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doi: 10.7717/peerj.3868. eCollection 2017.

New whaitsioids (Therapsida: Therocephalia) from the Teekloof Formation of South Africa and therocephalian diversity during the end-Guadalupian extinction

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New whaitsioids (Therapsida: Therocephalia) from the Teekloof Formation of South Africa and therocephalian diversity during the end-Guadalupian extinction

Adam K Huttenlocker et al. PeerJ..

Abstract

Two new species of therocephalian therapsids are described from the upper Permian Teekloof Formation of the Karoo Basin, South Africa. They include two specimens of a whaitsiid,Microwhaitsia mendrezi gen. et sp. nov., and a single, small whaitsioidOphidostoma tatarinovi gen. et sp. nov., which preserves a combination of primitive and apomorphic features. A phylogenetic analysis of 56 therapsid taxa and 136 craniodental and postcranial characters places the new taxa within the monophyletic sister group of baurioids-Whaitsioidea-withMicrowhaitsia as a basal whaitsiid andOphidostoma as an aberrant whaitsioid just outside the hofmeyriid+whaitsiid subclade. The new records support that whaitsioids were diverse during the early-late Permian (Wuchiapingian) and that the dichotomy between whaitsiid-line and baurioid-line eutherocephalians was established early on. The oldest Gondwanan whaitsiidMicrowhaitsia and additional records from the lower strata of the Teekloof Formation suggest that whaitsioids had diversified by the early Wuchiapingian and no later thanPristerognathus Assemblage Zone times. Prior extinction estimates based on species counts are reflected in an analysis of origination/extinction rates, which imply increasing faunal turnover from Guadalupian to Lopingian (late Permian) times. The new records support a growing body of evidence that some key Lopingian synapsid clades originated near or prior to the Guadalupian-Lopingian boundary ca. 260-259 million years ago, but only radiated following the end-Guadalupian extinction of dinocephalians and basal therocephalian predators (long-fuse model). Ongoing collecting in older portions of the Teekloof Formation (e.g.,Pristerognathus Assemblage Zone) will shed further light on early eutherocephalians during this murky but critical time in their evolutionary diversification.

Keywords: Extinction; Permian; Synapsid; Tetrapod; Therocephalians.

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Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Specimen provenance and stratigraphic context of Teekloof Formation whaitsioids.
1, Provenance of SAM-PK-K10990 and K10984, Badshoek farm (De Hoop 117), near Beaufort West, Western Cape Province; 2, Provenance of SAM-PK-K8516, Good Luck farm, near Fraserburg, Northern Cape Province. Bulleted numbers to right of stratigraphic column indicate ages of vertebrate assemblage zones in millions of years (Ma) (from Rubidge et al., 2013). Geologic map modified from Smith (1993). Abbreviations:CiAZ,Cistecephalus Assemblage Zone;DaptoAZ,Daptocephalus Assemblage Zone; Fm, Formation; M, Member;PristAZ,Pristerognathus Assemblage Zone;TapinoAZ,Tapinocephalus Assemblage Zone;TrAZ,Tropidostoma Assemblage Zone.
Figure 2
Figure 2. Holotypic skull ofMicrowhaitsia mendrezi gen. et sp. nov. (SAM-PK-K10990) in dorsal (A), ventral (B), and right lateral (C) views.
Figure 3
Figure 3. Interpretive line drawings of the holotypic skull ofMicrowhaitsia mendrezi gen. et sp. nov. (SAM-PK-K10990) in dorsal (A), ventral (B), and right lateral (C) views.
Abbreviations: d, dentary; C, upper canine; cr.ch, crista choanalis; f, frontal; f.l, lacrimal foramen; I5, fifth upper incisor; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; pal, palatine; pC, upper precanine; PC5, fifth upper postcanine; po, postorbital; pm, premaxilla; prf, prefrontal; pt, pterygoid; sa, surangular; sm, septomaxilla; sp, splenial.
Figure 4
Figure 4. Stereopair images of the palate of the holotypic skull ofMicrowhaitsia mendrezi gen. et sp. nov. (SAM-PK-K10990) in left oblique ventral (A) and posteroventral (B) views.
Note the narrow contact between the left crista choanalis and vomer without sutural connection.
Figure 5
Figure 5. Referred specimen ofMicrowhaitsia mendrezi gen. et sp. nov. (SAM-PK-K10984) in dorsal (A), ventral (B), and left lateral (C) views.
Figure 6
Figure 6. Interpretive line drawings of referred specimen ofMicrowhaitsia mendrezi gen. et sp. nov. (SAM-PK-K10984) in dorsal (A), ventral (B), and left lateral (C) views.
Abbreviations: C, upper canine alveolus; cr.ch, crista choanalis; ect, ectopterygoid; f, frontal; j, jugal; l, lacrimal; m, maxilla; m.pal.f, maxillo-palatine foramen; n, nasal; pal, palatine; PC5, fifth upper postcanine alveolus; prf, prefrontal; pt, pterygoid; v, vomer; v.suborb, suborbital vacuity.
Figure 7
Figure 7. Volumized HRXCT scans of the skull ofOphidostoma tatarinovi gen. et sp. nov. (SAM-PK-K8516) in dorsal (A), ventral (B), left lateral (C), and frontal (D) views.
Figure 8
Figure 8. Interpretive line drawings of the skull ofOphidostoma tatarinovi gen. et sp. nov. (SAM-PK-K8516) in dorsal (A), ventral (B), left lateral (C), and frontal (D) views.
Abbreviations: a, angular; d, dentary; ect, ectopterygoid; c, lower canine; C, upper canine; f, frontal; fen.m, mandibular fenestra; i, lower incisor; j, jugal; l, lacrimal; m, maxilla; n, nasal; p, parietal; part, prearticular; pbs, para-basisphenoid; PC6, sixth upper postcanine; po, postorbital; pm, premaxilla; prf, prefrontal; pt, pterygoid; q-qj, quadrate-quadratojugal complex; sa, surangular; sm, septomaxilla; sp, splenial; sq, squamosal; v.ipt, interpterygoid vacuity; v.suborb, suborbital vacuity.
Figure 9
Figure 9. Conservative phylogenetic relationships of the major clades of eutherocephalians, showing conflicting arrangements obtained from Bayesian and parsimony analyses as polytomies (tree length = 381; consistency index (CI) = 0.438; retention index = 0.789; res).
Figure 10
Figure 10. New specimen of the hofmeyriidMirotenthes digitipes Attridge, 1956 (SAM-PKK11188) from the upperCistecephalus Assemblage Zone of ‘Good Luck.’
Specimen shown in dorsal oblique view, showing the large temporal fenestra and broad, anvil-shaped epipterygoid (ept) processus ascendens.
Figure 11
Figure 11. Stratigraphically calibrated phylogeny of middle Permian through Triassic therocephalians showing calibration points for minimum divergence dates of major clades (A).
Light gray lines represent hypothetical phylogenetic branching, whereas black bars represent observed stratigraphic ranges (dashed ends indicate taxa having unknown upper or lower ranges). Graph (B) shows peak levels of eutherocephalian origination/extinction by the Wuchiapingian stage. Abbreviations: An, Antarctica; Ch, China; Chx, Changxingian;Ci AZ,Cistecephalus Assemblage Zone;Dapto AZ,Daptocephalus Assemblage Zone; Ind, Induan; Na, Namibia; Olen, Olenekian;Prist AZ,Pristerognathus Assemblage Zone; Roa, Roadian; Ru, Russia; SA, South Africa;TapinoAZ,Tapinocephalus Assemblage Zone;Tr AZ,Tropidostoma Assemblage Zone; Tz, Tanzania; Wor, Wordian; Za, Zambia.
Figure 12
Figure 12. Representative hofmeyriid from the late Capitanian or earliest Wuchiapingian of the Karoo Basin, South Africa, compared to other known specimens ofHofmeyria.
SAM-PK-K10525 (A), Hofmeyriidae from thePristerognathus Assemblage Zone of Lombardskraal, Beaufort West district, Western Cape Province. Specimen shows short, high rostrum, prefrontal-postorbital contact in orbit, anteriorly expanded epipterygoid, and conical, non-serrated/non-carinated maxillary teeth. BP/1/4404 (BP, former Bernard Price Institute, now Evolutionary Studies Institute, Johannesburg) (B),Hofmeyria cf.H. atavus from theCistecephalus Assemblage Zone of Matjiesfontein (Highlands), Victoria West district, Northern Cape Province. BP/1/1399 (C),Hofmeyria cf. H. atavus from theCistecephalus Assemblage Zone of Driehoeksfontein, Murraysburg district, Western Cape Province. Numbers 14–136 are characters listed in the phylogenetic analysis (see online Supplemental Information 1) followed by the derived state in parentheses corresponding to hofmeyriids or other early whaitsioids. Abbreviations: AZ, Assemblage Zone; PC, postcanine position #.
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Grants and funding

Adam K. Huttenlocker has been supported by NSF DEB-1209018 and DBI-1309040. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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