“Phylogenetic patterns in fossil and living billfishes (Istiophoriformes, Istioiphoridae): evidence from the Central Mediterranean”
By: De Gracia, C., Villalobos‐Segura, E., Ballen, G. A., Carnevale, G., & Kriwet, J.
Summarized by Cianna Geni: Cianna Geni is a biology major at Binghamton University. She is a senior and plans to graduate in May of 2025. She is currently involved in research with Decker College on fall prevention for older adults in Broome County. When she is not working on her schoolwork, she likes to listen to live music, go out to eat with her friends, and dance. She is involved in the Binghamton University dance club where she performs 5 styles of dance: ballet, modern, lyrical, jazz, and contemporary.
Purpose of the paper: This study looked at six billfish species from the Mediterranean Sea during the Late Miocene, which was about seven million years ago. The fossil fish were found in southern Italy. The purpose of the paper is to understand the diversification patterns of billfish through time by looking at the evolutionary relationships between fossil and living billfishes.
Data that were examined: Billfish fossils were collected from the southern part of the Salento Peninsula, province of Lecce, Italy, which is in the south of Italy. This work presents new as well as previously published species. The fossils were studied using linear and cross-sectional measurements of the billfish’s long, sword-like bill, known as the rostrum (Figure 1). The measurements were taken at half (0.5L) and one quarter (0.25L) of the total rostral length (L). The skull, jawbones, and back bones were also measured using previously established methods. To understand how the shape of billfish evolved, the earliest known billfish, known as the Hemingway sarissa, was used as a comparison group. The dataset was previously constructed by De Gracia et al. (2020). It includes information on the physical traits of 105 living billfish from five species, as well as 21 fossils.
Methodology: A Principal Component analysis (PCA) was conducted on 13 rostral variables to examine the data. A principal component analysis is a statistical technique that reduces the dimensions of a large dataset to make a dataset easier to analyze and understand the total variation between the data. The results from the first PCA were used to estimate the straight-line distances between all specimens. To evaluate the similarity between the fossil specimens with living species. the distance from the fossil and each living individual of the same species was measured. A second analysis was done using the same method, using the 0.5 L region of the billfish’s bill. An interactive Bayesian phylogenetic analysis was conducted to examine the billfish. A Bayesian phylogenetic analysis is a statistical method that tests different possible family trees to determine how species are related to one another. Data on physical characteristics and genetic information was usedfor both living and extinct species. DNA sequences for three genes were used for 13 different living species. A total of 55 physical characteristics were included for all of the species in the genetic dataset, as well as 15 extinct species.
Results: The scientists analyzed the differences across species using two points on the billfish’s bill, 0.5 L and 0.25 L. A second analysis was run with just the 0.5 L measurements to include specimens that were missing the tip of the bill. The results did not change when the 0.25 L measurements were removed, indicating that the billfish can be examined using only the anterior half of the rostrum. However, if only the 0.5 L measurements are used, some major shape differences are missed. Through the analysis performed, six different billfish species were identified from the fossils found in southern Italy. Four species were new, Pizzikoskerma salentina, Sicophasma macrocanalata,, Makaira adensa, and Makaira cyclovata. It was found that Pizzikoskerma salentina shares traits with marlins and sailfish. Sicophasma macrocanalata was found to have a completely different bill shape that has never been seen in any living or extinct species. The physical characteristics of Makaira adensa were found to be associated with the blue marlin, with a large, oval bill. In contrast, Makaira cyclovata has a robust, depressed bill that changes to a round shape. The phylogenetic analysis used revealed that the billfish family had several distinct groups. They found that some features appeared in early billfish. These features included a round bill, a slim body, and long dorsal fin. Traits like a larger body size, 13 tail bones, and well-developed tail muscles evolved later and are specific to giant marlins. The results suggest that billfish adapted to become larger, and different billfish species can be grouped together based on bill shape.
Why is this important? This study significantly contributed to the understanding of the evolution of the billfish. It is seen in the results of this study that billfish have adapted to become stronger predators. There have been major changes in their overall size, backbones, and muscles, all making them larger and more fit for hunting prey. Understanding the evolution of these traits can give scientists a better understanding of the role that billfish played in past ecosystems and the role they may currently play in the ecosystem.
Broader Implications: Understanding how the billfish adapted to their environment can help predict how they might respond to future environmental changes, offering insights on their conservation needs. Knowing how the billfish species may adapt and respond to climate change and habitat destruction, for example, can allow for the appropriate conservation efforts to be made. In addition, studying evolutionary adaptations of billfish in relation to other marine species can help us understand the broader evolutionary patterns of marine species. By understanding how other marine predators have adapted to their environment, we can better understand the role environmental factors play in their evolution. This addresses the interconnected roles that marine species have we one another, which can aid in protecting marine biodiversity.
Citation: De Gracia, C., Villalobos‐Segura, E., Ballen, G. A., Carnevale, G., & Kriwet, J. (2024). Phylogenetic patterns in fossil and living billfishes (Istiophoriformes, Istiophoridae): evidence from the Central Mediterranean. Papers in Palaeontology, 10, e1559.