The basicranial morphology of madtsoiid snakes (Squamata, Ophidia) and the earliest Alethinophidia (Serpentes)
2003; Taylor & Francis; Volume: 23; Issue: 4 Linguagem: Inglês
10.1671/24
ISSN1937-2809
Autores Tópico(s)Paleontology and Evolutionary Biology
ResumoJOHN D. SCANLON*, School of Biological Sciences, University of New South Wales, UNSW Sydney 2052, AustraliaSnakes of the extinct family Madtsoiidae are known from early LateCretaceous to Eocene deposits in Madagascar, western and northernAfrica, southwestern Europe (Spain and possibly France), and SouthAmerica (reviewed by Rage, 1998; Rage and Werner, 1999). Two gen-era occur in both the Campanian or Maastrichtian of Argentina and theearly Eocene of Australia (Patagoniophis and Alamitophis, Albino,1986; Scanlon, 1993; see Boles, 1999, for recent discussion and con-firmation of the Eocene date), and Australia is the only region in whichmadtsoiids are known later than the Eocene. Wonambi naracoortensisSmith, 1976, occurs in Pleistocene and Pliocene deposits (Scanlon andLee, 2000), and large species of Yurlunggur Scanlon, 1992, also rangefrom late Oligocene to late Pleistocene (Mackness and Scanlon, 1999).The highest known diversity and some of the best-preserved materialof madtsoiids are from the late Oligocene and Miocene of Riversleigh,northwestern Queensland, including Wonambi barriei, one or more un-named species of Yurlunggur, two small species of Nanowana, and atleast one additional new taxon (Scanlon, 1996, 1997; Scanlon and Lee,2000).Cranial remains of Wonambi naracoortensis from Naracoorte, SouthAustralia (Barrie, 1990; Scanlon and Lee, 2000), provide the best evi-dence of the morphology and affinities of any madtsoiid (though thefamily as currently recognized may not be monophyletic; see below).These specimens were originally interpreted as supporting the inclusionof Madtsoiidae in Alethinophidia (Barrie, 1990; Scanlon, 1992), butreinterpretation of the morphology and more comprehensive phyloge-netic analyses placed this lineage outside a clade including all livingsnakes, including scolecophidians as well as alethinophidians (Scanlon,1996; Scanlon and Lee, 2000; Lee and Scanlon, 2002). These resultsconfirm the interpretations of Hoffstetter (1961:155) and McDowell(1987) regarding the primitive features of madtsoiid vertebrae relativeto those of all living snakes, and conflict with the widespread assump-tions that scolecophidians are basal snakes and that all known fossilsnakes are either scolecophidians or alethinophidians (e.g., Underwood,1967; Rage, 1984, 1987; Rieppel, 1988; Zaher and Rieppel, 1999;Tchernov et al., 2000).Part of the braincase of a second Australian madtsoiid, similar to thatof Wonambi but differing conspicuously in proportions, has been rec-ognized from a late Oligocene or early Miocene deposit at Riversleigh,northwestern Queensland. This deposit contains vertebrae, ribs, and jawelements representing several taxa of madtsoiids including Nanowanagodthelpi, N. schrenki, and Wonambi barriei (Scanlon, 1996, 1997;Scanlon and Lee, 2000). However, the only vertebrae consistent in sizewith the braincase fragment are similar to those of Yurlunggur cam-fieldensisScanlon, 1992, allowing the braincase fragment to be referredto the same genus (Scanlon, 1996). All Yurlunggur vertebrae knownfrom Riversleigh have relatively higher neural spines than the somewhatlater Y. camfieldensis, so are considered specifically distinct, but taxo-nomic treatment of vertebrae is deferred pending study of recently dis-covered articulated remains.As well as Wonambi, comparisons are made with extant snakes ofsome basal lineages (anilioids and booids) and with Dinilysia patagon-* Present address: Department of Environmental Biology, Univer-sity of Adelaide, and Department of Palaeontology, South AustralianMuseum North Terrace, Adelaide SA 5000, Australia, e-mail: scanlon.john@saugov.sa.gov.auica Woodward, 1901 (?Coniacian, Late Cretaceous; Estes et al., 1970;Caldwell and Albino, 2001), which has been interpreted as a basal al-ethinophidian or a pre-alethinophidian snake of similar grade to madt-soiids (reviewed by Scanlon and Lee, 2000). I also make some com-parisons with a putative madtsoiid braincase fragment from the Ceno-manian of Wadi Abu Hashim, Sudan (Rage and Werner, 1999), andcomment on its significance.Comparisons with recent taxa are based on collections of the Queens-land Museum, Australian Museum, Macleay Museum, South AustralianMuseum, M. Archer, D. J. Barrie, and the author (details available onrequest).Riversleigh fossils are prepared using acetic acid (e.g., Archer et al.,1991) and the specimen described here is completely free of carbonatematrix. The course of canals and foramina was determined visuallyunder a binocular microscope, using a hair as a probe.Terminology for cranial anatomy either follows that in Rieppel’s(1979) review of snake basicranial evolution, or Rieppel’s terms arenoted parenthetically when different ones are preferred.Institutional Abbreviations QM F, Queensland Museum (Pa-laeontology), Brisbane.SYSTEMATIC PALEONTOLOGYREPTILIASQUAMATAOPHIDIAYURLUNGGUR Scanlon, 1992YURLUNGGUR sp.Material QM F23041.Locality Mike’s Menagerie Site (Mike’s Menagerie Local Fauna),Godthelp Hill, Riversleigh World Heritage Fossil Property, northwesternQueensland.Age The deposit forms part of ‘Tertiary System B,’ interpreted tobe late Oligocene or early Miocene in age (Archer et al., 1989, 1997).Description A fragment 22.0 mm in length comprises most of theco-ossified basisphenoid and parasphenoid (Fig. 1), here referred to as‘sphenoid’ for brevity; the width of the cultriform process immediatelyanterior to the basipterygoid processes is 7.3 mm; the same, immedi-ately anterior to ossified portions of trabeculae is 5.0 mm; the maximumwidth across the basipterygoid processes is 10.7 mm; the length of thecanal for the abducens nerve is 6.4 mm; the length of the articulatorysurface of the basipterygoid process (right) is 7.5 mm; the length of thevidian canal is greater than 6.6 mm.The dorsal surface (Fig. 1A) bears an oval, bowl-like hypophysial pit(sella turcica) centered just anterior to a line joining the posterior endsof the basipterygoid processes. It is not recessed below the posteriordorsum sellae (crista sellaris); the posterior and lateral walls are nearlyvertical, while the anterior wall is more oblique but demarcated ante-riorly by a shallowly overhanging crest approximately 2 mm across.This crest is interrupted by three small troughs probably accommodatingblood vessels (one to the left of the midline, two smaller ones to theright). A similar pattern of three anterior troughs is seen in Calabariareinhardti, and a slightly less similar condition in Xenopeltis unicolorand Loxocemus bicolor (Rieppel, 1979:figs. 5, 7), where they representthe anterior course of the ramus cranialis of the cerebral carotid.In the midline within the hypophysial pit, 0.7 mm posterior to thetransverse anterior crest, is a small foramen opening posteriorly, re-
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