A new lepidosaur clade: the Tritosauria
311 Collinsville Avenue, Collinsville, Illinois 62234 U.S.A.
ABSTRACT—Several lizard-like taxa do not nest well within the Squamata or the
Rhynchocephalia. Their anatomical differences separate them from established clades. In
similar fashion, macrocnemids and cosesaurids share few traits with putative sisters
among the prolacertiformes. Pterosaurs are not at all like traditional archosauriforms.
Frustrated with this situation, workers have claimed that pterosaurs appeared without
obvious antecedent in the fossil record. All these morphological ‘misfits’ have befuddled
researchers seeking to shoehorn them into established clades using traditional restricted
datasets. Here a large phylogenetic analysis of 413 taxa and 228 characters resolves these
issues by opening up the possibilities, providing more opportunities for enigma taxa to
nest more parsimoniously with similar sisters. Remarkably, all these ‘misfits’ nest
together in a newly recovered and previously unrecognized clade of lepidosaurs, the
Tritosauria or ‘third lizards,’ between the Rhynchocephalia and the Squamata. Tritosaurs
range from small lizard-like forms to giant marine predators and volant monsters. Some
tritosaurs were bipeds. Others had chameleon-like appendages. With origins in the Late
Permian, the Tritosauria became extinct at the K–T boundary. Overall, the new tree
topology sheds light on this clade and several other ‘dark corners’ in the family tree of
the Amniota. Now pterosaurs have more than a dozen antecedents in the fossil record
documenting a gradual accumulation of pterosaurian traits.
The Lepidosauria was erected by Romer (1956) to include diapsids lacking
archosaur characters. Later, with the advent of computer-assisted phylogenetic analyses,
many of Romer’s ‘lepidosaurs’ (Protorosauria/Prolacertiformes, Trilophosauria, and
Rhynchosauria) were transferred to the Archosauromorpha (Benton, 1985; Gauthier,
1986). With these transfers Gauthier et al. (1988) restricted the definition of the
Lepidosauria to the last common ancestor of Squamata and Rhynchocephalia, and all
descendants of that ancestor.
An enclosing clade, the Lepidosauriformes, was defined (Gauthier et al., 1988) as
the Lepidosauria plus the Kuehneosauridae, their last common ancestor and all of its
A larger enclosing clade, the Lepidosauromorpha, was erected for Lepidosauria
and all taxa sharing a more recent common ancestor with it than with Archosauria
(Gauthier, 1986). According to Evans and Jones (2010), the earliest recognized
lepidosauromorphs, Lanthanolania (Modesto and Reisz, 2002) and Saurosternon
(Carroll, 1975), are Late Permian in age.
In the nineteenth century, the Rhynchocephalia was erected (Günther, 1867) for
Sphenodon and its closest fossil relatives. Estes et al., (1988) defined the Squamata as the
most recent common ancestor of Iguania and Scleroglossa and all of its descendants.
Evans and Jones (2010) redefined the Squamata as all lepidosaurs more closely related to
snakes than to Sphenodon. They thought the first radiation of squamates likely occurred
between the Late Triassic and Middle Jurassic, as many Jurassic to Early Cretaceous taxa
are either stem-squamates or basal members of major clades in their view.
Historical interest in the possible precursors of lizards and snakes arose with the
description of Sphenodon (then known as Hatteria; Günther, 1867) and later with the
discovery of several dozen diapsid fossil taxa, including Prolacerta (Parrington, 1935;
Camp, 1945; von Huene, 1956). However, Gow (1975) demonstrated that Prolacerta was
more closely related to archosaurs than to squamates. More recently de Braga and
Rieppel (1997) recovered turtles, sauropterygians and lepidosaurs in a single clade.
Wiens et al., (2012) produced a molecule study of extant taxa that rearranged prior
squamate trees, nesting Dibamus and gekkos at the base while nesting Anguimorpha and
Iguania as derived sister clades. Pyron et al., (2013) produced a very large study of 4161
extant squamates that recovered a similar tree topology, but included no extinct taxa and
their basalmost squamate was again, the legless Dibamus.
Several prehistoric lizard-like taxa are currently considered enigmas because they
don’t nest well within either the Rhynchocephalia or the Squamata. Lizard-like
Lacertulus (Carroll and Thompson, 1982) is not a squamate according to Benton (1985)
and Evans (2003). Huehuecuetzpalli (Reynoso, 1998) nests outside the Squamata.
Scandensia (Evans and Barbadillo, 1998; Bolet and Evans, 2011) cannot be
accommodated within existing squamate clades, according to Evans (2003).
In summary, membership within the Lepidosauria has shifted over time.
Interrelationships have likewise found little consensus. Molecule studies do not match
Here a phylogenetic analysis large enough to provide hundreds of possible nesting
opportunities for extant and extinct amniote taxa is presented. Rather than trying to
shoehorn misfit taxa into existing clades, the present study opens to the possibility of
recovering new clades.
Institutional Abbreviations—AMNH, American Museum of Natural History,
New York, U.S.A.; BES SC, Museo Civico di Storia Naturale di Milano, Italy; BSPHM,
Bayerische Staatssammlung für Paläontologie und historische Geologie, Münich,
Germany; BPI, Bernard Price Institute for Palaeontological Research, University of the
Witwatersrand, South Africa; FMNH (UC), Field Museum of Natural History
(University of Chicago), Chicago, U.S.A.; GMV, Geological Museum of China, Beijing,
China; IVPP, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing,
China; KUVP, University of Kansas Museum of Natural History, Lawrence, U.S.A.;
MCZ, Museum of Comparative Zoology, Harvard University, Cambridge, U.S.A.;
MFSN, Museo Friulano di Storia Naturale of Udine, Italy; MNG, Museum der Natur in
Gotha, Germany; MPUM, Museo Paleontologia Universita degli Studi di Milano, Italy;
NMS G, National Museums Scotland, Edinburgh Scotland; PIMUZ, Paläontologisches
Institut und Museum der Universität Zürich, Zürich, Switzerland; PIN, Palaeontological
Institute, Russian Academy of Sciences, Moscow, Russia; PVL: Paleontologia de
Vertebrados Lillo, Universidad Nacional de Tucuman, Tucuman, Argentina; PVSJ,
Museo do Ciencias Naturales, Universidad Nacional de San Juan, Argentina; QR/C,
National Museum, Bloemfontein, South Africa; RC, Rubidge Collection, Wellwood,
Graaff Reinet, South Africa; SAM, South African Museum, Cape Town, South Africa;
SMF: Senckenberg Museum, Frankfurt, Germany; SMNS, Staatliches Museum für
Naturkunde, Stuttgart, Germany; UC, University of Chicago, Chicago, U.S.A.; T,
Universität Zürich Paläontologisches Institut und Museum, Zurich, Switzerland; TA,
Adpression code for Museum für Naturkunde Chemnitz, Germany; TM, Ditsong:
National Museum of Natural History (formerly Transvaal Museum), Pretoria, South
MATERIALS AND METHODS
The present phylogenetic analysis (Supp. Data) employs 413 specimen- to genus-
based extinct and extant taxa along with 228 characters. The great size of the present
study minimizes the effects of tradition and/or subjective decision-making while creating
a taxon inclusion set. The large list also provides a greater number of possible nesting
sites for all included taxa.
Although some characters used here are similar to those from various prior
analyses, the present list of character traits (Supp. Data) was largely built from scratch.
Characters were chosen or invented for their ability to lump and split large clades and for
the trait’s visibility in a majority of taxa. Small and hard-to-see foramina were not
Due to the size of the inclusion set, data were collected from firsthand observation,
digital photographs, and the literature. Taxa and characters were compiled in MacClade
4.08 (Maddison and Maddison1990) then imported into PAUP* 4.0b (Swofford 2002)
and analyzed using parsimony analysis with the heuristic search algorithm. All characters
were treated as unordered and no character weighting was used. Bootstrap support figures
for 100 replicates were calculated for overlapping subsets; then combined and
documented in the tree (Fig. 1, Supp. Data).
The present phylogenetic analysis of 413 taxa and 228 characters recovered three
optimal trees (Supp. Data), each with a length of 6465 steps, a Consistency Index (CI)
of .091, a Retention Index (RI) of .748, a Rescaled Consistency Index (RC) of .068 and a
Homoplasy Index (HI) of .909. The homoplasy score was high due to the great propensity
of tested taxa to converge on traits and to the high number of taxa within the inclusion set.
Loss of resolution occurred only at the node in which the skull of Gualosuchus nested
with the skull-less Lagerpeton (Supp. Data). Otherwise smaller subsets (Fig. 1) recovered
single optimal trees with the same topology. Virtually all branches had high Bootstrap
scores. Lower scores associate with incomplete taxa.
A subset of that large tree is presented here (Fig. 1). The taxon list was reduced to
the 65 taxa that surround and include the 26 members of a new clade of lepidosaurs
nesting between the Rhynchocephalia and the Squamata. This single tree had a length of
1103 steps, a Consistency Index (CI) of .316, a Retention Index (RI) of .677, a Rescaled
Consistency Index (RC) of .214 and a Homoplasy Index (HI) of .684. In the subset 30
characters are constant and 11 variable characters are parsimony uninformative. The
character: taxon ratio is 2.87:1 based on the 187 informative characters.
The present phylogenetic analysis (Fig. 1, Supp. Data) produced a clear record of
the interrelationships between the various tested specimens leading to and within the
Amniota. Sister taxa all appear similar (share a large number of traits) with no great
morphological gaps separating them.
The New Lepidosauromorpha
At the first dichotomy (Supp. Data) the Amniota splits the new
Lepidosauromorpha (taxa closer to Lepidosauria; Gauthier, 1986) from the new
Archosauromorpha (taxa closer to Archosauria). Gephyrostegus bohemicus (Jaeckel,
1902) is their last common ancestor.
Basal taxa in the new Lepidosauromorpha include in ascending order:
Bruktererpeton, Thuringothyris, a clade that includes the Captorhinomorpha, Saurorictus,
Milleretta, a clade that includes the Caseasauria, Diadectomorpha and Procolophonia
(sans Owenettidae), a clade that includes the Pareiasauria and Chelonia, a clade that
includes Macroleter and Lanthanosuchus, Nyctiphruretus and the Owenettidae.
The Lepidosauriformes include Lepidosauria, Kuehneosauridae, and their last
common ancestor (Gauthier et al., 1988). Here (Fig. 1, Supp. Data) those last common
ancestors are Sophineta (Evans and Borsuk-Bialynicka, 2009) and Santaisaurus (Koh,
1940). It is interesting to note that only one other Early Triassic precursor taxon,
Paliguana (Broom, 1903), also has an upper temporal fenestra and is the most basal
taxon in this lineage with this trait. Broom (1903) considered it a ‘true lizard,’ and until
Sophineta and Santaisaurus were included in the present tree, Paliguana was that last
common ancestor of Lepidosauria and Kuehneosauridae.
Derived from Late Permian owenettids, the base of the Lepidosauriformes
includes Paliguana, Sophineta, and Santaisaurus (all Early Triassic). The next dichotomy
splits the Kuehneosauridae plus their non-gliding ancestors (Late Permian to Early
Cretaceous) from the Lepidosauria (Late Permian to the present). Note that the two
former lepidosauromorphs mentioned earlier, Lanthanolania and Saurosternon, now nest
within the Lepidosauriformes as ‘rib’-glider precursors.
The first dichotomy within the Lepidosauria splits the Rhynchocephalia (Middle
Triassic to the present day) from the remaining lepidosaurs. Basal rhynchocephalians
include Gephyrosaurus, Marmoretta, Megachirella and the Sphenodontia. Derived
members include Azendohsaurus, Trilophosaurus, Mesosuchus, Priosphenodon, and the
Rhynchosauria (Early Triassic to early Late Cretaceous).
Scandensia (Early Cretaceous) nests as a transitional taxon between the base of
the Rhynchocephalia and the remaining Lepidosauria. A sister taxon, the MFSN 19235
specimen (originally and erroneously attributed to Langobardisaurus, Bizzarini and
Muscio, 1995; Bizzarini et al., 1995; Renesto and Dalla Vecchia, 2007; Late Triassic)
nests as the last common ancestor of squamates and the new clade of lepidosaurs.
The base of the new lepidosaur clade includes Homoeosaurus, the IVPP V 14386
specimen, and Dalinghosaurus. Other basal taxa include Hoyalacerta, Carusia,
Meyasaurus, the Daohugou lizard (IVPP V 13747), Bavarisaurus, Lacertulus, Tijubina,
and Huehuecuetzpalli. The next dichotomy divides Jesairosaurus, Hypuronector, and the
Drepanosauridae from several Macrocnemus specimens plus Dinocephalosaurus. The
next dichotomy divides Langobardisaurus plus Tanytrachelos and Tanystropheus from
the Fenestrasauria (Peters, 2000), which includes Cosesaurus, Kyrgyzsaurus,
Sharovipteryx, Longisquama and the Pterosauria.
In the Squamata the first dichotomy recovered the Iguania and the Scleroglossa,
matching Estes, et al. (1988). Contra de Braga and Rieppel (1997), turtles and
sauropterygians do not nest with lepidosaurs in the present study (Supp. Data). Contra
Benton (1985) and Gauthier et al., (1988) Trilophosaurus and the Rhynchosauria do not
nest with the Archosauriformes, but with derived rhynchocephalians. Contra Gauthier et
al. (1988) and Nesbitt (2011) pterosaurs do not nest with archosaurs or archosauriforms,
but in the new clade of lepidosaurs. Several other novel taxon nestings are also recovered
The present results shed new light on lepidosaur origins and interrelationships.
Taxa once removed from the Lepidosauria, including Trilophosaurus and the
Rhynchosauria (Benton 1985, Gauthier et al., 1988), are returned here. Taxa once thought
related to Prolacerta, such as Macrocnemus and Tanystropheus (Benton, 1985; Gauthier
et al., 1988; Peters, 2000), are nested more parsimoniously within the new lepidosaur
clade. The Pterosauria, once considered to have appeared in the fossil record without
obvious antecedent (Hone and Benton, 2007), now nests in a lepidosaur lineage that
clearly demonstrates a gradual accumulation of pterosaurian traits over a dozen taxa
(Peters 2000, 2001, see below). Here (Fig. 1; Supp. Data) several other former enigmas
and problematic taxa now nest with similar sister taxa.
The present phylogenetic analysis shows that the last common ancestor of
lepidosaurs and archosaurs is the basalmost amniote, Gephyrostegus bohemicus in the
Westphalian (310 Ma). More derived, yet more ancient amniotes, including Westlothiana
and Casineria, appear thirty million years earlier, in the Viséan (340 Ma). The present
topology expands the traditional taxon list for both the Archosauromorpha and the
Lepidosauromorpha. The topology also indicates that the diapsid skull morphology
evolved separately in archosaurs and lepidosaurs.
The traditional taxon list for the Lepidosauriformes (Lepidosauria +
Kuehneosauridae) does not change in the present tree topology. The traditional taxon list
for the Lepidosauria is supplemented with the addition of a new clade.
The proposed name for the new lepidosaur clade is the Tritosauria, or ‘third
lizards,’ because this clade nests between the two traditional lepidosaur clades, the
Rhynchocephalia and the Squamata. The Tritosauria also nests outside of the two major
lizard clades, the Iguania and the Scleroglossa. The Tritosauria is defined as Pteranodon,
Dalinghosaurus, their last common ancestor and all of its descendants. No unique
individual traits identify this clade. Tritosaurs do have an unfused proximal tarsus,
distinct from most other lepidosaurs, but that trait is convergent with rhynchosaurs, a
clade that rejoins the lepidosaurs here. Tritosaurs have a unique suite of traits (see below)
that could only have been recovered in phylogenetic analysis. The removal of twenty
derived tritosaurs from the present analysis does not affect tree topology. Rather it
indicates that the remaining six basal tritosaurs were themselves a distinct clade.
Representatives of the Tritosauria first appeared in the Late Permian with
Lacertulus. The Tritosauria reached the acme of their diversity in the Triassic, and then
became extinct at the K-T boundary with the disappearance of Quetzalcoatlus. Most
clade members were small terrestrial, lizard-like forms. Some, the drepanosaurs, were
small and arboreal (Pinna, 1980). Others, including Dinocephalosaurus (Li et al., 2004),
were large and aquatic. The Tritosauria also includes the first flying reptiles, the
Ironically, several basal taxa, like Huehuecuetzpalli and Scandensia, are only
known from Early Cretaceous sediments. Several derived taxa, like Macrocnemus and
Tanystropheus, are only known from Triassic sediments. These and other anachronisms
testify to a largely undocumented radiation of tritosaurs in the Middle to Late Permian
along with the ability of basal taxa to conserve traits and survive as a species for over 100
Tritosaur Character Trait Evolution
The following tested characters appear within basal members of the Tritosauria to
the exclusion of a penultimate outgroup taxon, the MFSN 19235 specimen. Reversals can
and do occur in derived taxa. Traits restricted to tritosaur offshoot clades are not listed, so
in essence this list documents the gradual accumulation of traits leading to the most
derived tritosaur taxon listed here, the MPUM 6009 specimen, a basal pterosaur.
Tritosaur proximal outgroup taxa include two basal members of the Squamata,
Iguana and Liushusaurus. Several character traits listed below for basal tritosaurs are
noted with an asterisk because these traits are shared with these basal squamates.
Basal Tritosauria Clade One (Homoeosaurus, Dalinghosaurus, IVPP V
14386) and Descendant Taxa—(1) pineal foramen smaller than 20 percent of parietal
length*; (2) frontal nasal suture anteriorly oriented (posteriorly pointed)*; (3) jugal does
not contact squamosal; (4) posterior ectopterygoid aligns with posterior pterygoid
transverse process without a sharp lateral pterygoid angle; (5) retroarticular process
straight; (6) cervical centra longer than tall; (7) scapula and coracoid subequal; (8)
scapulocoracoid fenestrated*; (9) manual unguals not trenchant and without penultimate
phalanges longer than others; (10) astragalus and calcaneum not fused; (11) metatarsus
compact; (12) metatarsal one less than half the length of metatarsal three.
Basal Tritosauria Clade Two: (Hoyalacerta and Descendant Taxa)—(1) in
lateral view, rostral shape straight (not convex); (2) naris displaced or posteriorly
elongate; (3) orbit half again longer than tall; (4) lateral temporal arch absent*; (5)
posterior maxillary tooth at mid orbit*; (6) scapula and coracoid subequal*.
Tritosauria Clade Three: (Meyasaurus, Carusia and Descendant Taxa)—(1)
skull table convex; (2) major axis of naris horizontal to 30º; (3) mandible tip straight
(does not rise); (4) second caudal transverse process not wider than centrum; (5)
metacarpal three is the longest; (6) manual 4.4 not longer than manual 4.3 (digit 4,
Tritosauria Clade Four: (IVPP V 13747 and Descendant Taxa)—(1) naris
opening lateral; (2) postorbital-parietal contact tentative; (3) caudal transverse processes
absent beyond eighth caudal; (4) proximal metatarsals subequal in width; (5) metatarsal 5
Tritosauria Clade Five: (Lacertulus, Bavarisaurus and Descendant Taxa)—
(1) premaxilla invades nasals; (2) more than four premaxillary teeth; (3) ventral mandible
straight; (4) tibia not less than twice ilium length.
Tritosauria Clade Six: (Tijubina and Descendant Taxa)—(1) premaxilla
orientation horizontal (not transverse); (2) orbit length shorter than rostrum; (3) quadrate
anterior lean; (4) premaxillary teeth not tiny; (5) cervical number seven or more; (6)
metatarsal one longer than half of metatarsal three.
Tritosauria Clade Seven: (Huehuecuetzpalli and Descendant Taxa)—(1)
premaxilla ascending process extends beyond naris; (2) postfrontal does not contact
upper temporal fenestra; (3) squamosal descending process extends to mid orbit; (4)
coronoid process low; (5) cervicals number eight or more; (6) mid caudal vertebrae not
three times longer than tall; (7) metacarpal three equals metatarsal four in length; (8)
ilium with small anterior process; (9) fibula diameter not greater than half tibia diameter;
(10) longest metatarsal(s) three and four; (11) metatarsal five is the widest; (12)
metatarsal five torsioned.
Tritosauria Clade Eight: (Jesairosaurus, Drepanosauridae and Descendant
Taxa)—(1) preorbital skull longer than postorbital skull; (2) antorbital fenestra without a
fossa; (3) quadratojugal appears on jugal ramus; (4) procumbent premaxillary teeth; (5)
gastralia present (reversed in drepanosaurs); (6) scapula larger (taller) than coracoid; (7)
pubis ventrally oriented; (8) tibia not shorter than femur; (9) fibula appressed to tibia.
Tritosauria Clade Nine, Tapinoplatia: (Peters, 2000; Macrocnemus,
Dinocephalosaurus and Descendant Taxa)—(1) skull shorter than cervicals; (2) nasals
longer than frontals; (3) squamosal ledge present; (4) lower temporal arch present; (5)
quadrate vertical; (6) supratemporal fused to squamosal; (7) retroarticular ascends; (8)
cervical ribs with free anterior process; (9) cervical ribs slender, parallel to centra; (10)
chevrons parallel to centra; (11) caudals shorter than precaudals; (12) scapula/coracoid
not fenestrated; (13) olecranon process not present; (14) femur not shorter than half the
Tritosauria Clade Ten, Characiopoda: (Peters, 2000; Langobardisaurus,
Tanytrachelos, Tanystropheus and Descendant Taxa)—(1) narial opening dorsolateral;
(2) naris not larger than antorbital fenestra (antorbital fenestra lost in Tanystropheus); (3)
prefrontal does not contact maxilla; (4) jugal posterior process straight; (5) dorsal
vertebrae with transverse processes; (6) 25 or fewer presacrals (reduced from 26 or
more); (7) second caudal transverse process wider than centrum width; (8) advanced
metatarsal type of tarsus.
Tritosauria Clade Eleven, Fenestrasauria: (Peters, 2000; Cosesaurus and
Descendant Taxa)—(1) skull width less than 1.2x height; (2) orbit not half again longer
than tall; (3) maxilla palatal process present; (4) premaxilla excluded from choana; (5)
internal nares deflected medially with narrow vomers; (6) vomer teeth absent; (7)
pterygoid narrow, transverse process absent; (8) palatal teeth absent; (9) premaxillary
teeth not procumbent; (10) four sacral vertebrae; (11) caudals not shorter than presacrals;
(12) interclavicle fused to sternum (creating a sternal complex); (13) expanded
fenestration erodes coracoid to stem shape; (14) ilium anterior process longer than
acetabulum length; (15) ilium posterior process not longer than anterior process; (16)
ventral pelvis fused; (17) prepubis present; (18) tibia less than twice ilium length.
Tritosauria Clade Twelve: (Kyrgyzsaurus and Descendant Taxa)—(1) lacrimal
deeper than maxilla; (2) pineal foramen absent; (3) quadrate not posteriorly concave; (4)
postorbital extends to posterior parietal; (5) vomer maxilla contact; (6) posterior
mandible not deeper anteriorly; (7) retroarticular straight.
Tritosauria Clade Thirteen: (Sharovipteryx and Descendant Taxa)—(1)
squamosal descending process acute; (2) quadrate posterior lean; (3) internal nares not
close to premaxillary teeth; (4) multicusp teeth; (5) five or more sacral vertebrae; (6)
midcaudal vertebrae three times longer than tall; (7) olecranon process present; (8) fore
limb/hind limb ratio less than 0.55; (9) radiale and ulnare enlarged to blocks; (10) manus
and pes subequal; (11) metatarsus not compact; (12) longest metatarsal four; (13) pedal
3.1 not longer than pedal 2.1.
Tritosauria Clade Fourteen: (Longisquama and MPUM 6009, Pterosaur)—
(1) orbit does not enter anterior half of skull; (2) jugal posterior process descends; (3)
squamosal descending process extends only to the dorsal cheek; (4) retroarticular process
descends; (5) cervical centra not longer than tall; (6) cervicals decrease anteriorly; (7)
clavicles fused medially; (8) manual unguals trenchant with penultimate phalanges longer
Tritosauria Clade Fifteen: (MPUM 6009, Pterosaur)—(1) snout-occiput length
not less than half the presacral length; (2) premaxillary teeth procumbent; (3) lacrimal not
deeper than maxilla; (4) dentary contributes to coronoid process; (5) humerus longer than
femur; (6) fore limb/hind limb ratio more than 1.0; (7) manus larger than pes; (8) manual
4.4 longer than manual 4.3; (9) pedal digit five has three phalanges (including the
In Addition to the Above—Tooth implantation becomes thecodont perhaps at
clade eight, certainly at clade nine. The radius and ulna are parallel and appressed at
clade eight. The epipterygoid is lost at clade nine. Cervicals, often elongate, descend
from the back of the skull in a sine curve at clade nine. Pedal 5.1 becomes metapodial at
clade ten. The scapula is strap-like and the interclavicle develops an anterior process at
clade eleven. Uropatagia and other extradermal membranes appear at clade eleven.
Facultative bipedal locomotion appears at clade eleven and obligate bipedalism appears
at clade thirteen. The humerus develops a large deltopectoral crest at clade thirteen. The
clavicles wrap posteriorly around the sternal complex rim at clade fourteen.
Hyperelongation of manual digit 4 and axial rotation of metacarpal 4 to facilitate wing
folding (Peters, 2001) appears at clade fifteen. Multicusped posterior teeth appear at clade
fifteen or perhaps thirteen with convergence in Langobardisaurus at clade ten.
The present phylogenetic analysis of 413 taxa recovers a new tree topology in
which a third clade of lepidosaurs, the Tritosauria, is recovered between the two
traditional clades, the Rhynchocephalia and the Squamata. Tritosaurs include a wide
variety of morphologies. All but drepanosaurs had unfused proximal tarsals, distinct from
those of most other lepidosaurs. Some tritosaurs evolved thecodont teeth and an
antorbital fenestra. Some tritosaurs became bipeds. Some became volant, others aquatic.
The new tree topology sheds light on lepidosaur origins and radiations.
[There is no Acknowledgments section. Experts I contacted did not reply.]
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Submitted October 16, 2014; accepted MONTH, DD, YYYY.
FIGURE 1. A subset of the 1253-taxon tree (Supp. Data), reduced to the 65 taxa that
surround and include the 26 members of the Tritosauria, a new lepidosaur clade nesting
between the Rhynchocephalia and the Squamata. Bootstrap scores are shown. Gray type
refers to chronological age: LP, Late Permian; ETr, Early Triassic; MTr, Middle
Triassic; LTr, Late Triassic, EJu, Early Jurassic; MJu, Middle Jurassic; LJu, Late
Jurassic; EK, Early Cretaceous. [one column]
Schoenesmahl (formerly Bavarisaurus)
Daohugou lizard IVPP V13747
IPB R 535 Homoeosaurus tail
Not Ascendonanus MNC TA1045
JZC Bu1803 - amber
70 Draco volans
JZC Bu154 in amber
Bavarisaurus (= Homoeosaurus) macrodactylus
Macrocnemus BES SC 111
LPV 30280 w/embryo
Tanystropheus k and q
Bergamodactylus MPUM 6009
Yabeinosaurus IVPP V13284
Bahndwivici FMNH PR2260
Saniwa ensidens FMNH
Slavoia holotype ZPAL MgR-I/8
Slavoia ZPAL MgR-III/77
JKZ Bu267 -amber