Two chondrichthyan assemblages of Late Mississippian/Early Pennsylvanian age are now recognized from the western Grand Canyon of northern Arizona. The latest Serpukhovian Surprise Canyon Formation has yielded thirty-one taxa from teeth and dermal elements, which include members of the Phoebodontiformes, Symmoriiformes, Bransonelliformes, Ctenacanthiformes, Protacrodontoidea, Hybodontiformes, Neoselachii (Anachronistidae), Paraselachii (Gregoriidae, Deeberiidae, Orodontiformes, and Eugeneodontiformes), Petalodontiformes, and Holocephali. The euselachian grade taxa are remarkably diverse with four new taxa recognized here; the Protacrodontidae: Microklomax carrieae new genus new species and Novaculodus billingsleyi new genus new species, and the Anchronistidae: Cooleyella platera new species and Amaradontus santucii new genus new species The Surprise Canyon assemblage also has the youngest occurrence of the elasmobranch Clairina, previously only known from the Upper Devonian. The Surprise Canyon Formation represents a nearshore fluvial infilling of karstic channels, followed by a shallow marine bioherm reef, and finally deeper open water deposition. The early Bashkirian Watahomigi Formation represents open marine deposition and contains only two taxa: a new xenacanthiform, Hokomata parva new genus new species, and the holocephalan Deltodus. The relationship between the Surprise Canyon and Watahomigi chondrichthyan assemblages and other significant coeval chondrichthyan assemblages suggests that there may have been eastern and western distinctions among the Euamerican assemblages during the Serpukhovian due to geographic separation by the formation of Pangea.

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The ammonite Hybonoticeras authariformis new species [M] is erected from the lower Tithonian of Mexico, adding a new example of endemism for the genus Hybonoticeras in records from epicontinental areas. The newly described species is the first evidence of unequivocal lowermost Tithonian macroconchiate hybonoticeratines reported from the Mexico-Caribbean area. Precise biostratigraphic control based on bed-by-bed sampling is first reported for the combined record of macroconchiate Hybonoticeras Breistroffer, 1947 with Mazapilites Burckhardt, 1919 in Mexico, indicating an early but not earliest Tithonian age. A preliminary revision of the type material of species assigned to the genus Mazapilites points to an inconclusive understanding of both intraspecies diversity and the real meaning of the nominal species formulated by Burckhardt, thus revealing defective knowledge about precise biostratigraphy at both the genus and species levels. Published hybonoticeratines and mazapilitines from Mexico and Cuba are revisited to update precise interpretation of their systematics, biostratigraphy, and correlation potential, and to investigate their combined occurrence. Previous information about Cuban hybonoticeratines and mazapilitines is too limited to be conclusively interpreted; their combined record cannot be demonstrated in Cuba. Special relevance is given to a potential occurrence of Mazapilites in uppermost Kimmeridgian horizons in Cuba. The obtained results update the biostratigraphic meaning and systematic interpretation of the investigated ammonites, and signal topics for future research of interest in their paleobiological and palebiogeographic interpretation.

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The Emigrant Formation at Clayton Ridge, Nevada, consists of 420 m of variably interbedded shale, siltstone, and limestone representing an outer shelf environment. It ranges in age from the youngest portion of the Dyeran Stage (Laurentian Waucoban Series; Cambrian Stage 4, Series 2) to Skullrockian Stage (Ibexian Series; Tremadocian Stage, Lower Ordovician). Consequently, it is condensed compared to other localities. For example, the age-equivalent succession in the House Range and the Wendover Range of Utah and Nevada, respectively, is seven times thicker.

The 100 m thick lower limestone and siltstone member of the Emigrant Formation at Clayton Ridge ranges in age from the Bolbolenellus euryparia/Nephrolenellus multinodus Zone (Laurentian Dyeran Stage) to the Cedaria brevifrons Zone (Laurentian Marjuman Stage; Drumian Stage; this study). The 40 trilobites described herein from two closely spaced sections of the lower member belong to the Glossopleura walcotti/Ptychagnostus praecurrens Zone (Laurentian Delamaran Stage; Stage 5), Ehmaniella Zone (Laurentian Topazan Stage; Stage 5), and Cedaria selwyni to C. brevifrons zones (Laurentian Marjuman Stage; Drumian Stage) zones. The lower Emigrant Formation is <10% as thick as age-equivalent age strata elsewhere in Nevada, California, and Utah. This condensed nature of the lower Emigrant Formation began with the flooding event at the beginning of the Oryctocephalus indicus biochron and the subsequent build-ups of the thick carbonate platforms to the south and northeast.

New species are Pagetia aspinosa, P. claytonensis, and Syspacephalus mccollumorum.

Despite 70 years of study, Dickinsonia remains one of the Ediacara biota’s most enigmatic taxa with both morphological characters and phylogenetic affinities still debated. A large population of relatively small Dickinsonia costata present on a semi-contiguous surface from the Crisp Gorge fossil locality in the Flinders Ranges (South Australia) provides an opportunity to investigate this taxon in its juvenile form. This population supports earlier findings that suggest D. costata’s early growth was isometric, based on the relationship between measured variables of length and width. The number of body units increases with length, but at a decreasing rate. A correlation between a previously described physical feature, present as a shrinkage rim partially surrounding some specimens and a novel, raised lip in some specimens, suggests that both features may have been the result of a physical contraction in response to the burial process, rather than due to a gradual loss of mass during early diagenesis. A marked protuberance in 15% of the population is also noted in limited specimens within the South Australian Museum collections and appears to be present only in juvenile D. costata. Both the abundance and narrow size range of this population support the notion that Dickinsonia was a hardy opportunist, capable of rapid establishment and growth on relatively immature textured organic-mat substrates.

The latest discovery of microfossils from the lower Cambrian (Fortunian Stage) Zhangjiagou Lagerstätte in South China are presented. This lagerstätte is rich in exceptionally preserved microfossils, including embryos of Olivooides multisulcatus, Olivooides mirabilis, and Pseudooides prima; hatched stages of O. multisulcatus, O. mirabilis, Hexaconularia sichuanensis, and Quadrapyrgites quadratacris; and cycloneuralians represented by Eopriapulites sphinx. The largest known fragment of O. mirabilis implies that its adult length can be more than 9.0 mm with at least 50 annuli, and the longest known specimen of Q. quadratacris has at least 18 annuli. These unusually large specimens refute the non-feeding larvae hypothesis for Olivooides and Quadrapyrgites.

Based on the current material, it is inferred that (1) early cnidarians have a high diversity in the Fortunian Stage; (2) P. prima might represent the embryonic stages of H. sichuanensis; (3) adults of Olivooides and Quadrapyrgites may have reached centimeter-scale dimensions with more than 50 annuli; (4) Olivooides and Quadrapyrgites may be better interpreted as coronate scyphozoans; (5) cycloneuralians also had a high diversity in the Zhangjiagou Lagerstätte; and (6) cycloneuralians might have originally been part of the early Cambrian meiofauna rather than belonging to the macrobenthos. Such ancestral cycloneuralians might have been Eopriapulites-like, possessing pentaradially symmetric, backward pointing, and internally hollow introvert scalids used as locomotory devices.

A large number of well-preserved chancelloriid scleritomes from the Guanshan biota, early Cambrian of Yunnan, China, are described as a new species, Allonnia tenuis n. sp., and provide solid evidence for the original appearance of these enigmatic animals, based on specimens compacted laterally and top-down. With the assistance of a flexible integument, chancelloriids, especially Allonnia from early and middle Cambrian, may have had the ability to partially or completely expand and contract the body, which might have played an important role in feeding. A new metazoan with single-element spines, Nidelric gaoloufangensis n. sp., is also described. Preservation and affinity are discussed. Detailed comparison of the morphology of the body and spines of this metazoan indicate that it shares many similarities with chancelloriids, of which it may be an unusual form.

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The Cambrian-Ordovician Diversity Plateau, between the Cambrian Explosion and the Ordovician Radiation, is punctuated by a series of well-documented Laurentian trilobite extinction events. These events define the bounding surfaces of trilobite ‘biomeres’ that correspond to North American stages, including those of the Sunwaptan and Skullrockian. Trilobites show a consistent pattern of recovery across these boundaries, and commonly each extinction and replacement of taxa is interpreted as a single event as changing environmental conditions spurred shoreward migration of shelf or oceanic faunas that displaced established cratonic faunas. Linguliform brachiopods are also abundant in strata of this interval, and we investigate their stratigraphic distribution across the Sunwaptan–Skullrockian Stage boundary in Texas through high-resolution stratigraphic sampling of subtidal sediments. We document complete genus- and species-level turnover of the linguliform brachiopod fauna coincident with trilobite extinction events, suggesting that these brachiopods were affected by the same factors that affected trilobites. The Skullrockian replacement fauna was cosmopolitan, with ties to Gondwana and Kazakhstan and to the Laurentian shelf environment. The timing of appearances of taxa suggests that the faunal migration onto the Laurentian shelf came from elsewhere during a transgression. The disappearance of the Sunwaptan fauna and the arrival of the Skullrockian fauna are distinct events. We suggest that ‘biomere’ events may be complex, and the cause of the extinction is not necessarily the same event that facilitates the appearance of a replacement fauna. We describe one new species, Schizambon langei.

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Two new species of Nilssoniopteris of the order Bennettitales, Nilssoniopteris hamiensis Zhao and Deng, new species and Nilssoniopteris crassiaxis Zhao and Deng, new species, are established from the Xishanyao Formation (Middle Jurassic) of Sandaoling Coal Mine in Hami, Xinjiang, China, based on leaf macromorphology and cuticular features. Nilssoniopteris hamiensis n. sp. is characterized by its varied leaf shapes and trichome bases of 1–4 cells on the abaxial epidermis. Nilssoniopteris crassiaxis n. sp. is characterized by its broad midrib (especially near the leaf base) and trichome bases of 1–3 cells on the abaxial epidermis. Both species possess unique venation patterns that are not only simple and free, but also forked and merged to form closed loops. These anastomosing veins are even more complicated in N. crassiaxis n. sp. in that the veins can fork once, twice, or even three times, the forked veins can later merge with each other or with an adjacent vein to form a closed loop, which may later further disjoin. The generic diagnosis of Nilssoniopteris is thus accordingly emended, particularly in the venation pattern. In addition, the stratigraphic and geographical distributions of all 45 Jurassic Nilssoniopteris species worldwide have been summarized and analyzed to better understand their brief evolutionary history, indicating that Nilssoniopteris might be able to grow not only in subtropical regions as the living cycads are, but also in warm climatic regions.

The family Cardiliidae has been scarcely studied. It was historically placed in the superfamily Mactroidea. Members of this family are characterized by a cordiform shell with a typical mactrid hinge, posterior adductor muscle placed into a myophore and three ornamental areas on the external surface of the shell. Six extant and 14 exclusively fossil species have been previously mentioned in the literature as belonging to the genus Cardilia. The geographical distribution, stratigraphic range, type material and type locality of each extant and fossil species are provided. In this work, four extant species and 11 exclusively fossil species belonging to the genus Cardilia are recognized. Extant species are from the western Pacific Ocean, Indian Ocean and eastern Atlantic Ocean, while fossil taxa are recorded from deposits of middle Eocene to late Pliocene in Europe and Asia,. One of them is formally described herein as Cardilia edwardsi new species.

The planktonic medusiform taxon Pararotadiscus guizhouensis (Zhao and Zhu, 1994) is one of the most abundant components of the Kaili Biota. Many specimens are in direct association with other taxa, including trilobites, brachiopods, hyolithids, echinoderms, and algae, as well as the trace fossil Gordia. Four types of interrelationships between P. guizhouensis and associated fossils are recognized: symbiosis, co-burial, attachment of benthic taxa on P. guizhouensis carcasses, and scavenging of P. guizhouensis carcasses. These associations of P. guizhouensis within the Kaili Biota are unique among occurrences of medusiform fossils in Burgess Shale-type biotas worldwide and provide important insights concerning ecological complexity in the Kaili Biota and in Cambrian marine communities in general.

The Precordilleran species Ahtiella argentina Benedetto and Herrera, 1986 is redescribed and illustrated and Monorthis coloradoensis Benedetto, 1998b from northwestern Argentina is reassigned to the genus Ahtiella Öpik, 1932. Ahtiella famatiniana new species from volcaniclastic rocks of the Famatina range (western Argentina) and Ahtiella tunaensis new species from the Precordillera basin (Cuyania terrane) are proposed. Paleogeographic and stratigraphic evidence strongly suggests that Ahtiella originated in the Andean region of Gondwana to further migrate to Avalonia, Baltica, and Cuyania. Contrary to previous assumptions, the fossil record from the Famatina volcaniclastic succession suggests that the plectambonitoid Ahtiella famatiniana n. sp. evolved from the hesperonomiid orthoid Monorthis transversa Benedetto, 2003 that always occurs in the underlying strata. Phylogenetic analysis of Ahtiella species shows that A. famatiniana n. sp. and the Peruvian A. zarelae Villas in Gutiérrez-Marco and Villas, 2007 are not only the earliest species of the genus but also are morphologically intermediate between Monorthis Bates, 1968 and the later and more derived species of Ahtiella from Baltica and Cuyania. If, as empirical evidence presented here shows, Ahtiella originated from Monorthis through a series of minor transformations, then the impressive morphological gap between orthides and strophomenides was bridged through short-time cladogenesis events, suggesting that it might not have a definite discontinuity between the species level evolution and the origin of higher taxa (macroevolution).

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The early Cambrian Carinachitidae, a family in the subclass Conulata, are intriguing and important small shelly fossils. Their gently tapering, tube-shaped skeletons consist of convex faces separated from each other by broad, deep corner sulci, and they exhibit triradial, pentaradial, or predominantly tetraradial symmetry. However, the morphology of the aperture and the modes of growth of carinachitid skeletons as well as the anatomy of their soft parts are unknown. Examination of a single new, exceptionally well-preserved specimen of tetramerous Carinachites spinatus Qian, 1977, collected from the lower Cambrian Kuanchuanpu Formation in South China, reveals: (1) that its aperture is connected to a small mass of relic soft tissue and (2) that the apertural end of each of the four faces is developed into a subtriangular lappet or oral lobe that is smoothly folded toward the long axis of the tube, partially closing the tube aperture. Similarities between thorn-like spines on the faces and the oral lobes indicate that the transverse ribs were periodically displaced from the perradial portion of the aperture during formation of new ribs. In addition, the tube walls may have undergone secondary thickening during growth. The growth pattern of the tube and the spatial relationships between the tube aperture and soft parts are analogous to those of co-occurring olivooids. These findings further strengthen the previously proposed hypothesis that coeval carinachitids, olivooids, hexangulaconulariids, and Paleozoic conulariids are closely related taxa within the subphylum Medusozoa. Finally, carinachitids most likely represent an evolutionary intermediate between olivooids and hexangulaconulariids.

Exquisitely preserved three-dimensional examples of the classic Ediacaran (late Neoproterozoic; 570–541 Ma) frond Charniodiscus arboreus Jenkins and Gehling, 1978 (herein referred to as Arborea arborea Glaessner in Glaessner and Daily, 1959) are reported from the Ediacara Member, Rawnsley Quartzite of South Australia, and allow for a detailed reinterpretation of its functional morphology and taxonomy. New specimens cast in three dimensions within sandy event beds showcase detailed branching morphology that highlights possible internal features that are strikingly different from rangeomorph and erniettomorph fronds. Combined with dozens of well-preserved two-dimensional impressions from the Flinders Ranges of South Australia, morphological variations within the traditional Arborea morphotype are interpreted as representing various stages of external molding. In rare cases, taphomorphs (morphological variants attributable to preservation) represent composite molding of internal features consisting of structural supports or anchoring sites for branching structures. Each primary branch consists of a central primary branching stalk from which emerge several oval secondary branches, which likely correspond to similar structures found in rare two-dimensional specimens. Considering this new evidence, previous synonymies within the Arboreomorpha are no longer justified, and we suggest that the taxonomy of the group be revised.

In this contribution, four species of Agathoxylon are described from the La Matilde Formation, Gran Bajo de San Julián and central and south-western sectors of Santa Cruz Province, Argentina. Agathoxylon agathioides (Kräusel and Jain) n. comb., Agathoxylon santalense (Sah and Jain) n. comb., Agathoxylon termieri (Attims) Gnaedinger and Herbst, and the new species Agathoxylon santacruzense n. sp. are described based on a detailed description of the secondary xylem. In this work, it was possible to construct scatter plots to elucidate the anatomical differences between the fossil species described on quantitative anatomical data. Comparisons are made with other Agathoxylon species from Gondwana. These parameters can be used to discriminate genera and species of wood found in the same formation, as well as to establish differences/similarities between other taxa described in other formations. Some localities contain innumerable “in situ” petrified trees, which allowed us to infer that these taxa formed small forests, or local forests, or small forests within a dense forest, which is a habitat coincident with the extant Araucariaceae.

Scalidophoran worms diversified in the Cambrian Fortunian, as indicated by recent reports from this stage, with two described species and two more unnamed forms exclusively from Orsten-type Lagerstätten yielding three-dimensionally phosphatized fossils. Here, we report new material of scalidophoran worms in Orsten-type preservation from the Cambrian Fortunian Xinli section in northern Sichuan Province, South China. At least five forms of scalidophoran worms were recovered from this location, including Eokinorhynchus rarus Zhang et al., 2015 and four unnamed taxa—Forms A, B, C, and D. Co-occurring disassociated spinose small shelly fossils might also be isolated cuticular elements of these early scalidophoran worms. The ontogeny of Eokinorhynchus rarus is revised. Forms A, C, and D are assigned to total-group Scalidophora to indicate their uncertain positions within Scalidophora, while Form B might be a close relative of Eokinorhynchus rarus. The current work highlights the significance of Orsten-type Lagerstätten in uncovering the morphology, ontogeny, and taxonomy of early Scalidophora and Cycloneuralia, made particularly available by the new finds in China.