Jack Stack

Evolution of Paleozoic Ray-Finned Fishes

The majority of my ongoing work focuses on the fossil record of ray-finned fishes (Actinopterygii). I aim to characterize the historical patterns and evolutionary processes that have driven the assembly of their extant biodiversity (over 32,000 species). Unfortunately, the Paleozoic history of this group is poorly understood because of understudy and a spotty fossil record. To address this, I am describing Paleozoic ray-finned fishes from understudied faunas in North America to improve our understanding of the morphology, ecology, and evolution of these problematic early groups of actinopterygians.
I am describing a well-preserved ray-finned fish from the early Middle Permian Minnekahta Limestone of South Dakota. I am applying traditional descriptive methods and microCT scanning to describe the morphology of a taxon represented by an exceptionally well-preserved individual. My goal is to describe the morphology of this taxon and integrate it into an existing framework to examine its phylogenetic placement relative to other early ray-finned fishes. This research will improve the documented fossil record of Permian ray-finned fishes and will help to address the historic paucity of Permian taxa in phylogenetic analyses of ray-finned fishes, helping to stabilize future analyses of early actinopterygian evolution.

depo. map

I am describing a ray-finned fish from the Minnekahta Limestone (Above), which was deposited on the eastern margin of an early Middle Permian marine basin in what is now the Black Hills of South Dakota. After Piper and Link (2002) Figure 1. Scale bar equals 1 km.

Evolution of skull elongation in ray-finned fishes

There are a plethora of distinct skull forms within the ray-finned fishes, which has allowed this group to diversify into a wide range of niches. Characterizing the history and evolution of ray-finned fish skull morphologies has the potential to lend insight into the mechanisms that have driven the construction of their modern diversity. Elongate skull morphologies are prevalent and seemingly repeated forms that are well represented in both the fossil record and extant families. The macroevolutionary patterns surrounding the repeated appearance of elongate skull morphologies are unclear as the degree of convergence between these forms has not been documented nor has their structural diversity been examined.
In a project stemming from my undergraduate thesis research, I (with Lauren Sallan) am surveying the literature to describe the morphology and structural diversity of elongate cranial structures in ray-finned fishes. Our goal is to characterize the pattern of convergent evolution of these structures and to determine if there are broader patterns in skull structure amongst these fishes.

longnose fish

Chelmon rostratus, a long-nosed butterflyfish that I examined while gathering data for my senior thesis research (ANSP 78292).