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A comprehensive approach to the study of plesiosaurs: paleobiology, paleophysiology, and phylogeny

Marx, Miguel LU orcid (2025)
Abstract
Plesiosaurs are charismatic marine reptiles of the Mesozoic Era. Life-like reconstructions of long-necked forms are typically ‘shrink-wrapped’ with a narrow, snake-like neck and a sea turtle-like body; a depiction that has changed little since the initial discovery of plesiosaurs over 200 years ago. Despite their long geological history and importance in founding paleontology as a scientific discipline, minimal attention has hitherto been paid to the paleobiology of plesiosaurs—the behaviors and adaptations these animals evolved to become one of the most successful lineages of marine tetrapods in Earth`s history. The objective of this thesis entails the study of these ancient reptiles using a suite of approaches to provide a better... (More)
Plesiosaurs are charismatic marine reptiles of the Mesozoic Era. Life-like reconstructions of long-necked forms are typically ‘shrink-wrapped’ with a narrow, snake-like neck and a sea turtle-like body; a depiction that has changed little since the initial discovery of plesiosaurs over 200 years ago. Despite their long geological history and importance in founding paleontology as a scientific discipline, minimal attention has hitherto been paid to the paleobiology of plesiosaurs—the behaviors and adaptations these animals evolved to become one of the most successful lineages of marine tetrapods in Earth`s history. The objective of this thesis entails the study of these ancient reptiles using a suite of approaches to provide a better understanding of the life, appearance, and relationships of plesiosaurs.
The exceptionally preserved specimens from the world-renowned Posidonia Shale (Posidonienschiefer Formation) in Germany formed the primary source of information for the majority of the papers included in this thesis. Among these, are MH 7 (Plesiopterys wildi), which represents an essentially complete and articulated skeleton with fossilized soft tissues in the tail region and along the trailing edge of one flipper. In Paper I, I conclude that this plesiosaur had a mosaic of smooth, scaleless skin, and scales on different parts of the body. Furthermore, the remarkable preservation allowed a description of the integument, including keratinocytes and melanophore pigment cells. Assessment of the osteology of this new P. wildi fossil provided novel insights into the skeletal anatomy of this taxon and an updated diagnosis for the species, but also new inferences on the evolution and paleobiogeography of long-necked (plesiosauroid) plesiosaurians during the Early Jurassic (Paper II).
Another important species is Seeleyosaurus guilelmiimperatoris, which is represented by the holotype (MB.R.1992) and a second individual (SMNS 12039). Historically, this plesiosaur has been instrumental in providing a more complete concept of the external appearance of long-necked forms, as the holotype is a complete skeleton with preserved soft tissues in the right front flipper and distal tail region—leading Wilhelm Dames to publish the earliest scientific reconstruction of a plesiosaur based on soft-tissue remains in 1895. The osteology, phylogeny, and preserved tissues are the focus of Paper III, where I, along with my coauthors, found S. guilelmiimperatoris to be a derived Microcleidid plesiosaurian, diagnosable by a set of morphological characters that include one autapomorphy. Seeleyosaurus guilelmiimperatoris also formed the basis of Paper IV, as this plesiosaur exhibits a neural spine arrangement in the dorsal vertebral series that appears to be virtually identical to that of many modern-day cetaceans equipped with a fleshy dorsal fin. Morphometric analysis of Seeleyosaurus and other Posidonia Shale plesiosaurs identified three individuals with a shift in the orientation of the dorsal neural spines from recumbent to procumbent. In Paper IV, I conclude that this directional change likely represents an osteological correlate for a dorsal fin.
Paper V deals with the hydro- and thermodynamic capabilities of long-necked plesiosaurs using computational fluid dynamics (CFD) simulations. Our CFD analyses demonstrate that a thicker neck, insulated with peripheral blubber, would have benefitted these ancient reptiles, especially individuals living in cold ocean waters near the poles. Additionally, a thicker neck did not create a negative effect on the overall drag. Thus, I conclude that plesiosaurs likely possessed an insulating peripheral layer of blubber to protect against the thermal conductivity of water, which in turn creates a more of a torpedo-shaped body form—a profile typical for many marine tetrapods today.
Paper VI comprises a review of plesiosaur finds from the Cretaceous of Angola, which have provided new insights into plesiosaur paleobiology and evolution. These discoveries include the bones of aristonectine elasmosaurids that exhibit an external morphology that is immature, yet their histology is like that of skeletally mature individuals, indicating ontogenetic paedomorphism. Further inferences on the evolution of paedomorphic traits and adaptations for life in a pelagic environment are presented in the skeletal anatomy of Cardiocorax mukulu. A femur of the first known polycotylid plesiosaurian from sub-Saharan Africa is also described, along with aristonectine basioccipitals that provide insights into plesiosaur biodiversity. A review of the taphonomy of the ‘Bench 19 Bonebed’ in Bentiaba reveals that plesiosaur skeletal elements often show bitemarks inflicted by sharks but not mosasaurs, which were otherwise abundant contemporaries of plesiosaurs along the coast of what is today Angola.
Collectively, this thesis shows that plesiosaurs lost the scalation on their body (apart from the flippers), and presumably evolved a dorsal fin and blubber as adaptations for pelagic life. These results thus provide a noteworthy update of their appearance from shrink-wrapped creatures to animals that were well-adapted to thrive in the oceans. Additional findings from Angola provide a rare window into the evolution and diversity of plesiosaurs at the end of the Mesozoic.
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author
supervisor
opponent
  • Associate Professor Fischer, Valentin, University of Liège, Belgium
organization
publishing date
type
Thesis
publication status
published
subject
keywords
adaptations, Angola, blubber, dorsal fin, pelagic, phylogeny, scales, skin, thermodynamics
pages
404 pages
publisher
Lund University
defense location
Pangea, Geocentrum II, Geologiska institutionen. Join via zoom: https://lu-se.zoom.us/j/68873661036?pwd=mYwAfSY7OUd4Ybfxfor8HJaauC0bav.1 password: 142227
defense date
2025-09-19 13:00:00
ISBN
978-91-87847-90-5
978-91-87847-91-2
project
A holistic approach to the biology, physiology and phylogeny of Mesozoic plesiosaurs (Reptilia, Sauropterygia)
A holistic approach to the biology, physiology and phylogeny of plesiosaurs
language
English
LU publication?
yes
id
ec944b1c-a0d7-4568-9bc9-34967e0cb176
date added to LUP
2025-08-26 11:55:49
date last changed
2025-08-26 13:45:11
@phdthesis{ec944b1c-a0d7-4568-9bc9-34967e0cb176,
  abstract     = {{Plesiosaurs are charismatic marine reptiles of the Mesozoic Era. Life-like reconstructions of long-necked forms are typically ‘shrink-wrapped’ with a narrow, snake-like neck and a sea turtle-like body; a depiction that has changed little since the initial discovery of plesiosaurs over 200 years ago. Despite their long geological history and importance in founding paleontology as a scientific discipline, minimal attention has hitherto been paid to the paleobiology of plesiosaurs—the behaviors and adaptations these animals evolved to become one of the most successful lineages of marine tetrapods in Earth`s history. The objective of this thesis entails the study of these ancient reptiles using a suite of approaches to provide a better understanding of the life, appearance, and relationships of plesiosaurs.<br/>The exceptionally preserved specimens from the world-renowned Posidonia Shale (Posidonienschiefer Formation) in Germany formed the primary source of information for the majority of the papers included in this thesis. Among these, are MH 7 (Plesiopterys wildi), which represents an essentially complete and articulated skeleton with fossilized soft tissues in the tail region and along the trailing edge of one flipper. In Paper I, I conclude that this plesiosaur had a mosaic of smooth, scaleless skin, and scales on different parts of the body. Furthermore, the remarkable preservation allowed a description of the integument, including keratinocytes and melanophore pigment cells. Assessment of the osteology of this new P. wildi fossil provided novel insights into the skeletal anatomy of this taxon and an updated diagnosis for the species, but also new inferences on the evolution and paleobiogeography of long-necked (plesiosauroid) plesiosaurians during the Early Jurassic (Paper II).<br/>Another important species is Seeleyosaurus guilelmiimperatoris, which is represented by the holotype (MB.R.1992) and a second individual (SMNS 12039). Historically, this plesiosaur has been instrumental in providing a more complete concept of the external appearance of long-necked forms, as the holotype is a complete skeleton with preserved soft tissues in the right front flipper and distal tail region—leading Wilhelm Dames to publish the earliest scientific reconstruction of a plesiosaur based on soft-tissue remains in 1895. The osteology, phylogeny, and preserved tissues are the focus of Paper III, where I, along with my coauthors, found S. guilelmiimperatoris to be a derived Microcleidid plesiosaurian, diagnosable by a set of morphological characters that include one autapomorphy. Seeleyosaurus guilelmiimperatoris also formed the basis of Paper IV, as this plesiosaur exhibits a neural spine arrangement in the dorsal vertebral series that appears to be virtually identical to that of many modern-day cetaceans equipped with a fleshy dorsal fin. Morphometric analysis of Seeleyosaurus and other Posidonia Shale plesiosaurs identified three individuals with a shift in the orientation of the dorsal neural spines from recumbent to procumbent. In Paper IV, I conclude that this directional change likely represents an osteological correlate for a dorsal fin.<br/>Paper V deals with the hydro- and thermodynamic capabilities of long-necked plesiosaurs using computational fluid dynamics (CFD) simulations. Our CFD analyses demonstrate that a thicker neck, insulated with peripheral blubber, would have benefitted these ancient reptiles, especially individuals living in cold ocean waters near the poles. Additionally, a thicker neck did not create a negative effect on the overall drag. Thus, I conclude that plesiosaurs likely possessed an insulating peripheral layer of blubber to protect against the thermal conductivity of water, which in turn creates a more of a torpedo-shaped body form—a profile typical for many marine tetrapods today.<br/>Paper VI comprises a review of plesiosaur finds from the Cretaceous of Angola, which have provided new insights into plesiosaur paleobiology and evolution. These discoveries include the bones of aristonectine elasmosaurids that exhibit an external morphology that is immature, yet their histology is like that of skeletally mature individuals, indicating ontogenetic paedomorphism. Further inferences on the evolution of paedomorphic traits and adaptations for life in a pelagic environment are presented in the skeletal anatomy of Cardiocorax mukulu. A femur of the first known polycotylid plesiosaurian from sub-Saharan Africa is also described, along with aristonectine basioccipitals that provide insights into plesiosaur biodiversity. A review of the taphonomy of the ‘Bench 19 Bonebed’ in Bentiaba reveals that plesiosaur skeletal elements often show bitemarks inflicted by sharks but not mosasaurs, which were otherwise abundant contemporaries of plesiosaurs along the coast of what is today Angola.<br/>Collectively, this thesis shows that plesiosaurs lost the scalation on their body (apart from the flippers), and presumably evolved a dorsal fin and blubber as adaptations for pelagic life. These results thus provide a noteworthy update of their appearance from shrink-wrapped creatures to animals that were well-adapted to thrive in the oceans. Additional findings from Angola provide a rare window into the evolution and diversity of plesiosaurs at the end of the Mesozoic.<br/>}},
  author       = {{Marx, Miguel}},
  isbn         = {{978-91-87847-90-5}},
  keywords     = {{adaptations; Angola; blubber; dorsal fin; pelagic; phylogeny; scales; skin; thermodynamics}},
  language     = {{eng}},
  month        = {{08}},
  publisher    = {{Lund University}},
  school       = {{Lund University}},
  title        = {{A comprehensive approach to the study of plesiosaurs: paleobiology, paleophysiology, and phylogeny}},
  url          = {{https://lup.lub.lu.se/search/files/226257429/Kappa_Miguel_Marx_LUCRIS.pdf}},
  year         = {{2025}},
}