Cambrian Trilobites Research Articles

Dual role of enrolment for moulting and protection in a Cambrian trilobite from Poland

Dual role of enrolment for moulting and protection in a Cambrian trilobite from Poland

Cambrian trilobites and associated fossils from the Uinta Mountains of Utah (USA)

Abstract Fossils are rare in Cambrian strata of the Uinta Mountains of northeastern Utah, and are important because they can help integrate our understanding of laterally adjacent but discontiguous rock units, e. g., the Tintic Quartzite of Utah and the Lodore Formation of Utah-Colorado. New body fossils from strata previously mapped as Tintic or Cambrian Undifferentiated, but here interpreted as the Ophir Formation, include indeterminate hyoliths and hyolithids, brachiopods including a linguloid, and the trilobites Trachycheilus Resser, 1945 and Elrathiella Poulsen, 1927. The last two assign these strata to the Ehmaniella Biozone (uppermost Wuliuan Stage; Miaolingian Series) or traditional Laurentian middle Cambrian. These data, together with fossil occurrences elsewhere in Utah, require that the Tintic Quartzite was deposited prior to and/or during the early Wuliuan, and suggest that the unit could be correlative to much of the Lodore Formation of Utah and Colorado.

Faunal and paleoenvironmental changes at a Cambrian (Jiangshanian; Steptoean–Sunwaptan boundary interval) trilobite extinction event, in contrasting deep- and shallow-subtidal settings, Nevada and Oklahoma

Abstract Successions in Oklahoma and Nevada record trilobite extinction and replacement near the Steptoean–Sunwaptan boundary in inner-shelf and outer-shelf settings, respectively. Prior to the extinctions, different trilobite biofacies occupied these environments, but faunas became similar in composition across the environmental gradient in the overlying I. “major” and Taenicephalus zones. Faunal changes in the outer shelf at the I. “major” Zone begin at a drowning unconformity that brought dark, laminated calcisiltite and silty lime mudstone above a subtidal carbonate succession. In contrast, Oklahoma shows facies continuity in a succession of tidally influenced bioclastic carbonates. Loss of genera and a dramatic abundance “spike” of Irvingella are features of the I. “major” Zone in both regions. Turnover of biofacies occurred in the succeeding Taenicephalus Zone, with both the inner and outer shelf dominated by Orygmaspis (Parabolinoides). Blooms of orthid brachiopods in shallow water settings are underappreciated signals of faunal change in the extinction interval. Although absent from the outer shelf in Nevada, orthids became abundant enough in Oklahoma to form shell beds in the lower Taenicephalus Zone, but became rare in overlying strata. Carbon isotope stratigraphy includes a modest positive δ13C excursion that peaks in the extinction interval at 1.4‰ (Oklahoma) and 2.2‰ (Nevada), which is congruent with previous reports from Utah and Wyoming. Although consistent with regional upwelling of dysoxic waters, the absence of sedimentary evidence for significant environmental change over much of the shelf is problematic. This suggests that physical environmental change acted primarily as a catalyst for cascading ecological and biogeographic effects.

A new Cambrian (Jiangshanian, Sunwaptan) trilobite fauna from Oklahoma and its biostratigraphic significance.

AbstractThe Cambrian (Jiangshanian, Sunwaptan) Honey Creek Formation in the Wichita Mountains region of Oklahoma yielded a new fauna dominated by Monocheilus Resser, 1937 (senior synonym of Stigmacephalus Resser, 1937) in association with Ptychaspis Hall, 1863. It occupies the same stratigraphic position as similar faunas in the Upper Mississippi Valley and Alberta, lying a little above an interval characterized by species of Taenicephalus Ulrich and Resser in Walcott, 1924 and Orygmaspis Resser, 1937. Revision of Ptychaspis bullasa Lochman and Hu, 1959 from type material from Idaho and sclerites attributed to the species from Texas reveals a plexus of pseudocryptic species that share tuberculate sculpture on the cranidium. New species are Monocheilus reginae, Monocheilus richardi, Ptychaspis occulta, and Ptychaspis matuszaki.UUID: www.zoobank.org/c2771c63-db4b-434a-ae58-3e3fda19ecb0

Exceptional lower Cambrian fossils from a long‐lost locality in Vermont, USA

Recent excavations at the site of Vermont's historically important Parker Quarry, long considered worked out where fossils were concerned, have yielded not only spectacular lower Cambrian trilobites but also soft‐bodied animals including the early chordate Emmonsaspis cambrensis and a new multi‐segmented bivalved arthropod Vermontcaris montcalmi. The first radiodont specimen from the locality indicates the presence of one of these apex predators more than 30‐cm long. New discoveries from this Burgess Shale‐type deposit add to our knowledge of the geographical diversity of animals that evolved during the Cambrian explosion.

Morphology, variation, and systematics of the late Cambrian Laurentian dikelocephalid trilobiteWalcottaspis vanhornei(Walcott, 1914)

AbstractWalcottaspis vanhornei(Walcott, 1914) is a large, late Cambrian trilobite with a unique pygidial morphology known only from a narrow outcrop belt of the St. Lawrence Formation in the Upper Mississippi Valley. Found in carbonate-rich layers within heterolithic facies that represent the toesets of a prograding shoreface, it is restricted to a single or small number of parasequences. Only four specimens of any of its sclerites have been illustrated previously. Here holaspid examples of all its biomineralized sclerites are described and illustrated, along with a morphometric analysis of cranidial landmarks and landmarks plus semilandmarks for the pygidium. Ontogenetic allometry accounts for 29% of the variance among holaspid cranidia and includes a relative shortening and narrowing of the palpebral lobe and a reduction in the relative length and width of the frontal area. Notable pygidial phenotypic variation occurs in the extent of the postaxial region and in the proportion of the structure occupied by the axis. Phylogenetic analysis suggests thatW. vanhorneiis sister taxon toDikelocephalus minnesotensisOwen, 1852, which also occurs in the St. Lawrence Formation and has a broadly similar cephalon but distinctive trunk. The holaspid pygidium ofW. vanhorneiis uniquely characterized by the interpleural furrows of the first two segments becoming abruptly obsolete on approaching the axial furrow. Some pygidia show narrow, shallow, flat-bottomed grooves etched into the internal sides of the dorsal surface or doublure that apparently represent infestation of the live trilobite.

New trilobite assemblage from the lower Cambrian (upper Stage 4) of the Lake Zone, western Mongolia

AbstractThe western Mongolian Lake Zone was a Neoproterozoic to early Paleozoic volcanic arc where tuffs, lavas, fossiliferous siliciclastics, and carbonates accumulated during the early Cambrian. An uppermost Cambrian Series 2 (upper Stage 4) trilobite assemblage is described here from the Burgasutay Formation representing a continuous lower Cambrian succession at the Seer Ridge of the Great Lake Depression. The new assemblage is dominated by dorypygids and consists of 13 trilobite genera belonging to nine families includingCatinouyia heyunensisnew species. These fossils comprise the youngest and richest lower Cambrian trilobite assemblage in Mongolia. The composition of the Lake Zone fauna suggests its biogeographic affinity with the Siberian Platform and Altay-Sayan Foldbelt, but the presence of inouyiids also implies a connection of this region with East Gondwana.UUID:http://zoobank.org/fb0ebe23-144f-46ed-9543-7df9eea85fbc

The oldest trilobites in Cambria: Early Cambrian trilobite faunas from the Llanberis Slates Formation, Gwynedd, North Wales

Historical published works on the fossil fauna of the Llanberis Slates Formation in Gwynedd, North Wales, concentrated on the endemic trilobite Pseudatops viola (Woodward, 1888), and placed the formation towards the top of Stage 3 (Series 2) of the Cambrian chronostratigraphy.The impression given was that the fauna is not particularly diverse and fossils are rare. However, recent collecting has produced a comprehensive fauna of sponges, hyolithids and diverse arthropods including over 250 trilobite specimens from two localities of the uppermost Green Slate horizon. Among them are examples of the endemic trilobite Pseudatops viola, sufficiently well preserved to enable a reappraisal of its status. The most abundant trilobite is a form of Strenuella (cf. strenua), but the collection includes previously unrecorded eodiscoid trilobites and specimens representing unrecorded and potentially new taxa. These additions result in the most comprehensive lower Cambrian trilobite assemblage yet described from Wales, and place it in the lower part of Stage 4, Series 2 in standard global terms.

Assessment of morphological variation in the early Cambrian trilobite Protoryctocephalus

ABSTRACT Studies focused on morphological variation are key for chrono- and biostratigraphy. Morphological variability can be induced by biological and taphonomical biases. Their distinction can become a difficult task due to the lack of population control. Here, we analyse three populations belonging to the genus Protoryctocephalus, two populations from China (P. arcticus and P. balangensis) and a third population of P. arcticus from Greenland. Protoryctocephalus balangensis was collected from the lowermost part of the Kaili Formation where fossils are tectonically deformed while P. arcticus from the ‘Tsinghsutung’ and Greenland specimens are non-deformed. Geometric morphometrics analysis shows that these three populations indeed belong to the same species. However, the large allometry measured in P. balangensis compared with the ‘Tsinghsutung’ population and the Greenland population, which is represented by meraspid and early holaspid individuals, suggested that the morphological variation is taphonomically controlled and non-biological. The results suggest that Protoryctocephalus arcticus from the ‘Tsinghsutung’ Formation is suitable for international correlation, and further studies focus on different aspects such as ontogeny, segment development or fluctuating asymmetry and modularity.

Drifting with trilobites: The invasion of early post-embryonic trilobite stages to the pelagic realm

The Ordovician Radiation shaped Paleozoic marine ecosystems and led to an increase in the biodiversity of marine organisms. The onset of the Plankton Revolution in the late Cambrian is an important step within the Ordovician Radiation. During this revolution, various organisms invaded pelagic realms, which affected the marine trophic web through the introduction of phytoplankton, zooplankton, as well as plankton- and suspension-feeding animals. Trilobites, a main Paleozoic group of marine metazoans, played a major role during the Ordovician Radiation. Previous studies showed that some trilobites evolved planktic larvae during the Furongian and Early Ordovician. Herein, we quantify the appearance of trilobite planktic larvae by providing highly resolved Cambrian and Ordovician data on 144 trilobite species with well-known developmental sequences. We show that Cambrian trilobites were dominated by species and families with exclusively benthic early post-embryonic stages. On the contrary, Ordovician seas comprised a remarkable number of trilobites with one or more planktic stages. However, species and families with exclusively benthic early stages still constituted about half of the Ordovician trilobite diversity. The first trilobites with planktic larvae might have been present in the Miaolingian, but their earliest fossil record is from the mid-Furongian. The appearance of planktic forms was accentuated later in the Ordovician with many trilobite lineages adapting a multi-staged planktic mode of life – more than one developmental stage colonizing the water column during ontogeny. Between the Miaolingian and the Middle Ordovician, both species- and family-level data show a progressive increase in the number of taxa incorporating planktic larvae in their development, highlighting a gradual transition in the structure of marine ecosystems during the early Paleozoic.

Unique Cambrian trilobite Eodontopleura: an example of strong convergence in trilobite evolution

ABSTRACT The lower Cambrian trilobite Eodontopleura Chien and Lin in Yin and Lee 1978 from South China was once thought to be an ancestor of the post-Cambrian trilobite Odontopleurida due to its unique odontopleurid-like glabella. Here, we revise this genus as an oryctocephalid based on the articulated exoskeletons found recently in the Balang Formation (Cambrian Series 2, Stage 4) of South China. Phylogenetic analysis supports that Eodontopleura represents a typical example of trilobite convergent evolution, suggesting that even the most exclusive features may have been repeated in the evolutionary history of trilobites, which additionally reminds us of the universality of convergence and its possible misleading effect on trilobite taxonomic studies. Moreover, our discovery indicates the remarkable specialisation potential of oryctocephalids, which highlights the evolution of early deep-water trilobites.

The putative earliest Cambrian trilobite–brachiopod association in southern Sichuan Basin of South China

ABSTRACT Parabadiella is considered the earliest trilobite representative in South China and was originally recovered from the mid-upper part of the Guojiaba Formation, in Liangshan section. Previous studies suggested that the earliest brachiopod co-occurred with the oldest trilobite, and the Parabadiella–Eoobolus association from the Xihaoping Member (Cambrian Series 2, Stage 3), in southern Shaanxi was considered the first trilobite–brachiopod assemblage zone in South China. Therein, brachiopods occur together with trilobites recovered in Well JS103 seemingly extending the First Appearance Datum deeply in the lower Cambrian at the central Yangtze Platform. Well JS103 is a shale gas exploration well that targets the lower Cambrian Jiulaodong Formation in southern Sichuan Basin. The uppermost fossiliferous layers are siliciclastic rocks nearly 10 metres thick. Here, two distinct trilobite zones are found, including the lower Parabadiella Zone and the upper Wutingaspis–Eoredlichia Zone. Additionally, the lowermost part of the Guojiaba Formation is poorly fossiliferous, and ranges from 200 to 250 metres in thickness. Thus, the discovery of the brachiopod–trilobite assemblage provides new insights into the biostratigraphy in Sichuan and is of great potentials for biostratigraphic correlation of the siliciclastic rocks in the western margin of the Yangtze Platform.

Cambrian correlation within the Perigondwana Faunal Realm

Stratigraphic positions of Redlichioidea trilobites found in the Lower Cambrian of Morocco, Spain, South France, Sardinia, Jordan, Doberlug and Gorlitz (both in Germany), and those from Central Asia, Himalayan region, Australia and Antarctica are correlated with that of the Chinese biostratigraphic scheme. During the Middle Cambrian, biostratigraphic correlation between the Mediterranean region (including Morocco and Central Europe) and China is very difficult because of the complete absence of Paradoxides-fauna in China. Based on shallow-shelf and open-shelf trilobite faunas, the Middle and Upper Cambrian biostratigraphy of the Near East, Central, South and Southeast Asia, Australia and Antarctica are correlated with that of both China's shallow-shelf and open-shelf biostratigraphic schemes. Late Cambrian trilobite faunas of eastern Asiatic affinities also occur in Morocco, Spain, South France and Turkey. So far, there is no trilobite fauna of the Late Cambrian Fengshanian Stage found in Europe.

The stratigraphically lowest known Cambrian trilobites from the Dial Range Trough, northwest Tasmania and from western Tasmania

The stratigraphically lowest known agnostoids and trilobites from both the Dial Range Trough of northwest Tasmania and from western Tasmania are described. Those from the Dial Range Trough occur in the Isandula Road area and comprise the agnostoid Acadagnostus cf. rakuroensis, and the trilobites Pagetia sp., Nepea cf. nans and Paibianomocare? sp., thus suggesting a range between the Triplagnostus gibbus and Euagnostus opimus zones. Loxonepea is placed in synonymy with Nepea. The Sticht Range Beds of western Tasmania contain only two poorly preserved trilobite specimens referred to Anomocarellidae gen. et sp. indet.; a definite age cannot be obtained from this material. James B. Jago [jim.jago@unisa.edu.au], University of South Australia—STEM, Mawson Lakes, South Australia, 5095, Australia Christopher J. Bentley [bigfossil@bigpond.com], 30 Albert Street, Clare, South Australia, 5453, Australia

A new Cambrian catillicephalid trilobite from the Shallow Bay Formation of western Newfoundland, Canada

A new Cambrian catillicephalid trilobite from the Shallow Bay Formation of western Newfoundland, Canada

Complex axial growth patterns in an early Cambrian trilobite from South Australia.

The exceptional fossil record of trilobites provides our best window on developmental processes in early euarthropods, but data on growth dynamics are limited. Here, we analyse post-embryonic axial growth in the Cambrian trilobite Estaingia bilobata from the Emu Bay Shale, South Australia. Using threshold models, we show that abrupt changes in growth trajectories of different body sections occurred in two phases, closely associated with the anamorphic/epimorphic and meraspid/holaspid transitions. These changes are similar to the progression to sexual maturity seen in certain extant euarthropods and suggest that the onset of maturity coincided with the commencement of the holaspid period. We also conduct hypothesis testing to reveal the likely controls of observed axial growth gradients and suggest that size may better explain growth patterns than moult stage. The two phases of allometric change in E. bilobata, as well as probable differing growth regulation in the earliest post-embryonic stages, suggest that observed body segmentation patterns in this trilobite were the result of a complex series of changing growth controls that characterized different ontogenetic intervals. This indicates that trilobite development is more complex than previously thought, even in early members of the clade.

New Findings of Lower Cambrian Trilobites in the Southern Hövsgöl Area (Mongolia) and Their Significance for Stratigraphy and Interregional Correlation

Abstract —Based on the materials collected by L.N. Repina in the southern Hövsgöl area (Mongolia) in 1986–1988, we describe three sections and identify lower Cambrian trilobites. The sections of Mt. Hurtel Harna and along the Ujigin Gol River were studied earlier. We consider trilobites that have been found in these sections for the first time: Redlihia zharkovi, Lermontoviella shanganica, Erbia granulosa, Kootenia siberica, and Parapoulsenia lata. The section along the ravine of the Zuun-Shuvuutyn-Sair Brook and the findings of trilobites in it are described for the first time. The found new trilobites make it possible to correlate the coeval lower Cambrian strata in the southern Hövsgöl area, Altai–Sayan folded area, and western Siberian Platform and refine the age of the certain parts of the Egyin Gol, Ukhaa Tolgoi, and Ujigin Gol formations.

The first systematic description of Cambrian fossils from Myanmar: Late Furongian trilobites from the southern part of the Shan State and the early Palaeozoic palaeogeographical affinities of Sibumasu

The existence of late Cambrian (Furongian) trilobites in Myanmar (Burma) has been acknowledged since the 1970s, but no formal systematic descriptions of such fossils have been published to date. Herein, we provide such descriptions of some trilobites from the Molohein Group’s Myet-Ye Formation from the Linwe area, Ye-Ngan Township of the southern Shan State. Three species from two genera are reported: Asioptychaspis (A. asiatica, previously known from the North China Block, and a new species, A. lata) and Eosaukia buravasi, also known from peninsular Thailand. The Molohein Group was initially assigned a late Cambrian age based on the reported, but unsubstantiated, occurrence of the Laurentian genera Saukiella and Drumaspis, and this age assessment is supported by the fauna we present, although Saukiella or Drumaspis remain unconfirmed from Myanmar. Asioptychaspis asiatica first appears in late Jiangshanian strata, and Eosaukia buravasi ranges up to the middle of Stage 10. Thus these ranges provide a more specific constraint on the age of the Molohein Group. Similarities are strong between upper Cambrian and Lower Ordovician successions in Sibumasu and northwestern Australia, particularly those from the Canning Basin succession. Regional geological data supports placement of Sibumasu adjacent to Western Australia during the Cambrian, without the Lhasa Block intervening between them, and Baoshan at the western end of Sibumasu during the early Paleozoic, towards the Himalayan margin. The new Burmese fauna is consistent with these suggestions, as they belong to the Sino-Australian faunal province.

Quantifying the middle–late Cambrian trilobite diversity pattern in South China

The middle–late Cambrian is a key interval between the Cambrian Explosion and the Great Ordovician Biodiversification Event (GOBE) that marks a major biologic evolutionary transition in the geologic record. Diversity (i.e. richness) patterns in this interval show that macro-biota experienced evolutionary setbacks for the first time. However, relatively little attention has been paid to this interval in previous macroevolutionary studies and very different conclusions about the diversity patterns in coarse time-resolution have been documented. As a dominate group of marine benthic organisms in the Cambrian, trilobites provide insightful information to understand the history of biodiversity in the Cambrian marine ecosystem from the Cambrian Explosion to the GOBE. South China is a region with relatively good preservation of Cambrian fossil materials and sections, and 4 out of 6 Cambrian GSSPs were established in South China. In this paper, we use constrained optimization (CONOP) to correlate 19 sections from South China to reduce the Signor-Lipps effect and integrate the results with high-resolution chronostratigraphic data to evaluate the middle–late Cambrian trilobite diversity pattern in South China. This study, for the first time, constructs a high time-resolution (about 60 kyr) trilobite species-level richness curve with estimated time from Age 4 to the Paibian. A double-peaked species diversification is separated by a minor extinction in Stage 4; this is followed by a gradual decline of species diversity over the entire Wuliuan Age. A radiation of three times increase of species diversity in the Drumian and Guzhangian is exhibited and the diversity remains high for most of the Guzhangian Stage; this is followed by a great extinction at the end of the Guzhangian with around 50% species lost. Detailed comparison with previous composite studies and fossil material from single sections revealed that the Signor-Lipps effect could produce large biases in diversity pattern. In addition, a precise analysis of species evolution features compared with environmental indices provides a perspective about trilobite evolutionary mechanisms associated with environmental changes related to the carbon cycle and biotic competition.

Biomechanical analyses of Cambrian euarthropod limbs reveal their effectiveness in mastication and durophagy.

Durophagy arose in the Cambrian and greatly influenced the diversification of biomineralized defensive structures throughout the Phanerozoic. Spinose gnathobases on protopodites of Cambrian euarthropod limbs are considered key innovations for shell-crushing, yet few studies have demonstrated their effectiveness with biomechanical models. Here we present finite-element analysis models of two Cambrian trilobites with prominent gnathobases-Redlichia rex and Olenoides serratus-and compare these to the protopodites of the Cambrian euarthropod Sidneyia inexpectans and the modern American horseshoe crab, Limulus polyphemus. Results show that L. polyphemus, S. inexpectans and R. rex have broadly similar microstrain patterns, reflecting effective durophagous abilities. Conversely, low microstrain values across the O. serratus protopodite suggest that the elongate gnathobasic spines transferred minimal strain, implying that this species was less well-adapted to masticate hard prey. These results confirm that Cambrian euarthropods with transversely elongate protopodites bearing short, robust gnathobasic spines were likely durophages. Comparatively, taxa with shorter protopodites armed with long spines, such as O. serratus, were more likely restricted to a soft food diet. The prevalence of Cambrian gnathobase-bearing euarthropods and their various feeding specializations may have accelerated the development of complex trophic relationships within early animal ecosystems, especially the 'arms race' between predators and biomineralized prey.