A new, exceptionally well-preserved Permian actinopterygian fish from the Minnekahta Limestone of South Dakota, USA

Goodvin

Kolmann

et al. 2023

Nature

Section: Discussionmentioning

confidence: 99%

Exceptional fossil preservation and evolution of the ray-finned fish brain

Goodvin

Kolmann

et al. 2023

Nature

“…However, both groups show extreme morphological specialisations resulting from their long independent evolutionary histories. As a stem actinopterygian separated from the common ancestor of all living species by tens—rather than hundreds—of millions of years 3,29,52,53 , † Coccocephalichthys provides unique information bearing on primitive brain anatomy in ray-finned fishes and sequences of change within the group. Most notably, the brain of † Coccocephalichthys allows us to clarify neurological synapomorphies of the ray-finned fish total group (i.e.…”

Section: Discussionmentioning

confidence: 99%

Exceptional fossil preservation and evolution of the ray-finned fish brain

Goodvin

Kolmann

et al. 2022

Preprint

Brain anatomy provides key evidence for ray-finned fish relationships, but two key limitations obscure our understanding of neuroanatomical evolution in this major vertebrate group. First, the deepest branching living lineages are separated from the group's common ancestor by hundreds of millions of years, with indications that aspects of their brain morphology--like other aspects of their anatomy--are specialised relative to primitive conditions. Second, there are no direct constraints on brain morphology in the earliest ray-finned fishes beyond the coarse picture provided by cranial endocasts: natural or virtual infillings of void spaces within the skull. Here we report brain and cranial nerve soft-tissue preservation in Coccocephalichthys wildi, a ~319-million-year-old (Myr) ray-finned fish. This oldest example of a well-preserved vertebrate brain provides a unique window into neural anatomy deep within ray-finned fish phylogeny. Coccocephalichthys indicates a more complicated pattern of brain evolution than suggested by living species alone, highlighting cladistian apomorphies and providing temporal constraints on the origin of traits uniting all extant ray-finned fishes. Our findings, along with a growing set of studies in other animal groups, point to the significance of ancient soft tissue preservation in understanding the deep evolutionary assembly of major anatomical systems outside of the narrow subset of skeletal tissues.

“…However, little is known regarding the interactions between the mandibular fangs and the palate in most of these taxa. Taxa with these attributes appear to be dispersed through the stem of the ray‐finned fish tree rather than united as a monophyletic lineage of large‐fanged fossil taxa (Argyriou et al, 2022 ; Figueroa et al, 2019 ; Giles et al, 2017 ; Stack & Gottfried, 2021 ). Few of these fishes are sufficiently well preserved to determine how jaw closing accommodated enlarged dentition.…”

Section: Introductionmentioning

confidence: 99%

Fitting fangs in a finite face: A novel fang accommodation strategy in a 280‐million‐year‐old ray‐finned fish

Andrews

2022

Journal of Anatomy

Though Paleozoic ray‐finned fishes are considered to be morphologically conservative, we report a novel mode of fang accommodation (i.e., the fitting of fangs inside the jaw) in the Permian actinopterygian † Brazilichthys macrognathus , whereby the teeth of the lower jaw insert into fenestrae of the upper jaw. To better understand how fishes have accommodated lower jaw fangs through geologic time, we synthesize the multitude of ways living and extinct osteichthyans have housed large mandibular dentition. While the precise structure of fang accommodation seen in † Brazilichthys has not been reported in any other osteichthyans, alternate strategies of upper jaw fenestration to fit mandibular fangs are present in some extant ray‐finned fishes—the needlejaws Acestrorhynchus and the gars of the genus Lepisosteus . Notably, out of our survey, only the two aforementioned neopterygians bear upper jaw fenestration for the accommodation of mandibular fangs. We implicate the kinetic jaws of neopterygians in this trend, whereby large mandibular fangs are more easily fit between the multitude of upper jaw and palatal bones. The restricted space available in early osteichthyan jaws may have led to a proliferation of novel ways to accommodate large dentition. We recommend a greater survey of Paleozoic actinopterygian jaw morphology, in light of these results and other recent reevaluations of jaw structure in early fossil ray‐fins.