Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de RodrõÂguez, Central Me xico V|¨ ctor-Hugo Reynoso* Redpath Museum, McGill University, 859 Sherbrooke St West, Montre¨ al, Canada H3A 2K6 Huehuecuetzpalli mixtecus gen. et sp. nov. is characterized by a combination of characters unlike those of any of the previously described Late Jurassic or Early Cretaceous lizards. It has most of the synapomorphies common to modern squamates, but still retains primitive features rare in living taxa. Autapomorphic char- acters include an anteroposteriorly elongated premaxilla that results in the elongation of the snout and the apparent retraction of the external nares. A small rounded postfrontal and a parietal foramen on the fronto- parietal suture suggest a¤nities with iguanians, but the retention of divided premaxillae, amphicoelous vertebrae, thoracolumbar intercentra, entepicondylar foramen, and a second distal tarsal supports the hypothesis that Huehuecuetzpalli has a more basal position relative to the extant squamates. Although its appearance is late in the fossil record of lizards, Huehuecuetzpalli is the ¢rst report of a basal squamate. It provides important information on early transformation of characters in lizard evolution. Many primitive characters present in some modern squamates are usually explained by paedomorphosis; however, these characters are common in early lizards suggesting that derived states may have been ¢xed later in lizard evolution. If Huehuecuetzpalli is an iguanian, then it would be the earliest known representative of this lineage and extends their fossil record into the Albian. This paper presents an extensive review of the char- acters and character states used in previously published cladistic analyses of the Squamata. Keywords: Lepidosauria; Squamata; Iguanidae; cladistics; biogeography; Tlayua Quarry are uncertain and they may be basal lepidosauromorph 1. INTRODUCTION taxa rather than lizards (C. A. M. Meszoely, personal The Squamata is a group of highly diversi¢ed diapsid communication). The earliest well-documented squamates reptiles with a world-wide distribution, yet very little is are the middle Jurassic anguimorphs Parviraptor estesi known about their origin, early evolution, and diversi¢- (Evans 1994a) from Kirtlington, England (Bathonian), cation. The Squamata is divided in six major taxa: and Changetisaurus estesi (Fiederov & Nessov 1992) from iguanians, anguimorphs, scincomorphs, gekkotans, snakes Kyrgyztan, Central Asia (Callovian). Towards the Late and amphisbaenians. The vernacular term `lizard' is Jurassic, the squamate fossil record is better known, but applied to the ¢rst four taxa. Squamates are grouped still from a very small number specimens, most of them together with sphenodontians in the Lepidosauria, which restricted to localities in Europe and North America. In in turn is included with some other primitive forms in the most localities the remains are very fragmentary and Lepidosauromorpha, one of the two major branches of consist mostly of disarticulated material. Parviraptor the diapsid evolution. To date almost 3300 species of lizards, anguimorph Dorsetisaurus, and the scincomorphs Paramacel- 2300 of snakes, and 130 of amphisbaenians have been lodus, Becklesius, Saurillus and Saurillodon (also known in described (Rage 1992). Kirtlington; Evans 1995) have been reported from the The history of the Lepidosauromorpha can be extended Guimarota lignite mine (Oxfordian^Kimmeridgian) in to the Upper Permian (Carroll 1975, 1977; Estes 1983a); Leira, Portugal (Sei¡ert 1973). Dorsetisaurus and however, the earliest known squamates are from the Paramacellodus are also known from the Late Kimmeridgian Middle Jurassic of Britain (Evans 1993; Waldman & and Early Tithonian deposits in Como Blu¡, Wyoming Evans 1994). They consist of scattered material of very (Prothero & Estes 1980; Chure 1992). The scincomorph distinctive lizard elements that can be assigned to crown Sharovisaurus was reported from the Kimmeridgian of squamate taxa. Early Jurassic lizards were reported by Kazachstan, Central Asia (Hecht & Hecht 1984), and the Meszoely et al. (1987), however, their speci¢c a¤nities skink Mimobecklesisaurus (Li 1985) from the Upper Jurassic of the Gansu province of China. Euposaurus from the Kimmeridgian of Cerin, France, long believed to be an *Address for correspondence: Departamento de Zoolog|¨a, Instituto de Biolog|¨a, UNAM AP 70-153, Me¨ xico DF 04510, Me¨ xico iguanian (Cocude-Michel 1963; Estes 1983b), is now known ([email protected]) to have been described on the basis of an assemblage of Phil. Trans. R. Soc. Lond. B (1998) 353, 477^500 477 & 1998 The Royal Society Received 19 November 1996 Accepted 02 January 1997 478 V.-H. Reynoso Basal squamate from Me¨ xico lepidosaurs from di¡erent taxa, and only the poorly Me¨ xico (Clark & Herna¨ ndez 1994), might be the only preserved type can be assigned to the Squamata with squamate sister-group reported, particular burrowing uncertain relationships (Evans 1994b). Finally, the genera specializations make it far from the expected primitive Ardeosaurus, Eichstaettisaurus, Bavarisaurus and Palaeolacerta squamate type. were described from the lower Tithonian deposits of The Albian deposits of Tepexi de Rodr|¨guez, Central Solnhofen (Ho¡stetter 1953, 1964, 1966; Cocude-Michel Mexico, bear some of the most superbly preserved fossil 1963, 1965; Ostrom 1978; Mateer 1982; Evans 1993, lepidosaurs world-wide (Reynoso 1995, 1997). Skeletons 1994c). The previously considered early lizard Cteniogenys are fully articulated, but heavily compressed. Fortunately, from Como Blu¡ (Gilmore 1928; Prothero & Estes 1980) their oblique preservation provides full view of the organ- and Guimarota (Sei¡ert 1973), is now considered a choris- isms, facilitating reconstruction and giving a good amount todere (Evans 1989, 1990), and Lisboasaurus, also from of information. The lizard described here, even though Guimarota, is a small, unusual, archosaur (Buscalioni et somewhat late in the fossil record, shows many features of al. 1996). an earlier stage of squamate evolution and provides The fossil record of lizards during the Early Cretaceous evidence of early character transformation within was poor, leaving a large gap in our understanding of early squamates. lizard evolution. For many years, only two genera were known: Meyasaurus from the Berriasian^Valanginian deposits in Montsec, Spain (Vidal 1915; Barbadillo & 2. SYSTEMATIC PALAEONTOLOGY Evans 1995); and Yabeinosaurus from Berriasian (?) deposits (a) Lepidosauromorpha Benton, 1983 of northeastern China (Endo & Shikama 1942). Very Lepidosauria Dumeril & Bibron, 1839 recently, a number of new localities have yielded numerous Possibly Squamata Oppel, 1811 specimens some of which are superbly preserved. The (i) Genus Huehuecuetzpalli gen. nov. scincomorph Ilerdaesaurus (probably synonymous to Etymology. From huehuetl (the ancient) and cuetzpalli Meyasaurus; Barbadillo & Evans 1995) was added to the (lizard), Na¨ huatl. Montsec collection (Ho¡stetter 1965). Parviraptor, Dorsetisaurus, Paramacellodus, Saurillus and Becklesius all Diagnosis. As for the type and only known species. known from the late Jurassic are also found in the Type Species: Huehuecuetzpalli Mixtecus sp. nov. Berriasian deposits of Purbeck with two other scinco- morphs: Pseudosaurillus and Durotrigia (Ho¡stetter 1967; Holotype. Instituto de Geolog|¨a, Universidad Nacional Sei¡ert 1973; Ensom et al. 1991; Evans 1995). Remains of Auto¨ noma de Me¨ xico. Catalogue no. IGM 7389 (¢gure 1). the earliest snake (Rage & Richter 1994), eggshells of the Crushed, but beautifully preserved complete skeleton. possibly earliest gecko (Kohring 1991), additional Paratype. Catalogue no. IGM 4185 (see ¢gure 2). Crushed specimens of Ilerdaesaurus, Becklesius, Paramacellodus and but beautifully preserved skeleton of a juvenile lizard pre- the new possibly anguimorph Cuencasaurus were found served in part and counterpart blocks. Limbs, girdles and in the Late Barremian deposits of U·a and Galve, the posterior part of the vertebral column are preserved in Spain (Richter 1991, 1994a,b). Deposits of similar age in ventral view in one of the blocks; the broken head and the Las Hoyas, Spain yield a new assemblage of lizards to anterior part of the vertebral column are visible in dorsal be described (Barbadillo & Evans 1995; Evans & Barba- view on the other. Some cartilaginous and soft tissues are pre- dillo 1996). Outside Europe, only a new species of served. Paramacellodus from the Berriasian (?) of Anoual, Morocco (Richter 1994a), and Hoburogecko, the earliest Etymology. For La Mixteca, the native name given to the known gecko, from the Aptian^Albian of Mongolia broad geographical area were the Tlayua Quarry is located. (Alifanov 1989), have been described. In North America, Early Cretaceous squamates are even more Locality. Tlayua Quarry, 2 km south-east of the Colonia scarce. A single primitive helodermatid maxillary frag- Morelos, near Tepexi de Rodr|¨guez, Puebla, Me¨ xico. ment was reported from the Albian of Utah, USA (Cifelli & Nydam 1995). Horizon. Middle Member of the Tlayua Formation (Pan- Although some Late Jurassic and Early Cretaceous toja-Alor 1992). Early Cretaceous. Middle or Late Albian squamates are represented by well-preserved specimens, (Seibertz & Buitro¨ n 1987). IGM 7389 was collected in locality very few contribute to our understanding of the early IGM-1995-NSF number 2, level