[dinosaur] Scelidosaurus postcranial skeleton

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Ben [email protected]=0A=0AA new paper:=0A=0A=0ADavid B. Norma=
n (2019)=0AScelidosaurus harrisonii from the Early Jurassic of Dorset, Engl=
and:=0Apostcranial skeleton.=0AZoological Journal of the Linnean Society, z=
lz078=0Adoi: https://urldefense.proofpoint.com/v2/url?u=3Dhttps-3A__doi.org=
_10.1093_zoolinnean_zlz078&d=3DDwIFaQ&c=3DclK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8=
p7CSfnc_gI&r=3DRy_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=3Dy4SF6BKPYwAF=
l3YTsL51E9-aeWHfPhHZ1nL-9ccb8aQ&s=3D_-e0xkJp3BxcYuCSGCAGcjMKgTqE_AdrJGpb8jd=
pdWk&e=3D=20=0Ahttps://urldefense.proofpoint.com/v2/url?u=3Dhttps-3A__acade=
mic.oup.com_zoolinnean_advance-2Darticle-2Dabstract_doi_10.1093_zoolinnean_=
zlz078_5679623&d=3DDwIFaQ&c=3DclK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&r=
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eWHfPhHZ1nL-9ccb8aQ&s=3DYURMnw7htNFJOmubtz5mqRcRmtpdayM_7wzprZeHFzc&e=3D=20=
=0A=0A=0AScelidosaurus fossils were first discovered during the commercial =
quarrying=0Aof the Liassic sea-cliffs between Charmouth and Lyme Regis in D=
orset during=0Athe late 1850s. The original specimens included a well-prese=
rved skull=0Aembedded in a block of argillaceous limestone (marlstone). Sho=
rtly after=0Athis skull was retrieved, a series of more-or-less contiguous =
marlstone=0Aslabs were recovered, containing most of the skeleton of the sa=
me animal=0A(NHMUK R1111). After rudimentary (hammer and chisel) mechanical=
=0Apreparation, Owen published descriptions of this material (Owen, 1861,=
=0A1863). These two monographs have been the sole references pertaining to =
the=0Aanatomy of Scelidosaurus for > 150 years. The skeleton of the lectoty=
pe of=0AScelidosaurus harrisonii (NHMUK R1111) has since been extracted fro=
m the=0Asurrounding matrix using an acid-immersion technique. Some addition=
al=0Aspecimens held in the collections of the Natural History Museum London=
, the=0ABristol City Museum and the Sedgwick Museum in Cambridge provide an=
atomical=0Amaterial that allows detailed description of this taxon, for whi=
ch we have=0Ahad, until now, a surprisingly poor understanding.=0A=0AAxial =
skeleton: The axial skeleton of Scelidosaurus comprises eight=0Acervical, 1=
6 dorsal, four sacral and > 40 caudal vertebrae. During=0Aontogeny, the pos=
terior centrum articular surface of the 16th dorsal=0Avertebra develops a f=
irm, ligament-bonded junction with the succeeding=0Asacral centrum. Apart f=
rom the atlas rib, which is single headed,=0Adouble-headed ribs are present=
 throughout the presacral vertebral series,=0Aand none shows any indication=
 of fusion to its associated vertebra.=0AHowever, those ribs attached to ce=
rvical vertebrae 2=E2=80=934 were evidently bound=0Afirmly by connective ti=
ssue to rugose diapophyses. The last two (presacral)=0Adorsal ribs show mer=
ger of the capitulum and tuberculum, meaning that they=0Aare separated by o=
nly a step. The angulation and arching of the dorsal ribs=0Asuggest that th=
ese animals had a broad (barrel-like) torso. Intercostal=0Aplates were pres=
ent, attached to the posterior margins of some of the=0Alargest dorsal ribs=
. Their attachment sites are clearly marked, and these=0Aplates might have =
been composed of calcified cartilage in larger=0Aindividuals. The sacral ve=
rtebrae fuse progressively during ontogeny, in an=0Aanterior-to-posterior s=
equence. The sacral ribs are long and robust, and=0Atilt the iliac blade ou=
tward dorsally. A sacricostal 'yoke' (created by the=0Afusion of the distal=
 ends of adjacent sacral ribs) never forms. The base of=0Athe tail has a un=
ique ball-and-socket-style joint between the centra of=0Acaudal vertebrae 1=
 and 2 in only one skeleton. This might have permitted=0Apowerful, but cont=
rolled, movements of the tail as a defensive weapon (or=0Aincreased flexibi=
lity at the base of the tail, which might have been=0Anecessary for reprodu=
ction). Caudal ribs are initially long, blade-shaped=0Aprojections that gra=
dually decrease in size and become stub-like remnants=0Athat persist as far=
 back as the midtail (approximately caudal vertebra 25).=0AHaemal arches (c=
hevrons) disappear nearer to the distal end of the tail=0A(approximately ca=
udal vertebra 35). Ossified tendons are preserved as=0Aepaxial bundles that=
 are clustered in the =E2=80=98axillary=E2=80=99 trough (between the=0Aneur=
al spine and transverse processes on either side of the midline).=0AOssifie=
d tendons are restricted to the dorsal and sacral region. Flattened=0Aossif=
ied tendons are fused to the sides of sacral neural spines. In life,=0Athe =
ossified tendons might have formed a low-angled trellis-like=0Aarrangement.=
=0A=0AAppendicular skeleton: The pectoral girdle comprises a long scapula, =
with a=0Adistally expanded blade. The proximal portion is expanded and supp=
orts an=0Aoblique promontory, forming an acromial process anteriorly and a =
thick,=0Acollar-like structure posteriorly above the glenoid. Between these=
 two=0Afeatures is a shallow basin, bordered ventrally by a sutural edge fo=
r the=0Acoracoid. The scapula=E2=80=93coracoid suture remains unfused in la=
rge (5-m-long)=0Aindividuals. The coracoid bears a discrete foramen and for=
ms a subcircular=0Adished plate, with the shallowest of embayments along it=
s posterior edge.=0AClavicles are present as small fusiform bones attached =
to the acromial=0Aprocess of the scapulae and leading edge of each coracoid=
. A sternum was=0Areported as =E2=80=98some partially ossified element of t=
he endoskeleton=E2=80=99 Owen=0A(1863: 13), but subsequent preparation of t=
he skeleton has removed all=0Atrace of this material. The humerus is relati=
vely long and has a prominent=0Arectangular and proximally positioned delto=
pectoral crest. The ulna is=0Arobust and tapers distally, but there is no e=
vidence of an olecranon=0Aprocess. The radius is more rod-like and terminat=
es distally in an=0Aenlarged, subcircular and convex articular surface for =
the carpus. The=0Acarpus is represented by an array of five discoid carpals=
. The manus is=0Apentadactyl and asymmetrical, with short, divergent metaca=
rpals and digits=0Athat terminate in small, arched and pointed unguals on d=
igits 1=E2=80=933 (only).=0AThe phalangeal formula of the manus is 2-3-4-3-=
2. The pelvis is dominated=0Aby a long ilium; the preacetabular process is =
arched, transversely broad,=0Aand curves laterally. In juveniles, this proc=
ess is short and horizontal,=0Abut during ontogeny it increases considerabl=
y in length and becomes arched.=0AThe iliac blade is tilted laterally, mean=
ing that its dorsal blade partly=0Aoverhangs the femur. The acetabulum form=
s a partial cupola, and there is a=0Acurtain-like medial wall that reduces =
the acetabular fenestra to a=0Acomparatively low, triangular opening betwee=
n the pubis and ischium. The=0Apostacetabular portion of the ilium is long =
and supports a brevis shelf.=0AThe ischium has a long, laterally compressed=
 shaft that hangs almost=0Avertically beneath the ilium, and there is no ob=
turator process. The pubis=0Ahas a long, narrow shaft and a relatively shor=
t, deep, laterally compressed=0Aprepubic process that twists laterally (its=
 distal end lies almost=0Aperpendicular to the long axis of the ilium). The=
 articular pad on the=0Apubis for the femoral head faces posteriorly. The o=
bturator foramen is not=0Afully enclosed within the pubis, but its foramen =
is closed off posteriorly=0Aby the pubic peduncle of the ischium. The femur=
 is stout and has a slightly=0Amedially offset femoral head, and the greate=
r trochanter forms a sloping=0Ashoulder continuous with, and lateral to, th=
e femoral head. The anterior=0A(lesser) trochanter is prominent and forms a=
 thick, thumb-shaped projection=0Aon the anterolateral corner of the femora=
l shaft. The fourth trochanter is=0Apendent and positioned at midshaft. In =
larger individuals, it appears to=0Abecome thickened and reinforced by beco=
ming coated with metaplastic bone=0Aderived from the tendons attached to it=
s surface. The distal end of the=0Afemoral shaft is slightly curved and exp=
ands to form condyles. There is a=0Adeep and broad posterior intercondylar =
groove, but the anterior=0Aintercondylar groove is barely discernible in ju=
veniles and not much better=0Adeveloped in subadults. The tibia and fibula =
are shorter than the femur.=0AThe tibia is structurally dominant, and the s=
horter fibula is comparatively=0Aslender and bowed. The proximal tarsals ar=
e firmly bound by connective=0Atissue to the distal ends of the tibia and f=
ibula. The distal end of the=0Atibia is stepped, which aids the firm interl=
ock between the crus and=0Aproximal tarsals. There appear to be two roughly=
 discoid tarsals (distal=0Atarsals 3 and 4), and a rudiment of distal tarsa=
l 5 appears to be sutured=0Ato the lateral margin of distal tarsal 4. Five =
metatarsals are preserved,=0Abut the fifth is a splint of bone attached to =
the proximal end of=0Ametatarsal 4. Metatarsals 2=E2=80=934 are dominant, l=
ong and are syndesmotically=0Ainterlocked proximally, but their shafts spla=
y apart distally. Metatarsal 1=0Ais much shorter than the other three, but =
it retains two functional=0Aphalanges (including a short, pointed ungual). =
The foot is anatomically=0Atetradactyl but functionally tridactyl. The peda=
l digit formula is=0A2-3-4-5-0. The digits diverge, but each appears to cur=
ve medially along its=0Alength, creating the impression of asymmetry. This =
asymmetry is emphasized,=0Abecause the three principal unguals are also twi=
sted medially. The ungual=0Aof digit 2 is the largest and most robust of th=
e three, whereas that of=0Adigit 4 is the smallest and least robust.=0A=0AT=
he general girth of the torso and the displacement of the abdomen=0Aposteri=
orly (a consequence of the opisthopubic pelvic construction in this=0Adinos=
aur) constrained the excursion of the hindlimb during the protraction=0Apha=
se of the locomotor cycle. The anterolateral displacement of the=0Ahindlimb=
 during protraction is in accord with the freedom of motion that is=0Aevide=
nt at the acetabulum, the susceptibility of the hindlimb to torsion=0Abetwe=
en and within its component parts, and the asymmetry of the foot. It=0Ais p=
robable that eurypodan thyreophorans (notably, ankylosaurs) used a=0Asimila=
r oblique-parasagittal hindlimb excursion to accommodate their=0Aequally la=
rge and wide abdomens. This surmise accords with the structure of=0Athe pel=
ves and hindlimbs of ankylosaurs. Derived stegosaurs might have=0Aobviated =
this 'problem', in part, because their hindlimbs were longer and=0Atheir to=
rsos and abdomens narrower and capable of being 'stretched'=0Avertically to=
 a greater extent. Nevertheless, the structure of their=0Aacetabula and hin=
dlimbs indicates that the oblique-parasagittal style of=0Ahindlimb excursio=
n remained a possibility and might be an evolutionary=0Aremnant of the loco=
motor style of basal, shorter-limbed stegosaurs.=0A=0AA reconstruction of t=
he endoskeleton of Scelidosaurus is presented on the=0Abasis of this update=
d description. Although quadrupedal, this animal was=0Aonly facultatively s=
o, judged by its forelimb-to-hindlimb proportions and=0Astructure; it there=
fore betrays bipedality in its ancestry.=0A=

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<div dir=3D"ltr"><div><br></div>Ben Creisler<div><a href=3D"mailto:bcreisle=
[email protected]">[email protected]</a></div><div><br></div><div>A new paper:<=
br><div><br></div><div><br></div><div>David B. Norman (2019)<br>Scelidosaur=
us harrisonii from the Early Jurassic of Dorset, England: postcranial skele=
ton.<br>Zoological Journal of the Linnean Society, zlz078<br>doi: <a href=
=3D"https://urldefense.proofpoint.com/v2/url?u=3Dhttps-3A__doi.org_10.1093_=
zoolinnean_zlz078&amp;d=3DDwMFaQ&amp;c=3DclK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p=
7CSfnc_gI&amp;r=3DRy_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&amp;m=3Dy4SF6=
BKPYwAFl3YTsL51E9-aeWHfPhHZ1nL-9ccb8aQ&amp;s=3D_-e0xkJp3BxcYuCSGCAGcjMKgTqE=
_AdrJGpb8jdpdWk&amp;e=3D">https://doi.org/10.1093/zoolinnean/zlz078</a><br>=
<a href=3D"https://urldefense.proofpoint.com/v2/url?u=3Dhttps-3A__academic.=
oup.com_zoolinnean_advance-2Darticle-2Dabstract_doi_10.1093_zoolinnean_zlz0=
78_5679623&amp;d=3DDwMFaQ&amp;c=3DclK7kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_=
gI&amp;r=3DRy_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&amp;m=3Dy4SF6BKPYwAF=
l3YTsL51E9-aeWHfPhHZ1nL-9ccb8aQ&amp;s=3DYURMnw7htNFJOmubtz5mqRcRmtpdayM_7wz=
prZeHFzc&amp;e=3D">https://academic.oup.com/zoolinnean/advance-article-abst=
ract/doi/10.1093/zoolinnean/zlz078/5679623</a></div><div><br><br>Scelidosau=
rus fossils were first discovered during the commercial quarrying of the Li=
assic sea-cliffs between Charmouth and Lyme Regis in Dorset during the late=
 1850s. The original specimens included a well-preserved skull embedded in =
a block of argillaceous limestone (marlstone). Shortly after this skull was=
 retrieved, a series of more-or-less contiguous marlstone slabs were recove=
red, containing most of the skeleton of the same animal (NHMUK R1111). Afte=
r rudimentary (hammer and chisel) mechanical preparation, Owen published de=
scriptions of this material (Owen, 1861, 1863). These two monographs have b=
een the sole references pertaining to the anatomy of Scelidosaurus for &gt;=
 150 years. The skeleton of the lectotype of Scelidosaurus harrisonii (NHMU=
K R1111) has since been extracted from the surrounding matrix using an acid=
-immersion technique. Some additional specimens held in the collections of =
the Natural History Museum London, the Bristol City Museum and the Sedgwick=
 Museum in Cambridge provide anatomical material that allows detailed descr=
iption of this taxon, for which we have had, until now, a surprisingly poor=
 understanding.<br><br>Axial skeleton: The axial skeleton of Scelidosaurus =
comprises eight cervical, 16 dorsal, four sacral and &gt; 40 caudal vertebr=
ae. During ontogeny, the posterior centrum articular surface of the 16th do=
rsal vertebra develops a firm, ligament-bonded junction with the succeeding=
 sacral centrum. Apart from the atlas rib, which is single headed, double-h=
eaded ribs are present throughout the presacral vertebral series, and none =
shows any indication of fusion to its associated vertebra. However, those r=
ibs attached to cervical vertebrae 2=E2=80=934 were evidently bound firmly =
by connective tissue to rugose diapophyses. The last two (presacral) dorsal=
 ribs show merger of the capitulum and tuberculum, meaning that they are se=
parated by only a step. The angulation and arching of the dorsal ribs sugge=
st that these animals had a broad (barrel-like) torso. Intercostal plates w=
ere present, attached to the posterior margins of some of the largest dorsa=
l ribs. Their attachment sites are clearly marked, and these plates might h=
ave been composed of calcified cartilage in larger individuals. The sacral =
vertebrae fuse progressively during ontogeny, in an anterior-to-posterior s=
equence. The sacral ribs are long and robust, and tilt the iliac blade outw=
ard dorsally. A sacricostal &#39;yoke&#39; (created by the fusion of the di=
stal ends of adjacent sacral ribs) never forms. The base of the tail has a =
unique ball-and-socket-style joint between the centra of caudal vertebrae 1=
 and 2 in only one skeleton. This might have permitted powerful, but contro=
lled, movements of the tail as a defensive weapon (or increased flexibility=
 at the base of the tail, which might have been necessary for reproduction)=
. Caudal ribs are initially long, blade-shaped projections that gradually d=
ecrease in size and become stub-like remnants that persist as far back as t=
he midtail (approximately caudal vertebra 25). Haemal arches (chevrons) dis=
appear nearer to the distal end of the tail (approximately caudal vertebra =
35). Ossified tendons are preserved as epaxial bundles that are clustered i=
n the =E2=80=98axillary=E2=80=99 trough (between the neural spine and trans=
verse processes on either side of the midline). Ossified tendons are restri=
cted to the dorsal and sacral region. Flattened ossified tendons are fused =
to the sides of sacral neural spines. In life, the ossified tendons might h=
ave formed a low-angled trellis-like arrangement.<br><br>Appendicular skele=
ton: The pectoral girdle comprises a long scapula, with a distally expanded=
 blade. The proximal portion is expanded and supports an oblique promontory=
, forming an acromial process anteriorly and a thick, collar-like structure=
 posteriorly above the glenoid. Between these two features is a shallow bas=
in, bordered ventrally by a sutural edge for the coracoid. The scapula=E2=
=80=93coracoid suture remains unfused in large (5-m-long) individuals. The =
coracoid bears a discrete foramen and forms a subcircular dished plate, wit=
h the shallowest of embayments along its posterior edge. Clavicles are pres=
ent as small fusiform bones attached to the acromial process of the scapula=
e and leading edge of each coracoid. A sternum was reported as =E2=80=98som=
e partially ossified element of the endoskeleton=E2=80=99 Owen (1863: 13), =
but subsequent preparation of the skeleton has removed all trace of this ma=
terial. The humerus is relatively long and has a prominent rectangular and =
proximally positioned deltopectoral crest. The ulna is robust and tapers di=
stally, but there is no evidence of an olecranon process. The radius is mor=
e rod-like and terminates distally in an enlarged, subcircular and convex a=
rticular surface for the carpus. The carpus is represented by an array of f=
ive discoid carpals. The manus is pentadactyl and asymmetrical, with short,=
 divergent metacarpals and digits that terminate in small, arched and point=
ed unguals on digits 1=E2=80=933 (only). The phalangeal formula of the manu=
s is 2-3-4-3-2. The pelvis is dominated by a long ilium; the preacetabular =
process is arched, transversely broad, and curves laterally. In juveniles, =
this process is short and horizontal, but during ontogeny it increases cons=
iderably in length and becomes arched. The iliac blade is tilted laterally,=
 meaning that its dorsal blade partly overhangs the femur. The acetabulum f=
orms a partial cupola, and there is a curtain-like medial wall that reduces=
 the acetabular fenestra to a comparatively low, triangular opening between=
 the pubis and ischium. The postacetabular portion of the ilium is long and=
 supports a brevis shelf. The ischium has a long, laterally compressed shaf=
t that hangs almost vertically beneath the ilium, and there is no obturator=
 process. The pubis has a long, narrow shaft and a relatively short, deep, =
laterally compressed prepubic process that twists laterally (its distal end=
 lies almost perpendicular to the long axis of the ilium). The articular pa=
d on the pubis for the femoral head faces posteriorly. The obturator forame=
n is not fully enclosed within the pubis, but its foramen is closed off pos=
teriorly by the pubic peduncle of the ischium. The femur is stout and has a=
 slightly medially offset femoral head, and the greater trochanter forms a =
sloping shoulder continuous with, and lateral to, the femoral head. The ant=
erior (lesser) trochanter is prominent and forms a thick, thumb-shaped proj=
ection on the anterolateral corner of the femoral shaft. The fourth trochan=
ter is pendent and positioned at midshaft. In larger individuals, it appear=
s to become thickened and reinforced by becoming coated with metaplastic bo=
ne derived from the tendons attached to its surface. The distal end of the =
femoral shaft is slightly curved and expands to form condyles. There is a d=
eep and broad posterior intercondylar groove, but the anterior intercondyla=
r groove is barely discernible in juveniles and not much better developed i=
n subadults. The tibia and fibula are shorter than the femur. The tibia is =
structurally dominant, and the shorter fibula is comparatively slender and =
bowed. The proximal tarsals are firmly bound by connective tissue to the di=
stal ends of the tibia and fibula. The distal end of the tibia is stepped, =
which aids the firm interlock between the crus and proximal tarsals. There =
appear to be two roughly discoid tarsals (distal tarsals 3 and 4), and a ru=
diment of distal tarsal 5 appears to be sutured to the lateral margin of di=
stal tarsal 4. Five metatarsals are preserved, but the fifth is a splint of=
 bone attached to the proximal end of metatarsal 4. Metatarsals 2=E2=80=934=
 are dominant, long and are syndesmotically interlocked proximally, but the=
ir shafts splay apart distally. Metatarsal 1 is much shorter than the other=
 three, but it retains two functional phalanges (including a short, pointed=
 ungual). The foot is anatomically tetradactyl but functionally tridactyl. =
The pedal digit formula is 2-3-4-5-0. The digits diverge, but each appears =
to curve medially along its length, creating the impression of asymmetry. T=
his asymmetry is emphasized, because the three principal unguals are also t=
wisted medially. The ungual of digit 2 is the largest and most robust of th=
e three, whereas that of digit 4 is the smallest and least robust.<br><br>T=
he general girth of the torso and the displacement of the abdomen posterior=
ly (a consequence of the opisthopubic pelvic construction in this dinosaur)=
 constrained the excursion of the hindlimb during the protraction phase of =
the locomotor cycle. The anterolateral displacement of the hindlimb during =
protraction is in accord with the freedom of motion that is evident at the =
acetabulum, the susceptibility of the hindlimb to torsion between and withi=
n its component parts, and the asymmetry of the foot. It is probable that e=
urypodan thyreophorans (notably, ankylosaurs) used a similar oblique-parasa=
gittal hindlimb excursion to accommodate their equally large and wide abdom=
ens. This surmise accords with the structure of the pelves and hindlimbs of=
 ankylosaurs. Derived stegosaurs might have obviated this &#39;problem&#39;=
, in part, because their hindlimbs were longer and their torsos and abdomen=
s narrower and capable of being &#39;stretched&#39; vertically to a greater=
 extent. Nevertheless, the structure of their acetabula and hindlimbs indic=
ates that the oblique-parasagittal style of hindlimb excursion remained a p=
ossibility and might be an evolutionary remnant of the locomotor style of b=
asal, shorter-limbed stegosaurs.<br><br>A reconstruction of the endoskeleto=
n of Scelidosaurus is presented on the basis of this updated description. A=
lthough quadrupedal, this animal was only facultatively so, judged by its f=
orelimb-to-hindlimb proportions and structure; it therefore betrays bipedal=
ity in its ancestry.<br><br><br></div></div></div>=0A=

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