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. 2018 Jan 10;285(1870):20172012.
doi: 10.1098/rspb.2017.2012.

Diversity and disparity of sparassodonts (Metatheria) reveal non-analogue nature of ancient South American mammalian carnivore guilds

Darin A Croft  1 , Russell K Engelman  2 , Tatiana Dolgushina  3 , Gina Wesley  4
Affiliations

Diversity and disparity of sparassodonts (Metatheria) reveal non-analogue nature of ancient South American mammalian carnivore guilds

Darin A Croft et al. Proc Biol Sci. .

Abstract

This study investigates whether terrestrial mammalian carnivore guilds of ancient South America, which developed in relative isolation, were similar to those of other continents. We do so through analyses of clade diversification, ecomorphology and guild structure in the Sparassodonta, metatherians that were the predominant mammalian carnivores of pre-Pleistocene South America. Body mass and 16 characters of the dentition are used to quantify morphological diversity (disparity) in sparassodonts and to compare them to extant marsupial and placental carnivores and extinct North American carnivoramorphans. We also compare trophic diversity of the Early Miocene terrestrial carnivore guild of Santa Cruz, Argentina to that of 14 modern and fossil guilds from other continents. We find that sparassodonts had comparatively low ecomorphological disparity throughout their history and that South American carnivore palaeoguilds, as represented by that of Santa Cruz, Argentina, were unlike modern or fossil carnivore guilds of other continents in their lack of mesocarnivores and hypocarnivores. Our results add to a growing body of evidence highlighting non-analogue aspects of extinct South American mammals and illustrate the dramatic effects that historical contingency can have on the evolution of mammalian palaeocommunities.

Keywords: Carnivora; Sparassodonta; dentition; marsupial; palaeobiology; palaeoecology.

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Conflict of interest statement

We have no competing interests.

Figures

Figure 1.
Figure 1.
Representative sparassodont upper dentitions in occlusal view (a–c) and lower dentitions in lingual (d) and buccal (e–g) views, anterior to right. (a) Hondadelphys fieldsi, left P1-P2 roots and P3-M4 (reversed), UCMP 37960; (b) Sipalocyon gracilis, left C-M4, cast of YPM-PU 15373; (c) Arctodictis sinclairi, left C-M4 (reversed), MLP 85-VII-3–1; (d) Pseudothylacynus rectus, left p1-m4, MACN-A 52-369; (e) Sipalocyon gracilis, left i1-m4 (reversed), MACN-A 691; (f) Arctodictis sinclairi, right c-m4, MLP 85-VII-3-1; (g) Thylacosmilus atrox, left c-m4 (reversed), FMNH P14344. Scale bars equal 1 cm. For collection abbreviations, see the electronic supplementary material, table S5. (Online version in colour.)
Figure 2.
Figure 2.
Graphs of diversity (a) and disparity (b) through time for South American (SA) sparassodonts and North American (NA) carnivoramorphans. Only Eocene to Early Pliocene bins are shown because sparassodont disparity cannot be calculated beyond this range (less than 3 OTUs). X-axis values are midpoints of 2-million-year time bins. Bins represented in the South American fossil record are labelled with the corresponding interval (see the electronic supplementary material, table S1 for abbreviations); parentheses indicate bins with fewer than three sparassodont OTUs (for which disparity cannot be calculated). (Online version in colour.)
Figure 3.
Figure 3.
(a) Plot of all OTUs (sparassodonts, dasyuromorphians, didelphimorphians, North American Cenozoic carnivoramorphans and modern carnivorans) on first two canonical axes (CAs) of an analysis of 16 functional characters of the dentition and body mass. ‘Other Feliformia’ includes Eupleridae, Herpestidae, Nandiniidae, Prionodontidae and Viverridae. Characters (Ch.) with positive or negative loadings greater than 1.0 are plotted on the corresponding CA. See the electronic supplementary material, tables S10 and S11, for character loadings and scores for individual taxa, respectively. (b) Inset box of (a) showing only modern taxa with CA1 values < 0.5 and CA2 values < 1.0 and sparassodonts coded for 12 or more characters. Shaded areas represent entire morphospace occupied by group in (a). Abbreviations: BM, body mass (Ch. 17); CarBA, lower carnassial buccal angle (Ch. 11); CarOA, upper carnassial occlusal angle (Ch. 10); LGA, lower grinding area (Ch. 16); MNo, number of upper molars (Ch. 14); PNo, number of upper premolars (Ch. 3); PSh, upper premolar shape (Ch. 4); PSp, upper premolar spacing (Ch. 5).
Figure 4.
Figure 4.
Stacked bar graphs comparing diversity of hypercarnivores (Hyper), mesocarnivores (Meso) and hypocarnivores (Hypo) in the Santa Cruz Formation of Argentina to three modern and 11 fossil terrestrial carnivore guilds, arranged by decreasing number of species. Age abbreviations (in parentheses): e, Early; E, Eocene; l, Late; m, Middle; M, Miocene; O, Oligocene; P, Palaeocene. Superscript numbers for Santa Cruz indicate: 1, diets following Ercoli et al. [23], with phorusrhacids (terror birds) included; 2, diets following Ercoli et al. [23] and 3, diets following Marshall [10]. See the electronic supplementary material, table S9 for species lists and dietary categories for Santa Cruz, White River Group biozones (Ch3, Or2, Wh2; USA), and modern guilds. Data for other fossil guilds are from table 10.1 of Morlo et al. [27] with ‘bone/meat’ species grouped with hypercarnivores, ‘carnivore’ species treated as mesocarnivores, and ‘insectivorous’ species grouped with hypocarnivores. (Online version in colour.)
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