The megatoothed sharks have been pretty much beaten to death on this website, however, Carcharocles has long begged for its own genus page. Taxa assigned to Carcharocles continue the morphing of tooth-designs reflected in the Otodus-Carcharocles chronospecies. With that said, this page picks-up where the Otodus page and Segue slideshow left off.

By the beginning of the Middle Eocene, the Palaeocene to Early Eocene species Otodus obliquus (AGASSIZ, 1843) had completed a transition in which the cutting-edge had developed regular and complete serrations. This tooth-design has been ascribed to, and generally accepted as, auriculatus BLAINVILLE, 1818.

Blainville placed this species in Carcharodon SMITH, in Muller & Henle 1838 where it resided until 1923 when it was used as the type for Carcharocles by Jordan & Hannibal. In 1960, Casier dumped the megatoothed sharks (auriculatus through megalodon) into Procarcharodon because he did not accept that the modern Great white shark Carcharodon was related to the megatoothed sharks. He produced a "family tree" suggesting that the Great white shark had evolved from "Isurus" hastalis and that the Palaeocene genus Palaeocarcharodon was also a separate and unrelated lineage.

Glikman (1964) accepted Casier's opinions. He recognized the transition from obliquus to auriculatus and moved the latter and angustidens to Otodus. However Glikman considered the loss of lateral cusplets significant and erected a separate genus Megaselachus for chubutensis & megalodon.

In 1987, Cappetta recognized the auriculatus-megalodon lineage. He pointed out that there was a prior name for the megatoothed sharks with lateral cusps — Carcharocles Jordon & Hannibal 1923. Although they had coined this name, assuming that the cuspleted megatoothed sharks (C. auriculatus and C. angustidens) were ancestors of the Great white shark, their name is valid and has priority over Casier's Procarcharodon. In effect, they did the right thing for the wrong reasons. Moreover they did it first so Casier's Procarcharodon is a junior synonym. Cappetta did not accept that in the angustidens-megalodon transition (the loss of lateral cusplets), a change in genus was of any benefit, so he synonymized Megaselachus with Carcharocles.

Russian workers, particularly Zhelezko (1999) argue that the transition between Otodus and Carcharocles, the acquisition of a serrated crown, is not sufficient to change the genus. This argument has some merit and the debate is not over. In this case the names used are less important than the understanding of the lineage.

Attempts were subsequently made to argue that these megatoothed sharks were ancestoral to the modern Great white and that they should be assigned to Carcharodon1. Although not numerous, advocates of this position still exist but are generally limited to the US.

The Chronospecies

There might seem to be an over abundance of species described for the auriculatus-megalodon lineage, and there is. Some of them are based on limited specimens from problematic horizons and others are well represented circumglobally from multiple horizons. When carefully plotted (design-type/time) there is a gradual progression of the Carcharocles tooth-design from the Eocene to Pliocene — triangularization of the crown, standardization of serrations and disappearance of cusplets. When viewing this data it becomes apparent that the teeth of a single biological species are gradually evolving over time (most evident in the ontogentically adjusted loss of lateral cuslplets2.) This conclusion makes greater sense than the oceans swarming with various megatoothed sharks at any given point in time. However, from a paleontological perspective, there are characteristic-sets that transcend location and are clearly associated with a particular epoch/age. The 'chronospecies' serves that function for descriptive purposes -- a specific name ascribed for a particular characteristic-set. For purposes of this webpage we are including six broadly-defined chronospecies:
 

  • C. aksuaticus (MENNER, 1928) [late Early Eocene]
  • C. auriculatus (BLAINVILLE, 1818) [early Middle Eocene]
  • C. sokolovi (JAEKEL, 1895) [late Middle Eocene to Early Oligocene]
  • C. angustidens (AGASSIZ, 1843) [Early Oligocene]
  • C. chubutensis AMEGHINO, 1906 [Late Oligocene]
  • C. megalodon (AGASSIZ, 1835 or 1837) [Miocene-Pliocene]

    C. aksuaticus occupies the morphospace between the smooth-crowned O. obliquus and the irregularly serrate C. auriculatus. The serrae vary (with stratigraphic time) between very fine crenulations on the basal half of the cutting edge of the principal cusp, to fine but irregular serrae over 75% of the crown. Teeth with very fine crenulations have been called Otodus obliquus var. mugodzharicus ZHELEZKO, 1999. Unfortunately the teeth of the type series of mugodzharicus vary between slightly serrate to fully serrate, so the two forms are probably synonymous with aksuaticus as the senior synonym. It could be possible to slip in an additional species into this transition, for the forms with just fine crenulations on the cutting edge, rather than discrete serrae. Whether these are regarded as serrated Otodus or the earliest Carcharocles is unimportant, a matter of (man-made) terminology. (How many slices can you get out of a loaf of bread?)

    C. auriculatus is a species characterised by large ragged lateral cusps and a crown whose somewhat irregular serrae diminish in size towards the crown tip. It is a rare, short-lived stage in the lineage.

    C. sokolovi has lateral cusplets with fine regular serrae, and a fully serrate crown. The Kazakh species C. poseidoni Zhelezko in Zhelezko & Kozlov, 1999 can be regarded as an early variety of C. sokolovi. The root is wide with a relatively narrow crown.

    The succeeding species, C. angustidens has a wider, less lanceolate crown. The lateral cusplets remain clearly distinct from the cusp. Russian authors (Zhelezko & Kozlov, 1999), blessed with a good fossil record, have subdivided angustidens further, but these subdivisions have not been recognised outside their type areas.

    C. chubutensis is another short-lived chronospecies. It bridges the loss of of the lateral cusps that characterises C. megalodon.

    C. megalodon, as suggested above, is the morphology where the lateral cusplets are absent. Upper teeth of Carcharocles from the Late Oligocene Chandler Bridge Fm. of South Carolina sometimes lack cusplets so technically must be called C. megalodon, however this trend is not normally seen until the Early Miocene.

    The Caveat

    So far this is not too difficult, however the situation is about to get much more complicated. These definitions are based on the adult morphology - the teeth of a fairly mature shark. Juveniles in any one deposit may have teeth of a different, usually more primitive design. Thus in the Middle Miocene Pungo River marl, adult teeth, in the order of 4 inches/10cm long generally lack cusplets (megalodon) whilst smaller teeth (of similar tooth positions) have incipient cusps (chubutensis) or well-developed cusplets (angustidens). So, if we just use shape to describe a species we will fall in a trap of having two or more species in a fauna rather than one.

    In the Miocene, juveniles of C. megalodon have cusps. This is not news; it was pointed out by Menesini in 1974 in her monograph on Maltese sharks' teeth. This makes terminology difficult if one is thinking solely in terms of shape and forgetting that teeth are just part of a whole organism that grows continually though out its life. So one can call a cuspleted-tooth of angustidens design, a C. angustidens, or a juvenile C. megalodon. Which you use depends on whether you are thinking in terms of tooth shape alone, or trying to understand the lineage and the whole animal. Neither are wrong, but we feel that it is important to try to progress beyond a "stamp collecting" mentality.

    By the Early Pliocene, C. megalodon teeth lack cusplets, even in the juveniles. This is a significant stage in the lineage but is not marked by a name change. Perhaps it should be. It marks the stage where new-born megs could feed directly on small marine mammals rather than fish. Ultimately this was a fatal step as it made the lineage too specialised, too dependant on a single, unstable food source.3

    The Dentition

    Carcharocles is known from isolated and/or associated (chubutensis & megalodon) teeth and vertebrae. The teeth become more triangular in shape over time. Prior to the Pliocene, they bear triangular and divergent lateral cusplets diminishing in size in later chronospecies. The dentition begins (aksuaticus through sokolovi) as a tearing-design4 and slowly evolves into a cutting-design. The anteriors are upright, but the laterals (and posteriors) become more inclined distally. Insufficient associated dentitions preclude a precise dental formula. However, it can be generally described as having three upper & lower anteriors and at least eight latero-posteriors. The first five laterals can be readily traced over time, but the difference between them and adjacent anteriors gradually diminishes. Teeth from the reduced posterior positions may vary in count. There appears to have been a loss of file-positions (one or two posteriors) over the ages. There is no evidence, or reason to believe, that this dentition included intermediate teeth5. The accompanying associated dentition provides a guide for establishing tooth position.


    The Teeth

    The crown's enameloid is smooth and the lingual face convex (growing stronger as teeth increase in size). Earlier species have laterally compressed crowns with irregular serrae, the crowns broaden over time and the serrae become smaller and more regular. The simple lateral cusplets of Otodus become serrate (and quite ornate) but gradually diminish in size, disappearing entirely in C. megalodon.6 A distinct neck is always present, but becomes more diagnostic by the Miocene. In Carcharocles, the chevron-shaped tissue scar has become an icon of the genus and indeed the family. The root is robust and clearly displays two strong lobes. In earlier chronospecies the basal margin is U-shaped, this gradually evolves to a more V-shaped appearance. The accompanying images are chrono-snapshots of the evolution of these teeth.

    Footnotes

      1.   Well summarized in Purdy et al 2001.
      2.   The file position is also relevant, cusplets tend to remain present in more distal file positions.
      3.   Small heart-shaped teeth of young C. megalodon are affectionately referred to as "Hubbell teeth" (examples: A | B).
      4.   Cappetta 1987 provides definitons of various dentition-designs. They are also available in the introduction of the Dentition slideshow on this website.
      5.   As used in the text, an intermediate file-group refers to one or more files of teeth residing on the bar or rise that separates the anterior hollow from the latero-posterior (as for example in the sand tigers). This should not be confused with the usage of this term by some authors (i.e., Purdy & Gottfried) wherein the reduced, distal-most anteriors (i.e., the upper A3 of Carcharodon, Isurus and Alopias vulpinus) are referred to as "intermediates".
      6.   The lateral-most files (posteriors) tend to be more conservative in design. For that reason, they may bear cusplets in Pliocene deposits.

    References

        Agassiz, L. J. R. 1833-1844.. Recherches sur les poissons fossiles. Text (5 vols; I., xlix+188 pp., II xii+310+366 pp., III viii+390 pp., IV xvi+296 pp., V xii+122+160 pp.) and Atlas (5 vols; I 10 pl., II., 149 pl., III 83 pl., IV, 61 pl., V, 91 pl.). Neuchâtel.
        Ameghino, F., 1906.. Les formations sédimentaries du Crétacé supérieur et du Tertiare de Pategonie avec un parallèle entre leurs faunes mammalogiques et celles de l'ancien continent. Anales del Museo Nacional de Buenos Aires, 3(15)8:1-508, 358 figures, 3 plates.
        Blainville, H.M.D., 1818. Poissons fossiles. Nouveau Dictionnaire 27. Paris.
        Bruner, J., 1997. El Tiburn Megadiente Carcharodon megalodon De dientes duros y enormes. Mundo Marino Revista Internacional de Vida Marina. Septiembre - Octubre 1997(5):6-11
        Cappetta, H., 1987.. Handbook of Paleoichthyology. Chondrichthyes II: Mesozoic and Cenozoic Elasmobranchii. Gustav Fischer Verlag, Stuttgart and New York, 193 pages.
        Casier, E., 1960.. Note sur la collection des poissons paléocènes et éocènes de l'Enclave de Cabinda (congo). Annales du Musée Royal du Congo Belge, series A, 3(1)2:1-48, plates 1,2.
        Glikman, L.S., 1964.. Akuly paleogena i ikh stratigraphicheskoe znachenie. Akademii Nauk Soyuza Sovetskikh Sotsialisticheskikh Respublik, 1-228 Moscow.
        Glikman, L.S., 1980.. Evolution of Cretaceous and Caenozoic Lamnoid Sharks:3-247, pls.1-33. Moscow.
        Jaekel, 1895. Unter-Tertiare Selachier aus Sudrussland. Trud. Geologicheskago Komiteta, 9(4): 19-35, 2 tabs. S.-Peterburg
        Jordan, D.S. & Hannibal, H., 1923. Fossil Sharks and Rays of the Pacific Slope of North America. Bulletin of the Southern California Academy of Sciences, 22:27-63, plates 1-9.
        Menesini, E., 1974. Ittiodontoliti delle formazioni terziarie dell'archipelago maltese. Palaeontographica Italica. Memorie di Paleontologia, 68(n. ser.3737):121-162, 8 pls, 3 text-figs. Pisa.
        Menner, V. V. 1928. The Palaeogene sharks of Mangyschlak, Emba and from the east of Oural. Bulletin de la Société des Naturalistes de Moscou Section, Géologique vol. 6(3-4): 291-338. Moscow In Russian.
        Smith, in Müller, J. & Henle, J., 1838-41. Systematische beshreibung der plagiostomen. Berlin. Veit & Co., pp 1-38 (1838), pp 39-102 (1839), pp 103-200 (1841), 60 pls.
        Zhelezko , V. I. & Kozlov, V. A., 1999a. The new Palaeogene species Otodus poseidoni Zhelezko sp. nov. (Family Otodontidae, Lamniformes). Materials on stratigraphy and Palaeontology of the Urals Vol. 2. Ekkaterinburg: Urals Branch Russian Academy of Sciences Science Publishing House,. pp 227-231, 2 pls.
        Zhelezko , V. I. & Kozlov, V. A. 1999b. Elasmobranchii and Palaeogene biostratigraphy of Transurals and Central Asia. Materials on stratigraphy and Palaeontology of the Urals Vol. 3. Russian Academy of Sciences Urals Branch Uralian Regional Interdepartment Stratigraphical Comissian, Ekkaterinburg. 324 pp, 61pls

     

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