely resemble modern priapulids. Their fossils are not rare and they occur in various localities in China (even in the 535 Ma-old-Kuanchuanpu Formation) (Wang et al., 2021, 2023)
A variety of skeletal fossils have been identified in the lowermost Cambrian of Estonia, including Sabellidites cambriensis Yanichevsky, Sabellidites sp., Platysolenites antiquissimus Eichwald, P. lontova Öpik, Spirosolenites spiralis (Posti), Yanichevskyites petropolitanus (Yanichevsky), Aldanella kunda (Öpik), as well as pyritized casts of hyolithids and "hyolithelminthes", chitinous horn-like sclerites, fragments of brachiopods, and agglutinated tubes of Onuphionella agglutinata Kirjanov (Mens & Pirrus, 1977, 1997; Mens, 2003). The upper part of the lower Cambrian also contains trilobites, Volborthella, and Mickwitzia (Meidla, 2017). There are Treptichnus pedum burrows in the lower Cambrian of Estonia (Palij et al., 1979). These burrow systems are likely to have been made by priapulid-like worms (see Kesedis et al., 2019; Vannier et al., 2010)
The aim of the paper is to: 1) describe a priapulid-like scalidophoran from the lower Cambrian of Baltica, and 2) discuss its ecology and paleobiogeography.
During the early Cambrian, Baltica was positioned in the southern hemisphere, between 60 and 30 degrees, in a cold-temperate zone (Lindström, 1972; Cocks & Torsvik, 2005). The area that is now Estonia was submerged under a shallow epicontinental sea. The Cambrian Baltic Basin is known for its terrigenous sedimentation. The lowermost part of the trilobite-bearing Cambrian on the East European Platform, deposited during the Liivi evolutionary stage in the East Baltic region (Mens & Pirrus, 1997), is defined as the Dominopol' Stage (Series 2) (Meidla, 2017).
In Estonia, the Dominopol' Stage is represented by three consecutive formations: Sőru, Lükati, and Tiskre, which are easily distinguished based on lithological and palaeontological evidence. The Dominopol' strata are distributed in the West Estonian Archipelago islands (except Ruhnu) and in the western, northern, and central parts of mainland Estonia. Only the upper part of the stage (Lükati and Tiskre formations) is exposed along the North Estonian Klint, stretching from the Pakri Peninsula in the west to the Narva River in the east. Key localities include Türisalu, Rannamőisa, Kakumägi, Lükati, Saviranna, Kunda, and Utria. The maximum thickness of the stage (76.6 m) has been recorded in the Kalana borehole, where all three formations are present (Mens & Pirrus, 1997). The Dominopol Stage corresponds to the Cambrian Series 2 (Jankauskas & Lendzion, 1994; Mens & Pirrus, 1997).
The stage consists mainly of siliciclastics, primarily sandstones. The lower boundary of the stage is distinct both lithologically and in terms of faunal composition, and in some locations, it is marked by conglomerate lenses (Mens & Pirrus, 1997).
Fossils in the lower part of the stage (Sőru Formation) are scarce, represented mostly by trace fossils, rare tests of agglutinated foraminifers, and a few acritarchs. The latter include leiosphaerides and rare Globosphaeridium cf. cerinum (Volk.), Asteridium pallidum (Volk.), Loposphaeridium tentativum (Volk.), and Tasmanites bobrowskae Waz. (Mens & Pirrus, 1997). This part of the stage corresponds to the Rusophycus parallelum Zone (Mens & Pirrus, 1997).
The middle part of the stage (Lükati Formation) is well characterized palaeontologically. Typical species include Volborthella tenuis Schm., V. conica Schindewolf, Schmidtiellus mickwitzi (Schm.), Mickwitzia monilifera (Linnars.), torellellids, hyolithids, agglutinated foraminifers (Luekatiella estonica Zhigulina, 1999), and, in the west, Platysolenites antiquissimus Eichwald in the basal beds. The acritarch assemblage in this part of the stage is abundant and diverse, with baltisphaerids being dominant (Mens & Pirrus, 1997). The middle and upper parts of the stage correspond to the Schmidtiellus mickwitzi Zone (Mens & Pirrus, 1997).
The upper part of the stage (Tiskre Formation) is well characterized palaeontologically only in its lower part (Kakumägi Member), particularly in the conglomerate lenses, which contain Mickwitzia monilifera (Linnars.), M. formosa Wiman, M. concentrica Gorjansky, Paterina rara Gorjansky, Scenella discinoides Schm., S. tuberculata Schm., Bradoria? estonica Melnikova, Konicekion kundaensis Melnikova, and fragments of trilobites. In the uppermost part (Rannamőisa Member), only occasional, indeterminable fragments of brachiopods and trace fossils are found. Acritarchs have been identified in the Kakumägi Member and, once, in the Rannamőisa Member (Muraste-2 borehole) (Mens & Pirrus, 1997).
A fossil of priapulid-like worm from the
Dominopol Stage (Häädemeeste 172 borehole, depth 599.4m) (Fig. 1 
)
was cleaned and photographed with a digital camera (Canon
EOS 5DSR). The details were photographed using the apochromatic zoom system
Leica Z16 APO. The measurements of the specimens were obtained from calibrated
high-resolution photographs. The studied specimen (GIT 293-400) is deposited at
the Department of Geology, Tallinn University of Technology (GIT).
|
Figure 1:
Location of Häädemeeste borehole. |
Phylum Priapulida Delage et Hérouard, 1897
Genus Yunnanpriapulus Huang et al., 2004b
Yunnanpriapulus? sp.
Description: The animal can be divided into
three distinct parts: an anterior introvert, a slightly constricted elongated
neck, and a slightly bulbous elongated posterior trunk. The neck and anterior
part of the trunk show poorly developed but regular annulation. The annuli are
about 0.2 mm thick. The worm is 8.7 mm long. The trunk is 4.7 mm long and 1.2 to
2.0 mm wide, widest at proximal ˝ of the trunk, and thinnest at the neck. The
neck is separated from the trunk via shallow but well-defined constriction. The
neck is 3.4 mm long and 1.2 mm to 1.6 mm wide, widest near the introvert. The
introvert is short, about 0.8 mm long, and slightly bulbous, about 1.8 mm wide.
There is a prominent constriction between the neck and the introvert. Posterior
end of the trunk with rudimentary or broken caudal appendage. The caudal
appendage is not branched. Some longitudinal structures are visible along the
trunk that may correspond to scalid rows (Fig. 2.B ).
Comparison: The described specimen resembles Yunnanpriapulus Huang et al., 2004b (p. 221, Fig. 4 a-f) in its small size, presence of subspherical introvert, well-defined neck and anterior part of the trunk that shows fine annulations and increases slightly in diameter backward. The described species has only a rudimentary caudal appendage, though it might be broken, which differs from the longer caudal process of Yunnanpriapulus. The described specimen also resembles Eximipriapulus globocaudatus Ma et al., 2014 (Fig. 8 IV-V) by bulbous trunk and broad introvert. It differs by much longer neck region. The body orientation could be reverse with the introvert composing the largest part of the body based on the anatomy of many modern priapulids (Martín-Durán et al., 2012), but the location of the caudal appendage is the reason why we oriented the body in that way.
|
Figure 2:
Yunnanpriapulus? sp. (GIT
293-400) from the Dominopol Stage (Cambrian, Series 2), Häädemeeste 172
borehole, depth 599.0m. A, General view in original state. B, General view in
different light after some preparation. C, Lateral view of whitened specimen. |
|
Figure 3:
Schematic line drawing of Yunnanpriapulus?
sp. (GIT 293-400). |
Kesidis et al. (2019) described exceptionally preserved trace and body fossils from sandstones of the lower Cambrian (Stage 4) File Haidar Formation of southern Sweden that can unequivocally be assigned to a scalidophoran producer. There is a great morphological similarity between priapulid burrows (i.e., trace fossils) and their molds (i.e., body fossils). The major question concerning the described specimen from the lower Cambrian of Estonia is whether it represents a moldic preservation of priapulid or it is a priapulid burrow preserved in positive relief. All previously described priapulid burrows, both Recent and fossil, show a great amount of irregularity in their morphology (see Kesidis et al., 2019, Figs. 3b-d, 4a-c) as compared to moldic preservation of body fossils (see Kesidis et al., 2019, Fig. 3a). In this respect, the studied specimen resembles much more the priapulid mold (Kesidis et al., 2019, Fig. 3a) than burrows (Kesidis et al., 2019, Figs. 3b-d, 4a-c). Moreover, the studied specimen shows both ends that a very well preserved and discrete which cannot be said for the trace fossils and Recent burrows. The last but not least, careful examination of the terminal part of the studied specimen reveals the presence of a short caudal appendage preserved as cast which cannot be seen in any priapulid burrow. Thus, considering the reasons mentioned above, we are inclined to interpret our specimen as a moldic preservation of a "priapulid" worm (i.e., body fossil). One could ask why we have attributed this fossil to "priapulids" as these scalidophorans have a very specific set of sensory-locomotory appendages, a peculiar symmetry of their arrangement, etc. which are not detectable on the fossil. The lack of these characters is due to the preservation mode as mold composed of fine grained sandstone. Similarly preserved molds have been assigned to "priapulids" with confidence by Kesidis et al. (2019, Fig. 3a). We acknowledge that definite Cambrian priapulids are extremely rare fossils (if any). Almost certainly studied fossil represents either total-group, or stem-group scalidophorans. It may also represent a total-group and stem-group cycloneuralians (e.g., Wang et al., 2025).
The specimen is preserved as a three-dimensional cast in the fine-grained sandstone and is oriented parallel to the bedding plane. The color of the fossil is light brown while the surrounding matrix is greenish-grey. We did not find sedimentological differences in the grain size between the matrix and fossil that could suggest a trace fossil. The light brown color could be caused by the higher pyrite content of the fossil as compared to the surrounding rock. The originally organic priapulid was presumably preserved via pyritization (Briggs, 2003). The rapid burial helped protect the organism from scavengers and decay, providing the opportunity for fossilization. The mineralization of soft tissues did not lead to a full replacement, but rather to the preservation of the organism's external form as a mold. Over time, mineral-rich waters in the sandstone could seep into the mold, hardening and preserving the fossil's shape. The further mineralization and incoming sand from surrounding sediments filled the cavity and preserved the worm as a cast. We assume that studied specimens could represent a similar way of preservation to priapulid mold from the lower Cambrian of Sweden that was recently described and illustrated by Kesidis et al. (2019, Fig. 3a).
Yunnanpriapulus was likely a burrowing predator (Huang et al., 2004a, 2004b, 2014). Similarly, most other Cambrian priapulids are thought to be predators (Conway Morris, 1977; Huang et al., 2004a, 2004b; Hu, 2005; Huang, 2006; Peel, 2017). A direct evidence of predation comes from preserved gut contents in Ottoia (see Vannier, 2012). Moreover, extant priapulids are also chiefly carnivorous, though occasionally they ingest mud too (Huang et al., 2004a, 2004b). The early Cambrian priapulids had a burrowing lifestyle (Zhang et al., 2006; Han et al., 2007; Vannier et al., 2010; Huang et al., 2014; Kesedis et al., 2019). Since these animals had an endobenthic lifestyle, it is possible that a massive input of sediment made it impossible for the worm to escape and reach the water sediment-interface. The preservation of the fossil on a bedding plane likely resulted from post-mortem transportation of the dead animal, presumably due to a storm event on a relatively shallow terrigenous shelf. Fine-grained sands formed a suitable substrate for burrowing, and during its life, Yunnanpriapulus was likely submerged in sediment leaving only its apertural part free on the surface of seafloor. The priapulid likely hunted a high variety of animals for food as suggested by studies of their gut content (Vannier, 2012). The numerous worm burrows in the lower Cambrian sediments of Estonia suggest that the sea floor may have contained diverse scalidophoran fauna. The data on early Cambrian predators in the Baltic Basin is scarce (see Mens & Pirrus, 1997), and it is possible that priapulids may have been among the top predators.
The early Cambrian priapulids have been reported only from a few places, most of them in China. The oldest total-group scalidophoran fossils come from Kuanchuanpu Formation (Wang et al., 2025). The most famous locality is Chengjiang Lagerstätte, which also contains the most diverse fauna of priapulid worms (Huang et al., 2004a, 2004b, 2014; Ma et al., 2014). Recently, 4 palaeoscolecidans that differ from priapulids (Zhuravlev et al., 2011) and one corynetiid were reported from the Guanshan fossil Lagerstätte (Cambrian Stage 4, Series 2) from East Yunnan, SW China (Hu et al., 2012). Total-group scalidophorans also occur in Sirius Passet Lagerstätte (Cambrian Series 2, Stage 3) (Peel, 2017). The discovery of possible priapulid in the lower Cambrian of Estonia (Baltica) indicates that these worms had wider paleobiogeographic distribution in the early Cambrian than previously known. The similarity of the Estonian specimen to the Chinese species suggests that there may have been some faunal exchange between the remote continents of Baltica and south China. On the other hand, the larval stages of modern priapulids are not swimming. They are loricate larvae (Vannier, 2024). Thus, the larval stage was likely not the primary mode of dispersal for priapulid worms.
O.V. was financially supported by the Estonian Research Council grant PRG2591. This project was supported by the Ongoing Research Funding program (ORF-2025-900), King Saud University, Riyadh, Saudi Arabia. We are grateful to Gennadi Baranov for the digital photos of the specimen, and to Jean Vannier (Université Lyon 1) and Andrey Zhuravlev (Lomonosov Moscow State University) for the constructive comments on the manuscript.
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