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1. Late Cretaceous sturgeons (Acipenseridae) from North America, with two new species from the Tanis site in the Hell Creek Formation of North Dakota

   https://doi.org/10.1017/jpa.2022.81  

   Hilton, Eric J.; Grande, Lance (January 2023, Journal of Paleontology)

   Abstract Although the Cretaceous is widely regarded as a time of great evolutionary transition for the freshwater fish fauna of North America, the fossil record of this period is notoriously poor, consisting mostly of fragments and isolated skeletal elements. Exceptions include the acipenseriforms, discussed in this paper, and some exceedingly rare teleosts. Here we describe two new species of well-preserved sturgeons (Acipenseridae) from the Tanis site in the Late Cretaceous Hell Creek Formation of North Dakota. The type and referred materials were preserved in a loosely consolidated matrix. † Acipenser praeparatorum n. sp. is represented by multiple body fossils (including the head and relatively complete postcranial remains) and a specimen of an intact, three dimensionally preserved skull and pectoral girdle. This taxon can be diagnosed based on features of the opercular elements (exceptionally tall and narrow branchiostegal). The second species, † Acipenser anisinferos n. sp., is represented by a partially preserved skull, and can be diagnosed by a relatively elongate preorbital region (i.e., snout) and the absence of thorn-like spines on the skull roofing bones. Most known sturgeon fossils from the Cretaceous are represented only by undiagnosable fragmentary remains (i.e., scutes and pectoral-fin spines) or poorly preserved partial skeletons (e.g., † Protoscaphirhynchus ), with † Priscosturion and † Anchiacipenser (both monotypic) being rare exceptions. Therefore, the newly discovered Tanis fossils give a rare glimpse into the evolution of Acipenseridae at a critical time in the phylogenetic history of acipenseriforms, and suggest significant morphological and taxonomic diversity early in the evolution of this group. UUID: http://zoobank.org/375b586a-2dd8-4a31-b6c4-42151e6e8fc8 

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2. New genus and species of djadochtatheriid multituberculate (Allotheria, Mammalia) from the Upper Cretaceous Bayan Mandahu Formation of Inner Mongolia

   https://doi.org/10.2992/007.085.0401  

   Wible, John R.; Shelley, Sarah L.; Bi, Shundong (December 2019, Annals of Carnegie Museum)

   The superfamily Djadochtatherioidea is a distinctive clade of multituberculates from Upper Cretaceous beds of Mongolia and Inner Mongolia, China. Because many of the 11 included genera are known from skulls, more is known about the cranial anatomy of djadochtatherioids than any other clade of multituberculates. Within Djadochtatherioidea, the most diverse and widely accepted group is the family Djadochtatheriidae. Within the family, the basal genus, Kryptobaatar Kielan-Jaworowska, 1970, is small with a skull length of about 30 mm, whereas the other four genera, Djadochtatherium Simpson, 1925, Catopsbaatar Kielan-Jaworowska, 1994, Tombaatar Rougier et al., 1997, and Mangasbaatar Rougier et al., 2016, have skulls approximately twice as long. Here, we describe a new genus and species, Guibaatar castellanus, based on a single specimen from the Upper Cretaceous Bayan Mandahu Formation, Inner Mongolia that we refer to Djadochtatheriidae. Guibaatar is represented by a relatively complete rostrum, a partial right braincase, and partial lower jaws. As revealed by CT scanning, the specimen is a juvenile, with deciduous enlarged upper and lower incisors with permanent replacements forming, m2 erupting, and M2 forming. Based on the preserved cranial parts, we estimate the skull length to be approximately 50 mm, but as an adult, Guibaatar would have been in the size range of the larger djadochtatheriids. Phylogenetic analysis including Guibaatar, known djadochtatherioids, and outgroups places Guibaatar within Djadochtatheriidae, as sister to a clade of Mangasbaatar and Catopsbaatar. We suspect the relationships of djadochtatherioids are likely to be refined given the announcements by other researchers that skulls are known for the djadochtatheriids Tombaatar and Djadochtatherium, which were previously represented by incomplete material. 

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3. Craniofacial morphology of Adalatherium hui (Mammalia, Gondwanatheria) from the Late Cretaceous of Madagascar

   https://doi.org/https://doi.org/10.1080/02724634.2020.1808665  

   Krause, D.W.; Hoffmann, S.; Rossie, J.B.; Hu, Y.; Wible, John R.; Rougier, G.W.; Kirk, E.C.; Groenke, J.R. (December 2020, Journal of vertebrate paleontology)

   null (Ed.)

   The cranium of Adalatherium hui, as represented in the holotype and only specimen (UA 9030), is only the second known for any gondwanatherian mammal, the other being that of the sudamericid Vintana sertichi. Both Adalatherium and Vintana were recovered from the Upper Cretaceous (Maastrichtian) Maevarano Formation of northwestern Madagascar. UA 9030 is the most complete specimen of a gondwanatherian yet known and includes, in addition to the cranium, both lower jaws and a complete postcranial skeleton. Aside from Adalatherium and Vintana, gondwanatherians are otherwise represented only by isolated teeth and lower jaw fragments, belonging to eight monotypic genera from Late Cretaceous and Paleogene horizons of Madagascar, the Indian subcontinent, Africa, South America, and the Antarctic Peninsula. Although the anterior part of the cranium is very well preserved in UA 9030, the posterior part is not. Nonetheless, comparable parts of the crania of Adalatherium and Vintana indicate some level of common ancestry through possession of several synapomorphies, primarily related to the bony composition, articular relationships, and features of the snout region. Overprinted on this shared morphology are a host of autapomorphic features in each genus, some unique among mammaliaforms and some convergent upon therian mammals. The cranium of Adalatherium is compared with the crania of other mammaliamorphs, particularly those of allotherians or purported allotherians (i.e., haramiyidans, euharamiyidans, multituberculates, Cifelliodon, and Megaconus). Particular emphasis is placed on several recently described forms: the enigmatic Cifelliodon from the Early Cretaceous of Utah and several new taxa of euharamiyidans from the Late Jurassic of China. 

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4. Cretaceous to Miocene magmatism, sedimentation, and exhumation within the Alaska Range suture zone: A polyphase reactivated terrane boundary

   https://doi.org/10.1130/GES02014.1  

   Trop, J.; Benowitz, J. (June 2019, Geosphere)

   The Alaska Range suture zone exposes Cretaceous to Quaternary marine and nonmarine sedimentary and volcanic rocks sandwiched between oceanic rocks of the accreted Wrangellia composite terrane to the south and older continental terranes to the north. New U-Pb zircon ages, 40Ar/39Ar, ZHe, and AFT cooling ages, geochemical compositions, and geological field observations from these rocks provide improved constraints on the timing of Cretaceous to Miocene magmatism, sedimentation, and deformation within the collisional suture zone. Our results bear on the unclear displacement history of the seismically active Denali fault, which bisects the suture zone. Newly identified tuffs north of the Denali fault in sedimentary strata of the Cantwell Formation yield ca. 72 to ca. 68 Ma U-Pb zircon ages. Lavas sampled south of the Denali fault yield ca. 69 Ma 40Ar/39Ar ages and geochemical compositions typical of arc assemblages, ranging from basalt-andesite-trachyte, relatively high-K, and high concentrations of incompatible elements attributed to slab contribution (e.g., high Cs, Ba, and Th). The Late Cretaceous lavas and bentonites, together with regionally extensive coeval calc-alkaline plutons, record arc magmatism during contractional deformation and metamorphism within the suture zone. Latest Cretaceous volcanic and sedimentary strata are locally overlain by Eocene Teklanika Formation volcanic rocks with geochemical compositions transitional between arc and intraplate affinity. New detrital-zircon data from the modern Teklanika River indicate peak Teklanika volcanism at ca. 57 Ma, which is also reflected in zircon Pb loss in Cantwell Formation bentonites. Teklanika Formation volcanism may reflect hypothesized slab break-off and a Paleocene–Eocene period of a transform margin configuration. Mafic dike swarms were emplaced along the Denali fault from ca. 38 to ca. 25 Ma based on new 40Ar/39Ar ages. Diking along the Denali fault may have been localized by strike-slip extension following a change in direction of the subducting oceanic plate beneath southern Alaska from N-NE to NW at ca. 46–40 Ma. Diking represents the last recorded episode of significant magmatism in the central and eastern Alaska Range, including along the Denali fault. Two tectonic models may explain emplacement of more primitive and less extensive Eocene–Oligocene magmas: delamination of the Late Cretaceous–Paleocene arc root and/or thickened suture zone lithosphere, or a slab window created during possible Paleocene slab break-off. Fluvial strata exposed just south of the Denali fault in the central Alaska Range record synorogenic sedimentation coeval with diking and inferred strike-slip displacement. Deposition occurred ca. 29 Ma based on palynomorphs and the youngest detrital zircons. U-Pb detrital-zircon geochronology and clast compositional data indicate the fluvial strata were derived from sedimentary and igneous bedrock presently exposed within the Alaska Range, including Cretaceous sources presently exposed on the opposite (north) side of the fault. The provenance data may indicate ~150 km or more of dextral offset of the ca. 29 Ma strata from inferred sediment sources, but different amounts of slip are feasible. Together, the dike swarms and fluvial strata are interpreted to record Oligocene strike-slip movement along the Denali fault system, coeval with strike-slip basin development along other segments of the fault. Diking and sedimentation occurred just prior to the onset of rapid and persistent exhumation ca. 25 Ma across the Alaska Range. This phase of reactivation of the suture zone is interpreted to reflect the translation along and convergence of southern Alaska across the Denali fault driven by highly coupled flat-slab subduction of the Yakutat microplate, which continues to accrete to the southern margin of Alaska. Furthermore, a change in Pacific plate direction and velocity at ca. 25 Ma created a more convergent regime along the apex of the Denali fault curve, likely contributing to the shutting off of near-fault extension- facilitated arc magmatism along this section of the fault system and increased exhumation rates. 

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5. Skeleton of a Cretaceous mammal from Madagascar reflects long-term insularity

   https://doi.org/https://doi.org/10.1038/s41586-020-2234-8  

   Krause, D.W.; Hoffmann, S.; Hu, Yaoming; Wible, John. R.; Rougier, Guillermo W.; Kirk, E. Christopher; Groenke, Joseph R.; Rogers, Raymond R.; Rossie, James B.; Schultz, Julia A.; et al (May 2020, Nature)

   The fossil record of mammaliaforms (mammals and their closest relatives) of the Mesozoic era from the southern supercontinent Gondwana is far less extensive than that from its northern counterpart, Laurasia. Among Mesozoic mammaliaforms, Gondwanatheria is one of the most poorly known clades, previously represented by only a single cranium and isolated jaws and teeth. As a result, the anatomy, palaeobiology and phylogenetic relationships of gondwanatherians remain unclear. Here we report the discovery of an articulated and very well-preserved skeleton of a gondwanatherian of the latest age (72.1–66 million years ago) of the Cretaceous period from Madagascar that we assign to a new genus and species, Adalatherium hui. To our knowledge, the specimen is the most complete skeleton of a Gondwanan Mesozoic mammaliaform that has been found, and includes the only postcranial material and ascending ramus of the dentary known for any gondwanatherian. A phylogenetic analysis including the new taxon recovers Gondwanatheria as the sister group to Multituberculata. The skeleton, which represents one of the largest of the Gondwanan Mesozoic mammaliaforms, is particularly notable for exhibiting many unique features in combination with features that are convergent on those of therian mammals. This uniqueness is consistent with a lineage history for A. hui of isolation on Madagascar for more than 20 million years. 

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