Disparity trends in the shell coiling shape of ammonoids...Disparity trends in the shell coiling...

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!