Journal of Vertebrate Paleontology A new and unusual ... · 716 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 3, 2010 FIGURE 1. Phonodus dutoitorum, gen. et sp. nov., NMQR 3564.Photographs

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A new and unusual procolophonid parareptile from the Lower TriassicKatberg Formation of South AfricaSean P. Modesto a; Diane M. Scott b; Jennifer Botha-Brink cd;Robert R. Reisz b

a Department of Biology, Cape Breton University, Sydney, Nova Scotia, Canada b Department ofBiology, University of Toronto in Mississauga, Mississauga, Ontario, Canada c Karoo Palaeontology,National Museum, Bloemfontein, South Africa d Department of Zoology and Entomology, Universityof the Free State, Bloemfontein, South Africa

Online publication date: 19 May 2010

To cite this Article Modesto, Sean P. , Scott, Diane M. , Botha-Brink, Jennifer andReisz, Robert R.(2010) 'A new andunusual procolophonid parareptile from the Lower Triassic Katberg Formation of South Africa', Journal of VertebratePaleontology, 30: 3, 715 — 723To link to this Article: DOI: 10.1080/02724631003758003URL: http://dx.doi.org/10.1080/02724631003758003

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Journal of Vertebrate Paleontology 30(3):715–723, May 2010© 2010 by the Society of Vertebrate Paleontology

ARTICLE

A NEW AND UNUSUAL PROCOLOPHONID PARAREPTILE FROM THE LOWER TRIASSICKATBERG FORMATION OF SOUTH AFRICA

SEAN P. MODESTO,*,1 DIANE M. SCOTT,2 JENNIFER BOTHA-BRINK,3 and ROBERT R. REISZ2

1Department of Biology, Cape Breton University, Sydney, Nova Scotia, B1P 6L2, Canada, sean [email protected];2Department of Biology, University of Toronto in Mississauga, 3359 Mississauga Road, Mississauga, Ontario, L5L 1C6, Canada,

[email protected];3Karoo Palaeontology, National Museum, P.O. Box 266, Bloemfontein 9300, South Africa; Department of Zoology and

Entomology, University of the Free State, Bloemfontein, 9300, South Africa, [email protected]

ABSTRACT—A small skull collected from the base of the Katberg Formation of South Africa represents a new Early Tri-assic procolophonid parareptile. Phonodus dutoitorum, gen. et sp. nov., is diagnosed by a roughly straight ventral temporalmargin, prefrontals that contact each other along the dorsal midline, presence of a large posterior maxillary tooth, an eden-tulous pterygoid, a reduced transverse flange of the pterygoid, and other autapomorphies. A cladistic analysis identifies P.dutoitorum as a basal member of the procolophonid clade Leptopleuroninae. The presence of large maxillary teeth, their po-sitioning ventral to strongly developed antorbital buttresses, and the loss of the ventral temporal emargination are suggestiveof a durophagous diet. Phonodus dutoitorum is recognized as the oldest known leptopleuronine. Optimization of geographicdistributions onto procolophonid phylogeny indicates that the presence of P. dutoitorum in the Karoo Basin of South Africais explained most parsimoniously as the result of migration from Laurasia. Phonodus dutoitorum is the fifth procolophonoidspecies to be described from the Induan of the Karoo Basin, providing further support for the hypothesis that procolophonoidevolution was not greatly perturbed by the end-Permian extinction event.

INTRODUCTION

Parareptiles were the most taxonomically and ecologically di-verse reptiles at the end of the Paleozoic Era, but were eclipsedby eureptiles following the end-Permian mass extinction of 252million years ago (Mundil et al., 2004). Procolophonoids are theonly parareptiles that survived this extinction event, and phyloge-netic studies suggest that they experienced a reduced extinctionlevel (Modesto et al., 2001, 2003) compared to other tetrapods.Recent field work in South Africa (Botha et al., 2007) indicatesthat procolophonoids of the earliest Triassic (Induan) appear tohave flourished in the wake of the Mother of Mass Extinctions(sensu Erwin, 1993). Indeed, procolophonoid fossils are often lo-cally abundant where they are present (Kitching, 1977; Li, 1983;Botha et al., 2007).

In the course of field work in the Lower Triassic LystrosaurusAssemblage Zone, Karoo Basin of South Africa, the authors col-lected the skull of a small tetrapod in a block of intraforma-tional conglomerate from the Lower Triassic Katberg Forma-tion on the Northern Cape farm Bergendal. Little more than theweathered tips of the transverse flanges, quadrate condyles, andthe alveolar regions of the maxillae were exposed in ventral as-pect. Mechanical preparation revealed the skull of a small rep-tile of unusual morphology, one characterized by a large toothin each maxilla, a palate with edentulous palatines and ptery-goids, a reduced transverse flange of the palate, and the pres-ence of a small lateral temporal opening. Although most of theskull table, the braincase, and the mandible are missing, thespecimen preserves a suite of apomorphies that, among Permo-Triassic reptiles, is known only in procolophonids. We describethe Bergendal specimen as a new genus and species of procolo-

*Corresponding author.

phonid reptile, and discuss its implications for procolophonidevolution.

Institutional Abbreviation—NM, National Museum, Bloem-fontein.

GEOLOGICAL SETTING

The skull described in this paper (NMQR 3564) was collectedas part of a small block of conglomerate found ex situ atopthe first major sandstone exposed on the Northern Cape farmBergendal. The block appeared to have been ‘calved’ from asandstone layer that lies less than 1 m above the lowermost sand-stone. Collecting at the locality yielded numerous specimens ofthe genus Lystrosaurus attributable to L. murrayi and possiblyL. declivis, and a single specimen of a small therocephalian at-tributable to Tetracynodon darti (NMQR 3597). The specimensof the former genus indicate that the Lystrosaurus AssemblageZone (AZ) broadly crops out on Bergendal. Tetracynodon dartiis known from Lystrosaurus-AZ localities in both the northernand southern portions of the Karoo Basin: the holotype is fromthe farm New Castle (formerly an annex of the farm AdmiraltyEstates) in KwaZulu-Natal Province (Sigogneau, 1963; Kitching,1977), for which an exact placement of the fossiliferous stratain the Lystrosaurus AZ has not been determined. All referredspecimens of T. darti have been collected from localities in thesouthern part of the Karoo Basin, and have been positioned inthe Triassic portion of the Palingkloof Member of the BalfourFormation (Damiani et al., 2004; Botha and Smith, 2006). Thespecimen of T. darti collected at Bergendal was found in situapproximately 1 m below the first major sandstone. We inferthat this sandstone marks the base of the Katberg Formation onBergendal, and that NMQR 3564 comes from the base of thisformation.

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716 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 3, 2010

FIGURE 1. Phonodus dutoitorum, gen. et sp. nov., NMQR 3564. Photographs of skull in (A) left lateral, (B) palatal, (C) oblique posterolateral, and(D) occipital views.

MATERIAL AND METHODS

NMQR 3564 is preserved ventral up in the conglomerate(Fig. 1). As preparation progressed dorsally, up the lateral sur-faces of the skull roof, we realized that not only was the braincasemissing, but the skull table (consisting of the frontals, the pari-etals, the postfrontals [if present as distinct elements], the postor-bitals, the supratemporals, and the postparietals) was lost priorto burial as well. In order to ensure the integrity of the snout andtemporal regions, we decided not to remove the skull completelyfrom the block, but to leave it attached via the dorsolateral sur-face of the right side; only the left side together with the dorsalsurface of the snout of the skull roof is revealed for the followingdescription.

SYSTEMATIC PALEONTOLOGY

PARAREPTILIA Olson, 1947PROCOLOPHONIDAE Lydekker in Nicholson and Lydekker,

1889LEPTOPLEURONINAE Ivachnenko, 1979

PHONODUS DUTOITORUM, gen. et sp. nov.(Figs. 1, 2)

Diagnosis—Small procolophonid characterized by the fol-lowing autapomorphies: ventral temporal roughly straight withcontact between maxilla and quadratojugal; bifurcated maxil-lary process of premaxilla; relatively large posterior-most max-illary tooth; prefrontal-prefrontal dorsal midline contact; lat-eral temporal fenestra present; vomer with two large conicalteeth; pterygoid edentulous; transverse process of pterygoid rel-atively small; and small accessory process present medially onquadrate.

Holotype—NMQR 3564, a partial skull.Locality and Horizon—A locality on the farm Bergendal in

Noupoort District, Northern Cape Province, Republic of SouthAfrica. Katberg Formation, Beaufort Group, Karoo Supergroup.NMQR 3564 is positioned low stratigraphically in the KatbergFormation and, thus, low in the Lystrosaurus Assemblage Zone(Groenewald and Kitching, 1995). Lower Triassic; Induan Stage.Detailed locality data are available from the Department of Ka-roo Palaeontology of the National Museum, Bloemfontein, toqualified researchers.

Etymology—From phonos and odus, Greek for ‘murderous’and ‘tooth’ respectively, gender masculine. The specific epithethonors Jan and Susan du Toit, owners of the farm Bergendal, fortheir hospitality and interest in our work.


MODESTO ET AL.—NEW TRIASSIC PROCOLOPHONID PARAREPTILE 717

DESCRIPTION

The holotype and only known specimen of Phonodus dutoito-rum preserves little more than half of the skull roof. The pre-maxillae have been eroded away almost entirely, and the alveolarportions of both maxillae are heavily weathered. The palate, in-cluding both quadrates, is preserved in articulation with the skullroof, but the transverse flanges and condyles of both quadratesare weathered to varying degrees. The braincase, the mandible,and the skull table are not preserved.

The skull is 25 mm long, a length that falls in the range of ju-venile skulls of Procolophon trigoniceps (Carroll and Lindsay,1985) and Hypsognathus fenneri (Sues et al., 2000). The deeplyserrate dorsal midline suture formed by the nasals suggests, how-ever, that the skull is that of an adult individual. We use this crite-rion of ontogenetic age from the cranial description of H. fenneriby Sues and colleagues, which documents a straight internasalcontact in a juvenile specimen (Sues et al., 2000:fig. 3a) and aninterfingering suture in an adult (Sues et al., 2000:fig. 2a).

Skull Roof

Little more than fragments remain of both premaxillae. Thelargest fragments are the enlarged maxillary processes and thetips of the palatal processes. The former has an extensive con-tact with the anterior end of the maxilla and consists of twodorsally extending processes. The anterior process makes con-tact with the ventral margin of the nasal, thereby excluding themaxilla from the external naris. The posterior ramus overlies thelateral surface of the maxilla and forms the posterior boundaryof the maxillary depression (sensu Carroll and Lindsay, 1985).The palatal processes extend slightly farther posteriorly than themaxillary processes. Each appears to contact the anterior end ofthe vomer via a scarf joint. The dorsal processes of the premax-illae are preserved as tiny fragments in contact with the anteriortips of the nasals. In ventral view the cross-section of each dorsalprocess is seen to be transversely compressed (i.e., narrow), asin procolophonoids and their close relatives (deBraga and Reisz,1996).

Septomaxillae are usually prominent elements positioned pos-teriorly in or along the posterior margin of the external naris,but no such structures are present. A pair of thin, weakly curvedbones, exposed in section in palatal aspect immediately postero-medial to the external nares, may be all that remains of the sep-tomaxillae.

The maxilla is a relatively deep, semilunar bone. Its lateral sur-face is characterized by an extensive anterior fossa, the maxillarydepression, and two conspicuous foramina. The maxillary depres-sion is a relatively shallow excavation with a distinct, nearly verti-cally aligned posterior margin and a bowed anterior margin thatextends to the suture with the nasal and the anterior ramus ofthe maxillary process of the premaxilla. Just posterior to the pos-terior ramus of the maxillary process of that element and dor-sal to the ventral margin of the maxilla lies the anterior lateralmaxillary foramen (sensu Laurin and Reisz, 1995). It is approx-imately twice the size of the posterior foramen and it opens an-terolaterally, as this opening does in other parareptiles (Modesto,1999). The smaller opening appears to be a supralabial foramen,in the position that one or two such openings are usually seenin procolophonoids (Modesto et al., 2002:fig.1a; Reisz and Scott,2002:fig. 2d). The slightly serrate suture with the nasal is relativelylong compared to those with the lacrimal and the jugal. Althoughthe maxilla and the quadratojugal are separated on both sides inpalatal aspect, this appears to be the result of lithostatic compres-sion and we infer that these two elements made a touch contactand excluded the jugal from the ventral margin. In lateral aspectthe ventral margin of the maxilla is slightly concave, but anteri-orly the alveolar margins of both elements are heavily weathered.There is no ventral beveling of the lateral surface of the bone

that would be indicative of the insetting seen in Procolophonand other procolophonids (Carroll and Lindsay, 1985:fig. 3; Sueset al., 2000:fig. 2e). Posteromedially the maxilla contacts the pala-tine and the ectopterygoid, and forms the medial margin of thechoana. Posteriorly the maxilla reaches the subtemporal fenestraand separates the jugal from the ectopterygoid in palatal aspect.

What is preserved of the maxillary dentition on both sides isa single, relatively enormous tooth crown base that is positionedjust anterior to the level of the antorbital margin (Fig. 2B). Inpalatal aspect the crown bases on both sides are irregularly oval inoutline. The mesiodistal diameter of both teeth is slightly greaterthan a third of the antorbital length of the skull. Damage to bothteeth allows us to determine that the thickness of the tooth wall(sensu Modesto and Reisz, 2008) measures approximately 0.2–0.3mm. The left tooth base is more complete than the right, and whatremains of its profile in both lateral and occipital aspects suggeststhat it was a bulbous molariform tooth similar to the large maxil-lary tooth of the Late Triassic procolophonid Haligonia bolodon(Sues and Baird, 1998:fig. 2). No other maxillary teeth are pre-served, but a small, circular, ventrally facing pocket immediatelyanterior to the left tooth base is probably the weathered alveolusfor a small tooth.

Both nasals are preserved but only the left is exposed enoughfor description. In lateral view the nasal is a relatively long, gen-tly curving sheet of bone that extends from the anterior-most tipof the snout posteriorly to the prefrontal. It forms nearly the en-tire dorsal margin of the external naris. The dorsal surface of thebone is smooth apart from a prominent, anteriorly directed fora-men. This opening is in the same relative position as a cluster ofsimilarly oriented foramina on the nasal of Coletta seca (Modestoet al., 2002:fig. 1b) and Contritosaurus simus (Ivachnenko, 1974),although the nasal in NMQR 3564 does not appear to contributeto the maxillary depression as it does in those taxa. The obliqueview shows that the nasals formed a deeply serrate sagittal sutureand that the nasal was bounded posteriorly by the prefrontal (i.e.,no contact with the frontal).

The prefrontals contact each other dorsally and form a short,deeply serrate suture along the midline (Fig. 2C). Heretofore aprefrontal midline contact among parareptiles was known onlyin owenettids (Reisz and Scott, 2002; Cisneros et al., 2004). Theprefrontal forms the anterodorsal corner of the orbit and the dor-sal half of a relatively broad antorbital buttress. It contacts thenasal via a weakly sigmoidal suture, and shares deeply interfin-gering contacts with the lacrimal and the palatine. Dorsally theposteromedial margin of the left prefrontal is well preserved andindicates that it shared a serrate suture with the frontal as well. Aprefrontal ‘spur’ is not present.

The lacrimal is closely comparable to that of Procolophon(Carroll and Lindsay, 1985). It has a roughly triangular facial por-tion that contacts the nasal anteriorly, the prefrontal dorsally, andthe maxilla and the jugal ventrally, and a tongue-like orbital ex-tension that overlies the lateral edge of the palatine and contactsthe ectopterygoid. Together the lacrimal and the palatine, andperhaps a superficial contribution from the ectopterygoid as well,form the dorsal opening of the suborbital foramen, as in otherprocolophonids (Carroll and Lindsay, 1985:fig. 9b; Modesto et al.,2001:fig. 1a). Two lacrimal foramina, the dorsal one slightly largerthan the ventral, perforate the bone along the antorbital margin(Fig. 2C).

Phonodus dutoitorum is an unusual procolophonid in the sensethat it exhibits neither a ventral temporal emargination nor aquadratojugal cheek spine. The jugal does not have an exposedventral margin because the maxilla and the quadratojugal makecontact and form a distinctly sigmoidal ventral margin for theskull roof. The jugal forms an extensive and deeply serrate su-ture with the quadratojugal, and a prominent foramen issuesanteriorly approximately midway along this contact. Anteriorlythe jugal contacts the lacrimal and the ectopterygoid, and has a



FIGURE 2. Phonodus dutoitorum, gen. et sp. nov., NMQR 3564. Interpretive drawings of skull in (A) left lateral, (B) palatal, (C) oblique postero-lateral, and (D) occipital views. Abbreviations: ar fl, arcuate flange; b r, basicranial recess; de, maxillary depression; ec, ectopterygoid; f, vomerinefang; j, jugal; l, lacrimal; ltf, lateral temporal fenestra; m, maxilla; mf, anterior lateral maxillary foramen; n, nasal; pal, palatine; prf, prefrontal; prm,premaxilla; pt, pterygoid, q, quadrate; q fl, quadrate flange of the pterygoid; qj, quadratojugal; sm, septomaxilla; sq, squamosal; t, maxillary tooth; trfl; transverse flange of the pterygoid; v, vomer.

moderately long overlapping suture with the maxilla. Anterodor-sally the jugal forms the gently concave ventral margin of theorbit, and posterodorsally it projects an acuminate process thatbears an elongate contact surface for the postorbital. Interest-ingly, the posterior edge of the posterodorsal end of the ju-gal forms a free, moderately concave margin, which has itscounterpart in a shallow, anteriorly facing emargination in thesquamosal. Thus, a small lateral temporal fenestra was present.The dorsal margin of this opening was presumably formed bythe postorbital and, as suggested by the extensive contact surfacethat runs along the entire dorsal edge of the squamosal, possiblyby the supratemporal as well, in analogous fashion to the lateraltemporal fenestra restored for the owenettid Candelaria barbouri(Cisneros et al., 2004).

The quadratojugal forms the ventral margin of the temporalregion and the ventral half of the posterior temporal emargina-tion. The latter is defined ventrally by a dorsoventrally deep pos-teroventral extension of the facial portion of the quadratojugal.The facial portion of the bone is smooth and featureless. The

most conspicuous features of the quadratojugal, that it shares anextensive interfingering contact with the jugal and excludes thatbone from the ventral margin in making a touch contact with themaxilla, were noted above.

Both squamosals are present and are typically procolophonidin construction. The facial portion of the bone, however, is greatlyreduced to a slender, gently curving strip bordering the posteriortemporal emargination. The anterodorsal edge of the bone formsthe posterior margin of the small, elongate lateral temporal fen-estra ventrally and a narrowly quadrangular contact surface forthe supratemporal. The squamosal forms the approximate dor-sal half of the deep posteromedially aligned flange within theposterior temporal emargination. This portion extends ventrallyto terminate just dorsal to the condylar region of the quadrate.The posterior margin of this region of the squamosal is thick-ened and has the appearance of a pilaster in occipital view. Thesquamosal has a deep overlapping contact with the dorsal lamellaof the quadrate, and a less extensive overlapping contact with thequadrate process of the pterygoid.



Palate

The vomer is a narrow bone that bridges the premaxilla to therest of the palate (Fig. 2B). The ventral surface of each vomeris dominated by two sharp, conical fangs. The double pairedvomerine fang complex is positioned directly between the largepair of maxillary teeth. The interchoanal portion is slightly thick-ened and is the broadest region of the bone, whereas the pos-terior, post-dental third is conspicuously narrower and largelyconfluent with the ventral surface of the neighboring palatineand pterygoid. Although the bones are slightly separated ante-riorly, what is visible of the sagittal contact (anterior and poste-rior to matrix that has been left to shore up the vomerine fangs)suggests that the intervomerine suture runs straight down theventral midline. In ventral aspect, the free lateral margin of thebone forming the medial edge of the choana is slightly convexon the right side and weakly sigmoidal on the right. Posteriorly,the vomer extends slightly more than half way (from the levelof the posterior end of the choana) to the interpterygoid open-ing and makes contact with the pterygoid via a deeply serratesuture.

The most striking feature of the palatine is the absence of teeth,an apomorphy that is shared only with the Late Triassic procolo-phonids Hypsognathus fenneri (Sues et al., 2000) and Leptopleu-ron lacertinum (Saila, 2008a). The palatine forms the shallowlyconcave posterior margin of the choana. It contacts the vomermedially, forms a conspicuously serrate suture with the pterygoidposteriorly, a weakly interfingering suture with the ectopterygoidlaterally, and abuts the maxilla anterolaterally. The suborbitalforamen opens dorsally between the palatine and the lacrimal,but there is no evidence of a ventral egress for this foramen. Indorsal aspect the palatine forms the ventral half of a relativelybroad antorbital buttress, the lateral margin of which forms themedial margin of the orbitonasal foramen.

In ventral aspect the ectopterygid is a slender, narrowlywaisted element. Its slightly expanded anterior end contacts themaxilla and the jugal, whereas medially and posteromedially theectopterygoid is bounded by the palatine and the pterygoid, re-spectively. The bone forms a distinctly thickened anteromedialmargin for the subtemporal fenestra. As in other procolophonids,the transversely thickened posterior end of the ectopterygoidcontributes to the structure of the transverse flange. The apices ofboth flanges have been planed down by weathering, and thus thefull extent of the relative contributions of the ectopterygoid andthe pterygoid to the flange is unknown, but the resultant sectionsreveal that the former element forms a slightly serrate internalcontact with the latter.

The structure of the pterygoid (Fig. 2B, C) differs in many re-spects from that seen in other Early Triassic procolophonids suchas Procolophon trigoniceps, and resembles more the pterygoid ofLate Triassic forms. Most notably, it is devoid of teeth, like thepterygoid of H. fenneri (Sues et al., 2000). Anteriorly the ptery-goids contact each other along the midline via a suture that pro-gresses from weakly meandering anteriorly to deeply serrate pos-teriorly. The interpterygoid vacuity is triangular in ventral aspectand appears relatively long. Unlike the long, triangular openingin the basal procolophonid Sauropareion anoplus (Modesto andDamiani, 2007), the interpterygoid vacuity of NMQR 3564 ex-tends anteriorly only as far as the level of the posterior endsof the palatines, as in Pr. trigoniceps (Cisneros, 2008a:fig. 3a)and phylogenetically younger procolophonids. A basicranial re-cess of moderate size demarcates the posterior end of the me-dial margin forming the interpterygoid vacuity. The transverseflange is reduced in lateral extent compared to that of Pr. trigo-niceps (Carroll and Lindsay, 1985), but not to the extent seen inH. fenneri (Sues et al., 2000) and L. lacertinum (Saila, 2008a).The occipital view reveals that the preserved portions of bothtransverse flanges extend ventrally to the level of the articulat-

ing surfaces of the quadrate condyles, indicating that when com-plete the transverse flange must have extended ventral to boththe quadrate and the ventral margin of the skull roof, as in H.fenneri and L. lacertinum. A thickened ridge runs posteriorlyfrom the posterior corner of the transverse flange to the me-dial edge of the arcuate flange formed by the ventral portionof the quadrate flange of the pterygoid, as it does in Pr. trigo-niceps. The quadrate flange extends posterolaterally from thepalatal portion of the bone. It is relatively abbreviated comparedto those of other procolophonids, comprising no more than about40% of the maximum length of the pterygoid, whereas this fig-ure is approximately 50% in Pr. trigoniceps (Carroll and Lind-say, 1985:fig. 1b). The occipital view shows the quadrate flange ofNMQR 3564 to be as deep as that in Pr. trigoniceps (Carroll andLindsay, 1985:fig. 1e, f). The dorsolateral corner of the quadrateflange has an overlapping contact with the deep portion of thesquamosal.

The quadrate differs little from those of other procolophonids.It consists of a condylar portion that abuts the medial surface ofthe quadratojugal and a dorsal lamella that appears to be sand-wiched between the squamosal and the pterygoid. The condy-lar portion appears to be the same approximate anteroposte-rior thickness as that seen in Pr. trigoniceps. The articulatingfacets of both elements are weathered and their former bound-aries cannot be delineated, but the facets appear to have beenat least twice as broad as they were anteroposteriorly long andvaguely dumbbell-shaped in outline. The dorsal lamella, nar-rowly exposed in occipital view between the squamosal andthe pterygoid, is relatively tall; it is approximately one-half thepreserved height of the skull. A remarkable feature of thequadrate is a small, posterodorsally directed and medially curv-ing process that extends from the posteromedial corner of thebone, where the condylar portion meets the dorsal lamella (Fig.2D). No other procolophonid exhibits a small process of thiskind.

DISCUSSION

Relationships of Phonodus dutoitorum

Despite the absence of procolophonid hallmarks such as thepresence of a ventral temporal margin or quadratojugal spines,NMQR 3564 exhibits apomorphies that are indicative of a phy-logenetic placement within Procolophonidae. These include thepresence of a maxillary depression, the presence of a large maxil-lary tooth, and contact between the lacrimal and the ectoptery-goid. In addition, the edentulous palatines are suggestive of aclose relationship with Leptopleuron lacertinum and Hypsog-nathus fenneri.

In order to test the hypothesis that Phonodus dutoitorum isa leptopleuronine procolophonid, we added this taxon to thedata matrix of Cisneros (2008b) and reran the augmented matrixin PAUP∗ 4.0b10 (Swofford, 2002). We added Kitchingnathusuntabeni to the matrix of Cisneros (2008b) using the line ofcoding provided by Cisneros (2008c), but changed the codingsfor characters 1 and 40 to ‘0’ and ‘2,’ respectively. We alsochanged the codings for characters 0, 1, 10, 24, and 37 to ‘0,’ ‘0,’‘0,’ ‘?,’ and ‘?,’ respectively, for Coletta seca (based on Modestoet al., 2002); the codings for characters 16 and 49 to ‘0 and ‘1,’respectively, for Sauopareion anoplus (based on Modesto andDamiani, 2007); the coding for character 1 to ‘0’ for Tichvinskiavjatkensis (based on Ivachnenko, 1973); and the coding forcharacter 37 to ‘0’ for Leptopleuron lacertinum (based on Saila,2008a). Whereas Cisneros (2008b) ordered six of his characters,we ran all characters unordered to minimize assumptions ofcharacter evolution. A branch-and-bound search discovered 90optimal trees (each 121 steps in length), the strict consensusof which is shown in Figure 3. Apart from the inclusion of P.



FIGURE 3. Strict consensus of 90 opti-mal trees discovered in a PAUP∗ 4.0b10analysis of a modified version of the datamatrix from Cisneros (2008b). Tree length= 121, consistency index (CI) = 0.67, CIexcluding uninformative characters = 0.66,rescaled CI = 0.53. We have condensednine of the terminal taxa into more inclusivetaxa for this figure, as follows: Theledectinae(‘Eumetabolodon’ dongshengensis, Theledectesperforatus), Procolophoninae (Eumetabolodonbathycephalus, Kapes spp., Procolophon trigo-niceps, Teratophon spinigenis, Thelephon con-tritus, Thelerpeton oppressus, Timanophonraridentatus). Phonodus dutoitorum is codedfor the 58 characters of Cisneros (2008b) asfollows: 1?A1111??? ?0001???1? ????????10?B0?1121?? ?????????? ???????? where ‘A’and ‘B’ indicate uncertainty for states 1 and 2and for states 3 and 4, respectively.

dutoitorum, the topology of the consensus tree is the same asthat presented by Cisneros (2008c:fig. 5), with the exception thatKitchingnathus untabeni forms a polytomy with Coletta seca,Pintosaurus magnidentis, and Sauropareion anoplus at the baseof Procolophonidae (whereas only C. seca, P. magnidentis, andS. anoplus formed a polytomy with a clade containing all otherprocolophonids in Cisneros, 2008b, and C. seca and S. anoplusformed a clade at the base of Procolophonidae in Cisneros,2008c [P. magnidentis was excluded in the analysis of Cisneros,2008c]).

In all of our optimal trees Phonodus dutoitorum is a leptopleu-ronine. In a third of the optimal trees P. dutoitorum is the sistertaxon of the least inclusive clade that includes Sclerosaurus ar-matus and Hypsognathus fenneri; in another third it is the sisterspecies of Neoprocolophon asiaticus; and in the remaining third itis the sister taxon of the least inclusive clade that includes N. asi-aticus and H. fenneri. The decay analysis reveals that most cladeswithin Procolophonidae collapse with the addition of a singlestep, and there is no resolution among procolophonids followingtwo extra steps.

Phonodus dutoitorum is the oldest known leptopleuronine.The Induan age of this species mandates downward range exten-sions for two or three leptopleuronine lineages, depending on theexact phylogenetic position of P. dutoitorum. The topology withthe least stratigraphic debt positions P. dutoitorum as the sistertaxon of a leptopleuronine clade that contains N. asiaticus, andrequires a long ghost lineage for Pentaedrusaurus ordosianus, ashort ghost lineage for N. asiaticus, and a ghost taxon for theancestor of the clade containing the latter species and the re-maining leptopleuronines (Fig. 4A). The other two tree topolo-gies (Fig. 4B, C) exhibit slightly greater stratigraphic debt, andrequire ghost lineages for both Pe. ordosianus and N. asiaticusand a ghost taxon for clade ‘N.’ These inferred range extensionsindicate that a modest leptopleuronine diversity should be rep-resented in continental vertebrate faunas of Olenekian age, butthis is not evident in fossil assembages of the late Early Triassic.In strong contrast, abundant fossils of representatives of the lep-topleuronine sister group, Procolophoninae, are not uncommonat localities of Olenekian age (Kitching, 1977; Li, 1983; Cisneros,2008b).

Paleobiology of Phonodus dutoitorumDietary modes in procolophonoid reptiles have been inferred

primarily on the basis of the marginal dentition. Owenettidsand basal procolophonids (e.g., Kitchingnathus untabeni) areregarded as insectivores because most exhibit numerous, sim-ple, non-occluding teeth, whereas larger and phylogeneticallyyounger procolophonids, including Procolophon trigoniceps andHypsognathus fenneri, are thought to be high-fiber herbivores be-cause they possess a reduced marginal dentition that features rel-atively large, occluding molariform teeth (Gow, 1978; Reisz andSues, 2000; Cisneros, 2008c). Sues et al. (2000) cautioned, how-ever, that the consumption of arthropods with hard exoskeletonsin addition to plant matter could not be ruled out for Pr. trigoni-ceps, H. fenneri, and closely related forms.

The severe weathering sustained by the marginal dentition ofNMQR 3564 greatly complicates an assessment of the diet ofPhonodus dutoitorum. Only the relatively enormous posteriormaxillary teeth remain of the marginal dentition. Although someprocolophonid taxa possess relatively large posterior maxillaryteeth (e.g., Anomoiodon liliensterni: Saila, 2008b; Thelerpeton op-pressus: Modesto and Damiani, 2003), only Haligonia bolodon,from the Norian of Nova Scotia (Sues and Baird, 1998), has a pos-terior maxillary tooth of such relative enormity. The remains of acomparably small alveolus immediately anterior to the left max-illary tooth in NMQR 3564 suggests that the maxilla supportedat least one much smaller tooth anterior to the large bulboustooth, akin to the condition seen in Ha. bolodon (Sues and Baird,1998:fig. 2). The large maxillary tooth of Ha. bolodon displays asmall lingual wear facet on its apex. Sues and Baird (1998:527)remark that this wear facet is poorly defined, and inferred thatocclusion between upper and lower dentitions in Ha. bolodonwas not developed to the degree seen in Pr. trigoniceps and H.fenneri. Possibly the occlusal condition seen in Ha. bolodon alsopertained to P. dutoitorum, but the utter absence of crown apicesin the latter precludes any inference into occlusion in that species.

Despite the lack of information on the crown morphology ofthe large maxillary teeth, certain aspects of the general skull mor-phology suggest that P. dutoitorum was durophagous: the largestmaxillary teeth are positioned ventral to well-developed antor-bital buttresses and, apart from the presence of a small lateral



FIGURE 4. Stratigraphically calibrated treesillustrating the implications of the three pos-sible phylogenetic positions of Phonodus du-toitorum within Leptopleuroninae for lepto-pleuronine diversity during the Olenekian. A,topology with the least stratigraphic debt. B–C,topologies with greater debt. The black bars in-dicate known ranges, the gray bar indicates un-certainty in the placement of the stratigraphicrange of Pentaedrusaurus (following Cisneros,2008b), and open bars indicate ghost lineagesand ghost taxa. Clade ‘N’ refers to the cladeof leptopleuronines identified in Figure 3. Nu-merical dates from Mundil et al. (2004) andLehrmann et al. (2006).

temporal fenestra, the temporal region is entirely roofed over inbone and there is no ventral emargination. The deeply interdig-itating suture between the jugal and the quadratojugal presum-ably served to resist the tensile forces that would have manifestedbetween the alveolar region and the jaw articulation when thelarge maxillary teeth were engaged during feeding. Our treetopology indicates that the temporal morphology seen in P. du-toitorum is clearly a secondary condition, one that is derived fromthe ventrally emarginated temporal condition retained in suchtaxa as Neoprocolophon asiaticus and Procolophon trigoniceps.The closure of the ventral temporal emargination in P. dutoito-rum is analogous to the closure of the lateral temporal fenestra inthe diapsid genus Araeoscelis, which was inferred by Reisz et al.(1984) to be an adaptative response to a durophagous diet ofinvertebrates. In P. dutoitorum, however, the ventral margin ap-pears to have been closed by extensions of both the jugal and thequadratojugal, resulting in a deeply interfingering contact. Giventhe uncertain relationship of P. dutoitorum to phylogeneticallyyounger taxa such as Scoloparia glyphanodon and Leptopleu-ron lacertinum, it is unclear whether the condition seen in P.dutoitorum is ancestral to the condition seen in those youngerleptopleuronines, in which a ventral emargination is also absentbut the ventral margin of the temporal region is markedly convex.

The evidence marshaled above for the hypothesis ofdurophagy in P. dutoitorum is seemingly at odds with the obser-vation that the walls of the large maxillary teeth appear relativelythin: the thickness of the tooth wall ranges 0.2–0.3 mm, formingroughly 8–12% of crown basal diameter (measured transverselyacross the right tooth). To our knowledge, no histological workhas been published on procolophonoid dentition, but the workof Ricqles and Bolt (1983:fig. 15) on the Early Permian eureptileCaptorhinus aguti (a durophagous captorhinid according to Hot-ton et al., 1997) documents that the crown walls of the labial-mosttooth in the multiple-rowed portion of the maxilla are 0.23–0.27mm thick and form 33–44% of the basal diameter of the crown.Thus, the crown walls of P. dutoitorum are approximately thesame absolute thickness as those of C. aguti, but they are thin

relative to overall tooth size. At first glance, this suggests that theteeth of the former taxon were structurally weaker than those ofthe former. However, Evans and Sanson (1998) remark that teethof the same shape but of different sizes require different forces topenetrate food items. A direct comparison of tooth efficiency be-tween P. dutoitorum and C. aguti is complicated by the damageto those of the former taxon and minor shape differences, buta corollary of Evans and Sanson’s (1998) observation on toothefficiency is that one needs to be mindful of the absolute sizeof the animal. It follows that it is possible that the smaller sizeof P. dutoitorum, with a skull length of 25 mm, could accountfor the absence of expected modifications for strengthening thewalls of its teeth, because this procolophonid was probably notable to generate the jaw adductor forces that individuals of C.aguti, which attained skull lengths of 80 mm (Seltin, 1959), wouldhave by virtue of their larger size. Pursuant to Evans and San-son’s (1998) statement on the relationship between tooth scaleand tooth efficiency, it is interesting that the largest teeth of theacleistorhinid parareptile Colobomycter pholeter are character-ized by folding of the relatively thin tooth walls (Modesto, 1999;Modesto and Reisz, 2008). Modesto and Reisz (2008:677) sug-gested that this folding may have served to strengthen the largestteeth in C. pholeter. In this respect, we note that the skull of C.pholeter is estimated to have attained at least 50 mm in length(Vaughn, 1958), thereby reaching twice the size of the skull of P.dutoitorum. The walls of the large maxillary teeth of the latterparareptile may not have required either thickening or mechan-ical support in the form of tooth folding because of the tiny sizeof its skull.

Finally, clues to the diet of Phonodus dutoitorum may bedrawn from the palatal dentition. The palate of this speciesis nearly edentulous apart from the presence of two pairs ofvomerine fangs. In addition to their conspicuous size, what is re-markable about the vomerine teeth is that they extend ventrallydirectly between the large, bulbous maxillary teeth. It is difficultto dismiss this organization of the marginal and palatal teeth ascoincidental, but given the incomplete crown morphology of the



large maxillary teeth, it would be premature to draw conclusionson the purpose of this dental organization. The vomerine teethdo not exhibit distinct facets or other conspicuous wear, soit seems likely that they were used to pierce or to hold fooditems. Pursuant to this observation, the apices of these fangs aredirected slightly posteriorly, which suggests that they served tokeep food from moving (or slipping) anteriorly. We know of noherbivorous tetrapods with remarkably few and relatively largepalatal teeth with this orientation, so it seems plausible to us thatP. dutoitorum preyed on small invertebrates. We hope that futurematerial will preserve more of the dentition than is present inthe holotype and only known specimen, to test these inferences.

Origins of the Karoo Procolophonid Fauna

Our description of Phonodus dutoitorum adds a new elementto the procolophonoid assemblage of the Induan part of theLystrosaurus Assemblage Zone of South Africa. Previously we(Botha et al., 2007) reported a modest diversity of Induan pro-colophonoids that spanned the uppermost strata of the BalfourFormation and lowermost strata of the Katberg Formation, andformed part of a Permo-Triassic recovery fauna (sensu Smithand Botha, 2005), and suggested that procolophonoids were notgreatly perturbed by the mass extinction of 252 million years ago.

This small assemblage of Induan-age Karoo procolophonoidsnow comprises two owenettids (‘Owenetta’ kitchingorum andSaurodektes rogersorum), two basal procolophonids (Coletta secaand Sauropareion anoplus), and a basal leptopleuronine procolo-phonid (Phonodus dutoitorum). It exceeds the taxonomic andmorphological diversity of procolophonoids from the LaurasianInduan, represented by Contritosaurus convector, C. simus, andPhaanthosaurus ignatjevi from the Russian Platform. TheseLaurasian taxa were thought to be so similar that Spencer andBenton (2000) regarded the former genus to be a junior synonymof the latter.

The owenettid and procolophonid members of the KarooInduan fauna are probably endemic forms (Modesto et al.,2002). Optimization of Laurasian and Gondwanan distributionsonto the tree seen in Figure 3 (Fig. 1S, Supplementary Data1, www.vertpaleo.org/jvp/JVPcontents.html) indicates that it ismost parsimonious to infer that a Laurasian distribution is an-cestral for Leptopleuroninae, and that P. dutoitorum is a lepto-pleuronine migrant to the Karoo Basin. Accordingly, the taxo-nomic diversity of Karoo Induan procolophonoids is comprisedpredominantly of endemic Gondwanan taxa (the owenettids, Co.seca, and S. anoplus), and it is enriched slightly by a faunal ele-ment of Laurasian aspect (P. dutoitorum).

The taxonomic and morphological diversity of the Karoo Ind-uan procolophonoids described here supports the hypothesis thatprocolophonoid reptiles were not greatly perturbed by the envi-ronmental degradation that must have characterized terrestrialenvironments in the wake of the extinctions that mark the Permo-Triassic boundary (PTB). This agrees with the general conclu-sions of Botha and Smith (2006) that terrestrial vertebrate fau-nas in the Karoo Basin recovered from the PTB extinctions rela-tively rapidly, within about 5 million years (time equivalent to theLystrosaurus AZ). This idea is consonant with the conclusions ofFraiser and Bottjer (2007) and Chen et al. (2007), but it contrastsstarkly with the interpretation that continental tetrapod faunasof the Russian Platform showed little sign of recovery in the 15million years following the PTB event (Benton et al., 2004), andthat full global recovery for continental tetrapod faunas requiredsome 30 million years (Sahney and Benton, 2008). Thus, it seemslikely that either continental environments in the Karoo Basinduring the Induan fostered a relatively rapid recovery of terres-trial faunas, possibly owing to the monsoonal climate that char-acterized central Gondwana (Smith and Botha, 2005), or the Ka-roo Basin was more successful in recruiting members for its PTB

recovery fauna from refugia in the Gondwanan hinterland. Thelatter hypothesis was proposed specifically to explain the originof the archosauromorph reptiles of the South African Triassic(Reisz et al., 2000). Yates and Warren (2000) considered the pos-sibility that stereospondyl temnospondyls may have weatheredthe end-Permian extinctions in a Gondwanan refugium possiblylocated in what is now Africa, but favored a putative refugium inAntarctica because they thought central Gondwana might havebeen too dry to support a diverse temnospondyl fauna during thePermian. Such conditions were probably less of an impedimentfor procolophonoids and other reptiles.

CONCLUSIONS

We describe the anatomy of a new genus and species of lepto-pleuronine procolophonid from the Lower Triassic Katberg For-mation of South Africa. Phonodus dutoitorum, gen. et sp. nov.,is an unusual leptopleuronine because it lacks quadratojugal pro-cesses and a ventral temporal emargination, but exhibits a lat-eral temporal fenestra. It is diagnosed also by the presence of asingle large maxillary tooth, midline dorsal contact between theprefrontals, reduced pterygoid flanges, and several other autapo-morphies. The damage to the marginal dentition and the nearlyedentulous palate together preclude a definitive statement on theprobable diet of P. dutoitorum, but the presence of large marginalteeth is suggestive of durophagy, and the presence and the mor-phology of well-developed vomerine fangs suggest that this lep-topleuronine preyed on invertebrates. A phylogenetic analysispositions P. dutoitorum basally in Leptopleuroninae. The pre-cise relationship between P. dutoitorum and the other leptopleu-ronines cannot be determined with the available evidence, butthe new species does not appear to be the most basal leptopleu-ronine. Each one of the three possible phylogenetic positions forP. dutoitorum suggests that the early evolutionary history of Lep-topleuroninae is poorly recorded in the Lower Triassic. The de-scription of P. dutoitorum increases the number of Karoo Ind-uan procolophonoids to five, and it supports the hypothesis thatprocolophonoid evolution was not greatly affected by the Permo-Triassic mass extinction.

ACKNOWLEDGMENTS

We thank Jan and Susan du Toit for permission to prospecton Bergendal, and reviewers J. Cisneros and L. Saila for usefulcommentary. S.P.M. thanks M.V.H. Wilson for going above andbeyond as editor to make last minute corrections to this paper.This project was funded by discovery grants (nos. 288126-04 and288126-07) from the Natural Sciences and Engineering ResearchCouncil (NSERC) of Canada to S.P.M. and R.R.R., a New Op-portunities Fund award from the Canadian Foundation for Inno-vation to S.P.M., and a grant (GUN 2061695) from the NationalResearch Foundation of South Africa to J.B.B.

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Submitted February 4, 2009; accepted August 24, 2009.


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Journal of Vertebrate Paleontology A new and unusual ... · 716 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 30, NO. 3, 2010 FIGURE 1. Phonodus dutoitorum, gen. et sp. nov., NMQR 3564.Photographs