This is how a Cambrian Trilobite Hunted

The Cambrian Period, which occurred between 541 million and 485 million years ago, is an important point in evolutionary history where most of the major groups of animals first appear in the fossil record. Often called the "Cambrian explosion," fossils from this time provide glimpses into evolutionary history as the world's ecosystems were rapidly diversifying. Most fossils preserve the physical remains of organisms and their structure; however, geologists and paleobiologists at the University of Missouri recently collaborated to study fossils that reveal the behaviors of predators preserved as traces in ancient sediments. Thus, fossils from southeast Missouri are helping scientists unlock clues about the behaviors of these predators and their interactions with their prey. Evidence shows that these ancient organisms were behaviorally sophisticated, tailoring their attacks for effectiveness.

Trilobites are a fossil group of extinct marine invertebrate animals with external skeletons (see photo). As predators and scavengers, they flourished in the Cambrian period and were very prominent in the oceans that once were located in Missouri.

"The Saint Francois Mountains in southeastern Missouri have been the focus of geological research for decades and were once islands in the Cambrian ocean," said Kevin Shelton, professor of geological sciences in the MU College of Arts and Science. "I've worked as a geologist studying ore deposits in the area for more than 30 years. In that time, I've run across thousands of fossilized trilobite burrows. It is rare that we get to study the activities of 500 million-year-old organisms, yet the fossils in this locality are helping us determine how these organisms behaved."

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Ordovician Eoharpes benignensis Trilobites Showed Gregarious Behaviour Hiding

SHELTERED GREGARIOUS BEHAVIOR OF MIDDLE ORDOVICIAN HARPETID TRILOBITES

Authors:

Fatka et al

Abstract:

The presence of six articulated exoskeletons of late holaspid specimens of the rare harpetid Eoharpes benignensis entombed under a pygidial shield of the large asaphid trilobite Nobiliasaphus repulsus from the Middle Ordovician Dobrotivá Formation of the Prague Basin, Czech Republic is interpreted as a unimodal monotaxic trilobite cluster. The sheltered preservation of the trilobites may be explained as; (1) hiding behavior associated with predation pressure; (2) storm disturbance; or (3) molting associated with feeding. It is herein suggested that these Middle Ordovician holaspid trilobites deliberately entered the restricted space under a large isolated asaphid trilobite pygidial shield to find a refuge and shared the space within restricted shelters with conspecifics. The completeness of all specimens of the rare taxon Eoharpes, combined with the presence of more than one individual in this restricted space, excludes the possibility of transportation by bottom currents. This exceptional find represents an example of “frozen behavior” and provides a new insight in the life strategy of Middle Ordovician benthic trilobites. Attack abatement, e.g., avoidance and dilution effects, is for the first time proposed as a possible explanation for this example of sheltered gregarious behavior in trilobites.

Evolution of the Eyes of Two Very Different Trilobites

Eyes and vision in the coeval Furongian trilobites Sphaerophthalmus alatus (Boeck, 1938) and Ctenopyge (Mesoctenopyge) tumida Westergård, 1922, from Bornholm, Denmark

Authors:

Schoenemann et al

Abstract:

The two olenid species Sphaerophthalmus alatus (Boeck, 1838) and Ctenopyge (Mesoctenopyge) tumida Westergård, 1922, occur together in the Ctenopyge tumida Zone (Zone 19) of the Furongian of Scandinavia. Material from Bornholm, Denmark, forms the basis of this study of the morphology and partial ontogeny of the eyes. The eyes of both species are directed laterally and have virtually panoramic vision, looking out sideways like those of a rabbit. The eye of S. alatus is comparatively smaller, with fewer lenses and a larger eye parameter; calculations show that this trilobite was adapted for dim light intensity, possibly suggesting a vagrant benthic habit. Ctenopyge (Mesoctenopyge) tumida, with a smaller eye parameter, was adapted for a higher light intensity, and this trilobite was most likely a pelagic swimmer. The two species, although preserved together, inhabited different levels in the water column.

Cambrian Trilobites From Argentina

Early middle Cambrian trilobites from La Laja Formation, Cerro El Molle, Precordillera of western Argentina

Authors:

Pratt et al

Abstract:

A tectonically undeformed portion of the lower part of La Laja Formation is exposed at Cerro El Molle near San Juan, Precordillera of western Argentina. It consists of shallow-water, variably argillaceous lime mudstone and sporadically interbedded bioclastic grainstone deposited in an inner shelf setting. The El Estero Member and the basal 0.2 m of the Soldano Member contain a trilobite fauna of olenelloids and ‘simple' ptychoparioids indicative of the early Cambrian (series 2, stage 4; Dyeran stage of Laurentia). The succeeding 50 m of the lower Soldano Member yield trilobites characteristic of the early middle Cambrian (series 3, stage 5; Delamaran stage of Laurentia). In ascending order of occurrence, Amecephalus arrojosensis, Kochiella maxeyi and Eokochaspis nodosa, along with several other taxa, including Ptychobaba n. gen. (type species Ptychoparella buttsi), belong to the traditional lower Plagiura–Poliella Biozone. However, while this fauna is similar to that of the Great Basin, the nominative species of the Eokochaspsis nodosa and overlying Amecephalus arrojosensis biozones recognized in southern Nevada occur in reverse order in the Soldano Member. This suggests that the ranges of these species overlap, thereby reducing the temporal resolution in the Precordillera into a combined Amecephalus arrojosensis–Eokochaspis nodosa Biozone. Argillaceous lime mudstones at the top yield Mexicella mexicana, indicative of the Mexicella mexicana Biozone recognized in the Great Basin, which is equivalent to the traditional Albertella Biozone of Laurentia. Because corynexochids are almost absent, the low-diversity ‘kochaspid'-dominated biofacies appears to typify the platform interior. The fauna is entirely Laurentian in composition, reinforcing notions of a close proximity of Cuyania to Laurentia during the Cambrian that enabled faunal migration and interchange. The absence of a late early Cambrian to early middle Cambrian hiatus correlative with the Hawke Bay Event, however, suggests no close affinity to the Iapetus-facing margin of eastern Laurentia.

Ordovician Trilobites From Argentina

Early Ordovician trilobites from the Nazareno Area, northwestern Argentina

Authors:

Tortello et al

Abstract:

The upper part of the Santa Rosita Formation (Ordovician, Tremadocian) in the Nazareno area, Cordillera Oriental, northwestern Argentina, records the vertical passage of high-energy, shallow water platform environments to offshore settings. Eighteen trilobite species are described from this locality for the first time. Although the taxa from the lower part of the succession (Leptoplastides sp., Asaphellus sp.) are scarce and non-age diagnostic, those from the upper part include diverse assemblages partially assigned to the late Tremadocian Notopeltis orthometopa Zone. Systematic descriptions of several species (Geragnostus nesossii Harrington and Leanza, G. callaveiformis Harrington and Leanza, Asaphellus jujuanus Harrington, Notopeltis orthometopa [Harrington], Mekynophrys nanna Harrington, Ceratopyge forficuloides Harrington and Leanza, Apatokephalus tibicen Přibyl and Vanĕk) are improved, the genus Nileus Dalman (including N. australis n. sp.) is first reported from the Tremadocian of western Gondwana, and new species of Asaphellus Callaway (A. nazarenensis n. sp.), Conophrys Callaway, and Apatokephalus Brøgger are described. The trilobites have their closest affinities with faunas from Norway and Sweden. Notopeltis orthometopa and Mekynophrys nanna are restricted to the uppermost part of the succession, well above the first records of most other trilobites recognized.

Ordovician Trilobites From Greenland

Early Ordovician (Skullrockian) trilobites of the Antiklinalbugt Formation, northeast Greenland, and their biostratigraphic significance

Authors:

McCobb et al

Abstract:

The Antiklinalbugt Formation of northeast Greenland comprises peritidal to subtidal carbonate sediments, deposited in shallow shelf settings during an early Tremadocian transgressive-regressive megacycle. The succession of shales and microbial, muddy and grainy limestone, with minor dolostone at the base and top, terminates at the cryptic Fimbulfjeld disconformity. The formation has yielded trilobites collected on Ella Ø, Albert Heim Bjerge, and Kap Weber by C. Poulsen (1920s and 1930s), J. W. Cowie and P. J. Adams (1950s), and during recent field studies in 2000 and 2001. The fauna includes dimeropygids Tulepyge cowiei and T. tesella n. spp., hystricurids Millardicurus and Hystricurus, and several species of Symphysurina. Micragnostus chiushuensis (Kobayashi, 1931) is rare, as are Chasbellus sp., Clelandia sp., and Lunacrania?. The presence of several Symphysurina species places the Antiklinalbugt Formation within the Symphysurina Zone. Chasbellus indicates the upper (lower Ordovician) part of the Symphysurina Zone for the lower upper Antiklinalbugt Formation. Conodonts place the middle lower formation in the Cordylodus intermedius conodont Biozone, the lower upper part in the Cordylodus angulatus conodont Biozone and the uppermost part in the Rossodus manitouensis conodont Biozone. This combined fauna is characteristic of the upper Skullrockian Stage of the Ibexian Series, with the lower part of the Antiklinalbugt Formation lying within the uppermost Cambrian of North America, and the upper part within the lower Ordovician. The entire formation lies within the global Tremadocian Stage of the early Ordovician.

Catalog of Organisms on Bobble-nosed Trilobites

While most fossil invertebrates manage to completely fly under the radar when it comes to popular culture (it's not as if we're drowning under cartoon depictions of euthycarcinoids or eldoniids), one group that will often get a passing nod is the trilobites. Any depiction of early animal life worth its salt is going to feature a couple of these crunchy bugs scurrying about. Nevertheless, the range of varieties of trilobite shown will generally be low, and will usually be something similar to Olenellus or Elrathia. Seeing as trilobites persisted for hundreds of millions of years, it should be no surprise that their actual diversity was much higher.

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Explaining the Behaviour and Niches of Trilobites

The palaeoecology of trilobites

Author:

Fortey

Abstract:

Trilobites comprise a major group of extinct marine arthropods, which thrived in a variety of habitats surrounding the Palaeozoic palaeocontinents. The evidence that can be used to infer their ecology is reviewed, including functional anatomy, field occurrence and geology in comparison with living arthropods and palaeogeography. Where different lines of evidence are consistent with one interpretation, the inferred life habits are considered well supported, but there remain some intriguing enigmas. Trilobites occupied many of the ecological niches available to living marine arthropods, including the pelagic realm. Benthic species included predator/scavengers, grazers and particle feeders, and specialist filter feeders. Different contemporaneous natural assemblages of trilobites occupied different habitats ranging from shallow water to deep environments, which are characterized by distinctive suites of genera (biofacies). Such differentiation was already well established in the Cambrian. Dispersed palaeocontinents through much of the Palaeozoic further encouraged the evolution of endemics and distinct suites of taxa in relation to palaeolatitude. Taken together, these factors go some way towards explaining the great variety of species that evolved during more than 250 million years of their history.

Phylogeny of Cambrian Spiny Trilobites

Phylogenetic analysis of the spiny oryctocephalids (Trilobita, Corynexochida?, Oryctocephalidae), Cambrian

Author:

Sundberg

Abstract:

Phylogenetic analyses of the Cambrian spiny oryctocephalids support the elevation to familiar rank of Oryctocephalidae Beecher, 1897 and indicate that the family can be divided into two clades, here designated as the subfamilies Oryctocephalinae Beecher, 1897 and Lancastriinae Kobayashi, 1935. Curvoryctocephaliinae Zhao and Yuan in Yuan et al., 2002 is considered here a junior synonym of Lancastriinae. Oryctocephalinae have tapered or parallel sided glabella and is composed of species of Oryctocephalus Walcott, 1886. The subgenera Oryctocephalus (Oryctocephalus) and O. (Eoryctocephalus) Zhao and Yuan in Yuan et al., 2002 do not form separate clades and are here rejected.

The genera of the Lancastriinae have expanding glabellae. The subfamily is composed of a broad variety of genera that can be divided into three major subclades: Lancastria, Protoryctocephalus, and Oryctocephalites. The Lancastria subclade is composed of Lancastria Kobayashi, 1935, Changaspis Lee in Chien, 1961, and Goldfieldia Palmer, 1964 occurring at the base of the Lancastriinae. Goldfieldia and Lancastria form a sister group to Changaspis. The long branches in the phylograms indicated significant differences between these taxa; thus, the genus Goldfieldia is maintained. The Protoryctocephalus subclade is monogeneric and forms a sister group to the Oryctocephalites subclade. The Oryctocephalites subclade consists of several species of this genus and the more derived forms Metabalangia Qian and Yuan in Zhang et al., 1980 and Tonkinella Mansuy, 1916. Oryctocephaloides Yuan in Zhang et al., 1980 is considered a junior synonym of Oryctocephalites Resser, 1939. The subgenera Oryctocephalites (Oryctocephalites) and O. (Parachangaspis) Zhao and Yuan in Yuan et al., 2002 do not form separate clades. The later subgenus occurs in the basal portion of the Oryctocephalites subclade indicating that it is a paraphyletic taxon.

Opsiosoryctocephalus Sundberg, 1994, Oryctocephalops Lermontova, 1940, and Curvoryctocephalus Zhao and Yuan in Yuan et al., 2002 are not consistent in their placement within the phylogenetic analyses, although they always occur in the Lancastriinae. As a result they are not placed within a subclade within Lancastriinae.

The type species Goldfieldia pacifica Palmer, 1964 was based solely on cranidia. This species is redescribed using topotype material that includes cranidia, librigenae, hypostomes, thorax, and pygidia.

Morphology and Ontogeny of a Cambrian Trilobite From China

Morphology and ontogeny of Hunanocephalus ovalis (trilobite) from the Cambrian of South China

Authors:

Dai et al

Abstract:

The juvenile morphology and ontogeny of the Cheiruroidid trilobite Hunanocephalus ovalis Lee, 1963 from the lower Cambrian Shuijingtuo Formation in Hubei Province, South China is presented. The new material comprises a relatively complete meraspid ontogenetic series (degree 0 to 10), which reveals more details on their morphological changes such as the contraction and disappearance of the pronounced posteromedial notch in the pygidium and the addition of the trunk segments, which are all documented for the first time and can also be used as developmental markers defining their ontogenetic phases. The trunk segmentation schedule of H. ovalis is also discussed, which is similar to the other early Cambrian oryctocephalid trilobites, i.e. as the boundary between the thorax and pygidium migrated posteriorly there is no change in the trunk segment number; the processes of liberation of the thoracic segment and segment insertion into the pygidium are separated from one another, implying that the control of trunk exoskeletal segment appearance and articulation might be decoupled in these trilobites.

Trilobites Invaded Tidal Flats During the Early Cambrian

Trilobites in early Cambrian tidal flats and the landward expansion of the Cambrian explosion

Authors:

Mángano et al

Abstract:

The timing of the early invasion of the continents, the routes to the land, and the environmental breadth of the Cambrian explosion are important topics because they are at the core of our understanding of early evolutionary breakthroughs. Illuminating some aspects of these problems are trilobite trace fossils in tidal-flat deposits from the lower Cambrian Rome Formation in the southern Appalachian Mountains of Tennessee (USA). Morphologic details and size range of the trace fossils suggest production by olenellid trilobites, which occur as body fossils in the same unit. The occurrence of this ichnofauna, together with physical structures indicative of periodic subaerial exposure (desiccation cracks) and deposition within the intertidal zone (flat-topped ripples), shows that trilobites forayed into the upper intertidal zone during the Cambrian. Our finding supports the migration of subtidal organisms into marginal-marine, intertidal settings at the dawn of the Phanerozoic, suggesting that trilobites contributed to the establishment of the intertidal ecosystem during the Cambrian. The sequence of events involved in the colonization of early Paleozoic tidal flats is consistent with the idea that most terrestrial taxa originated from marine rather than freshwater ancestors, and that direct routes to the land from marginal-marine ecosystems were involved in the colonization of continental environments early in the Phanerozoic.

Trilobites From the Planet MONGO...errm...Portugal

Giant trilobites have been discovered in a rock quarry in northern Portugal.

The finding, published in the journal Geology, adds a new chapter to the story of some of the most successful creatures that ever lived, and may even challenge current specimens for the largest the planet has ever seen.

The current record holder for the largest trilobite still officially stands at the 72 centimeter (28.3 inch)-long Isotelus rex, a fossil recovered in Manitoba, Canada in the year 2000.

Last year, Artur Sa of the University of Tras-os-Montes and Alto Douro and a team of colleagues unearthed a slew of similar giants between 50 and 70 centimeters (19.7 and 27.6 inches) long in a slate quarry in Arouca, Portugal.

They also found two fossilized tail sections which they believe belonged to 90 centimeter (35.4 inch)-long animals, the biggest in the world.

"Normally trilobites in the Iberian Peninsula and throughout Spain don't get bigger than 10 centimeters (3.9 inches) long," Sa said. "In the quarry, they are normally above 30 centimeters in length."

Uber sized! 3 ft 'bites. Nice!


Abstract:

Giant trilobites and trilobite clusters from the Ordovician of Portugal
Juan C. Gutiérrez-Marco1, Artur A. Sá2,*, Diego C. García-Bellido1, Isabel Rábano3 and Manuel Valério4

1Departamento de Paleontología, Instituto de Geología Económica (CSIC-UCM), Facultad de Ciencias Geológicas, 28040 Madrid, Spain
2Departamento de Geologia, Universidade de Trás-os-Montes e Alto Douro, 5001-801 Vila Real, Portugal; and Centro de Geociências da Universidade de Coimbra, 3000-272 Coimbra, Portugal
3Museo Geominero–IGME, Ríos Rosas 23, 28003 Madrid, Spain
4Centro de Interpretação Geológica de Canelas, 4450-252 Canelas, Portugal

*E-mail: asa@utad.pt.

Large quarrying surfaces of roofing slate in the Arouca Geopark (northern Portugal), formed under oxygen-depleted conditions, have yielded a unique Ordovician fossil lagerstätte that reveals new information on the social behavior of trilobites. It provides several of the world's largest trilobite specimens (some reaching 70 cm), showing evidence of possible polar gigantism in six different species, as well as numerous examples of monotaxic and polytaxic size-segregated autochthonous trilobite clusters, some of which contain as many as 1000 specimens. These reveal a very diverse social behavior, which includes temporary refuge from predation and synchronous molting and reproduction, demonstrated for the first time in five contemporary families of three different trilobite orders from a single formation.

Link to the paper.