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. 2014 Oct 8;9(10):e109232.
doi: 10.1371/journal.pone.0109232. eCollection 2014.

Anthracobunids from the middle eocene of India and pakistan are stem perissodactyls

Lisa Noelle Cooper  1 , Erik R Seiffert  2 , Mark Clementz  3 , Sandra I Madar  4 , Sunil Bajpai  5 , S Taseer Hussain  6 , J G M Thewissen  1
Affiliations

Anthracobunids from the middle eocene of India and pakistan are stem perissodactyls

Lisa Noelle Cooper et al. PLoS One. .

Abstract

Anthracobunidae is an Eocene family of large mammals from south Asia that is commonly considered to be part of the radiation that gave rise to elephants (proboscideans) and sea cows (sirenians). We describe a new collection of anthracobunid fossils from Middle Eocene rocks of Indo-Pakistan that more than doubles the number of known anthracobunid fossils and challenges their putative relationships, instead implying that they are stem perissodactyls. Cranial, dental, and postcranial elements allow a revision of species and the recognition of a new anthracobunid genus. Analyses of stable isotopes and long bone geometry together suggest that most anthracobunids fed on land, but spent a considerable amount of time near water. This new evidence expands our understanding of stem perissodactyl diversity and sheds new light on perissodactyl origins.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Cranial elements of anthracobunids from the middle Eocene of Indo-Pakistan.
(A) Crushed skull of A. pinfoldi (H-GSP 97106) in ventro-lateral view (left maxilla detached) and (B) dorsal view; (C) P2 of A. wardi (H-GSP 30229) in lingual view and (D) occlusal view; (E) Skull fragment of A. wardi (RR 411) in occlusal view, and (F) lateral view; (G) Mandible of A. wardi (H-GSP 96434) in occlusal view; (H) Mandible of A. wardi (H-GSP 96258) in lateral view, and (I) occlusal view. (J) Proximal phalanx of A. pinfoldi (H-GSP 97106.105) in dorsal view; (K) Proximal phalanx of A. pinfoldi (H-GSP 97106.101) in ventral view, and (L) lateral view; (M) Head of a metapodial of A. pinfoldi (H-GSP 97106.250) in dorsal view; (N) Phalangeal fragment of A. pinfoldi (H-GSP 97106.257) in dorsal-superior view; (O) Terminal phalanx of A. pinfoldi (H-GSP 97106.302) in dorsal-superior view. Scale bar is 1 cm in length.
Figure 2
Figure 2. Teeth of anthracobunids, other stem perissodactyls, and condylarths.
(A) Right P2-M2 of A. wardi (LUVP-15006) in occlusal view, and (B) labial view; (C) left M1-M3 of A. wardi (RR-411) in occlusal view, and (D) labial view; (E) left P3-M3 of A. pinfoldi (H-GSP 82-31P) in occlusal view; (F) left M3 of A. pinfoldi (H-GSP 82-31P) in labial view; (G) right C-M3 of the cambaythere Kalitherium (IITR-SB-VLM 931) in occlusal view; (H) right M3 of Kalitherium (IITR-SB-VLM 931) in labial view; (I) left P4-M2 of Nakusia in occlusal view; (J) left M2 of Nakusia in labial view; (K) Mx of Cambaytherium (IITR-SB-VLM-521) in occlusal view; (L) right M3 of the phenacodontid ‘condylarth’ Tetraclaenodon (KU-8052) in occlusal view; (M) left p1-m3 of A. wardi (WIF/A 1101) in occlusal view; (N) left c-m3 of A. wardi (H-GSP 96258) in occlusal view, and (O) labial view; (P) left p1-m3 of Obergfellia occidentalis (H-GSP 1981) in occlusal view, and (Q) labial view (M1 inverted from right side). Scale bar is 1 cm in length. Illustrations by Jacqueline Dillard.
Figure 3
Figure 3. Adams consensus of all trees recovered from parsimony analyses that included some ordered multistate characters, with continental geography (see states in upper left-hand corner) optimized onto the tree using parsimony (relationships among extant taxa were constrained by a “molecular scaffold”).
Bootstrap support for clades derived from each analysis contributing to the consensus is depicted by colored circles. A1  =  Atlantogenata constraint, transitions between polymorphic and “fixed” states in ordered morphoclines weighted as 0.5 steps; A2  =  Atlantogenata constraint, transitions between polymorphic and “fixed” states in ordered morphoclines weighted as one step; E1  =  Exafroplacentalia constraint, transitions between polymorphic and “fixed” states in ordered morphoclines weighted as 0.5 steps; E2  =  Exafroplacentalia constraint, transitions between polymorphic and “fixed” states in ordered morphoclines weighted as one step. Across all trees, anthracobunids and desmostylians were placed as perissodactyls, along with two enigmatic Asian taxa, the late Paleocene “condylarth” Radinskya and early Eocene Cambaytherium.
Figure 4
Figure 4. Histological midshaft sections for the (A) humerus of Ichthyolestes (H-GSP 96227), (B) femur of Odocoileus, and (C) radius of Anthracobune (H-GSP 97106).
(D) Bar diagram of bone compactness, a quantification of the amount of bone per midshaft cross-section, compared here between fossil and extant ungulates.
Figure 5
Figure 5. Bivariate plot of δ18O and δ13C values for enamel samples of early and middle Eocene mammals from India and Pakistan.
Results shown as mean ±S.D. for the sample populations. Data from (A) early Eocene and (B, C) middle Eocene taxa from India and Pakistan. Circles, perissodactyls; red circles, anthracobunids; squares, artiodactyls; triangles, cetaceans; inverse triangles, creodonts; diamonds, condylarths. See Suppl. Info. for details.
See this image and copyright information in PMC

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