The tooth-design traditionally referred to as "Isurus praecursor" has been reported from Eocene sediments of Asia, Europe, Africa and both North and South America. It inhabited waters as diverse as the tropics of Africa to the temperate of Seymour Island, Antarctica. However, as will be seen below, the actual identifications of these teeth as to genus and species has been highly inconsistent and often questionable. The underlying problem appears to be the reliance on tooth-design only as a basis for the identification of these teeth. There will be no attempt herein to resolve the many problems in the published record, but only to argue that the usage of tooth-design only has been a total failure and that dentition-design (a collection of particular tooth-designs) must be employed to better understand these "praecursor" teeth.
The tooth-design most frequently referred to as praecursor has a published record dating to the late 19th century when authors included them with Oxyrhina desori SISMONDA 1849.1 Certain papers are particularly relevant for the published history of this tooth-design.
Leriche 1905 (p. 128) without figuration described Oxyrhina desori var praecursor; the more commonly cited date for this taxon is 1906 when it was fully figured (with illustrations dated 1904). The species was erected for teeth he described as an Eocene variety of O. desori; since the latter is an equally problematic bucket, his illustrations are a more useful visual description of the taxon (see: Fig. & ). Other authors would follow Leriche's lead and refer Eocene specimens to the species praecursor. In 1931, White would be the first to use Isurus as the genus for these teeth.
This generalized description appears to have sufficed, for the next refinement was provided by Leriche (1942) based on Eocene material from Alabama he examined at the Smithsonian. In this paper he adds a couple comments that better distinguish praecursor from desori (teeth are squatter, crown broader and the laterals have two side expansions). He then goes on to erect O. americana for praecursor-like teeth in which the crown is narrower & not very thick, the root is high & compressed and the lobe strongly splayed (particularly in the laterals). He also noted it could be distinguished from the Oligocene design of O. praecursor, mut. flandrica LERICHE 1910 by having a crown which was relatively less high (see: Fig. & ). Western European and American authors continued to use praecursor with no evidence that as to whether americana was even considered.
Dartevelle & Casier (1943: 139; pl. X, fig. 1-13) reported Oxyrhina praecursor from the Eocene of Cabinda & Angola. The included figures suggest these teeth were from juveniles or young adults.
In 1964, in an attempt to better organize fossil lamniforms, Glikman erected Macrorhizodus to include praecursor, americana and flandrica which he perceived as isurids.
Cappetta (1987) included Isurus praecursor and I. desori flandrica, maintaining the strong association of these teeth with the makos.
Case & Cappetta (1990: 8, Pl. 2, fig. 22-39) reported Isurus praecursor from the Upper Middle - Late Eocene of Egypt. This paper included some detailed descriptions of various tooth-positions but made no reference to the papers of Leriche (1942) or Glikman (1964).
Cione & Reguere (1994) extended the range of of praecursor by reporting the taxon from the Middle-?Late Eocene of Seymour Island, Antarctica.
In the late-90s, Siverson and others began to follow Glikman (1964) by ascribing white shark lineage taxa to Cosmopolitodus -- this included not only hastalis-like Neogene teeth, but flandricus from the Oligocene as well.
In 1999, Zhelezko & Kozlov redescribed Zhelezko's Macrorhizodus nolfi for M. americana-like teeth with more defined cusplets from the Ypresian of Kazakhstan. Zhelezko & Kozlov 1999 also included M. americana in the Bartonian of Kazakhstan.
Case & Borodin (2000: 26, fig 21-26) included teeth of the americana-design as Isurus praecursor from the Lutetian of North Carolina.
By 2001, elasmo.com had adopted Glikman's generic names Cosmopolitodus and Macrorhizodus.
Although accepting Cosmopolitodus for hastalis, Cappetta 2006 did not recognize Macrorhizodus or some of the erected taxa noting:
- Macrorhizodus praecursor = Isurus praecursor
- Macrorhizodus americanus = Isurus americana
- Macrorhizodus nolfi = Isurus nolfi
- Cosmopolitodus flandricus = Isurus flandricus
It would be difficult to criticize an author for opting to use praecursor only for these teeth. The underlying descriptions were less than definitive and the noted differences well within the range that might be expected for regional, ontogenetic, individual or sexual variations. Other than Leriche himself, only the Russians appear to have appreciate the subtleties distinguishing these taxa.
If tooth-design cannot be relied on in this matter, dentition-design may prove more helpful. Fortunately, the Hubbell collection includes two associated dentition-sets from Kazakhstan -- Kozlov (Hubbell-Kozlov pers. com.) identified one as M. praecursor and the other as M. americana. These sets show much greater differences in dentition-design than might be inferred from tooth-design only. The accompanying images contrast these two designs.
In viewing the above images, a myriad of positional differences could be presented; however, few of them transcend the normal variations that may be represented in lamnid teeth. The hollow-based variations which would likely prove significant include:
Upper anterior tooth widths: In praecursor, the first three files are of similar (root) width; in Kozlov's "americana", the first position is mesial-distally compressed and the third file (if an anterior) expanded.2
Upper lateral relative tooth-heights: In Kozlov's "americana", the heights of the second and third laterals become more pronounced relative to the anteriors and other laterals.
Lower lateral relative tooth-heights: In praecursor, the first four laterals are very similar in size, while in "americana", the first two are more significant in height and width relative to each other and the anteriors.
These dentition-design variations (if the examples are complete), particularly the first, are much less likely to be subject to the vagaries associated with tooth-design and can serve as a basis for validating and differentiating the species. The tooth-designs as reflected in these Middle Eocene Kazakhstan specimens compare very well with Leriche (1942) figures. Possibly more important, is having a key for specimen identification -- the third file. The elongated mesial lobe of this tooth-position in Kozlov's "americana" can prove highly diagnostic but not necessarily definitive.
These three apparently valid taxa (praecursor, americana and the Ypresian, nolfi) as a group neither fit well into the mako nor white shark dentition-design envelopes, but appear to represent elements of each. Glikman's Macrorhizodus appears to be an excellent place-holder for this tooth-design until much more is known about lamnid evolution.
The North American record
Macrorhizodus teeth have been consistently reported from North American Middle Eocene sediments. The published record includes:
As discussed above, Leriche (1942) erected Isurus praecursor americana for the tooth-design he found present in the Middle Eocene seidments of southeastern North America.
White (1956; 125) included Isurus praecursor americana in his review of material from the Jackson "Formation" of Clarke's County, Alabama.
Case (1981: 57-58, pl 2, fig. 3-5) included this tooth-design as Isurus oxyrhinchus when reporting on the Twiggs Clay Mbr, Barnwell Fm, "Jacksonian" (Eocene) horizons of Georgia (US).
Weems 1984 included Isurus praecursor as present in the Piney Point Formation (Lutetian) of the Chesapeake Bay region.
Ward & Wiest (1990: 84) reported Isurus praecursor from the Piney Point Formation (Lutetian) of the Chesapeake Bay area.
Case & Borodin (2000a: 8, pl. 1 fig. 8-10) reported Isurus praecursor from the Late Eocene Irwinton Sand Member of the Barnwell Formation (Jacksonian), Wilkinson County, Georgia.
Case & Borodin (2000b: 26, pl.3, fig 21-26) included Isurus praecursor from Castle Hayne Fm (Lutetian) of North Carolina.
Parmley et al (2003: 165, fig 4a, 4b) reported Isurus praecursor from the Clinchfield Fm, Barnwell Group (Late Eocene) of central Georgia, USA
Other than Ward & Wiest (1990) which included no figures, none of the bibliographies of these papers reflect an awareness of Leriche (1942) which might explain the continued usage of praecursor for this tooth-design in all cases. In addition, none cite Glikman (1964) suggesting that an alternate generic assignment was not considered.
A Castle Hayne perspective
A preliminary investigation of Macrorhizodus teeth from Sequence 2 (Lutetian)3 of the Castle Hayne Formation suggests that more than one species is present in the fauna. Most positional tooth-designs compare very well with Leriche's "americanus" (ref figures -) and are likely the primary Macrorhizodus species in the fauna.
One of the Castle Hayne positional-designs also compares very well with the third upper file of the Kazakhstan "americana" dentition-set (fig. bottom and ).
However, these Castle Hayne specimens also include a typical lamnid UA3 tooth-design (fig. )4 which is not present in the Kazakh dentition-set(s). This cavaet suggests that either:
the Kazakh "americana" specimen is incomplete or a different species, or
the Castle Hayne material includes a yet to be described species.
There are currently too few Sequence 2 specimens available5 to confidently reconstruct tooth-sets for this fauna; they undoubtedly include M. americana, but others cannot yet be fully differentiated from praecursor or the Kozlov's Kazakh "americana".
Although tooth-designs for these "praecursor"-like specimens have been provided in varying detail by various authors, there have been no published attempts to document dentition-design. As can be seen above (and excluding M. nolfi), there are at least two and possibly three or more taxa sharing components of a single tooth-design envelope. For teeth found outside the relevant type area, it would likely be prudent to include quotes around the specific name until a dentition-set can be established to support attribution to a particular species.
Equally imprudent would be to ascribe these teeth to a modern genus (i.e., Isurus) or lineage (i.e., Cosmopolitodus). The mako and white shark lineages can only be tracked-back on the basis of dentition-design to the Early Miocene; as documented above, relying solely on tooth-design for these early lamnid teeth would be foolhardy. Adopting Glikman's Macrorhizodus for this tooth-design removes a mind-set bias associated with a particular modern taxon and better acknowledges how little we really know about lamnid evolution.
Lastly, the issue of Oligocene teeth needs to be addressed. If both the Eocene and Miocene include multiple lamnid dentition-designs, it is very likely that the less well documented Cosmopolitodus / Isurus flandricus tooth-design may also harbor more than one dentition-design. Glikman (1964) included the flandricus-design in Macrorhizodus, but following that lead would serve to contrast M. flandricus from those teeth referred to as Isurus desori; and by default, make Macrorhizodus a non-isurid lineage (white shark) solely based on the name employed. It would appear that of the remaining alternatives, to include desori in Macrorhizodus or flandricus in Cosmopolitodus, the first would be more logical and the second, more practical. For now, elasmo.com will opt for the latter.
The scope and content of this page would have been impossible without the sharing of specimens, ideas and documentation by numerous persons, these include: Richard Chandler, Pieter DeSchutter, Gordon Hubbell and David Ward. Charlie Underwood, Gilles Cuny and Fabrice Moreau were kind enough to review and provide feedback on this page.
||Case & Cappetta (1990: 8) provide a good listing of many early (Afro-centric) citations.|
||It is very important to note that the tooth-design of the third file appears to be similar to the first lateral position, not the third anterior. The tooth-set lacks an example that corresponds with a typical UA3 suggesting three possibilities: 1) the dentition has only two upper anteriors, 2) the third anterior position is missing from the associated dentition-set, or 3) the third anterior looks like the typical first upper lateral. A definitive conclusion on this specimen can only be based on speculation -- additional comparative material is required. With that noted, typical UA3s are known from the Schorym Fm (see: Fig. ).|
||Discussed specimens were limited Sequence 2 from one locale to minimize the effect of chrono- or regional variations.|
||Case (1981: pl 2, fig. 4) included at tooth captioned to be a lower anterior which also appears to be a third upper anterior.|
||At the time of this writing, only 67 specimens were available, far too few to confidently differentiate more than one similar species.|
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