Introduction
Jim Bourdon ©2002

Those interested in the evolution of Carcharodon carcharias have traditionally viewed this topic in near boolean terms — the predecessor was megalodon or not. The former group has lost advocates in recent years but there remain those that firmly believe the extant great white was derived from Carcharocles/Carcharodon megalodon. For the later group, the cozy comfort of Isurus as the alternate origin has now been called into question by the reintroduction of Cosmopolitodus. Genetic and now fossil evidence is separating the mako lineage from that of the great white. Even if Cosmopolitodus is accepted, questions will continue: where do species such as planus and escheri get assigned, or when to stop using Cosmopolitodus and start using Carcharodon as the genus?

For such a controversial topic, there seems to be a lack of basic information on the subject. The serious student needs to pair access to an excellent library with the time and money to study far flung collections. This web presentation is intended to make available some of the fossil evidence to interested parties. It is hoped that additional topics can be added in the future.

Two of the problems encountered, when discussing this topic, are associated with names and terminology. In an effort to minimize these issues, several points must be stressed.

Genus & Species Names

It was less confusing when Isurus was generally used and distinctions, when necessary, could be resolved by referring to some as the 'broad-toothed' makos. If these teeth were serrate, they were likely ascribed to escheri. It is no longer a near universal belief that the 'broad-toothed' makos were isurids, but may have been from the great white lineage (Cosmopolitodus). When discussing tooth design, including a genus with the species can bring additional off-topic baggage to the table. For example, if I were to state that a Carcharodon megalodon tooth was big, my observation may be overlooked as the genus is questioned. Therefore, the reader may note that the genus will be omitted whenever possible (i.e. escheri above).

Because other authors will be provided the opportunity to include papers in this presentation, there may be a lack of consistency from one topic to another. I for example will use C. escheri while Lutz Andres will refer to this tooth-design as from I. escheri. When a species is introduced, these alternate names will be noted.

Possibly more confusing will be instances where a commonly used name is abandoned. In 1996, Agassiz's xiphodon (1838 or 43) was resurrected by Purdy for the broad-form teeth of hastalis. ELASMO.COM was an early ascriber to this renaming — it appeared in these webpages that very year. When the basis for this reassignment was made in Purdy et al (2001), the utilization of this name came under additional scrutiny. However, it was rapidly adopted by many and remained a useful shortcut when discussing the two tooth-designs. This honeymoon of acceptance came to an end with Ward & Bonavia's (2001) paper on the Malta fauna. While reviewing these pages prior to release, both D. Ward and M Siverson (pers. coms.2002) strongly objected to the usage of xiphodon, declaring it a nomen dubium¹. Based on their remarks, I as author, will revert to distinguishing between these tooth-designs with the more wordy, broad or narrow-form notations. As editor however, I will show greater flexibility with the usage of this specific name by other contributors.

Terminology

Applegate's (1965) sand tiger tooth terminology when applied to non-sand tigers is problematic. Neither makos nor great whites have a sand tiger dentition-design and shoehorning their teeth into sand tiger file positions doesn't make sense. There are no intermediate teeth in the dentitions of extant members of those genera, and unique teeth, which might be interpreted as 'posteriors', aren't present. Both Carcharodon and Isurus have three teeth originating in the anterior hollows (upper & lower) and from eight to eleven (depending on species and jaw) from the lateral hollows. See Siverson (1999) or Cunningham (2000) for greater detail.

Acknowledgements

From an overall perspective, I'd like to thank David Ward & Mikael Siverson for taking the time to review pages represented in this slide show.

Footnotes

Attempting to be an unbiased bystander, it's tough to properly evaluate paleontological statements of fact. The "is it xiphodon or is it not" argument is a great example. Purdy et al. (2001) attribute I. xiphodon to Agassiz "1838", however Ward & Bonavia (2001) includes it as Agassiz "1843". Both bibliographies are essentially the same — Agassiz 1833-1844.

When faced with hurled citations, many readers (including myself) acquire a glazed look (I wish I had a copy and could read that language). Like politicians, questions or statements are often not directly answered. Authors tender opinions or 'facts' without specifically addressing the other's questions or statements. When reading Purdy et al., their arguments sound well thought out and expressed. Ward & Bonavia's attempts to counter these statements in broad terms that do not easily tie to the original statements. It would appear that Purdy et al's statement "If this specimen still exists, it should be designated the lectotype of this species" equates with Ward's "Leriche includes xiphodon in his synonymy of hastalis and points out the uncertainty of the origin, now lost, of xiphodon. Purdy refers to it as 'from the Bronn collection' but Ward & Bonavia prefered to cite Agassiz as being from the "Gypse of the Paris region," and comments that it is a "terrestrial/fluviate ?Eocene deposit". However, these equations are merely how I interpret their text.

References

Agassiz, L., 1843 (1833-1844). Recherches sur les Poissons fossiles. Text (5 vols; I xlix+188 pp., II xii+310+366 pp., III viii+390+32 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.). Neuchātel.
Applegate, S., 1965. Tooth Terminology and Variation in Sharks with Special Reference to the Sand Shark, Carcharias taurus Rafinesque. Contributions in Science 86: Los Angeles County Museum, Los Angeles, CA, 18 pp.
Cunningham, S. B. 2000. Tooth Study of a Recent Sand Tiger Shark Carcharias taurus (Rafinesque, 1810). ELASMO.COM
Martin, A., 1996. Systematics of the Lamnidae and the Origination Time of Carcharodon carcharias Inferred from the Comparative Analysis of Mitochondrial DNA Sequences. In: A.P. Kimley and D. G. Ainley. editors, Great White Sharks: The Biology of Carcharodon carcharias, pages 67-78. San Diego: Academic Press.
Purdy, R., 1996. Paleoecology of Fossil White Sharks. In: A.P. Kimley and D. G. Ainley. editors, Great White Sharks: The Biology of Carcharodon carcharias, pages 67-78. San Diego: Academic Press.
Purdy, R., Schneider, V., Appelgate, S., McLellan, J., Meyer, R. & Slaughter, R., 2001. The Neogene Sharks, Rays, and Bony Fishes from Lee Creek Mine, Aurora, North Carolina. In: Geology and Paleontology of the Lee Creek Mine, North Carolina, III. C. E. Ray & D. J. Bohaska eds. Smithsonian Contributions to Paleobiology, No 90. Smithsonian Institution Press, Washington D.C. pp. 71-202.
Siverson, M., 1999. A new large lamniform shark from the uppermost Gearle Siltstone (Cenomanian, Late Cretaceous) of Western Australia. Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol 90, pp 49-66.
Ward, D. & Bonavia, C., 2001. Additions to, and a review of, the Miocene shark and ray fauna of Malta. The Central Mediterranean Naturalist 3(3), Malta. pp 131-146.