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Occurrence of the megatoothed sharks (Lamniformes: Otodontidae) in Alabama, USA.

Ehret DJ, Ebersole J - PeerJ (2014)

Bottom Line: Carcharocles auriculatus is more common in the Eocene deposits of Alabama, but its occurrence has been largely overlooked in the literature.We also refute the occurrence of the Oligocene Carcharocles angustidens in the state.Raised awareness and increased collecting of under-sampled geologic formations in Alabama will likely increase sample sizes of O. obliquus and C. auriculatus and also might unearth other otodontids, such as C. megalodon and C. chubutensis.

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Affiliation: Alabama Museum of Natural History , Tuscaloosa, AL , USA.

ABSTRACT
The Otodontidae include some of the largest sharks to ever live in the world's oceans (i.e., Carcharocles megalodon). Here we report on Paleocene and Eocene occurrences of Otodus obliquus and Carcharocles auriculatus from Alabama, USA. Teeth of Otodus are rarely encountered in the Gulf Coastal Plain and this report is one of the first records for Alabama. Carcharocles auriculatus is more common in the Eocene deposits of Alabama, but its occurrence has been largely overlooked in the literature. We also refute the occurrence of the Oligocene Carcharocles angustidens in the state. Raised awareness and increased collecting of under-sampled geologic formations in Alabama will likely increase sample sizes of O. obliquus and C. auriculatus and also might unearth other otodontids, such as C. megalodon and C. chubutensis.

No MeSH data available.


Carcharocles auriculatus teeth from Alabama.Carcharocles auriculatus specimens from Alabama. Labial view on left, lingual view on right. (A) ALMNH 1988.29.1, Hatchetigbee Fm.; (B) MSC 20970, Lisbon-Tallahatta fms.; (C) MSC 20973, Lisbon-Tallahatta fms.; (D) RMM 2371, Gosport Sand; (E) ALMNH 2000.1.29.1, Yazoo Clay; (F) ALMNH 2000.1.33.1, Yazoo Clay; (G) ALMNH 2005.6.294, Unknown formation; (H) MSC 20968, Lisbon-Tallahatta fms. Scale Bar = 5 cm.
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fig-4: Carcharocles auriculatus teeth from Alabama.Carcharocles auriculatus specimens from Alabama. Labial view on left, lingual view on right. (A) ALMNH 1988.29.1, Hatchetigbee Fm.; (B) MSC 20970, Lisbon-Tallahatta fms.; (C) MSC 20973, Lisbon-Tallahatta fms.; (D) RMM 2371, Gosport Sand; (E) ALMNH 2000.1.29.1, Yazoo Clay; (F) ALMNH 2000.1.33.1, Yazoo Clay; (G) ALMNH 2005.6.294, Unknown formation; (H) MSC 20968, Lisbon-Tallahatta fms. Scale Bar = 5 cm.

Mentions: The taxonomic assignment of the Otodontidae is a contentious subject that has been debated for over a century (Agassiz, 1843; Jordan & Hannibal, 1923; Glikman, 1964; Cappetta, 1987; Cappetta, 2012; Applegate & Espinosa-Arrubarrena, 1996; Zhelezko & Kozlov, 1999; Purdy et al., 2001; Nyberg, Ciampaglio & Wray, 2006; Pimiento et al., 2010; Pimiento et al., 2013; Ehret, Hubbell & MacFadden, 2009; Ehret et al., 2012). Original descriptions by Agassiz (1843) placed the megatoothed sharks within the Lamnidae, however they have since been reclassified as the Otodontidae by Glikman (1964) to recognize their distinct evolutionary history. Since being formally described in the 1840s, the taxonomy of the otodontids has undergone a multitude of changes reflecting reinterpretations of their relationships by a host of researchers (see references above). It is beyond the scope of this study to address the taxonomic stability of the otodontid sharks, however we recognize the genera Otodus and Carcharocles for the lineage ending with Carcharocles megalodon. This arrangement stands in contrast with Glikman (1964) and Cappetta (2012), who both referred species with large lateral cusplets to Otodus, and those with small or no cusplets to the genus Megaselachus. Cappetta (2012) revised the taxonomy further, by separating the genus Otodus into three subgenera based on the presence, absence, or size of serrations and cusplets as well as differences in root morphology. Furthermore, Zhelezko & Kozlov (1999) separated many of the Otodus and Carcharocles species into subspecies (e.g., Otodus obliquus mugodzharicus and Otodus poseidoni poseidoni) based on specimens from Kazakhstan. These constructions only further complicate the taxonomy of the Otodontids and do little to elucidate the relationships of the megatoothed sharks. We also argue that, under a biological species concept, it is not possible to recognize subgenera and subspecies in the fossil record. Therefore, we reject these confusing and somewhat subjective designations. Otodontids do likely represent a chronospecific sequence, with individual species derived from a pattern of development that replaces one species with another sequentially through geologic time by incremental morphological and genetic changes (Applegate & Espinosa-Arrubarrena, 1996; Cappetta, 2012). This mechanism results in a descendant that is much different from its original ancestor, however when looking at smaller time intervals, species distinctions are much more difficult to discern. In the absence of a phylogenetic or a more thorough morphometric analysis, and until further work is conducted and published, we refer the unserrated form to Otodus obliquus and serrated forms to the genus Carcharocles.


Occurrence of the megatoothed sharks (Lamniformes: Otodontidae) in Alabama, USA.

Ehret DJ, Ebersole J - PeerJ (2014)

Carcharocles auriculatus teeth from Alabama.Carcharocles auriculatus specimens from Alabama. Labial view on left, lingual view on right. (A) ALMNH 1988.29.1, Hatchetigbee Fm.; (B) MSC 20970, Lisbon-Tallahatta fms.; (C) MSC 20973, Lisbon-Tallahatta fms.; (D) RMM 2371, Gosport Sand; (E) ALMNH 2000.1.29.1, Yazoo Clay; (F) ALMNH 2000.1.33.1, Yazoo Clay; (G) ALMNH 2005.6.294, Unknown formation; (H) MSC 20968, Lisbon-Tallahatta fms. Scale Bar = 5 cm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4201945&req=5

fig-4: Carcharocles auriculatus teeth from Alabama.Carcharocles auriculatus specimens from Alabama. Labial view on left, lingual view on right. (A) ALMNH 1988.29.1, Hatchetigbee Fm.; (B) MSC 20970, Lisbon-Tallahatta fms.; (C) MSC 20973, Lisbon-Tallahatta fms.; (D) RMM 2371, Gosport Sand; (E) ALMNH 2000.1.29.1, Yazoo Clay; (F) ALMNH 2000.1.33.1, Yazoo Clay; (G) ALMNH 2005.6.294, Unknown formation; (H) MSC 20968, Lisbon-Tallahatta fms. Scale Bar = 5 cm.
Mentions: The taxonomic assignment of the Otodontidae is a contentious subject that has been debated for over a century (Agassiz, 1843; Jordan & Hannibal, 1923; Glikman, 1964; Cappetta, 1987; Cappetta, 2012; Applegate & Espinosa-Arrubarrena, 1996; Zhelezko & Kozlov, 1999; Purdy et al., 2001; Nyberg, Ciampaglio & Wray, 2006; Pimiento et al., 2010; Pimiento et al., 2013; Ehret, Hubbell & MacFadden, 2009; Ehret et al., 2012). Original descriptions by Agassiz (1843) placed the megatoothed sharks within the Lamnidae, however they have since been reclassified as the Otodontidae by Glikman (1964) to recognize their distinct evolutionary history. Since being formally described in the 1840s, the taxonomy of the otodontids has undergone a multitude of changes reflecting reinterpretations of their relationships by a host of researchers (see references above). It is beyond the scope of this study to address the taxonomic stability of the otodontid sharks, however we recognize the genera Otodus and Carcharocles for the lineage ending with Carcharocles megalodon. This arrangement stands in contrast with Glikman (1964) and Cappetta (2012), who both referred species with large lateral cusplets to Otodus, and those with small or no cusplets to the genus Megaselachus. Cappetta (2012) revised the taxonomy further, by separating the genus Otodus into three subgenera based on the presence, absence, or size of serrations and cusplets as well as differences in root morphology. Furthermore, Zhelezko & Kozlov (1999) separated many of the Otodus and Carcharocles species into subspecies (e.g., Otodus obliquus mugodzharicus and Otodus poseidoni poseidoni) based on specimens from Kazakhstan. These constructions only further complicate the taxonomy of the Otodontids and do little to elucidate the relationships of the megatoothed sharks. We also argue that, under a biological species concept, it is not possible to recognize subgenera and subspecies in the fossil record. Therefore, we reject these confusing and somewhat subjective designations. Otodontids do likely represent a chronospecific sequence, with individual species derived from a pattern of development that replaces one species with another sequentially through geologic time by incremental morphological and genetic changes (Applegate & Espinosa-Arrubarrena, 1996; Cappetta, 2012). This mechanism results in a descendant that is much different from its original ancestor, however when looking at smaller time intervals, species distinctions are much more difficult to discern. In the absence of a phylogenetic or a more thorough morphometric analysis, and until further work is conducted and published, we refer the unserrated form to Otodus obliquus and serrated forms to the genus Carcharocles.

Bottom Line: Carcharocles auriculatus is more common in the Eocene deposits of Alabama, but its occurrence has been largely overlooked in the literature.We also refute the occurrence of the Oligocene Carcharocles angustidens in the state.Raised awareness and increased collecting of under-sampled geologic formations in Alabama will likely increase sample sizes of O. obliquus and C. auriculatus and also might unearth other otodontids, such as C. megalodon and C. chubutensis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Alabama Museum of Natural History , Tuscaloosa, AL , USA.

ABSTRACT
The Otodontidae include some of the largest sharks to ever live in the world's oceans (i.e., Carcharocles megalodon). Here we report on Paleocene and Eocene occurrences of Otodus obliquus and Carcharocles auriculatus from Alabama, USA. Teeth of Otodus are rarely encountered in the Gulf Coastal Plain and this report is one of the first records for Alabama. Carcharocles auriculatus is more common in the Eocene deposits of Alabama, but its occurrence has been largely overlooked in the literature. We also refute the occurrence of the Oligocene Carcharocles angustidens in the state. Raised awareness and increased collecting of under-sampled geologic formations in Alabama will likely increase sample sizes of O. obliquus and C. auriculatus and also might unearth other otodontids, such as C. megalodon and C. chubutensis.

No MeSH data available.