DOI: 10.5061/dryad.prr4xgxzv
title: Data from: Diverging trends in erythrocyte size elucidate cardiovascular evolution in stem dinosaurs and crocodilians

description: 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.
description: 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": 1. 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. 2. 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.