Taxonomy and biostratigraphy of the elasmobranchs and bony fishes (Chondrichthyes and Osteichthyes) of the lower-to-middle Eocene (Ypresian to Bartonian) Claiborne Group in Alabama, USA, including an analysis of otoliths

Abstract

The Tallahatta Formation, Lisbon Formation, and Gosport Sand are the three lithostratigraphic units that make up the lower-to-middle Eocene Claiborne Group. In Alabama, these marine units are among the most fossiliferous in the state and a long history of scattered reports have attempted to document their fossil diversity. In this study, we examined 20931 elasmobranch and bony fish elements, including otoliths, derived from Claiborne Group units in Alabama and identified 115 unequivocal taxa. Among the taxa identified, one new species is described, Carcharhinus mancinae sp. nov., and Pseudabdounia gen. nov. is a new genus erected to include two species formerly placed within Abdounia Capatta, 1980. New taxonomic combinations proposed include Pseudabdounia claibornensis (White, 1956) gen. et comb. nov., Pseudabdounia recticona (Winkler, 1874) gen. et comb. nov., Physogaleus alabamensis (Leriche, 1942) comb. nov., and Eutrichiurides plicidens (Arambourg, 1952) comb. nov. We also report the first North American paleobiogeographic occurrences of Aturobatis aff. A. aquensis Adnet, 2006, Brachycarcharias atlasi (Arambourg, 1952), Eutrichiurides plicidens comb. nov., Galeorhinus louisi Adnet & Cappetta, 2008, Ginglymostoma maroccanum Noubhani & Cappetta, 1997, Gymnosarda sp., Mennerotodus sp., Rhizoprionodon ganntourensis (Arambourg, 1952), Stenoscyllium aff. S. priemi Noubhani & Cappetta, 1997, Trichiurus oshosunensis White, 1926, and the first North American occurrence for a fossil member of the Balistidae Risso, 1810. Our sample also included 26 taxa that represented first paleobiogeographic occurrences for Alabama, including Abdounia beaugei (Arambourg, 1935), Albula eppsi White, 1931, Ariosoma nonsector Nolf & Stringer, 2003, Anisotremus? sp., Anomotodon sp., Brachycarcharias twiggsensis (Case, 1981), Burnhamia daviesi (Woodward, 1889), Eoplinthicus yazooensis Capetta & Stringer, 2002, Galeorhinus ypresiensis (Casier, 1946), Gnathophis meridies (Frizzell & Lamber, 1962), Haemulon? obliquus (Müller, 1999), Hypolophodon sylvestris (White, 1931), Malacanthus? sulcatus (Koken, 1888), Meridiania cf. M. convexa Case, 1994, Palaeocybium proosti (Storms, 1897), Paraconger sector (Koken, 1888), Paralbula aff. P. marylandica Blake, 1940, Phyllodus toliapicus Agassiz, 1844, Propristis schweinfurthi Dames, 1883, Pycnodus sp., Pythonichthys colei (Müller, 1999), Scomberomorus stormsi (Leriche, 1905), Signata stenzeli Frizzell & Dante, 1965, and Signata nicoli Frizzell & Dante, 1965, and the first Paleogene occurrences in Alabama of a member of the Gobiidae Cuvier, 1816. A biostratigraphic analysis of our sample showed stratigraphic range extensions for several taxa, including the first Bartonian occurrences of Eoplinthicus yazooensis, Jacquhermania duponti (Winkler, 1876), Meridiania cf. M. convexa, Phyllodus toliapicus, and “Rhinobatos” bruxelliensis (Jaekel, 1894), range extensions into the late Ypresian and Bartonian for Tethylamna dunni Cappetta & Case, 2016 and Scoliodon conecuhensis Cappetta & Case, 2016, the first late Ypresian records of Galeorhinus louisi, the first Lutetian occurrence of Gymnosarda Gill, 1862, and a range extension for Fisherichthys aff. F. folmeri Weems, 1999 into the middle Bartonian. Larger biostratigraphic and evolutionary trends are also documented, such as the acquisition of serrations in Otodus spp., possible population increases for the Rhinopterinae Jordan & Evermann, 1896 and Carcharhiniformes Compagno, 1973 in the Bartonian, and the apparent diversification of the Tetraodontiformes Berg, 1940 during the same stage. This study helps better our understanding of early-to-middle Eocene elasmobranch and bony fish diversity, paleobiogeography, and biostratigraphy in the Gulf Coastal Plain of North America.

Diversity and renewal of tropical elasmobranchs around the Middle Eocene Climatic Optimum (MECO) in North Africa: New data from the lagoonal deposits of Djebel el Kébar, Central Tunisia

“…Coming from contemporaneous deposit (unverified), this tooth could represent a western record of these fossil great requiem sharks in the Tethys seaway, when those of Egypt would be the eastern representatives. Adnet et al (2010) and Underwood and Gunter (2012) suspected that the great Carcharhinus and related genera arose as a dominant tropical marine clade during the Middle-Late Eocene.The new species and the coeval C. mancinae recently described by Ebersole et al (2019) in contemporaneous deposits of Alabama, USA, confirm and precisely date the rise of the requiem sharks to Bartonian in Western Central Atlantic (Alabama) -Western Tethys seaway (Tunisia) with a sufficient and well-dated material.…”

“…Samonds et al (2019) described a Middle-Late Eocene species of Carcharhinus (C. underwoodi) from Madagascar considering that the youngest C. balochensis from the Indian Ocean was invalid and should be synonymized with Galeocerdo eaglesomei. However, as noticed by Ebersole et al (2019), the latter statement is currently unsupported, eluding that C. balochensis shares classic dignathic heterodonty of Carcharhinus (contrary to Galeocerdo), a compound serration (never doubly serrate in G. eaglesomei) and does not show the V-shape root morphology (underlined with the concave labial crown-root boundary) of usual Galeocerdo eaglesomei. In fact, C. underwoodi (Samonds et al, 2019, Figure 3G-R) probably displays a similar dignathic heterodonty with C. balochensis, if we consider the figured lower teeth finely serrated (Samonds et al, 2019, figure 2M-O) incorrectly attributed to Galeocerdo eaglesomei.…”

“…If we exclude Carcharhinus mancinae from the Bartonian (see Ebersole et al, 2019) and Carcharhinus underwoodi dated with uncertainty to the Middle or Late Eocene (see Samonds et al, 2019), Middle Eocene records of Carcharhinus with serrated upper teeth have been sometimes reported but the material remains extremely scarce and often, have been either incorrectly dated or based on misidentification of other genera (Underwood and Gunter, 2012). Among them, a tooth from the GE (upper middle Eocene) was figured under the name Carcharhinus sp.1 by Case and Cappetta (1990, pl.…”

“…The morphology of teeth is similar to that of those from the Late Eocene of Fayum attributed to Hemipristis curvatus by Case and Cappetta (1990, figures 4, 80-81). Hemipristis curvatus is primarily known from all tropical seas during the late Middle-Late Eocene, from the Tethys seaway (e.g., Case and Cappetta, 1990;Mustafa and Zalmout, 2002; to the Western Central Atlantic (Case and Borodin, 2000;Ebersole et al, 2019). However, reported this species in MI (but not illustrated), when it is typically more common throughout the remainder of the Wadi al Hitan succession (see also Underwood et al 2011, figure 5B and 5C from BQ), and especially since the GE (A-C) (around the Bartonian/Priabonian boundary).…”

“…If Noubhani and Cappetta (1997) already synonymized N. fourtaui with N. obliquus, the teeth of N. blanckenhorni have a morphology reminiscent to that of N. obliquus, and as such both species are probably synonymous (e.g., Cappetta and Case, 2016), even if this first is always signalled in Late Paleogene deposits (Samonds et al, 2019). Ebersole et al (2019) recently discussed about the tooth differences between N. obliquus and N. thielensis and suggested that they seem rather a reflection of heterodonty than separate species, at least concerning the post Ypresian representatives. Considering these recent observations and the doubt about systematics validity, this Diagnosis.…”