The Origin and Early Diversification of Squamates

doi:10.1017/9781108938891.004

2 - The Origin and Early Diversification of Squamates

from Part I - The Squamate and Snake Fossil Record

Published online by Cambridge University Press: 30 July 2022

Susan E. Evans

Edited by

David J. Gower and

Hussam Zaher

Show author details

David J. Gower: Affiliation:
Natural History Museum, London
Hussam Zaher: Affiliation:
Universidade de São Paulo

Book contents

Summary

Squamata, the group that comprises lizards, snakes, and amphisbaenians, is the largest and most diverse major group of living reptiles. Although most recent estimates place their divergence from Rhynchocephalia in the early Triassic, the first unequivocal records of squamates currently date from the Middle Jurassic, and the first crown squamates, representing Scincoidea, Anguimorpha, and possibly Gekkota, are known from the Late Jurassic. The record then improves substantially in the Early Cretaceous, with squamate fossils recorded from most major continents and showing evidence of expansion into a diversity of specialist niches. Despite recent claims to the contrary, the earliest unequivocal snake fossils also date from this period, with fragmentary remains from the Aptian-Cenomanian of North Africa and North America, followed by a more substantial global record from the Cenomanian onwards. The re-interpretation of the Middle Jurassic to Early Cretaceous parviraptorids as snakes was based on a misinterpretation of the original material, as shown by new associated specimens from the Middle Jurassic of Scotland.

Keywords

snakes lizards evolution palaeontology anatomy systematics fossils Jurassic Cretaceous Mesozoic

Type: Chapter
Information: The Origin and Early Evolutionary History of Snakes , pp. 7 - 25

DOI: https://doi.org/10.1017/9781108938891.004 [Opens in a new window]

Publisher: Cambridge University Press

Print publication year: 2022

2.1 Introduction

Squamata, the group that encompasses snakes, lizards, and amphisbaenians, is the largest (>10,500 sp.) and most disparate group of modern reptiles. Extant squamates are distributed over all but the coldest parts of the world; range in size (snout–vent length, SVL) from millimetres to metres; and show a diversity of diets, shapes, locomotor patterns, and reproductive strategies. Snakes (Serpentes) account for roughly 35 per cent of all extant squamate species and their origin and relationships, which have long intrigued herpetologists, are the focus of this volume. This chapter aims to provide a foundation for subsequent chapters, by reviewing what is currently known of the early stages of squamate evolution and diversification.

Most researchers recognize eight extant major squamate clades (Fig. 2.1): Dibamidae; Gekkota; Scincoidea (=Scinciformata [Reference Vidal and Hedges1]), encompassing Xantusiidae, Scincidae, and Cordyliformes; Lacertoidea (=Laterata [Reference Vidal and Hedges1]), encompassing Lacertidae and Teiioidea; Amphisbaenia; Iguania; Anguimorpha; and Serpentes. Although Camp [Reference Camp2] considered Gekkota to be primitive squamates (part of his Ascalabota), the first comprehensive cladistic analysis [Reference Estes, De Queiroz, Gauthier, Estes and Pregill3], based on morphological characters, placed Iguania as the sister group of other squamates (Scleroglossa). Within Scleroglossa, Estes et al. [Reference Estes, De Queiroz, Gauthier, Estes and Pregill3] united Scincoidea + Lacertoidea in Scincomorpha, and Scincomorpha + Anguimorpha as Autarchoglossa. The position of three limb-reduced clades, Dibamidae, Amphisbaenia, and Serpentes, was unresolved within Scleroglossa. The topology of Estes et al. [Reference Estes, De Queiroz, Gauthier, Estes and Pregill3] remained the working hypothesis for most herpetologists until 2004 with the publication of phylogenies based on molecular data [Reference Townsend, Larson, Louis and Macey4, Reference Vidal and Hedges5]. The molecular trees placed Gekkota rather than Iguania as the sister group of other squamates (invalidating Scleroglossa), with Scincoidea, and then Lacertoidea (including Amphisbaenia) as successive outgroups to a Toxicofera that encompassed Iguania, Anguimorpha, and Serpentes [Reference Vidal and Hedges1]. Although morphological data sets (e.g., [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6]) tend to replicate the Estes et al. [Reference Estes, De Queiroz, Gauthier, Estes and Pregill3] tree, subsequent molecular and combined evidence analyses [Reference Wiens, Hutter and Mulcahy7–Reference Burbrink, Grazziotin and Pyron13] agree with those of Townsend et al. [Reference Townsend, Larson, Louis and Macey4] and Vidal and Hedges [Reference Vidal and Hedges5]. The molecular tree is therefore used as the phylogenetic framework herein (Fig. 2.1).

Figure 2.1 Molecular time tree for Squamata, redrawn and simplified from Jones et al. [Reference Jones, Anderson and Hipsley14], showing putative early representatives of major clades discussed in the text. (1) Eichstaettisaurus (Upper Jurassic, Germany); (2) Hoburogekko (Lower Cretaceous, Mongolia); (3) Paramacellodidae and Saurillodon (Upper Jurassic, Portugal); (4) Asagaolacerta, Kuwajimalla , Polyglyphanodontia (Lower Cretaceous, Japan); (5) Purbicella (Lower Cretaceous, UK); (6) Kaganaias (Lower Cretaceous, Japan); (7) ‘Coniophis ’ (Albian-Cenomanian, North America) and terrestrial + aquatic snakes (Albian-Cenomanian, Algeria); (8) Dalinghosaurus (Lower Cretaceous, China); (9) Dorsetisaurus (Upper Jurassic to Lower Cretaceous, Pan-Laurasia); (10) ?Xenostius (Early Cretaceous, Mongolia); (11) Primaderma (Albian–Cenomanian, North America); (12) ?Hoyalacerta (Early Cretaceous, Spain). See Supplementary Figure 2.S1 for terminal taxon labels in full.

2.2 The Early Squamate Fossil Record

Within Lepidosauria, Squamata is the sister group of Rhynchocephalia. Rhynchocephalia is represented today only by the genus Sphenodon (New Zealand), but the group has a relatively good fossil record through much of the Mesozoic. The occurrence of a primitive rhynchocephalian in the Middle Triassic of Germany [Reference Jones, Anderson and Hipsley14] provides a latest possible age for the division of the lepidosaurian stem, although that division, and thus the origin of Squamata, probably occurred in the Early Triassic [Reference Pyron12, Reference Jones, Anderson and Hipsley14]. However, although there are many records of Triassic rhynchocephalians, there are currently no unequivocal records of Triassic squamates. Those described last century have all been re-assigned to other reptile groups or to the lepidosaurian stem [Reference Evans15, Reference Evans, Jones and Bandyopadhyay16].

Tikiguana estesi, represented by a single jaw with an acrodont dentition collected from Upper Triassic deposits in India [Reference Datta and Ray17], was shown to be a modern intrusion [Reference Hutchinson, Skinner and Lee18]. More recently, Simões et al. [Reference Simões, Caldwell and Tałanda19] placed three monotypic genera, Sophineta cracoviensis (Lower Triassic, Poland, [Reference Evans and Borsuk-Białynicka20]), Megachirella wachtleri (Upper Triassic, Italy [Reference Renesto and Posenato21]), and Marmoretta oxoniensis (Middle Jurassic, UK [Reference Evans22]) into Squamata. However, re-analyses, based on new data for Marmoretta [Reference Griffiths, Ford, Benson and Evans23], do not support a squamate attribution for either Marmoretta or Sophineta , and leave the position of Megachirella as equivocal.

Paikasisaurus indicus is based on two jaw fragments from the Lower–Middle Jurassic Kota Formation of India [Reference Yadagiri24]. The designated holotype bears two teeth, neither of which is obviously pleurodont, whereas the referred specimen bears a single tooth with little resemblance to that of the holotype. Bharatagama rebbanensis, also from the Kota Formation, is represented by multiple jaws bearing both pleurodont and acrodont teeth [Reference Evans, Prasad and Manhas25]. It was described as a possible acrodont iguanian but could also be an aberrant rhynchocephalian [Reference Hutchinson, Skinner and Lee18, Reference Conrad26].

The earliest unequivocal squamates are from the Middle Jurassic (Bathonian) of the United Kingdom, Russia, Kyrgyzstan, and Morocco. One of the most productive Bathonian localities has been Kirtlington Quarry (UK, [Reference Evans27, Reference Evans28]). In addition to the lepidosauromorph Marmoretta , Kirtlington yielded five named squamate genera: Balnealacerta, Bellairsia, cf. Saurillodon, Oxiella, and Parviraptor . Squamate bones were also reported from roughly contemporaneous deposits on the Isle of Skye, Scotland [Reference Griffiths, Ford, Benson and Evans23], and new fieldwork on Skye has yielded both isolated elements and associated material, including specimens referable to the Kirtlington genera Balnealacerta, Bellairsia, and Parviraptor [Reference Pancirioli, Benson and Walsh29]. These specimens both validate the original associations [Reference Evans27, Reference Evans28], contra Caldwell et al. [Reference Caldwell, Nydam, Palci and Apesteguia30], and add new morphological data for phylogenetic analysis. Work on this material is in progress, but it highlights the clear morphological gap between lepidosaurian stem taxa, like Marmoretta, and squamates from the Middle Jurassic onward that show derived features including biradiate squamosals, loss of quadrate–pterygoid fixation, loss of quadratojugal, a synovial epipterygoid–pterygoid joint, and subdivision of the metotic fissure in the braincase.

Among other Middle Jurassic records, Changetisaurus estesi (Bathonian, Kyrgyzstan [Reference Fedorov and Nessov31]) is a partial skeleton attributed to Squamata, but it requires re-study. Squamate remains are also recorded from the Bathonian Berezovsk Mine, western Siberia (a possible paramacellodid, two ‘scincomorphs’: [Reference Averianov, Martin and Skutschas32]) and from similar aged deposits in Morocco (‘scincomorphs’, ‘Parviraptor-like’ taxon [Reference Haddoumi, Allain and Meslouh33]). An osteoderm-covered lizard was briefly described from Callovian–Oxfordian age deposits at Shishougou (Junggar Valley, China [Reference Conrad, Wang, Xu, Pyron and Clark34]), but a detailed description and analysis has yet to be published. Roughly contemporaneous deposits at Daohugou, Chinese Inner Mongolia, have also yielded associated lizard skeletons, one of general proportions and the other with elongate limbs [Reference Evans and Wang35, Reference Evans and Wang36], but both are immature and the preservation is poor. More recently, however, a complete lizard skeleton was recovered from Daohugou equivalent deposits at Guancaishan, Liaoning Province (Hongshanxi xiei, [Reference Dong, Wang, Mou, Zhang and Evans37]).

Moving into the Upper Jurassic, squamate material is known from several additional Laurasian localities, notably: Portugal (Oxfordian, Guimarota [Reference Seiffert38]), Kazakhstan (Oxfordian–Kimmeridgian, Karabastau Formation [Reference Hecht and Hecht39]), North America (Kimmeridgian, Morrison Formation [Reference Prothero and Estes40–Reference Evans and Chure42]), Germany (Tithonian, Solnhofen and neighbouring localities [Reference Conrad26, Reference Cocude-Michel43–Reference Talanda48] and France (Kimmeridgian, Cerin [Reference Evans49]). Unfortunately, the only contemporaneous Gondwanan record is a ‘paramacellodid’ osteoderm from the Tendaguru Formation of Tanzania [Reference Zils, Werner, Moritz and Saanane50], but this identification is unconfirmed.

The squamate fossil record improves substantially in the Early to Middle Cretaceous (i.e., Berriasian–Cenomanian), with specimens from Europe, Africa, the Middle East, Asia, and the Americas. Concurrent with this apparent global expansion, Early Cretaceous (Barremian) specimens include some of the first known occurrences of squamate gliding [Reference Li, Gao, Hou and Xu51], body elongation with limb reduction [Reference Evans, Manabe, Noro, Isaji and Yamaguchi52], viviparity [Reference Wang and Evans53], herbivory [Reference Evans and Manabe54], and specialist climbing [Reference Evans and Barbadillo55, Reference Arnold and Poinar56].

2.3 The First Records of Crown-Group Squamates

Most recent molecular divergence estimates date the first radiation of crown-group squamate lineages to the Early–Middle Jurassic [Reference Pyron12–Reference Jones, Anderson and Hipsley14], with further splitting of major lineages in the Late Jurassic. As yet, however, none of the known Middle Jurassic taxa, and relatively few of those from the Late Jurassic, can be placed unequivocally into crown lineages (Fig. 2.1). There is some improvement in the Early Cretaceous, but many lizards from this period are phylogenetically problematic and behave as wild cards in analyses.

2.3.1 Gekkota

Given that gekkotans are now considered to be one of the first of the major branches to diverge from the ancestral crown squamate, they should be well represented in early squamate assemblages. Their apparent absence could be due to preservational or ecological constraints, or a failure of identification due to a lack of distinctive gekkotan characters in their early history. Several Late Jurassic and Early Cretaceous genera (notably Ardeosaurus, Bavarisaurus, Eichstaettisaurus, Palaeolacerta, Yabeinosaurus ) were originally attributed to Gekkota (e.g., [Reference Hoffstetter44]), but a majority of these have been re-assigned. One exception is Eichstaettisaurus (Upper Jurassic, Germany [Reference Cocude-Michel43]; Lower Cretaceous, Spain, Italy [Reference Evans, Lacasa-Ruiz and Erill Rey57, Reference Evans, Raia and Barbera58]) which is frequently placed on the gekkotan stem (e.g., [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6, Reference Pyron12, Reference Conrad59]), albeit with limited evidence. The first unequivocal stem gekkotan is Hoburogekko suchanovi (Aptian–Albian, Höövor, Mongolia [Reference Alifanov60, Reference Daza, Bauer and Snively61]) although Norellius nyctisaurops (Aptian–Albian, Mongolia [Reference Conrad and Norell62, Reference Conrad and Daza63]) has also been assigned to Gekkota (e.g., [Reference Pyron12], but see [Reference Reeder, Townsend and Mulcahy9]), based primarily on the combination of notochordal vertebrae and paired parietals. In recent years, Cretaceous amber has offered an important window into gekkotan history because it is able to preserve small, delicate skeletons, often with exquisite soft tissues (e.g., Cretaceogekko burmae [Reference Arnold and Poinar56]). The Albian–Cenomanian amber deposits of north-western Myanmar are particularly rich in gekkotans and stem gekkotans from a rarely sampled tropical forest ecosystem [Reference Daza, Stanley, Wagner, Bauer and Grimaldi64, Reference Fontanarrosa, Daza and Abdala65].

2.3.2 Dibamidae

The phylogenetic position of this small, specialized, and biogeographically disparate clade (Dibamus , South East Asia, New Guinea, Philippines; Anelytropsis , Mexico) has long been problematic (e.g., [Reference Estes, De Queiroz, Gauthier, Estes and Pregill3, Reference Greer66]). Molecular analyses have provided greater clarity but there remains uncertainty as to whether dibamids are sister to all other squamates including gekkotans [Reference Zheng and Wiens10, Reference Streicher and Wiens11], to gekkotans alone [Reference Burbrink, Grazziotin and Pyron13], or to all squamates except gekkotans [Reference Pyron12]. Unfortunately, the group has no Mesozoic record. The only putative fossil dibamid is Hoeckosaurus mongoliensis from the Oligocene of Mongolia [Reference Cernansky67].

2.3.3 Scincoidea

Estes et al. [Reference Estes, De Queiroz, Gauthier, Estes and Pregill3] grouped scincoids and lacertoids within Scincomorpha. Consequently, many fossil lizard remains are classified simply as ‘scincomorphs’, making them difficult to attribute to any clade. Scincoidea is probably represented by the Jurassic–Cretaceous Paramacellodidae [Reference Estes and Sauria68] with their body covering of rectangular osteoderms, and possibly by short-jawed Jurassic–Cretaceous taxa like Saurillodon (Fig.2.1). Saurillodon (S. proraformis, S. henkeli ) was first described from Guimarota (Oxfordian, Portugal) based on short robust dentaries with a few large conical teeth [Reference Seiffert38, Reference Kosma69], resembling the jaws of limb-reduced modern scincids and amphisbaenians. Similar jaws were reported from Anoual (Lower Cretaceous, Morocco, Tarratosaurus anoualensis [Reference Broschinski and Sigogneau‑Russell70]) and from Kirtlington (Middle Jurassic, UK [Reference Evans28]). The Kirtlington specimens were referred to Saurillodon, and tentatively associated with unusual elongated vertebrae. If the association is correct, then this Middle Jurassic taxon would be of considerable interest as an early long-bodied, and presumably limb-reduced, squamate. Balnealacerta , also from Kirtlington [Reference Evans28] was attributed to Paramacellodidae based on similarities in jaw and tooth structure, as were dentaries from contemporaneous localities on Skye [Reference Griffiths, Ford, Benson and Evans23]. However, no osteoderms were recovered from among the many kilos of residue from Kirtlington sorted by the author, nor are they known from Skye (e.g., in association with the new material of Balnealacerta [Reference Pancirioli, Benson and Walsh29]), and therefore attribution of these Middle Jurassic remains to Paramacellodidae remains tentative. Nonetheless, paramacellodids (including osteoderms) are recorded from Upper Jurassic deposits including those from Guimarota (Oxfordian [Reference Seiffert38, Reference Broschinski, Martin and Krebs71]), Kazakhstan (Kimmeridgian, Sharovisaurus [Reference Hecht and Hecht39]), and the Morrison Formation, USA (Kimmeridgian [Reference Prothero and Estes40, Reference Evans and Chure41]), as well as from the Lower Cretaceous of the United Kingdom [Reference Hoffstetter72], China [Reference Li73], Russia [Reference Averianov and Skutchas74], Spain [Reference Richter75], Morocco [Reference Richter75], and North America [Reference Nydam and Cifelli76]. Most recently, a partial lizard skeleton, Neokotus sanfranciscanus (Valanginian, Brazil), was described as a possible Gondwanan paramacellodid [Reference Bittencourt, Simões, Caldwell and Langer77], but no osteoderms are associated with the skeleton and the attribution is based mainly on dental morphology.

Other than paramacellodids, the well-preserved Tepexisaurus tepexii (Albian, Mexico [Reference Reynoso and Callison78]) may also be a scincoid [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6], but other attributions have less support. Talanda [Reference Talanda48] argued that Ardeosaurus (Upper Jurassic, Germany) was a scincid, but this was based on an interpretation of cranial ornamentation as representing compound osteoderms. By contrast, Simões et al. [Reference Simões, Caldwell, Nydam and Jiminez-Huidabro47] recovered Ardeosaurus as a gekkotan, whereas other researchers (e.g., [Reference Pyron12]) found Ardeosaurus to be a wild-card taxon in analyses. Finally, Calanguban alamoi is known from a poorly preserved skeleton from Brazil (Aptian–Albian, Crato Formation [Reference Simões, Wilner, Caldwell, Weinschutz and Kellner79]). It was recovered within Cordyliformes in an analysis using the Conrad [Reference Conrad59] matrix, but unresolved using Gauthier et al.’s [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6] matrix. Neither analysis attempted to use a molecular constraint.

2.3.4 Lacertoidea

Lacertoidea encompasses lacertids, amphisbaenians, teiids and gymnophthalmids, and may be represented by Purbicella ragei from the Lower Cretaceous of England (Berriasian, Purbeck Limestone Group [Reference Evans, Jones and Matsumoto80]). Meyasaurus spp. (Barremian, Spain) was proposed to lie on the teiioid stem by Evans and Barbadillo [Reference Evans and Barbadillo81], but within anguimorphs by Richter [Reference Richter82] and Conrad [Reference Conrad59]. Tijubina pontei (Aptian–Albian, Crato Formation, Brazil) was originally attributed to Teiidae [Reference Bonfim-Junior and Marques83], but subsequent researchers either failed to place it securely within the squamate crown [Reference Bonfim-Junior and Avila84, Reference Simões85] or suggested that it and a second Brazilian species (Olindalacerta brasiliensis [Reference Evans and Yabumoto86]) might be polyglyphanodonts [Reference Simões, Wilner, Caldwell, Weinschutz and Kellner79]. Until recently, Polyglyphanodontia were classified as teiioids (e.g., [Reference Estes and Sauria68, Reference Alifanov87, Reference Nydam, Eaton and Sankey88]), a position also recovered by Pyron [Reference Pyron12] using a combined morphological [Reference Conrad59] and molecular matrix. However, Gauthier et al. [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6] recovered polyglyphanodonts on the stem of ‘Scleroglossa’, whereas Pyron [Reference Pyron12], combining the Gauthier et al. [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6] matrix with a molecular dataset, found polyglyphanodonts to be the sister group of Iguania. The position of this large and important fossil group therefore remains problematic, but it is attributed to Teiioidea in Figure 2.1. The earliest attributed polyglyphanodonts are Kuwajimalla kagaensis [Reference Evans and Manabe54] and Asagaolacerta tricuspidens [Reference Evans and Matsumoto89] from the Tetori Formation (Barremian–Aptian, Japan). An unnamed lizard specimen preserved in amber (Albian–Cenomanian, Myanmar) was also described as a crown lacertoid [Reference Daza, Stanley, Wagner, Bauer and Grimaldi64], but this attribution was based primarily on comparison with polyglyphanodonts.

Molecular divergence estimates (e.g., [Reference Pyron12]) date the separation of stem amphisbaenians and lacertids to the Late Jurassic–Early Cretaceous, but the earliest unequivocal record of amphisbaenians is from the Palaeocene [Reference Sullivan90]. Hodzhakulia magna (Albian, Uzbekistan [Reference Nessov91]; Mongolia [Reference Alifanov92]) and Sineoamphisbaena hexatabularis (Santonian–Campanian, China [Reference Wu, Brinkman and Russell93]) were originally classified as stem amphisbaenians, but Hodzhakulia is fragmentary (‘scincomorph’ [Reference Alifanov92]) and Sineoamphisbaena may be related to polyglyphanodonts [Reference Pyron12]. The limb-reduced Slavoia darevskii has also been proposed as a candidate stem amphisbaenian [Reference Talanda94]. The type material is from the Campanian of Mongolia, but older ‘slavoiids’ were reported from the Albian Mongolian locality of Höövor [Reference Alifanov95].

2.3.5 Anguimorpha

Parviraptorids (Middle Jurassic–Early Cretaceous, UK [Reference Evans27]) were originally attributed to Anguimorpha, based on jaw and tooth morphology. This attribution will be tested by new, in progress, analyses based on associated material from Skye (Middle Jurassic). The Middle Jurassic Changetisaurus (Bathonian, Kyrgyzstan) was also attributed to Anguimorpha [Reference Fedorov and Nessov31], but this taxon needs re-examination. Currently, the earliest generally accepted anguimorph is Dorsetisaurus purbeckensis. As its name suggests, this taxon was first described from the Lower Cretaceous (Berriasian) Purbeck Limestone Group of England [Reference Hoffstetter72], but dorsetisaurs have subsequently been reported from the Upper Jurassic of Portugal (Guimarota, Oxfordian [Reference Seiffert38, Reference Broschinski, Martin and Krebs71] and the USA (Morrison Formation, Kimmeridgian [Reference Prothero and Estes40], as well as the Early Cretaceous of Mongolia (Aptian–Albian, Paradorsetisaurus postumus [Reference Alifanov96] (Fig. 2.1). Additionally, a small lizard skeleton (Indrasaurus wangi [Reference O’Connor, Zheng and Dong97] found as gut contents within an Early Cretaceous Chinese Microraptor has a dorsetisaur-like dentition and may be related to dorsetisaurs.

Further anguimorph taxa are recorded from the Lower Cretaceous of Mongolia (Aptian–Albian, Xenostius futilis , crown xenosaur [Reference Alifanov95]); Uzbekistan (Albian, xenosaur [Reference Gao and Nessov98]); Thailand (Barremian, eggs with embryos [Reference Fernandez, Buffetaut and Suteethorn99]); China (Barremian, Dalinghosaurus longidigitus , stem shinisaur [Reference Evans and Wang100]); North America (Albian–Cenomanian, Primaderma, stem monstersaur [Reference Cifelli and Nydam101, Reference Nydam102]); England (Wealden, indet. [Reference Sweetman, Evans and Batten103]); and Spain (Barremian–Aptian, Arcanosaurus ibericus , ‘varanoid’ [Reference Houssaye, Rage and Fernandez-Baldor104]), although many of these records are based on isolated elements. The tiny attenuate Barlochersaurus winhtini from the mid-Cretaceous amber of Myanmar was also tentatively attributed to Anguimorpha [Reference Daza, Bauer and Stanley105], but a more mature specimen is needed to verify this because the skull is poorly preserved.

The relationships of mosasaurians, also frequently grouped within Anguimorpha, are discussed separately (§ 2.3.7).

2.3.6 Iguania

This major squamate clade, comprising both pleurodont and acrodont jawed taxa, is first recorded with certainty from the Late Cretaceous (e.g., Mongolia, North America [Reference Estes and Sauria68]. Some analyses (e.g., [Reference Conrad59]) recovered Hoyalacerta sanzi , a short-limbed lizard from the Lower Cretaceous of Spain (Barremian, Las Hoyas [Reference Evans and Barbadillo106]) on the iguanian stem but further specimens are needed to test this attribution. Conrad [Reference Conrad59] also recovered the enigmatic Huehuecuetzpalli mixtecus (Albian, Mexico [Reference Reynoso107]) as a stem iguanian, although other researchers (e.g., [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6, Reference Reynoso107]) inferred that it lies on the squamate stem. Huehuecuetzpalli combines primitive characters (e.g., notochordal vertebrae, trunk intercentra, retained second distal tarsal) with derived ones (e.g., retracted nares, anterior parietal foramen). A stem-iguanian position was also recovered by Pyron [Reference Pyron12], evaluating both the Conrad [Reference Conrad59] and the Gauthier et al. [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6] matrices using time calibration and combined evidence. Such major inconsistencies in tree position are, unfortunately, rather common for Jurassic–Early Cretaceous taxa.

Xianglong zhaoi , a gliding lizard from the Lower Cretaceous (Barremian) of China was described as an acrodontan [Reference Li, Gao, Hou and Xu51], but this was based on the misinterpretation of the jagged broken edge of the crushed juvenile skull as an acrodont jaw (pers. obs.). Its affinities remain unknown. The Albian–Cenomanian amber of Myanmar has also yielded possible acrodontans [Reference Daza, Stanley, Wagner, Bauer and Grimaldi64], but this attribution is based on postcranial material and needs to be confirmed from well-preserved skulls. A stem chameleon described from the same deposits [Reference Daza, Stanley, Wagner, Bauer and Grimaldi64] is actually an albanerpetontid amphibian [Reference Matsumoto and Evans108]. Jeddaherdan aleadonta , a partial dentary from the Cenomanian of Kem Kem, in Morocco, is possibly an early acrodontan [Reference Apesteguia, Daza, Simões and Rage109], but Gueragama sudamerica (Turonian–Campanian, Brazil [Reference Simões, Wilner, Caldwell, Weinschutz and Kellner79]) is a partial dentary with teeth like those of scincoids or teiids, and is unlikely to be an acrodontan as proposed.

2.3.7 Mosasauria

This group encompasses the Mosasauroidea (Late Cretaceous mosasaurs and aigialosaurs), and several smaller, long-necked, long-bodied taxa (‘dolichosaurs’) from the Early–Late Cretaceous. Mosasaurians are included briefly in this review chapter for completeness (see the relevant chapters in this volume for a more detailed discussion).

Generally considered close relatives of varanids and/or lanthanotids within Anguimorpha (e.g., [Reference McDowell and Bogert110, Reference Carroll and De Braga111; Chapter 9]), several subsequent cladistic analyses distanced mosasaurians from varanids, albeit to varying degrees (e.g., [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6, Reference Caldwell, Carroll and Kaiser112–Reference Simões, Vernygora, Paparella, Jimenez-Huidobro and Caldwell114]). The proposal that mosasaurians were closely related to snakes (e.g., [Reference Caldwell113, Reference Lee115, Reference Lee116] and subsequent papers by the same authors and their collaborators) led Lee and Caldwell [Reference Lee and Caldwell117] to resurrect Cope’s [Reference Cope118] name Pythonomorpha for their mosasaurian + snake clade, and generated the associated, and more controversial, suggestion of a marine origin for snakes [Reference Lee and Caldwell117, Reference Lee119] (see also Chapter 7).

There is general agreement as to the monophyly of Mosasauroidea, but not of Aigialosauridae ([Reference Caldwell113] versus [Reference Lee115, Reference Caldwell120, Reference Dutchak121; Chapter 8]). Both groups have their earliest representatives in the Cenomanian [Reference Mekarski, Pierce and Caldwell122]. ‘Dolichosaurs’ are more problematic, mainly because their skulls are poorly known. Recent papers, often with overlapping groups of authors, disagree as to whether ‘dolichosaurs’ are monophyletic (e.g., [Reference Paparella, Palci, Nicosia and Caldwell123; Chapter 9]) or paraphyletic (e.g., [Reference Mekarski, Pierce and Caldwell122, Reference Pierce and Caldwell124]), how they are defined and diagnosed (contrast [Reference Palci and Caldwell125] with [Reference Paparella, Palci, Nicosia and Caldwell123, Reference Pierce and Caldwell124]), and whether they are closer to snakes (forming the Ophidiomorpha of [Reference Mekarski, Pierce and Caldwell122, Reference Palci and Caldwell125]) or to mosasauroids [Reference Paparella, Palci, Nicosia and Caldwell123]. Most ‘dolichosaur’ genera were recovered from shallow marine deposits associated with either the remnant Tethys seaway (Slovenia, Croatia, Kazakhstan, Lebanon, Palestine, United Kingdom, Germany, France, Spain) or the Western Interior Seaway (North America) [Reference Mekarski, Pierce and Caldwell122]. However, the earliest accepted ‘dolichosaurs’ are from freshwater deposits: in Spain (Barremian, vertebrae originally identified as snake [Reference Rage and Richter126]), Japan (Barremian–Albian Kaganaias [Reference Evans, Manabe, Noro, Isaji and Yamaguchi52]); and Australia (Albian [Reference Scanlon, Hocknull and Everhard127]). The enigmatic snake-like Tetrapodophis amplectus (Albian, Brazil [Reference Martill, Tischlinger and Longrich128]), also from a freshwater deposit, was recovered by Paparella et al. [Reference Paparella, Palci, Nicosia and Caldwell123] on the stem of a Mosasauroidea + Dolichosauridae clade that is proposed to be the sister group of snakes (see also Chapter 8).

2.3.8 Pan-Serpentes

The morphological specializations of the snake skeleton and the lack of early fossil representatives have hampered attempts to resolve the relationships of snakes to extant lizards. McDowell and Bogert [Reference McDowell and Bogert110] argued that snakes were related to anguimorphs, particularly varanids and/or lanthanotids, and several cladistic analyses (e.g., [Reference Lee115, Reference Lee116, Reference Paparella, Palci, Nicosia and Caldwell123, Reference Pierce and Caldwell124, Reference Lee129]) supported this (snake–mosasaurian relationships notwithstanding). However, convergence between snakes and other limbless squamates (e.g., amphisbaenians, dibamids, limbless scincids, and anguids) tends to confound analyses based solely on phenotypic data (e.g., [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6, Reference Conrad59, Reference Lee116, Reference Simões, Caldwell and Kellner130]), leading to artificial groupings. Molecular and combined evidence analyses avoid this problem, and unite Serpentes, Anguimorpha, and Iguania within Toxicofera (e.g., [Reference Vidal and Hedges1]). Most analyses find Serpentes + [Iguania + Anguimorpha] (e.g., [Reference Vidal and Hedges1, Reference Pyron, Burbrink and Wiens8, Reference Zheng and Wiens10, Reference Streicher and Wiens11, Reference Burbrink, Grazziotin and Pyron13, Reference Mulcahy, Noonan and Moss131]) but the sister-group relationship between Iguania and Anguimorpha is not strongly supported. Furthermore, this does not resolve the position of mosasaurians with respect to snakes, because their common placement within an extended Anguimorpha (e.g., [Reference Lee115, Reference Lee116, Reference Paparella, Palci, Nicosia and Caldwell123, Reference Pierce and Caldwell124, Reference Lee132]) is incompatible with the molecular results. Pyron [Reference Pyron12] ran combined evidence analyses using either the matrix of Conrad [Reference Conrad59] or that of Gauthier et al. [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6] for the morphological component. Predictably, he obtained very different results. His optimal tree for the Conrad matrix placed mosasaurians as sister to varanids (i.e., within Anguimorpha) and only distantly related to snakes, whereas the equivalent tree for the Gauthier et al. [Reference Gauthier, Kearney, Maisano, Rieppel and Behlke6] matrix placed mosasaurians as the sister group of snakes, as did Reeder et al. [Reference Reeder, Townsend and Mulcahy9] (see Augusta et al. and Zaher et al., this volume, for further discussion of snake and mosasaurian relationships).

The first unequivocal snake fossils are isolated vertebrae from the Lower Cretaceous of Algeria (Albian–Cenomanian [Reference Hoffstetter133, Reference Cuny, Jaeger, Mahboubi and Rage134]), reportedly from both terrestrial (Lapparentophis sp.) and aquatic taxa [Reference Rage and Escuillié135], and isolated vertebrae referred to ‘Coniophis ’ sp. from North America (terrestrial, Aptian–Cenomanian [Reference Gardner and Cifelli136]). A much more extensive suite of snake fossils is recorded from the Cenomanian. This Cenomanian record is dominated (and biased) by aquatic taxa from the widespread shallow marine deposits of this period, notably the simoliophiids (or pachyophiids; see Zaher et al., this volume): Simoliophis spp. (France, Portugal, Egypt, Morocco, western Europe and North Africa [Reference Rage and Escuillié135, Reference Rage and Dutheil137]), Pachyophis woodwardi (Bosnia-Herzegovina [Reference Lee, Caldwell and Scanlon138]), Pachyrhachis problematicus (Palestine [Reference Haas139–Reference Zaher and Rieppel142]); Eupodophis descouensi (Lebanon [Reference Rage and Escuillié143]), and Haasiophis terrasanctus (Palestine [Reference Tchernov, Rieppel, Zaher, Polcyn and Jacobs144]), as well as the enigmatic aquatic Lunaophis aquaticus (Venezuela [Reference Albino, Carillo-Briceno and Neenan145]). The current Cenomanian record of terrestrial snakes is more limited, but this is likely to be a gross underestimate considering the global distribution of these taxa: Pouitella pervetus (France [Reference Rage146]), Xiaophis myanmarensis (Myanmar [Reference Xing, Caldwell and Chen147]), Najash rionegrina (Argentina [Reference Apesteguía and Zaher148, Reference Garberoglio, Apesteguia and Simões149]), Seismophis septentrionalis (Brazil [Reference Hsiou, Albino, Medeiros and Santos150]), and Norisophis begaa (Morocco [Reference Klein, Longrich, Ibrahim, Zouhri and Martill151]).

Snakes had clearly diversified, both ecologically and geographically, by the mid-Cretaceous. This is consistent with molecular divergence estimates that place the separation of stem snakes from other toxicoferans during the Jurassic (e.g., [Reference Zheng and Wiens10, Reference Pyron12]). Nonetheless, there remains a significant gap in the fossil record. Filling this gap, Caldwell et al. [Reference Caldwell, Nydam, Palci and Apesteguia30] re-interpreted specimens referred to the Middle Jurassic–Early Cretaceous lizard Parviraptor [Reference Evans27] as stem snakes. Based only on jaw fragments, Caldwell et al. [Reference Caldwell, Nydam, Palci and Apesteguia30] named Eophis underwoodi (Middle Jurassic, UK, dentary symphysis), Diablophis gilmorei (Upper Jurassic, Morrison Formation, USA, maxilla), and Portugalophis lignites (Upper Jurassic, Portugal, maxilla). However, this revision excluded most of the non-dental elements originally attributed to Parviraptor [Reference Evans27], based on the claim that Parviraptor as originally described was a chimaera of several different lizard taxa. New associated parviraptorid material from the Middle Jurassic of Skye confirms the original attribution of elements, both the preserved association on the Lower Cretaceous holotype block and the inferred association from Kirtlington (Middle Jurassic). These elements include paired frontals and parietals, the latter enclosing a parietal foramen, short palatines, and vertebrae that are notochordal and amphicoelous in immature individuals, becoming procoelous with maturity [Reference Evans27]. Work on the new Skye material and other parviraptorids is ongoing but Parviraptor as originally diagnosed is not a chimaera, and phylogenetic analyses must therefore include all of the attributed skeletal elements, rather than selecting only those (maxillae, dentaries) consistent with a particular hypothesis. Preliminary analyses (work in progress) do not support the inclusion of parviraptorids within Pan-Serpentes, and the Middle Jurassic age of the first recorded parviraptorid should therefore not be used to date snake origins in molecular divergence estimates (e.g. [Reference Harrington and Reeder152]).

2.4 Discussion and Conclusion

Although the squamate stem probably extended back into the Early Triassic, morphologically diagnosable squamates are currently unknown prior to the Middle Jurassic of Eurasia and North Africa. Molecular divergence estimates predict that major squamate clades had arisen by this time but, as yet, none of the currently known Middle Jurassic squamates can be placed confidently into the crown. A few Late Jurassic taxa, notably the dorsetisaurs (Anguimorpha), the paramacellodids (Scincoidea), and perhaps Eichstaettisaurus (Gekkota), may lie on the stems of crown clades, but the first unequivocal snake fossils currently date from the mid Cretaceous. The near global distribution of both terrestrial (France, USA, Gondwana) and aquatic (mostly Tethyan) snakes by the Cenomanian provides strong evidence of an earlier origin, but recent reports of Jurassic snake fossils [Reference Caldwell, Nydam, Palci and Apesteguia30] are based on misconception (see above). Given the close relationship between iguanians, anguimorphs and snakes, as strongly supported by molecular data, stem iguanians and stem anguimorphs have the potential to shed light on the expected morphology of the earliest stem snakes – given that stem toxicoferans presumably resembled one another morphologically until they diverged. Taxa like the dorsetisaurs, Huehuecuetzpalli , Hoyalacerta , and perhaps Parviraptor may therefore provide insights into early toxicoferan morphology, and may help to refine ideas on ancestral traits (e.g., [Reference Da Silva, Fabre and Savriama153]). Moreover, if mosasaurians (in total or in part) are genuinely the sister group of snakes (but see Augusta et al. and Zaher et al., this volume), then stem members of that clade also need to be identified, probably from terrestrial and/or freshwater deposits.

Further progress in unravelling the early history of squamates generally, and snakes in particular, will therefore require a combination of new fossil material; accurate (and objective) re-description of existing material using CT scan technology where possible; and a concerted effort to recover early squamate material from biogeographically and ecologically diverse deposits. Unfortunately, most Jurassic and Early Cretaceous squamate taxa are phylogenetically unstable when analysed in matrices combining living and extinct taxa. The topographic position of Mesozoic squamates is sensitive to analysis variables like data input (character choice and definition, ingroup and outgroup taxa sampled, incorporation of temporal data), and the use of ordering, weighting, or molecular constraints. Moreover, apomorphic skeletal features that characterize individuals of modern clades may be absent in early or stem representatives of those clades, further complicating their phylogenetic placement, especially when incomplete. Improving tree resolution is not simply a question of adding more phenotypic characters. We need to develop a greater understanding of those characters, and of the developmental and functional relationships between them.

References

Vidal, N. and Hedges, S. B., The phylogeny of squamate reptiles (lizards, snakes, and amphisbaenians) inferred from nine nuclear protein-coding genes. Comptes Rendus Biologies, 328 (2005), 1000–1008.CrossRef Google Scholar PubMed

Camp, C. L., Classification of the lizards. Bulletin of the American Museum of Natural History, 48 (1923), 289–481.Google Scholar

Estes, R., De Queiroz, K., and Gauthier, J., Phylogenetic relationships within Squamata. In Estes, R., and Pregill, G., eds., Essays Commemorating Charles L. Camp. Phylogenetic Relationships of the Lizard Families (Stanford, CA: Stanford University Press, 1988), pp. 119–281.Google Scholar

Townsend, T. M., Larson, A., Louis, E., and Macey, J. R., Molecular phylogenetics of Squamata: the position of snakes, amphisbaenians, and dibamids, and the root of the squamate tree. Systematic Biology, 53 (2004), 735–757.CrossRef Google Scholar PubMed

Vidal, N. and Hedges, S. B., Molecular evidence for a terrestrial origin of snakes. Proceedings of the Royal Society of London, series B: Biological Sciences, 271 (2004), suppl: S226–S229.Google Scholar

Gauthier, J. A., Kearney, M., Maisano, J. A., Rieppel, O., and Behlke, A. D. B., Assembling the squamate tree of life: perspectives from the phenotype and the fossil record. Bulletin of the Peabody Museum of Natural History, 53 (2012), 3–308.Google Scholar

Wiens, J. J., Hutter, C. R., Mulcahy, D. G., et al., Resolving the phylogeny of lizards and snakes (Squamata) with extensive sampling of genes and species. Biology Letters, 8 (2012), 1043–1046.Google Scholar

Pyron, R. A., Burbrink, F. T., and Wiens, J. J., A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology, 13 (2013), 93.Google Scholar

Reeder, T. W., Townsend, T. M., Mulcahy, D. G., et al., Integrated analyses resolve conflicts over squamate reptile phylogeny and reveal unexpected placements for fossil taxa. PLoS ONE, 10 (2015), e0118199.Google Scholar

Zheng, Y. and Wiens, J. J., Combining phylogenomic and supermatrix approaches, and a time-calibrated phylogeny for squamate reptiles (lizards and snakes) based on 52 genes and 4162 species. Molecular Phylogenetics and Evolution, 94 (2016), 537–547.CrossRef Google Scholar

Streicher, J. W. and Wiens, J. J., Phylogenomic analyses of more than 4000 nuclear loci resolve the origin of snakes among lizard families. Biology Letters, 13 (2017), 20170393.CrossRef Google Scholar PubMed

Pyron, R. A., Novel approaches for phylogenetic inference from morphological data and total-evidence dating in squamate reptiles (lizards, snakes, and amphisbaenians). Systematic Biology, 66 (2017), 38–56.Google Scholar PubMed

Burbrink, F. T., Grazziotin, F. G., Pyron, R. A., et al., Interrogating genomic-scale data for Squamata (lizards, snakes, and amphisbaenians) shows no support for key traditional morphological relationships. Systematic Biology, 69 (2020), 502–520.Google Scholar

Jones, M. E. H., Anderson, C. L., Hipsley, C. A., et al., Integration of molecules and new fossils supports a Triassic origin for Lepidosauria (lizards, snakes, and tuatara). BMC Evolutionary Biology, 13 (2013), 208.Google Scholar

Evans, S. E., At the feet of the dinosaurs: the origin, evolution and early diversification of squamate reptiles (Lepidosauria: Diapsida). Biological Reviews, 78 (2003), 513–551.Google Scholar

Evans, S. E. and Jones, M. E. H., The origins, early history and diversification of lepidosauromorph reptiles. In Bandyopadhyay, S., ed., New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132 (Berlin, Germany: Springer-Verlag, 2010), pp. 27–44.Google Scholar

Datta, P. M. and Ray, S., Earliest lizard from the Late Triassic (Carnian) of India. Journal of Vertebrate Paleontology, 26 (2006), 795–800.Google Scholar

Hutchinson, M. N., Skinner, A., and Lee, M. S. Y., Tikiguana and the antiquity of squamate reptiles (lizards and snakes). Biology Letters, 8 (2012), 665–669.Google Scholar

Simões, T. R., Caldwell, M. W., Tałanda, M., et al., The origin of squamates revealed by a Middle Triassic ‘lizard’ from the Italian Alps. Nature, 557 (2018), 706–709.Google Scholar

Evans, S. E. and Borsuk-Białynicka, M., A small lepidosauromorph reptile from the Early Triassic of Poland. Palaeontologica Polonica, 65 (2009), 179–202.Google Scholar

Renesto, S. and Posenato, R., A new lepidosauromorph reptile from the Middle Triassic of the Dolomites (Northern Italy). Rivista Italiana di Paleontologia i Stratigrafia, 109 (2003), 463–474.Google Scholar

Evans, S. E., A new lizard-like reptile (Diapsida: Lepidosauromorpha) from the Middle Jurassic of Oxfordshire. Zoological Journal of the Linnean Society, 103 (1991), 391–412.Google Scholar

Griffiths, E. F., Ford, D. P., Benson, R. B. J., and Evans, S. E., New information on the Jurassic lepidosauromorph Marmoretta oxoniensis . Papers in Palaeontology, 7:4 (2021), 2255–2278 Google Scholar

Yadagiri, P., Lower Jurassic lower vertebrates from Kota Formation, Pranhita-Godavari valley, India. Journal of the Palaeontological Society of India, 31 (1986), 89–96.Google Scholar

Evans, S. E., Prasad, G. V. R., and Manhas, B., Fossil lizards from the Jurassic Kota Formation of India. Journal of Vertebrate Paleontology, 22 (2002), 299–312.CrossRef Google Scholar

Conrad, J. L., A new lizard (Squamata) was the last meal of Compsognathus (Theropoda: Dinosauria) and is a holotype in a holotype. Zoological Journal of the Linnean Society, 183 (2018), 584–634.Google Scholar

Evans, S. E., A new anguimorph lizard from the Jurassic and Lower Cretaceous of England. Palaeontology, 37 (1994), 33–49.Google Scholar

Evans, S. E., Crown group lizards from the Middle Jurassic of Britain. Palaeontographica, Abt.A 250 (1998), 123–154.Google Scholar

Pancirioli, E., Benson, R. B. J., Walsh, S., et al., Diverse vertebrate assemblage of the Kilmaluag Formation (Bathonian, Middle Jurassic) of Skye, Scotland. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 111 (2020), 135–56.Google Scholar

Caldwell, M. W., Nydam, R. L., Palci, A., and Apesteguia, S., The oldest known snakes from the Middle Jurassic–Lower Cretaceous provide insights on snake evolution. Nature Communications, 6 (2015), 5996.Google Scholar

Fedorov, P. V. and Nessov, L. A., A lizard from the boundary of the Middle and Late Jurassic of north-east Fergana, Bulletin of St . Petersburg University, Geology and Geography, 3 (1992), 9–14 [In Russian].Google Scholar

Averianov, A., Martin, T., Skutschas, P. P., et al., Middle Jurassic vertebrate assemblages of Berezovsk coal mine in western Siberia, (Russia). Global Geology, 19 (2016), 187–204.Google Scholar

Haddoumi, H., Allain, R., Meslouh, S., et al., Guelb el Ahmar (Bathonian, Anoual Syncline, eastern Morocco): first continental flora and fauna including mammals from the Middle Jurassic of Africa. Gondwana Research, 29 (2016), 290–319.Google Scholar

Conrad, J. L., Wang, Y., Xu, X., Pyron, R. A., and Clark, J., Skeleton of a heavily armoured and long-legged Middle Jurassic lizard (Squamata, Reptilia). Journal of Vertebrate Paleontology Supplement, Annual Meeting Abstracts, 73 (2013), 108.Google Scholar

Evans, S. E. and Wang, Y., A juvenile lizard from the Late Jurassic/Early Cretaceous of China. Naturwissenschaften, 94 (2007), 431–439.CrossRef Google Scholar

Evans, S. E. and Wang, Y., A long-limbed lizard from the Upper Jurassic/Lower Cretaceous of Daohugou, Inner Mongolia, China. Vertebrata Palasiatica, 47 (2009), 21–34.Google Scholar

Dong, L. P., Wang, Y., Mou, L., Zhang, G., and Evans, S. E., A new Jurassic lizard from China. Geodiversitas, 41 (2019), 623–641.Google Scholar

Seiffert, J., Upper Jurassic lizards from Central Portugal. Memoria, Serviços Geológicos de Portugal, 22 (1973), 1–85.Google Scholar

Hecht, M. K. and Hecht, B. M., A new lizard from Jurassic deposits of Middle Asia. Paleontological Journal, 18 (1984), 133–136.Google Scholar

Prothero, D. R. and Estes, R., Late Jurassic lizards from Como Bluff Wyoming, and their palaeobiogeographic significance. Nature, 286 (1980), 484–486.Google Scholar

Evans, S. E. and Chure, D. C., Paramacellodid lizard skulls from the Jurassic Morrison Formation at Dinosaur National Monument, Utah. Journal of Vertebrate Paleontology, 18 (1998), 99–114.Google Scholar

Evans, S. E. and Chure, D. C., Morrison lizards: structure, relationships and biogeography. Modern Geology, 23 (1998), 35–48.Google Scholar

Cocude-Michel, M., Les rhynchocéphales et les Sauriens des Calcaires Lithographiques (Jurassique supérieur) d’Europe Occidentale. Nouvelles Archives du Muséum d’Histoire naturelle de Lyon, 7 (1963), 1–187.Google Scholar

Hoffstetter, R., Les Sauria du Jurassic supérieur et specialement les Gekkota de Bavière et de Mandchourie. Senckenbergiana Biologie, 45 (1964), 281–322.Google Scholar

Mateer, N. J., Osteology of the Jurassic lizard Ardeosaurus brevipes (Meyer). Palaeontology, 25 (1982), 461–9.Google Scholar

Evans, S. E., The Solnhofen (Jurassic: Tithonian) lizard genus Bavarisaurus: new skull material and a reinterpretation. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 192 (1994), 37–52.Google Scholar

Simões, T. R., Caldwell, M. W., Nydam, R. L., and Jiminez-Huidabro, P., Osteology, phylogeny, and functional morphology of two Jurassic lizard species and the early evolution of scansoriality in geckoes. Zoological Journal of the Linnean Society, 180 (2017), 216–241.Google Scholar

Talanda, M., An exceptionally preserved Jurassic skink suggests lizard diversification preceded the fragmentation of Pangaea. Palaeontology, 61 (2018), 659–677.Google Scholar

Evans, S. E., A re-evaluation of the late Jurassic (Kimmeridgian) reptile Euposaurus (Reptilia: Lepidosauria) from Cerin, France. Geobios, 27 (1994), 621–631.Google Scholar

Zils, W., Werner, C., Moritz, A., and Saanane, C., Tendaguru, the most famous dinosaur locality of Africa. Review, survey and future prospects. Documenta naturae, Munich, 97 (1995), 1–41.Google Scholar

Li, P. P., Gao, K. Q., Hou, L. H., and Xu, X., A gliding lizard from the Early Cretaceous of China. Proceedings of the National Academy of Sciences of the U.S.A., 104 (2007), 5507–5509.CrossRef Google Scholar PubMed

Evans, S. E., Manabe, M., Noro, M., Isaji, S., and Yamaguchi, M., A long-bodied lizard from the Lower Cretaceous of Japan. Palaeontology, 49(6) (2006), 1143–1165.Google Scholar

Wang, Y. and Evans, S. E., A gravid lizard from the Early Cretaceous of China: insights into the history of squamate viviparity. Naturwissenschaften, 98 (2011), 739–743.Google Scholar

Evans, S. E. and Manabe, M., A herbivorous lizard from the Early Cretaceous of Japan. Palaeontology, 51 (2008), 487–498.Google Scholar

Evans, S. E. and Barbadillo, L. J., An unusual lizard (Reptilia, Squamata) from the Early Cretaceous of Las Hoyas, Spain. Zoological Journal of the Linnean Society, 124 (1998), 235–266.Google Scholar

Arnold, E. N. and Poinar, G., A 100 million year old gecko with sophisticated adhesive toepads preserved in amber from Myanmar. Zootaxa, 1847 (2008), 62–68.Google Scholar

Evans, S. E., Lacasa-Ruiz, A., and Erill Rey, J., A lizard from the Early Cretaceous (Berriasian-Hauterivian) of Montsec. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 215 (1999), 1–15.Google Scholar

Evans, S. E., Raia, P., and Barbera, C., New lizards and rhynchocephalians from the Early Cretaceous of southern Italy. Acta Palaeontologica Polonica, 49 (3) (2004), 393–408.Google Scholar

Conrad, J. L., Phylogeny and systematic of Squamata (Reptilia) based on morphology. Bulletin of the American Museum of Natural History, 310 (2008), 1–182.Google Scholar

Alifanov, V. R., The oldest gecko (Lacertilia: Gekkonidae) from the Lower Cretaceous of Mongolia. Paleontological Journal, 23 (1990), 128–131.Google Scholar

Daza, J. D., Bauer, A. M., and Snively, E. D., On the fossil record of Gekkota. Anatomical Record, 297 (2014), 433–462.Google Scholar

Conrad, J. L. and Norell, M. A., High-resolution X-ray computed tomography of an early Cretaceous gekkonomorph (Squamata) from Öösh (Övörkhangai: Mongolia). Historical Biology, 18 (2006), 405–431.Google Scholar

Conrad, J. L. and Daza, J. D., Naming and re-diagnosing the Cretaceous gekkonomorph (Reptilia, Squamata) from Öösh (Övörkhangai, Mongolia). Journal of Vertebrate Paleontology, 35 (2015), e980891.Google Scholar

Daza, J. D., Stanley, E. L., Wagner, P., Bauer, A., and Grimaldi, D. A., Mid-Cretaceous amber fossils illuminate the past diversity of tropical lizards. Science Advances, 2 (2016), e1501080.Google Scholar

Fontanarrosa, G., Daza, J. D., and Abdala, V., Cretaceous fossil gecko hand reveals a strikingly modern scansorial morphology: qualitative and biometric analysis of an amber-preserved lizard hand. Cretaceous Research, 84 (2018), 120–133.Google Scholar

Greer, A. E., The relationships of the lizard genera Anelytropsis and Dibamus. Journal of Herpetology, 19 (1985), 116–156.Google Scholar

Cernansky, A., The first potential fossil record of a dibamid reptile (Squamata; Dibamidae): a new taxon from the early Oligocene of Central Mongolia. Zoological Journal of the Linnean Society, 187 (2019), 782–799.Google Scholar

Estes, R. and Sauria, Amphisbaenia. Handbuch der Paläoherpetologie/Encyclopedia of Paleontology, Part 10A (Stuttgart: Gustav Fischer, 1983).Google Scholar

Kosma, R., The dentitions of recent and fossil scincomorphan lizards (Lacertilia, Squamata). Systematics, functional morphology, palaeoecology. Unpublished PhD Thesis, University of Hannover (2004).Google Scholar

Broschinski, A. and Sigogneau‑Russell, D., Remarkable lizard remains from the lower Cretaceous of Anoual (Morocco). Annales de Paléontologie (Vert.‑Invert.), 82 (1996), 147–175.Google Scholar

Broschinski, A., The lizards from the Guimarota mine. In Martin, T. and Krebs, B., eds., Guimarota. A Jurassic Ecosystem (Munich: Dr. Friedrich Pfeil, 2000), pp. 59–68.Google Scholar

Hoffstetter, R., Coup d’oeil sur les Sauriens (Lacertiliens) des couches de Purbeck (Jurassique Supérieur d’Angleterre). Problemes Actuels de Paleontologie (Evolution des Vertebrates), Colloques Internationaux du Centre National de la Recherche Scientifique, 163 (1967), 349–371.Google Scholar

Li, J.-L., A new lizard from the late Jurassic of Subei, Gansu. Vertebrata PalAsiatica, 23 (1985), 13–18.Google Scholar

Averianov, A. O. and Skutchas, P. P., Paramacellodid lizard (Squamata, Scincomorpha) from the Early Cretaceous of Transbaikalia. Russian Journal of Herpetology, 6 (1999), 115–117.Google Scholar

Richter, A., Lacertilia aus der Unteren Kreide von Uña und Galve (Spanien) und Anoual (Marokko). Berliner geowissenschaftliche Abhandlungen, 14 (1994), 1–147.Google Scholar

Nydam, R. L. and Cifelli, R. L., Lizards from the Lower Cretaceous (Aptian-Albian) Antlers and Cloverley Formations. Journal of Vertebrate Paleontology, 22 (2002), 286–298.Google Scholar

Bittencourt, J. S., Simões, T. R., Caldwell, M. W., and Langer, M. C., Discovery of the oldest South American fossil lizard illustrates the cosmopolitanism of early South American squamates. Communications Biology, 3 (2020), 201.Google Scholar

Reynoso, V. H. and Callison, G., A new scincomorph lizard from the Early Cretaceous of Puebla, Mexico. Zoological Journal of the Linnean Society, 130 (2000), 183–212.Google Scholar

Simões, T. R., Wilner, E., Caldwell, M. W., Weinschutz, L. C., and Kellner, A. W. A., A stem-acrodontan lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana. Nature Communications, 6 (2015), 9149.Google Scholar

Evans, S. E., Jones, M. E. H., and Matsumoto, R., A new lizard skull from the Purbeck Limestone Group of England. Bulletin of the Geological Society of France, 183 (2012), 517–524.Google Scholar

Evans, S. E. and Barbadillo, L. J., Early Cretaceous lizards from las Hoyas, Spain. Zoological Journal of the Linnean Society, 119 (1997), 23–49.Google Scholar

Richter, A., Der problematische Lacertilier Ilerdaesaurus (Reptilia: Squamata) aus der Unter-Kreide von Uña und Galve. Berliner geowissenschaftliche Abhandlungen, 13 (1994), 135–161.Google Scholar

Bonfim-Junior, F. C. and Marques, R. B., Um novo lagarto do Cretáceo do Brasil (Lepidosauria, Squamata, Lacertilia – formação Santana, Aptiano da Bacia do Araripe). Anuario do Instituto de Geociencias, 20 (1997), 233–240.Google Scholar

Bonfim-Junior, F. C. and Avila, L. D. S., Phylogenetic position of Tijubina pontei Bonfim and Marques 1997 (Lepidosauria, Squamata), a basal lizard from the Santana Formation, Lower Cretaceous of Brazil. Journal of Vertebrate Paleontology, 22 (Supplement to 3) (2002), 37A–38A.Google Scholar

Simões, T. R., Redescription of Tijubina pontei, and Early Cretaceous lizard (Reptilia; Squamata) from the Crato Formation of Brazil. Anais da Academia Brasileira de Ciencias, 84 (2012), 1.Google Scholar

Evans, S. E. and Yabumoto, Y., A lizard from the Early Cretaceous Crato Formation, Araripe Basin, Brazil. Neues Jahrbuch für Paläontologie und Geologie, Monatshefte 1998 (1998), 349–364.Google Scholar

Alifanov, V. R., New lizards of the Macrocephalosauridae (Sauria) from the Upper Cretaceous of Mongolia, critical remarks on the systematics of the Teiidae (sensu Estes, 1983). Paleontological Journal, 27 (1993), 70–90.Google Scholar

Nydam, R. L., Eaton, J. G., and Sankey, J., New taxa of transversely-toothed lizards (Squamata; Scincomorpha) and new information on the evolutionary history of ‘teiids’. Journal of Paleontology, 81 (2007), 538–549.Google Scholar

Evans, S. E. and Matsumoto, R., An assemblage of lizards from the Early Cretaceous of Japan. Palaeontologica Electronica, 18.2.36A (2015), 1–36.Google Scholar

Sullivan, R. M., A new middle Paleocene (Torrejonian) rhineurid amphisbaenian, Plesiorhineura tsentasi new genus, new species, from the San Juan Basin, New Mexico. Journal of Paleontology, 59 (1985), 1481–1485.Google Scholar

Nessov, L. A., Rare bony fishes, terrestrial lizards and mammals from the lagoonal zone of the litoral lowlands of the Cretaceous of the Kyzylkumy. Yearbook of the All-Union Palaeontological Society, Leningrad, 28 (1985), 199–219.Google Scholar

Alifanov, V. R., Lizards of the family Hodzhakuliidae (Scincomorpha) from the Lower Cretaceous of Mongolia. Paleontological Journal, 50 (2016), 504–513.Google Scholar

Wu, X.-C., Brinkman, D. B., and Russell, A. P., Sineoamphisbaena hexatabularis: an amphisbaenian (Diapsida: Squamata) from the Upper Cretaceous redbeds at Bayan Mandahu (Inner Mongolia, People’s Republic of China), and comments on the phylogenetic relationships of the Amphisbaenia. Canadian Journal of Earth Sciences, 33 (1996), 541–577.CrossRef Google Scholar

Talanda, M., Cretaceous roots of the amphisbaenian lizards. Zoologica Scripta, 45 (2015), 1–8.Google Scholar

Alifanov, V. R., Lizards of the families Eoxantidae, Ardeosauridae, Globauridae, and Paramacellodidae (Scincomorpha) from the Aptian-Albian of Mongolia. Paleontological Journal, 53 (2019), 74–88.Google Scholar

Alifanov, V. R., Lizards of the families Dorsetisauridae and Xenosauridae (Anguimorpha) from the Aptian–Albian of Mongolia. Paleontological Journal, 53 (2019), 183–193.Google Scholar

O’Connor, J. M., Zheng, X., Dong, L., et al., Microraptor with ingested lizard suggests non-specialized digestive function. Current Biology, 29 (2019), 2423–2429.CrossRef Google Scholar PubMed

Gao, K. Q. and Nessov, L. A., Early Cretaceous squamates from the Kyzylkum Desert, Uzbekistan. Neues Jahrbüch für Geologie und Paläontologie, Abhandlungen, 207 (1998), 289–309.Google Scholar

Fernandez, V., Buffetaut, E., Suteethorn, V., et al., Evidence of egg diversity in squamate evolution from Cretaceous anguimorph embryos. PLoS ONE, 10 (2015), e0128610.Google Scholar

Evans, S. E. and Wang, Y., The Early Cretaceous lizard Dalinghosaurus from China. Acta Palaeontologica Polonica, 50 (2005), 725–742.Google Scholar

Cifelli, R. L. and Nydam, R. L., Primitive, helodermatid-like platynotan from the Early Cretaceous of Utah. Herpetologica, 51 (1995), 286–291.Google Scholar

Nydam, R. L., A new taxon of helodermatid-like lizard from the Albian-Cenomanian of Utah. Journal of Vertebrate Paleontology, 20 (2000), 285–294.Google Scholar

Sweetman, S. C. and Evans, S. E., Lepidosaurs (lizards). In Batten, D. J., ed., Palaeontological Association Field Guide to Fossils, 14 . English Wealden Fossils (London: The Palaeontological Association, 2011), pp. 264–284.Google Scholar

Houssaye, A., Rage, J.-C., Fernandez-Baldor, F. T., et al., A new varanoid squamate from the Early Cretaceous (Barremian-Aptian) of Burgos, Spain. Cretaceous Research, 41 (2013), 127–135.Google Scholar

Daza, J. D., Bauer, A. M., Stanley, E. L., et al., An enigmatic miniaturized and attenuate whole lizard from the mid-Cretaceous amber of Myanmar. Breviora, 563 (2018), 1–18.Google Scholar

Evans, S. E. and Barbadillo, L. J., A short-limbed lizard from the Lower Cretaceous of Spain. Special Papers in Palaeontology, 60 (1999), 73–85.Google Scholar

Reynoso, V. H., Huehuecuetzpalli mixtecus gen. et sp. nov.: a basal squamate (Reptilia) from the early Cretaceous of Tepexi de Rodriguez, Central Mexico. Philosophical Transactions of the Royal Society of London , Biological Sciences, 353 (1998), 477–500.Google Scholar

Matsumoto, R. and Evans, S. E., The first record of albanerpetontid amphibians (Amphibia, Albanerpetontidae) from East Asia. PLoS ONE, 13 (2018), e0189767.Google Scholar

Apesteguia, S., Daza, J. D., Simões, T. R., and Rage, J.-C., The first iguanian lizard from the Mesozoic of Africa. Royal Society Open Science, 3 (2016), 160462.Google Scholar

McDowell, S. B. and Bogert, C. M., The systematic position of Lanthanotus and the affinities of the anguinomorphan lizards. Bulletin of the American Museum of Natural History, 105 (1954), 1–142.Google Scholar

Carroll, R. L. and De Braga, M., Aigialosaurus: mid-Cretaceous varanoid lizards. Journal of Vertebrate Paleontology, 12 (1992), 66–86.Google Scholar

Caldwell, M. W., Carroll, R. L., and Kaiser, H., The pectoral girdle and forelimb of Carsosaurus marchesetti (Aigialosauridae) with a preliminary phylogenetic analysis of mosasauroids and varanoids. Journal of Vertebrate Paleontology, 15 (1995), 516–531.Google Scholar

Caldwell, M. W., Squamate phylogeny and the relationships of snakes and mosasauroids. Zoological Journal of the Linnean Society, 125 (1999), 115–147.Google Scholar

Simões, T. R., Vernygora, O., Paparella, I., Jimenez-Huidobro, P., and Caldwell, M. W., Mosasauroid phylogeny under multiple phylogenetic methods provides new insights on the evolution of aquatic adaptations in the group. PLoS ONE 12 (2017), e0176773.Google Scholar

Lee, M. S. Y., The phylogeny of varanoid lizards and the affinities of snakes. Philosophical Transactions of the Royal Society, Biological Sciences, 352 (1997), 53–91.Google Scholar

Lee, M. S. Y., Convergent evolution and character correlation in burrowing reptiles: towards a resolution of squamate phylogeny. Biological Journal of the Linnean Society, 65 (1998), 369–453.CrossRef Google Scholar

Lee, M. S. Y. and Caldwell, M. W., Adriosaurus and the affinities of mosasaurs, dolichosaurs, and snakes. Journal of Paleontology, 74 (2000), 915–37.Google Scholar

Cope, E. D., On the reptilian orders, Pythonomorpha and Streptosauria. Proceedings of the Boston Society of Natural History, 12 (1869), 250–66.Google Scholar

Lee, M. S. Y., Molecular evidence and marine snake origins. Biology Letters, 1 (2005), 227–230.Google Scholar

Caldwell, M. W., On the aquatic squamate Dolichosaurus longicollis Owen, 1850 (Cenomanian, Upper Cretaceous), and the evolution of elongate necks in squamates. Journal of Vertebrate Paleontology, 20 (2000), 720–735.Google Scholar

Dutchak, A. R., A review of the taxonomy and systematics of aigialosaurs. Netherlands Journal of Geosciences, 84 (2005), 221–229.CrossRef Google Scholar

Mekarski, M. C., Pierce, S. E., and Caldwell, M. W., Spatiotemporal distributions of non-ophidian ophidiomorphs, with implications for their origin, radiation, and extinction. Frontiers in Earth Science, 7 (2019), article 24.Google Scholar

Paparella, M., Palci, A., Nicosia, U., and Caldwell, M. W., A new fossil marine lizard with soft tissues from the Late Cretaceous of southern Italy. Royal Society Open Science, 5 (2018), e172411.Google Scholar

Pierce, S. E. and Caldwell, M. W., Redescription and phylogenetic position of the Adriatic (Upper Cretaceous; Cenomanian) dolichosaur Pontosaurus lesinensis (Kornhuber, 1873). Journal of Vertebrate Paleontology, 24 (2004), 373–386.Google Scholar

Palci, A. and Caldwell, M. W., Redescription of Acteosaurus tommasinii Von Meyer 1860, and a discussion of evolutionary trends within the clade Ophiodiomorpha. Journal of Vertebrate Paleontology, 30 (2010), 94–108.Google Scholar

Rage, J.-C. and Richter, A., A snake from the lower Cretaceous (Barremian) of Spain: the oldest known snake. Neues Jahrbuch für Geologie und Paläontologie, Monatshefte, 1995 (1995), 561–565.Google Scholar

Scanlon, J. D. and Hocknull, S. A., A dolichosaurid lizard from the latest Albian (mid-Cretaceous) Winto Formation, Queensland, Australia. In Everhard, M. J., ed., Proceedings of the Second Mosasaur Meeting, Fort Hays Studies Special Issue, 3 (2008), 131–136.Google Scholar

Martill, D. M., Tischlinger, H., and Longrich, N. R., A four-legged snake form the Early Cretaceous of Gondwana. Science, 349 (2015), 416–419.CrossRef Google Scholar

Lee, M. S. Y., Squamate phylogeny, taxon sampling, and data congruence. Organisms, Diversity, and Evolution, 5 (2005), 25–45.Google Scholar

Simões, T. R., Caldwell, M. W., and Kellner, A. W. A., A new Early Cretaceous lizard species from Brazil, and the phylogenetic position of the oldest known South American squamates. Journal of Systematic Palaeontology, 13 (2015), 601–614.Google Scholar

Mulcahy, D. G., Noonan, B. P., Moss, T., et al., Estimating divergence dates and evaluating dating methods using phylogenomic and mitochondrial data in squamate reptiles. Molecular Phylogenetics and Evolution, 65 (2012), 974–991.Google Scholar

Lee, M. S. Y., Hidden support from unpromising data sets strongly unites snakes with anguimorph ‘lizards’. Journal of Evolutionary Biology, 22 (2009), 1308–1316.Google Scholar

Hoffstetter, R., Un serpent terrestre dans le Crétacé inférieur du Sahara. Bulletin de la Société Géologique de France, 1 (1959), 897–902.Google Scholar

Cuny, G., Jaeger, J. J., Mahboubi, M., and Rage, J.-C., Les plus anciens serpentes (Reptilia, Squamata) connus. Mise au point sur l’age géologiques des Serpents de la partie moyenne du Crétacé. Comptes rendus des séances de l’Académie des Sciences Paris , Series 2, 311 (1990), 1267–1272.Google Scholar

Rage, J.-C. and Escuillié, F., The Cenomanian: stage of hind-limbed snakes. Notebooks on Geology, (1) (2003), (CG2003 A01 JCR-FE).Google Scholar

Gardner, J. D. and Cifelli, R. L., A primitive snake from the Cretaceous of Utah. Special Papers in Palaeontology, 60 (1999), 87–100.Google Scholar

Rage, J.-C. and Dutheil, D. B., Amphibians and squamates from the Cretaceous (Cenomanian) of Morocco. A preliminary study. Palaeontographica Abteilung A, 286 (2008), 1–22.Google Scholar

Lee, M. S. Y., Caldwell, M. W., and Scanlon, J. D., A second primitive marine snake: Pachyophis woodwoodi from the Cretaceous of Bosnia-Herzgovina. Journal of Zoology, 248 (1999), 509–520.Google Scholar

Haas, G., On a new snake-like reptile from the lower Cenomanian of Ein Jabrud, near Jerusalem. Bulletin du Muséum National d’Histoire Naturelle de Paris, 1 (1979), 51–64.Google Scholar

Caldwell, M. W. and Lee, M. S. Y., A snake with legs from the marine Cretaceous of the Middle East. Nature, 386 (1997), 705–709.Google Scholar

Zaher, H., The phylogenetic position of Pachyrachis within snakes (Squamata, Lepidosauria). Journal of Vertebrate Paleontology, 18 (1998), 1–3.Google Scholar

Zaher, H. and Rieppel, O., The phylogenetic relationships of Pachyrachis problematicus and the evolution of limblessness in snakes (Lepidosauria, Squamata). Comptes Rendus de l’Academie de Sciences, Series IIA – Earth and Planetary Science, 329 (1999), 831–837.Google Scholar

Rage, J.-C. and Escuillié, F., Un nouveau serpent bipède du Cénomanien (Crétacé). Implications phylétiques. Comptes Rendus de l’Academie des Sciences, Series IIA - Earth and Planetary Science, 330 (2000), 513–520.Google Scholar

Tchernov, E., Rieppel, O., Zaher, H., Polcyn, M. J., and Jacobs, L. L., A fossil snake with limbs. Science, 287 (2000), 2010–2012.Google Scholar

Albino, A., Carillo-Briceno, J. D., and Neenan, J. M., An enigmatic aquatic snake from the Cenomanian of northern South America. PeerJ, 4 (2016), DOI 10.7717/peerj.2027 e2027.Google Scholar

Rage, J.-C., Un serpent primitif (Reptilia, Squamata) dans le Cénomanien (base du Crétacé supérieur). Comptes rendus de l’Academie des Sciences, Paris, 307 (1988), 1027–1032.Google Scholar

Xing, L., Caldwell, M. W., Chen, R., et al., A mid-Cretaceous embryonic-to-neonate snake in amber from Myanmar. Science Advances, 4 (2018), eaat5042.CrossRef Google Scholar PubMed

Apesteguía, S. and Zaher, H., A Cretaceous terrestrial limbed snake with robust hindlimbs and sacrum, Nature, 440 (2006), 1037–1040.CrossRef Google Scholar PubMed

Garberoglio, F. F., Apesteguia, S., Simões, T. R., et al., New skulls and skeletons of the Cretaceous legged snake Najash, and the evolution of the modern snake body plan. Science Advances, 5 (2019), eaax5833.CrossRef Google Scholar PubMed

Hsiou, A. S., Albino, A. M., Medeiros, M. A., and Santos, R. A. B., The oldest Brazilian snakes from the Cenomanian (early Late Cretaceous). Acta Palaeontologica Polonica, 59 (2013), 635–642.Google Scholar

Klein, C. G., Longrich, N. R., Ibrahim, N., Zouhri, S., and Martill, D. M., A new basal snake from the mid-Cretaceous of Morocco. Cretaceous Research, 72 (2017), 134–141.Google Scholar

Harrington, S. M. and Reeder, T. W., Phylogenetic inference and divergence dating of snakes using molecules, morphology and fossils: new insights into convergent evolution of feeding morphology and limb reduction. Biological Journal of the Linnean Society, 121(2017), 379–394.Google Scholar

Da Silva, F. O., Fabre, A.-C., Savriama, Y., et al., The ecological origins of snakes as revealed by skull evolution. Nature Communications, 9 (2018), 376.Google Scholar

Figure 2.1 Molecular time tree for Squamata, redrawn and simplified from Jones et al. [14], showing putative early representatives of major clades discussed in the text. (1) Eichstaettisaurus (Upper Jurassic, Germany); (2) Hoburogekko (Lower Cretaceous, Mongolia); (3) Paramacellodidae and Saurillodon (Upper Jurassic, Portugal); (4) Asagaolacerta, Kuwajimalla, Polyglyphanodontia (Lower Cretaceous, Japan); (5) Purbicella (Lower Cretaceous, UK); (6) Kaganaias (Lower Cretaceous, Japan); (7) ‘Coniophis’ (Albian-Cenomanian, North America) and terrestrial + aquatic snakes (Albian-Cenomanian, Algeria); (8) Dalinghosaurus (Lower Cretaceous, China); (9) Dorsetisaurus (Upper Jurassic to Lower Cretaceous, Pan-Laurasia); (10) ?Xenostius (Early Cretaceous, Mongolia); (11) Primaderma (Albian–Cenomanian, North America); (12) ?Hoyalacerta (Early Cretaceous, Spain). See Supplementary Figure 2.S1 for terminal taxon labels in full.