Ac a Palaeon ol. Pol. 69 (2): 263–280, 2024 h ps://doi.o g/10.4202/app. 01133.2024
A new species o mixosau id ich hyosau om he Middle
T iassic o Luxi Coun y, Yunnan P o ince, Sou h China
YE-WEI FANG, ANDRZEJ S. WOLNIEWICZ, and JUN LIU
Fang, Y.-W., Wolniewicz, A.S., and Liu, J. 2024. A new species o mixosau id ich hyosau om he Middle T iassic o
Luxi Coun y, Yunnan P o ince, Sou h China. Ac a Palaeon ologica Polonica 69 (2): 263–280.
Ich hyosau s, an iconic lineage o Mesozoic ma ine ep iles, we e an impo an componen o eco e ing ecosys ems
a e he Pe mo-T iassic Mass Ex inc ion e en . Mixosau idae, a clade o small, ea ly-di e ging ich hyosau s, we e o
pa icula signi icance o his p ocess, being abundan p eda o s in Middle T iassic shallow seas. Despi e he abundance
o well-p ese ed mixosau id specimens om Sou h China, Mixosau us panxianensis emains he only comp ehensi ely
desc ibed species, hinde ing ou unde s anding o he a iabili y, axonomy and di e si y o mixosau ids om his e-
gion. He e, we epo a new species o Mixosau us, Mixosau us luxiensis, om Luxi Coun y, Yunnan P o ince, Sou h
China. The wide pos o bi al skull po ion di e en ia es he new species om Mixosau us co nalianus and Mixosau us
kuhnschnyde i om cen al Eu ope. The non-du ophagous den i ion, composed o iny pie cing mesial ee h and obus
bu poin ed dis al ee h, esembles he den i ion o M. co nalianus. Howe e , he dis al ee h o M. luxiensis sp. no . a e
wice he size o he mesial ones, in con as o M. co nalianus, in which he mesial and dis al ee h a e app oxima ely
equal in size. The o elimb exhibi s a unique mo phology, including a p opo ionally na ow adius, he p esence o a
pe iphe al no ch on he ulna, and a la ge me aca pal V. A p elimina y phylogene ic analysis sugges s a close a ini y o
he new axon wi h M. co nalianus om Wes e n Te hys. Ou s udy in oduces impo an , new ana omical in o ma ion
on Mixosau us om Sou h China, use ul o u u e s udies o mixosau id di e si y.
Key wo ds: Ich hyosau ia, Mixosau idae, ma ine ep ile, phylogeny, bio ic eco e y, Guanling Fo ma ion, Anisian,
T iassic.
Ye-Wei Fang [[email p o ec ed]; ORCID: h ps://o cid.o g/0000-0002-8150-6331 ] and Jun Liu [[email p o ec ed].
cn; ORCID: h ps://o cid.o g/0000-0001-7859-5209 ] (co esponding au ho ), School o Resou ces and En i onmen al
Enginee ing, He ei Uni e si y o Technology, 193 Tunxi Road, He ei 230009, Anhui, China.
And zej S. Wolniewicz [[email p o ec ed]; ORCID: h ps://o cid.o g/0000-0002-6336-8916 ], School o Resou ces and
En i onmen al Enginee ing, He ei Uni e si y o Technology, 193 Tunxi Road, He ei 230009, Anhui, China; Depa men
o Ea h Sciences, Uni e si y o Camb idge, Downing S ee , Camb idge, CB2 3EQ, UK; Ins i u e o Paleobiology,
Polish Academy o Sciences, Twa da 51/55, 00-818 Wa saw, Poland.
Recei ed 8 Janua y 2024, accep ed 10 Ap il 2024, published online 14 June 2024.
Copy igh © 2024 Y.-W. Fang e al. This is an open-access a icle dis ibu ed unde he e ms o he C ea i e Commons
A ibu ion License ( o de ails please see h p://c ea i ecommons.o g/licenses/by/4.0/), which pe mi s un es ic ed use,
dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal au ho and sou ce a e c edi ed.
In oduc ion
The Pe mo-T iassic Mass Ex inc ion (PTME) was he mos
se e e ex inc ion e en in he Phane ozoic (Bambach 2006).
Despi e i s de as a ing e ec on biodi e si y, T iassic eco-
sys ems eco e ed wi hin only a ew million yea s a e he
PTME (B aya d e al. 2017; Dai e al. 2023). The ichness o
ben hic communi ies inc eased apidly in he ea ly Middle
T iassic (Anisian) and s abilized owa ds i s end (Chen and
Ben on 2012; F iesenbichle e al. 2021), while pelagic eco-
sys ems pe haps egene a ed e en ea lie (Song e al. 2018;
Qiao e al. 2022). Mesozoic ma ine ep iles, such as ich hyo-
sau s and sau op e ygians, colonized he ma ine ealm in
he a e ma h o he PTME and quickly became impo an
p eda o s in T iassic seas (Ca oll 1997; F öbisch e al. 2013;
Liu e al. 2014; Li and Liu 2020; Sande e al. 2021). Because
p eda o s a e impo an indica o s o ecosys em complexi y,
ob aining a de ailed knowledge o hei axonomic and eco-
logical di e si y h oughou he T iassic is impo an o un-
de s anding he p ocess o ma ine ecosys em eco e y a e
he PTME (Ben on e al. 2013; Scheye e al. 2014; Mo ani
e al. 2015; Liu and Sande 2019).
Ich hyosau s we e one o he mos success ul g oups o
Mesozoic ma ine ep iles (Mo ani 2005a; Ba de e al. 2014).
The ea lies ich hyosau ossils a e known om he Ea ly
T iassic, bu i is unclea i he clade o igina ed in he la es
Pe mian o ea lies T iassic (Mo ani e al. 2017; Kea e al.
2023). Ich hyosau s achie ed a b oad geog aphic dis ibu-
264 ACTA PALAEONTOLOGICA POLONICA 69 (2), 2024
ion and high ecological di e si y by he Middle T iassic
(Callaway 1989; Sande and Mazin 1993; McGowan and
Mo ani 2003; Liu 2011). Mixosau idae was a sho -li ed, bu
abundan clade o ich hyosau s om he Middle T iassic.
They e ol ed a usi o m body plan and had powe ul jaw
muscles (Mo ani e al. 1996; Maisch and Ma zke 2000;
McGowan and Mo ani 2003; Renes o e al. 2020). Thei
ossils a e known mainly om shallow wa e sedimen s,
like he Muschelkalk in Ge many and Poland (Maisch and
Ma zke 1998a), he Besano Fo ma ion in I aly/Swi ze land
(B inkmann 1997; Renes o e al. 2020), he Vega-Ph oso
sil s one and he Llama membe s o he Sulphu Moun ain
Fo ma ion in Canada (Callaway and B inkman 1989), and
he Uppe Membe o he Guanling Fo ma ion in Sou h
China (Ben on e al. 2013; Liu e al. 2013), bu hey a e also
ound in mo e pelagic sedimen s, such as he Bo neheia
Fo ma ion in Spi sbe gen (Maxwell and Kea 2013; Hu um
e al. 2014) and he Fossil Hill Membe o he Fa e
Fo ma ion in he wes e n Uni ed S a es (Schmi z e al. 2004;
Sande e al. 2021). Mixosau ids ha e a long his o y o
esea ch, da ing back o he 19 h cen u y (Quens ed 1852;
Hulke 1873; Bassani 1886; Bau 1887) and a e one o he
be e -known ich hyosau g oups. Thei ana omy (Callaway
1997; Mo ani 1999b; B inkmann 2004), his ology (Kolb e
al. 2011), ep oduc ion (B inkmann 1996; Miedema e al.
2023b), on ogeny (Kolb e al. 2011; Miedema e al. 2023a),
in aspeci ic a ia ion (Maisch and Ma zke 1998b; Zhou e
al. 2022), and e en body ou line (Renes o e al. 2020) ha e
all been s udied in de ail.
The monophyly o Mixosau idae is well-es ablished
and suppo ed by se e al synapomo phies o he ci -
cumna ial a ea, skull oo , gi dles, limbs, and e eb ae
(Liu 2011; Ji e al. 2016; Moon 2019). Howe e , he axo-
nomy o Mixosau idae emains incomple ely unde s ood.
Mixosau idae a e adi ionally di ided in o wo gene a,
Mixosau us and Phala odon, which di e om each o he
in na ial shel , den i ion, hume us and caudal cen um mo -
phology (Schmi z e al. 2004; Schmi z 2005; Jiang e al.
2006; Liu e al. 2013). None heless, he axonomic com-
posi ion and phylogene ic opology wi hin hese gene a
di e be ween s udies. Whe eas he majo i y o ich hyo-
sau esea che s ollow he Mixosau us–Phala odon dicho-
omy (Jiang e al. 2006; Ji e al. 2016; Mo ani e al. 2017;
Økland e al. 2018; Huang e al. 2019; Robe s e al. 2022),
Maisch (2010) and Moon (2019) sepa a ed Mixosau us
panxianensis and Phala odon a a us in o dis inc gene a
(Ba acudasau oides and Con ec opala us, espec i ely).
In addi ion, some phylogene ic analyses ha e ailed o e-
co e Mixosau idae esol ed in o a simple Mixosau us–
Phala odon dicho omy (Liu 2011; Huang e al. 2019; Moon
2019). The e o e, i is possible ha he axonomy and phy-
logeny o mixosau ids a e mo e complex han he cu en
pa adigm sugges s.
O e he pas 20 yea s, abundan ossils o mixosau-
ids ha e been eco e ed om he Middle T iassic s a a
o Sou h China (Mo ani e al. 2008; Jiang e al. 2009; Hu e
al. 2011). Despi e he abundance o ossils, he axonomic
composi ion o mixosau ids om Sou h China emains only
pa ly known. A o al o six species o Mixosau us has been
e ec ed based on Chinese ma e ials (“Mixosau us mao-
aiensis” om Renhuai Ci y, ea ly Anisian [Young 1965],
“Mixosau us guanlingensis” om Guanling bio a, ea ly
Ca nian [Yin e al. 2000], Mixosau us panxianensis om
Panxian auna, Pelsonian, Anisian [Jiang e al. 2005, 2006],
“Mixosau us yangjuanensis” om Panxian auna [Liu and
Yin 2008], “Mixosau us xindianensis” om Panxian auna
[Chen and Cheng 2010], and “Mixosau us xinzhaiensis”
om Luoping bio a, Pelsonian, Anisian [Chen e al. 2016]).
In addi ion, he occu ence o ou addi ional mixosau id
species, known om Eu ope and he USA, was also e-
po ed om Sou h China (Phala odon c . P. aasi om
Panxian auna [Jiang e al. 2007], Phala odon a a us om
Luoping bio a [Liu e al. 2013], “Mixosau us co nalianus”
om Panxian auna [Liu and Yin 2008], and “Mixosau us
kuhnschnyde i” om Luoping bio a [Chen and Cheng
2009]). Fu he mo e, h ee mixosau id specimens, e e able
only o amily o genus le el, we e also desc ibed om
Sou h China (Phala odon sp. om Panxian auna [Jiang
e al. 2003], Mixosau idae gen. e sp. inde . om Luoping
bio a [Liu e al. 2011], Mixosau us sp. om Fuyuan Coun y,
uppe Ladinian [Chen e al. 2016]), bu i is no clea whe he
hese specimens ep esen new axa o a e e e able o any
o he cu en ly known mixosau id species.
Howe e , h ee o he Mixosau us species epo ed om
Sou h China (“M. mao aiensis”, “M. guanlingensis”, and
“M. yangjuanensis”), and one occu ence o an o he wise
Eu opean axon (“M. co nalianus”), we e subsequen ly
iden i ied as in alid (McGowan and Mo ani 2003; Jiang e
al. 2006, 2007, 2008a). Among he emaining species new
o Sou h China, “M. xindianensis” and “M. xinzhaiensis”
we e inadequa ely igu ed and only b ie ly desc ibed (due
o inaccessibili y o he holo ype o s udy, he o me was
e en ega ded as species inqui endae by Liu e al. 2013). As
a consequence, Mixosau us panxianensis is he only species
o Mixosau us om Sou h China ha has been comp e-
hensi ely desc ibed and well-illus a ed (Jiang e al. 2005,
2006), bu whe he i ep esen s a species o Mixosau us
(Jiang e al. 2006; Ji e al. 2016) o a sepa a e genus (Maisch
2010; Moon 2019) emains a ma e o deba e. Incomple e
knowledge o he ana omy and axonomy o Mixosau us
species om Sou h China hinde s ou unde s anding o he
global di e si y, phylogene ic in e ela ionships, and palae-
obiogeog aphy o mixosau ids.
He e, we epo a new species o Mixosau us collec ed
om a ecen ly disco e ed shallow ma ine auna in Luxi
Coun y, Yunnan P o ince, Sou h China (Wen e al. 2020;
Xu e al. 2022; Hu and Liu 2023; Lu and Liu 2023; Hu e
al. 2024) (see Fig. 1 o locali ies o he eosau op e ygians
No hosau oidea inde . (Hu and Liu 2023) and Dianmeisau us
mu aensis nea Mu a (Hu e al. 2024) and he anys opheid
Luxisau us e es is nea Suomeiluo (Lu and Liu 2024).
An ana omical desc ip ion o he new species is p o ided,
FANG ET AL.—NEW MIXOSAURID ICHTHYOSAUR FROM THE MIDDLE TRIASSIC OF CHINA 265
highligh ing he mos impo an di e ences and simila i ies
wi h o he species o Mixosau us. A p elimina y phyloge-
ne ic analysis o mixosau id in e ela ionships, inco po a -
ing ana omical in o ma ion om he new species, is also
p esen ed and discussed.
Ins i u ional abb e ia ions.—CCCGS, Chengdu Cen e
o China Geological Su ey, China; GMPKU, Geological
Museum o Peking Uni e si y, Beijing, China; HFUT,
Geological Museum o He ei Uni e si y o Technology,
China; PIMUZ, Depa men o Palaeon ology, Uni e si y
o Zü ich, Swi ze land ( o me ly Paläon ologisches Ins i u
und Museum de Uni e si ä Zü ich, Swi ze land); PMU,
Paleon ological Museum, Uni e si y o Uppsala, Sweden;
SMNS, S aa liches Museum ü Na u kunde S u ga ,
Ge many; YIGMR, Yichang Ins i u e o Geology and
Mine al Resou ces (cu en ly WCCGS, Wuhan Cen e o
China Geological Su ey), China.
Nomencla u al ac s.—This published wo k and he nomen-
cla u al ac s i con ains ha e been egis e ed in ZooBank:
u n:lsid:zoobank.o g:ac :AF9FF8CE-A718-48E3-9132-A11
FA3392666
Ma e ial and me hods
HFUT HL-21-08-002 was collec ed om a qua y abou one
kilome e sou heas o Huale Village, Luxi Coun y, Yunnan
P o ince, China (Fig. 1). I o igina es om he Uppe Mem-
be (also known as Second Membe o Membe II) o he
Guanling Fo ma ion ( o me ly pa o he Gejiu Fo ma ion)
and is Pelsonian (middle Anisian) in age (Wen e al. 2020;
Xu e al. 2022; Hu and Liu 2023; Lu and Liu 2023; Hu e al.
2024), simila o he Luoping and Panxian aunas loca ed
nea by (Ben on e al. 2013). The ock ma ix o hinly lam-
Fig. 1. A. Map o China showing loca ion o he s udy a ea. B. The geological map o he a ea a ound Luxi, Yunnan P o ince, Sou h China, showing he
locali y o HFUT HL-21-08-002 (modi ied a e Hu and Liu 2022; Lu and Liu 2023; Hu e al. 2024). Abb e ia ion: Fm., Fo ma ion.
266 ACTA PALAEONTOLOGICA POLONICA 69 (2), 2024
ina ed mic i c limes one wi h al e na ing in e laye s indi-
ca es an in apla o m sedimen a y acies, simila o he
deposi ional se ing o he Luoping Bio a (Hu e al. 2011;
Wen e al. 2020).
HFUT HL-21-08-002 is accessioned in he collec ions o
he Geological Museum o He ei Uni e si y o Technology
in He ei, Anhui P o ince, China (HFUT). I was p epa ed
using moun ed needles and pneuma ic ools in he paleon-
ological p epa a ion labo a o y o HFUT. De ailed obse -
a ions o he specimen we e aken unde a LEICA S9i mi-
c oscope. Canon EOS 80D and Nikon D7200 came as wi h
mac o lenses we e used o specimen pho og aphy.
The phylogene ic analysis was based on a ecen ly pub-
lished, comp ehensi e da a ma ix o ich hyosau s (Huang e
al. 2019). HFUT HL-21-08-002 was added o his cha ac e -
axon ma ix. Cha ac e s 43(?), 50(?), 51(?), 175(?), 187(?)
we e e-coded o M. co nalianus o 43(0), 50(0), 51(0),
75(0), 187(0) (based on Miedema e al. 2023a). Cha ac e
43 was e-coded o M. kuhnschnyde i om 43(?) o 43(0)
(based on PIMUZ T 1324; B inkmann 2004). Cha ac e
112 was e-coded o M. panxianensis om 112(1) o 112(0)
(based on GMPKU-P-1008 and GMPKU-P-1038 [holo ype];
Jiang e al. 2005, 2006), o M. co nalianus om 112(1) o
112(0&1) (based on igu es in Maisch and Ma zke 1998b,
Mo ani 1999a, Renes o e al. 2020, and Zhou e al. 2022),
and o M. kuhnschnyde i om 112(1) o 112(?) (based on
PIMUZ T 1324; B inkmann 2004). The phylogene ic ma ix
(SOM 2, Supplemen a y Online Ma e ial a ailable a h p://
app.pan.pl/SOM/app69-Fang_e al_SOM.pd ) was edi ed in
Mesqui e 3.81 (Maddison and Maddison 2023) and analyzed
in TNT 1.5 (Golobo and Ca alano 2016). All cha ac e s
we e ea ed as uno de ed and equally weigh ed. Max. ees
was se o 10 000. Collapsing was se o “max. leng h = 0”,
using ule 3-collapse. T adi ional Sea ch using 1000 Wagne
ee eplica ions was applied o ob ain maximum pa simony
ees. The B eme suppo alues we e calcula ed using TBR
b anch-swapping om exis ing ees, e aining ees subop-
imal by 100 s eps. I e a i e Posi ional Cong uence Reduced
(I e PCR) was used o p une uns able axa in a second analy-
sis, in o de o ob ain a be e - esol ed educed s ic consen-
sus cladog am (Pol and Escapa 2009).
Sys ema ic palaeon ology
Ich hyosau ia de Blain ille, 1835
Mixosau idae Bau , 1887
Genus Mixosau us Bau , 1887
Type species: Mixosau us co nalianus Bassani, 1886; Mon e San Gio -
gio, I aly and Swi ze land; la e Anisian–ea ly Ladinian, Middle T iassic.
Emended diagnosis (modi ied a e B inkmann 2004;
Jiang e al. 2006; Liu 2011; Ji e al. 2016; and Renes o e al.
2020).—Cen um heigh /leng h a io mode a ely inc eased
in he mid-caudal egion, bu no exceeding a alue o 3.0
(cen um heigh /leng h index signi ican ly inc eased in he
mid-caudal egion o a alue o o e 3.0 in Phala odon); in-
e cla icle T-shaped wi h ans e sal ba s pe pendicula o
he pos e io p ocess (in e cla icle V-shaped, wi h pos e io
p ocess iangula and b oad, and ans e sal ba s iangula ,
na ow and p ojec ing an e ola e ally in Phala odon); hu-
me us ela i ely b oad wi h p oximodis al leng h subequal
o an e opos e io wid h (hume us na ow, p oximodis ally
longe han an e opos e io ly wide in Phala odon).
Mixosau us luxiensis sp. no .
Figs. 2–7; SOM 1: igs. S1, S2, ables S1, S2.
ZooBank LSID: u n:lsid:zoobank.o g:ac :AF9FF8CE-A718-48E3-9132-
A11FA3392666
E ymology: In e e ence o he ype locali y in Luxi Coun y.
Holo ype: HFUT HL-21-08-002, a nea ly comple e skele on, wi h he
pos c anium mos ly disa icula ed.
Type locali y: Huale Village, Luxi Coun y, Yunnan P o ince, China.
Type ho izon: Uppe (Second) Membe o he Guanling Fo ma ion,
Pelsonian, Anisian, Middle T iassic.
Diagnosis.—A species o Mixosau us cha ac e ised by he
ollowing combina ion o cha ac e s a es: an e io e ace
o sup a empo al enes a eaching only he mos pos e io
pa o nasal (an e io e ace eaches he le el o he ex e -
nal na is in M. panxianensis, M. co nalianus, and M. kuhn-
schnyde i); pos o bi al b oad and pos o bi al po ion o he
skull a ound hal he leng h o he o bi (simila o M. panx-
ianensis and “M. xindianensis”, p opo ionally longe han
in M. co nalianus and M. kuhnschnyde i); jugal wi hou
pos e o en al p ocess ( a iable in M. panxianensis, absen
in M. co nalianus); no dis inc pliciden ine (also absen in
M. co nalianus, p esen in M. panxianensis); an e io ee h
slende and ema kably small (simila o M. co nalianus,
di e en om M. panxianensis and M. kuhnschnyde i, in
which he an e io den i ion is ela i ely la ge ); den i ion
weakly he e odon ous, pos e io ee h obus bu poin ed
(simila o M. co nalianus, di e en om “M. xindianen-
sis”, M. pan xianensis, and M. kuhnschnyde i, in which he
pos e io ee h a e mola i o m and mesiodis ally elonga ed);
cen um heigh /leng h a io a ying om <1.5 (an e io do -
sal) o 2.0 (pos lexu al caudal) (up o 2.0 o M. co nalianus
[Schmi z e al. 2004; Schmi z 2005], highe han 2.0 in M.
panxianensis [Zang 2014], M. kuhnschnyde i [B inkmann
2004], and “M. xindianensis” [Chen and Cheng 2010]); a-
dius na ow (p oximodis al leng h/midsha wid h a io =
2.4; 1.5–1.9 o M. panxianensis and M. co nalianus), ca y-
ing wo no ches on he leading edge (p esen in M. panxian-
ensis, a iable in M. co nalianus, absen in M. kuhnschny-
de i and “M. xindianensis”); single no ch on he pos e io
ma gin o he ulna (p esen in “M. xindianensis”, a ely
occu ing in M. pan xia nensis, absen in M. co nalianus,
M. kuhns chnyde i, and “M. xinzhaiensis”); me aca pal V
la ge in size han dis al ca pal IV and p obably bea ing a
no ch (small and wi hou no ch in o he Mixosau us species,
bu simila in size and mo phology o he Luoping specimen
o Phala odon a a us [Liu e al. 2013]); p oximal phalanges
in digi 1 well-ema gina ed a he leading edge o he o e in
FANG ET AL.—NEW MIXOSAURID ICHTHYOSAUR FROM THE MIDDLE TRIASSIC OF CHINA 267
(an e io ma gin comple e in M. co nalianus, also ema gin-
a ed in M. panxianensis and “M. xinzhaiensis”). Excep o
displaying he diagnos ic ea u es o Mixosau us, HFUT
HL-21-08-002 possesses he ollowing cha ac e s a es in-
consis en wi h a e e al o Phala odon: na ial shel and
buccal idge absen ; den al g oo e p esen pos e io ly; den-
a y labial shel absen ; pliciden ine absen .
Desc ip ion.—HFUT HL-21-08-002 comp ises an almos
comple e, pa ially a icula ed skele on exposed in igh la -
e al iew, wi h only he pos e io caudals missing (Fig. 2).
Fig. 2. The holo ype o he mixosau id ich hyosau Mixosau us luxiensis sp. no . (HFUT HL-21-08-002) om Huale Village, Luxi Coun y, Yunnan
P o ince, China (Pelsonian, Anisian). Pho og aph (A1) and in e p e a i e d awing (A2). Dashed lines indica e in e ed ma gins.
268 ACTA PALAEONTOLOGICA POLONICA 69 (2), 2024
The hume al head o HFUT HL-21-08-002 is no con ex
and e iden s ia ions a e p esen on i s su ace. On he o he
hand, he basioccipi al has a midline idge and la e al bulges
de eloped, and lacks a en al in agina ion. These ea u es
indica e he specimen likely ep esen s an ad anced ju enile
o os eologically imma u e adul (Liu 2011; Liu e al. 2013;
Miedema e al. 2023a). The es ima ed o al leng h o HFUT
HL-21-08-002 is a ound 75 cm (based on he mandibu-
la leng h, ollowing he o mula p o ided by B inkmann
2004), making M. luxiensis sp. no . one o he smalles
known mixosau ids, compa able in size o M. kuhnschny-
de i (B inkmann 1998b, 2004). The mandible o HFUT HL-
21-08-002 (160 mm in leng h) is abou he same leng h as
ha o he holo ype o M. kuhnschnyde i (PIMUZ T 1324)
(mandible leng h 164 mm; B inkmann 1998b), bu i s basio-
ccipi al and appendicula elemen s a e la ge han hose o
PIMUZ T 1324 (basioccipi al leng h 15 mm s. 12.5 mm;
basioccipi al wid h 12.6 mm s. 11 mm; scapula leng h
46 mm s. 40 mm; co acoid leng h 47 mm s. 32 mm; hu-
me us leng h 24.1 mm s. 20.5 mm; adius leng h 19.9 mm
s. 15.6 mm) (B inkmann 1998a, 2004).
Skull: The skull is mediola e ally comp essed and expo-
sed om i s igh la e al aspec (Fig. 3). Howe e , because
he skull was sepa a ed in o wo con ala e al hal es, he
medial su aces o he le pa o he snou and he le skull
oo can be seen exposed abo e he igh side o he skull.
A ound 20 mm o he an e io ips o he p emaxillae a e
missing. The p ese ed po ion o he skull (leng h 131.2 mm,
heigh 45.0 mm) is sho e han he comple e mandibula
ami (leng h ~160 mm). The o bi (leng h 36.8 mm, heigh
25.0 mm) is app oxima ely o al in ou line, al hough i s do sal
ma gin is s aigh . The pos o bi al pa o he skull (cheek
egion) is longe han hal o he o bi leng h (18.5 mm) and
occupies 27% o he pos na ial leng h o he skull (68.6 mm).
The pos o bi al egion o HFUT HL-21-08-002 is simila
in p opo ions o he pos o bi al egion o M. panxianensis,
P. a a us, and P. callawayi (Schmi z e al. 2004; Jiang e al.
2005), bu di e s om he condi ion in M. co nalianus and
M. kuhnschnyde i, in which he pos o bi al po ion o he
skull is ma kedly sho e (B inkmann 2004; Schmi z e al.
2004; Renes o e al. 2020).
The p emaxillae cons i u e mos o he leng h o he
slende snou . Pos e io ly, he p emaxilla wedges in be ween
he nasal and maxilla, con ibu ing sligh ly o he an e o-
en al ma gin o he ex e nal na is, a ea u e common in
mixosau ids (Schmi z e al. 2004; Liu e al. 2011, 2013). The
ex e nal na is is an e opos e io ly elonga ed and sli -like.
I is bounded by he maxilla en ally, whe eas he nasal
cons i u es i s whole do sal ma gin. The maxilla possesses a
e y long an e io p ocess, ex ending an e io ly nea ly as a
as he nasal. The slende pos e o en al p ocess o he max-
illa, oge he wi h he ape ing pos e o en al p ocess o he
lac imal, con ac s he jugal a he le el o he an e io ma -
gin o he o bi . The pos na ial p ocess o he maxilla, which
is sligh ly damaged, con ac s he p e on al and sepa a es
he ex e nal na is om he lac imal and p e on al. Some
mixosau ids ha e la ge neu o ascula o amina on he ex-
e nal su ace o he maxilla (Maisch and Ma zke 2001;
B inkmann 2004; Schmi z e al. 2004; Jiang e al. 2005), bu
in HFUT HL-21-08-002 hese o amina seem o be absen .
The lac imal comp ises he an e o en al ma gin o he
o bi and con ac s he p e on al do sally, o ming p omi-
nen , do sal ex ensions. A p onounced an o bi al idge ex-
ends om he an e odo sal o he pos e o en al pa o
he lac imal. The p e on al p oduces se e al p ojec ions
an e o en ally, which in e lock wi h he co esponding p o-
jec ions o he lac imal, o ming a se a e su u e. The na -
ow pos e io pa o he p e on al comp ises he an e io
pa o he do sal ma gin o he o bi , whe eas he ex ensi e
an e io po ion con ac s he nasal, lac imal and he pos na -
ial p ocess o he maxilla. Pos e io ly, he p e on al seems
o con ac he pos on al along an oblique su u e, bu be-
cause o bone su ace damage, his canno be disce ned wi h
con idence. The p ominen sup ao bi al c es is o med by
he aised do sal ma gins o he p e on al and he pos on-
al. The do sal pa o he empo al egion is sligh ly dam-
aged, bu he pos on al seems o con ac he sup a empo al
pos e io ly, excluding he pos o bi al om pa icipa ion in
he uppe empo al enes a, like in o he mixosau ids wi h
well-p ese ed skulls (Mo ani 1999b; Maisch and Ma zke
2001; Schmi z e al. 2004).
Di ec obse a ion o he an e io ex en o he an e io
e ace o he sup a empo al enes a on he nasal is hinde ed
by he mediola e al comp ession o he skull. Howe e , con-
as ing he well-p ese ed and con ex su ace o he nasal
wi h he c ushed and collapsed su ace o he on al e eals
ha mos pa s o he nasal, excep o i s pos e odo sal co -
ne , likely did no con ibu e o he an e io e ace. The
sagi al c es , which o ms he medial wall o he an e io e -
ace, is all and an e opos e io ly elonga ed. I is o med by
he pa ie al, on al and nasal, wi h he on al comp ising i s
majo i y. Howe e , because o nume ous su ace c acks, he
su u al con ac s be ween hese bones canno be con iden ly
de e mined. An e io ly, he sagi al c es ex ends o he le el
o he pos e io end o he ex e nal na is, being sho e han
he sagi al c es s in species o Phala odon and M. panxian-
ensis, which ex end beyond he an e io end o he ex e -
nal na is (Me iam 1910; Maisch and Ma zke 1998a, 2000;
Schmi z e al. 2004; Jiang e al. 2005). The sagi al c es ,
which is aised ma kedly abo e he sup ao bi al c es in la -
e al iew, dec eases in heigh an e io ly and o ms a smoo h
ansi ion wi h he snou , in con as o o ming an appa en
e minal “s ep”, which is p esen in species o Phala odon
(Maisch and Ma zke 1998a; Schmi z e al. 2004). Pos e io ly,
he sagi al c es e mina es a he pa ie al-sup a empo al
su u e.
The sup a empo al is di ided in o a la e al, a medial and
a en al p ocess. I o ms he pos e io im o he skull oo
and he conca e, pos e io ma gin o he uppe empo al
enes a. The squamosal is alle han long and possibly
p oduces an an e o en al p ocess, bu his is di icul o
con i m because he bone is se e ely damaged and pos-
FANG ET AL.—NEW MIXOSAURID ICHTHYOSAUR FROM THE MIDDLE TRIASSIC OF CHINA 269
sesses se e al su ace c acks. The pos o bi al cons i u es
he pos e odo sal ma gin o he o bi and con ac s he ad-
jacen sup a empo al, pos on al, squamosal, and jugal. I
is a ela i ely b oad elemen , simila o he pos o bi al in
species o Phala odon (Mo ani 1999b; Schmi z e al. 2004)
and M. panxianensis (Jiang e al. 2005, 2006), bu di e -
en om he slende pos o bi als o M. co nalianus and M.
kuhnschnyde i (B inkmann 2004; Renes o e al. 2020). The
jugal o ms he en al and pos e o en al ma gins o he
o bi . I is a slende bone, wi h an app oxima ely s aigh and
na ow an e io amus and a p opo ionally b oade pos o -
bi al amus. In con as o he holo ype o M. panxianensis,
Fig. 3. The skull and lowe jaw o he mixosau id ich hyosau Mixosau us luxiensis sp. no . (HFUT HL-21-08-002) om Huale Village, Luxi Coun y,
Yunnan P o ince, China (Pelsonian, Anisian). Pho og aph (A1) and in e p e a i e d awing (A2). Dashed lines indica e in e ed ma gins. The ’ symbol
indica es le elemen s. Abb e ia ions: an, angula ; a , a icula ; ax, axis; bo, basioccipi al; cb, ce a ob anchial; d, den a y; , on al; j, jugal; l, lac imal;
m, maxilla; mc, Meckelian canal; n, nasal; p, pa ie al; pa , p ea icula ; pl, pala ine; pm, p emaxilla; po, pos o bi al; po , pos on al; p , p e on al; p ,
p e ygoid; q, quad a e; qj, quad a ojugal; san, su angula ; sc, scle al pla e; sp, splenial; sq, squamosal; s , sup a empo al.
270 ACTA PALAEONTOLOGICA POLONICA 69 (2), 2024
he jugal does no p oduce a dis inc pos e o en al p ocess
(Jiang e al. 2006).
Some o he c anial elemen s a e disa icula ed om he
es o he skull and displaced om hei o iginal posi ion.
The b oad quad a e can be seen inside he o bi . I has a la ge
ounded do sal lamella, and a smalle , s ou a icula condyle,
which bea s a ans e se g oo e. The quad a e possesses a
small, iangula p ocess, also p esen in Besanosau us and
Guanlingsau us (Bindellini e al. 2021). The basioccipi al is
exposed in en al iew and is e y simila o he basioccip-
i al o M. co nalianus, wi h bo h possessing an ex ensi e ex-
acondyla a ea (Maisch e al. 2006; Miedema e al. 2023a).
The con ex basioccipi al condyle is smoo h and bea s a sub-
le no ocho dal pi . The ex acondyla a ea has a midline
idge and p o uding la e al wings, wi h no en al in ag-
ina ion p esen (Miedema e al. 2023a). A bone exposed in
he lowe empo al embaymen immedia ely pos e io o he
jugal possibly ep esen s he pos e ola e al pa o he p e y-
goid. The la ge shee -like bones isible inside he en al pa
o he o bi p obably comp ise he p e ygoids and pala ines.
Some ex emely comp essed scle al pla es a e p ese ed on
he su ace o he exposed pala al elemen s.
Mandible: The wo mandibula ami a e disa icula ed
om each o he . The le amus is p ese ed in ana omi-
cal posi ion, bu he igh amus unde wen a 180° o a ion
and lies en al o he skull. As a esul , bo h ami ully
expose hei medial sides. The Meckelian canal o ms a
longi udinal g oo e on he den a y, un il i becomes pos-
e omedially closed by he splenial. The splenial p oduces
wo long, p ong-like p ocesses along he pos e odo sal
and pos e o en al ma gins o he Meckelian canal, which
clea ly con ac he den a y. Howe e , he su u al con ac s
be ween he splenial and he angula and su angula a e
inde e mina e due o nume ous su ace c acks caused by
he collapse o he medial wall o he Meckelian canal. The
su u e be ween he den a y and su angula is also inde-
e mina e. The su angula is exposed in he pos e odo sal
pa o he medial wall o he mandibula amus, and bea s
a e y small pa aco onoid p ocess (= co onoid p ocess o
Schmi z e al. 2004) (Miedema e al. 2023a). Pos e io ly, he
p ea icula exposes i s iangula medial su ace. I wedges
in be ween he do sally posi ioned su angula and he en-
ally posi ioned angula , and con ac s he splenial an e o-
en ally. The a icula comp ises he mos caudal pa o
each mandibula amus. An e io ly, i bea s a shallowly
conca e a icula su ace o he quad a e, and possesses a
smoo h, saddle-shaped medial su ace. Two ba -like bones
lying be ween he mandibula ami a e in e p e ed o be he
ce a ob anchials o he hyoid appa a us. They a e s aigh
and ha e a unca ed an e io end.
Den i ion: As in mos o he mixosau ids (wi h he excep-
ion o P. a a us; Liu e al. 2013; Engelschiøn e al. 2023),
he e odon y is clea ly exhibi ed by HFUT HL-21-08-002.
Because he an e io ip o he uppe jaw is missing, he mos
mesial ee h a e only p ese ed in he mandible, whe eas
middle and dis al ee h a e well p ese ed in bo h he uppe
jaws and he mandibula ami. The e y ip o he lowe jaw
is eden ulous, wi h he i s oo h p ese ed 6.0 mm pos e-
io o he ip o he le mandibula amus. This is simila o
he condi ion in Phala odon aasi, which was also epo ed
o ha e an eden ulous snou ip (Nicholls e al. 1999). The
den a y ee h a e se in a con inuous den al g oo e, which
has a labial wall e iden ly highe han he lingual wall,
and is e y p onounced pos e io ly. Indi idual oo h al eoli
seem o be absen and some ee h a e spaced e y closely
o each o he , so he oo h implan a ion mode in he den-
a y can be de e mined as aulacodon y o sub hecodon y
(i unexposed socke s a e p esen a he bo om o he den al
g oo e) (Mo ani 1997b; Be in e al. 2018). The mode o
oo h implan a ion in he uppe jaws in no possible o in e .
The mos mesial ee h a e ex emely small, wi h he
c own heigh o he i s p ese ed oo h measu ing
only a ound 1.1 mm in heigh and 0.7 mm in basal wid h
(heigh :wid h a io 1.57). Mo e dis ally, in he middle o he
den ige ous egion, he ee h become la ge and mo e o-
bus . The pos e io den i ion bea s he la ges ee h, wi h he
la ges o he ully exposed pos e io ee h eaching a c own
heigh o abou 2.5 mm and a c own basal wid h o abou
2.1 mm (heigh :wid h a io = 1.19), being mo e han wice
he size o he an e io ee h. The mos pos e io ee h a e
smalle han he p eceding ones bu a e mo e obus , wi h
hei c owns being no iceably b oadened (mesiodis ally),
wi h basal wid hs exceeding hei heigh s (e.g., he las igh
den a y oo h has a c own heigh o 1.7 mm and a c own
basal wid h o 1.8 mm, which gi es a heigh :wid h a io o
0.94). The e is no shape di e ence be ween he co espond-
ing uppe and lowe ee h.
All ee h, including he pos e io ones, ha e a poin ed
apex. The e a e no mola i o m ee h p esen , in con as
o M. kuhnschnyde i, M. panxianensis, P. callawayi, and
P. aasi (B inkmann 1998b; Schmi z e al. 2004; Mo ani
2005a; Jiang e al. 2006; Chen and Cheng 2010). Longi udinal
s ia ions can be obse ed along he en i e heigh o he c own
su aces. The oo s ha e a ma e su ace ex u e, di e en
om he shiny c own enamel su ace. Many o he oo s a e
mediola e ally la ened, which migh e lec he c ushing o
pulp ca i ies. No u ows indica ing he p esence o den ine
in olding can be obse ed in he oo s o HFUT HL-21-
08-002, which esembles he condi ion in M. co nalianus
(Maxwell e al. 2012a), bu con as s wi h he mo phology in
o he mixosau ids, like species o Phala odon and M. panx-
ianensis, in which pliciden ine is p esen (Me iam 1910;
Nicholls e al. 1999; Schmi z e al. 2004; Jiang e al. 2006;
Chen and Cheng 2010; Maxwell e al. 2012a). In gene al, he
den i ion o HFUT HL-21-08-002 is mos simila o he den-
i ion o M. co nalianus (e.g., PIMUZ T 2418), as bo h axa
sha e mode a e he e odon y wi h iny, mesial-mos ee h and
s ou e , non-mola i o m pos e io ee h (Fig. 4). Howe e ,
he den i ion o bo h axa di e s in ha he dis al ee h o
M. co nalianus a e abou he same size as he mesial ee h,
whe eas in HFUT HL-21-08-002 he dis al ee h a e abou
wice he size o he mesial ee h.
FANG ET AL.—NEW MIXOSAURID ICHTHYOSAUR FROM THE MIDDLE TRIASSIC OF CHINA 271
Axial skele on: The majo i y o he e eb al column is
disa icula ed, bu h ee ce ical neu al a ches (2–4) and he
middle caudal e eb ae a e p ese ed as a icula ed se ies.
Only he axial neu al a ch is a icula ed wi h i s co espond-
ing cen um (axis), whe eas he wo o he neu al a ches a e
isola ed. The neu al spine o he axis is apezoid in ou line
and bea s a e ical g oo e on i s la e al su ace. I is 10 mm
high and 8 mm wide a i s base and is ma kedly b oade han
he subsequen ce ical neu al spines. All h ee p ese ed
ce ical neu al a ches bea subo al, do so en ally elon-
ga ed diapophyses, which a icula ed wi h he ube culum
o he bicipi al ce ical ibs (SOM 1: ig. S1). This condi ion
is simila o he one epo ed o Phala odon callawayi, in
which he diapophysis is also loca ed on he ce ical neu al
a ch (Schmi z e al. 2004). An e io ly p ojec ing p ezyga-
pophyses and pos e io ly p ojec ing pos zygapohyses a e
well-de eloped in he ce ical neu al a ches.
The amphicoelous pos e io do sal and an e io caudal
cen a a e disa icula ed and sca e ed in he pos e io po -
ion o he specimen and hei co esponding neu al a ches
a e also disa icula ed and o en b oken. Se e al hexagonal
(in a icula iew) and mediola e ally comp essed cen a,
ep esen ing he mo e pos e io caudal cen a, a e also sca -
e ed in he same a ea. Mos do sal cen a possess single
ib ace s, bu some cen a loca ed close o he sac al e-
gion ha e double ib ace s. In he middle do sal egion, he
cen a a y om abou 8–9 mm in heigh and 6–7 mm in
leng h, wi h hei co esponding neu al a ches eaching up
o 20 mm in heigh . In he pos e io do sal/an e io caudal
egion, cen a achie e hei maximum size, he la ges being
o e 10 mm in heigh and a ound 7–8 mm in leng h. The
longes neu al spine om his egion is abou 21 mm all.
A se ies o 18 consecu i e cen a and wo incomple e
neu al spines, measu ing 112.9 mm in o al leng h, com-
p ises he mos pos e io pa o he p ese ed e eb al
column (SOM 1: ig. S2, able S2). Based on he ela i e
leng h and o ien a ion o he neu al spines, as well as he
disappea ance o ib ace s in he se en h cen um in he
p ese ed se ies, hese e eb ae can be con iden ly iden-
i ied as ep esen ing he caudal peak and i s immedia e
icini y. The cen um heigh /leng h a ios in he cen a lo-
ca ed immedia ely pos e io o he caudal peak a e only
Fig. 4. A compa ison o den i ion in species o he mixosau id ich hyosau Mixosau us. A. Mixosau us panxianensis Jiang e al., 2006, om Panzhou,
China, middle Anisian, GMPKU P-1039. B. Mixosau us kuhnschnyde i B inkmann, 1998b, om Mon e San Gio gio, I aly and Swi ze land, uppe
Anisian–lowe Ladinian, PIMUZ T 1324. C. Mixosau us co nalianus (Bassani, 1886) om Mon e San Gio gio, I aly and Swi ze land, uppe Anisian–
lowe Ladinian, PIMUZ T 2418. D. Mixosau us luxiensis sp. no . om Luxi, China, middle Anisian, HFUT HL-21-08-002. B and C depic he mandibula
den i ion only. Scale ba s 10 mm.
278 ACTA PALAEONTOLOGICA POLONICA 69 (2), 2024
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