Biology subjects

Brownstein, C. D.

Publications and source records attributed to Brownstein, C. D..

5 recordsLinked to original sources

bioRxiv2025

Geographic distribution of the Birmingham Darter Etheostoma birminghamense

Southeastern North America harbors the richest freshwater biodiversity hotspot in the northern hemisphere and is home to numerous species with extremely narrow ranges. Among these are the six species of the Etheostoma chermocki species complex, which exclusively inhabit small streams spanning fewer than 100 square kilometers in Alabama, USA. One of these species, the Birmingham Darter Etheostoma birminghamense, was described in April 2025 from Valley Creek and its associated tributaries, which extend into the urban core of Birmingham, AL, and its suburbs. At least one population of E. birminghamense is feared extirpated, highlighting the imperilment of this microendemic species. Here, we report the results of recent collections that extend the range extension of E. birminghamense into Little Blue Creek, Nabors Branch, Halls Creek, and localities in the mainstem of Valley Creek. As previously hypothesized, occurrences of E. birminghamense are associated with exhumed Cambrian-Ordovician- and Mississippian-age carbonate units, which in Little Blue Creek appear only as pockets of exposed bedrock at the base of the channel and on the banks. Our observations demonstrate that E. birminghamense is distributed throughout the majority of the Valley Creek drainage, highlighting the need for rapid assessment of its conservation status.

zoology↗

bioRxiv2025

Cryptovaranoides is not a squamate

Accurate reconstruction of the timescale of organismal evolution requires placement of extinct representatives among living branches. In this way, the fossil record has the capacity to revise hypotheses of organismal evolution by producing representatives of clades that far pre-date the age of the clade inferred using phylogenies built from molecular data and previous fossil calibrations. Recently, one fossil with the potential to drastically change current understanding surrounding the timescale of reptile diversification was described from Triassic fissure-fill deposits in the United Kingdom. This taxon, {dagger}Cryptovaranoides microlanius, was originally placed deep within the squamate crown clade, suggesting that many lineages of living lizards and snakes must have appeared by the Triassic and implying long ghost lineages that paleontologists and molecular phylogeneticists have failed to detect using all other available data. Our team challenged this identification and instead suggested {dagger}Cryptovaranoides had unclear affinities to living reptiles, but a crown-squamate interpretation was later re-iterated by the team that originally described this species. Here, we again challenge the morphological character codings used to support a crown squamate affinity for {dagger}Cryptovaranoides microlanius and illustrate several empirical problems with analyses that find this taxon is a crown squamate. Our analyses emphasize the importance of stringency in constructing hypodigms of fossils, particularly when they may be key for proper time calibration of the Tree of Life.

paleontology↗

bioRxiv2024

Cenozoic evolutionary history obscures the Mesozoic origins of acanthopterygian fishes

Sister lineage comparisons provide a valuable tool for understanding evolutionary origins of species-rich clades. Percomorpha, comprising over 18,900 species, represents one of the most species-rich vertebrate clades. However, the phylogenetic resolution of its sister lineage remains unclear, obscuring whether contrasts in histories of diversification provide insights into the factors that gave rise to this clades diversity. Using 887 ultraconserved element loci and Sanger-sequenced nuclear genes, we resolve the phylogenetic relationships of the three closest relatives of Percomorpha-the roughies, flashlightfishes, porcupinefishes and fangtooths (Trachichthyiformes), the squirrelfishes and soldierfishes (Holocentridae), and the whalefishes, bigscales, and alfonsinos (Berycoidei)-and the placement of percomorphs among them. Contrary to expectations from the fossil record, we demonstrate that living lineages of Berycoidei, Holocentridae, and Trachichthyiformes all diversified after the Cretaceous-Paleogene mass extinction. Our findings show that multiple clades in Trachichthyiformes and Berycoidei independently colonized deep ocean habitats during the climatically unstable Eocene and Oligocene and shallow-water reefs during the extensive hotspot migration and faunal turnover of the Early Miocene. Due to their complex evolutionary history, the closest relatives of Percomorpha are not ideal for understanding the origins of this exceptionally species-rich clade.

evolutionary biology↗

bioRxiv2024

The Paleozoic assembly of the holocephalian body plan far preceded post-Cretaceous radiations into the ocean depths

Among cartilaginous fishes, Holocephali represents the species-depauperate, morphologically conservative sister to sharks, rays, and skates and the last survivor of a once far greater Paleozoic and Mesozoic diversity. Currently, holocephalian diversity is concentrated in deep-sea species, suggesting this lineage might contain relictual diversity that persisted in the ocean depths. Yet, the relationships of living holocephalians to their extinct relatives and the timescale of diversification of living species remains unclear. Here, we reconstruct the evolutionary history of holocephalians using comprehensive morphological and DNA sequence datasets. Our results suggest that living holocephalians entered and diversified in deep (>1000 m) ocean waters after the Cretaceous-Paleogene mass extinction, contrasting with the hypothesis that this ecosystem has acted as a refugium of ancient cartilaginous fishes. These invasions were decoupled from the evolution of key features of the holocephalian body plan, including crushing dentition, a single frontal clasper, and holostylic jaw suspension, in the Paleozoic Era, and considerably postdated the appearance of the living familes by 150 million years ago during a major period of biotic turnover in oceans termed the Mesozoic Marine Revolution. These results clarify the origins of living holocephalians as the recent diversification of a single surviving clade among numerous Paleozoic lineages.

evolutionary biology↗

bioRxiv2022

Hidden species diversity in a living fossil vertebrate

Ancient, species-poor lineages persistently occur across the Tree of Life. These evolutionarily unique lineages are likely to contain unrecognized species diversity masked by the low rates of morphological evolution that characterize living fossils [1, 2]. Halecomorphi is a major clade of ray-finned fishes that diverged from its closest relatives over 200 million years ago [3, 4] yet is represented by only one recognized living species in eastern North America, the Bowfin Amia calva Linnaeus. Here, we use double digest restriction-site associated DNA (ddRAD) sequencing and high-resolution computed tomography to illuminate recent speciation in the bowfins. Our results support the resurrection of a second living species of Bowfin with the timing of diversification dating to the Pleistocene. In turn, we expand the species diversity of an ancient lineage that is integral to studies of vertebrate genomics and development [2, 3, 5], yet is facing growing conservation threats driven by the caviar fishery [6].

evolutionary biology↗