A new chondrichthyan fauna from the Late Jurassic of the Swiss Jura (Kimmeridgian) dominated by hybodonts, chimaeroids and guitarfishes

Abstract

The fossil record of chondrichthyans (sharks, rays and chimaeroids) principally consists of isolated teeth, spines and dermal denticles, their cartilaginous skeleton being rarely preserved. Several Late Jurassic chondrichthyan assemblages have been studied in Europe based on large bulk samples, mainly in England, France, Germany and Spain. The first study of this kind in Switzerland is based on controlled excavations in Kimmeridgian deposits related to the construction of the A16 motorway in the Swiss Jura (Porrentruy, NW Switzerland). This study is based on more than 2000 isolated chondrichthyan remains (teeth, dental plates, spines and dermal denticles) and adds to our knowledge of the chondrichthyan distribution at a regional scale in Europe. We describe and identify this new fauna, define a new species of hybodont with crushing-type dentition (Asteracanthus udulfensis sp. nov.) and report for the first time the carcharhiniform Corysodon cirinensis in Switzerland. By the Late Jurassic, modern neoselachian sharks had overtaken hybodonts in European marine realms, the latter being gradually confined to brackish or freshwater environments. However, while the associated fauna of the Porrentruy platform indicates marine conditions, neoselachian sharks are surprisingly rare. The chondrichthyan assemblage is largely dominated by hybodonts, guitarfishes (rays) and chimaeroids that are all known to be euryhaline. This unexpected chondrichthyan faunal composition questions the presence of fresh to brackish water in the vicinity of the platform, and the occurrence of salinity fluctuations within a general context marine. This could explain the scarcity of neoselachian sharks and the extended success of hybodonts in the Porrentruy area as late as the Late Jurassic.

A new Pliensbachian elasmobranch (Vertebrata, Chondrichthyes) assemblage from Europe, and its contribution to the understanding of late Early Jurassic elasmobranch diversity and distributional patterns

“…Jurassic hybodontiform sharks are generally assumed to have been negatively affected by the radiation of Jurassic neoselachians due to increasing competition, resulting in a diversity decline towards the end of the Jurassic and subsequent displacement towards continental waters by the Early Cretaceous onwards (e.g., Thies and Reif 1985;Rees and Underwood 2008;Cuny 2012;Leuzinger et al 2017). Notably, late Early Jurassic hybodontiform sharks seem to have been unaffected by the radiation of neoselachians (Fig.…”

“…The late Early Jurassic is considered to mark a key time interval in the evolutionary history of neoselachian elasmobranchs, because the Toarcian witnessed a first major radiation event resulting in a significant taxonomic and ecological diversity increase (Underwood 2006;Kriwet et al 2009;Guinot et al 2012;Guinot and Cavin 2016). Obviously, it was the time when most crown-group neoselachians (i.e., Heterodontiformes, Orectolobiformes, Squantiniformes, and Batomorphii) became abundant in the fossil record for the first time (e.g., Thies 1983;Lepage 1990, 1993;Delsate and Thies 1995;Delsate and Candoni 2001), suggesting an abrupt and nearly simultaneous colonization of a wide range of marine habitats (Underwood 2004(Underwood , 2006, probably accompanied by a subsequent diversity decline of hybodontiforms within marine environments (e.g., Rees and Underwood 2008;Leuzinger et al 2017). On the other hand, the Early Jurassic elasmobranch fossil record is strongly biased towards isolated material such as teeth and placoid scales from open marine, offshore environments; material from marginal marine, near-shore facies remains extremely rare due to the scarcity of productive localities (Rees 1998).…”

Peculiar tooth renewal in a Jurassic ray‐finned fish (Lepisosteiformes, †Scheenstia sp.)

“…), pterosaurs (Marty & Billon‐Bruyat ), chondrichthyans (Leuzinger et al . ), as well as actinopterygians, mainly pycnodonts, lepisosteiforms and caturids (Leuzinger et al . ).…”

New material of “Eurysternidae” (Thalassochelydia, Pan-Cryptodira) from the Kimmeridgian of the Swiss Jura Mountains

“…The other fossil-rich bed of the Reuchenette Formation -the Banné Marls -is especially rich in invertebrates (Comment et al, 2015;Koppka, 2015), but also contains remains of vertebrates such as turtles (see below), crocodilians (Schaefer et al, 2018), and fishes (Leuzinger et al, 2017a(Leuzinger et al, , 2017b. The turtle fauna of the Banné Marls consists of Tropidemys langii (the dominating taxon; Püntener et al, 2014), Plesiochelys bigleri Raselli & Anquetin, 2019), and Solnhofia sp.…”