Everything you always wanted to know about the Carnegie Diplodocus (but were afraid to ask)

I’m really delighted today to announce the publication of my, and my co-authors’, new paper on the Carnegie Diplodocus:

• Taylor, Michael P., Amy C. Henrici, Linsly J. Church, Ilja Nieuwland and Matthew C. Lamanna. 2025. The history and composition of the Carnegie Diplodocus. Annals of the Carnegie Museum 91(1):55–91. doi: to follow.

Taylor et al. 2025: Figure 13. Skeletal atlas of the Carnegie mount of Diplodocus as originally erected in 1907, with bones color-coded according to the specimen they belonged to or were cast or sculpted from. Modified from a skeletal reconstruction by Scott Hartman, used with permission. Bones are colored as follows: CM 84 (most of the skeleton), yellow; CM 94 (right scapulocoracoid, lower right hindlimb, much of the tail and some chevrons), sculpted left tibia, red; CM 307 (the rest of the tail), not pictured; CM 662 (sculpted braincase, right humerus, radius and ulna), green; AMNH 965 (sculpted forefeet and carpus), purple; CM 21775 (left humerus, radius and ulna), cyan; CM 33985 (left fibula and lateral metatarsals), orange; USNM 2673 (sculpted remainder of skull), gold. White elements were sculpted, but the specimens on which these sculptures were based are not defi nitively known, though are most likely the corresponding CM 84 elements from the other side. Hyoids, clavicles, interclavicle, sternal ribs, and gastralia were all omitted from the mounted skeleton. Source of chevrons past the first seven is uncertain. See Table 2 and text for details. ” data-medium-file=”https://svpow.com/wp-content/uploads/2025/05/figure-13-composition-of-the-carnegie-diplodocus-50percent.jpeg?w=300″ data-large-file=”https://svpow.com/wp-content/uploads/2025/05/figure-13-composition-of-the-carnegie-diplodocus-50percent.jpeg?w=480″ class=”size-full wp-image-23576″ src=”https://svpow.com/wp-content/uploads/2025/05/figure-13-composition-of-the-carnegie-diplodocus-50percent.jpeg” alt=”" width=”480″ height=”178″ />

Taylor et al. 2025: Figure 13. Skeletal atlas of the Carnegie mount of Diplodocus as originally erected in 1907, with bones color-coded according to the specimen they belonged to or were cast or sculpted from. Modified from a skeletal reconstruction by Scott Hartman, used with permission. Bones are colored as follows: CM 84 (most of the skeleton), yellow; CM 94 (right scapulocoracoid, lower right hindlimb, much of the tail and some chevrons), sculpted left tibia, red; CM 307 (the rest of the tail), not pictured; CM 662 (sculpted braincase, right humerus, radius and ulna), green; AMNH 965 (sculpted forefeet and carpus), purple; CM 21775 (left humerus, radius and ulna), cyan; CM 33985 (left fibula and lateral metatarsals), orange; USNM 2673 (sculpted remainder of skull), gold. White elements were sculpted, but the specimens on which these sculptures were based are not definitively known, though are most likely the corresponding CM 84 elements from the other side. Hyoids, clavicles, interclavicle, sternal ribs, and gastralia were all omitted from the mounted skeleton. Source of chevrons past the first seven is uncertain. See Table 2 and text for details.

“But Mike”, you say, “surely the Carnegie Diplodocus is the single best-known sauropod in the world? Didn’t Ilja Nieuwland (2019) write the definitive book about it only six years ago?”

And you’re not wrong. Lots has been written about the history of this specimen, not least my own paper on the concrete cast in Vernal, Utah (Taylor et al. 2013). And yet, surprisingly little has been written about the actual science of this keystone specimen: nothing very substantial, really, since Hatcher’s (1901) original monograph and Holland’s (1906) follow-up.

As I recounted in How the Concrete Diplodocus paper came to be, this new paper initially arose from one seemingly simple question which I wanted to be able to answer in the Concrete Diplodocus paper: what actual bones were the Carnegie casts taken from. And the answer turned out to be complicated. (That answer is summarised in the caption to Figure 13, above.)

As I started trying to figure this out, I got into correspondence with Matt Lamanna, the Carnegie’s very helpful curator of vertebrate palaeontology, and it quickly became apparent that Matt’s substantial contributions warranted co-authorship. Through Matt, I also got in touch with Amy Henrici, then the Carnegie’s collection manager for VP (now retired); and then with Linsly Church, a curatorial assistant in the same department. Both Amy and Linsly also went far beyond the call of duty, so joined the authorship. Meanwhile, as I was working on the brief historical introduction of the paper, I kept finding new rabbit-holes, and got so much help from Ilja Nieuwland that that section grew substantially and he, too, ended up as a co-author. So we ended up with five of us working on this thing, as it grew from a brief note to 27 deliciously detailed pages with 22 illustrations. (Lots of other people helped, too: see the acknowledgements.)

Taylor et al. 2015: Figure 16. Right forefeet of the Carnegie Diplodocus and its casts, all in approximately anterior view. A, the feet as originally mounted in 1905 (in the London cast), 1907 (in the first iteration of the Carnegie Museum original-material mount), and subsequent casts, as supervised by Hatcher and Holland and executed by Coggeshall. This photograph shows the right forefoot of the Paris mount, which is unchanged since its original mounting. This forefoot material, sculpted from the camarasaurid specimen AMNH 965, has elongate metacarpals splayed in a semi-plantigrade posture, with multiple phalanges on each of the three medial digit and large unguals on digits I, II, and III. Photograph by Vincent Reneleau (MNHN); B, the right forefoot of the Berlin mount, as remounted in 2006 by Research Casting International, supervised by Kristian Remes. This consists of the original casts mounted in 1908 by Holland and Coggeshall, reposed in a more modern digitigrade posture, with superfluous phalanges and unguals discarded (see text). Photograph by Verónica Díez Díaz (MfN); C, the forefeet of Galeamopus (= “Diplodocus”) hayi HMNS 175 (formerly CM 662), casts of which were used in the Carnegie mount between 1999 and 2007. Note the much shorter metacarpals, the fully digitigrade posture, the reduction in phalangeal count, and the single large manual ungual on digit I. Photograph by Jeremy Huff (TAMU); D, the present forefeet of the Carnegie mount, modelled in 2007 after those of WDC-FS001A, then thought to belong to Diplodocus carnegii (Bedell and Trexler 2005) but currently thought to belong to an as-yet unnamed basal diplodocine (Tschopp et al. 2015:229–230). Note the resemblance to the diplodocine forefoot in part C, with short metacarpals, digitigrade posture, reduced phalangeal count, and a single large manual ungual. Photograph by Matthew C. Lamanna. ” data-medium-file=”https://svpow.com/wp-content/uploads/2025/05/figure-17-manus-through-the-ages.jpeg?w=300″ data-large-file=”https://svpow.com/wp-content/uploads/2025/05/figure-17-manus-through-the-ages.jpeg?w=480″ class=”size-full wp-image-23584″ src=”https://svpow.com/wp-content/uploads/2025/05/figure-17-manus-through-the-ages.jpeg” alt=”" width=”480″ height=”480″ />

Taylor et al. 2015: Figure 16. Right forefeet of the Carnegie Diplodocus and its casts, all in approximately anterior view. A, the feet as originally mounted in 1905 (in the London cast), 1907 (in the first iteration of the Carnegie Museum original-material mount), and subsequent casts, as supervised by Hatcher and Holland and executed by Coggeshall. This photograph shows the right forefoot of the Paris mount, which is unchanged since its original mounting. This forefoot material, sculpted from the camarasaurid specimen AMNH 965, has elongate metacarpals splayed in a semi-plantigrade posture, with multiple phalanges on each of the three medial digit and large unguals on digits I, II, and III. Photograph by Vincent Reneleau (MNHN); B, the right forefoot of the Berlin mount, as remounted in 2006 by Research Casting International, supervised by Kristian Remes. This consists of the original casts mounted in 1908 by Holland and Coggeshall, reposed in a more modern digitigrade posture, with superfluous phalanges and unguals discarded (see text). Photograph by Verónica Díez Díaz (MfN); C, the forefeet of Galeamopus (= “Diplodocus”) hayi HMNS 175 (formerly CM 662), casts of which were used in the Carnegie mount between 1999 and 2007. Note the much shorter metacarpals, the fully digitigrade posture, the reduction in phalangeal count, and the single large manual ungual on digit I. Photograph by Jeremy Huff (TAMU); D, the present forefeet of the Carnegie mount, modelled in 2007 after those of WDC-FS001A, then thought to belong to Diplodocus carnegii (Bedell and Trexler 2005) but currently thought to belong to an as-yet unnamed basal diplodocine (Tschopp et al. 2015:229–230). Note the resemblance to the diplodocine forefoot in part C, with short metacarpals, digitigrade posture, reduced phalangeal count, and a single large manual ungual. Photograph by Matthew C. Lamanna.

It turns out there was still plenty of history to be uncovered, and that some well-known parts of the story aren’t quite right after all. Also, that the composition of the Carnegie mount has changed a lot through the years — something that has not been publicly documented until now. And no-one really knows even how long this dinosaur is.

We dug into all of this, with the hope that the new paper would become a one-stop-shop for anyone who needs to know anything about this keystone specimen. It’s been a joy to work on (and especially to work with Matt L., Amy, Linsly and Ilja), and I hope you will enjoy reading it.

(A note on the venue of publication: I went against my usual policy of open-access venues only because the museum’s in-house journal, Annals of the Carnegie Museum, seemed so historically appropriate for this work. I liked the idea of following the footsteps of Hatcher and Holland — even if their early-1900s monographs were in the now discontinued Memoirs rather than the Annals. In fact, the Annals is not even paywalled: there is no online version at all hosted by the publisher (which is the museum itself). It is a print-only journal. So you can consider the PDF on my own website to be the definitive electronic copy.)

Oh, and we have a sidebar page about the new paper, containing full-resolution copies of all 22 illustrations.

References

• Hatcher, John Bell. 1901. Diplodocus (Marsh): its osteology, taxonomy, and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1:1-63.
• Holland, W. J. 1906. Osteology of Diplodocus Marsh with special reference to the restoration of the skeleton of Diplodocus carnegiei Hatcher presented by Mr Andrew Carnegie to the British Museum, May 12 1905. Memoirs of the Carnegie Museum 2(6):225-278.
• Nieuwland, Ilja. 2019. American dinosaur abroad: a cultural history of Carnegie’s plaster Diplodocus. University of Pittsburgh Press. ISBN:978-0822945574. doi:10.2307/j.ctvh4zh5n
• Taylor, Michael P., Steven D. Sroka and Kenneth Carpenter. 2023. The Concrete Diplodocus of Vernal — a Cultural Icon of Utah. Geology of the Intermountain West 10:65-91. doi: 10.31711/giw.v10.pp65-91
• Taylor, Michael P., Amy C. Henrici, Linsly J. Church, Ilja Nieuwland and Matthew C. Lamanna. 2025. The history and composition of the Carnegie Diplodocus. Annals of the Carnegie Museum 91(1):55–91. doi: to follow.