New Cretaceous lungfishes (Dipnoi, Ceratodontidae) from western North America

Abstract

Ceratodontid lungfishes are generally rare, poorly represented elements of North America’s Mesozoic ecosystems, with previously known maximum diversity in the Late Jurassic. Herein we describe four new species of the form genusCeratodus, from the Cretaceous of the Western Interior, considerably expanding fossil representation of post-Triassic dipnoans in North America. To model taxonomic and morphologic diversity, we adopt a four-fold system of phenetically based species groups, named for exemplars from the Morrison Formation.Ceratodus kirklandin. sp. (Potamoceratodus guentherigroup) andC.kempaen. sp. (C.frazierigroup) represent a hitherto unsampled time interval, the Valanginian.Ceratodus nirumbeen. sp. andC.molossusn. sp. extend the temporal ranges of theC.fossanovumandC.robustusgroups upward to the Albian and Cenomanian, respectively. These new occurrences show that ceratodontids maintained their highest diversity from the Late Jurassic through the mid-Cretaceous (Albian–Cenomanian), an interval of ~60 Myr. The existing record suggests that some of the later (mid-Cretaceous) ceratodontids may have been tolerant of salt water; to date, there is no evidence that they aestivated. Only a few occurrences are known from horizons younger than Cenomanian. Demise of ceratodontids appears to be part of a broader pattern of turnover that occurred at the Cenomanian-Turonian boundary in North America.

Lungfish tooth plates (Sarcopterygii, Dipnoi) from the Late Cretaceous (Santonian) Eutaw Formation of Alabama and Mississippi, USA

“…No single ridge is separated from an adjacent ridge by more than 33°. These tooth plate measurements are comparable with specimens of Ceratodus frazieri reported from North America (Kirkland, 1987; Parris et al, 2004; Frederickson and Cifelli, 2017).…”

“…C. frazieri ); NJSM 18774 (Parris et al, 2004, as Ceratodus aff. C. frazieri ); USNM 546680, USNM 547214, USNM 546249, USNM 546795 (Oreska et al, 2013); OMNH 60408 (Frederickson and Cifelli, 2017); ALMNH 8723 (herein).…”

“…The angles between the ridges depend on two factors, the angle of growth and the angle of wear, but only the angle of growth can be used for taxonomic determination (Kemp, 1997). As has been previously reported, lungfish exhibit considerable intraspecific variation in tooth plate morphology; therefore, it can be difficult to identify them to the specific or even generic level without additional cranial material (Schultze, 1981; Pardo et al, 2010; Otero, 2011; Frederickson and Cifelli, 2017). However, some authors argue that isolated tooth plates can be reliably used as taxonomic indicators (e.g., Kemp, 1998).…”

Faunal composition and paleoenvironment of the Arundel Clay (Potomac Formation; Early Cretaceous), Maryland, USA

“…Based on the large amount of ontogenetic and intraspecific variation that is present in modern dipnoans (Kemp 1996(Kemp , 1997, it is impossible to determine whether these plates represent upper or lower plates, or to determine their species. It could be that these specimens represent juvenile C. kranzi, but it is equally plausible that they represent a different species of dipnoan, as multiple species of lungfish commonly co-occur elsewhere in Jurassic and Cretaceous rocks of North America (Kirkland, 1987(Kirkland, , 1998Frederickson and Cifelli, 2017).…”

“…A comparison with roughly contemporaneous terrestrial formations from western North America shows that the Arundel far exceeds the typical relative abundance of chondrichthyans for the Aptian-Cenomanian (Figure 7). The Arundel has at least one species of Ceratodus, a genus known to occur in both terrestrial and nearshore deposits (Schultze, 1981;Kirkland, 1987;Frederickson and Cifelli, 2017). Indeed, many of the groups represented in the Arundel assemblage, such as hybodonts, crocodilians, and ceratopsians, show affinities for coastal settings in other rock units (Brinkman, 1990;Brinkman et al, 2005).…”