Reassessing Patterns of Morphological Variation among Squalicorax Teeth from Monmouth County, New Jersey

The Cretaceous-aged exposures of New Jersey have long been noted for preserving a rich and diverse assemblage of marine fossils. Among the most abundant of these fossils are teeth of the extinct anacoracid shark, Squalicorax Whitley, 1939. Professional and avocational paleontologists have historically divided New Jersey samples of these teeth into two species, the smaller and more common, Squalicorax kaupi (Agassiz, 1843), and the larger and rarer, Squalicorax pristodontus (Agassiz, 1843). However, differentiating between teeth attributed to these two purported species has proven challenging to numerous researchers. Here, we employ two-dimensional geometric morphometrics to analyze patterns of morphological variation among a large sample of Squalicorax teeth from Monmouth County. We find a high degree of morphological overlap between teeth attributed to S. kaupi and S. pristodontus and demonstrate that differences between these two groups cannot be statistically distinguished from those expected under one continuous ontogenetic series. Further comparisons reveal that all Squalicorax teeth in this collection from New Jersey, including those which had been assigned to S. pristodontus, are morphologically distinct from a sample of teeth from Morocco attributed to S. pristodontus. In light of these findings, we argue against the separation of the Monmouth County material into two species and advocate for the referral of all specimens from these New Jersey localities to Squalicorax sp. aff. S. kaupi. We also argue that the specific epithet, S. pristodontus, is likely a “wastebasket taxon” containing more than one biological species.