Kyung Soo Kim, Jong Deock Lim, Martin G. Lockley, Lida Xing & Yeongi Choi (2017)
Korean trackway of a hopping, mammaliform trackmaker is global first from the Cretaceous.
Cretaceous Research (advance online publication)
A trackway of a small hopping mammaliform trackmaker from the Jinju Formation (Lower Cretaceous) of the Jinju City area, Korea, is the first of this type reported from the Mesozoic of Asia, and globally. The animal left a narrow trackway (∼20 mm wide) with small tetradactyl footprints averaging less than 10 mm in diameter. Only two footprints registered with each hop (mean length 41 mm) thus indicating a bipedal gait. All trackway evidence suggests a small “mouse-like” trackmaker. Previous reports of trackways made by hopping tetrapods from the Mesozoic are rare and presently restricted to ichnogenus Ameghinichnus isp. indet., from the Jurassic of Argentina. Ichnogenus Musaltipes from the Cenozoic of North America, is the only other ichnogenus representing a hopping mammal. The Korean specimen here named Koreasaltipes jinjuensis, is different from these aforementioned ichnogenera in digit count, digit proportion and trackway configuration, as well as lack of tail trace. Koreasaltipes jinjuensis is from a lake shore paleoenvironment associated with nematode tracks (Cochlichnus isp.), other small tetrapod tracks attributed to avian theropods (birds), pterosaurs and crocodylomorphs, as well as larger saurischian dinosaurs.
Torsten M. Scheyer, Elena V. Syromyatnikova, and Igor G. Danilov (2017)
Turtle shell bone and osteoderm histology of Mesozoic and Cenozoic stem-trionychian Adocidae and Nanhsiungchelyidae (Cryptodira: Adocusia) from Central Asia, Mongolia, and North America.
Fossil Record 20: 69-85
The record of fossil turtles from the Cretaceous and Cenozoic of Asia and North America is very rich, including several lineages of cryptodiran turtles. Here we survey the shell bone histology of two important closely related groups of stem trionychians, the Adocidae and Nanhsiungchelyidae, which have representatives in both Asia and North America. All studied taxa show shell bones in which the diploe is framed by well-developed cortical compact bone layers. Taxa of both groups also express external regular surface sculpturing of their shell bones, and in the case of the nanhsiungchelyid genus Basilemys also on the osteoderms, which is also reflected in the internal histological bone structures. Besides similarities of the regular ornamentation patterns, both groups share a number of microanatomical and histological characters such as the zonation of external cortex with rather homogeneous fine-fibred interwoven structural fibres (ISF) in the more internal zone and a dominance of vertically oriented fibres in the ISF and the presence of growth marks in the more external zone. On the other hand, growth marks, i.e. lines of arrested growth, which are visible as wavy lines in thin sections, extend subparallel to the external bone surface in adocids, but they are not parallel/subparallel in nanhsiungchelyids. Thickness and structure of bone trabeculae in the cancellous interior regions depends on the shell bone thickness of the individual samples. The internal cortices of all taxa except the North American samples of Adocus usually consist of parallel-fibred bone that locally grades into lamellar bone. Secondary bone remodelling is more frequent in nanhsiungchelyids compared to adocids, and Sharpey's fibres that extend perpendicular to the bone margins extending across subparallel growth marks are more commonly found in adocids. In addition, bone histology served to identify trionychid specimens in the adocid and nanhsiungchelyid samples, especially as bone surface sculpturing patterns were weathered or eroded in those cases. The histological data present thus supplement the numerous previously reported differences in external shell morphology between adocids and nanhsiungchelyids on the one hand and trionychids and carettochelyids on the other.
Daniel J. Urban, Neal Anthwal, Zhe-Xi Luo, Jennifer A. Maier, Alexa Sadier, Abigail S. Tucker, Karen E. Sears (2017)
A new developmental mechanism for the separation of the mammalian middle ear ossicles from the jaw.
Proceedings of the Royal Society B 2017 284: 20162416
Published 8 February 2017.
Multiple mammalian lineages independently evolved a definitive mammalian middle ear (DMME) through breakdown of Meckel's cartilage (MC). However, the cellular and molecular drivers of this evolutionary transition remain unknown for most mammal groups. Here, we identify such drivers in the living marsupial opossum Monodelphis domestica, whose MC transformation during development anatomically mirrors the evolutionary transformation observed in fossils. Specifically, we link increases in cellular apoptosis and TGF-BR2 signalling to MC breakdown in opossums. We demonstrate that a simple change in TGF-β signalling is sufficient to inhibit MC breakdown during opossum development, indicating that changes in TGF-β signalling might be key during mammalian evolution. Furthermore, the apoptosis that we observe during opossum MC breakdown does not seemingly occur in mouse, consistent with homoplastic DMME evolution in the marsupial and placental lineages.
Silvia Danise & Steven M. Holland (2017)
Faunal response to sea-level and climate change in a short-lived seaway: Jurassic of the Western Interior, USA.
Palaeontology (advance online publication)
Understanding how regional ecosystems respond to sea-level and environmental perturbations is a main challenge in palaeoecology. Here we use quantitative abundance estimates, integrated within a sequence stratigraphic and environmental framework, to reconstruct benthic community changes through the 13 myr history of the Jurassic Sundance Seaway in the western United States. Sundance Seaway communities are notable for their low richness and high dominance relative to most areas globally in the Jurassic, and this probably reflects steep temperature and salinity gradients along the 2000 km length of the Seaway that hindered colonization of species from the open ocean. Ordination of samples shows a main turnover event at the Middle–Upper Jurassic transition, which coincided with a shift from carbonate to siliciclastic depositional systems in the Seaway, probably initiated by northward drift from subtropical latitudes to more humid temperate latitudes, and possibly global cooling. Turnover was not uniform across the onshore–offshore gradient, but was higher in offshore environments. The higher resilience of onshore communities to third-order sea-level fluctuations and to the change from a carbonate to a siliciclastic system was driven by a few abundant eurytopic species that persisted from the opening to the closing of the Seaway. Lower stability in offshore facies was instead controlled by the presence of more volatile stenotopic species. Such increased onshore stability in community composition contrasts with the well-documented onshore increase in taxonomic turnover rates, and this study underscores how ecological analyses of relative abundance may contrast with taxonomically based analyses. We also demonstrate the importance of a stratigraphic palaeobiological approach to reconstructing the links between environmental and faunal gradients, and how their evolution through time produces local stratigraphic changes in community composition.