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[dinosaur] Aquilolamna, new Cretaceous shark + aquatic bird forelimb muscles + carnivore teeth




Ben Creisler
bcreisler@gmail.com

Some recent non-dino papers:

Aquilolamna milarcae gen. et sp. nov.

Romain Vullo, Eberhard Frey, Christina Ifrim, Margarito A. GonzÃlez GonzÃlez, Eva S. Stinnesbeck & Wolfgang Stinnesbeck (2021)
Manta-like planktivorous sharks in Late Cretaceous oceans.
Science 371(6535): 1253-1256
DOI: 10.1126/science.abc1490
https://science.sciencemag.org/content/371/6535/1253


A soaring shark

Modern sharks occupy marine ecosystems across the world but display little morphological diversity, being mostly streamlined predators. Vullo et al. describe a new species of shark from the late Cretaceous that shows that the lack of current variation is not due to limited morphological "exploration" in the past. Specifically, Aquilolamna milarcae displays many features similar to modern manta rays, notably long, slender fins and a mouth seemingly adapted to filter feeding, suggesting that it was planktivorous. This finding indicates both that elasmobranchs evolutionarily experimented with other forms and that the planktivorous âsoarersâ emerged in this group at least 30 million years earlier than previously recognized.

Abstract

The ecomorphological diversity of extinct elasmobranchs is incompletely known. Here, we describe Aquilolamna milarcae, a bizarre probable planktivorous shark from early Late Cretaceous open marine deposits in Mexico. Aquilolamna, tentatively assigned to Lamniformes, is characterized by hypertrophied, slender pectoral fins. This previously unknown body plan represents an unexpected evolutionary experimentation with underwater flight among sharks, more than 30 million years before the rise of manta and devil rays (Mobulidae), and shows that winglike pectoral fins have evolved independently in two distantly related clades of filter-feeding elasmobranchs. This newly described group of highly specialized long-winged sharks (Aquilolamnidae) displays an aquilopelagic-like ecomorphotype and may have occupied, in late Mesozoic seas, the ecological niche filled by mobulids and other batoids after the CretaceousâPaleogene boundary.

***

News:

https://www.sciencemag.org/news/2021/03/eagle-shark-once-soared-through-ancient-seas-near-mexico

https://phys.org/news/2021-03-discovery-winged-shark-cretaceous-seas.html

https://www.nationalgeographic.com/science/article/shark-like-fossil-with-manta-wings-is-unlike-anything-seen-before

https://www.livescience.com/ancient-shark-flew-through-dinosaur-age-seas.html


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Free pdf:

Fernanda Bribiesca-Contreras, Ben Parslew & William I. Sellers (2021)
Functional morphology of the forelimb musculature reflects flight and foraging styles in aquatic birds
Journal of Ornithology (advance online publication)
doi: https://doi.org/10.1007/s10336-021-01868-y
https://link.springer.com/article/10.1007/s10336-021-01868-y

Free pdf:

https://link.springer.com/content/pdf/10.1007/s10336-021-01868-y.pdf


Aquatic birds show a great diversity of locomotion styles and wing morphologies, from penguins that are fully specialized for an aquatic life to species of aerial flyers that also use their wings for underwater propulsion (e.g. auks and shearwaters). Moving between the airâwater interface exerts conflicting pressures on the body and wing anatomy of diving birds. In this work, we investigated the functional morphology of the forelimb musculature of 18 species of aquatic birds that display a variety of flight and foraging styles. Muscle architecture was related to function, with special emphasis on muscle mass. Dissections of one of the forelimbs of 20 specimens of waterbirds were performed to obtain numerical data of muscle architecture. Total wing muscle mass scaled isometrically to body mass1.0, whereas fascicle length scaled to muscle mass0.284, which is consistent with previous results of scaling in wings of raptors. A principal component analysis (PCA) of normalised muscle masses resulted in a biplot where three main morphological groups can be distinguished. Anatids (ducks and geese) occupy a space represented by muscles that are activated during downstroke. Auks and penguins clustered together in a region dominated by muscles that assist in wing elevation and showed a degree of hypertrophy. The rest of the species grouped together in the lower limits of both PCs where muscles that facilitate wing flexionâextension and stabilisation are loaded. The distribution of mass in the wing muscles of the aquatic birds seemed to be related to flight and foraging style and showed non-significant influence of shared phylogenetic history (Kmult: 0.71, p value: 0.083, 10,000 permutations).

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Dana M. Reuter, Samantha S. B. Hopkins & Edward B. Davis (2021)
Carnivoran intraspecific tooth-size variation shows heterogeneity along the tooth row and among species.
Journal of Mammalogy 102(1): 236â249
doi: https://doi.org/10.1093/jmammal/gyaa157
https://academic.oup.com/jmammal/article-abstract/102/1/236/6175216



Developing morphological diagnoses for fossil mammals requires an understanding of intraspecific variation in the anatomical elements under study. Dental traits along with tooth size can be informative of taxonomic identify for extinct species. However, it is unclear what selective or developmental processes are responsible for documented patterns in tooth-size variation making application to the fossil record difficult. We assessed combined species tooth-type variation and intraspecific tooth-size variation for 19 species to evaluate whether developmental controls or occlusion-driven functional demands influence carnivoran tooth-size variation. We also estimated phylogenetic signal for the coefficient of variation (CV). Combined species tooth-size variation separated by tooth type shows that canines are more variable than molars and lower premolars. We found intraspecific tooth-size variation patterns differ between species. However, comparisons of the CVs did not support the hypotheses that developmental controls or functional demands of occlusion constrain size variation in mammal teeth. Our results suggest that a combination of factors influence carnivoran tooth-size variation, such as differences in ontogeny, diet, sexual dimorphism, and evolutionary history. Patterns of carnivoran intraspecific tooth-size variation suggest a better understanding of dental size variation in extant species is essential for accurate morphological studies of fossil taxa.



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