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Travels with trilobites : adventures in the paleozoic
\"Trilobites hold the distinction of being among the world's first dominant forms of complex animal life, arthropods that rank second only to the hallowed dinosaur in terms of their paleontological appeal. These bizarrely beautiful three-lobed creatures initially appeared in the seas more than 520 million years ago, emerging when the oceans had become ripe for the blossoming of biodiversity. These Paleozoic inhabitants would populate the planet's marine ecosystems for the next 270 million years. During that span, trilobites generated more than 25,000 scientifically recognized species - a fact that places these creatures among the most successful animal classes ever to exist on our world. There are a few examples that due to either their unique combination of rarity, beauty, or the noteworthy role they've played in paleontological history, stand head and shoulders (or perhaps we should say glabella and occipital lobe) above all others. From pristine examples of relatively common trilo-types to one-of-a-kind treasures, the book will feature hundreds of high-resolution photographs of an amazing array of the most incredible specimens of trilobites collected from localities around the globe, including specimens that have never before been seen outside of private collections. Travels with Trilobites explains the varying orders of trilobites, locations around the world where their fossils are found and the time periods those fossils can be dated to, and myriad other points of interest: the first trilobites, the uniqueness of trilobite eyes, trilobite eggs, feeding behavior, behind-the-scenes stories from the fossil collecting world, and more\"-- Provided by publisher.
Book
Trilobite evolutionary rates constrain the duration of the Cambrian explosion
Trilobites are often considered exemplary for understanding the Cambrian explosion of animal life, due to their unsurpassed diversity and abundance. These biomineralized arthropods appear abruptly in the fossil record with an established diversity, phylogenetic disparity, and provincialism at the beginning of Cambrian Series 2 (∼521 Ma), suggesting a protracted but cryptic earlier history that possibly extends into the Precambrian. However, recent analyses indicate elevated rates of phenotypic and genomic evolution for arthropods during the early Cambrian, thereby shortening the phylogenetic fuse. Furthermore, comparatively little research has been devoted to understanding the duration of the Cambrian explosion, after which normal Phanerozoic evolutionary rates were established. We test these hypotheses by applying Bayesian tip-dating methods to a comprehensive dataset of Cambrian trilobites. We show that trilobites have a Cambrian origin, as supported by the trace fossil record and molecular clocks. Surprisingly, they exhibit constant evolutionary rates across the entire Cambrian, for all aspects of the preserved phenotype: discrete, meristic, and continuous morphological traits. Our data therefore provide robust, quantitative evidence that by the time the typical Cambrian fossil record begins (∼521 Ma), the Cambrian explosion had already largely concluded. This suggests that a modern-style marine biosphere had rapidly emerged during the latest Ediacaran and earliest Cambrian (∼20 million years), followed by broad-scale evolutionary stasis throughout the remainder of the Cambrian.
Journal Article
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.
Journal Article
Quantification of leg mobility in the Burgess Shale Olenoides serratus indicates functional differences between trilobite and xiphosuran appendages
Background
Euarthropod appendages are specialized for diverse roles including feeding, walking, and mating, which require precise morphologies and ranges of motion. Cambrian fossils preserve exceptional details of extinct euarthropod appendages that can illuminate their anatomy and ecology. However, fossils are typically restricted by small sample sizes or incomplete preservation, and thus functional studies of the appendages usually rely on idealized reconstructions. The Burgess Shale
Olenoides serratus
is unique among trilobites owing to the availability of numerous specimens with soft tissue preservation that allow us to quantify its appendages’ functional morphology.
Results
We measured the range of motion of the legs in
Olenoides serratus
and the extant horseshoe crab
Limulus polyphemus
. Despite repeated ecological comparisons between trilobites and xiphosurans, we find significant differences in the appendages’ mobility between these taxa, with
Limulus
showing greater flexibility between the podomeres.
Conclusions
O. serratus
legs have a more restricted range of motion relative to
L. polyphemus,
particularly in their distal region. Flexure between the protopodite played a critical role in allowing the endopodite to create known trilobite trace fossils and bring food toward the ventral groove.
Journal Article
Precise early Cambrian U–Pb zircon dates bracket the oldest trilobites and archaeocyaths in Moroccan West Gondwana
New U–Pb radioisotopic ages on early Cambrian volcanic zircons condition a high-resolution Bayesian age model that constrains the first occurrences and zonations of West Gondwanan archaeocyaths and trilobites in southern Morocco. The oldest archaeocyaths in the Tiout Member of the Igoudine Formation (519.71 + 0.26/− 0.35 Ma) are c. 6 Ma younger than the oldest Siberian archaeocyaths. The oldest Moroccan trilobite fragments, from the lower member of the Igoudine, are constrained to 519.95 + 0.43/− 0.40 Ma. The succeeding Issendalenian Stage (i.e. Hupetina antique – Eofallotaspis tioutensis – Fallotaspis plana – Choubertella – Daguinaspis trilobite zones) spans c. 1.5 Ma (519.78 + 0.26/− 0.37 Ma to 518.43 + 0.25/− 0.69 Ma). Identifiable Moroccan fallotaspidids and bigotinids, among Earth’s oldest trilobites, occur above a positive δ13C excursion dated with our age model at 520.27 + 0.59/− 0.57 Ma, and correlated with the IV excursion peak within the lower range of Siberian Atdabanian Stage trilobites (Repinaella Zone). This excursion is the best standard for a Cambrian Series 2 base. The oldest West Gondwana trilobite fragments are c. 1 Ma younger than those in Siberia and c. 0.5 Ma older than the oldest Avalonian trilobites (Callavia Zone). This diachrony means a trilobite first appearance datum is an inappropriate chronostratigraphic base for Cambrian Series 2. Taxonomic differences in the oldest trilobites between Cambrian palaeocontinents are in accordance with trace fossil evidence for the group’s appearance possibly as late as c. 530 Ma in the Cambrian Evolutionary Radiation. Coeval 519–517 Ma dates from Avalonia (cool-water siliciclastic shelf) and West Gondwana (tropical carbonate platform) sections with distinct macrofaunas emphasize these successions were latitudinally separate by the late Ediacaran Period.
Journal Article
Malformed individuals of the trilobite Estaingia bilobata from the Cambrian Emu Bay Shale and their palaeobiological implications
Malformed trilobite specimens present important insight into understanding how this extinct arthropod group recovered from developmental or moulting malfunctions, pathologies, and injuries. Previously documented examples of malformed trilobite specimens are often considered in isolation, with few studies reporting on multiple malformations in the same species. Here we report malformed specimens of the ellipsocephaloid trilobite Estaingia bilobata from the Emu Bay Shale Konservat-Lagerstätte (Cambrian Series 2, Stage 4) on Kangaroo Island, South Australia. Ten malformed specimens exhibiting injuries, pathologies, and a range of teratologies are documented. Furthermore, five examples of mangled exoskeletons are presented, indicative of predation on E. bilobata. Considering the position of malformed and normal specimens of E. bilobata in bivariate space, we demonstrate that the majority of malformed specimens cluster among the larger individuals. Such specimens may exemplify larger forms successfully escaping predation attempts, but could equally represent individuals exhibiting old injuries that were made during earlier (smaller) growth stages that have healed through subsequent moulting events. The available evidence from the Emu Bay Shale suggests that this small, extremely abundant trilobite likely played an important role in the structure of the local ecosystem, occupying a low trophic level and being preyed upon by multiple durophagous arthropods. Furthermore, the scarcity of malformed E. bilobata specimens demonstrates how rarely injuries, developmental malfunctions, and pathological infestations occurred within the species.
Journal Article
Exploring abnormal Cambrian-aged trilobites in the Smithsonian collection
Biomineralised trilobite exoskeletons provide a 250 million year record of abnormalities in one of the most diverse arthropod groups in history. One type of abnormality—repaired injuries—have allowed palaeobiologists to document records of Paleozoic predation, accidental damage, and complications in moulting experienced by the group. Although Cambrian trilobite injuries are fairly well documented, the illustration of new injured specimens will produce a more complete understanding of Cambrian prey items. To align with this perspective, nine new abnormal specimens displaying healed injuries from the Smithsonian National Museum of Natural History collection are documented. The injury pattern conforms to the suggestion of lateralised prey defence or predator preference, but it is highlighted that the root cause for such patterns is obscured by the lumping of data across different palaeoecological and environmental conditions. Further studies of Cambrian trilobites with injuries represent a key direction for uncovering evidence for the Cambrian escalation event.
Journal Article
Palaeozoic arthropods in Baltoscandian erratics from the coastal cliffs near Gdynia in northern Poland
Fossils recovered from Baltoscandian erratic boulders and cobbles, collected on the beach near Orłowo and Oksywie Cliff (the latter for the first time) near Gdynia in northern Poland constitute an interesting lot. Several trilo-bite taxa have been discovered, such as
? sp.,
? sp., Chasmopsinae indet.,
sp. and Proetidae indet. Another group of arthropods represented here is Ostracoda, mostly comprising taxa of the family Beyrichiidae, assigned to the order Palaeocopida. The preservation of all fossils certainly leaves much to be desired. Nevertheless, after preparation it has turned out possible to provide some taxonomic identification and the estimated stratigraphical provenance of the erratics studied. In addition, on the basis of taxonomic composition, palaeoecological and palaeogeo-graphical patterns have been worked out. The present paper ranks amongst the very few recent publications dedicated to erratic fossils from Poland in general and those on arthropods specifically.
Journal Article