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Papers in
Palaeontology
VOLUME 8
|
PART 2
|
MARCH/APRIL 2022
www
www
.palass.org
.palass.org
The Palaeontological Association
The Palaeontological Association
The dawn of the flying reptiles: first Triassic record in the
southern hemisphere
by RICARDO N. MART
INEZ
1
,BRIANANDRES
2
, CECILIA APALDETTI
1,3
and IGNACIO A. CERDA
3,4
1
Instituto y Museo de Ciencias Naturales, Universidad Nacional de San Juan, Avda. Espa~
na 400 norte, 5400 San Juan, Argentina; martinez@unsj.edu.ar,
cecilia.apaldetti@gmail.com
2
Department of Animal & Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK; brian.andres@aya.yale.edu
3
Consejo Nacional de Investigaciones Cient
ıficas y T
ecnicas (CONICET), Buenos Aires, Argentina; cecilia.apaldetti@gmail.com, nachocerda6@gmail.com
4
Instituto de Investigaciones en Paleobiolog
ıa y Geolog
ıa, Universidad Nacional de R
ıo Negro, Museo Carlos Ameghino, Belgrano 1700, Paraje Pichi Ruca (predio
Marabunta), 8300, Cipolletti, R
ıo Negro, Argentina; nachocerda6@gmail.com
Typescript received 22 September 2020; accepted in revised form 30 November 2021
Abstract: Pterosaurs were the first vertebrates to evolve
powered flight. The timing of their origin is still debated,
and hypotheses range from the end of the Permian Period,
to the lower Mesozoic Era, and through to the Middle–Late
Triassic epochs. Regardless of when they originated, the
oldest records are restricted to the Upper Triassic Norian
Stage in the northern hemisphere (Europe, USA and Green-
land). We report two new raeticodactylid pterosaurs, Yela-
phomte praderioi gen. et sp. nov. and Pachagnathus benitoi
gen. et sp. nov. from the upper Norian to Rhaetian Queb-
rada del Barro Formation in north-western Argentina. The
new specimens (an isolated dentary symphysis, partial
rostrum, and distal half of ulna) are the first unequivocal
Triassic records of pterosaurs in the southern hemisphere,
confirming that the absence of pterosaurs outside north-
western Pangaea during the Late Triassic was the result of
poor sampling rather than true absence. These new discov-
eries provide evidence of a greater diversity of pterosaurs
living in terrestrial habitats and a wider global distribution
of pterosaurs from the beginning of their evolution on
Earth.
Key words: pterosaur, Triassic, southern hemisphere, land
dwelling.
PTEROSAURS were flying reptiles that lived during most
of the Mesozoic Era. The phylogenetic position of ptero-
saurs as a basal ornithodirans is widely accepted (e.g.
Gauthier 1984; Padian 1984; Gauthier & Padian 1985;
Benton 1990; Sereno 1991; Ezcurra et al. 2020) but their
palaeobiological aspects are still controversial, especially
the context of their origin and early radiation (Unwin
1996; Wang et al. 2005; Andres 2012). Their origin has
been variously hypothesized to have been in the lower
Mesozoic Era (Padian 1984), at the end of the Permian
Period (Wild 1978), during the Middle–Upper Triassic
Epochs (Unwin 2006), or pre-Carnian Age (Upchurch
et al. 2014). After the Triassic Period, pterosaurs became
globally distributed with remains known from every con-
tinent, including Antarctica (e.g. Hammer & Hickerson
1994; Kellner et al. 2019a), before finally becoming
extinct at the end of the Cretaceous Period. To date, the
oldest putative record is a controversial specimen from
late Carnian to early Norian strata in North America
assigned to Eudimorphodon (Murry 1986; Lucas & Luo
1993; Andres 2006). Nevertheless, the oldest undisputed
record of pterosaurs is from marine beds of Middle
Norian age of Lombardy and Friuli in northern Italy (e.g.
Eudimorphodon ranzii Zambelli, 1973, Peteinosaurus zam-
bellii Wild, 1978; Carniadactylus rosenfeldi (Dalla Vecchia,
1995) (Dalla Vecchia 2009); Preondactylus buffarinii Wild,
1984; Austriadactylus cristatus Dalla Vecchia et al., 2002;
Seazzadactylus venieri Dalla Vecchia, 2019) and Austria
(e.g. Austriadactylus cristatus Dalla Vecchia et al., 2002,
Austriadraco dallavecchiai Kellner, 2015). There is a
slightly younger record from upper Norian to Rhaetian
rocks of Switzerland (e.g. Raeticodactylus filisurensis Ste-
cher, 2008; Caviramus schesaplanensis Fr€
obisch &
Fr€
obisch, 2006), as well upper Norian to Rhaetian conti-
nental strata from the USA (Caelestiventus hanseni Britt
et al., 2018) and Rhaetian rocks from Greenland (Eudi-
morphodon cromptonellus Jenkins et al., 2001). To date,
the only Triassic record from southern hemisphere is Fax-
inalipterus minima Bonaparte et al., 2010 from the Norian
Caturrita Formation in southern Brazil. However, recent
studies deny its pterosaur status, alleging the absence of
unequivocal pterosaur features (Dalla Vecchia 2013;
Soares et al. 2013) and suggesting a basal Ornithodira sta-
tus (Soares et al. 2013).
©2022 The Palaeontological Association doi: 10.1002/spp2.1424 1
[Papers in Palaeontology, 2022, e1424
Here, we describe the first unequivocal Triassic record
of pterosaurs in the southern hemisphere. The specimens
are from the upper Norian to Rhaetian Quebrada del
Barro Formation, continental Marayes –El Carrizal Basin,
cropping out in north-western Argentina. These pterosaur
remains corroborate the suggestion that the absence of
pterosaurs outside north-western Pangaea during the Late
Triassic was the result of poor sampling rather than true
absence (Butler et al. 2009; Upchurch et al. 2014), and
indicate that pterosaurs lived in terrestrial habitats as
early as the Late Triassic Epoch.
GEOLOGICAL SETTING
The four specimens (PVSJ 913, 914, 1080, 1094) were
found in the upper Norian to Rhaetian Quebrada del
Barro Formation during fieldwork carried out by the
Museo de Ciencias Naturales of the Universidad Nacional
de San Juan in 2012 and 2014 (Mart
ınez et al. 2015). The
Quebrada del Barro Formation crops out in north-
western Argentina and forms part of the continental
Triassic–Jurassic Marayes –El Carrizal Basin (Fig. 1).
The Marayes –El Carrizal Basin, like its neighbour the
Ischigualasto –Villa Union Basin, corresponds to a series
of extensional basins developed during the early Mesozoic
along the south-western edge of Pangaea (Spalletti 1999).
The stratigraphy of the basin includes the Marayes Group
resting unconformably on the crystalline basement of the
Valle Fertil Group (Bossi 1976) and covered at an erosive
unconformity by the Cretaceous El Gigante Group (Flores
& Criado Roque 1972) (Fig. 1). The Marayes Group is
composed of the Esquina Colorada, Carrizal, Quebrada
del Barro, and Balde de Leyes formations (Bossi 1976;
Colombi et al. 2015) (Fig. 1).
The Esquina Colorada Formation (Middle Triassic)
consists of a sequence of 450–550 m of thick fine con-
glomerates of metamorphic fragments as well as mid-
micaceous sandstones and massive diamictites, both red
in colour and interbedded with tuffaceous facies that
represent distal and partially proximal piedmont facies
with anastomosed channels (Bossi 1976; Bossi et al.
1976). Borrello (1946) mentioned the presence of bone
fragments in the ‘Quebrada del Carrizal’, although these
were not studied in detail. The age was tentatively
assigned to the Middle Triassic by correlation with
Cha~
nares, Ischichuca and Los Rastros formations from
Ischigualasto –Villa Union Basin (Yrigoyen & Stover
1970).
The Carrizal Formation (upper Carnian to lower Nor-
ian), consists of 100–350-m-thick carbonaceous sand-
stones, conglomeratic sandstones, and conglomerates
interbedded with siltstone and coal. This unit has been
interpreted as a fluvial environment, dominated by bed
load sediment in the lower portion and mixed river sys-
tem to the top. Within this unit, abundant palaeofloral
remains corresponding to the Dicroidium Flora have been
found, which have allowed biostratigraphic correlation
with Cacheuta and Potrerillos Formations from the Cuyo
Basin (Lutz & Arce 2013).
The Quebrada del Barro Formation, from which the
specimens described here were collected, has a variable
thickness between 600–1400 m. The unit is formed by
coarse sandstones and conglomerates interbedded with
sandy claystone with sabulitic clasts (Fig. 1A, B). The
depositional environment has recently been reinterpreted
as a distributive fluvial system, in which fluvial channels
with a large range of sinuosity forms a complex deposit
with mudflow-dominated floodplains, and terminal
splays that are formed by heterolithic sandstone and
mudstone accumulations (Colombi et al. 2015, 2021).
Based on the faunal assemblage known from the upper
section of Quebrada del Barro Formation, a late Norian
to Rhaetian age is suggested for this unit (Mart
ınez et al.
2013, 2015).
The Balde de Leyes Formation consists of a 130-m-
thick section of channel and floodplain deposits (Colombi
et al. 2015, 2021). The sequence is composed of a
reddish-brown coarse sandstone and conglomerate chan-
nels interlaid with fine clay-rich mudstones characterized
by calcisol development. The unit has been interpreted as
the feeder zone of a megafan (Mart
ınez et al. 2013;
Colombi et al. 2015, 2021). The age of the unit is sug-
gested to be Early Jurassic based on the presence of the
massospondylid sauropodomorph dinosaur Leyesaurus
marayensis Apaldetti et al., 2011 (Mart
ınez et al. 2013).
The specimens described here were found in upper
layers of the Quebrada del Barro Formation, in two dif-
ferent fossil localities, both corresponding to the southern
outcrops of the unit: PVSJ 913 and PVSJ 1094 in the
‘Bone-bed’ locality (Fig. 1A) and PVSJ 914 and
PVSJ 1080 in the ‘Quebrada del puma’ locality (Fig. 1B).
The specimens are part of a vertebrate assemblage also
composed of opisthodontid sphenodontians, stem testudi-
natans, tritheledontid cynodonts, non-crocodylomorph
and crocodylomorph pseudosuchians, non-dinosaur dino-
sauromorphs, and theropod and sauropodomorph dino-
saurs (Mart
ınez et al. 2013, 2015, 2016, 2017; Apaldetti
et al. 2018; Sterli et al. 2020).
MATERIAL AND METHOD
Terminology
We use the term ‘basal’ for the first branches of a lineage
with respect to later, more-derived branches. We employ
traditional, or ‘Romerian’, anatomical and directional
2PAPERS IN PALAEONTOLOGY
terms over veterinarian alternatives (Wilson 2006). ‘Ante-
rior’ and ‘posterior’, for example, are used as directional
terms rather than the veterinarian alternatives ‘cranial’
and ‘caudal’.
Bone histology
To assess the ontogenetic growth stage of PVSJ 913, his-
tological thin sections were made from this right ulna.
Samples for sectioning were obtained from the proximal
shaft of the element. Two cross-sections were studied.
Preparation of the histological sections was carried out at
the Departamento de Geolog
ıa of the Universidad Nacio-
nal de San Luis, Argentina. The sections were prepared
employing standard methods outlined by Chinsamy &
Raath (1992) and studied using a petrographic polarizing
microscope (Nikon Eclipse E400 POL). Nomenclature
and definitions of structures used in this study follow
Francillon-Vieillot et al. (1990) and Chinsamy-Turan
(2005).
Computed tomography
The superficial surface of PVSJ 914 was exposed by man-
ual preparation. Anatomical investigation of the interior
utilized micro-computed tomography (µCT). PVSJ 914
was scanned at the High-resolution X-ray Computed
Tomography Facility of the Natural History Museum,
London, UK. It was scanned in a single rotation using
cone-beam data acquisition. The dataset included a total
of 3140 coronal CT slices exported as 16 bit TIFF files
that measure 1024 91008 pixels.
FIG. 1. Geological map of the Marayes –El Carrizal Basin and stratigraphic sections of the fossil localities. A, Quebrada del Barro
Formation at the ‘Bone-bed’ locality. B, upper levels of the Quebrada del Barro Formation at the ‘Quebrada del puma’ locality. Modi-
fied from Mart
ınez et al. (2015).
MART
IN E Z ET AL.: DAWN OF FLYING REPTILES 3
Phylogenetic analysis
To determine the phylogenetic position of PVSJ 914 and
1080 within the Pterosauria, these specimens were added
to an updated version of the phylogenetic data matrix
published by Andres et al. (2014). Primarily, the ingroup
was limited to non-pterodactyloid pterosaurs with Ptero-
dactylus antiquus S€
ommerring, 1812, Kryptodrakon pro-
genitor Andres et al., 2014, and a pterosaur specimen
from the Painten Formation of Germany (Tischlinger &
Frey 2013) used as exemplar taxa for Pterodactyloidea. A
number of basal pterosaurs were also added to create a
55 species by 275-character matrix: Dolicorhamphus buck-
landi (Meyer, 1832), Dolicorhamphus depressirostris (Hux-
ley, 1859), Herbstosaurus pigmaeus Casamiquela, 1975,
Rhamphinion jenkinsi Padian, 1984, Kunpengopterus sinen-
sis Wang et al., 2010, Fenghuangopterus lii L€
uet al., 2010,
‘Archaeoistiodactylus’linglongtaensis L€
u & Fucha, 2010,
Luopterus mutoudengensis (L€
u & Hone, 2012), Orientog-
nathus chaoyangensis L€
uet al., 2015, Allkaruen koi
Codorni
uet al., 2016, Darwinopterus zhengi (Wang et al.,
2017), Klobiodon rochei O’Sullivan & Martill, 2018, Cae-
lestiventus hanseni Britt et al., 2018, and Seazzadactylus
venieri Dalla Vecchia, 2019. The new dataset was analysed
using the maximum parsimony-based phylogenetic pro-
gram TNT v.1.5 (Goloboff et al. 2008). Ambiguous
branch support was not used, which is compatible with
the reductive coding of inapplicable states (Strong & Lips-
comb 1999), zero-length branches were automatically col-
lapsed, and the resultant trees were filtered for best score.
All characters were equally weighted and continuous char-
acters were limited to four significant figures as well as
rescaled to unity (Goloboff & Catalano 2016). TNT limits
continuous characters to 0–65 (Goloboff et al. 2008), so
some characters that have states with greater values (e.g.
tooth number) were divided by 100 to fit in this range.
Ordered and unordered characters were implemented and
are listed as such in the taxon–character matrix. Four
outgroups were included, with Euparkeria capensis
Broom, 1913 used as the primary outgroup and therefore
listed first in the matrix. Basic tree-searches of 10 000
random addition sequence replicates were conducted fol-
lowed by branch swapping phases using tree bisection
and rerooting (TBR) as well as subtree pruning and
regrafting (SPR) with trees kept from all replications. This
analysis was also rerun with the ratchet to confirm the
results. Ensemble consistency and retention indices were
calculated using the Stats.run script available at the
PhyloWiki website (http://phylo.wdfiles.com/local--files/
tntwiki/Stats.run). This updated matrix is available in
MorphoBank (Mart
ınez et al. 2022) and can be automati-
cally executed with the procedure command.
As a secondary test for the inclusion of PVSJ 914 and
1080 in the Pterosauria, these taxa were added to a
phylogenetic analysis of diapsid reptile intrarelationships.
There are a number of these analyses that include ptero-
saurs, however, their efficacy for determining the relation-
ships of PVSJ 914 and 1080 as well as pterosaurs in
general should be approached with caution because they
are not designed for this purpose and lack the characters
to resolve pterosaur intrarelationships. With this in mind,
we used the analysis of Ezcurra et al. (2020). Although
there are some issues with this analysis (Bennett 2020),
we did not correct any of the codings but added
PVSJ 914 and 1080 as well as including Scleromochlus tay-
lori Woodward, 1907 (which was excluded from one set
of the analyses by Ezcurra et al. 2020). The discrete parsi-
mony version of the analysis was implemented (i.e.
excluding the morphometric character used in one subset
of analyses by Ezcurra et al. 2020). The analytical proto-
cols implemented were the same as for the primary analy-
sis. This matrix is also available in MorphoBank
(Mart
ınez et al. 2022).
Institutional abbreviations. PVSJ, Instituto y Museo de Ciencias
Naturales, San Juan, Argentina; DGEO-CTG-UFPE, Departamento
de Geologia, Centro de Tecnologia e Geoci^
encias da Universidade
Federal de Pernambuco, Recife, Brazil; NHMUK, Natural History
Museum, London, UK.
SYSTEMATIC PALAEONTOLOGY
ARCHOSAURIA Cope, 1869 sensu Gauthier & Padian (2020)
PTEROSAURIA Owen, 1842 sensu Andres & Padian (2020)
EOPTEROSAURIA Andres et al., 2014
RAETICODACTYLIDAE Andres et al., 2014
Genus YELAPHOMTE nov.
LSID. urn:lsid:zoobank.org:act:25398AC3-1B62-46D3-8CC3-
2F1F498B8408
Derivation of name. The name derives from the Allentiac (native
language spoken by the Huarpe people of San Juan Province,
central Argentina), yelap =beast, homtec =air, referring to the
extreme pneumaticity of the rostrum of the new species and its
capacity to flight in air.
Type species. Yelaphomte praderioi.
Diagnosis. As for the type and only species.
Yelaphomte praderioi sp. nov.
Figure 2
LSID. urn:lsid:zoobank.org:act:17D80B70-6B98-4831-A5DD-
DC51C493A2E1
4PAPERS IN PALAEONTOLOGY
MART
IN E Z ET AL.: DAWN OF FLYING REPTILES 5
Derivation of name. The specific name ‘praderioi’ honours Angel
Praderio, the team member who discovered the new specimen.
Holotype. PVSJ 914, fragment of the rostrum preserving the
anterior part of both maxillae and palatines from the anterior
border of the narial fenestra as well as a posterior portion of
both premaxillae (Fig. 2).
Type locality & horizon. ‘Quebrada del Puma’ locality, Caucete
Department, San Juan Province, Argentina (Fig. 1). The fossilif-
erous locality corresponds to the southern outcrops of the upper
Norian to Rhaetian Quebrada del Barro Formation included in
the Marayes –El Carrizal Basin (Bossi 1976; Colombi et al.
2015). The reddish muddy sandstones of the horizon including
PVSJ 914 is located 60 m below the top of the formation.
Diagnosis. Small pterosaur characterized by unique combination
of characters (autapomorphy denoted with *): premaxillary crest
with set of thin well-spaced radial grooves on lateral surfaces*;
straight fused suture between premaxilla and maxilla extending
anteroventrally from anteroventral corner of narial fenestra; at
least six pairs of evenly spaced and slightly procumbent maxil-
lary teeth; and edentulous anterior part of maxilla.
Description. PVSJ 914 is three-dimensionally preserved without
any diagenetic plastic deformation. The specimen is a fragment
of a narrow and laterally attenuated rostrum, preserving the
anterior part of both maxillae and palatines (at the anterior bor-
der of the narial fenestra) and a posterior portion of both pre-
maxillae (Fig. 2; Table 1). Dorsoventrally, the preserved portion
of the skull is deep and attenuates anteriorly with a preserved
length about one-and-a-half times the preserved height.
The premaxillary rostrum is triangular in transverse section
with the apex oriented dorsally (Fig. 2D). It tapers anteriorly,
and the two premaxillae are fused together along their entire
contact so that the mid-line suture cannot be traced. The
anterior-most portion of the rostrum is not preserved and so it
cannot be determined if there was an anterior lateral expansion,
but there is no lateral expansion of the middle of the rostrum.
Dorsally, the premaxillae extend into a thin sagittal crest, which
is found in the eopterosaurs Au.cristatus and Ra.filisurensis,
angustinaripterin rhamphorhynchids, darwinopterans, and sev-
eral pterodactyloid groups (Andres et al. 2014). The premaxillary
crest in PVSJ 914 extends anteroposteriorly along the entire pre-
served fragment, but the anterior and posterior broken borders
show that the crest was larger, extending anteriorly and posteri-
orly beyond those limits (Fig. 2A, D). The lack of the anterior,
posterior and dorsal portions of the crest precludes determina-
tion of its height and shape (Fig. 2A, D), but it appears to be
tall judging by the thickness of the preserved portion and the
low degree to which the lateral surfaces taper dorsally. However,
this breakage shows that the crest was a solid plate of bone
instead of two plates separated by a series of trabeculae
(Fig. 2D). The lateral surfaces of the crest present a set of thin
radial striae in the form of grooves that are well-separated from
TABLE 1. Measurements of the specimens PVSJ 913, 914, 1080
and 1094.
Specimen Measured feature Measurement
(mm) / ratio
PVSJ 913 Preserved ulna length 134.2
Maximum width of the shaft
(close to the expansion of distal
end)
9.7
Minimum width of the shaft 8.0
Maximum proximodistal length
of distal expansion
23.2
Maximum dorsoventral height of
distal expansion
18.9
Maximum anteroposterior width
of distal expansion
14.6
PVSJ 1080 Preserved dentary symphysis
length
61.5
Maximum preserved width 12.2
Maximum preserved height 19.7
Maximum bone cortex thickness 1.0
PVSJ 914 Preserved rostrum length 15.4
Preserved rostrum height at
anterior end of the naris
10.1
Preserved crest height 3.7
Preserved crest length 7.7
Preserved naris length 5.6
Preserved toothrow length 9.5
Mesiodistal tooth base length 1.1
Preserved tooth crown height 11.1
PVSJ 1094 Mesiodistal tooth crown base
length
2.9
Labiolingual tooth crown base
width
2.1
Mesiodistal length / crown length
ratio
0.26*
Mesiodistal pulp cavity length 1.1
*Estimate
FIG. 2. Yelaphomte praderioi, gen. et sp. nov. (PVSJ 914), fragment of the rostrum. A, right lateral view: photograph, interpretative
line drawing and CT-scan 3D image. B, ventral view: photograph and interpretative line drawing. C, dorsal view: photograph and
interpretative line drawing. D, anterior view: photograph and CT-scan 3D image. E, dorsal view, CT-scan 3D image of the rostral
pneumatic cavities; black arrow indicates anterior direction. F, anterior view, CT-scan 3D of the rostral pneumatic cavities.
G, silhouette of the skull of Ra. filisurensis, closest relative to Y. praderioi, showing the location of the preserved fragment (not to
scale). Abbreviations: a, alveolus; dpmf, dorsal palatal median fossa; f, foramen; g, palatine–maxilla suture groove; lg, lateral groove of
the maxilla; lvr, left ventral ridge; Mx, maxilla; nf, narial fenestra; Pal, palatines; Pmx, premaxilla; Pmxc, premaxillary crest; ptr, pro-
cumbent teeth roots; rsm: radial striae marks; rvr, right ventral ridge; t, tooth; tr, trabeculae; vpmf, ventral palatal medial fossa. Scale
bar represents 10 mm.
6PAPERS IN PALAEONTOLOGY
each other (Fig. 2A). A radial pattern sculpting the lateral sur-
faces of the sagittal crest is also present in the eopterosaurs
Au. cristatus and Ra. filisurensis, but in these other pterosaurs
the sculpture consists of a series of alternating ridges and
grooves close together. Striae marks are also present in darwi-
nopterans and some pterodactyloids (e.g. Germanodactylus and
Gnathosaurus) (Andres et al. 2014), but in them they are
arranged in a sub-parallel and vertical orientation. Posteriorly,
the premaxilla contacts the maxilla at the anteroventral corner
of the narial fenestra forming its anterodorsal border, but not
contributing to its ventral border (Fig. 2A, D), similar to
Ra. filisurensis and some rhamphorhynchids (e.g. Rhamphor-
hynchus muensteri (Goldfuß, 1831), Dorygnathus banthensis
(Theodori, 1830)) and Campylognathoides zitteli Plieninger, 1895
(Padian 2008). This premaxilla–maxilla suture is different from
the eopterosaurian Au. cristatus and the dimorphodontid Dimor-
phodon macronyx (Buckland, 1829) and Caelestiventus hanseni in
which the premaxilla forms the anterior part of the ventral bor-
der of the narial fenestra, and also different from the rhamphor-
hynchids Angustinaripterus longicephalus He et al., 1983 and
Scaphognathus crassirostris (Goldfuß, 1831) in which the maxilla
forms part of the anterodorsal border of the narial fenestra. Ven-
trolaterally, the premaxilla contacts the maxilla with a long
straight fused suture, only visible in the µCT-scan slices, that
extends anteroventrally from the anteroventral corner of the nar-
ial fenestra to the anteroventral tip of the preserved portion of
the rostrum (Fig. 2A, D). Ventrally, the premaxillae are firmly
fused to the maxillae without any external traces of the suture.
In anterior view, the cross-section of the premaxillary rostrum
shows extreme pneumaticity, constituted by an intricate set of
trabeculae distributed over the cross-section (Fig. 2D–F). This
series of symmetrically positioned trabeculae (two on the mid-
line and four on each side laterally) increase in thickness con-
verging posteriorly in three major cavities, which in turn
converge posteriorly in a main cavity that occupies the entire
medial volume forming a deep cavity anterior to the narial
fenestra (Fig. 2D–F).
PVSJ 914 preserves the anterior-most portions of both maxillae.
The fragment only contains the anterior (premaxillary) process and
the anterior portion of the body. Laterally, the maxilla is almost
horizontal, dorsoventrally very thin, and tapering anteriorly. The
lateral surface of the anterior portion of the maxilla has a groove
bordered by a dorsal shelf. In this groove is a linear series of oval
foramina spaced at every other alveolus, as reported in other non-
novialoid pterosaurs (Andres et al. 2014). The long, anteriorly
tapering, thin premaxillary process of the maxilla extending from
the anteroventral corner of the narial fenestra, is different from the
short and dorsoventrally wide process of Ra. filisurensis,Carniadac-
tylus rosenfeldi,E. ranzii,Dg.banthensis,andCampylognathoides
zitteli as well as the long and dorsoventrally wider process of the
rhamphorhynchids Rh.muensteri and An.longicephalus, and the
monofenestratans Darwinopterus modularis L€
uet al., 2010, and
Germanodactylus rhamphastinus Wagner, 1851. Preondactylus buf-
farinii,Au. cristatus and Caelestiventus hanseni have a long and thin
premaxillary process, but entirely located under the narial fenestra.
In dorsal and ventral view, the lateral borders of the maxillae are
straight and taper anteriorly (Fig. 2B, C). The palatines are fused
medially forming an extensive palate. The ventral surface of the
palate presents a shallow concavity delimited laterally by two con-
spicuous ridges, which run parallel to the alveolar border and are
separated from the maxillae by narrow grooves, the palatine–max-
illa sutures (Fig. 2B). There is no median ridge on the palate. The
dorsal surface of the palate has a median fossa extending from the
posterior-most preserved area to the level of the anterior border of
the narial fenestra (Fig. 2C).
The alveolar borders of both maxillae are thin and straight
occlusal ridges that preserve the anterior-most five alveoli on the
right side and six on the left (Fig. 2A, B). The tooth row ends
5.5 mm before the anterior end of the preserved fragment of max-
illa, presenting an anterior edentulous area longer than the length
occupied by four anterior alveoli (Fig. 2A, B). This condition may
be related to the shorter edentulous gap, or diastema, between the
premaxillary and maxillary teeth present in non-novialoid ptero-
saurs. An edentulous anterior-most part of the maxilla is reported
in dsungaripterid pterosaurs but is not present in most known
non-pterodactyloid pterosaurs in which the tooth row anteriorly
extends until the end of the maxilla, including most eopterosaurs
(e.g. Au. cristatus,E. ranzii and Pr. buffarinii), and rhamphor-
hynchids (e.g. Rh. muensteri and Dg. banthensis).
The alveoli contain the five anterior-most teeth from the right
and four (third to sixth) from the left side (Fig. 2A, B). All teeth
are broken off at the base precluding knowledge of the shape of
the crowns. The teeth have a single root, are separated by a dis-
tance less than the mesiodistal tooth length (Fig. 2A, B), and are
evenly distributed. This dental spacing is closely spaced as in
eopterosaurs (e.g. E. ranzii, Pr. buffarinii, Au. cristatus and
Ra. filisurensis). In cross-section (at the base of the crowns) all
teeth are oval, about twice mesiodistally longer than labiolin-
gually wide, and similar to the cheek teeth in other eopterosaurs
as well as dsungaripterids. Judging from the tooth roots, the
maxillary teeth are procumbent at about 60°to the alveolar
border (Fig. 2A) but labiolingually vertical (Fig. 2D), different
from the upright crowns of eopterosaurs (e.g. Au. cristatus,
Ra. filisurensis,E. ranzii and Pr. buffarinii) and the anterolater-
ally oriented teeth present in rhamphorhynchids (e.g.
Rh. muensteri and Dg. banthensis; Wellnhofer 1975; Padian
2008). However, it should be noted that the inclination of tooth
crowns might be different from their roots in pterosaurs, espe-
cially for more mesial teeth.
Genus PACHAGNATHUS nov.
LSID. urn:lsid:zoobank.org:act:031292D6-CAF9-46C7-9651-
F7FE2AAA255A
Derivation of name. The generic name derives from the Aymara
(native American language spoken by the Aymara people of the
Andes), Pacha =Earth, referring to the inland environment in
which the new species lived; and the Latin, gnathus from the
Greek, gnathos =jaws.
Type species. Pachaganthus benitoi.
Diagnosis. As for the type and only species.
MART
IN E Z ET AL.: DAWN OF FLYING REPTILES 7
Pachagnathus benitoi sp. nov.
Figure 3
LSID. urn:lsid:zoobank.org:act:50FF5550-030B-4C46-9985-
0727024BAF5B
Derivation of name. The specific name benitoi honours Benito
Leyes, inhabitant of the small town Balde de Leyes, who found
the first fossils in Balde de Leyes locality and guided RNM and
his team to the site.
Holotype. PVSJ 1080, partial mandibular symphysis lacking
anterior end, preserving one tooth (lacking the apex) and three
alveoli from the left side, and the roots of three teeth and two
alveoli from the right side (Fig. 3).
Type locality & horizon. ‘Quebrada del Puma’ locality, Caucete
Department, San Juan Province, Argentina (Fig. 1). The fossilif-
erous locality corresponds to the southern outcrops of the upper
Norian to Rhaetian Quebrada del Barro Formation included in
the Marayes –El Carrizal Basin (Bossi 1976, Colombi et al.
FIG. 3. Pachagnathus benitoi gen. et sp. nov. (PVSJ 1080), partial mandibular symphysis. A, right lateral view: photograph and inter-
pretative line drawing. B, left lateral view: photograph and interpretative line drawing. C, dorsal view: photograph and interpretative
line drawing. D, anterior view: photograph and interpretative line drawing. E, silhouette of the skull of Ra. filisurensis, closest relative
to Pa. benitoi, showing the location of the preserved fragment (not to scale). Black arrows indicate anterior direction. Abbreviations:
f, foramen; idm, invaginated dental margins; k, keel; la1–5, first to fifth left alveoli; lt, left tooth; ra1, first right alveolus; rt, right
tooth; se, symphyseal eminence; sf, symphyseal fossa; sr, symphyseal ridge; st, striae. Scale bar represents 10 mm.
8PAPERS IN PALAEONTOLOGY
2015). The reddish muddy sandstones of the horizon including
PVSJ 1080 is located 30 m below the top of the formation.
Diagnosis. Moderate-sized pterosaur characterized by unique
combination of characters (autapomorphies denoted with *):
elongate fused symphysis including at least five pairs of teeth;
dorsal symphyseal surface forming a ridge that bifurcates
between each pair of teeth and joins again in single ridge in
interalveolar sections*; strongly invaginated dental margins
forming bowl-shaped structures*; very narrow and laterally com-
pressed anterior end of mandible with lateral margins parallel in
horizontal plane*; keeled symphysis lacking crest; long spike-like
symphyseal teeth with parallel striations, spaced at distance
greater than twice mesiodistal tooth-length; and three anterior-
most pairs of teeth anterolaterally oriented forming wide angle
with fourth and fifth pairs.
Description. The specimen PVSJ 1080 is three-dimensionally pre-
served without any plastic deformation. It corresponds to an ante-
rior part of a long mandibular symphysis (Fig. 3; Table 1). The
bone cortex is very thin, being broken in several places exposing
some alveoli in lateral view (Fig. 3A–C). Both dentaries are firmly
fused at the midline along all the preserved fragment of the sym-
physis without any trace of the suture (Fig. 3C), as in other raeti-
codactylids and all breviquartossans except for the anurognathids
(Andres et al. 2014). The symphysis has at least five pairs of ante-
rior alveoli. In dorsal view, the symphysis forms a narrow and
prominent ridge at the midline in the sections corresponding to
the diastemata between teeth, but in the alveolar sections the ridge
splits into a pair of ridges that converge again at the section of the
next diastema. This specimen has both a midline ridge and occlu-
sal ridges depending the position of teeth. This ridge pattern that
bifurcates and joins again forming deep elliptical fossae between
the teeth (Fig. 3C) is not reported in other pterosaurs. It is likely
to be the result of occlusal ridges being greatly emarginated by lat-
eral bowl-shaped structures. A tiny foramen is present in the
anterior-most preserved elliptical fossa. The lateral surfaces of the
dentaries bend inwards and meet ventrally to form a keel resulting
in a subtriangular cross-section that is twice as deep as wide
(Fig. 3D). The lateral surfaces lack nutrient foramina, but these
could have been present more posterior than the preserved frag-
ment. Almost the entire ventral border of the symphysis is damaged,
except a short anterior section in which it forms a keel without a lat-
eral expansion or a crest. The symphysis reaches its maximum depth
in the area of the two anterior pair of alveoli due to a high eminence
on the dorsal surface of the mandible and an oblique angle with the
ventral margin of the symphysis (Fig. 3A, B). This eminence is pre-
sent in eudimorphodontoids (e.g. E.ranzii) becoming quite high in
the raeticodactylids (e.g. Ra.filisurensis).
The left dental margin preserves five alveoli, three of them with
roots of teeth (Fig. 3A, C). The right dental margin preserves four
alveoli, the third with a tooth lacking the apical half of the crown
(Fig. 3B, C). The alveoli have a single cavity, are elliptical in cross-
section, and form distinct bulges with concavities between them,
creating a strongly invaginated dental margin (Fig. 3A–C). This
invaginated dental margin forms deep bowl-shaped structures not
present in other pterosaurs. These structures are comparable to
the cup-shaped structures reported in Ra. filisurensis (Stecher
2008) and Cav. schesaplanensis (Fr€
obisch & Fr€
obisch 2006), but
are distinct in their size, orientation and position. These mesial
alveoli are equally spaced and separated by a distance greater than
twice the mesiodistal tooth length, as in some dimorphodontians
(e.g. Dimorphodon macronyx) and rhamphorhynchids (e.g.
Rh.muensteri and Dg.banthensis). The tooth cross-sections are
elliptical, almost twice mesiodistally longer than labiolingually
wide. The surface of the tooth enamel is basiapically striated, with
a well-defined anterior and posterior keel lacking serrations. Stri-
ated teeth are also present in E. ranzii,Sd. venieri,Ra. filisurensis,
and some pterodactyloids. If the borders of the only partially pre-
served crown (preserved height: 12 mm; mesiodistal base width:
5 mm) are projected upwards, the tooth shape is a slightly poste-
riorly recurved spike more than five times taller than the basal
width, similar to that present in rhamphorhynchids (e.g.
Rh.muensteri,An.longicephalus and Sericipterus wucaiwanensis
Andres et al., 2010). The first two pairs of teeth, judging by the
root of the right tooth and the alveoli of the left side, are relatively
larger than the successive teeth (mesiodistal length 15% larger).
Strikingly, the anterior-most three pairs of teeth (or alveoli) are
anterolaterally oriented, but the fourth and fifth are more vertical,
forming a wide angle between the roots of the third and fourth
teeth (Fig. 3A, B).
PTEROSAURIA Owen, 1842 sensu Andres & Padian (2020)
gen. et sp. indet.
Figures 4–5
Material. PVSJ 913, distal half of the right ulna.
Locality & horizon. ‘Bone-bed’ locality, Caucete Department,
San Juan Province, Argentina (Fig. 1). The fossiliferous locality
corresponds to the southern outcrops of the upper Norian to
Rhaetian Quebrada del Barro Formation included in the
Marayes –El Carrizal Basin (Bossi 1976; Colombi et al. 2015).
The reddish muddy sandstones of the horizon including
PVSJ 913 are located 20 m below the top of the formation.
Description. The right ulna (PVSJ 913) lacks both the proximal
end and the proximal portion of the shaft. It is three-
dimensionally preserved without plastic deformation. The more
proximal portion of the preserved fragment consists of just the
medullary cavity of the shaft, lacking the external bone cortex
(Fig. 4). PVSJ 913, although incomplete, seems to be moderately
long (ratio of length of preserved fragment to width of the shaft,
>16.7) with a gracile and straight shaft as well as a very
expanded distal end (Fig. 4; Table 1). The preserved portion of
the shaft is sub-oval in cross-section (dorsoventrally oriented
major axis) with a very slight increase in diameter towards the
distal expansion. The shaft is hollow in cross-section, with a
medullary cavity occupying approximately three-quarters of the
area of the shaft. The preserved surface of the shaft is almost
featureless. The only visible trait is a 4-mm-wide, smooth,
rounded knob located on the anterior surface proximal to the
expanded distal end (Fig. 4A, C, D).
The distal expansion is proximodistally elongate (Fig. 4;
Table 1). This large expansion of the distal end is different from
MART
IN E Z ET AL.: DAWN OF FLYING REPTILES 9
the comparatively short distal expansions of other known ptero-
saur ulnae such as that of the Late Jurassic rhamphorhynchids
Rh.muensteri (Wellnhofer 1975, fig. 12) and Sp. wucaiwanensis
(Andres et al. 2010, fig. 6), the Early Cretaceous Ornithocheirus
sp. (NHMUK PV OR 35324) and Anhangueridae indet. (DGEO-
CTG-UFPE 7571; Duque & Barreto 2018), as well as the Late
Cretaceous Pteranodon sp. (Bennett 2001, fig. 76; NHMUK PV
R 2933) and the Cretaceous Keresdrakon vilsoni (Kellner et al.,
2019b). The ventral surface of the distal end has a longitudinal
well-developed ventral expansion in the shape of a laminar crest,
the attachment site for ulnocarpal ligaments (Bennett 2001). The
distal end of this crest expands forming a protruding styloid
prominence, the attachment site for the collateral ligament of
the wrist.
The distal end anterior surface presents a rugose ridge in its
middle, the origin of the pronator quadratus (Bennett 2001).
This ridge delimits two elongated and concave surfaces, one ven-
tral and the other dorsal to the ridge. The ventral surface forms
a platform that supports the radius, which is smooth and
extends along the entire distal end, and the dorsal surface is the
flexor tendon groove, which extends less proximally than the
other surface. The dorsal part of the distal end anterior surface
bears a ventrally curving crest for the retinaculum of the flexor
tendon (Bennett 2001). The anterodorsal surface of this
protruding crest is marked by a deep groove, not reported in
other pterosaurs (Fig. 4A, C).
The distal end posterior surface is characterized by the sub-
triangular and slightly convex dorsal articular surface for the
proximal syncarpal, delimited dorsally and ventrally by slightly
concave surfaces. The dorsal surface is a sub-rhomboidal smooth
area, and the ventral surface is a subtriangular deep fossa, in a
similar location as in some derived pterosaurs such as Pterano-
don (NHMUK PV R 2933; Bennett 2001). Inside this fossa is a
foramen connected to the deep sulcus on the distal surface of
the ulna. These two fossae united by a foramen is a trait not
present in other pterosaurs. A small posterior knob is located
proximoventral to the dorsal articular surface.
The distal surface of the ulna is more expanded dorsoventrally
for the articulation with the proximal syncarpal. It is character-
ized by a ventrally located prominent styloid prominence, a
slightly concave fovea, a low-developed subpyramidal distal
tuberculum, a deep anteroposteriorly elongated sulcus, and a
dorsally located dorsal articular surface protruding posterodis-
tally (Fig. 4E).
Histology. The cortical region of PVSJ 913 is composed of
compact bone and borders a large marrow cavity (Fig. 5A).
The perimedullary region is lined with a thin layer of
FIG. 4. PVSJ 913, right ulna in: A, anterior; B, posterior; C, dorsal; D, ventral; E, distal view. Directions for distal view: A, anterior;
P, posterior; D, dorsal; V, ventral. Abbreviations: adr, anterodistal rugose ridge; ak, anterodistal knob; das, dorsal articular surface;
dc, dorsal ventrally curving crest; ds, distal sulcus; dt, distal tuberculum; fov, fovea; ftg, flexor tendon groove; g, groove; pf, pneumatic
foramen; pk, posterodistal knob; ras, platform supporting the radius; r, dorsal articular surface rise; sp, styloid prominence; vc, ventral
crest. Scale bar represents 10 mm.
10 PAPERS IN PALAEONTOLOGY
endosteally deposited lamellar bone (i.e. inner circumferential
layer) containing flattened osteocyte lacunae (Fig. 5B). The cor-
tex is mostly formed by coarse-compacted cancellous bone,
which reaches the subperiosteal margin in some areas. It is
worth noting that the lamellar bone that commonly predomi-
nates in this secondarily compacted bone has been strongly
altered by diagenetic processes. Primary bone tissue occurs as a
narrow layer located at the outermost region of the compacta.
The fibrillar organization of the primary bone matrix varies
from lamellar to parallel-fibred bone, the last being the most
abundant (Fig. 5C, D). Parallel-fibred bone, however, does not
exhibit the typical fibrillar organization in which collagen fibrils
have the same orientation, extending approximately parallel to
each other (Francillon-Vieillot et al. 1990; Reid 1996). Instead,
theintrinsicfibresofthesampledboneareorganizedintwo
main orientations: parallel and concentric to the element main
axis. Whereas fibres parallel to the element main axis predomi-
nate in some areas, they are less abundant in others. Bone cell
lacunae possess elongate shapes, and they are arranged follow-
ing the orientation of intrinsic fibres in which they are embed-
ded. Vascular spaces are abundant, and they are longitudinally
arranged. A single growth mark, which corresponds with an
annulus, can be discerned in the primary cortex. The annulus
has been partially eroded by modeling processes (Enlow 1963).
Three possible lines of arrested growth are also observed in the
compacta. However, because these structures are tenuous and
AB
CD
FIG. 5. Bone microstructure of the right ulna, PVSJ 913. A, entire cross section of the element; compact bone is mostly composed
of coarse compacted cancellous bone. B, general view of the cortical bone (large boxed area in A); note that the lamellar bone of the
coarse compacted cancellous bone has been mostly altered. C, detailed view of the cortical bone (boxed area in B). D, detail of the
annulus formed in the cortical bone (small boxed area in A); note the high degree of birefringence of this growth mark. A, cross
polarized light with lambda compensator; B–C, normal transmitted light; D, cross polarized light. Abbreviations: an, annulus;
cccb, coarse compacted cancellous bone; icl, inner circumferential layer; lb, lamellar bone; mc, medullary cavity. Scale bars represent:
2 mm (A); 0.3 mm (B); 0.1 mm (C); 0.2 mm (D).
MART
IN E Z ET AL.: DAWN OF FLYING REPTILES 11
they cannot be clearly traced along the cortex, their identifica-
tion is dubious.
The absence of an ‘external fundamental system’ (i.e. periph-
eral band of lamellar or parallel fibred bone with closely packed
growth lines) in the sampled ulna suggests that the individual
was not somatically mature at time of death (Chinsamy-Turan
2005). The presence of at least one growth cycle indicates a min-
imum age of one year for the individual. Nevertheless, given the
extensive reduction of the cortical thickness by an increased
development of the medullary cavity (Ricql
es et al. 2000; Steel
2008), most of the growth record is actually lost and the mini-
mum estimated age is possibly greatly underestimated. In the
particular case of PVSJ 913, the growth record lost is even more
pronounced because the section does not correspond with the
midshaft of the element, but with the proximal shaft. The high
proportion of coarse compacted cancellous bone in the sample
is also congruent with the sampling site.
An interesting feature observed in the primary bone consists
of intrinsic fibre orientation, which exhibits at least two differ-
ent orientations. This pattern does not correspond with the
‘plywood’ organization first described by Ricql
es et al. (2000)
for other pterosaurs and considered by these authors to be a
unique feature of the Pterosauria. The observed pattern is also
different, in a strict sense, from typical parallel fibred bone.
Instead, the primary cortical bone described for PVSJ 913
resembles to the ‘crossed parallel fibred bone’ recently
described in the basal cortex of aetosaur osteoderms (Cerda
et al. 2018). Interestingly, the same tissue has been reported
for other pterosaurs, but misidentified as fibrolamellar tissue
(e.g. Steel 2008, fig. 3B). Ricql
es et al. (2000) inferred that the
plywood organization of the primary bone tissue, which is
actually present in several taxa (e.g. Padian et al. 2004; Ricql
es
et al. 2000; Say~
ao 2003; Steel 2008) but not in all (e.g. Chin-
samy et al. 2009; Prondvai et al. 2012) provides mechanical
properties to this particular bone tissue. In a similar way, and
as previously discussed by Cerda et al. (2018), crossed parallel
fibred bone can also be linked with mechanical requirements
of the elements. An integrative study considering its distribu-
tion among different taxa and elements must be performed to
test this hypothesis.
REPTILIA Laurenti, 1768
INCERTAE SEDIS
Figure 6
Referred material. PVSJ 1094, isolated tooth.
Locality & horizon. ‘Bone-bed’ locality, Caucete Department,
San Juan Province, Argentina (Fig. 1). The fossiliferous locality
corresponds to the southern outcrops of the Norian–Rhaetian
Quebrada del Barro Formation included in the Marayes –
El Carrizal Basin (Bossi 1976; Colombi et al. 2015). The reddish
muddy sandstones of the horizon including PVSJ 1094 is located
20 m below the top of the formation.
Remarks. We refrain from assigning a formal diagnosis to this
specimen as it does not retain any clearly autapomorphic
characters and is thus taxonomically ambiguous. We offer a brief
description of the specimen.
Description. The preserved portion of this tooth presumably
includes most of the crown, lacking the root and the apical tip
(Fig. 6). The remaining crown is slender, slightly curved, and
lacks preserved enamel. The tooth is tall with the maximum pre-
served height at least four times the maximum mesiodistal
length. The cross-section at the base is elliptical and the pulp
cavity is subcircular, measuring 40% of the mesiodistal tooth
width (Fig. 6D; Table 1). The surface lacks striae, and both the
mesial and distal borders lack well-defined keels; although this
may be an artefact of the missing enamel.
Remarks. PVSJ 1094 is unique among known toothed verte-
brates from Quebrada del Barro Formation. The crown section,
estimated crown length and curvature are similar to those of
several pterosaurs, such as the rhamphorhynchids. However, this
feature is not synapomorphic to any known clades, and thus is
not enough to assign this specimen to a clade beyond Reptilia.
PHYLOGENETIC ANALYSIS
The phylogenetic analysis of Yelaphomte praderioi and
Pachagnathus benitoi with the relationships of the basal
pterosaurs resulted in a single most parsimonious tree of
613.662 steps with a consistency index of 0.469 and a
retention index of 0.755 (Fig. 7). The tree topology
matches the results of Andres et al. (2014) with the excep-
tion of the additional taxa and the relationships within
Anurognathidae. The two new species are recovered in a
trichotomy with Ra. filisurensis within Raeticodactylidae, a
clade within the exclusively Triassic Eopterosauria.
PVSJ 914 and 1080 do not overlap in preservation, and so
it is not possible to resolve their relationships to one
FIG. 6. PVSJ 1094, Isolated tooth in: A, labial?; B, lingual?;
C, cross-section; D, distal view. Scale bar represents 5 mm.
12 PAPERS IN PALAEONTOLOGY
FIG. 7. Chronostratigraphically-calibrated strict consensus tree showing phylogenetic relationships of the new taxa Pachagnathus
benitoi and Yelaphomte praderioi, and the relationships of basal pterosaurs. Ranges for species denote the greatest temporal resolution
of stratigraphic dating. Outgroup relationships are not shown.
MART
IN E Z ET AL.: DAWN OF FLYING REPTILES 13
another or to Ra. filisurensis to a greater degree. Their
close relationship to Ra. filisurensis is supported by the
even spacing of teeth in Y.praderioi as well as a mandibu-
lar keel and striated teeth in Pa. benitoi, although it should
be noted that this is a rather homoplastic character. Char-
acter states diagnostic for Raeticodactylidae can only be
found in Pa. benitoi: a high mandible eminence, a deep
fused symphysis, as well as cup-shaped structures and
ridged occlusal margins on the mandible anterior end.
Similarly, eudimorphodontoid synapomorphies of a man-
dible eminence and only procumbent anterior teeth are
also only present in Pa. benitoi; all of the preserved teeth
are procumbent in Y.praderioi.
The secondary analysis incorporating Y. praderioi and
Pa. benitoi into the diapsid reptile matrix of Ezcurra et al.
(2020) resulted in 162 most parsimonious trees of 5012
steps and a strict consensus identical to the analysis run
without Y. praderioi and Pa. benitoi. Therefore, only the
relationships of the pterosaurs are depicted in Figure 8.
Yelaphomte praderioi and Pa. benitoi were both recovered
in the Pterosauria, confirming the results of the primary
analysis and their classification as pterosaurs. The addi-
tion of these species resulted in two extra most parsimo-
nious trees because of the alternative positions for
Pa. benitoi.Pachagnathus benitoi was recovered in a tri-
chotomy with either Allkaruen koi and Rh. muensteri or
with Cacibupteryx caribensis and a A. koi +Rh. muensteri
sister group, two positions separated by a single branch.
Yelaphomte praderioi was recovered in a trichotomy with
Ra. filisurensis and Carniadactylus rosenfeldi. Although
Y. praderioi is essentially in the same phylogenetic posi-
tion as the primary analysis, for Pa. benitoi is in a much
higher position, either in the Rhamphorhynchidae or Bre-
viquartossa depending on the classification of A. koi.
DISCUSSION
Yelaphomte praderioi (PVSJ 914) and Pachagnathus benitoi
(PVSJ 1080) are in a polytomy with Ra. filisurensis within
the Raeticodactylidae (Fig. 7). It is a concern when frag-
mentary specimens are recovered in polytomies that they
might belong to the other species. PVSJ 914 and 1080 do
not overlap in preservation but do overlap in the coding
of some characters, supporting their erection as separate
species. For instance, cheek alveoli of PVSJ 1080 have
raised rims unlike those of PVSJ 914. In addition to the
shape of the alveolar rims, the phylogenetic analysis
recovered the procumbent teeth of Y. praderioi as an
autapomorphy with respect to Pa. benitoi, as well as all
pterosaurs in the analysis save for the derived
Rh. muensteri and Painten pterodactyloid specimen.
Pachagnathus benitoi has procumbent anterior teeth, but
these become upright posteriorly, unlike the posterior
procumbent teeth found in Y. praderioi. Even if the pres-
ence of procumbent teeth in the rostral dentition and
upright teeth in the mandibular dentition were possible,
it would make occlusion exceedingly difficult. In addition,
the extreme size disparity between the specimens supports
their assignment as separate species. These size differences
could be ontogenetic. The highly fused bones of the ros-
trum of the tiny Y. praderioi (i.e. absence of visible suture
between the premaxilla and maxilla, as well as between
left and right premaxillae and palatines) may indicate its
maturity and adult size, but the rostrum and mandible
bones of pterosaurs fuse at early age (Bennett 1993).
Additionally, the estimated skull size ratio of about five
between PVSJ 1080 and PVSJ 914 is inordinately large for
the same species in pterosaurs.
Regardless of whether PVSJ 1080 and PVSJ 914 repre-
sent one species or two, both are clearly distinct from
their closest other relative Ra. filisurensis. The raised rims
that distinguish Pa.benitoi from Y. praderioi also differ-
entiate it from Ra. filisurensis. In addition, the phylo-
genetic analysis also recovered procumbent teeth and
cheek teeth spaced less than the diameters of the teeth
but not nearly touching as an autapomorphy for
Y. praderioi and a laterally compressed mandible anterior
FIG. 8. Strict consensus tree using the dataset for diapsid rep-
tile intrarelationships published by Ezcurra et al. (2020), show-
ing phylogenetic relationships of the new taxa Pachagnathus
benitoi and Yelaphomte praderioi within Pterosauria. Grey
branches indicate two alternative placements for Pachagnathus.
14 PAPERS IN PALAEONTOLOGY
end as an autapomorphy for Pa.benitoi within the Eop-
terosauria. In addition, there are a number of features
found in both Ra. filisurensis and the South American
species that are distinct in their morphology. Both
Ra.filisurensis and Y. praderioi share a striated premaxil-
lary crest but the striae are more widely spaced and radi-
ally oriented in Y. praderioi; both share a straight
premaxilla–maxilla suture but Y. praderioi has a more
ventrally located suture; both also share an edentulous
area on the anterior part of the maxilla but this area is
much longer in Y. praderioi (longer than the length occu-
pied by four well-spaced alveoli). Also, both
Ra. filisurensis and Pa.enitoi share a rather elongate man-
dible symphysis but the symphysis extends the entire
length of the specimen with over five pairs of teeth and
was likely to have been even longer in Pa. benitoi. Both
share cup-shaped structures on the mandible anterior end
but they are deeper and lack foramina in Pa.benitoi; both
share striated teeth but Ra. filisurensis has striations in
the labial surface of its anterior teeth whereas Pa.benitoi
has striations of both sides of its teeth, and although the
only specimen of Ra. filisurensis is preserved laterally
compressed in a slab, even its mandible symphysis does
not approach the lateral compression found in
Pa.benitoi.Yelaphomte praderioi is also notable for its
high degree of pneumatization, although diagnostic for
pterosaurs (Romer 1956; Kellner 1996; Sereno 1991; Well-
nhofer 1978), the intricate set of trabeculae distributed
over all of the cross-section of the premaxilla suggests a
high degree of pneumatization of the rostrum. Pachag-
nathus benitoi is also unusual in having a mandible sym-
physis occlusal surface consisting of both a midline keel
and a series of fossa; this is obscured in the Ra. filisurensis
specimen but not reported in any other pterosaur speci-
men. These specimens are distinct species with a signifi-
cant number of autapomorphies.
Of note is the number of features homoplastically pre-
sent in the South American species and rhamphorhynchid
pterosaurs, which brings up the alternative hypothesis
that these species represent the oldest known rhamphor-
hynchids. Although most teeth of Pa. benitoi are broken
at the base of the crown, the only partial crown preserved
in PVSJ 1080 suggests a crown height more than four
times the base width, which is also present in the Rham-
phorhynchidae. This similarity in morphology is strength-
ened by the isolated tooth PVSJ 1094, which was found
in similar stratigraphic layers of the unit and has similar
proportions to rhamphorhynchid teeth. Fused mandible
symphyses longer than Ra. filisurensis are found in the
breviquartossans, but among non-pterodactyloid ptero-
saurs they are the longest in the rhamphorhynchines.
Raised alveolar rims are also present in an unnamed clade
consisting of Dg. banthensis, K. rochei, Dr.bucklandi, and
Dr.depressirostris. In conclusion, Y. praderioi and
Pa.benitoi might be early rhamphorhynchids, possibly
closely related to Dg. banthensis, but the data and phylo-
genetic analysis do not support that hypothesis. In addi-
tion, the symphysis of rhamphorhynchids has no more
than four pairs teeth, differing from Pa. benitoi, which
has at least five pairs of symphyseal alveoli. Unfortu-
nately, it will not be possible to test these hypotheses fur-
ther until more complete specimens are found. An even
more unusual case of homoplasy occurs with the Creta-
ceous dsungaripterid pterodactyloids, which share a large
edentulous anterior-most part of the maxilla and out-
growths of the jaw bones that form expanded bulbous
ring-like walls surrounding the teeth with the Triassic
South American pterosaurs.
PVSJ 913, the distal half of the ulna, is a problematic spec-
imen. To date, only a handful of three-dimensional distal
ulnae of pterosaurs have been described in detail (e.g. Well-
nhofer 1975; Bennett 2001; Andres et al. 2010). Although
several eopterosaurs have preserved ulnae, all of the speci-
mens are two-dimensionally preserved, obscuring many fea-
tures. Within more derived non-monofenestratan pterosaurs,
the only comparison can be made with the rhamphorhynch-
ids Rh.muensteri and Sp. wucaiwanensis.PVSJ913shares
with both of these taxa the presence of a very long and thin
ulna, but the distal ends differ in being less proximodistally
expanded with a proximodistally shorter ventral expansion.
Among monofenestratans, the ulnae are usually more robust,
shorter, and have a proximodistally shorter distal expansion
than in PVSJ 913 (e.g. NHMUK PV OR 35324 Ornitho-
cheirus sp. and NHMUK PV R 2933 Pteranodon sp.) On the
other hand, PVSJ 913 has several traits not reported in other
pterosaurs (i.e. deep distal sulcus, wide and deep foramen
connecting with the distal sulcus, very elongate distal expan-
sion, and deep groove on the crest for the retinaculum of the
flexor tendon). Although PVSJ 913 has unequivocal ptero-
saur traits (e.g. thin cortex; proximodistally expanded distal
end, three distinct distal articular surfaces), the scarcity of
descriptions for three-dimensional distal ends of ulnae and
the lack of diagnostic characters coded for these bones in the
published literature precludes determining the phylogenetic
relationships of PVSJ 913 within the Pterosauria. Although
PVSJ 913 comes from a different locality to Pa.benitoi and
Y.praderioi, all belong to similar stratigraphic levels in the
Quebrada del Barro Formation, not ruling out the possibility
that PVSJ 913 may belong to one of these species.
PVSJ 1094 is unique among known toothed vertebrates
from Quebrada del Barro Formation. The crown cross-
section, estimated crown length and curvature are similar
to that present in rhamphorhynchids, however, this fea-
ture is not synapomorphic to any known clades, and thus
is not enough to assign this specimen to a clade beyond
Reptilia.
Until recently, the early record of pterosaurs showed a
diverse Eopterosauria during the Late Triassic of northern
MART
IN E Z ET AL.: DAWN OF FLYING REPTILES 15
hemisphere, but the oldest record of its sister clade including
the rest of the Pterosauria, the Macronychoptera, was from
the Early Jurassic (Sinemurian Age). Even then, the only
Early Jurassic pterosaurs were dimorphodontians, Campylog-
nathoides, and the rhamphorhynchid Dg. banthensis,withall
the other major pterosaur groups appearing in the Late Juras-
sic (Andres et al. 2014). This record implies significantly
undersampled lineages, explained as a possible evolution in
terrestrial environments were the fragile bones of pterosaurs
have a lower probability of preservation (Unwin 2006; L€
u
et al. 2010; Andres et al. 2014; Upchurch et al. 2014). In
2018, the discovery of the late Norian to Rhaetian dimorpho-
dontian Caelestiventus hanseni in a terrestrial environment
would seem to corroborate this hypothesis. Nevertheless, the
other basal clades of the Macronychoptera, (e.g. Novialoidea
and Breviquartossa) remain absent from the Triassic fossil
record. The new Triassic pterosaurs described here,
Y. praderioi and Pa. benitoi, were found in a continental
environment far from the coast, illustrating that they were
certainly terrestrial dwelling animals. This reinforces the the-
ory of possible early evolution of pterosaurs in terrestrial
environments as early as the Late Triassic.
Finally, Y.praderioi and Pa.benitoi from the upper Norian
to Rhaetian Quebrada del Barro Formation, north-western
Argentina, are the first unequivocal records of Triassic ptero-
saurs in the southern hemisphere, supporting the assumption
of an underestimated sample instead of true absence outside
north-western Pangaea during early Mesozoic. The presence
of two new species from Triassic continental environments
in South America evidences a more global distribution and a
significantly greater diversity of pterosaurs almost from the
beginning of its evolutionary history.
CONCLUSION
In this paper we describe the first record of Triassic ptero-
saurs from the Quebrada del Barro Formation (upper Norian
to Rhaetian), San Juan province, Argentina. From these spec-
imens (an isolated dentary symphysis (PVSJ 1080); partial
rostrum (PVSJ 914); and distal half of ulna (PVSJ 913)) we
name two new genera and species: Pachagnathus benitoi
(PVSJ 1080) and Yelaphomte praderioi (PVSJ 914).
The new species Yelaphomte praderioi and Pachagnathus
benitoi are recovered in a polytomy with Ra. filisurensis
within the Raeticodactylidae.
The discoveries of Pa. benitoi and Y. praderioi, both
from Late Triassic continental environments of South
America, support the assumption of an underestimated
sample instead of true absence outside north-western
Pangaea during the early Mesozoic, and reinforces the
theory of a possible early radiation of pterosaurs in terres-
trial environments as early as the Late Triassic.
The specimens described here are the first unequivocal
records of Triassic pterosaurs in the southern hemisphere
evidencing a more global distribution and a significantly
greater diversity of pterosaurs almost from the beginning
of its evolutionary history.
Acknowledgements. We thank Paul Barrett who allowed the use
of µCT-scanning facilities at the Natural History Museum, Lon-
don, UK. Thanks to Laura Codorni
u for the preliminary discus-
sions about the specimens. The comments and suggestions of
the editor, Chris Bennett and the other anonymous reviewers
enhanced the quality of this contribution. This research was pos-
sible thanks to PICT 2015-711 (to RNM) granted by FONCyT.
Special thanks to the Secretar
ıa de Ciencia, T
ecnolog
ıa e
Innovaci
on of the San Juan Province.
DATA ARCHIVING STATEMENT
This published work and the nomenclatural acts it contains, have been
registered in ZooBank: http://zoobank.org/References/1865F707-1B28-
41D4-BF91-B762526ACBC4
The matrix for the phylogenetic analysis and the µCT-Scan slices are
available on MorphoBank: http://morphobank.org/permalink/?P3887
Editor. Philip Mannion
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