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Body Size Evolution of Echinoderms

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Echinoderms are a large, diverse phylum of exclusively marine invertebrate animals.  Echinoderms include groups commonly found in today's oceans like sea stars and sea urchins, groups like the sea lilies (crinoids) that still around today but less common and extinct groups, many of which are bizarre looking.  Five groups of History of Life Interns studied
the evolution body size in Echinodermata in 2013.

echinoderm starfish fossil
Echinoderm starfish fossil

Intern Research Projects Presented at the 2013 AGU Meeting

Blastoid Body Size – Changes from the Carboniferous to the End-Permian

by Long Nguyen and Rufhiline Tolosa

Climate, known for affecting biodiversity within genera of animal species, is often addressed as a major variable of geological systems. The Mississippian subperiod of the Carboniferous was noted for its lush, tropical climate that sustained a variety of biological life. In contrast, the Permian era was marked primarily by an ice age that had started earlier during the Pennsylvanian. The blastoids, a class of the Echinodermata phylum, were in existence from the Silurian (443.4 Ma) to the end of the Permian (252.28 Ma). This study focused on whether climate affected blastoid theca size over the span of those one hundred million years between the Mississippian and the Permian or if was simply a negligible factor. We analyzed size data from the Treatise on Invertebrate Paleontology and correlated it to both Cope’s Rule, which states that size increases with geologic time, and Bergmann’s Rule, which states that latitude and temperature are catalysts for size change. CO2 levels from known records served as a proxy for global temperature. Our results indicated that the blastoids increased in size by 59% over geologic time. The size of the blastoids increased over geologic time, following Cope’s Rule. According to our graphs in R, there was an inverse relationship between volume and climate. Size decreased as temperature increased, which follows Bergmann’s Rule. However, we also wanted to observe spatial factors regarding Bergmann’s Rule such as paleolatitude and paleolongitude.  This info was taken from the Paleobiology Database and showed that a majority of the blastoids were found near the equator, which, according to the other part of Bergmann’s Rule, suggests that they would therefore increase in size. Further tests implied strong correlations between temperature, volume, and paleolocation. We ultimately believe that although Cope’s Rule is in effect, Bergmann’s mechanisms for size may not apply to the blastoids due to the environments that the blastoids lived in or their anatomical compositions.

Studying the Body Sizes of Echinoidea during the Mesozoic Era

by Edgar Tenorio, Saigopini Panneerselvam, Adyota Gupta

  • We are studying which of the two principles, Bergmann’s rule or Cope’s rule, is dominant in the class Echinoidea during the Mesozoic Era.
  • Because CO2 is a greenhouse gas, we used rCO2 as a proxy for paleotemperature.
  • We found that rCO2 and max area had a small, but significant, negative correlation, proving Bergmann’s rule, but showing that there are other significant factors affecting the body sizes of Echinoids during this time period.
  • After plotting the sizes against the latitude, we found that these two factors had an inverse correlation during the Jurassic and Cretaceous periods. Therefore, Bergmann’s rule does not apply to the class Echinoidea during the Mesozoic.

Effect of environmental variables on body size evolution of crinoids between periods of mass extinctions

by Trisha Jani

  • Earth’s history documents 5 major mass extinctions: Ordovician-Silurian, late Devonian, Permian, Triassic-Jurassic, Cretaceous-Tertiary
  • There have been documented changes in CO2 concentration, O2 concentration, and sea level
  • Environmental changes may affect body size: alter fitness and sustainability in local area
  • Graphs provide visual correlation between these 3 variables and average crinoid area
  • CO2 concentration has greatest effect on size in periods between mass extinctions, followed by sea level, and lastly O2
  • Body size evolution trends follow unbiased random walk or stasis in between mass extinctions
  • Never follows driven trend

Studying the Relative Strengths of Environmental Factors that Influence Echinoderm Body Size Trends

by Andrew Low and Sahej Randhawa

  • Body size is often a useful metric in observing how a clade responds to environmental changes. Previous research has uncovered how environmental factors such as carbon dioxide and oxygen levels influence body size evolution.
  • However, we wanted to look into how these natural factors interact and which factors seem to have a stronger relative influence on echinoderm body size. We analyzed carbon dioxide levels, a proxy for paleotemperature, oxygen levels, and sea level.
  • We divided our data into the following three subsets to uncover more specific relationships: 1) A set that included all echinoderm data in the phylum Echinodermata 2) A set that focused on the two classes with the most recorded data, Echinoidea and Crinoidea 3) A set that focused on the crinoid specimens that originated in the Paleozoic and in the post-Paleozoic.
  • We found incredible diversity in body size responses to environmental factors within echinoderms.

Mass extinctions show selective patterns in crinoid body size

by Alondra Soto, Cathy Tang and Mayra Pelagio

There have been five major extinctions on planet Earth: the end of the Ordovician, late Devonian, late Permian, late Triassic and the late Cretaceous and through all of these, Crinoids have still managed to prosper.  Our project attempts to find a correlation between these five mass extinctions and the body size of Crinoids.  Past research has shown that bigger animals are more prone to extinction compared to smaller sized ones because of their complex environmental niches.  We hypothesized that small-sized Crinoids would have a higher possibility of survival compared to the larger-sized Crinoids. We first graphed Crinoids’ maximum body size and the five major extinctions throughout time for any visual correlation between them.  We then used t-tests as our statistical analyses to find any differences between the size of survivors and.  There was no mean difference between the mean size of victims and survivors with the exception of the end of the Triassic extinction.  There are many possible explanations for this difference in the end of the Triassic such as 1) a rise in atmospheric CO2, 2) a combination was volcanic CO2 and catastrophic dissociation of gas hydrate, and/or 3) a cooling in temperature and oceanic changes occurred.