Abstract:Jurassic and Cretaceous marine deposits worldwide show that ophthalmosaurid ichthyosaurs are major components of marine tetrapod communities for almost 76 myr. One of the major features characterizing this clade is the complexity and diversity of their stylopodium-zeugopodium morphology. Upper Jurassic deposits of the Vaca Muerta Formation in north-west Patagonia (Argentina) have yielded the richest Tithonian ophthalmosaurid records from Gondwana. Here, we present a new ophthalmosaurid from this lithostratigra… Show more
“…Noteworthy, within a general tendency towards more integrated and modular fins, the thunnosauria morphospace is expanded in all directions. Similar results have been obtained through the analysis of humerus and zeugopodium morphology among ophthalmosaurids [20]. Other lines of evidence, like those provided by bone microanatomy, e.g., [30,31], also suggest that thunnosaurs, and particularly ophthalmosaurids, were ecologically diverse throughout the Jurassic.…”
Section: Morphospace Occupationsupporting
confidence: 80%
“…The Early/Middle Jurassic transition, although poorly documented [17][18][19], witnessed the emergence of the ophthalmosaurians. In contrast, the Jurassic/Cretaceous transition marks a profound drop in the diversity (and probably disparity) of the clade [16,20].…”
After the end-Triassic extinction, parvipelvian ichthyosaurs diversified and became dominant elements of marine ecosystems worldwide. By the Early Jurassic, they achieved a thunniform body plan that persisted for the last 100 m.y.a of their evolution. Diversification and extinctions of thunniform ichthyosaurs, and their swimming performance, have been studied from different perspectives. The transformation of limbs into hydrofoil-like structures for better control and stability during swimming predates thunniform locomotion. Despite their importance as control surfaces, fin evolution among thunnosaurs remains poorly understood. We explore ichthyosaur fin diversity using anatomical networks. Our results indicate that, under a common hydrofoil controller fin, the bone arrangement diversity of the ichthyosaur fin was greater than traditionally assumed. Changes in the connectivity pattern occurred stepwise throughout the Mesozoic. Coupled with other lines of evidence, such as the presence of a ball-and-socket joint at the leading edge of some derived Platypterygiinae, we hypothesize that fin network disparity also mirrored functional disparity likely associated with different capabilities of refined maneuvering. The ball-and-socket articulation indicates that this local point could be acting like a multiaxial intrafin joint changing the angle of attack and thus affecting the maneuverability, similar to the alula of flying birds. Further studies on large samples and quantitative experimental approaches would be worthy to test this hypothesis.
“…Noteworthy, within a general tendency towards more integrated and modular fins, the thunnosauria morphospace is expanded in all directions. Similar results have been obtained through the analysis of humerus and zeugopodium morphology among ophthalmosaurids [20]. Other lines of evidence, like those provided by bone microanatomy, e.g., [30,31], also suggest that thunnosaurs, and particularly ophthalmosaurids, were ecologically diverse throughout the Jurassic.…”
Section: Morphospace Occupationsupporting
confidence: 80%
“…The Early/Middle Jurassic transition, although poorly documented [17][18][19], witnessed the emergence of the ophthalmosaurians. In contrast, the Jurassic/Cretaceous transition marks a profound drop in the diversity (and probably disparity) of the clade [16,20].…”
After the end-Triassic extinction, parvipelvian ichthyosaurs diversified and became dominant elements of marine ecosystems worldwide. By the Early Jurassic, they achieved a thunniform body plan that persisted for the last 100 m.y.a of their evolution. Diversification and extinctions of thunniform ichthyosaurs, and their swimming performance, have been studied from different perspectives. The transformation of limbs into hydrofoil-like structures for better control and stability during swimming predates thunniform locomotion. Despite their importance as control surfaces, fin evolution among thunnosaurs remains poorly understood. We explore ichthyosaur fin diversity using anatomical networks. Our results indicate that, under a common hydrofoil controller fin, the bone arrangement diversity of the ichthyosaur fin was greater than traditionally assumed. Changes in the connectivity pattern occurred stepwise throughout the Mesozoic. Coupled with other lines of evidence, such as the presence of a ball-and-socket joint at the leading edge of some derived Platypterygiinae, we hypothesize that fin network disparity also mirrored functional disparity likely associated with different capabilities of refined maneuvering. The ball-and-socket articulation indicates that this local point could be acting like a multiaxial intrafin joint changing the angle of attack and thus affecting the maneuverability, similar to the alula of flying birds. Further studies on large samples and quantitative experimental approaches would be worthy to test this hypothesis.
“… Fig. 14 Phylogenetic topology from our second analysis (based on [ 76 ]). Thickened lines denote known stratigraphic ranges.…”
Section: Descriptionmentioning
confidence: 99%
“…We are confident of the ophthalmosaurian affinities of the genus due to the morphology of the angular and basioccipital. We reanalyzed PIMUZ A/III 5279 in the ophthalmosaurian-specific matrix of [ 76 ], in order to better resolve its position within Ophthalmosauria. We added Nannopterygius enthekiodon , Catutosaurus gasparinae , and Thalassodraco etchesi to the matrix, since based on the preliminary analysis PIMUZ A/III 5279 is recovered near the base of Ophthalmosauria within ophthalmosaurine-grade ophthalmosaurians, thus these genera are pertinent to better resolving its phylogenetic relationships.…”
Section: Descriptionmentioning
confidence: 99%
“…However, these minor morphological distinctions between both sides Fig. 14 Phylogenetic topology from our second analysis (based on [76]). Thickened lines denote known stratigraphic ranges.…”
The Middle Jurassic is an important time period for the evolutionary history of marine reptiles as it represented a transitional phase for many clades. Notably, in ichthyosaurs, many early parvipelvian taxa went extinct. The Middle Jurassic saw the emergence of the derived Ophthalmosauria, ultimately becoming the dominant ichthyosaurian clade by the end of the epoch. Even though this is an important period in the evolutionary history of Ophthalmosauria, our understanding remains limited in terms of morphology and taxonomy due to the scarcity of vertebrate-bearing strata. Here we present a large new ichthyosaur from the Bajocian of Switzerland, represented by an almost complete skull with 3D-preserved bones, the (inter)clavicles and a large portion of the postcranial skeleton. After CT- and surface scanning, we reconstructed the 3D in vivo morphology. Our morphological observations and phylogenetic analyses show that the new taxon named Argovisaurus martafernandezi is nested at the base of the Ophthalmosauria. The holotype and only known specimen of Argovisaurus likely represents an adult individual. Bajocian members of the Ophthalmosauria (Mollesaurus and Argovisaurus) were large-bodied animals, a trait typically associated with the more derived Platypterygiinae. This hints at the importance of a large body size early in ophthalmosaurian evolution.LSID: urn:lsid:zoobank.org:act:C3312628-1544-4B87-BBE3-B12346A30BE3LSID: urn:lsid:zoobank.org:act:23C2BD71-8CF0-4D99-848A-0D631518415B
Jurassic and Cretaceous marine deposits worldwide show that ophthalmosaurid ichthyosaurs are major components of marine tetrapod communities for almost 76 myr. One of the major features characterizing this clade is the complexity and diversity of their stylopodium-zeugopodium morphology. Upper Jurassic deposits of the Vaca Muerta Formation in north-west Patagonia (Argentina) have yielded the richest Tithonian ophthalmosaurid records from Gondwana. Here, we present a new ophthalmosaurid from this lithostratigraphic unit, Sumapalla argentina gen. et sp. nov., recognized based on several unique features of the skull roof, forefin, scapular, and pelvic girdles. On phylogenetic analysis it was recovered as a basal member of Platypterygiinae. The peculiar morphology of the forefin of the new taxon indicates a previously unnoticed morphological diversity in the ophthalmosaurid appendicular skeleton and provides an excellent opportunity to test its range of variation. For this purpose, we implemented a holistic approach, using 2D geometric morphometric analysis focused on the humerus, and disparity analysis of the zeugopodium. Our results reveal a long duration of one humeral morphotype characterizing Arthropterygius spp. and closely related taxa. Furthermore, we found a peak of zeugopodial disparity during the Kimmeridgian, followed by a decrease by the end of the Jurassic, and then a recovery by the Early Cretaceous.
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