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1. Assessing the Morphological Impacts of Ammonoid Shell Shape through Systematic Shape Variation

   https://doi.org/10.1093/icb/icaa067  

   Hebdon, Nicholas; Ritterbush, Kathleen; Choi, YunJi (June 2020, Integrative and Comparative Biology)

   null (Ed.)

   Synopsis A substantial body of research has been accumulated around ammonoids over several decades. A core aspect of this research has been attempting to infer their life mode from analysis of the morphology of their shells and the drag they incur as that shell is pushed through the water. Tools such as Westermann Morphospace have been developed to investigate and scaffold hypotheses about the results of these investigations. We use computational fluid dynamics to simulate fluid flow around a suite of 24 theoretical ammonoid morphologies to interrogate systematic variations within this space. Our findings uphold some of the long-standing expectations of drag behavior; conch inflation has the greatest influence over ammonoid drag. However, we also find that other long-standing assumptions, such as oxyconic ammonoids being the best swimmers, are subject to substantial variation and nuance resulting from their morphology that is not accounted for through simple drag assessment. 

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2. Twirling torticones: hydrostatics and hydrodynamics of helically-coiled ammonoids

   Peterman, DJ; Hebdon, N; Ritterbush, KA (February 2021, The American Association of Petroleum Geologists bulletin)

   Slattery, J (Ed.)

   Of the many shell morphologies produced by ammonoid cephalopods, the helical torticone shape appears poorly-suited to rapid locomotion. We investigate torticone hydrostatics and hydrodynamics through virtual modeling, computational fluid dynamics simulations, and water-chamber experiments, using the Cenomanian (Cretaceous) turrilitid Mariella brazoensis (Roemer, 1852) as a test case. Our hydrostatic model suggests that M. brazoensis, and other torticones, could attain neutral buoyancy. This morphotype is highly stable compared to planispiral cephalopods with a slightly tilted, apex-upward orientation. The corresponding mass distribution, relative to the source of jet propulsion at the hyponome, suggests that jet thrust would be more efficiently transmitted into upwards movement than horizontal movement. Most directions of thrust would send the shell spinning about its vertical axis. We 3D printed shell models to have either surpluses or deficiencies in buoyancy that imparted estimated thrusts of extant cephalopod analogues in the vertical directions within a water chamber. The models consistently rotate aperture-backwards during upward movement, and aperture-forwards during downward movement. A neutrally buoyant model was used to assess rotational aptitude during active locomotion. The model required low torques to sustain rotation. Simulations of water flow around the shell support the movement directions observed in the physical experiments and demonstrate that hydrodynamic drag is lower in the vertical directions than the horizontal directions. These results show that the animal within a torticone shell could spin about its vertical axis easily; perhaps even simple respiration could have allowed rotation at ~20 degrees per second. Hydrostatic and hydrodynamic properties of torticones suggest that rotation and vertical movement potential constrained the behavior of these helically-coiled cephalopods. We interpret that torticone ammonoids, prominent throughout neritic and epeiric seas during the Albian and Cenomanian (Cretaceous), may have used passive spiral motions to feed upon small food items through the water column, and may have had low metabolic demands compared to modern-day coleoids. 

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3. The concept of ‘heteromorph ammonoids’

   https://doi.org/10.1111/let.12443  

   Landman, Neil H.; Machalski, Marcin; Whalen, Christopher D. (August 2021, Lethaia)

   ‘Heteromorph ammonoids’ encompass all ammonoid species whose shapes do not conform to a closely coiled planispiral shell. The term is useful as a broad description for such ammonoids. However, as a concept, ‘heteromorph ammonoids’ no longer has any scientific value or explanatory power. Although such ammonoids have traditionally been considered aberrant forms, they represent instead an integral part of the evolutionary history of the Ammonoidea. ‘Heteromorph ammonoids’, as a whole, are a poly- phyletic group, consisting of a heterogeneous mixture of taxa without any phylogenetic, morphological or ecological coherence. Their treatment as a single entity risks conflating convergences and phylogenetic affinities. It also vastly oversimplifies the stunning array of morphologies and ecological niches occupied by these animals. Investigation into the uncoiling (and recoiling) of ammonoids is a legitimate and worthwhile enterprise, especially in view of the realization that this phenomenon occurred several times in the history of the Ammonoidea. However, few insights can be gained by treating ‘heteromorph ammonoids’ as a single entity. Studies of such ammonoids should focus on monophyletic groups within a well‐constrained phylogenetic and stratigraphical framework to yield meaningful results. 

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4. Buoyancy control in ammonoid cephalopods refined by complex internal shell architecture

   https://doi.org/10.1038/s41598-021-87379-5  

   Peterman, David J.; Ritterbush, Kathleen A.; Ciampaglio, Charles N.; Johnson, Erynn H.; Inoue, Shinya; Mikami, Tomoyuki; Linn, Thomas J. (December 2021, Scientific Reports)

   null (Ed.)

   Abstract The internal architecture of chambered ammonoid conchs profoundly increased in complexity through geologic time, but the adaptive value of these structures is disputed. Specifically, these cephalopods developed fractal-like folds along the edges of their internal divider walls (septa). Traditionally, functional explanations for septal complexity have largely focused on biomechanical stress resistance. However, the impact of these structures on buoyancy manipulation deserves fresh scrutiny. We propose increased septal complexity conveyed comparable shifts in fluid retention capacity within each chamber. We test this interpretation by measuring the liquid retained by septa, and within entire chambers, in several 3D-printed cephalopod shell archetypes, treated with (and without) biomimetic hydrophilic coatings. Results show that surface tension regulates water retention capacity in the chambers, which positively scales with septal complexity and membrane capillarity, and negatively scales with size. A greater capacity for liquid retention in ammonoids may have improved buoyancy regulation, or compensated for mass changes during life. Increased liquid retention in our experiments demonstrate an increase in areas of greater surface tension potential, supporting improved chamber refilling. These findings support interpretations that ammonoids with complex sutures may have had more active buoyancy regulation compared to other groups of ectocochleate cephalopods. Overall, the relationship between septal complexity and liquid retention capacity through surface tension presents a robust yet simple functional explanation for the mechanisms driving this global biotic pattern. 

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5. SOLIS: XVI. Mass ejection and time variability in protostellar outflows: Cep E

   https://doi.org/10.1051/0004-6361/202142931  

   de A. Schutzer, A.; Rivera-Ortiz, P. R.; Lefloch, B.; Gusdorf, A.; Favre, C.; Segura-Cox, D.; López-Sepulcre, A.; Neri, R.; Ospina-Zamudio, J.; De Simone, M.; et al (June 2022, Astronomy & Astrophysics)

   Context. Protostellar jets are an important agent of star formation feedback, tightly connected with the mass-accretion process. The history of jet formation and mass ejection provides constraints on the mass accretion history and on the nature of the driving source. Aims. We characterize the time-variability of the mass-ejection phenomena at work in the class 0 protostellar phase in order to better understand the dynamics of the outflowing gas and bring more constraints on the origin of the jet chemical composition and the mass-accretion history. Methods. Using the NOrthern Extended Millimeter Array (NOEMA) interferometer, we have observed the emission of the CO 2–1 and SO N J = 5 4 –4 3 rotational transitions at an angular resolution of 1.0″ (820 au) and 0.4″ (330 au), respectively, toward the intermediate-mass class 0 protostellar system Cep E. Results. The CO high-velocity jet emission reveals a central component of ≤400 au diameter associated with high-velocity molecular knots that is also detected in SO, surrounded by a collimated layer of entrained gas. The gas layer appears to be accelerated along the main axis over a length scale δ 0 ~ 700 au, while its diameter gradually increases up to several 1000 au at 2000 au from the protostar. The jet is fragmented into 18 knots of mass ~10 −3 M ⊙ , unevenly distributed between the northern and southern lobes, with velocity variations up to 15 km s −1 close to the protostar. This is well below the jet terminal velocities in the northern (+ 65 km s −1 ) and southern (−125 km s −1 ) lobes. The knot interval distribution is approximately bimodal on a timescale of ~50–80 yr, which is close to the jet-driving protostar Cep E-A and ~150–20 yr at larger distances >12″. The mass-loss rates derived from knot masses are steady overall, with values of 2.7 × 10 −5 M ⊙ yr −1 and 8.9 × 10 −6 M ⊙ yr −1 in the northern and southern lobe, respectively. Conclusions. The interaction of the ambient protostellar material with high-velocity knots drives the formation of a molecular layer around the jet. This accounts for the higher mass-loss rate in the northern lobe. The jet dynamics are well accounted for by a simple precession model with a period of 2000 yr and a mass-ejection period of 55 yr. 

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