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A New genus of coccolepidid fishes (Actinopterygii, Chondrostei) from the continental Jurassic of Patagonia

Adriana López-Arbarello, Emilia Sferco, and Oliver W.M. Rauhut

Plain Language Abstract

The Acipenseriformes (paddlefishes and sturgeons) are one of the most primitive lineages of modern bony fishes, but their fossil history is still incompletely known. A detailed anatomical reappraisal of a coccolepidid fish that was originally described as Oligopleurus groeberi from the Late Jurassic (c. 150-160 Ma) of Patagonia is presented, mainly based on new and well-preserved material. This work showed that this species is best classified in a new genus, for which the name Condorlepis is proposed, and led to the recognition of numerous characters that coccolepidids share with acipenseriforms, indicating that these animals belong to the fossil stem-lineage of the latter.

Resumen en Español

Un género nuevo de peces coccolepididos (Actinopterygii, Chondrostei) del Jurásico continental de Patagonia

Los peces jurásicos de agua dulce están poco estudiados todavía. La única asociación conocida de esa edad en el sur de Sudamérica es la Fauna de Almada, contenida en la Formación Cañadón Calcáreo (Oxfordiano-Titoniano) de Chubut, Argentina. Esta fauna está compuesta principalmente por abundantes teleósteos y algunos actinopterigios basales originalmente descriptos como †Oligopleurus groeberi pero que actualmente se clasifican en el género †Coccolepis. Este último taxón es re descripto en este trabajo, en base al material original y a numerosos ejemplares nuevos y bien preservados provenientes de varias localidades dentro de la Formación Cañadón Calcáreo. La especie muestra varias diferencias con otros taxones de coccolepididos incluyendo la presencia apomórfica de un canal sensorial en la placa gular, y no se la puede referir a ninguno de los géneros conocidos. Por lo tanto se propone un nombre genérico nuevo, †Condorlepis gen. nov. La descripción anatómica detallada de †Condorlepis gen. nov. groeberi provee evidencia adicional en favor de la inclusión de Coccolepididae en Chondrostei y sus relaciones cercanas con los Acipenseriformes, ya que esta especie presenta seis caracteres que han sido considerados autapomorfías de este último clado. Una comparación de la fauna de Almada con otras faunas dulceacuícolas jurásicas de Gondwana muestra similitud cercana con la fauna de Talbragar, Australia, que es aproximadamente contemporánea y también incluye un teléosteo basal muy abundante y coccolepididos. Por el contrario, existen notables diferencias con las faunas del Jurásico Temprano a Medio de la Formación Kota en la India, las capas del Jurásico Medio a Tardío de Stanleyville en la República Democrática del Congo, y con la Formación Tacuarembó de edad probablemente Jurásica Tardía en Uruguay, en las cuales los neopterigios no teleósteos y los sarcopterigios son abundantes.

Palabras clave. Género nuevo; Chondrostei; Coccolepididae; Patagonia; Jurásico Superior; peces dulceacuícolas.

Traducción: authors

Résumé en Français

In progress

Translator: Olivier Maridet

Deutsche Zusammenfassung

Eine neue Gattung coccolepidider Fische (Actinopterygii, Chondrostei) aus dem kontinentalen Jura Patagoniens

Jurassische Fischfaunen aus dem Süßwasser sind immer noch wenig bekannt, und die einzige Assoziation dieses Alters aus Südamerika ist die „Almada-Fauna" aus der Cañadón Calcáreo Formation (Oxford-Tithon) aus Chubut, Argentinien. Diese Fauna besteht hauptsächlich aus sehr häufigen Teleosteern und deutlich selteneren basalen Actinopteryiern, die ursprünglich unter dem Namen †Oligopleurus groeberi beschrieben wurden und heute üblicherweise zu der Gattung †Coccolepis gestellt werden. Dieses Taxon wird hier auf der Basis des Originalmateriales und zahlreicher, besser erhaltener Neufunde aus mehreren Lokalitäten in der Cañadón Calcáreo Formation neu beschrieben. Die Art zeigt mehrere Unterschiede zu anderen Vertretern der Coccolepididae, darunter dir apomorphen Merkmale des Vorhandenseins einer Sinneslinien in der Gularplatte, und kann daher nicht zu einer bekannten Gattung gestellt werden. Daher wird hier der neue Gattungsname †Condorlepis gen. nov. für diese Art vorgeschlagen. Die detaillierte Beschreibung von †Condorlepis gen. nov. groeberi ergibt weitere Hinweise auf eine Zugehörigkeit der Coccolepididae zu den Chondrostei und für eine nahe Verwandtschaft mit den Acipenseriformes innerhalb dieser Gruppe, da die Art sechs Merkmale aufweist, die bisher as Autapomorphien für die letzere Gruppe angesehen wurden. Ein Vergleich der Almada Fauna mit anderen Jurassischen Süßwasserfaunen Gondwanas zeigt eine große Übereinstimmung mit der ungefähr gelichaltrigen Fauna von Talbragar, Australien, die ebenfalls sehr häufige Teleosteer sowie Coccolepididen enthält. Andererseits gibt es deutlich Unterschiede zu den Faunen der unter- oder mitteljurassischen Kota Formation Indiens, der mittel- bis oberjurassischen Stanleyville Beds der Demokratischen Republik Kongo und zu der vermutlich oberjurassischen Tacuarembó Formation in Uruguay, in denen basale Neopterygier, die nicht den Teleosteern angehören und Sarcopterygier häufig sind.

Schlüsselwörter. Neue Gattung; Chondrostei; Coccolepididae; Patagonien; Oberer Jura; Süßwasser-Fische.

Translators: authors

Arabic

348 arab

Translator: Ashraf M.T. Elewa

 

 

FIGURE 1. Geographic location and extension of the outcrops of the Cañadón Calcáreo Formation (represented in red) and the Cañadón Asfalto Formation (represented in dark gray) in the Chubut province, Patagonia, Argentina. The white spots on the outcrops of the Cañadón Calcáreo Formation in the detailed map on the bottom right represent the main fish localities, which are precisely indicated in Figure 2.

figure 1

FIGURE 2. Geographic location of the fish localities: 1, Puesto Almada; 2, Punta Biotita; 3. Estancia Limonao; 4, Cañadón Los Chivos 1; 5, Cañadón Los Chivos 2; 6, Cañadón Las Minas; 7, La Manea. Geographic information was drawn on a Google earth image (© 2012 Digital Globe).

figure 2

FIGURE 3. Relative abundance of the main fish groups represented in the Cañadón Calcáreo Formation. 3.1, General taxonomic composition in four of the different localities: Puesto Almada: n= 131; Estancia Limonao: n=44; La Manea: n=125; Cañadón Los Chivos 1: n=11 (see geographic distribution of these localities in Figure 2). 3.2, Detailed taxonomic composition present in the different fish-bearing layers (L1 to L7 from the top to the base of the sequence) of the La Manea locality: Layer 1: n=9; layer 3: n=18; layer 4: n=11; layer 5: n= 8; layer 6: n=11; layer 7: n=7.

 figure3

FIGURE 4. Photographs of two type specimens of †Condorlepis groeberi (Bordas, 1943) n. comb. 4.1, MACN 14434 (lectotype); 4.2, MACN 14433 (paralectotype). Scale bars equals 2 cm.

figure 4

FIGURE 5. Photograph of the specimen MPEF-PV 1731A of †Condorlepis groeberi. Scale bar equals 2 cm.

figure 5

FIGURE 6. Photograph of the skull of †Condorlepis groeberi in MACN 14434 (lectotype). Scale bar equals 5 mm.

figure 6

FIGURE 7. Line drawing of the skull of †Condorlepis groeberi in MPEF-PV 1731B.

figure 7

FIGURE 8. Snout bones in †Condorlepis groeberi. 8.1, Line drawing of the slightly disarticulated postrostral, nasal and antorbital bones in MPEF-PV 3958. 8.2 Line drawing of the articulated postrostral and nasal bones in MPEF-PV 1732B.

 figure 8

FIGURE 9. Line drawing of the skull of †Condorlepis groeberi in MPEF-PV 3958.

 figure9

FIGURE 10. Upper jaw of †Condorlepis groeberi. 10.1, Detailed photograph of MPEF-PV 1731B showing the premaxilla; the anterior process of the parasphenoid is also well shown in this picture; scale bar equals 2 mm. 10.2, Disarticulated maxilla in MPEF-PV 1496-5A, scale bar equals 5 mm.

figure 10

FIGURE 11. Vertebral column of †Condorlepis groeberi. Detailed photographs of the specimen MPEF-PV 1731B: 11.1, anterior portion of the abdominal region, directly behind the skull; 11.2, central portion of the vertebral column showing the transitional morphologies between the abdominal and caudal regions.

figure 11

FIGURE 12. Caudal skeleton of †Condorlepis groeberi. 12.1, Photograph of MPEF-PV 1732B; 12.2, photograph of MPEF-PV 3958A. Scale bars equals 2 mm.

figure 12

FIGURE 13. Detailed features of the caudal skeleton of †Condorlepis groeberi. 13.1, Photograph of MPEF-PV 1731B showing the exquisitely preserved small cercus-like extension of the body lobe, which is indicated by the black arrow; 13.2, detailed photograph of the ventral margin of the caudal fin in MPEF-PV 3958B showing the distal segments of two marginal fin rays intercalating between the fringing fulcra (black arrows). Scale bars equals 2 mm.

figure 13

FIGURE 14. Dorsal and anal fins of †Condorlepis groeberi. 14.1, dorsal fin support in MPEF-PV 10506 showing separated proximal and middle radials; 13.2, anal fin support in MPEF-PV 1731B. Scale bars equals 2 mm.

figure 14

FIGURE 15. Photograph of †Condorlepis groeberi (MPEF-PV 1766) showing the pectoral spine. Scale bar equals 5 mm.

figure 15

FIGURE 16. Body squamation in †Condorlepis groeberi (MPEF-PV 1556-6). Scale bar equals 5 mm.

figure 16

FIGURE 17. Detailed features of the scales in †Condorlepis groeberi. 17.1 Photograph of scales in MPEF-PV 1558 showing the ridges radiating from the growth center towards the borders of the scales; 17.2 photograph of scales in MPEF-PV 1556-6 showing the very fine and pointed denticles irregularly arranged. Scale bars equal 1 mm.

figure 17

 

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adrianaBayerische Staatssammlung für Paläontologie und Geologie
Richard-Wagner-Strasse 10
D-80333 München
Germany
and Museo Paleontológico Egidio Feruglio
Av. Fontana 140
9100 Trelew
Argentina

Adriana López-Arbarello is an Argentinean biologist dedicated to the study of fossil actinopterygian fishes. She graduated and completed her PhD at the University of Buenos Aires and had her first postdoc at the Museum für Naturkunde in Berlin. She then returned to Argentina for a couple of years, but later moved back to Germany and is now settled in Munich, supported by the German Research Foundation (DFG) since 2006. After exploring the anatomy and systematics of different fish groups, she has been captured by the fascinating history of actinopterygians during the early Mesozoic. She is fully dedicated to the study of Mesozoic neopterygians, overloaded with taxonomic work, deciphering the network of their phylogenetic relationships and weaving ideas on the mode of evolution of some anatomical structures related to the rise and diversification of the modern fishes.

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emiliaLaboratorio de Paleontología Evolutiva de Vertebrados
Departamento de Geología
Facultad de Ciencias Exactas y Naturales
Universidad de Buenos Aires
Ciudad Universitaria
Pabellón II
1428 Buenos Aires
Argentina
and Museo Paleontológico Egidio Feruglio
Av. Fontana 140
9100 Trelew
Argentina

Emilia Sferco is a PhD student at the University of Buenos Aires, Argentina. She received her undergraduate degree from the University of La Plata, Buenos Aires (2007) and she is now finishing her PhD Thesis on the phylogenetic and biogeographical aspects of the Late Jurassic freshwater basal teleosts from Patagonia, Argentina. She is interested on the phylogenetic relationships of Jurassic and Cretaceous basal teleosts and the origin of teleosts. After her PhD Thesis she will be working on the taxonomical and phylogenetical aspects of Lower Cretaceous teleosts from Patagonia.

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oliverBayerische Staatssammlung für Paläontologie und Geologie
Richard-Wagner-Strasse 10
D-80333 München
Germany
and Museo Paleontológico Egidio Feruglio
Av. Fontana 140
9100 Trelew, Argentina
and Department of Earth and Environmental Sciences and GeoBioCenter
Ludwig-Maximilians-University
Richard-Wagner-Strasse 10
80333 Munich
Germany

Oliver Rauhut mainly works on dinosaur anatomy and evolution, but is interested in everything to do with Mesozoic, and especially Jurassic, terrestrial ecosystems. He got a diploma from the Free University of Berlin in 1995 and a PhD from the University of Bristol in 2000. As a postdoc at the Museo Paleontológico Egidio Feruglio in Trelew, Argentina, he developed a field work program in the Middle and Late Jurassic units of Chubut Province, and has been working on biota from these formations since. He is currently curator of lower vertebrates at the Bayerische Staatssammlung für Paläontologie und Geologie in Munich, Germany, where he also works on Jurassic reptiles from Europe and other continents.

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TABLE 1. Morphometric proportions measured on the six complete specimens. Abbreviations: TL, total length; HL, head length; BD, maximal depth of the body; PreV, length from the anterior border of the nasals to the origin of the ventral fins; PreD, length from the anterior border of the nasals to the origin of the dorsal fin; PreA, length from the anterior border of the nasals to the origin of the anal fin.

 

Specimen

LT

HL/TL

HD/HL

BD/TL

PreV/TL

PreD/TL

PreA/TL

MPEF-PV 1732

8,5

0,24

0,80

0,18

0,40

0,46

0,59

MPEF-PV 1767

9,9

0,21

0,79

0,17

0,37

0,43

0,57

MPEF-PV 1733

11

0,23

0,79

0,17

0,35

0,43

0,54

MPEF-PV 3958

11,1

0,23

0,81

 

0,38

0,42

0,58

MPEF-PV 1731

11,6

0,23

0,84

0,17

0,43

0,47

0,65

MACN 14434

12,6*

0,23*

0,85

0,25

0,41

0,52

0,65