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[dinosaur] Eutherian fossil record across K/Pg + multituberculate femur from Cretaceous of Madagascar + snake ear evolution




Ben Creisler
bcreisler@gmail.com


Some recent non-dino papers:


Thomas W. Davies, Mark A. Bell, Anjali Goswami and Thomas J. D. Halliday (2017)
Completeness of the eutherian mammal fossil record and implications for reconstructing mammal evolution through the Cretaceous/Paleogene mass extinction.
Paleobiology (advance online publication) 
DOI: https://doi.org/10.1017/pab.2017.20 
https://www.cambridge.org/core/journals/paleobiology/article/completeness-of-the-eutherian-mammal-fossil-record-and-implications-for-reconstructing-mammal-evolution-through-the-cretaceouspaleogene-mass-extinction/01629D0BC0A14BE60B1209A77159995A


There is a well-established discrepancy between paleontological and molecular data regarding the timing of the origin and diversification of placental mammals. Molecular estimates place interordinal diversification dates in the Cretaceous, while no unambiguous crown placental fossils have been found prior to the end-Cretaceous mass extinction. Here, the completeness of the eutherian fossil record through geological time is evaluated to assess the suggestion that a poor fossil record is largely responsible for the difference in estimates of placental origins. The completeness of fossil specimens was measured using the character completeness metric, which quantifies the completeness of fossil taxa as the percentage of phylogenetic characters available to be scored for any given taxon. Our data set comprised 33 published cladistic matrices representing 445 genera, of which 333 were coded at the species level.


There was no significant difference in eutherian completeness across the Cretaceous/Paleogene (K/Pg) boundary. This suggests that the lack of placental mammal fossils in the Cretaceous is not due to a poor fossil record but more likely represents a genuine absence of placental mammals in the Cretaceous. This result supports the “explosive model” of early placental evolution, whereby placental mammals originated around the time of the K/Pg boundary and diversified soon after.


No correlation was found between the completeness pattern observed in this study and those of previous completeness studies on birds and sauropodomorph dinosaurs, suggesting that different factors affect the preservation of these groups. No correlations were found with various isotope proxy measures, but Akaike information criterion analysis found that eutherian character completeness metric scores were best explained by models involving the marine-carbonate strontium-isotope ratios (87Sr/86Sr), suggesting that tectonic activity might play a role in controlling the completeness of the eutherian fossil record.



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David W. Krause, Simone Hoffmann & Sarah Werning (2017)
First postcranial remains of Multituberculata (Allotheria, Mammalia) from Gondwana.
Cretaceous Research (advance online publication)
doi: https://doi.org/10.1016/j.cretres.2017.08.009
http://www.sciencedirect.com/science/article/pii/S0195667117301398

Highlights

We discovered a multituberculate femur from the Late Cretaceous of Madagascar.

This represents the first postcranial remains of multituberculates from Gondwana.

Previous records were based on inconclusive identifications of dental remains.

The femur exhibits at least three autapomorphies of Multituberculata.

This discovery independently confirms the presence of Multituberculata on Gondwana.



Abstract

Multituberculates (Allotheria) are generally regarded as the evolutionarily most successful and longest-lived (Middle Jurassic to late Eocene) clade of Mesozoic and early Paleogene mammals. Despite this “reputation” and the fact that the group is particularly well represented in both taxonomic diversity and relative abundance on Laurasian landmasses during the Cretaceous and Paleocene, multituberculates are exceedingly poorly represented on the southern supercontinent Gondwana. Previous records on Gondwanan landmasses have been based on fragmentary dental remains and all except the three most recently published (each represented by a single isolated tooth or fragment of tooth) have been disputed and allocated to either Haramiyida or Gondwanatheria. Furthermore, several previous records, disputed or not, are based on fragmentary dental remains of a type (plagiaulacoid) that has evolved independently several times in mammalian evolution.


Here we place on record a multituberculate femur from the Upper Cretaceous (Maastrichtian) Maevarano Formation of the Mahajanga Basin, Madagascar. This specimen, although fragmentary as well, exhibits a number of features common to all multituberculate femora: neck cylindrical in cross section and set apart from shaft; greater trochanter prominent, extending proximally beyond head, inclined dorsally, and separated from neck by deep incisure; lesser trochanter prominent and protruding ventrally; posttrochanteric fossa present on ventral aspect, lateral to lesser trochanter; subtrochanteric tubercle present on dorsal aspect, distal to incisure between greater trochanter and neck; diaphysis straight, elliptical in cross section (slightly compressed dorsoventrally); and third trochanter absent. Three of these features (prominent, ventrally placed lesser trochanter; presence of posttrochanteric fossa; presence of subtrochanteric tubercle) are regarded as autapomorphies of Multituberculata. This specimen therefore not only independently and conclusively confirms the presence of the clade on Madagascar—previously based on a small molar fragment—but on the entire supercontinent as well.


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Free pdf:


Alessandro Palci, Mark N. Hutchinson, Michael W. Caldwell & Michael S. Y. Lee (2017)
The morphology of the inner ear of squamate reptiles and its bearing on the origin of snakes.
Royal Society Open Science 2017 4 170685
DOI: 10.1098/rsos.170685
http://rsos.royalsocietypublishing.org/content/4/8/170685
http://rsos.royalsocietypublishing.org/content/royopensci/4/8/170685.full.pdf



The inner ear morphology of 80 snake and lizard species, representative of a range of ecologies, is here analysed and compared to that of the fossil stem snake Dinilysia patagonica, using three-dimensional geometric morphometrics. Inner ear morphology is linked to phylogeny (we find here a strong phylogenetic signal in the data that can complicate ecological correlations), but also correlated with ecology, with Dinilysia resembling certain semi-fossorial forms (Xenopeltis and Cylindrophis), consistent with previous reports. We here also find striking resemblances between Dinilysia and some semi-aquatic snakes, such as Myron (Caenophidia, Homalopsidae). Therefore, the inner ear morphology of Dinilysia is consistent with semi-aquatic as well as semi-fossorial habits: the most similar forms are either semi-fossorial burrowers with a strong affinity to water (Xenopeltis and Cylindrophis) or amphibious, intertidal forms which shelter in burrows (Myron). Notably, Dinilysia does not cluster as closely with snakes with exclusively terrestrial or obligate burrowing habits (e.g. scolecophidians and uropeltids). Moreover, despite the above similarities, Dinilysia also occupies a totally unique morphospace, raising issues with linking it with any particular ecological category.


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Free pdf:

Camila Cupello, François J. Meunier, Marc Herbin, Philippe Janvier, Gaël Clément & Paulo M. Brito (2017)
The homology and function of the lung plates in extant and fossil coelacanths
Scientific Reports 7, Article number: 9244 (2017)
doi:10.1038/s41598-017-09327-6
https://www.nature.com/articles/s41598-017-09327-6



The presence of a pulmonary organ that is entirely covered by true bone tissue and fills most of the abdominal cavity is hitherto unique to fossil actinistians. Although small hard plates have been recently reported in the lung of the extant coelacanth Latimeria chalumnae, the homology between these hard structures in fossil and extant forms remained to be demonstrated. Here, we resolve this question by reporting the presence of a similar histological pattern–true cellular bone with star-shaped osteocytes, and a globular mineralisation with radiating arrangement–in the lung plates of two fossil coelacanths (Swenzia latimerae and Axelrodichthys araripensis) and the plates that surround the lung of the most extensively studied extant coelacanth species, L. chalumnae. The point-for-point structural similarity of the plates in extant and fossil coelacanths supports their probable homology and, consequently, that of the organ they surround. Thus, this evidence questions the previous interpretations of the fatty organ as a component of the pulmonary complex of Latimeria.



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