Nested ANOVA results for colony area.

<p>* = <i>p</i><0.05; ** = <i>p</i><0.01; *** = <i>p</i><0.001.</p>a<p>Negative estimates of variance components associated with non-significant F-ratios were assigned zero values in keeping with standard practice <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087048#pone.0087048-Taylor1" target="_blank">[26]</a>.</p

The Lilliput Effect in Colonial Organisms: Cheilostome Bryozoans at the Cretaceous–Paleogene Mass Extinction

<div><p>Consistent trends towards decreasing body size in the aftermath of mass extinctions – Lilliput effects – imply a predictable response among unitary animals to these events. The occurrence of Lilliput effects has yet to be widely tested in colonial organisms, which are of particular interest as size change may potentially occur at the two hierarchical levels of the colony and the individual zooids. Bryozoans are particularly useful organisms in which to study colonial size response as they have well-defined zooids. Additionally, a number of analyses of present-day bryozoans have shown that zooid size reflects local environmental conditions, most notably seawater temperature and possibly also food supply. Following the hypothesised decline in primary productivity at the Cretaceous–Paleogene (K–Pg) mass extinction, it is predicted that bryozoan zooid size should decline in the early Paleogene, resulting in a Lilliput effect. To test this prediction, zooid size was compared across the K–Pg boundary at the assemblage level and also within 4 surviving genera. Analysis of 59 bryozoan species from assemblages on either side of the K–Pg boundary showed no significant change in zooid length. Zooid size was also measured in 98 Maastrichtian colonies and 162 Danian colonies belonging to four congeneric species. Only one of these genera showed a significant size decrease across the K–Pg boundary, the other three maintaining constant zooidal lengths, widths and areas. Additionally, the sizes of 210 Maastrichtian colonies and 163 Danian colonies did not show consistent size decrease across the K–Pg boundary in these same species, although maximum colony size did decline in three out of four genera. Furthermore, this lack of consistent size change is uniform between two distinct biogeographical regions, Denmark and the southeastern USA.</p></div

Nested ANOVA results for zooid length of all species.

<p>* = <i>p</i><0.05; ** = <i>p</i><0.01; *** = <i>p</i><0.001.</p

Nested ANOVA results for zooid area.

<p>*  = <i>p</i><0.05; **  = <i>p</i><0.01; ***  = <i>p</i><0.001.</p>a<p>Negative estimates of variance components associated with non-significant F-ratios were assigned zero values in keeping with standard practice <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087048#pone.0087048-Taylor1" target="_blank">[26]</a>.</p>b<p>Denominator of the F-test is zero.</p

Mean, minimum and maximum colony size for taxa.

<p>Colony sizes of taxa analysed from the Maastrichtian Prairie Bluff Chalk/Højerup Member (K) and the Paleogene Clayton Formation/Korsnæb Member (Pg). The total number of colonies measured is indicated above each data point. <i>p</i>>0.05 across the K–Pg boundary for each pair.</p

Number of (A) colonies measured, (B) zooids measured and (C) species, from which zooids were measured in Denmark.

<p>Locality abbreviations: H.  =  Holtug Kridtbrud; S.  =  Stevns Kridtbrud; R.  =  Rødvig.</p

Mean zooid width and length for all colonies.

<p><i>Balantiostoma</i>: K = Cretaceous Prairie Bluff Chalk (<i>Balantiostoma nomas</i>); Pg = Paleogene Clayton Formation (<i>B. midwayanica</i>). <b><i>Tricephalopora:</i></b>K = Cretaceous Prairie Bluff Chalk (<i>Tricephalopora larwoodi</i>); Pg = Paleogene Clayton Formation (<i>T. levigatum</i>). <i>Pliophloea</i>:K = Cretaceous Højerup Member; Pg = Paleogene Korsnæb Member. <i>Stichomicropora</i>: K = Cretaceous Højerup Member; Pg = Paleogene Korsnæb Member. Error bars show minimum and maximum width and length measured for each colony.</p

Locality maps and stratigraphical logs for the two study regions, Denmark and the southeastern USA.

<p>Stratigraphical formations and members are shown to highlight the units from which specimens were collected for analysis. Global palaeomap adapted from: <a href="http://scotese.com/K/t.htm" target="_blank">http://scotese.com/K/t.htm</a>.</p

Nested ANOVA results for zooid width.

<p>* = <i>p</i><0.05; ** = <i>p</i><0.01; *** = <i>p</i><0.001.</p>a<p>Negative estimates of variance components associated with non-significant F-ratios were assigned zero values in keeping with standard practice <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087048#pone.0087048-Taylor1" target="_blank">[26]</a>.</p>b<p>Denominator of the F-test is zero.</p

Nested ANOVA results for zooid length.

<p>* = <i>p</i><0.05; ** = <i>p</i><0.01; *** = <i>p</i><0.001.</p>a<p>Negative estimates of variance components associated with non-significant F-ratios were assigned zero values in keeping with standard practice <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087048#pone.0087048-Taylor1" target="_blank">[26]</a>.</p>b<p>Denominator of the F-test is zero.</p