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Link to original content: https://pubmed.ncbi.nlm.nih.gov/27044713
Breeding Young as a Survival Strategy during Earth's Greatest Mass Extinction - PubMed Skip to main page content
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. 2016 Apr 5:6:24053.
doi: 10.1038/srep24053.

Breeding Young as a Survival Strategy during Earth's Greatest Mass Extinction

Jennifer Botha-Brink  1   2 , Daryl Codron  3   4 , Adam K Huttenlocker  5   6 , Kenneth D Angielczyk  7 , Marcello Ruta  8
Affiliations

Breeding Young as a Survival Strategy during Earth's Greatest Mass Extinction

Jennifer Botha-Brink et al. Sci Rep. .

Abstract

Studies of the effects of mass extinctions on ancient ecosystems have focused on changes in taxic diversity, morphological disparity, abundance, behaviour and resource availability as key determinants of group survival. Crucially, the contribution of life history traits to survival during terrestrial mass extinctions has not been investigated, despite the critical role of such traits for population viability. We use bone microstructure and body size data to investigate the palaeoecological implications of changes in life history strategies in the therapsid forerunners of mammals before and after the Permo-Triassic Mass Extinction (PTME), the most catastrophic crisis in Phanerozoic history. Our results are consistent with truncated development, shortened life expectancies, elevated mortality rates and higher extinction risks amongst post-extinction species. Various simulations of ecological dynamics indicate that an earlier onset of reproduction leading to shortened generation times could explain the persistence of therapsids in the unpredictable, resource-limited Early Triassic environments, and help explain observed body size distributions of some disaster taxa (e.g., Lystrosaurus). Our study accounts for differential survival in mammal ancestors after the PTME and provides a methodological framework for quantifying survival strategies in other vertebrates during major biotic crises.

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Figures

Figure 1
Figure 1
Osteohistological sections of Permian (a–c) and Triassic (d–f) late subadult or adult therapsids. Numerous growth marks (arrows) characterise Permian taxa, whereas two, but generally no growth marks characterise Early Triassic taxa. (a) Dicynodont Lystrosaurus maccaigi, humerus NMQR 3663a. (b) Therocephalian Moschorhinus, humerus NMQR 3939a. (c) Cynodont Procynosuchus, radius BP/1/3747. (d) Lystrosaurus murrayi, humerus BP/1/3236. (e) Moschorhinus, humerus BP/1/4227a. (f) Cynodont Thrinaxodon, radius BP/1/4282a. Scale bars equal 1000 μm (a,b,d); 500 μm (e); 100 μm (c,f).
Figure 2
Figure 2. Growth mark counts mapped onto a phylogeny of Permo-Triassic therapsids.
Coloured + black columns: observed stratigraphic ranges; faded colours: ghost lineages. Dates taken from, phylogeny taken from. Anis, Anisian; Cap, Capitanian; Chx, Changxingian; Ind, Induan; Olen, Olenekian; Wor, Wordian; Wuc, Wuchiapingian; CAZ, Cynognathus Assemblage Zone; CiAZ, Cistecephalus Assemblage Zone; DAZ, Daptocephalus Assemblage Zone; EAZ, Eodicynodon Assemblage Zone; LAZ, Lystrosaurus Assemblage Zone; PAZ, Pristerognathus Assemblage Zone; TAZ, Tropidostoma Assemblage Zone; TapAZ, Tapinocephalus Assemblage Zone; KB; Karoo Basin; PTB, Permo-Triassic boundary, SGCS, Standard Global Chronostratigraphic Scale. Grey shading indicates theriodont therapsids.
Figure 3
Figure 3. Differences in population structure, life expectancy, age at reproductive maturity and fecundity.
(a) Body size distributions based on basal skull length (%BSLmax) showing distinct differences between Permian (blue) and Triassic (red) species of Lystrosaurus (see text and Supplementary Material for results of chi-squared analysis comparing frequency distributions of larger and smaller individuals across taxa). (b) Modelled size class distribution under six scenarios: Early breeding (triangles) results in the observed Triassic pattern (i.e. fewer % of larger individuals). Blue, long life; Red, short life. Circles, late breeding and low fecundity; Triangles, early breeding, low fecundity; Squares, late breeding, high fecundity. Results are simulated stable size class distributions resulting from matrix model projections, presented as means with 95% confidence intervals over 1 000 permutations of each model condition. (c) Extinction rates for the six scenarios. Early-breeding taxa have the lowest extinction rates. log Wx, proportion of individuals at size class X at stable size distributions; Pext, probability of extinction.
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