If a particular shark tooth were to be chosen as an index fossil for the Late Cretaceous of North America, the crow shark, Squalicorax, would be an ideal donor. These teeth are both abundant and readily identifiable to genus, even when damaged or water-worn. Having a worldwide distribution, their fossil record includes skeletal remains attributed to S. falcatus, pristodontus and kaupi as well as isolated teeth and vertebral centra. They are placed in the family ANACORACIDAE, but there isn't unanimous agreement as to the order to which this family should be ascribed. Cappetta (1987: 109-110) provided his reasons for choosing Lamniformes. Shimada & Cicimurri (2005:256-57) included a good overview of this topic, but found no definitive characteristic; they concluded by citing Compagno (1988:404) - Squalicorax was a lamnoid with carcharhinoid-like adaptations.
Cappetta (1987:109-10) consolidated into Squalicorax various serrate anacoracid teeth previously included in genera such as Anacorax, Eoanacorax, Microcorax, Palaeocorax, Palaeoanacorax, Paraanacorax, Praeptychocorax and Sinkorax. He noted that the Russian genera were artificial, overrelying on stratigraphy rather than morphology, and that "all generic separations were premature". This advice was largely taken; Siverson et al 2007 described two new species (pawpawensis & priscoserratus) and included them in Squalicorax; Shimada (2008) took a similar conservative approach with S. microserratodon. Underwood & Cumbaa (2010:934-35) broke with this practice by resurrecting Palaeoanacorax and including in that genus microserratodon, pawpawensis, priscoserratus, volgensis and other small species. Palaeoanacorax volgensis (type, Ceno.) certainly appears morphologically distinct from Squalicorax pristodontus (type, Maas.) and the downside of this decision minimal -- one large wastebasket exchanged for two (albeit more useful) smaller ones. Bourdon et al (2011:11-15) erected Scindocorax novimexicanus for small serrate anacoracid teeth with a morphology distinct from both groups discussed above.
Shimada & Cicimurri (2005) included a detailed study of skeletal remains of Squalicorax from the Cretaceous inland sea of North America. This research allowed them to draw certain conclusions on "falcatus", "kaupi" and "pristodontus":
Medium to large in size; skeletal remains of two to three meter individuals with isolated centra suggesting the possibility of lengths reaching five meters.
Neurocranial features reflect a taxon that relied more on smell than sight.
Placoid scale design associated with fast swimming sharks.
Dentition-design suggests feeding dynamics similar to modern tiger shark, but with the potential of greater biting force. There was no evidence of the presence of an anterior hollow (bulla). The enlarged teeth of pristodontus are partially the result of a lower tooth-count, not solely body size.
Broad head with short, blunt snout and five branchial arches.
Circular vertebral centra indicates a pelagic, not benthic, genus.
North American Record
The North American fossil record includes tooth-designs attributed to:
S. baharijensis STROMER 1927: Reported by Case & Cappetta 1999 from the Cenomanian of Texas, Siverson et al (2007: 942) included this tooth-design as Squalicorax aff. S. baharijensis. Spielmann et al (2011: 387, figs. 3a-h) included S. ? ?baharijensis from the Cenomanian of NM.
S. bassanii (GEMMELLARO 1920): Known from North Africa and the Middle East (see S. yangaensis below).
S. curvatus (WILLISTON 1900): Reported from the Cenomanian through Coniacian of the gulf and Interior Seaway. Siverson et al (2007:945) were highly dubious of the validity of this taxon and deemed specimens depicted in Welton & Farish (1993: 116) to represent the North American "falcatus"-design and baharijensis.
S. "falcatus" (AGASSIZ 1843): A paleo-bucket for a general tooth-design found in more than one taxon from the lower Late Cretaceous of NA. [See below.]
S. hartwellii (COPE 1872): A taxon erected for a specific tooth-design (usually included as "falcatus") from the Niobrara Chalk -- the favored interpretation of Siverson. [See below.]
S. "kaupi" (AGASSIZ 1843): Formerly used for Santonian-Maastrichtian Squalicorax teeth of the East & Gulf Coasts and Interior Seaway. In North America, multiple tooth-design variations have been reported as Agassiz's Corax kaupi -- none of which show detailed representative tooth-sets. The usage of this name can only be viewed as a paleobucket at this time, albeit one that is growing smaller. [See lindstromi and yangaensis.]
S. lindstromi (DAVIS 1890): Santonian-Maastrichtian of the East & Gulf Coasts and southern Interior Seaway. Depending on author, this tooth-design may have been identified as S. kaupi or S. falcatus. [See below.]
S. microserratodon SHIMADA 2008: Small (<5mm class) anacoracid teeth from the Smoky Hill Chalk of Kansas (?Coniacian) based on a 18 associated teeth.
S. pawpawensis SIVERSON et al 2007: Erected for anacoracid teeth from the upper Albian of Texas. This tooth-design is represented by most of the Welton & Farish (1993: 121) Squalicorax sp and a portion of the the Cappetta & Case (1999: 14) S. volgensis specimens.
S. priscoserratus SIVERSON et al 2007: Erected for anacoracid teeth from the upper Albian of Texas; includes the first two teeth depicted by Welton & Farish (1993: 121) as Squalicorax sp.
S. "pristodontus" (AGASSIZ 1843): Early Campanian - Late Maastrichtian of the East & Gulf Coasts and Interior Seaway. [See below.]
S. volgensis (GLIKMAN, in Glikman and Shvazhaite 1971): Reported by Case & Cappetta (1999: 14) from the upper Albian through lower Coniacian of Texas. Siverson et al (2007: 14) included these designs in their newly erected taxa (priscoserratus & pawpawensis).
S. cf yangaensis (DARTEVELLE & CASIER, 1943). Teeth of this design are common near the Santonian-Campanian boundary of Mississippi and Campanian of North Carolina. Along the East Coast, these teeth were often referred to as S. bassanii. [See below.]
undescribed: At least one readily recognizable yet undescribed taxon exists in the Coniacian-Santonian of the inland sea. The propensity to lump teeth into generalized form-designs and a lack of attention to detail, as discussed in Siverson et al (2007: 948-49), suggests the above list should grow/change over time.
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:
root surface porosity and
Upper Late Cretaceous (Santonian-Maastrichtian)
East of the Rockies, the NA Upper Late Cretaceous record for Squalicorax was primarily limited to: S. falcatus, kaupi, pristodontus and the occasional mention of S. yangaensis. Williston 1900 shoe-horned NA tooth-designs into European names. Bilelo (1969) preferred having S. kaupi limited to the Cenomanian, falcatus for the Ceno.-Sant. and pristodontus for Camp. & later. Meyer (1974) viewed taxa as age-based favoring S aff kaupi for the Santonian, kaupi for the Campanian and pristodontus for uCamp-Maas. Some authors seem to prefer S. falcatus for Coni-Sant, kaupi for Camp-Maas and pristodontus in the Maas.
It is rarely possible to unwind the conclusions drawn by various authors from a published work: inconsistency of rules and/or their application, and a lack of sufficient quantity or perspectives of, and/or detail in, the images. In the Santonian of Mississippi and New Mexico, at least two Squalicorax species are present lindstromi and yangaensis; and the record of each extends at least into the Campanian. Little remains resolved in the Western Interior Seaway. S. kaupi as applied to FHSM VP-2213 (Fig. ) is not represented by lindstromi or yangaensis. S. falcatus is also used for a dentition design referred to herein as S. hartwelli.
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,
figure displays an deep distal notch with an enlarged first serration of the heel,
figure reflects a mesial edge which falls short of the root margin,
figure shows an oblique distal 'notch' & straight heel, and
figure depicts a lindstromi-like tooth (small homogeneous serrations but with a mesial heel).
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.
Lower Late Cretaceous (Cenomanian-Santonian)
The Atlantic-centric nature of elasmo.com makes it more difficult to fully evaluate older horizons as represented in Texas and the Interior Seaway; however, it sometimes makes it easier to step back and view the discussion from a different perspective. The below comments only partially address Squalicorax teeth from the Lower Late Cretaceous.
Squalicorax "falcatus" (AGASSIZ 1843):
Agassiz (1843); Figure below depicts the tooth suite provided for falcatus by Agassiz; note that the distal edge is relatively straight and distal notch rather angular (sometimes acute).
Leidy (1873: pl. 8, figs. 29-43) used Galeocerdo falcatus for various Squalicorax tooth-designs (Fig. below) from Texas, Kansas and Mississippi; a few of these resemble Agassiz's falcatus.
Williston (1900: 252) limited Corax falcatus to its current usage in North America -- small homogeneous serrations with a generally oblique distal notch; in doing so he synonymized Cope's S. hartwelli (below). His plate XXXI tooth-suites (fig ) and plate XXXII "associated" teeth1 (fig, below) reflect teeth with a convex distal edge and obtuse notch -- few if any of these teeth compare well (most very poorly) with Agassiz tooth-suite.
Glikman (1980: 107) designated Agassiz's plate 26a.1 (BMNH P. 4465) specimen as lectotype for falcatus (see Siverson 1996: 844). The specimen was from the Chalk at Lewes (Turonian), East Sussex, England and figured in Siverson et al (2007: 944, text fig 5).
Siverson (pers. com. 2009), having studied the original Agassiz material, is convinced that the NA "falcatus" material reflects more than one species, none of which compare well with the falcatus lectotype and would be better referred to as S. hartwellii (see Fig. below).
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.
Cope (p 355, see Hussakof 1908 p 30 fig. 6 -- Fig. above) erected Galeocerdo hartwellii for a tooth-design from the Niobrara Chalk (Ft. Wallace area, high chalk) that NA paleontologists would now refer to as "falcatus" but differs significantly from Agassiz's tooth-suite (as discussed above).
Williston (1900: 252) found Cope's type example to correspond with at least part of his material (particularly his pl. XXXI fig. 23 - Fig above); indirectly synonymizing them with his perception of falcatus.
Siverson (pers. com. 2009), based on the falcatus lectotype which doesn't compare well with the NA "falcatus" usage, suggested that S. hartwellii is a more appropriate name for this tooth-design (at least in part).
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.
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.
||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. |
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