[dinosaur] Reconstructions of Morrison Formation sauropod diversity (free pdf)

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Ben [email protected]=0A=0AA new open access paper not yet men=
tioned (holiday distractions...)=0A=0AFree pdf:=0A=0AD. Cary Woodruff (2019=
)=0AWhat factors influence our reconstructions of Morrison Formation saurop=
od=0Adiversity?=0AGeology of the Intermountain West 6: 93=E2=80=93112.=0A[N=
o doi??]=0Ahttps://urldefense.proofpoint.com/v2/url?u=3Dhttps-3A__giw.utahg=
eology.org_index.php_giw_article_view_38&d=3DDwIFaQ&c=3DclK7kQUTWtAVEOVIgvi=
0NU5BOUHhpN0H8p7CSfnc_gI&r=3DRy_mO4IFaUmGof_Yl9MyZgecRCKHn5g4z1CYJgFW9SI&m=
=3D4Hem2Ja0oMdgQJ_l7HQKhuPIflSWXQp7OH-6y837kuM&s=3DfqWaATCaJq1GLu-S8NULuxfa=
8Itny17WMMJ3pw6vPwg&e=3D=20=0A=0A=0AThe Upper Jurassic Morrison Formation c=
lassically represents the =E2=80=9CGolden=0AAge=E2=80=9D of sauropods, and =
the Morrison Formation is reported to have yielded=0A13 genera and 24 speci=
es of sauropods. This incredible diversity has=0Aproduced numerous theories=
 attempting to reconcile the co-occurrence of=0Asuch large, and similar tax=
a. Previously, a comparably high diversity has=0Abeen proposed for the Late=
 Cretaceous Hell Creek Formation of North America=0A=E2=80=93 possibly comp=
rising nearly three dozen species from over 20 genera of=0Aankylosaura, cae=
nagnathids, ceratopsians, dromaeosaurids, hadrosaurs,=0Aornithomimids, pach=
ycephalosaurs, thescelosaurs, and tyrannosaurs. However,=0Amuch of the morp=
hologic variation previously ascribed to taxonomic=0Adifferences has recent=
ly been shown to be a result of stratigraphy and/or=0Aontogeny =E2=80=93 re=
sulting in this rich assemblage being downsized to 13 genera=0Aand 16 speci=
es. Whereas still rich in diversity, such factors have an=0Aimmediate effec=
t towards our reconstruction of true richness.=0A=0AFollowing the example o=
f the Hell Creek Formation, we can investigate the=0Aontogenetic and strati=
graphic origin of possible diversity inflation in=0Aother formations, and w=
ithin this study, apply it to the Morrison=0AFormation. New dating techniqu=
es are resulting in finer temporal=0Aresolution, and are changing the tempo=
ral position of well-known quarries.=0ADifferences in body size and ontogen=
etic stages can also affect diversity=0Aestimates. Plotting body size strat=
igraphically, it initially appears that=0Alarger specimens (interpreted as =
different species) occur higher in the=0Asection. An increase in average bo=
dy size may be a legitimate trend, but=0Athere are several specimens that c=
ounter this "rule" for many genera.=0ALikewise, dramatic allometric ontogen=
etic trajectories have led to the=0Aerection of at least three diplodocid g=
enera =E2=80=93 Amphicoelias, Seismosaurus,=0Aand Suuwassea =E2=80=93 and i=
t is suspected that many more Morrison Formation=0A"species" could alternat=
ively be explained as ontogimorphs. We have a long=0Away to go towards reve=
aling the true nature of Morrison Formation sauropod=0Adiversity. Although =
dietary partitioning undoubtedly occurred at the level=0Aof both the specie=
s (e.g., Brachiosaurus vs. Diplodocus) and between=0Aontogenetic stages, a =
base of 24 levels of co-occurring divisions seems=0Aunlikely. The Morrison =
Formation may have exhibited a sauropod-rich=0Aassemblage unlike any other =
in North America, and the implications of=0Astratigraphy, ontogeny, and var=
iation may be minor, yet these factors alter=0Aperceived =E2=80=9Cdiversity=
.=E2=80=9D True diversity will not be fully understood unless=0Athese facto=
rs are considered.=0A=

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<div dir=3D"ltr"><br><div>Ben Creisler</div><div><a href=3D"mailto:bcreisle=
[email protected]">[email protected]</a></div><div><br></div><div>A new open ac=
cess paper not yet mentioned (holiday distractions...)</div><div><br></div>=
<div>Free pdf:</div><div><br></div><div>D. Cary Woodruff (2019)<br>What fac=
tors influence our reconstructions of Morrison Formation sauropod diversity=
?<br>Geology of the Intermountain West 6: 93=E2=80=93112.</div><div>[No doi=
??]<br><a href=3D"https://urldefense.proofpoint.com/v2/url?u=3Dhttps-3A__gi=
w.utahgeology.org_index.php_giw_article_view_38&amp;d=3DDwMFaQ&amp;c=3DclK7=
kQUTWtAVEOVIgvi0NU5BOUHhpN0H8p7CSfnc_gI&amp;r=3DRy_mO4IFaUmGof_Yl9MyZgecRCK=
Hn5g4z1CYJgFW9SI&amp;m=3D4Hem2Ja0oMdgQJ_l7HQKhuPIflSWXQp7OH-6y837kuM&amp;s=
=3DfqWaATCaJq1GLu-S8NULuxfa8Itny17WMMJ3pw6vPwg&amp;e=3D">https://giw.utahge=
ology.org/index.php/giw/article/view/38</a></div><div><br><br>The Upper Jur=
assic Morrison Formation classically represents the =E2=80=9CGolden Age=E2=
=80=9D of sauropods, and the Morrison Formation is reported to have yielded=
 13 genera and 24 species of sauropods. This incredible diversity has produ=
ced numerous theories attempting to reconcile the co-occurrence of such lar=
ge, and similar taxa. Previously, a comparably high diversity has been prop=
osed for the Late Cretaceous Hell Creek Formation of North America =E2=80=
=93 possibly comprising nearly three dozen species from over 20 genera of a=
nkylosaura, caenagnathids, ceratopsians, dromaeosaurids, hadrosaurs, ornith=
omimids, pachycephalosaurs, thescelosaurs, and tyrannosaurs. However, much =
of the morphologic variation previously ascribed to taxonomic differences h=
as recently been shown to be a result of stratigraphy and/or ontogeny =E2=
=80=93 resulting in this rich assemblage being downsized to 13 genera and 1=
6 species. Whereas still rich in diversity, such factors have an immediate =
effect towards our reconstruction of true richness.<br><br>Following the ex=
ample of the Hell Creek Formation, we can investigate the ontogenetic and s=
tratigraphic origin of possible diversity inflation in other formations, an=
d within this study, apply it to the Morrison Formation. New dating techniq=
ues are resulting in finer temporal resolution, and are changing the tempor=
al position of well-known quarries. Differences in body size and ontogeneti=
c stages can also affect diversity estimates. Plotting body size stratigrap=
hically, it initially appears that larger specimens (interpreted as differe=
nt species) occur higher in the section. An increase in average body size m=
ay be a legitimate trend, but there are several specimens that counter this=
 &quot;rule&quot; for many genera. Likewise, dramatic allometric ontogeneti=
c trajectories have led to the erection of at least three diplodocid genera=
 =E2=80=93 Amphicoelias, Seismosaurus, and Suuwassea =E2=80=93 and it is su=
spected that many more Morrison Formation &quot;species&quot; could alterna=
tively be explained as ontogimorphs. We have a long way to go towards revea=
ling the true nature of Morrison Formation sauropod diversity. Although die=
tary partitioning undoubtedly occurred at the level of both the species (e.=
g., Brachiosaurus vs. Diplodocus) and between ontogenetic stages, a base of=
 24 levels of co-occurring divisions seems unlikely. The Morrison Formation=
 may have exhibited a sauropod-rich assemblage unlike any other in North Am=
erica, and the implications of stratigraphy, ontogeny, and variation may be=
 minor, yet these factors alter perceived =E2=80=9Cdiversity.=E2=80=9D True=
 diversity will not be fully understood unless these factors are considered=
.<br></div></div>=0A=

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