The actinopterygian fish †Hemicalypterus weiri Schaeffer, 1967 is herein redescribed and rediagno... more The actinopterygian fish †Hemicalypterus weiri Schaeffer, 1967 is herein redescribed and rediagnosed based on new information collected from reexamination of museum specimens as well as examination of recently collected specimens from the Upper Triassic Chinle Formation of San Juan County, Utah, United States. †Hemicalypterus is distinguish-able by its deep, disc-shaped compressed body; ganoid-scaled anterior half and scaleless posterior half; spinose, prominent dorsal and ventral ridge scales anterior to dorsal and anal fins; hem-like dorsal and anal fins with rounded distal margins; small mouth gape; and specialized, multicuspid dentition. This type of dentition, when observed in extant fishes, is often associated with herbivory, and †Hemicalypterus represents the oldest known ray-finned fish to have possibly exploited an herbivorous trophic feeding niche. A phylogenetic analysis infers a placement of †Hemicalypterus within †Dapediiformes, with †Dapedii-formes being recovered as sister to Ginglymodi within holostean actinopterygians.
Fishes have evolved to exploit multiple ecological niches. Extant fishes in both marine (e.g., ra... more Fishes have evolved to exploit multiple ecological niches. Extant fishes in both marine (e.g., rabbitfishes, surgeonfishes) and freshwater systems (e.g., haplochromine cichlids, characiforms) have evolved specialized, scoop-like, multidenticulate teeth for benthic scraping, feeding primarily on algae. Here, I report evidence of the oldest example of specialized multidenticulate dentition in a ray-finned fish, †Hemicalypterus weiri, from the Upper Triassic Chinle Formation of southeastern Utah (∼210–205 Ma), USA. †H. weiri is a lower actinopterygian species that is phyloge- netically remote from modern fishes, and has evolved special- ized teeth that converge with those of several living teleost fishes (e.g., characiforms, cichlids, acanthurids, siganids), with a likely function of these teeth being to scrape algae off a rock substrate. This finding contradicts previously held no- tions that fishes with multicuspid, scoop-like dentition were restricted to teleosts, and indicates that ray-finned fishes were diversifying into different trophic niches and exploring differ- ent modes of feeding earlier in their history than previously thought, fundamentally altering our perceptions of the ecolog- ical roles of fishes during the Mesozoic.
The actinopterygian fish †Hemicalypterus weiri Schaeffer, 1967 is herein redescribed and rediagno... more The actinopterygian fish †Hemicalypterus weiri Schaeffer, 1967 is herein redescribed and rediagnosed based on new information collected from reexamination of museum specimens as well as examination of recently collected specimens from the Upper Triassic Chinle Formation of San Juan County, Utah, United States. †Hemicalypterus is distinguish-able by its deep, disc-shaped compressed body; ganoid-scaled anterior half and scaleless posterior half; spinose, prominent dorsal and ventral ridge scales anterior to dorsal and anal fins; hem-like dorsal and anal fins with rounded distal margins; small mouth gape; and specialized, multicuspid dentition. This type of dentition, when observed in extant fishes, is often associated with herbivory, and †Hemicalypterus represents the oldest known ray-finned fish to have possibly exploited an herbivorous trophic feeding niche. A phylogenetic analysis infers a placement of †Hemicalypterus within †Dapediiformes, with †Dapedii-formes being recovered as sister to Ginglymodi within holostean actinopterygians.
Fishes have evolved to exploit multiple ecological niches. Extant fishes in both marine (e.g., ra... more Fishes have evolved to exploit multiple ecological niches. Extant fishes in both marine (e.g., rabbitfishes, surgeonfishes) and freshwater systems (e.g., haplochromine cichlids, characiforms) have evolved specialized, scoop-like, multidenticulate teeth for benthic scraping, feeding primarily on algae. Here, I report evidence of the oldest example of specialized multidenticulate dentition in a ray-finned fish, †Hemicalypterus weiri, from the Upper Triassic Chinle Formation of southeastern Utah (∼210–205 Ma), USA. †H. weiri is a lower actinopterygian species that is phyloge- netically remote from modern fishes, and has evolved special- ized teeth that converge with those of several living teleost fishes (e.g., characiforms, cichlids, acanthurids, siganids), with a likely function of these teeth being to scrape algae off a rock substrate. This finding contradicts previously held no- tions that fishes with multicuspid, scoop-like dentition were restricted to teleosts, and indicates that ray-finned fishes were diversifying into different trophic niches and exploring differ- ent modes of feeding earlier in their history than previously thought, fundamentally altering our perceptions of the ecolog- ical roles of fishes during the Mesozoic.
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