Data from: Diverging trends in erythrocyte size elucidate cardiovascular evolution in stem dinosaurs and crocodilians
Data files
Aug 11, 2025 version files 13.95 KB
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Byrne_ESM.txt
11.71 KB
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README.md
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Abstract
Red blood cell (RBC) size constrains the rate of diffusion of gases between 1) the environment and the capillary beds of the gas exchanger, and 2) the blood and organs. In birds, small RBCs with a high surface area to volume ratio permit a high O2 diffusion capacity and facilitate sustained, vigorous exercise. Unfortunately, our knowledge of archosaur cardiovascular evolution is incomplete without fossilized RBCs and blood vessels. However, muscle capillary diameters closely match RBC width and, importantly, these microvessels leave a signature in bone in the fossil record. Here, we ask: do fossilized, histological indicators of RBC size, combined with phylogenetic information, support divergent patterns of cardiovascular evolution in Mesozoic crocodile-line and bird-line archosaurs? Building on a published dataset, we used vasculo-lacunar histometrics and phylogeny to retrodict RBC sizes in 20 extinct and 20 extant tetrapods. Our results indicate decreases in RBC size within the archosauromorph Prolacerta and in bird-line archosaurs (Avemetatarsalia). Conversely, crocodile-line archosaurs (Pseudosuchia) that transitioned to an aquatic environment demonstrated increases in RBC size. These patterns offer an opportunity to probe physiological hypotheses regarding archosaur cardiovascular evolution and can explain, in part, the contrasting aerobic capacities of extant species in these two major archosaur lineages.
Diverging trends in erythrocyte size elucidate cardiovascular evolution in stem dinosaurs and crocodilians
We use bone histology to model evolutionary trends in red blood cell size in extinct archosaurs. The early-diverging archosauromorph Prolacerta
and all bird-line (Avemetatarsalia) archosaurs show significant reductions in red blood cell size compared to other non-avian reptiles, suggesting that the
last common ancestor of archosaurs may have exhibited higher exercise capabilities and aerobic thresholds. Greater aerobic capacities may have allowed bird-line
archosaurs to be adaptable to tumultuous climatic extremes. In contrast, red blood cell size increased in the croc-line (Pseudosuchia) archosaurs with a
secondarily aquatic lifestyle, consistent with relaxed demands on oxygen diffusive capacity and lower oxygen needs during aquatic exercise.
Raw RBC and Histometric Data: Byrne_ESM
Code Language: R
Code Location: Byrne_ESM.txt
Raw Histometric Data Unit Information: Our histometric and blood smear data are are both recorded in µm.
To run code, set working directory, install necessary packages (i.e., MPSEM, evobiR, phytools, Metrics, ape, MASS, maps), download our data (S1), then,
begin to run code. Our workflow first adds in the data, extracts the eigenvectors from our data, and then integrates selected histometric variables with our data to
form a phylogentic eigenvector map. This will use the histometric data, as well as the structure of the phylogenetic tree, to predict the missing data with greater accuracy.
Included in this README is a key to interpret our raw data, available in "Byrne_ESM":
- Line #s 1-41: the species, lnRBClength, width, and area from the blood smear data (extant taxa (#s 1-20)), followed by our histometric data (lnOsteocytevol, lnHarmeanCanaldiameter, lnMinCanal) for our both our extinct and extant taxa.
These were derived from our thin section data, and are the data used to calculate RBC size in our extinct taxa. - Lines #s 42-191 contain our R code, which was used to generate the Phylogenetic Eigenvector Maps (PEMs).
Special Note: Empty cells are not applicable, as they do not denote missing data, but are just a product of spaces included in our txt. file.