North American Record

The North American fossil record includes tooth-designs attributed to:

In general, the Squalicorax dentition-design is most often compared with that of Galeocerdo -- gradational monognathic heterodonty of multi-purpose cutting-like teeth. Tooth-design actually spans a broader range, reflecting designs seen in the upper files of various Recent Carcharhinus and Sphyrna taxa. The more primitive Squalicorax tooth-designs tend to have narrower and more: distally inclined cusps, differentiated heels and bilobate roots. In younger taxa, the cusps broaden and become more erect, the heels less defined and root lobes less differentiated. The most "advanced" design is reflected by S. "pristodontus"; in these teeth, the bilobate root-design is largely lost and the root is labio-lingually compressed. The cusp is broader, the heel weakly differentiated and the serrations much stronger, a design similar to the upper teeth of the bull and dusky shark.

Despite the large study-sets and extensive research by both Siverson and Shimada in recent years, neither author has tendered a Squalicorax dentition-set or even proposed a means of distinguishing upper and lower teeth. This 'safety-net' of ambiguity is equally problematic as the overlooked/under appreciated characteristics as expressed by Siverson et al (2007). These key characteristics include:

Upper Late Cretaceous (Santonian-Maastrichtian)

Squalicorax lindstromi (DAVIS, 1890). Generally, small Squalicorax teeth from the Santonian-Campanian of NA with a notched distal edge were referred to as "falcatus" and/or "kaupi", depending on author. Einarsson et al (2010) resurrected the usage of S. lindstromi for a tooth design often placed in one of the preceding wastebaskets in North America. Bourdon et al (2011:15) note that positional tooth-designs, as figured by Davis (1890:412-13, pl. XLII, figs 3-11), are represented in the Santonian of New Mexico and Mississippi, and Campanian of the East Coast (pers. obs.). The crown has a sub-triangular distally inclined cusp and distal heel; the mesial margin is usually convex but may be slightly concave apically; the distal margin is nearly straight; serrations are small and homogeneous. Santonian examples lack a incised distal notch. The root is high and bilobate; the labial face below the crown includes multiple foramina. (This is one of those observations made by Siverson years ago. It wasn't until last year that it was finally published.)

In the below images, some specimens reflect variations of unknown relevance,

Squalicorax "pristodontus" (AGASSIZ 1843). This tooth-design is generally viewed as a large Squalicorax with homogeneous serrations which lacks a strong distal notch. The lateral margins of the crown extend to or may bulge beyond the root which appears more massive than in "kaupi". Smaller teeth are more problematic in that ontogenetic variations may prove less definitive. Queried below (Fig. ) is a specimen which includes erect distal and basally curved mesial (this may only be an artifact of the lack of wear) serrations. The "pristodontus" serrations are typically simplex; however, a Coon Creek (L Camp) example (Fig. ) has complex serrations. Shimada & Cicimurri (2006) reported S. pristodontus from Early Campanian Pierre Shale (SD) and Niobrara Chalk (KS).

Squalicorax cf yangaensis (DARTEVELLE & CASIER, 1943). The below images (Fig. - ) are of a tooth-design often referred to in the Eastern US as S. bassanii and are similar in size and shape to "kaupi" but with a mesial 'heel'; the distal heel is rather elongated and rather than the homogeneous serrations of "kaupi" & "pristodontus", those above the mesial heel are enlarged and often ragged (may be complex). Based on Gemmellaro's (1920) illustrations, the distal heel ('mammellone') of S. bassanii is much shorter than seen in cf yangaensis and the 'hump' of the mesial edge more pronounced.
Mikael Siverson (pers coms, 1999) reviewed images of NC specimens and noted:

".. occasionally get the mesial notch on anteriors in S. kaupi (from which S. bassanii is most likely derived) as well. True S. bassanii teeth have the mesial notch IN COMBINATION with a very marked increase in labiolingual thickness of the tooth.... I strongly suspect ... belong to another, similar looking anacoracid, more closely related to S. yangaensis (DARTEVILLE & CASIER, 1943). In true S. bassanii the cusp and the neck are broader and the basal edge of the root is less scalloped."

Figures in Darteville & Casier (1943 pl 1) show some slight differences between the North Carolina specimens and yangaensis. A large group of S. cf yangaensis specimens from the Santonian of Mississippi (including ontogenetic variations) compare very well with both the Darteville & Casier figures and specimens from North Carolina. Meyer (1974: 305-06) included this tooth-design as Squalicorax sp. aff. S. kaupi from Mississippi. S. yangaensis was first reported in North America by Wolberg & Bellis (1989) from the Late Cretaceous Dalton Sandstone of New Mexico.

Squalicorax "falcatus" (AGASSIZ 1843):

Unlike Siverson who cringes at the usage of S. falcatus in NA, I find it a useful albeit misleading nomenclature as long as it is viewed as a bucket representing a large tooth design-envelope (misleading when lacking quotation marks).

S. hartwellii (COPE 1872): If falcatus had been inappropriately used in North America, appropriate nomenclature is required.

Although hartwellii may be more appropriate than falcatus for this tooth-design, it raises questions as well. Cope's type specimen has a low, broad, relatively erect cusp; only represented in the first (significant) tooth position in the below (Fig. ) associated tooth-set. In Williston's representative tooth-designs (Fig. ), multiple examples have short rather erect cusps, including roots which suggest multiple tooth-positions. These teeth are not present in the associated tooth-set included as S. ? hartwellii below (and from the low chalk). Siverson (pers. com. 2009) views these differences as chrono-variations (evolutionary trends); caused by the intermix of specimens from the high and low chalk.

S. ? hartwellii : Because S. hartwelli (as represented by Cope's type material) cannot account for the most typical "falcatus" dentition-design (as represented in the below associated tooth-set; Fig. ), and many of those positional shapes are present in Williston's plates, it stands to reason another 'dentition-design' (not to be confused with 'taxon') is represented in the fauna. What is unknown to this author is whether this 'different' dentition-design represents another species, chrono-variation (as suggested by Siverson's research) or merely sexual dimorphism. As long as the "falcatus" bucket is indiscriminately used, the true nature of the Squalicorax Interior Seaway's paleo-history will remain cloaked.

Early Cretaceous (Albian)

The Cretaceous of Texas has a diverse group of anacoracids as reported by Welton & Farish (1993), Cappetta & Case (1999) and Siverson et al (2007). In addition to taxa currently reported from the Inland Sea, these more southerly waters include Squalicorax baharijensis, S. pawpawensis, S. priscoserratus and at least one undescribed species. Ed Swiatovy provided and Mikael Siverson identified examples included below. The pawpawensis tooth-design is more common and includes a broader neck and more gradationally mesial serrations. S. priscoserratus teeth have a narrow neck and more homogeneous serrations of the mesial edge, which may range from nearly smooth to coarse.

Aknowledgements

I'd like to thank individuals that helped-out and/or provided specimens used in this page -- Tom Caggiano, Howie Cohn, Pieter De Schutter, Kim Greene, Gary Grimsley, Gordon Hubbell, Earl Manning, George Phillips, Ed Swiatovy, Keith Wright, the Mississippi Museum of Natural Sciences and Miss. Geological Survey. Most importantly is the decade of comments, suggestions and identifications provided by Mikael Siverson.

Footnotes

1.

The text for Williston's (1900) plate XXXII states: "Figs. 1-1l - Corax falactus Agassiz, from a single individual". Although they may have been associated when found, this tooth-suite includes neither teeth of a single individual nor a single taxon. Siverson (pers com 2009) noted that only 1g appeared to be S. hartwellii in design and most of the others closer to S. lindstromi.

Selected References