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Refining the marine reptile turnover at the Early-Middle Jurassic transition - PubMed

  • ️Fri Jan 01 2021

Refining the marine reptile turnover at the Early-Middle Jurassic transition

Valentin Fischer et al. PeerJ. 2021.

Abstract

Even though a handful of long-lived reptilian clades dominated Mesozoic marine ecosystems, several biotic turnovers drastically changed the taxonomic composition of these communities. A seemingly slow paced, within-geological period turnover took place across the Early-Middle Jurassic transition. This turnover saw the demise of early neoichthyosaurians, rhomaleosaurid plesiosaurians and early plesiosauroids in favour of ophthalmosaurid ichthyosaurians and cryptoclidid and pliosaurid plesiosaurians, clades that will dominate the Late Jurassic and, for two of them, the entire Early Cretaceous as well. The fossil record of this turnover is however extremely poor and this change of dominance appears to be spread across the entire middle Toarcian-Bathonian interval. We describe a series of ichthyosaurian and plesiosaurian specimens from successive geological formations in Luxembourg and Belgium that detail the evolution of marine reptile assemblages across the Early-Middle Jurassic transition within a single area, the Belgo-Luxembourgian sub-basin. These fossils reveal the continuing dominance of large rhomaleosaurid plesiosaurians, microcleidid plesiosaurians and Temnodontosaurus-like ichthyosaurians up to the latest Toarcian, indicating that the structuration of the upper tier of Western Europe marine ecosystems remained essentially constant up to the very end of the Early Jurassic. These fossils also suddenly record ophthalmosaurid ichthyosaurians and cryptoclidid plesiosaurians by the early Bajocian. These results from a geographically-restricted area provide a clearer picture of the shape of the marine reptile turnover occurring at the early-Middle Jurassic transition. This event appears restricted to the sole Aalenian stage, reducing the uncertainty of its duration, at least for ichthyosaurians and plesiosaurians, to 4 instead of 14 million years.

Keywords: Aalenian; Bajocian; Cryptoclididae; Extinction; Faunal turnover; Ichthyosauria; Ophthalmosauridae; Plesiosauria; Toarcian.

© 2021 Fischer et al.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Figure 1
Figure 1. Number of collections of marine reptiles (Ichthyosauria, Plesiosauria, Thalattosuchia, Pleurosauria, Angolachelonia) per stage.

Data extracted from the paleobiology database on the 26th March 2020 (see Acknowledgements for the main contributors of these data). Silhouettes originate from phylopic.org, Licensed under CC BY 3.0 SA: Dakosaurus by Dmitry Bogdanov and T. Michael Keesey; Meyerasaurus, Eurhinosaurus, Temnodontosaurus, Plesiopterys and Ophthalmosaurus by Gareth Monger; Rhomaleosaurus and Stenopterygius by Scott Hartmann; Peloneustes by Nobu Tamura and T. Michael Keesey; Albertonectes by Frank Denota (CC 1.0).

Figure 2
Figure 2. Map of the fossiliferous localities investigated.
Figure 3
Figure 3. Thoursense Zone fauna, late Toarcian, Luxembourg.

Selected anatomy of specimen MNHNL TM212. (A and B) left coracoid in ventral (A) and anteroventral (B) views. (C, E and F) left humerus in anterodorsal (C), distal (E) and proximal (F) views. (D) Left forefin in ventral view.

Figure 4
Figure 4. Pseudoradiosa Zone fauna, late Toarcian, Luxembourg.

(A–E) rhomaleosaurid left humerus MNHNL DOU307 in ventral (A), anterior (B), dorsal (C), proximal (D), and distal (E) views. (F–H) rhomaleosaurid humerus MNHNL KA109 in dorsal/ventral (F), proximal (H) and distal (H) views.

Figure 5
Figure 5. Ichthyosaurians of the late Toarcian of Luxembourg and Belgium.

(A and B) large, Temnodontosaurus-like (Parvipelvia indet.) caudal centrum IRSNB R 436 in anterior (A) and lateral (B) views. (C and D) probable thunnosaurian caudal centrum IRSNB R 437

in anterior (C) and dorsal (D) views. (E and F) ichthyosaurian distal tooth IRSNB R 438 in labial (E) and mesial (F) views. (G and H) probable non-ophthalmosaurid (Parvipelvia indet.) left angular IRSNB R 439 in lateral (G) and medial (H) views. (I–K) ichthyosaurian right quadrate IRSNB R 440 in lateral (I), medial (J) and posterior (K) views.
Figure 6
Figure 6. Ichthyosaurians of the Aalensis Zone, late Toarcian, Luxembourg.

(A–C) left coracoid of a non-baracromian parvipelvian MNHNL DOU353 in ventral (A), lateral (B), and posterior (C) views. (D–F) large parvipelvian caudal centrum MNHNL DOU378 in dorsal (D), anterior (E), and cross-sectional (F) views. (G) small parvipelvian caudal centrum MNHNL DOU998 in anteroventral view. (H and I) parvipelvian dorsal centrum MNHNL DOU944 in anterior (H) and lateral (I) views.

Figure 7
Figure 7. Plesiosaurians of the Aalensis Zone, late Toarcian, Luxembourg.

(A) plesiosaurian tooth crown MNHNL DOU906 in ?mesial view. (B) rhomaleosaurid right humerus MNHNL DOU558 in dorsal view. (C–F) rhomaleosaurid right humerus MNHNL DOU324a in proximal (C), dorsal (D), posterior (E) and distal (F) views. (G) juvenile rhomaleosaurid propodial MNHNL DOU324b.

Figure 8
Figure 8. Plesiosaurian centra of the Aalensis Zone, late Toarcian, Luxembourg.

(A and B) rhomaleosaurid pectoral vertebra MNHNL DOU954 in anterior (A) and ventral (B) views. (C–G) cf. Microcleidus cervical vertebra MNHNL DOU978 in anterior (C), ventral (D), dorsal (E), lateral (F) and oblique (G) views. (H–J) rhomaleosaurid pectoral vertebra MNHNL DOU723 in anterior (H), lateral (I) and posterior (J) views. (K–N) plesiosaurian sacral vertebra MNHNL DOU724 in dorsal (K), anterior (L), posterolateral (M) and ventral (N) views. (O–Q) rhomaleosaurid pectoral vertebra MNHNL DOU722 in anterior (O), lateral (P) and posterior (Q) views.

Figure 9
Figure 9. Late Aalenian fauna, Luxembourg.

(A–D) non-cryptoclidid plesiosauroid cervical centrum MNHNL BU157 in anterior (A), dorsal (B), ventral (C) and oblique (D) views. (E–G) plesiosaur juvenile caudal centrum MNHNL HU384 in lateral (E), anterior (F) and anteroventral (G) views. (H and I) Fragmentary ichthyosaurian rostrum MNHN HU242.

Figure 10
Figure 10. Humphresianum Zone fauna, early Bajocian, Luxembourg.

(A–F) cryptoclidid propodial MNHNL BM782 in anterior (A), proximal (B), dorsal (C), ventral (D), posterior (E) and distal (F) views. (G and H) parvipelvian MNHNL BM392 centra (G) and sclerotic element in lateral view (H). (I–O) ophthalmosaurid surangular and teeth MNHNL BM780_781: anterior tooth in labial (I) and basal (J) views; mid-rostrum tooth in labial (K) and basal (L) views; posterior tooth in labial view (M); right angular in lateral (N) and medial (O) views. Abbreviation: PAE, posterior accessory epipodial element.

Figure 11
Figure 11. The new Humphresianum Zone ophthalmosaurid, early Bajocian, Luxembourg.

Selected anatomy of specimen MNHNL BM779. (A–C) right exoccipital in anterolateral (A), posteromedial (B) and posterior (C) views. (D and E) suraoccipital in posterior (D) and ventral (E) views. (F–H) left scapula in anterior (F), medial (G), and lateral (H) views. (I–K) right quadrate in lateral (I), anterior (J), and condylar (K) views. (L) right parietal in dorsal view. (M and N) right humerus in posterior (M) and dorsal (N) views. (O and P) right ulna in posterior (O) and dorsal (P) views.

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