NANOWANA GEN. NOV. .SMALL MADTSOIlD SNAKES FROM THE MIOCENE OF RIVERSLEIGH: SYMP A TRIC SPECIES WITH DIVERGENlL Y SPECIALISED DEN1111ON
JOHN D. SCANLON
Scanlon, J.D. 19970630: Nanowana gen. nov., small madtsoiid snakeS from the Miocene of Riversleigh: sympatric species with divergently specialised dentition. Memoirs of the Queensland Museum 41(2): 393-412. Brisbane. ISSN 0079-8835.
Two small early Miocene madtsoiid snakes from Riversleigh, NW Queensland are described as Nanowana godthelpi gen. et sp. nov. and N. schrenki gen. et sp. nov. Jaw elements of the former are depressed, lack ankylosed teeth, and have alveoli of nearly uniform size; these features are interpreted as signs of a coadapted character complex ( .arthrodonty , ) where the teeth are attached to the jaws by a fibrous hinge. This condition is associated with a diet of hard-scaled scincid lizards. The latter species retains ankylosis, and has strongly enlarged teeth on the anterior dentary and middle maxilla indicating a distinct method of subduing prey, but extant analogues are also predominantly scincivorous. Departure in each species from the nearly homodont, ankylosed condition in other madtsoiids is interpreted as adapta- tion to a diet of scincid lizards. These divergent, but functionally parallel specialisations are likely to be independently derived from the ancestral condition.
John D. Scanlon, School of Biological Sciences, University of New South Wales, New South Wales 2052, Australia (email: [email protected]): received 7 February 1997.
Madtsoiid snakes in Tertiary faunal assemblages plete anteriorly the numbers are spelled out in of Riversleigh(Scanlon 1992.1993,1995,1996) words. In illustrating cranial bones, views of the have been referred to Yurlunggur Scanlon, 1992 same specimen are usually arranged parallel to and Wonambi Smith, 1976. Other Riversleigh each other, in lateral, dorsal, medial, ventral as- madtsoiids cannot be included in previously pects. Figures of vertebrae have left lateral, ante- known genera. Two small species, estimated to rior, posterior, dorsal, and ventral views of each reach 1m long, are represented by upper and element in a vertical row. If more than one verte- lower jaw elements from System B (Archer et al., bra are shown in an illustration, they are arranged 1989, 1994) on Godthelp Hill. Some are associ- (I to r) in order from anterior to posterior. ated with vertebrae, but the two speciescannot be distinguished unambiguously on vertebral char- SYSTEMATICS acters. I include them in a single genus which possibly unnatural treatment allows generic iden- Family MADTSOIlDAE Hoffstetter, 1961 tification of isolated vertebrae from other sites. This paper provides descriptions of the two Nanowana gen. nov. speciesincluding some ontogenetic stages.While analysis of phylogeny of madtsoiids awaits de- TYPE SPECIES. Nanowana godthelpi sp. nov. tailed comparisons with other primitive snakes, OTHER SPECIES. Nanowana schrenki sp. nov. some functional and evolutionary points are noted by analogy with extant forms. ETYMOLOGY. Greek nanos, a dwarf and Warlbiri (Tanami Desert, central NT) Wana, Rainbow Serpent MATERIALS AND METHODS of Aboriginal mythology.
Material is housed in the Queensland Museum DIAGNOSIS. Small, upto 1.5m long; neural (QMF), Australian Museum (AMF), Northern spine low to moderately high, not extending close Territory Museum of Arts and Sciences(NTMP), to anterior edge of zygosphene; zygosphene shal- Museum of Victoria (NMVP), and South Austra- low, with anterodorsal edge straight, slightly con- lian Museum (SAMP). ...(SMNR) specimens ex- vex or concave in dorsal view; subcentral ridges amined in Paris by courtesy of J.-C. Rage. well-defined, straight or slightly concave or con- Teeth or alveoli are numbered beginning from vex in ventral view; haemal keel relatively nar- the anterior on complete jaw elements; on frag- row, with 'paired hypapophyses' in posterior ments where the tooth row is or may be incom- trunk defined laterally, but not projecting ven- 394 MEMOIRS OF THE QUEENSLAND MUSEUM
DISCUSSION. Vertebrae
can be distinguished from
FIG. I. Nanowana godthelpi sp. nov., QMF3I379, holotype, upper jaw bones other madtsoiids, but their
~rig.ht. (A) ~d left(B) m.axillae, p3;latines (C,D) and pterygoids (E,F) of a single common features (including
IlldlVldual) III palatal vIew, CS SIte. Scale bar=5mm. small size) may be sym-
plesiomorphic; the concept trally or separated by a median concavity; neural of Nanowana containing these 2 species can be
arch in posterior trunk depressed, its lateral por- described as a 'marriage of convenience'. The
tions strongly concave dorsad. Anterior t~p of phylogenetic relationships of these with other
maxilla with medial expansion (septomaxIllary madtsoiids remain unknown, but they are treated
process) contributing to floor of narial chamber; as a unit because their vertebrae (which provide NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 395 396 MEMOIRS OF THE QUEENSLAND MUSEUM
within Yurlunggur, and is proportionally similar with prominent, also lizard-like, ectopterygoid to Nanowana in some), but Nanowana differs processes. Proportions of jaws indicating a rela- from Yurlunggur in the shape of the zygosphene, tively long postorbital skull and moderately short, and the haemal keel of posterior trunk vertebrae rounded snout. being narrower and lacking a median concavity. Palatine: Left more complete than right, both Comparisons with non-Australian forms do not well-preserved. Eleven alveoli forming a sigmoid suggest any links closer than that with Yurlun- tooth row, convex laterad anterior to an inflection ggur, and will not be pursued here. The rib-heads and lateral concavity (slight, but definite and of Nanowana have not been considered in detail, angular) between 7th and 8th. Dorsolateral crest but appear to be similar in shape to those of arising above 3rd alveolus, bifurcating above 4th Yurlunggur and Wonambi (Scanlon, 1993). to form anterior edges of maxillary and choanal processes.Maxillary process with an obliqu~ an- Nanowana godthelpi sp. nov. terior edge (near 45° from sagittal plane), longi- (Figs 1-8, Table 1) tudinallateral edge and transverse posterior crest on its ventral face, level with the 5th alveolus on ETYMOLOGY. For Henk Godthelp, University of the left palatine (4th-5th on right side); process New SouthWales, in recognitionof his contributions not perforated or notched for the maxillary nerve. to Australianpalaeontology. Anterior edge of the choanal process smoothly concave anteriad for its full width, reaching be- MATERIAL. Holotype QMF31379, associatedele- mentsof a singleindividual comprisingpartial to com- tween level of 4th and 5th alveoli; then curving pletemaxillae, palatinesand pterygoidsof both sides. strongly anteroventrally, extending to front of ParatypesQMF 31383,31384associated dentaries and 2nd alveolus. Vertical anteromedial part of the compounds of a single individual; dentaries choanal process bilobed anteriorly, a dorsal lobe QMF20892,23052, 23053, 23054, 23056); maxillae curved mediad, the other laterad (forming articu- QMF31380, 31382,31386,31387; palatine lations with the parasphenoid and vomer); third, QMF31381;pterygoids QMF23058, 31393. All types posterolaterally pointed, lobe on the ventral edge from early Miocene (SystemB) Camel SputumSite, deflected laterad, contributing (along with the Godthelp Hill. Other material: Camel Sputum Site, trunk vertebrae QMF19741. Upper Site, dentary vomer and ectochoanal cartilage, presumably) to QMF31389; palatine QMF23066; maxilla fragment the floor of the choanal passage.Lamina of choa- QMF31390;pterygoids QMF23067, 31385; seriesof nal process strongly arched anteriorly, flatter pos- cloacal vertebrae.Mike's Menagerie Site, anterior teriorly, and ventrally deflected part of lamina fragmentof pterygoidQMF19742. Creaser's Ramparts reducing in depth posteriorly. Posteromedial cor- Site,dentary QMF23076. ner of process level with rear of 9th alveolus, posterior margin sinuous so that posterior process DIAGNOSIS. Palatine lateral process about as not sharply demarcated (as in some specimens); long as two alveoli (nearest to 4th and 5th), ven- margin concave medially, convex posteriorly. tral concavity of process with obtuse angle ac- Posterior extremities of choanal process and commodating posterolateral angle of palatine tooth row extending back level with each other, process of !11axilla. Maxilla with 23 tooth posi- both with lateral margin parallel to tooth row, and tions, palatine 11, pterygoid 9, dentary 16. Teeth separatedby a distinct triangular notch extending not ankylosed to alveoli; maxillary alveoli vary forward to middle of II th alveolus (thus, poste- only slightly in size, dentary alveoli largest in rior edge W -shaped); on dorsal face this notch centre of tooth row ( 4-8 or 5-8). Posterior part of continued as a tapering trough extending to rear maxilla strongly depressed. Dentary tooth row of9th; ventrally a step-like groove running from curved in dorsal view. Two or 3 mental foramina, the apex of the notch anteromediad to between all anterior to the 7th alveolus. 9th and lOth, with a shallow trough posterior and partly medial to the groove. Small foramen DESCRIPTION OF HOLOTYPE. Upper dentig- dorsomedially on the dentigerous process, just erous elements in a single block (without verte- below the ridge continuous with the anterior edge brae or other elements) are complete on one or of the choanal plate; a large foramen medial to both sides, missing bilaterally only the posterior the 8th alveolus, piercing the plate and emerging (quadrate) processesof the pterygoids (Figs 1,2). dorsally as a posteriorly widening foramen be- Maxillae long and flat posteriorly, supporting a tween 8th and 9th; another small foramen an- high lizard-Iike prefrontal process anteriorly; pal- teromedial to lOth alveolus. Dorsomedially on atines with 'alethinophidian' features; pterygoids the anterior dentigerous process with tip of a tooth NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 397
emerging from the bone (this is the only tooth associ- ated with jaws of this spe- cies). Right and left palatines al- most identical; spacing of al- veoli slightly different on different sides; alveoli 2-5 in the right shifted posteriorly, relative to the left (alveoli I and 2 on the left, 5 and 6 on the right, confluent). Lateral (maxillary) process with B - small but distinct angular concavity marking the lon- (",.rf('j~ ~ ~~-- ~ . gitudinal (lateral) and ;~' oblique (anterolateral) sec- tions of the margin. -'-"-'-"- ~I/~ Pterygoid. Nine alveoli ~ (complete row), anterior tip (length of approximately 1.5 alveoli) edentulous. Tooth row curving medially poste- riorly, following inner edge c .:.0.~ of bone; ventral face nar- -.,-'"';"' .,., -""'-"';. rowing to a point anterior to ..,¥,~--::::: "-- -~o ,,",'\~ tooth row, point interlocking I ~".""",,' with posterior notch of pala- ,...,.,..='0"~"2~~;;"- tine. Dorsal surface forming ,.::;:_.: a longitudinal trough, with ~~~- foramen above I st alveolus (opening anteriad),lateral to a dorsomedial ridge. Lateral D ,',;~ margin smoothly convex, diverging gradually from :!i;,~;!~~~'~!1!;,'!~'; tooth row; anterior edge of ectopterygoid process di- verging at about 120° from this margin, level with 7th alveolus. Process nearly as wide as rest of bone at this E point, about as long as wide; its anterior and lateral edges at 90° in dorsal or ventral ~, , view ,lateral margin inclined \, strongly posteroventrally, with posterior extremity produced as a knob-like ex- tension and posterior edge FIG. 3. Nanowanagodthelpi sp. nov. QMF31383,31384, paratype lower jaws. strongly concave. No part of A, B, ~eftdent.ary in lateral and me:dialview (uI?Perpo~terior process broken the ectopterygoid facet ex- ~d slIghtly dIsplaced).C, D, E, nght dentary In medIal, dorsal, and lateral pos d d II C vIew. Scale=5mm. e orsa y. oncave posterior surface of the pro- cesscontinuous with the ventrolateral face of the medially by a narrow extension of the ventral posterior lamina (quadrate process), bounded (occlusal) surface. Quadrate process broken off
~ 398 MEMOIRS OF THE QUEENSLAND MUSEUM
TABLE I. Measurements (mm) of jaws of Namowana godlhelpi sp. nov. C I, C2, etc.=single individuals; L=left, R=right. Alveoli were selected as landmarks for some measurements because they could be identified in fragments, but there is variation in the position of anterior alveoli (even between sides of an individual). Values in brackets are minima for measurements affected by damage. Palatine (ventral view): ptl=length of palatine from anterior tip of dentigerous process to posterior tip of tooth row spine or choanal process; pcl=base length of choanal process from intersection of anterior edge with dentigerous process to apex of posterior notch; pIll =length from anterior tip to anterior edge of II th alveolus; ptw=width across choanal and maxillary processes; pcw=width in same line of choanal process; prw=width in same line of tooth row bar; pmw=width in same line of maxillary process. Pterygoid (ventral view): ttl=length from anterior spine (in plane of alveoli, not dorsal lappets) to rear of 9th alveolus; trl=tooth row Ist-9th alveolus; tte=from anterior spine to furthest point of ectopterygoid process; t15= length across most posterior 5 alveoli (5-9); taw=width between near-parallel edges anterior to ectopterygoid process; tpw=width from basipterygoid facet to intersection of ectopterygoid process and dorsolateral edge of posterior lamina; ttw=width from basipterygoid facet to furthest point of ectopterygoid process. Maxilla: mtl=length; map=length from anterior tip to posteromedial angle of palatine process; m 712=length from anterior edgeS of7th-13th alveolus; mpw=width across palatine process; mph=depth at prefrontal process. Dentary: mff=number of mental foramina; dtl=straight-Iine length; dl 15=length to anterior tip of 15th alveolus; dlf=length to lateral fossa; d4t= posterior edge of 4th alveolus to posterior extremity; d4 15=posterior edge of 4th to anterior edge of 15th; d4f= posterior edge of 4th to lateral fossa; dl 7=anterior tip to anterior edge of 7th alveolus; dmd=depth from dorsolateral to ventromedial edge in middle part of bone; dpp=depth of upper
F 31379 ~-123058 I 31386 I 31380~ 31382 1_31393 I 23066 I 23067 I 31385 I C1 R CIL C2L C2L C2R C3R C3L- C4R UlL Ut R Ut L (7.6) 7.7 ~ 1 4.4 4.2 4.0 4.5 I 6.6 6.7 ~ 3.8 3.9 ~ 4.0 1.9 1.9 2.0 ~ 0.9 0.9 1.1 1.0
W 1.1 JLQ) (0.9) (0.8) ttl 5.7 trl 4.9 ne 6.8
tis 2.6 ~ 1.6.5 R ~ ~ 1:.IL 1.7 1.7 (1.0) 1.6 ].6
2.4 i 2.4 3.1 2.9 3.0
4.2 I 4.1 (3.9) 4.3 (3.9)
~ 7.4 5.4 5.7 4.6 5.2 2.3 . ~ 2.8 2.8 rnoh (3.3) i 3.9 3.6 3.3 Dentaries QMF I 31383 I 31384 I 20892123OS2lnQ531 23054 I 23056 I 31389 I 23076 I
Ind. CIR Cl L C2L C2R ~ C3R C4R ~ CRL mff 3 2 2 3 2 2 3
dtl 15.1
~ 15.6 14.1 13.3 dlf 12.3 11.4 11.2 12.4
d4t ~ ~ ~ 14.2 ~ 11.3 12.3 11.1 10.2 11.0 d4f !Q. 9.5 ~ 8.2 7.7 4.9 9.6
~ 7.8 6.5 6.3 8.0 dmd 3.2 3.0 2.7 2.6 3.3 (2.4) 1.6 2.9 ~ dDD 1.0 0.9 0.9 0.9 1.4 NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 399
posteriorly about half the length of the tooth row closer to medial edge; lateral edge forming a low behind the ectopterygoid process. Basipterygoid dorsolateral crest (possibly homologous with articular surface opposite ectopterygoid process, more prominent crests or bulges in snakes such an oval facet facing dorsally and slightly medi- as Dinilysia and pythons). Lateral as well as ally, beginning level with front of 8th alveolus medial parts of posterior maxilla apparently over- and extending to beyond 9th, only slightly dis- lapped by the ectoperygoid, forming slight con- tinct in outline from the rest of the medial edge. cavities on either side of a slight dorsal crest. Apart from the anterior foramen mentioned Between ectopterygoid facet and prefrontal pro- above,3 foramina dorsally, anterior, lateral and cess, the suborbital surface with a shallow longi- posterior to the facet; anterior 2 near the midline tudinal groove which probably either was, or of the bone, posterior foramen close to the medial bounded, a facet for the jugal (an element lost in edge. A shallow but distinct transverse groove on extant snakes but probably retained in l;>inilysia the dorsal surface of the ectopterygoid process. and madtsoiids, including Wonambi; Estes et al., Left pterygoid retaining posterior 8 alveoli, 1970, Scanlon, 1996). which are slightly smaller and more closely spacedthan on the right; possibly a lOth alveolus PARA TYPES. Right and left mandibles or longer edentulous gap anteriorly. (QMF31383, 31384), each compound and den- Maxilla. Alveoli 23, varying only slightly in tary , in loose articulation, lacking the splenial, size; row curved medially anteriorly, straight pos- angular and coronoid of each side (Figs 3, 4). teriorly. Anterior alveoli elongate anterolateral- Right: Tooth row incomplete posteriorly, bro- posteromedially; anterior of maxilla wider than ken through ISth alveolus; no sign ofankylosed deep, with dorsomedial edge forming a crest teeth. 4th to 8th largest alveoli, subequal, size above Ist-3rd alveoli, with slight concavities dor- reducing posteriorly and anteriorly. In lateral sal and medial to it. In lateral view, ventral margin view, dorsal edge convex dorsad from Ist to Sth slightly convex up to lOth alveolus, nearly alveolus, concave dorsad for rest of length. Ven- straight posteriorly; dorsal edge rising smoothly tral edge slightly concave anteriorly, remainder and increasingly steeply from the anterior tip to convex but somewhat worn. Three mental foram- between 6th and 7th alveoli; highest part of the ina, below 3rd, 4th and 6th alveoli, opening an- dorsal process (7th to 9th) forming the dorsomed- terodorsad. Posterior lateral fossa (compound ial surface for articulation with the prefrontal. On notch) extending to between lOth and I Ith. Lat- the posterior slope of the process, a low promi- eral face smooth but with dorsolateral ridge de- nence above the II th alveolus probably the inser- fined by slight longitudinal concavity through tion site for the postorbital ligament, but may also foramina. In dorsal view, tooth row concave me- mark the anterior extent of thejugal; by 13th bone diad, slightly more so anteriorly; alveoli round or very shallow, continuing so to the posterior ex- squarish except first two which are somewhat tremity. Large lateral (trigeminal) foramen open- elongate transversely. ISth alveolus on a narrow ing anteriorly above the 5th-6th alveoli; two process distinguished by an angular concavity smaller foramina, equally close to ventral edge, from the expanded dorsomedial shelf. The medial above 7th-8th and 9th- lOth, and 3 small foramina ridge forming the upper edge of Meckel's groove higher on the prefrontal process. Medial edge overhanging the groove distinctly up to the 8th forming a shelf-like 'septomaxillary' process alveolus; the overhanging edge of the upper facet from 2nd to 4th alveolus, separated from the for the splenial beginning below the 8th but more palatine process which widens gradually from 7th dorsally, forming with a slightly acute, pointed and then sharply at lOth, then gradually ap- posteroventral process separatedby a right-angle proaches maximum width at a sharply obtuse notch (in medial view) from the dorsal shelf. posteromedial angle between I I th and l2th. Me- Meckelian groove narrowing anteriad, anterior dial shelf narrowing steeply from this point, then end slightly expanded, communicating by a fora- very gradually, but with a step-like inflexion at men with alveolus of Ist tooth. Smooth bulb-like level of 18th alveolus (marking location of ante- swelling overhanging the groove medial to the I st rior tip of ectopterygoid). Large foramen entering and 2nd alveoli. maxilla at broadest part of the palatine process, Left: Two mental foramina, between 3rd and above I I th alveolus, and a smaller foramen exits 4th, and Sth and 6th. Posterior lateral fossa ex- at the same level above the 7th. Tooth row fol- tending to between II th and 12th alveoli. lowing lateral margin closely from 1st-ll th alve- Right compound. Elongate, shallow, 18.8mm oli, then gradually crossing over with 19th-23rd long, 16.8mm from anterior tip to dorsal extrem- 400 MEMOIRS OF THE QUEENSLAND MUSEUM NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 401
, i:';\ tacting the splenialand den-
1 -j -, 'I Leftthetary, right, brokencompound but brokenon bothsimilar ~steri-sides. to " \~:'l ; ~~~, , "' ,,- orly through the articular . .1 I facet. l- ~ When placed in articula-
ri ~ tion, the right compound and
1.:- dentary forming a smoothly ~. .. , ~ curved structure, with total
~~ straightline length approxi- \.~ \"' \~ , mately 29.5mm. , 1 ;:./,. Other paratypes and re- ~t ',. \q \ !{ / :;' ferred jaw elements (partial ~!'1..\ 1, dentaries, maxillae, pala- tines, pterygoids) show A B c D some individual variation (Figs 5, 6) and probably on-
togenetic changes of propor-
tions (allometry): the
smallest dentary, QMF
, 23056, is relatively deeper ~1 than larger specimens
(Table I ), while the largest,
QMF23076, is relatively
slender except for a particu- ,' :! 1.~ i~"' ,~.:. , " larly deep upper posterior
~\t process. ~;,'i' \ Vertebrae. In shape and ~l:\' r-:::~c ~~; ~(,.~. proportions, vertebrae sim- '{;.:.,..;~,;:~ ~ *)1",'";; { Q \;f;: ilar to, and intermediate be- ~ ~ ~i~ , 0, , tween Yurlunggur and Ldl \; ',"",," 0,:",. ) Patagoniophis and differ .0 , conspicuously from Al- amitophis, Wonambi and :;~u~,,~J , ~ \," Madtsoia. Typical anterior,
middle and posterior trunk
E F G H vertebrae recognised (cf.
LaDuke, 1991, Scanlon,
, vertebra1992, 1993);possibly most 3rd anteriorcervi-
FIG. 5. Nanowana godthelpi sp. nov., paratype, maxillae, CS Site, A-D, cal (cf. Y. camfieldensis
QMF31386,.in ventral, medial, dors.al, and lateral views. E-H, QMF31380, in Scanlon, 1992, fig. IA).
ventral, medial, dorsal, and lateral views. Scale=5mm. Centrum in ventral view rel-
a short section preserved on either side. In lateral atively long, similar in pro- portions to Patagoniophis sp. but with the sub- view the anterior edge of the compound rounded central ridges nearly straight rather than strongly dorsally, separatedby a right angle from a deeper concave. Cotyle slightly wider than the ventral concavity. In medial view, a long, taper- zygosphene, which is wider than the neural canal ing notch enclosed in the facet for the angular, (all about equal in the most anterior vertebra);
nearly reaching its posterior end (just posterior to condyle and cotyle wider than deep, ventral mar- middle of length of compound). A medial anterior gins flattened in anterior and middle trunk,
process (defined by dorsal and ventrallongitudi- rounder posteriorly.
nal fissures) bearing the continuation of facets for Zygapophyseal facets inclined at about 20°
the coronoid and angular , and probabl y also con- from the horizontal (at mid-trunk; flatter anteri-
~ 402 MEMOIRS OF THE QUEENSLAND MUSEUM NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 403
~ ~ "
@; 0,.-:.~ -..~ 1.;. , \'fi ~ ~ ~
~ ~
.,. ,~ .." $ ~ ~
~ 0 I;,ttP ~
~ ~ ~ ~ ~
~ .\; \ { ~ w , f\\ ~ tp ~ ~ w ~ FIG. 7. Nanowana godthelpi sp. nov., QMF19741, series of vertebrae from CS Site, possibly from the same individual as the holotype (QMF31379).
ina) from the approximate location of the largest bly from a single individual with short centrum, vertebrae in the skeleton, ridges increasing in size broad zygosphene, and condyle smaller than neu- in more posterior vertebrae and posterior point of ral canal (regional features allowing increased the median keel fading away, leaving the ridges flexibility in this region). Haemal keel smooth as paired hypapophyses, ventrolateral swellings (lacking the median ridge of Wonambi spp.), not of the keel. Haemal keel defined by smooth de- or barely projecting below the centrum posteri- pressions in the anterior trunk, these becoming orly. Two largest vertebrae with paradiapophyses better definC?dmore posteriorly and approaching indicating articulated ribs, but on one side of one the cotylar rim. More posterior vertebrae with of them the articular surface is expanded and distinct channels between keel and subcentral roughened suggesting an immobile cartilaginous ridges (subcentral paramedian lymphatic fossae, attachment (i.e. transitional to fixed Iymph- LaDuke,1991). apophyses). Three others with Iymphapophyses Most vertebrae from all regions of the body (broken distally); another with stumps of cylin- with swellings on the neural arch roof on either drical fixed ribs, possibly forking more distally. side of the spine, forming short longitudinal ridges. Similar features in some Wonambi from Nanowana schrenki sp. nov. Riversleigh are associated with small foramina (Figs 9-12, Table 2) (not the case here). Vertebrae similar to these and referred to Nanowana sp. (most of them probably MATERIAL. Holotype QMF31395, a right palatine N. godthelpl) from numerous sites at Riversleigh, from early Miocene Upper Site, GodthelpHill. Other Material: Upper Site: Maxilla fragmentsQMF 31390, including well-preserved examples from 31391, 31394. Mike's Menagerie Site: Dentary Wayne's Wok, Wayne's Wok 2, Mike's Me- QMF31392and vertebraQMF23043. Camel Sputum nagerie, and Upper Site. Site: Dentary QMF23051; maxilla fragments Vertebrae of the cloacal region (Fig. 8) proba- QMF23082,31388.
~ 404 MEMOIRS OF THE QUEENSLAND MUSEUM
TABLE 2. Measurements of ETYMOLOGY. For continuous with a dorsolateral ridge extending to Nanowana schrenki sp. nov ., Friedemann Schrenk, the anterior tip of the tooth-bearing process. A holotype and referred jaw el- He s si s c he s second ridge diverging medially from the antero- ements. Abbreviations as in La n des mus e u m . lateral comer of the process, bearing a distinct Table 1, with addition of ddg Darmstadt. for his en- knob above the tooth row and continuing onto the =depth of dentary at gth alve- couragement and fi- olus. nancial assistance for anterior edge of the choanal process, level with I g palaeontological co- the rear of the 4th alveolus. Anteromedial comer ~ 31395 31394! 23082 a operation between of choanal process (to articulate with posterior IND Germany and Aus- process of vomer and possibly parasphenoid) .tralia. missing. Medial edge intact, and smoothly con- vex, from level of 7th alveolus to rear of tooth DIAGNOSIS. Lat- row, but posterior process broken off. Cusp de- eral process of pala- fining lateral edge of choanal trough diverging tine about as long as posteromedially from the 6th tooth, disappearing 4 alveoli (3-6), with level with the 8th; 2 foramina close together in dorsolateral margin the space between and medial to 7th and 8th strongly notched; alveoli, one of them piercing the choanal plate to ventral ridge of pal- emerge dorsally in a more medial position and atine maxillary pro- opening medially. Tooth-bearing bar pointed mph I -2.0 I (1.0) cess without distinct posteriorly, tapering from the 9th tooth, abroad Dentaries angular concavity, parabolic surface for the retractor pterygoidei on matching smooth the ventral face with its apex beside the 9th, edge of maxillary becoming less distinct posterolaterally. Deep palatine process. notch to articulate with the pterygoid on the dor- Maxilla estimated to sal side between the tooth row and posterior have about 19 tooth process, extending to above the anterior edge of nositions; palatine the lOth tooth. Distinct growth lines through the with 11, pterygoid translucent choanal plate parallel to its curved unknown, dentary medial edge. 18 (or 17-18). Teeth ankylosed normally; Referred material. Maxilla represented by sev- 2nd to 4th of den- eral fragmentary specimens from different sized tary, and 4th to 7th individuals (Fig. 10). Tooth row curves mediad or 8th of maxilla, anteriorly (QMF23082), with a strong gradient of much larger than increasing alveolar diameter from 1 to 5; 5 and 6 others. Dentary -dpp 1 0.7 .0.4 .~ tooth row nearly subequal. Dorsal edge is a sharp, concave dorsomedial crest, extending to a high dorsal straight in dorsal process, levelling off above 6th alveolus; this view. Three mental foramina, the third posterior crest divides anteriorly, enclosing a shallow to the 7th tooth. trough above the first two alveoli (thus, maxilla partially flooring narial cavity). Lateral face DESCRIPTION. Holotype. Alveoli II, teeth an- mostly convex, with a shallow longitudinal kylosedin 1, 3, 4, 5, 6, 8, 9, 10,11; only 8, 10 and trough including a large foramen (opening an- 11 complete. Teeth with a simple curve, directed teriad and ventrad) above rear of the 4th tooth; a posteriorly. Tooth row deflected slightly medi- smaller foramen near the dorsal edge above the ally anteriorly, laterally posteriorly. Maxillary 5th. Medial face concave, with a trough just process slightly wider than the tooth-bearing bar, below the dorsomedial ridge containing a small extending from between 2nd and 3rd to between foramen just anterior to the medial one. Middle 6th and 7th teeth, with an anteriorly sharp lateral part of maxilla (QMF31394) with distinct knob- notch, and sharp posterolateral angle. Ventral like posterior part of prefrontal process and slop- surface of the process with a diagonal ridge from ing suborbital portion, becoming more rod-like the rear of the 4th tooth to the posterolateral and wider than high posteriorly. Tooth size de- angle, defining an anterolaterally concave facet creasing sharply, with increased alveolar spacing, to articulate with the palatal process of the max- just behind prefrontal process; longest (7th or illa. Anteriorly, the edge of the lateral process 8th?) 2.2mm long, curved at middle but straight NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 405
distally, with medial and lat- eral cutting ridges (like ...,-c -/ ~ ~""- ~ .;. longest tooth of dentary (t, Q --C ~ ---- QMF3139~, see below); , ".~ ' ' ~,. '~ ~: ~ more postenor teeth (broken -.;,' ~ ' ~ before drawing) with simple curve, about half as long. Palatine process diverging, ~ ~ ~ ~ a~. .-, r:~D~-R.~ :'"1-R. from tooth row at last large '\ 1;'. ' .../:._\ -, tooth ~nd reaching maxi- '- f : ~ " &' ' V' '.: ,[ ~ mum wI~thbetw~nthe next '\,?; r, , _.': ./.\5':'..~ 2 alveolI. MedIal edge of -~ ' ')\' .,' ,. , - the palatine p~ocess quite ';, I': ,-i!.t)j,~, £$ smooth, matchIng the con- ';jMr cavity of the maxillary pro- cess in the holotype; large (m , f ' ,: processopening foron palatinedorsal face nerve of; , r ! and blood supply through several foramina on late~al rn~. -\ J { ;;- surface. Teeth on postenor ~ ~ ~ partofmaxilla(QMF31391) 4 still ~educing in si.ze from ~, antenor to postenor, and ~; ::.!", , with slight double curve. ~T Posterior part triangular in section, with near vertical lateral and oblique dorsomedial faces both slightly concave, meeting at a dorsolateral ridge. Lateral edge straight, medial edge FIG. 8. Nanowanagodthelpi sp. nov " seriesof mostposterior trunk andcloacal produced as ridge with con- ,!ert~braefrom UpperSi~e, possibly from the sa~e individual asjaw elements vexity probably marking an- In Fig. 6. Lateral,postenor, dorsal, and ventral views. tenor limit of ectopterygoid. Dentaries. Two right dentaries, differing con- but only very weakly concave mediad. Third siderably in size (Fig. 11), representthe lower jaw tooth directed slightly laterad as well as poste- in this species. QMF31392 with complete row of riad; other teeth mediad, more strongly towards 18 alveoli, teeth ankylosed in 1 (possibly), 3, 6, the rear of the tooth row. Each tooth with a weak 8, 10, 11, Ij, 15, 16, and 18; 10thbroken,other lateral and medial cutting edge near the tip. Den- teeth in tact, and a replacement tooth apparently tary deepensgradually from anterior to posterior. in situ behind 15th. QMF23051 has 17 alveoli, Three mental foramina open anteriad below alve- but another may have been present posteriorly; I, oli 4, 7 and 9 (QMF31392) or 3, 6-7 and 8 4, 5, 6, 7, 9, 11, 12,13, 14 and 15 ankylosed, but (QMF23051), decreasing in size posteriorly. A all teeth broken near base (the jaw has also been shallow dorsal trough medial to 3rd and 4th alve- broken through 3rd alveolus and subsequently oli defined by a dorsomedial crest. Lateral fossa healed in life). Ist alveolus approximately same extends as far anteriorly as the rear of the 13th size as 5th, but 2nd to 4th considerably enlarged; tooth, blunt in outline; posterior edge of the ver- 3rd nearly twice diameter of 5th, size decreasing tical intramandibular septum smoothly concave, gradually more posteriorly; in the small speci- extending forward to between the 14th and 15tli men, lengths of teeth from anterior edge of base teeth. Differences between the two include shape to tip (mm) -, -, 1.26, --, 0.61, -, 0.63, -, -, 0.55, ofMeckel'sgroove (tapering more strongly in the -, 0.52, -, 0.40, -, 0.37, 0.28. Anterior alveoli small jaw, dorsal edge composed of two sharply ( 1-3) deflected ventrad and mediad relati ve to rest defined sections separated by a short gap below of tooth row, which is moderately concave dorsad 8th-9th alveoli, but no gap in the larger speci- 406 MEMOIRS OF THE QUEENSLAND MUSEUM
low, short precondylar constriction. Blunt haemal keel extending from just behind the cotylar rim, posteriorly forming a slightly prominent single hypapophysis extending below the condyle. Keel defined laterally by broad shallow depressions. Comparisons with Yurlunggur or Pataganiaphis would imply that a haemal keel of this form indicates a vertebra from close to the cardiac region (transitional between prominent single hypapophysis anteriorly and flattened or double keel posteriorly), and would thus be among the largest in the skeleton. Condyle and cotyle about / twice as wide as deep, slightly oblique in lateral / view; cotyle wider than the neural canal but not / as wide as the zygosphene. Zygapophyseal facets inclined at less than 20° above the horizontal, defining planes which intersect near the middle of the neural canal. Prezygapophyseal facets ob- ovate, with transverse anterior edge; postzyg- apophyseal facets more smoothly oval, and somewhat prominent posteriorly in dorsal view. Both pairs of facets are elongate anteropost- eriorly, with long axes at about 35° to the sagittal plane (as in anterior, but not middle trunk verte- .. bra of Pataganiaphis sp. cf. P. parvus; Scanlon, 1993). No prezygapophyseal processes. Paradiapophyses directed ventrolaterad, slightly wider than prezygapophyses, not extend- ing ventral to cotylar rim. Interzygapophyseal ridge smoothly concave laterally, only slightly wider than the centrum, and weakly defined in lateral view. Zygosphene thin, slightly arched; anterior edge smoothly but weakly concave (again, like ante- rior rather than middle vertebrae of Patagani- aphis). Zygosphenal facet (preserved on left FIG. 9. Nanowana schrenki sp. nov., holotype, only) dorsoventrally shallow, with dorsally con- QMF31395 from Upper Site, palatine in ventral (A), vex upper and lower edges, inclined at about 45° dorsal (slightly lateral) (8), dorsomedial (C), and from vertical; a plane tangent to the facet would lateral (D) views. Scale bar=2mm. pass close to the centre of the neural canal. Neural canal arched, about as high as wide, men), upper facet for splenial (with posteromed- lacking internal lateral ridges. Neural arch low, ial angle in the smaller, but a free-ending process with shallow concavities above and below the in the larger), and lateral fossa (constricted in the level of the zygosphene and extending to the smaller by deepened upper posterior process); posterior edge. Zygantral roof arched, thickness both narrowest in the region of the 6th to 8th uniform across its width. In dorsal view, rear of alveoli; but the larger specimen is relatively neural arch forming a broad concavity above the broader posteriorly. zygantrum, interrupted by the neural spine. Low Vertebra(Fig. 12) from mid-trunkofajuvenile, neural spine formed by a narrow, but sharply with short broad centrum, large neural canal, and defined anterior lamina rising from the rear of the condyle and cotyle much wider than deep. zygosphene and applied to a higher, columnar Weakly defined subcentral ridges narrow only portion posteriorly, overhanging the zygantrum. slightly behind the parapophyses, posterior half Dorsal surface of column broken off, with a sinus of centrum nearly parallel-sided except for a shal- wisible within the neural arch. Lateral and sub-
~ NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 407
central foramina present, any other obscured by den- ~ drites. ~ TROpmC ;:. , SPECIALISA TIONS ~ ~ ~ t: OF NANOWANA ~:~~ ,;;-~ ~" ~::~ -~ N. godthelpi sp. nov. The homogeneity in size, mor- phology and approximate p; stratigraphic position of r thesetoothless but otherwise well-preserved jaws makes r ~ \. it appear probable that the i:..~ ., ,J;;c ~: lack of ankylosed teeth is a'\, 'flf! ",. :,;;JY natural (and apomorphic) ,= ~ characteristic. To quote Owen's (1840) conclusion on the 'dislocated' tail of ~ ichthyosaurs, the toothless \, condition '... is too uniform 'l , Jc ; and common to be due en- ~.. ,,= ~. tirely to an accidental and ' "...",'c 'tii', ", ",;" i'i! .:,;..,..;
extrinsic cause'. Variation --"~"."" ..0',""" .. in the shapeand size of alve- J" ~ oli along the tooth rows, and F c 'r{t,: the presenceof 'frothy' bone ~ similar to bone of attach- ment in some cases, indi- f cates that different stages of , f!,:; i replacement are repre- f sented, so that absence of teeth is not explained by synchronised replacement. Some of these specimens are . -:'-.:" ~~..0,,-, (\ practically intact, preserving C delicate processes, and not worn in such away as to account for -the absence of even stumps of teeth; in . most other specimens from i the same deposits, parts of '------" teeth are typically retained even after heavy wear. The alveoli are shallow rather FIG. 10.Nanowana schrenki sp. nov., maxillary fragments.A-C, QMF31394, rectangular pits, so' that a Upper Site, middle part.of right.ma~illa in l~tera;l,dorsal, and medial.views. thecodont type of implanta- D-G, Q~23082, CS Site,antenor nght I?axllla In !ateral,dorsa;l, ~edlal, ~d ti . t . d . t d ventral view. H-J, QMF31391, Upper Site, postenor left maxilla In medial, on IS .no In Ica e .as an ventral, and lateral views. Not to same scale. alternative to ankylosis. Failure of teeth to anky- lose at any stage is rare among squamates, first living Alethinophidia; Cundall et at. 1993), ap- reported by Savitzky (1981). Anomochilus 1parently has fibrous tooth attachment rather than weberi, a small fossorial 'anilioid' (An- ankylosis (Cundall & Rossman, 1993). There are omochilidae is possibly the sister taxon to other ialso several lineages of snakes, and one ~enus of
~ 408 MEMOIRS OF THE QUEENSLAND MUSEUM
thought to act as a ratchet mechanism, fo]ding back rather than penetrating the derma] armour , and ]ocking in an upright position against the edges of the sca]es when the prey is oriented head-first for swallowing. In extant snakes other functionally associated apomorphies a]so occur; the teeth are small and numerous, often with a spatu]ate rather than conica] tip, and ]ack ename] on the posterior surface; and the ]evator angu]i oris musc]e (inserting on a ]ong upper posterior process of the dentary) is en]arged (Savitzky, ] 98] ). In the pygopodid Lialis teeth are of simi]ar form, and instead of increased intramandibu]ar kinesis there is pronounced kinetic abi]ity at the ~ ~;~ frontoparieta] joint (mesokinesis: Patchell & ...;8- =- Shine ]986b). Both types of kinesis allow the ~ jaws more effective]y to surround and compress -~ a cy]indrica] prey item, immobi]ising or even asphyxiating it. An equivalent adaptation for prey-ho]ding (without hinged teeth) is seen in the ]arge]y scincivorous bo]yeriid snakes, in which ~ the required kin~sis is provided by the unique]y ~ derived intramaxillary joint (Cundall & Irish, .,,~~~ ~~ ] 989). Savitzky (]983) described this set of adapta- tions to feeding on skinks, which has evo]ved independent]y in severa] ]ineages, as an instance of a 'coadapted character comp]ex' , among other cases of 'durophagy' (feeding on hard-bodied prey). Other durophagous snakes have distinct - p , specia]isations, and feed on other kinds of 'hard' , --, prey such as snai]s (pareine and dipsadine co]u- ~ brids) or crabs (the homa]opsine Fordonia). 'Durophagy' is thus a broad concept. I introduce 'arthrodonty'to refer specifically to the 'hinge- toothed' mode of durophagy. Whi]e soft-tissue structures such as fibrous hinges cannot be observed in fossi]s, absence of anky]osis imp]ies that attachment was fibrous and potentially flexib]e. N. godthelpi jaw material is FIG. II. Nanowana schrenki sp. nov ., right dentaries. simi]ar to that of extant arthrodont species after A-C, QMF230SI, CS Site, in medial, dorsal, and maceration, especia]]y Xenopeltis (Savitzky, lateral views. °_F, QMF31392, MM Site, in medial, pers. comm. ). Hutchinson ( ] 992) demonstrated dorsal, and lateral views. Scale bars=2 mm. that scincid ]izards were abundant and diverse in the Tertiary at Rivers]eigh; skinks today repre- lizards. where the attachment is not only fibrous sent a major food source for small terrestria] but forms a functional hinge allowing each tooth predators, inc]uding most extant Austra]ian snake to fold posteriorly under pressure and return up- species (Shine, ]99]). As functiona] arthrodonty has evo]ved in severa] ]ineages in association right when released (Savitzky. 1981. 1983; with predation on skinks, its presence in N. Patchell & Shine 1986c; cf.Edmund. 1969:141). godthelpi is a p]ausib]e exp]anation for the ]ack This hinge mechanism has been interpreted in of ankylosis. each case as an adaptation to feeding on scincid N. godthelpi appears to be ]ess specialised than or gerrhosaurid lizards in which the scales are each of the extant arthrodont snake ]ineages in underlain by osteoderms; the hinged teeth are some respects. The high number of near]y uni-
~ NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 409
reported only in one highly unusual extant taxon, Anomochilus, it is possibly a necessaryprecursor or incipient stage of arthrodonty (see below), and a mixed or 'semi-arthrodont' condition in N. godthelpi seems possible. Nanowana schrenki sp. nov. In the absence of articulated or strongly associated material, refer- ral of jaw elements described here to a single taxon can only be provisional. In particular, the 2 near-complete dentaries differ in several respects which make their assignment to the same species doubtful: in QMF23051 the upper edge of the Meckelian groove is a continuous ridge and ex- tends posteriorly as a free-ending process, while in QMF31392 it is interrupted at the 9th alveolus, c and appears to end abruptly. (Additionally, the larger specimen broadens more posteriorly, while the small one is widest at the 3rd tooth, but this difference may be allometric.) The teeth of snakes play several roles in the capture, subdual, puncturing or laceration, and swallowing of prey; in general they will be adapted for a combination of functions, but often either a single function is dominant, or certain stages are either not required (e.g. because inac- D tive or defenceless prey is taken) or carried out extra-orally (e.g. constriction). Teeth specialised for different functions are often separated be- FIG. 12. Nanowana schrenki sp. nov., vertebrae, QMF23043, MM Site, probably same juvenile as tween the front and rear of the mouth, in some dentary QMF31392 (Fig. 11) in anterior(A), poste- cases with diastemata between teeth of different rior(B), latera1(C), dorsal(D) and ventral (E) views. morphology (Frazzetta, 1966; Scanlon & Shine, 1988; Cundall & Irish, 1989). Numerous terms have been introduced for dif- form maxillary alveoli is typical of an arthrodont ferent patterns of tooth size and fang location species, but a similarly long tooth row is present (Smith 1952). Primitive snakes (Dinilysia, an- in Wonambi naracoortensis (Barrie 1990), and is ilioids) are isodont or mesodont, with relatively therefore likely to be a retained ancestral condi- few, stout teeth; while also capable of constric- tion rather than a specialisation. The overlap be- tion, they use a powerful 'crushing' bite in sub- tween dentary and compound is moderate, duing prey (Frazzetta, 1970; Greene, 1983). Such without any great elongation of the tooth-bearing a 'crushing' method seemspossible for Madtsoia posterior process; the extreme condition in extant cf. M. bai, in which the dentary is heavily built arthrodont lineages may be precluded by the and bears relatively few teeth (Hoffstetter, 1960), probable insertion of m. levator anguli oris on the but not for Australian madtsoiids. Different pat- relatively large coronoid rather than the dentary , terns of tooth-size variation in upper and lower but the overlap is actually shorter in this species jaws are known in each of the 4 best- represented than in Wonambi. taxa: The dentary alveoli of N. godthelpi are consid- In Wonambi naracoortensis the very numerous erably larger, especially in the middle part of the teeth (25 in the dentary, 22 or 23 in the maxilla) row, than those of the maxilla, so the lower teeth are proterodont, sharp and strongly inclined pos- may have functioned differently, and possibly teriorly and medially (Barrie, 1990); the jaws are lacked a functional hinge. In Xenopeltis, rela- shallow, suggesting a limited role in subduing tively large teeth are present on the middle part prey, and more emphasis on holding and swal- of the palate (posterior palatine and anterior pter- lowing functions. This implies that an extra-oral ygoid), but these appear to be fully hinged. While method of subduing prey (probably constriction) fibrous attachment of 'sessile' teeth has been was well-developed. When the upper and lower 410 MEMOIRS OF THE QUEENSLAND MUSEUM
jaws are both proterodont, teeth often have a EVOLUTION OF TEETH sigmoid curvature with the tips directed some- AND A 1T ACHMENT what anteriorly as in many pythons (Frazzetta, 1966), and seems to be associated with relatively Snake teeth are slender compared to other ver- soft-bodied prey such as mammals, birds, earth- tebrates; they break frequently during normal use worms (McDowell, 1969) and eels (Smith, 1926; and are quickly replaced (Edmund, 1969). The Cogger et al., 1987). have reduced occlusal area (sacrificing strength) Nanowana godthelpi apparently had a nearly to increase sharpness and depth of penetration. isodont marginal dentition. No complete tooth Tooth form is a compromise betwen competing crowns have been reported for this species, but selective forces defining a 'fitness landscape' over attainable phenotypes (Wright, 1932), and basedon alveolar sizes it was weakly proterodont local optima will be attained only if intermediate on the maxilla and mesodont on the dentary (Figs states are evolutionarily stable. If the rate of 1,3). breakage is too high, prey capture or swallowing The condition in Yurlunggur is less clear but efficiency (and consequently fitness) will be low. apparently the opposite; a dentary with well-pre- During the stages of feeding on a given range served teeth (Archer et al., 1991:71) is proterod- of prey types with given neuromuscular reper- ont, while the maxilla was apparently mesodont toires, forces on the tooth come from particular (Scanlon, 1996). directions with greater or lesser frequency and N. schrenki can be described as megadont magnitude, so it will generally be favourable for (Smith, 1952), having regions of distinctly en- the tooth to be asymmetrical rather than a simple larged teeth. Otherwise it has the same pattern of cone. The orientation of 'cutting ridges' (which enlargement as Yurlunggur, opposite to that of N. function as buttresses as well as blades), curves godthelpi, being mesomegadont on the maxilla in the shaft, and the shape of the tooth base, will and promegadont on the dentary. The dentary is confer maxima of resistance in one or more direc- relatively longer and less robust than in Madtsoia tions, at the expense of minima elsewhere. or Dinilysia, but not depressed as in Wonambi; Horizontal components of pressure (shear the teeth are intermediate in number and in mor- stress) at the tip of an approximately conical tooth phology (stouter and more erect than Wonambi, are converted to bending stressesat the base, i.e. but not so much as in Dinilysia or anilioids); and compression at one side and tension at the other . the enlarged teeth are a uniquely derived condi- The magnitudes of these forces will depend on tion within Madtsoiidae (albeit convergent with base diameter, but only tension and shear will many other lineages of snakes). tend to either break the shaft or disrupt the attach- Many snakes share this pattern of enlarged ment of tooth to bone. Bone of attachment can teeth at the front of the dentary and the part of the apparently withstand such stresseswithin a wide maxilla below the prefrontal articulation, range of values of the ratio of tooth length to basal whether or not they are set off by diastemata or diameter. A fibrous connection will remain stable local minima of tooth size. On the basis of occur- at low values of this ratio (short, broad teeth as in rence in scincivorous colubroids such as Anomochilus), and at intermediate values will have enough elasticity to return the tooth upright Lycodon, Glyphodon, Demansia, and Hemiaspis after displacement (functional arthrodont condi- signata (but not the anurophagous H. dameli; tion). At high values (longer, slender teeth) a Boulenger, 1896; Worrell, 1961; Shine, 1991; fibrous attachment would merely bend passively, Cundall & Irish, 1989; pers. obs.), this is here without developing enough tension to right the tentatively considered an adaptation to hard-bod- tooth; the orientation of the teeth would then not ied prey, often skinks. Snakeswith enlarged teeth be precisely controllable, and during prey capture offset between upper and lower jaws are able to and ingestion they would more often encounter trap hard, cylindrical prey items between a notch shear stressesat unfavourable angles, leading to in one tooth-row and one or more enlarged fang- rupture. Such a condition (elongate, slender teeth like teeth (sometimes true fangs) in the other with fibrous attachment) is unknown in any living (Cundall & Irish, 1989). As well as this 'trapping' snakes, and would presumably be evolutionarily function, having only a few long teeth in eachjaw unstable for most diets and feeding methods. maximises the probability of hard-bodied prey This consideration of the forces applied at the being deeply punctured, whereas this is avoided tooth tip and base suggests that arthrodonty and in arthrodont forms. elongate teeth are mutually exclusive conditions. NEW MIOCENE MADTSOIID SNAKE FROM RIVERSLEIGH 411
Thus the specialisationsofdentition andjaw mor- viduals, number of identifiable elements, and phology in Nanowana are most likely to be inde- quality of preservation) implies that N. godthelpi pendently derived from the nearly isodont, was more abundant close to the sites of deposi- ankylosed condition of other madtsoiids, and ap- tion, whereas N. schrenki may have been less parently represent alternative solutions to the abundant locally, and the more damaged remains problem of feeding on hard- scaled lizards. transported from further afield ( cf. LaDuke, Healed breaks ofthejaw elements (particularly 1991). Thus N. godthelpi lived near water (possi- dentaries) are not uncommon in snakes (pers. bly riparian, probably closed forest), whereas N. obs.), and presumably result in most cases from schrenki may have lived further from water, pos- attempts to capture or subdue relatively large and sibly in more open or drier areas such as clearings powerful prey. Sublethal trauma associated with or rocky hills. particular morphological specialisations may be Most sites where Nanowana vertebrae have an indicator of mechanisms of selection; there are been found have not produced jaw elements di- upper limits to prey size and strength for every agnostic to species. The genus as defined here, species of predator, and both prey selection and therefore provides a convenient level of descrip- behavioural aspects of prey-handling, as well as tion which can be applied to a larger set of sites, morphology, will be subject to selection. The but as yet all specimens referred to Nanowana are break through the third dentary alveolus of from Riversleigh. QMF230S1 (N. schrenki sp. nov.) would have occurred most easily (i.e. greatest stress would ACKNOWLEDGEMENTS occur) while the 3rd alveolus was unoccupied, and while a prey item was held by the enlarged I thank Mike Archer for the opportunity to 2nd tooth, but not the smaller posterior teeth. study Riversligh fossils under his supervision, Fractures of this kind could be expected to be less and Henk Godthelp, Sue Hand, Anna Gillespie, common (all else being equal) with a more uni- Jeanette Muirhead. Syp Prasouthsouk, and Ste- form dentition, but this possible disadvantage of phan Williams for preparation and other activities megadonty may have been outweighed by an in field and lab which made this work possible. I increased rate of capture success,or of retention also thank Mike Archer, John Barrie, Dino Frey, once a prey item was secured behind (or impaled Mark Hutchinson, Mike Lee, Ralph Molnar , on) the enlarged dentary teeth. Jean-Claude Rage, Alan Savitzky. Rick Shine, The ribbon-like posterior maxilla of N. Zbigniew Szyndlar, and Paul Willis, for insights, godthelpi presents an even more fragile appear- discussions, and accessto material; and Wighardt ance,but no specimens suggestbreaks during life. von Koenigswald and Friedemann Schrenk for While this is negative evidence, the rarity of such facilitating visits to Germany where much of the breaks would tend to support the presence of a paper was written. Support for research at jugal in the suborbital region. Presenceof ajugal Riversleigh has come from the Australian Re- in Wonambi naracoortensis can similarly be in- search Grant Scheme; the National Estate Grants ferred from the oblique trough crossing the max- Scheme (Queensland); the University of New ilia (Barrie,-1990; Scanlon, 1996) which would South Wales; the Commonwealth Department of otherwise be an obvious point of fragility. Environment, Sports and Territories; the Queens- land National Parks and Wildlife Service; the SYMPATRY OF RELATED SPECIES WITH Commonwealth World Heritage Unit; ICI Aus- SIMILAR DIETS tralia; the Australian Geographic Society; the Queensland Museum; the Australian Museum; The two species of Nanowana occur together the Royal Zoological Society of NSW; the in at least 3 Sites, existing sympatrically for a Linnean Society of NSW; Century Zinc; Mount significant period. They are thought to have had Isa Mines; Surrey Beatty & Sons; the Riversleigh sirnilardiets (skinks), and similar adult size. They Society; and private supporters including Elaine thus occupied quite similar niches, and were Clark, Margaret Beavis, Martin Dickson, Sue & strictly equivalent ecologically. They may have Jim Lavarack and Sue & Don Scott-Orr. Vital differed in aspectsofbehaviour which would not field assistance came from many hundreds of be discernible in the fossil record, but at least a volunteers as well as staff and postgraduate stu- difference in habitat can be suggested. dents of the University ofNSW. Skilled prepara- The different representation of the two species tion of most of the Riversleigh material has been when found together (minimum number of indi- carried out by Anna Gillespie. 412 MEMOIRS OF THE QUEENSLAND MUSEUM
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