Diversification of the Neoselachii (Chondrichthyes) during the Jurassic and Cretaceous

Abstract

The Neoselachii are a monophyletic group including all of the extant sharks and rays. They underwent rapid diversification throughout the Jurassic and Cretaceous, going from low-di versity assemblages of members of extinct orders in the Late Triassic to diverse assemblages con taining representatives of most extant clades by the end of the Cretaceous. The known fossil record of Mesozoic neoselachians is composed largely of isolated teeth, with articulated skeletal remains being known from a limited number of sites. The small tooth size of a large proportion of neose lachians, including almost all taxa in existence prior to the mid Cretaceous, led to very poor rep resentation in older publications. Their state of knowledge has improved dramatically since 1970 with the increased use of bulk sampling for isolated dental remains. Despite this, the high pro portion of Lazarus taxa from some stages suggests that the state of knowledge is still intermittent. Increase in assemblage diversity throughout the Jurassic and Cretaceous suggests that radiation events resulted in real and dramatic increases in diversity, and that the perceived diversification is not an artifact of poor knowledge. Cladogenesis inferred from the fossil record typically com pares more favorably with divergence predicted from molecular analysis, where Batoidea form a discrete basal clade, than with divergence predicted from morphological analysis, where Batoidea are considered a derived crown group within the Squalea. The timing of diversification events is discussed in light of the known fossil record, cladistically generated divergence times, and the paleoenvironmental distribution of faunas.

Node age estimations and the origin of angel sharks, Squatiniformes (Neoselachii, Squalomorphii)

“…So far, 34 fossil Squatina species mostly based on isolated teeth have been described (Cappetta 2006). While Underwood (2002Underwood ( , 2006 considered the oldest representative to be of Kimmeridgian age, de Carvalho et al (2008) showed that Late Jurassic squatiniforms all belong to a different taxon, †Pseudorhina. All pre-Kimmeridgian records that have been variously assigned to Squatina were considered to belong to orectolobiforms by Underwood (2006).…”

“…While Underwood (2002Underwood ( , 2006 considered the oldest representative to be of Kimmeridgian age, de Carvalho et al (2008) showed that Late Jurassic squatiniforms all belong to a different taxon, †Pseudorhina. All pre-Kimmeridgian records that have been variously assigned to Squatina were considered to belong to orectolobiforms by Underwood (2006). However, the squatiniform fossil record does not consist entirely of isolated teeth but includes several holomorphic specimens and skeletal remains from different stratigraphical ages throughout their evolutionary history.…”

Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover

“…This was followed by a species-level diversity decline at the J/K boundary, resulting from decreased origination rates and heightened extinction rates (Kriwet & Klug, 2008;Kriwet, Kiessling & Klug, 2009a). However, no major neoselachian clades went extinct at the J/K boundary, and their Early Cretaceous standing diversity was substantially higher than Late Jurassic levels (Underwood, 2006;Kriwet et al, 2009a;Kriwet, Nunn & Klug, 2009b;Guinot, Adnet & Cappetta, 2012;Klug & Kriwet, 2013). A recent study showed that nearly all major extant lineages of sharks were already present in the latest Jurassic or earliest Cretaceous, with the origins of Squaliniformes, Squatiniformes, Orectolobidae, Lamniformes, and Carchariniformes occurring immediately prior to the boundary, and the timing of diversification of multiple important sublineages intimately associated with the J/K boundary (Sorenson, Santini & Alfaro, 2014).…”

Development of understanding of the Mesozoic and Cenozoic chondrichthyan fossil record

“…Samples from Mesozoic rocks (e.g. Underwood andWard 2004, Guinot et al 2013) have yielded teeth absent in coarser samples in mesh sizes of 355m. In these studies, finer mesh sizes only produced additional teeth of species present in coarser fractions.…”

“…In the subsequent century, improvements in knowledge of the diversity of fossil species, their taxonomic affinity and their palaeobiological context has dramatically changed our understanding of fossil chondrichthyan faunas (e.g. Underwood 2006, Guinot et al 2013. Whilst this improvement in knowledge is a global phenomenon, it is especially striking when the shark and ray faunas of Britain, which formed the basis for most of Woodward's work and provided a lot of Agassiz's type specimens are considered.…”