Michael P. Taylor and Mathew J. Wedel

transcript

Re-evaluating “Apatosaurus” minimus,a bizarre Morrison Formation sauropod

with diplodocoid and macronarian features

Department of Earth SciencesUniversity of Bristol

England

College of Osteopathic Medicine of the Pacificand College of Podiatric MedicineWestern University of Health SciencesCalifornia, USA.

The Morrison Formation

1.5 million km2; 9.5 million years (156.3±2 Mya to 146.8±1 Mya)

Many sauropod genera in the Morrison

ValidApatosaurusBarosaurusBrachiosaurusCamarasaurusDiplodocusHaplocanthosaurusSupersaurusSuuwassea

Apatosaurus ajax holotype YPM 1860Cervical vertebra, left lateral view

QuestionableAmphicoeliasDyslocosaurus [if Jurassic)]DystrophaeusEobrontosaurus

Amphicoelias fragillimus holotype AMNH 5777Dorsal vertebral neural arch, posterior view

SynonymisedAtlantosaurusBrontosaurusCathetosaurusDystylosaurusElosaurusMorosaurusSeismosaurusUintasaurusUltrasauros [sic]

Dystylosaurus edwini holotype BYU 4503Dorsal vertebral, right anterolateral view

Not yet namedNew diplodocoid (Vietti and Hartman 2004)AMNH diplodocine"Apatosaurus" minimus

ApatosaurusApatosaurus Composite skeleton on displayin public gallery at AMNH.

Apatosaurus has many species

Apatosaurus ajax, excelsus, lousiae, parvus, ?yahnahpin, ?minimus, grandis, laticollis, amplus, alanquerensis

Apatosaurus (= “Brontosaurus”) excelsus holotype YPM 1980

Atlantosaurus montanus, immanis

Brontosaurus Elosaurus

Camarasaurus grandis

Atlantosaurus montanus, immanis

Eobrontosaurus

Brontosaurus Elosaurus

Lourinhasaurus

Apatosaurus species

Upchurch et al. (2005)Figure 15.

Specimen-levelphylogenetic analysisStrict consensus

What is AMNH 675?

Henry Fairfield Osborn (1904)Figure 4.

“Anterior, posterior and leftlateral views of the sacrum andilium of Brontosaurus sp.No. 675, Amer. Mus.”

“The inferior view of thesevertebrae corresponds incharacter with Marsh's figuresof Brontosaurus excelsus andof B. amplus.”

What is AMNH 675?

Charles C. Mook (1917)Figure 2.

“A. Outline of right pubisof Apatosaurus minimus.B. Outline of right ischiumof Apatosaurus minimus.”

No reason given forassociation of material.

Why is AMNH 675 Apatosaurus?

“It appears that the well-preserved sacrum and pelvisof No. 675 of the American Museum collections belongsto a species of Apatosaurus which has not hithertobeen described.”

“The inferior portion of the sacral rib of primary sacral 2has an oblique ridge on its inferior surface resemblingthose present in the types of A. ajax, Brontosaurusexcelsus, and B. amplus. This is a characteristic structurein Apatosaurus. The inferior surfaces of the centra arebroadly rounded, contrasting with those of Diplodocus. Theinferior portions of the sacral ribs are not twisted as inCamarasaurus. These characters together with the tallspines which have the characteristic Apatosaurus laminationindicate conclusively that the specimen under considerationbelongs to the genus Apatosaurus.”

Not very convincing

“Apatosaurus” minimusholotype AMNH 675,sacrum in right lateral view.

“Apatosaurus” minimus holotype AMNH 675, sacrum in left lateral view.

Real? Fabricated?

“Apatosaurus” minimus holotype AMNH 675, left ischium in medial view.

“Apatosaurus” minimus holotypeAMNH 675, left ischium in posterior view.

“Apatosaurus” minimusholotype AMNH 675, left ischium

“Apatosaurus” minimusholotype AMNH 675, incomplete rightischium

“True medial”

“Apatosaurus” minimusholotype AMNH 675, partial left pubis

“Apatosaurus” minimusholotype AMNH 675, Composite pelvis

Slightly foreshortened,But effect is not great.

e.g. inclined inward 20°cos(20°) = 0.94So orthogonal length is 94%

“Apatosaurus” minimusholotype AMNH 675, Composite pelvis

Slightly foreshortened,But effect is not great.

e.g. inclined inward 20°cos(20°) = 0.94So orthogonal length is 94%

Out of proportion.Is the associationgood?

Is it Apatosaurus?

“The species cannot belong to Apatosaurus ... The ilia are low,and their preacetabular processes are directed stronglylaterally somewhat as in the titanosaurids.”

– McIntosh 1990a (The Dinosauria, 1st ed.)

“From the shape of the distal end of the ischium and varioussacral characters, particularly the height of the neuralspines, it is now clear that this animal is not Apatosaurus,and also must be excluded from the Diplodocidae.”

– McIntosh 1990b:59

“The pubis has an ischial articular surface whose length isnearly 50% of the length of this element, a derived conditionin Camarasauromorpha (one of several features distinguishing“A.” minimus from Apatosaurus at the generic or highertaxonomic levels). ... This form is perhaps a basal macronarianor basal camarasauromorph.”

– Upchurch et al. 2004 (The Dinosauria, 2nd ed.)

Is it Apatosaurus?

“The species cannot belong to Apatosaurus ... The ilia are low,and their preacetabular processes are directed stronglylaterally somewhat as in the titanosaurids.”

– Upchurch et al. 2004 (The Dinosauria, 2nd ed.)No.No.“The species cannot belong to Apatosaurus ... The ilia are low,and their preacetabular processes are directed stronglylaterally somewhat as in the titanosaurids.”

– Upchurch et al. 2004 (The Dinosauria, 2nd ed.)

Apatosaurus excelsus“Apatosaurus” minimus

Diplodocus carnegii“Apatosaurus” minimus

Dicraeosaurus hansemanni“Apatosaurus” minimus

Haplocanthosaurus priscus“Apatosaurus” minimus

Camarasaurus lentus (subadult)“Apatosaurus” minimus

Giraffatitan brancai“Apatosaurus” minimus

Rapetosaurus krausei“Apatosaurus” minimus

Mamenchisaurus hochuanensis“Apatosaurus” minimus

Seems to be something new

McIntosh 1990a (Dinosauria, 1st ed.)Fig. 16.13: comparison of ilia

Tall, narrow neural spines on wide sacrumTall, narrow neural spines on wide sacrum

Sacral plates do not extend to iliumSacral plates do not extend to ilium

““Turtle-mimic” rugosities on sacral platesTurtle-mimic” rugosities on sacral plates

“Turtle-mimic” rugosities on sacral plates

Long, low ilium

Ilium vertical even while flaring.

Lateral “shelf” on bottom of iliumLateral “shelf” on bottom of ilium

Lateral “shelf” on bottom of iliumLateral “shelf” on bottom of iliumLateral “shelf” on bottom of ilium

Pubic pedunclePubic pedunclePubic peduncle

Lateral foramina (“pleurocoels”) absentfrom S1 and S6

Mike: We have an identification problem

Matt: Let's use cladistics!

Mike: We have an identification problem

Matt: Let's use cladistics!

Mike: Now we have two problems.

Analysis of Taylor (2009) after Harris (2006)

Strict consensusof 107 MPTs

Neosauropoda inBig polytomy

Macronaria dissolved

Neosauropoda inBig polytomy

BrachiosauridaeRebbachisauridae

Flagellicaudata

Macronaria dissolved

50% majority rule consensusof 107 MPTs

Neosauropoda backin shape

85 trees (79%)

Neosauropoda backin shape

Is “Apatosaurus” minimus a saltasaurid?It's an appealing idea.Would be first Morrison titanosaur

SaltasaurusPhoto by Randy Irmis

Is “Apatosaurus” minimus a saltasaurid?

Opisthocoelicaudia zdanskyi

Is “Is “ApatosaurusApatosaurus” ” minimusminimus a saltasaurid? a saltasaurid?

Opisthocoelicaudia Opisthocoelicaudia zdanskyizdanskyi

Is “Is “ApatosaurusApatosaurus” ” minimusminimus a saltasaurid? a saltasaurid?

Opisthocoelicaudia Opisthocoelicaudia zdanskyizdanskyi

No.No.

On changing onequestionable character

Analysis of Whitlock (2011)Strict consensus of 3 MPTs

Only polytomy is withinDiplodocinae

Basal diplodocoid(sister to Flagellicaudata)

But only a tiny sampleof macronarians

Analysis of Whitlock (2011)

Back to analysis of Taylor (2009)

85 trees (79%)

Back to analysis of Taylor (2009)

85 trees (79%)

Other MPTs

Interim conclusion

Cladistics is no substitutefor actual palaeontology.

Key split: Diplodocoidea vs. Macronaria

lodoco

It's a diplodocoid!

Neural spines tall, narrow, laminated as in diplodocoids

Neural spines laminated as in diplodocoids

Distal end of right ischium

'V'-shaped distal articulation of ischia

It's a macronarian!

Six fully fused sacrals connecting to ilium

Ilium without distal expansion

Diplodocus sacrum AMNH 3532, anterior

“Apatosaurus” minimus and Diplodocus sacra

“A.” minimus and Apatosaurus sacra

Apatosaurus parvussacrum and fused ilia(Gilmore 1936: fig. 31)

Do not mess with Gilmore.

GILMORE SAYSGILMORE SAYS

REJECT WITHOUT REVIEW.REJECT WITHOUT REVIEW.

Apatosaurus ajax “Tokyo specimen”

Diplodocus“Apatosaurus” minimus

Tokyo Apatosaurus ajax Apatosaurus parvus

Nearly at the conclusions ...

1. “Apatosaurus” minimus ain't Apatosaurus.

2. In fact, it's not any known sauropod.

3. Heck if we know what it is.

Sauropod diversity still underestimated

Underestimated even in the Morrison

Just like it's underestimated in the Early Cretaceous North America

+ Yellow Cat camarasaur (Britt?)+ Yellow Cat brachiosaur (Britt?)+ Yellow Cat titanosaur (Britt?)+ Long Walk brachiosaur (Tidwell?)+ CEU brachiosaur (Burge? Bird?)+ Cloverly 2nd sauropod (D'Emic?)

Just like it's underestimated in the Wealden

+ “Pelorosaurus” becklesi+ the Barnes High sauropod+ a titanosaur based on good caudals+ those “Eucamerotus” dorsals etc.

Is it underestimated everywhere?

… whatever Horner says.

AcknowledgementsAcknowledgements

Mark Norell and Carl Mehlingfor access to the specimen.

AcknowledgementsAcknowledgements

Mark Norell and Carl Mehlingfor access to the specimen.

Some sauropod genera have many species

Apatosaurus ajax, excelsus, lousiae, parvus, ?yahnahpin, ?minimusBarosaurus lentus, ?affinis, ?africanus, ?gracilisBrachiosaurus altithorax, ?brancai, ?fraasi, ?nougaredi, ?atalaiensisCamarasaurus supremus, grandis, lentus, ?lewisiDiplodocus longus, ?carnegii, hayi, hallorumHaplocanthosaurus priscus, ?utterbacki, delfsiSupersaurus vivianaeSuuwassea emilieae

Brontosaurus Elosaurus Morosaurus Cathetosaurus

Seismosaurus

Giraffatitan

Tornieria

Lusotitan

Eobrontosaurus

Brontosaurus Elosaurus Morosaurus Cathetosaurus

Seismosaurus

“Turtle-mimic” rugosities on sacral plates

Lateral “shelf” on bottom of iliumLateral “shelf” on bottom of ilium

Lateral “shelf” on bottom of ilium

Michael P. Taylor and Mathew J. Wedel

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