Rhamphorhynchus intraspecific variation + Enalioetes, new metriorhynchid from Lower Cretaceous of Germany

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

New papers:

Free pdf:

Michael B. Habib & David WE. Hone (2024)
Intraspecific variation in the pterosaur Rhamphorhynchus muensteri—implications for flight and socio-sexual signaling.
PeerJ 12: e17524
doi: https://doi.org/10.7717/peerj.17524
https://peerj.com/articles/17524/


Pterosaurs were the first powered flying vertebrates, with a fossil record that stretches back to about 230 million years before present. Most species are only known from one to three specimens, which are most often fragmentary. However, Rhamphorhynchus muensteri is known from numerous excellent specimens, including multiple specimens with soft tissue preservation. As such, Rhamphorhynchus muensteri is one of the only pterosaurs amenable to analysis for intraspecific variation. It has been previously predicted that elements directly involved in the flight apparatus, such as those of the forelimb, will be more highly constrained in their proportions than other parts of the skeleton. We investigated the degree of variation seen in elements and body parts of Rhamphorhynchus, which represents the best model system among pterosaurs for testing these expectations of intraspecific variation. We recover evidence for high levels of constraint throughout the appendicular and axial elements (head, neck, torso, tail, forelimbs, hindlimbs), suggesting that all were important for flight. We further find that tail variation increases among the largest specimens, suggesting reduced constraint and/or stronger sexual selection on the tail in more mature individuals.

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Enalioetes schroederi gen. et sp. nov.

Sven Sachs,Mark T. Young,Jahn J. Hornung,Thomas Cowgill,Julia A. Schwab &Stephen L. Brusatte (2024)
A new genus of metriorhynchid crocodylomorph from the Lower Cretaceous of Germany
Journal of Systematic Palaeontology 22(1): 2359946
doi: https://doi.org/10.1080/14772019.2024.2359946
 https://www.tandfonline.com/doi/full/10.1080/14772019.2024.2359946


Here we describe a new genus and species of metriorhynchid crocodylomorph, Enalioetes schroederi gen. et sp. nov., from the lower Valanginian Stadthagen Formation (Lower Cretaceous) of north-western Germany. Enalioetes schroederi is the most complete and well-preserved Cretaceous metriorhynchid skull known to date, preserving most of the cranium and mandible, the atlas-axis complex and the first postaxial cervical vertebra. The specimen was previously attributed to the coeval enigmatic metriorhynchid Enaliosuchus (a nomen dubium) and, more recently, to Cricosaurus. Although the specific epithet schroederi has been used frequently in the literature, it has never been formally established. Herein, we demonstrate that the new taxon is distinct from all known metriorhynchids by a unique combination of characters including several autapomorphies such as: the lack of bulbous dorsolateral expansion in the posterior nasal cavity; mediolateral distance between the orbital canals being approximately 1.5 times the diameter of the orbital canals; lacrimal with dorsoventrally deep anterior process ventral to the preorbital fossa being equal to or greater than the depth of the jugal anterior process and the anterodorsal process of the lacrimal; and ascending processes at atlas intercentrum extending far dorsally to level of neural canal. Enalioetes schroederi contributes to the sparse global record of Cretaceous metriorhynchids and represents one of the stratigraphically youngest occurrences of the group. It can thus help to enhance our understanding of the metriorhynchid diversity during the Cretaceous Period.

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[Tim Williams]

> Michael B. Habib & David WE. Hone (2024)
> Intraspecific variation in the pterosaur Rhamphorhynchus muensteri—implications for flight and socio-sexual signaling.

Regarding socio-sexual signaling, the majority of pterosaurs had either a head-crest or a tail-vane.   _Rhamphorhynchus_ had a tail-vane, but no head-crest; as did _Sordes_.  _Pterorhynchus_ had both.  Most short-tailed pterosaurs had a head-crest of some kind.  One notable exception is the anurognathids -  but is this because they might have been crepuscular/nocturnal, and visual displays weren't much use in the dark?

On the rigid tail in long-tailed pterosaurs, as Habib & Hone note: 

"This functional explanation is consistent with striking similarities between the tails of dromaeosaurids and rhamphorhynchids, including the relative dorsoventral rigidity of the tail (provided by caudal rods) and the comparative lateral mobility of the tail (Persons & Currie, 2013)."

Persons & Currie (2013) devoted a whole paper to the uncanny resemblance between the tails of rhamphorhynchids and dromaeosaurids, with their caudal rods that constrained up-and-down motion of the tail.  Persons & Currie came up with some heterodox explanations (such as derived dromaeosaurids being secondarily flightless, and running like Groucho Marx).  Back in 1968, Ostrom proposed that the stiffened tail of _Deinonychus_ worked as a dynamic stabilizer during predatory attacks, such as when leaping against larger prey.  

Among long-tailed pterosaurs, not all have the tail reinforced by caudal rods, and even among basal pterosaurs this feature varies - so it wasn't essential to early flight in pterosaurs.  Maybe the caudal rods allowed the long tail to be held off the ground during leaping, and/or prevented it from contacting the ground during ground-to-air take-offs in pterosaurs and volant dromaeosaurids like _Microraptor_.

[Mike Habib]

Excellent thoughts all around, Tim. While it was outside the scope of the paper, the broader comparative context that you summarized is another line of reasoning that pushes Dave and I towards the idea that the tails were mostly under social selection, and that any locomotor function was probably related to movement *other* than flight. 

The fact that the tail is stiffened in a way that very closely matches a group of largely non-flying animals (Microraptorans notwithstanding), is consistent with this. Perhaps Rhamphorhynchus was quite acrobatic on substrates, or climbed a lot. Unfortunately, since nearly all of the Solnhofen fossils come from lagoons, we can’t reasonably test with trackway evidence. 

Cheers,

—Mike

Michael B. Habib, MS PhD
Director of Data Visualization
Adjunct Associate Professor of Medicine
UCLA Cardiac Arrhythmia Center
Division of Cardiology
Vatche and Tamar Manoukian Medical Building
100 Medical Plaza, Suite 660
Los Angeles, CA 90095
MBH...@mednet.ucla.edu

Research Associate, Dinosaur Institute
Los Angeles County Museum of Natural History
900 W Exposition Blvd. Los Angeles, 90007

biology...@gmail.com
+1 (443) 280-0181

On Jul 21, 2024, at 1:45 AM, Tim Williams <tij...@gmail.com> wrote:



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