Post on 21-May-2020
Matthew E. ClaphamUniversity of California, Santa Cruz
mclapham@ucsc.edu
Disparity trends in the shell
coiling shape of ammonoids
Ammonoid coiling geometry
From Korn & Klug, 2012
The coiled shells of ammonoid cephalopods have evolved a huge array of geometric shapes
Ammonoid morphometrics
Villier & Korn, 2004 Saunders et al., 2008
The regular geometric shapes of ammonoid shells make them well suited for morphometric studies to examine trends in disparity over their evolutionary history and across important eventsSaunders & Swan 1984; Dommergues et al., 1996 ; Saunders et al. 2004, 2008; McGowan 2004, 2007; Villier & Korn 2004; Korn & Klug 2012; Brosse et al. 2013, etc.
Ammonoid measurements
Traditional parameters of whorl width (W) and height (H), umbilical diameter (U), and diameter
Principal components analysis of W/D, H/D, and U/D ratios
Modified from Brosse et al., 2013
Heteromorph ammonoids
Heteromorph ammonoids have uncoiled whorls or deviate from planispiral coiling form, so cannot reasonably be quantified with W/D, H/D, or U/D measurements and are excluded
Ammonoid morphospace
Morphospace defined by axes from evolute to involute coiling (U/D and H/D) and from compressed to depressed whorl widths (W/D)
8515 specimens2687 species
Morphospace occupation
Areas of morphospace occupation and degree of morphological variability differed widely among time intervals
Disparity trends in shell coiling
Pennsylvanian-Permian peak
Guadalupian-Lopingian drop
Jurassic-Cretaceous low
Taxonomic contributions
Shape variation among orders
Post-Paleozoic and especially post-Triassic disparity is reduced because ceratites and especially ammonites are increasingly restricted to a narrow region of the morphospace
Globular shells (high W/D) are common among goniatites but extremely rare among ammonites
Ammonoid size
Average shell volume increased by more than an order of magnitude from Paleozoic to the Jurassic
Ammonoid size
On average, ammonites were ~10 times as large as goniatites
Perhaps globular morphotypes are unfeasible at large size?
Size and shell shape
Highly globular shells were more common among small goniatites, but globular ammonites tended to be large
Competitors?
Perhaps other groups (heteromorph ammonites or non-ammonite taxa like crustaceans or fish) were occupying the ecological role formerly occupied by globular goniatites?
Phytoplankton and food web dynamics
Post-Paleozoic shift from prasinophytes to bloom-forming phytoplankton (dinoflagellates, nannoplankton) (Falkowski et al., 2004)
Perhaps altered the nature of food webs to favor groups with different ecological strategies?
Acritarchs
Prasinophytes
Dinoflagellates
Calcareous nannoplankton
Diatoms
Conclusions
1. Ammonoids peaked in the diversity of coiling morphologies
(excluding heteromorphs) in the late Paleozoic
2. Major decline during Guadalupian-Lopingian transition and
never recovered Paleozoic levels of disparity
3. Jurassic and Cretaceous ammonites had low coiling disparity
because they rarely evolved the globular morphotypes
common in goniatites
4. Loss of globular morphotypes may have resulted from other
groups occupying those niches or from loss of that niche
altogether due to post-Paleozoic food web restructuring
Ammonoid shell web app
https://mclapham.shinyapps.io/ammonShape/
Make your own plots of PCA results by taxon and time interval
Acknowledgments
All of the ammonoid measurements used here are in the PBDBJeanette Sullivan (2013) and Jocelynn Morales (2014) for data entry
R code at: https://github.com/mclapham/ammonShape
These slides and ammonite measurements at:http://figshare.com/authors/Matthew_Clapham/593028
PBDB data enterers, especially:
Me, Wolfgang Kiessling, Austin Hendy
You too can make data useful with the PBDB!