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Wsb 472x116 Crows006

Squalicorax kaupi from the Mount Laurel Formation.

Squalicorax, also called crow sharks for their habit of scavenging, is an extinct genus of lamniform shark known to have lived during the Cretaceous period. A fully articulated (fully-formed) 1.9 m long fossil skeleton of Squalicorax (S. falcatus) has been found in Kansas, evidence of its presence in the Western Interior Seaway. Large numbers of fossil teeth have been found in Europe, North Africa, and other parts of North America. From the size of its largest known teeth, it can be estimated that Squalicorax pristodontus grew to 5 m (16.5 ft) in length.

OverviewEdit

Squalicorax was a predator, but also scavenged as evidenced by a Squalicorax tooth found embedded in the metatarsal (foot) bone of a terrestrial hadrosaurid dinosaur that most likely died on land and ended up in the water. Other food sources included turtles, mosasaurs, Ichthyodectes and other bony fishes and sea creatures.

Squalicorax 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 of 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.

Squalicorax apparently also scavenged, a feeding mode that has earned them the name "crow sharks" in some circles. Paleontologist David Schwimmer and his co-workers have found direct evidence of Squalicorax scavenging, including a decayed mosasaur vertebral centrum with an embedded Squalicorax tooth and many tooth-scarred tetrapod bones. Recently, Schwimmer found a fossilized Squalicorax tooth embedded in a metatarsal (foot) bone of a juvenile hadrosaur (duck-billed dinosaur). Schwimmer speculates that Squalicorax may have relied on scavenging to provide much of its diet and that competition from predatory marine reptiles may have forced these sharks to scavenge carcasses of large creatures - including those of terrestrial animals that somehow ended up in the water, such as the hapless hadrosaur whose remains he found. This may be stretching the fossil evidence a little too far, as remains of fish prey are far more delicate and rarely preserved than those of tetrapods - and most sharks (including the super predatory Great White) will scavenge, given the opportunity.

According to Shimada, another species of Squalicorax, S. falcatus, scavenged its larger cousin, Cretoxyrhina mantelli. Other food items of S. falcatus include turtles, mosasaurs, the mackerel-like Ichthyodectes, and the swordfish-like Protosphyraena. Shimada suggests that in their broad-spectrum diet, Squalicorax resembled the modern Tiger Shark (Galeocerdo cuvier). In any case, little else is known about Squalicorax. Even having articulated remains with which to work, paleontologists are uncertain how Squalicorax is related to other lamnoids.

DescriptionEdit

Shimada & Cicimurri (2005) includes 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 brachial arches.
  • Circular vertebral centra indicates pelagic not benthic genus.

Western Interior SeawayEdit

Squalicorax sp. Smokychalk1

Squalicorax sp. from the Smoky Chalk Member of the Niobrara Formation, Kansas.

The genus Squalicorax evolved through several "species" during the deposition of the chalk in the Western Interior Seaway, approx. 87-82 million years ago. Squalicorax falcatus is known from the Middle Cenomanian in Kansas. S. kaupi begins to appear in small numbers during the Early Santonian and pretty much replaces S. falcatus in Kansas by the Early Campanian. A few S. pristodontus teeth have been found right at the top of the Smoky Hill Chalk.

DietEdit

The idea of Squalicorax being a scavenger was discussed by Wiley and Stewart (1977) and Schwimmer and Williams (1991). On the other hand, Druckenmiller et al. (1993) reported a partial skeleton of S. falcatus that contained elements belonging to Ichthyodectes ctenodon, turtles, and a mosasaur, all within what are thought to be gastric residues. Druckenmiller et al. (1993) suggested that S. falcatus was an opportunistic feeder in the Niobrara sea, like the extant Galeocerdo. Stewart (1993) reported Squalicorax bite marks on the fin surfaces of Protosphyraena nitida. A more comprehensive survey on the evidence of Squalicorax scavenging activities in North America was recently conducted by Schwimmer et al. (1995, 1997) arguing that the Santonian-Campanian species of Squalicorax were preeminent scavengers of various vertebrate carcasses. My study further supports the idea that species of Squalicorax frequently scavenged dead vertebrates. The addition of Cretoxyrhina mantelli as a food source makes Squalicorax more unspecialized in its diet, favoring the idea of Galeocerdo as a living counterpart of Squalicorax guildwise. Its wide food range allows interpretation that Squalicorax was an important consumer for the early breakdown of energy matter in the Late Cretaceous seas.

SpeciesEdit

ReferencesEdit

Mantell's Iguanodon restoration

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