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Sawskates (Rajiformes, Sclerorhynchoidei) and the concept of pristification

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Tyler Greenfield at University of Wyoming
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December 1–15th, 2021
Book of Abstracts
3rd Palaeontological Virtual Congress
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From an original idea of Vicente D. Crespo
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Date of Publication December 9, 2021
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Book of Abstracts of the 3rd Palaeontological Virtual Congress, 304 pp.
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203
SAWSKATES (RAJIFORMES, SCLERORHYNCHOIDEI)
AND THE CONCEPT OF PRISTIFICATION
T. Greeneld
Webster City, Iowa, United States (no institutional aliation)
*tgreeneld999@gmail.com
Keywords
Sclerorhynchoidei, sawskates, pristication, convergent evolution
Two extant clades of chondrichthyans, sawshes (Pristoidei)
and sawsharks (Pristiophoriformes), convergently evolved saws.
A saw is an elongated, dorsoventrally–compressed rostrum
with lateral rows of enlarged denticles. It functions as both a
sensory organ and a weapon for detecting and dispatching
prey. An extinct clade from the Cretaceous, Sclerorhynchoidei,
also had saws and were previously considered to be sawshes.
However, sclerorhynchoids are distinguished from pristoids by
several notable characteristics. The rostral denticles attached
directly to the edges of the rostrum and were not embedded
in alveoli. They were continually replaced, which resulted in
extreme rostral asymmetry in some genera. Further rows of
large denticles lined the sides of the head and the dorsal side
of the body. The pectoral and pelvic ns were adjoining, both
dorsal ns were located behind the pelvic ns, and the caudal n
was greatly reduced. Additionally, recent phylogenetic analyses
have recovered Sclerorhynchoidei as the sister clade to skates
(Rajoidei). All this evidence indicates that sclerorhynchoids are
a third clade that convergently evolved saws. I propose they
should be called ‘sawskates’ to separate them from sawshes
and emphasize their anities to skates. The repeated evolution
of saws has been recognized but not named, for which I
suggest the term ‘pristication’. These terms are intended for
use in science communication; while specialists are aware of
the relationships of saw–bearing shes, the general public
is usually not. This remarkable case of convergent evolution
should be made accessible to a wider audience.
GENERAL SESSION: MESOZOIC3rd Virtual Palaeontological Congress | December 1–15th, 2021
R
Q
... Here the term 'pristification' is proposed for the repeated convergence of saws in sharks and rays. It was coined previously (Greenfield, 2021b) but is formally defined for the first time. Not only does it highlight a remarkable convergent structure, but it also serves as a template for future terminology. ...
... They were long classified as primitive sawfishes, but were first proposed to be a separate group by Cappetta (1974;1980b). Their close relationship to skates (Rajoidei) was unknown until more recent phylogenetic analyses (Villalobos-Segura et al., 2019;2021a;2021b). They are still often called sawfishes, but this misnomer should be avoided in favor of the more accurate sawskates (Greenfield, 2021a;2021b). ...
... Their close relationship to skates (Rajoidei) was unknown until more recent phylogenetic analyses (Villalobos-Segura et al., 2019;2021a;2021b). They are still often called sawfishes, but this misnomer should be avoided in favor of the more accurate sawskates (Greenfield, 2021a;2021b). They were the most diverse of the three clades, comprising over 20 genera, and they went extinct during the Cretaceous-Paleogene mass extinction (Kriwet & Kussius, 2001;Cappetta, 2012). ...
Pristification: Defining the convergent evolution of saws in sharks and rays (Chondrichthyes, Neoselachii)
Preprint
Full-text available
  • Aug 2023
Saws are elongated rostra with enlarged denticles that are used for hunting and feeding. They convergently evolved in three groups of sharks and rays, the extinct sawskates and the extant sawsharks and sawfishes. Saws and saw-bearing fishes are briefly reviewed here, including their anatomy, ecology, and phylogeny. The term 'pristification' is proposed for this convergence and defined. It is an example of repeated, iso-convergent evolution and is the evolution of a structure without an associated bauplan.
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