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1. Cynodontium luthii sp. nov.: a permineralized moss gametophyte from the Late Cretaceous of the North Slope of Alaska

   https://doi.org/10.1002/ajb2.1617  

   Bippus, Alexander C. ; Rothwell, Gar W. ; Stockey, Ruth A. ( March 2021 , American Journal of Botany)

   Mosses are a major component of Arctic vegetation today, with >500 species known to date. However, the origins of the Arctic moss flora are poorly documented in the fossil record, especially prior to the Pliocene. Here, we present the first anatomically preserved pre‐Cenozoic Arctic moss and discuss how the unique biology of bryophytes has facilitated their success in polar environments over geologic time.

   A permineralized fossil moss gametophyte within a block of Late Cretaceous terrestrial limestone, collected along the Colville River on the North Slope of Alaska, was studied in serial sections prepared using the cellulose acetate peel technique.

   The moss gametophyte is branched and has leaves with a broad base, narrow blade, and excurrent costa. We describe this fossil asCynodontium luthiisp. nov., an extinct species of a genus that is known from the High Arctic today.Cynodontium luthiiis the oldest evidence of the family Rhabdoweisiaceae (by ≥18 Ma) and reveals that genera of haplolepideous mosses known in the extant Arctic flora also lived in high‐latitude temperate deciduous forests during the Late Cretaceous.

   The occurrence ofC. luthiiin Cretaceous sediments, together with a rich Pliocene‐to‐Holocene fossil record of extant moss genera in the High Arctic, suggests that some moss lineages have exploited their poikilohydric, cold‐ and desiccation‐tolerant physiology to live in the region when it experienced both temperate and freezing climates.

    

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2. Osteohistological analyses reveal diverse strategies of theropod dinosaur body-size evolution

   https://doi.org/10.1098/rspb.2020.2258  

   Cullen, Thomas M. ; Canale, Juan I. ; Apesteguía, Sebastián ; Smith, Nathan D. ; Hu, Dongyu ; Makovicky, Peter J. ( November 2020 , Proceedings of the Royal Society B: Biological Sciences)

   null (Ed.)

   The independent evolution of gigantism among dinosaurs has been a topic of long-standing interest, but it remains unclear if gigantic theropods, the largest bipeds in the fossil record, all achieved massive sizes in the same manner, or through different strategies. We perform multi-element histological analyses on a phylogenetically broad dataset sampled from eight theropod families, with a focus on gigantic tyrannosaurids and carcharodontosaurids, to reconstruct the growth strategies of these lineages and test if particular bones consistently preserve the most complete growth record. We find that in skeletally mature gigantic theropods, weight-bearing bones consistently preserve extensive growth records, whereas non-weight-bearing bones are remodelled and less useful for growth reconstruction, contrary to the pattern observed in smaller theropods and some other dinosaur clades. We find a heterochronic pattern of growth fitting an acceleration model in tyrannosaurids, with allosauroid carcharodontosaurids better fitting a model of hypermorphosis. These divergent growth patterns appear phylogenetically constrained, representing extreme versions of the growth patterns present in smaller coelurosaurs and allosauroids, respectively. This provides the first evidence of a lack of strong mechanistic or physiological constraints on size evolution in the largest bipeds in the fossil record and evidence of one of the longest-living individual dinosaurs ever documented. 

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3. A new species of Gulo from the Early Pliocene Gray Fossil Site (Eastern United States); rethinking the evolution of wolverines

   https://doi.org/10.7717/peerj.4648  

   Samuels, Joshua X. ; Bredehoeft, Keila E. ; Wallace, Steven C. ( April 2018 , PeerJ)

   The wolverine (Gulo gulo) is the largest living terrestrial member of the Mustelidae; a versatile predator formerly distributed throughout boreal regions of North America and Eurasia. Though commonly recovered from Pleistocene sites across their range, pre-Pleistocene records of the genus are exceedingly rare. Here, we describe a new species ofGulofrom the Gray Fossil Site in Tennessee. Based on biostratigraphy, a revised estimate of the age of the Gray Fossil Site is Early Pliocene, near the Hemphillian—Blancan transition, between 4.9 and 4.5 Ma. This represents the earliest known occurrence of a wolverine, more than one million years earlier than any other record. The new species of wolverine described here shares similarities with previously described species ofGulo, and with early fishers (Pekania). As the earliest records of bothGuloandPekaniaare known from North America, this suggests the genus may have evolved in North America and dispersed to Eurasia later in the Pliocene. Both fauna and flora at the Gray Fossil Site are characteristic of warm/humid climates, which suggests wolverines may have become ‘cold-adapted’ relatively recently. Finally, detailed comparison indicatesPlesiogulo, which has often been suggested to be ancestral toGulo, is not likely closely related to gulonines, and instead may represent convergence on a similar niche.

    

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4. The significance of enamel thickness in the teeth of Alligator mississippiensis and its diversity among crocodyliforms

   https://doi.org/10.1111/jzo.12707  

   Sellers, K. C. ; Schmiegelow, A. B. ; Holliday, C. M. ( July 2019 , Journal of Zoology)

   Enamel is the hardest tissue in the vertebrate body. Although variation in enamel microstructure is often linked with diet, the gross proportions of the tissues that compose vertebrate teeth remain relatively unexplored in reptiles. To investigate the patterns of enamel thickness in crocodyliforms, we used micro‐computed tomography scanning to evaluate enamel thickness in teeth ofAlligator mississippiensisfrom rostral, intermediate and caudal locations in the tooth row from an ontogenetic range of animals. We also evaluated enamel thickness in the derived teeth of several extinct crocodyliforms with disparate craniodental morphologies. Our data show that enamel thickness scales isometrically with skull length. We also show that enamel is relatively thicker in caudal teeth than teeth in more rostral positions, concordant with the higher bite forces they experience during feeding. We compared our data with existing enamel thickness data reported from dinosaurs and mammalian taxa to find that archosaurs have markedly thinner enamel than most mammals. These findings serve as a basis for future investigations into the diversity and function of the proportions of dental tissues.

    

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5. Molecular tests support the viability of rare earth elements as proxies for fossil biomolecule preservation

   https://doi.org/10.1038/s41598-020-72648-6  

   Ullmann, Paul_V ; Voegele, Kristyn_K ; Grandstaff, David_E ; Ash, Richard_D ; Zheng, Wenxia ; Schroeter, Elena_R ; Schweitzer, Mary_H ; Lacovara, Kenneth_J ( September 2020 , Scientific Reports)

   The rare earth element (REE) composition of a fossil bone reflects its chemical alteration during diagenesis. Consequently, fossils presenting low REE concentrations and/or REE profiles indicative of simple diffusion, signifying minimal alteration, have been proposed as ideal candidates for paleomolecular investigation. We directly tested this prediction by conducting multiple biomolecular assays on a well-preserved fibula of the dinosaurEdmontosaurusfrom the Cretaceous Hell Creek Formation previously found to exhibit low REE concentrations and steeply-declining REE profiles. Gel electrophoresis identified the presence of organic material in this specimen, and subsequent immunofluorescence and enzyme-linked immunosorbant assays identified preservation of epitopes of the structural protein collagen I. Our results thereby support the utility of REE profiles as proxies for soft tissue and biomolecular preservation in fossil bones. Based on considerations of trace element taphonomy, we also draw predictions as to the biomolecular recovery potential of additional REE profile types exhibited by fossil bones.

    

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