[Paleontology • 2024] Rapid Volcanic Ash Entombment reveals the 3D Anatomy of Cambrian Trilobites

Artistic reconstruction of two species of trilobite an instant before burial in a flow of volcanic ash 510 million years ago.
Gigoutella mauretanica (Ortega-Hernández, Azizi, Hearing, Harvey, Edgecombe, Hafid & El Hariri, 2017)

in El Albani, Mazurier, Edgecombe, Azizi, El Bakhouch, ... et Paterson, 2024. 

DOI: 10.1126/science.adl4540

Abstract

Knowledge of Cambrian animal anatomy is limited by preservational processes that result in compaction, size bias, and incompleteness. We documented pristine three-dimensional (3D) anatomy of trilobites fossilized through rapid ash burial from a pyroclastic flow entering a shallow marine environment. Cambrian ellipsocephaloid trilobites from Morocco are articulated and undistorted, revealing exquisite details of the appendages and digestive system. Previously unknown anatomy includes a soft-tissue labrum attached to the hypostome, a slit-like mouth, and distinctive cephalic feeding appendages. Our findings resolve controversy over whether the trilobite hypostome is the labrum or incorporates it and establish crown-group euarthropod homologies in trilobites. This occurrence of moldic fossils with 3D soft parts highlights volcanic ash deposits in marine settings as an underexplored source for exceptionally preserved organisms.

Microtomographic reconstruction of the trilobite species Gigoutella mauretanica in ventral view

Gigoutella mauretanica (Ortega-Hernández, Azizi, Hearing, Harvey, Edgecombe, Hafid & El Hariri, 2017)

Abderrazak El Albani, Arnaud Mazurier, Gregory D. Edgecombe, Abdelfattah Azizi, Asmaa El Bakhouch, Harry O. Berks, El Hafid Bouougri, Ibtissam Chraiki, Philip C. J. Donoghue, Claude Fontaine, Robert R. Gaines, Mohamed Ghnahalla, Alain Meunier, Alain Trentesaux and John R. Paterson. 2024. Rapid Volcanic Ash Entombment reveals the 3D Anatomy of Cambrian Trilobites. SCIENCE. 384, 6703; 1429-1435. DOI: doi.org/10.1126/science.adl4540

 

Editor’s summary: Trilobites are probably the best known denizens of the Cambrian Period. Their distinctive fossilized external forms are well recognized from an extensive fossil record spanning the early Cambrian to the Permian extinction. The vast majority of trilobite fossils display only external morphology, however, leaving much unknown about their internal morphology. El Albani et al. describe several trilobite fossils created by rapid death and preservation due to an underwater pyroclastic flow. This preservation created three-dimensional fossils with a remarkably well-preserved anatomy. This enhanced understanding of trilobite anatomy has revealed several new features and provided key insights into crown group euarthropods. —Sacha Vignieri

 

COVER: This reconstruction of a shallow marine environment shows trilobites being rapidly engulfed by volcanic ash from an eruption that occurred more than 500 million years ago. Recently discovered trilobite fossils from Cambrian-aged rocks in Morocco have revealed three-dimensional soft-tissue anatomy, including features not previously observed in these extinct arthropods. This find highlights marine volcanic ash deposits as important sites of exceptional fossil preservation. || Image: A. El Albani

[Paleontology • 2023] Tarutaoia techawani, Caznaia imsamuti, Tsinania sirindhornae, etc. • Trilobites of Thailand's Cambrian–Ordovician Tarutao Group and their geological setting

ตะรุเตาเอีย เตชวาลนิ  Tarutaoia techawani, 

จี่หนานเนีย สิรินธรเน่  Tsinania sirindhornae

A, Ao Phante Malacca section at low tide. 

B, hummocky cross-stratified sandstone bed at Ao Talo Udang.

D, ball-and-pillow structures at 4.6 m above the base in the Ao Phante Malacca section. 

 Wernette, Hughes, Myrow & Sardsud, 2023

DOI: 10.1002/spp2.1516 

news.UCR.edu

 

Abstract

Tuff-bearing upper Cambrian to lowermost Ordovician strata on Ko Tarutao island, Satun province, southernmost peninsular Thailand, contain a rich trilobite fauna relevant to global biostratigraphy, peri-Gondwanan palaeogeography and shifting evolutionary mode. This area of Sibumasu, a lower Palaeozoic marginal Gondwanan terrane, is shown to have been closely associated with Australia, North China (Sino-Korea) and other continental fragments from the supercontinent's northern equatorial sector, including South China at that time. Shared faunas also suggest a Kazakhstani and Laurentian association. Collections from eight sections yielded 10 newly discovered species and one new genus from ancient shoreface and inner shelf siliciclastic deposits. With the new taxa and revision of taxa known previously, we refine the age of the upper two formations of the Tarutao Group to the middle of Cambrian Stage 10, and lower–middle Tremadocian. Two biozones are erected for Sibumasu: the Eosaukia buravasi Zone, encompassing all Cambrian sections from Ko Tarutao, and the Asaphellus charoenmiti Zone, encompassing the Tremadocian fauna discussed herein. The new genus is Tarutaoia and new species are Tsinania sirindhornae, Pseudokoldinioidia maneekuti, Pagodia? uhleini, Asaphellus charoenmiti, Tarutaoia techawani, Jiia talowaois, Caznaia imsamuti, Anderssonella undulata, Lophosaukia nuchanongi and Corbinia perforata. Other taxa reported for the first time from Tarutao are Mansuyia? sp., Parakoldinioidia callosa Qian, Pseudagnostus sp., Homagnostus sp., Haniwa mucronata Shergold, Haniwa sosanensis? Kobayashi, Lichengia simplex Shergold, Pacootasaukia sp., Wuhuia? sp., Plethopeltella sp., Apatokephalus sp., Akoldinioidia sp. 1 and Koldinioidia sp.

Keywords: Thailand, Trilobita, Cambrian, Ordovician, Sibumasu, Gondwana

  

Map of Ko Tarutao.
AML, Ao Mo Lae; APM, Ao Phante Malacca; ATD, Ao Talo Udang; ATT, Ao Talo Topo; ATTw, Ao Talo Topo west; ATW, Ao Talo Wao,
type section of the Talo Wao Formation; LHN, Laem Hin Ngam; S1–S3, ATD Sections 1–3.

Modified from Burrett & Chaodumrong (2017).

A, Ao Phante Malacca section at low tide. B, hummocky cross-stratified sandstone bed at Ao Talo Udang; hammer is 18.5 cm long.
C, hummocky cross-stratified and coquina beds at the 3.4–3.7 m zone at Ao Mo Lae; pencil is 14 cm long. D, ball-and-pillow structures at 4.6 m above the base in the Ao Phante Malacca section; coin is 18 mm in diameter.
E, ball-and-pillow structures above two thin carbonate layers at Ao Phante Malacca 12.5 m; hammer is 18.5 cm long. F, tuff (38 cm thick) at Ao Phante Malacca 22.5 m; hammer is 35 cm long.

 

CONCLUSIONS: 

• The trilobite fauna of the Tarutao Group is significantly more diverse than previously known, with this work introducing 11 new species and 1 new genus, making for 42 discrete taxa, 25 of which have species-level resolution.

• The Ao Mo Lae Formation dates to the middle of Cambrian Stage 10, correlative with the Eosaukia, Mictosaukia perplexa and Mictosaukia striata zones of South Korea, Australia and South China, respectively.

• The Talo Wao Formation is middle Tremadocian where its fauna is most diverse, and may extend down into the lower Tremadocian.

• Sibumasu's first two formal biozones are erected, the Eosaukia buravasi Zone, encompassing all known sections of the Ao Mo Lae Formation, and the Asaphellus charoenmiti Zone, encompassing all known sections of the Talo Wao Formation. Their correlations are as noted in Conclusions 2 and 3 and Figure 12.

• Shared trilobite species and genera from these formations suggest that during the latest Furongian and early Tremadocian Sibumasu was palaeogeographically associated with South China, North China and Australia, with a less strong, but still notable, association with Kazakhstan. Sibumasu shared more taxa with Laurentia than did most other parts of Gondwana.

Shelly J. Wernette, Nigel C. Hughes, Paul M. Myrow and Apsorn Sardsud. 2023. Trilobites of Thailand's Cambrian–Ordovician Tarutao Group and their geological setting. Papers in Palaeontology. DOI: 10.1002/spp2.1516

 news.UCR.edu/articles/2023/11/20/trilobites-rise-ashes-reveal-ancient-map

1. จี่หนานเนีย สิรินธรเน่ Tsinania sirindhornae   2. ซูโดโคลดินิออยเดีย มณีขัติย์ Pseudokoldinioidia maneekuti 

3. พาโกเดีย เออเลนนิ Pagodia? uhleini   4. อซาเฟลลัส เจริญมิตรติ Asaphellus charoenmiti 

5. ตะรุเตาเอีย เตชวาลนิ Tarutaoia techawani   6. จิเอีย ตะโละวาวอิส Jiia talowaois 

7. แคซนาเอีย อิ่มสมุทรติ Caznaia imsamuti   8. แอนเดอร์สันเนลล่า อันดูลาตา Anderssonella undulata 

9. โลโฟซอเกีย นุชอนงค์งิ Lophosaukia nuchanongi   10. คอร์บิเนีย เพอร์ฟอราต้า Corbinia perforata 

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[Paleontology • 2022] Needmorella simoni • A New Trilobite Genus (Dalmanitidae: Synphoriinae) from the Lower–Middle Devonian of West Virginia

Needmorella simoni 

Holloway & Scott, 2022

DOI: 10.1017/jpa.2022.96 

 twitter.com/scottforteacher 

Abstract 

The trilobite Needmorella new genus, with type species Needmorella simoni new genus new species from the late Emsian to mid-Eifelian Needmore Shale of West Virginia, is a distinctive member of the subfamily Synphoriinae. It also occurs in the same formation in Pennsylvania and Virginia. It is not very similar to other Devonian representatives of the subfamily and is considered to have its origins in a morphologically less-derived ancestor because it shares certain similarities with Silurian genera, including the very short anterior cephalic border unmodified by crenulations or spines, S2 that is not largely reduced to a deep pit adaxially, the relatively low inflation of L3, and the well-defined interpleural furrows on the pygidium. Other particularly distinctive characters of the genus include the very long genal spines and the abaxially inflated and expanded posterior pleural bands on the thorax and pygidium that project slightly distally. The conventional concept of the Devonian synphoriine Anchiopsis Delo, 1935 appears to be incompatible with the holotype of the type species, judging from the early illustrations of the specimen, and the genus could be a synonym of Synphoria Clarke, 1894.

 

David J. Holloway and Brian M. Scott. 2022. Needmorella, A New Trilobite Genus of the Synphoriinae (Dalmanitidae) from the Lower–Middle Devonian of West Virginia. Journal of Paleontology. DOI: 10.1017/jpa.2022.96

  twitter.com/scottforteacher/status/1600246058730524673

[Paleontology • 2023] Uniquely preserved Gut Contents illuminate Trilobite Palaeophysiology

Bohemolichas incola  

in Kraft, Vaškaninová, Mergl, Budil, Fatka et Ahlberg, 2023.

 DOI: 10.1038/s41586-023-06567-7

Artwork: Jiri Svoboda.

Abstract

Trilobites are among the most iconic of fossils and formed a prominent component of marine ecosystems during most of their 270-million-year-long history from the early Cambrian period to the end Permian period1. More than 20,000 species have been described to date, with presumed lifestyles ranging from infaunal burrowing to a planktonic life in the water column2. Inferred trophic roles range from detritivores to predators, but all are based on indirect evidence such as body and gut morphology, modes of preservation and attributed feeding traces; no trilobite specimen with internal gut contents has been described3,4. Here we present the complete and fully itemized gut contents of an Ordovician trilobite, Bohemolichas incola, preserved three-dimensionally in a siliceous nodule and visualized by synchrotron microtomography. The tightly packed, almost continuous gut fill comprises partly fragmented calcareous shells indicating high feeding intensity. The lack of dissolution of the shells implies a neutral or alkaline environment along the entire length of the intestine supporting digestive enzymes comparable to those in modern crustaceans or chelicerates. Scavengers burrowing into the trilobite carcase targeted soft tissues below the glabella but avoided the gut, suggesting noxious conditions and possibly ongoing enzymatic activity.

 

a, Internal mould of specimen (inventory no. 8) in the nodule (coated with ammonium chloride). b–d, Scan model of the same specimen in dorsal (b), ventral (c) and left lateral (d) view. Exoskeleton in cream, hypostome in gold, digestive tract contents in shades of red and blue. The red dotted line indicates an anomalous position of segments five and six. Voxel size, 11.35 µm (applies for all figures and extended data). Scale bar, 10 mm.

a, In ventral view. b,c, Left lateral view of scan model of exoskeleton with hypostome reconstructed in life position (b) and reconstruction of the digestive tract (c). Locomotory (including spines) and respiratory appendages suppressed for clarity. Hypostome in a and c is transparent; exoskeleton in c is transparent.

Bohemolichas feeding on the sea floor, moments before it is engulfed, buried and preserved by an underwater mud flow.

Artwork: Jiri Svoboda.

Conclusion: 

The described specimen of Bohemolichas provides by far the most detailed source of information to date concerning the diet and the feeding mode of trilobites. This information includes indirect but robust evidence for a high-pH gut environment, aligning Bohemolichas with extant crustaceans and xiphosurans, and suggesting that such a digestive physiology may be primitive for the euarthropod crown group. It appears to have been an indiscriminate feeder on small, shelly, benthic invertebrates, most likely by scavenging rather than active hunting. Bohemolichas gives a unique glimpse of the role of lichid trilobites in an Ordovician marine ecosystem and provides evidence for the great antiquity of pH-neutral digestive physiology in arthropods.

Petr Kraft, Valéria Vaškaninová, Michal Mergl, Petr Budil, Oldřich Fatka and Per E. Ahlberg. 2023. Uniquely preserved Gut Contents illuminate Trilobite Palaeophysiology.  Nature.  DOI: 10.1038/s41586-023-06567-7

[Paleontology • 2023] Thulaspis tholops • A possibly deep branching artiopodan Arthropod from the lower Cambrian Sirius Passet Lagerstätte (North Greenland)

Thulaspis tholops 

Berks, Nielsen, Flannery-Sutherland, Nielsen, Park & Vinther, 2023

DOI: 10.1002/spp2.1495

 twitter.com/HarryBerks 

Abstract

Artiopoda was a diverse group of Palaeozoic euarthropods that proliferated in the early Palaeozoic, epitomized by the ubiquitous trilobites. Their possible phylogenetic position outside mandibulates and chelicerates offers the potential for understanding the evolution of euarthropods in more detail. However, this opportunity remains unexploited given that identification of deep-splitting artiopodans remains to be fully explored. Here, we describe a new non-trilobite artiopodan from the lower Cambrian Sirius Passet Lagerstätte, North Greenland. Thulaspis tholops gen. et sp. nov. is a large species with a broad, domed head shield, followed by a trunk consisting of 15 thoracic tergites and a small pygidium, giving the body an ovoid appearance when viewed dorsally. Thulaspis is distinctive with its rounded genae and anterior thoracic pleural tips, as well as short pleural spines posteriorly. A heart-shaped hypostome with an anterior lobe is present. Appendages, partly obscured by the tergal skeleton, have many moderate length gnathobasic spines, and large flap-like exopods with a fringe of small setae. Cladistic analyses recover Thulaspis as the sister taxon to Squamacula, a genus found in the Chengjiang and Emu Bay Shale biotas, in either a polytomy with a number of artiopodan taxa or as a sister group to all other artiopodans, indicating an important role in understanding the roots of artiopodan anatomy and evolution.

Keywords: Artiopoda, Euarthropoda, Sirius Passet Lagerstätte

Thulaspis tholops gen. et sp. nov. from the early Cambrian (Series 2, Stage 3) Sirius Passet Lagerstätte (North Greenland). MGUH 34172a, holotype.
A, photograph. B, interpretive camera lucida drawing of A.

Abbreviations: capp, cephalic appendage; gud, gut diverticulum; hs, head shield; hyp, hypostome; ttg, thoracic tergite. 

Scale bars represent 20 mm.

Thulaspis tholops gen. et sp. nov. specimen showing phosphatized gut (MGUH 34175a).
A, polynomial texture mapping (PTM) image using Static Multi Light rendering mode; outlined area enlarged in C. B, interpretive camera lucida drawing of A with orange colour representing the preserved gut and grey representing diagenetic trace fossils. C, alimentary canal with widened structure associated with head shield interpreted as a crop.

 Abbreviations: ac, alimentary canal; cr, crop; hs, head shield; ttg, thoracic tergite. 

Scale bars represent 10 mm.

SYSTEMATIC PALAEONTOLOGY

EUARTHROPODA Lankester, 1904

ARTIOPODA Hou & Bergström, 1997

Genus THULASPIS nov.

 

Type species: Thulaspis tholops from the lower Cambrian (Series 2, Stage 3) Sirius Passet Lagerstätte, Buen Formation, Peary Land, North Greenland.

Derivation of name: Greek: Thule, the term given to the northernmost lands, and aspis, shield; with the intended meaning of ‘shield of the northernmost lands’.

Thulaspis tholops sp. nov.

 

Derivation of name: Greek: thólos, dome, and ops, face; in reference to the reconstructed domed anterior of the head shield.

Diagnosis: Non-mineralized arthropod with ovate outline and 15 thoracic segments. Wide, semi-circular head shield about one-quarter the total length of the animal with small rounded genae. Anteriormost tergite bears slightly rounded spatulate pleural tips while posterior pleura increasingly curve backwards into short spines. Anteromedial expansions are present on the first five thoracic tergites and reduce in sagittal length distally. Tergites have substantial overlap axially and near the pleural tips. Pygidium is small and smooth, one-thirteenth of the total length and one-fifth of maximum width. Biramous limbs have broad, flap-like exopods with marginal setae.

 

Occurrence: Lower Cambrian (Series 2, Stage 3) Sirius Passet Lagerstätte, Buen Formation, Peary Land, North Greenland.

Fragmentary specimen of Thulaspis tholops gen. et sp. nov. showing large exopods (MGUH 34177)
A, photograph of specimen with fragmented parts placed together; outlined areas enlarged in B, D–E. B, fragment with exposed exopods bearing setae fringes (white arrows). C, interpretive camera lucida drawing of B. D–E, setae fringes on exopods.

Abbreviations: en, endopods; ex, exopod; hs, head shield; ttg, thoracic tergite. 

Scale bars represent: 10 mm (A–C); 5 mm (D, E).

Reconstruction of Thulaspis tholops gen. et sp. nov., showing post-antennal appendages using the appendages of Squamacula clypeata to help infer attachment of endopods and exopods to basipods (Zhang et al. 2004; Ortega-Hernández et al. 2013): A, dorsal view; B, ventral view.

CONCLUSIONS: 

• We describe Thulaspis tholops, a new genus and species of Cambrian arthropod from the Cambrian Sirius Passet Lagerstätte in North Greenland, thereby expanding the known diversity of this fauna.

• Thulaspis has a broad head, 15 thoracic segments and a small tail shield with biramous appendages bearing gnathobasic protopodites and large flap-like exopods with a margin of small setae.

• We uncover a close relationship between Thulaspis and the enigmatic artiopodan Squamacula and find that these taxa are likely to branch deeply within Artiopoda.

Harry O. Berks, Morten Lunde Nielsen, Joseph Flannery-Sutherland, Arne Thorshøj Nielsen, Tae-Yoon S. Park and Jakob Vinther. 2023. A possibly deep branching artiopodan Arthropod from the lower Cambrian Sirius Passet Lagerstätte (North Greenland). Papers in Palaeontology Papers. 9(3); e1495. DOI: 10.1002/spp2.1495

 twitter.com/HarryBerks/status/1669640244184875010

[Paleontology • 2019] Redlichia rex • The Trilobite Redlichia from the lower Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia: Systematics, Ontogeny and Soft-part Anatomy

Redlichia rex 

Holmes, Paterson & García-Bellido, 2019

 DOI: 10.1080/14772019.2019.1605411

The trilobite Redlichia Cossmann, 1902 is an abundant element of the lower Cambrian (Series 2, Stage 4) Emu Bay Shale (EBS) Konservat-Lagerstätte on Kangaroo Island, South Australia. Well-preserved, fully articulated specimens from this deposit are known to reach lengths of up to 25 cm, representing one of the largest known Cambrian trilobites. Until now, all Redlichia specimens from the EBS have been referred to Redlichia takooensis Lu, 1950, a species originally described from South China. Previous work recognized considerable differences in exoskeletal morphology among specimens of varying sizes, which was attributed to ontogeny. However, close examination of a large collection of recently acquired specimens shows that this variation actually represents two distinct morphs, interpreted here as separate species: R. takooensis, and a large, new species, Redlichia rex sp. nov. An analysis of morphological variation in holaspides (‘adults’) of the more common R. takooensis reveals considerable ontogenetic change occurred even during this later phase of growth. Some specimens of both Redlichia species from the EBS also exhibit exceptionally preserved soft-part anatomy, particularly the antennae and biramous appendages. Here, appendages (antenniform and biramous) and digestive structures are described, and biramous appendage reconstructions of R. rex sp. nov. are presented, which show a striking resemblance to some early Cambrian trilobites from South China. In particular, R. rex has a tripartite exopodite, as well as a dorsoventrally deep protopodite with gnathobasic spines used to shred or crush food items. Based on recent phylogenetic analyses, it is possible that an exopodite with tripartite subdivisions represents the plesiomorphic condition for Artiopoda (trilobites and kin). The digestive system of R. takooensis exhibits a series of paired digestive glands in the cephalon and anterior thorax, similar to those described for a number of other Cambrian and Ordovician trilobites.

Keywords: Arthropoda; Artiopoda; Redlichiida; geometric morphometrics; biramous appendage; antennae

Order Redlichiida Richter, 1932
Suborder Redlichiina Richter, 1932

Superfamily Redlichioidea Poulsen, 1927
Family Redlichiidae Poulsen, 1927

Genus Redlichia Cossmann, 1902

Type species. Hoeferia noetlingi Redlich, 1899 

from the early Cambrian of the Salt Range, Pakistan. 

Redlichia takooensis Lu, 1950
....

Redlichia rex sp. nov.

Derivation of name. Latin for ‘king’, in reference to the remarkable size of this species, the largest for the genus and the biggest Cambrian trilobite in Australia.

Redlichia rex sp. nov. [SAM P54286] from the Emu Bay Shale.  

Biramous appendage reconstructions for Redlichia rex sp. nov. illustrating the tripartite structure of the exopodite and the elongate protopodite.

James D. Holmes, John R. Paterson and Diego C. García-Bellido. 2019. The Trilobite Redlichia from the lower Cambrian Emu Bay Shale Konservat-Lagerstätte of South Australia: Systematics, Ontogeny and Soft-part Anatomy. Journal of Systematic Palaeontology. DOI: 10.1080/14772019.2019.1605411

    

[Paleontology | Ichnotaxa • 2016] Ichnofossil Record of Selective Predation by Cambrian Trilobites

Fig. 8. Diagram of trilobite interactions with worm, progressing step-wise from (A) to (C), with underside views of perpendicular handling (D) and parallel handing (E).

 [1.5 COLUMN, GREYSCALE].  doi: 10.1016/j.palaeo.2015.11.033

Highlights

• Trilobite Rusophycus traces are found intersecting vermiform burrows.

• Rusophycus trace size is positively correlated with intersected worm burrow size.

• Intersected vermiform burrows are significantly smaller than non-intersected burrows.

• Low angle attacks occur more frequently than expected due to random chance.

• Paired Davis Shale trace fossils may directly record predatory behavior.

Abstract

Evidence of predatory activity can be observed in the fossil record in the form of drill holes, repair scars, bite marks, and recognizable skeletal fragments in coprolites and preserved gut tracts. It is less common, however, to find fossil snapshots of predators caught in the act of feeding on their prey. Such interactions are preserved in recurring associations of the ichnogenera Rusophycus and Cruziana, most commonly attributed to trilobites, with burrows of likely vermiform (worm-like) organisms. In this study, we examine the Cambrian (Furongian Epoch, Steptoean Stage) Davis Formation, near Leadwood, southeastern Missouri, USA. In the lower to middle Davis Fm., several silty shale beds are extensively burrowed, from which we report a new occurrence and large number of Rusophycus traces associated with burrows of vermiform organisms. Within these beds, Rusophycus traces intersect vermiform burrows more often than expected by random chance and display a positive correlation in size between paired tracemakers. The median diameter of Rusophycus-associated vermiform burrows is significantly smaller than that of the non-intersected burrows. These results suggest that the paired traces record size selective predatory behavior. Moreover, low angle predator–prey trace intersections, though few in number, occurred more frequently than expected by random chance, supporting previous hypotheses that low angle attacks are preferred as they may improve prey handling success rates.

Keywords: Cambrian; Davis Formation; Rusophycus; vermiform burrows; predation

Fig. 3. Slab photograph, template for calculation of horizontal bioturbation intensity, and three-dimensional surface rendering. Sample JWH-DAV-01 showing the bottom of the slab with (A) light photography, (B) illustration of different traces (light grey = unknown, medium grey = vermiform, and dark grey = Rusophycus) used for bioturbation intensity calculations, and (C) 3D surface rendering topographic view below the upper plane of the slab (as it is preserved as positive hyporelief). Scale bar = 5 cm, with 1 cm demarcation. Color topography scale = 0–16 mm.

[SINGLE COLUMN, COLOR].  doi: 10.1016/j.palaeo.2015.11.033  

Fig. 4. Samples 13-DAV-20-057 (A–B), 13-DAV-071 (C–E), 13-DAV-20-003 (F), and 13-DAV-20-039 (G), showing the bottom of the slabs with (A, C, E–G) light photography, and (B, D) 3D surface rendering topographic view below the upper plane of the slab (as these traces are preserved as positive hyporelief). (A–F) Examples of Rusophycus-vermiform burrow intersections; (G) Examples of interpreted matground punctures. Scale bars = 1 cm, with 0.5 cm demarcation. Color topography scale in B = 0–12 mm, in D = 0–13 mm.

 [DOUBLE COLUMN FULL WIDTH, COLOR].  doi: 10.1016/j.palaeo.2015.11.033

 Conclusions

As indicated by our quantitative approach, the intersections between Rusophycus and vermiform burrows in the Davis Formation are most likely representative of active predatory behavior. Based on surface area, the Rusophycus traces appear to intersect vermiform burrows far more frequently than what would be expected by random chance alone. The frequency of these Rusophycus intersecting with vermiform burrows reveal that 30.7% of the traces reported here have the potential to be predatory. Of the traces that do show a potential predatory interaction, there is evidence of prey size selectivity. In fact, the trilobites chose from among the vermiform organisms a smaller, or more precisely narrower, prey size. Indeed, those prey selected show a significant and positive correlation with the size of the Rusophycus predator. Once the reported ichnofossil intersections were established as non-random in nature, angle of attack was assessed to determine if there was a preferred orientation. When modeling for a uniform distribution of angles, while simultaneously accounting for a reduced likelihood of intersection with reduced angle of intersection, we found that, though few in number, low angle attacks occurred more frequently than expected by random chance. We interpret the non-random distribution of angles of intersection to support the hypotheses of Jensen (1990) and Tarhan et al. (2012) that actively predating trilobites attacked at lower angles to maximize appendage to vermiform organism body exposure. While decreasing the chance of intersection or visibility during approach, this method would allow for trilobites to increase their grappling/handling success and efficiency by using their appendages to aid in both locating and capturing their prey. In sum, these results highlight the importance of the availability of large sample sizes that, in turn, enable a more rigorous quantitative approach to understand the nature and behavior of trace fossils and their makers.

Tara Selly, John Warren Huntley, Kevin L. Shelton and James D. Schiffbauer. 2015. Ichnofossil Record of Selective Predation by Cambrian Trilobites. Palaeogeography, Palaeoclimatology, Palaeoecology. In Press. doi: 10.1016/j.palaeo.2015.11.033