Falcarius forelimb biomechanics + 200 years of dinosaur discoveries

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

New papers:

David K. Smith (2026)
Biomechanics of the plesiomorphic forelimb of the basal therizinosaur Falcarius
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.70223
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70223


Therizinosaurs were a group of rapidly evolving basal maniraptoran theropods from the Upper Cretaceous of Asia and North America. Basal representatives were probably omnivorous, whereas more derived taxa may well have been herbivores. The earlier taxa, such as Falcarius, possessed a plesiomorphic maniraptoran body plan, but later ones, including Nothronychus, were extensively modified. Falcarius is known from many well-preserved but disarticulated elements found in an extensive bone bed in central Utah. The taxon was characterized by a well-developed but primitive forelimb. This paper presents the results of a biomechanical analysis of moment arms of major muscles spanning the shoulder and elbow. Many results are broadly similar to those found earlier for Nothronychus. Differences are attributed to allometry and changes in forelimb use related to trophic level between the two taxa. Important muscles spanning the shoulder include mm. pectoralis, supracoracoideus, and deltoid. In Falcarius, the first two exhibit abductor moment arms, while m. deltoid is complex in the abductor/adductor plane. Mm. pectoralis and supracoracoideus are synergistic protractors. Long axis rotation varies in these muscles. Muscles spanning the elbow, including mm. biceps and triceps, exhibited the expected antagonistic moment arms.

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Free pdf:

Donald M. Henderson (2026)
200 years of dinosaur discoveries –a visual portrayal of their geographic and historical origins.
PeerJ 14:e21351
doi: https://doi.org/10.7717/peerj.21351
https://peerj.com/articles/21351/


Background

The first dinosaur to be formally named was Megalosaurus in 1824. Over the subsequent 200 years more than 1,200 different species of dinosaur have been discovered and named. The discoveries come from every continent, but different regions are characterized with different species from different geological time periods. Given this multi-generational collection history, from a wide variety of geographic areas, and representing a huge diversity of animals, it was felt that a new type of visual summary of the current state of our knowledge of dinosaur diversity and discovery history would be much more informative and revealing than a simple list comprised of words and numbers.

Methods

Using recently published, comprehensive surveys of all known Mesozoic, non-avian dinosaurs, a series of computer-generated, horizontal, stacked, bar-type graphs are used to graphically show how our knowledge of dinosaur diversity has developed over the past 200 years at the decade level. The graphs use clusters of coloured boxes, with individual boxes scaled to the numbers of dinosaurs from a region, to enable comparisons of counts of dinosaur discoveries from different regions within and between decades. The colours are used to identify the countries and regions on an accompanying global map. This analysis of the historical growth in our knowledge of dinosaur diversity is presented in two ways: at the high level of the clades Theropoda, Sauropodomorpha and Ornithischia; and at a lower one with many detailed monophyletic and paraphyletic sub-group levels.

Results

As of end of 2025 this survey finds that there are 1,259 reliably known dinosaur species: 428 ornithischians, 366 sauropodomorphs and 465 theropods. From the entire 19th century only 58 dinosaur species can be viewed as having been discovered and still be considered valid today. These 19th century discoveries came from Europe and the United States of America with just three exceptions. Dinosaur discovery and naming rates were very low, typically no more than 10 per decade per major clade, until the 1970s when the decadal counts began to exceed the total 19th century counts for the first time. Discoveries from 1920s began to fully reveal to the true global extent of dinosaur occurrences. The early 2000s saw Argentina and China become the leading countries for new dinosaurs, but Europe and the United States continue to produce new discoveries up to the present.


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[Mickey Mortimer]

Regarding Henderson's paper, I trust the broad strokes are correct, but the primary data has a few issues. First is that "date of discovery" should actually be "date of official naming publication", as e.g. Megalosaurus' is given as 1824 but the lectotype dentary can be traced back to at least 1797 and the genus name goes back to 1822 as a nomen nudum. 

Second is inconsistency like Aristosuchus pusillus' date being given as 1876 when pusillus was named as a species of Poekilopleuron (Aristosuchus wasn't named until 1887), but Dryptosaurus aquilunguis' date is given as 1877 which was when Dryptosaurus was named, but it was originally Laelaps aquilunguis named in 1866. Henderson says "For the purposes of the present study, a species with a revised identification is considered to be `known' or `discovered' at the latest date that the revised name was established independent of whether it was a genus or species name change. Prior to the most recent, and presumably now correct naming, we can think of re-identified and re-named organisms as having been previously hidden and residing unknown inside an earlier name. As an example, Lydekker named `Titanosaurus australis' in 1893 based on fossils found in Argentina. Powell (1992) renamed the specimen as Neuquensaurus australis. Neuquensaurus has been set at 1992 in the data set as it can be considered to have been hidden inside `T. australis' until 1992." So by that logic Aristosuchus pusillus should have been 1887, but Dryptosaurus wasn't "hidden" in Laelaps, it WAS the type species of Laelaps, but a mite happened to be also named Laelaps. See also Betasuchus bredai, credited to 1883 when Megalosaurus bredai was named, but by Henderson's logic it should be 1932 when Huene named Betasuchus. 

Third is that neotypes have complicated things. So yes, Coelophysis was named in 1889, but none of those specimens are now thought to be referable to the genus, with the current material found in 1947. The same could be said for Allosaurus, named in 1877 based on a now supposedly indeterminate specimen, but the neotype wasn't found until 1883.

And that's just the fifteen theropods listed in Table 2 ("Nineteenth century dinosaur first occurrences organized by major clade and sorted by year of discovery."). 

Mickey Mortimer

[Stephen Poropat]

I reviewed the original submission of Henderson's paper (raising many issues you do here, Mickey) but did not have sufficient time to review subsequent versions. From what you write, Mickey, many of the problems that I originally flagged with this paper remain. 

One statement in particular in the original paper grabbed my attention because I knew it was simply wrong: "...low numbers of dinosaurs [were] discovered during the years 1900 to 1970...Especially depauperate are the sauropods with just one (!) new species being reported in each of the decades 1910-19 and 1960-69."

In the paper it now says "Especially depauperate are the sauropods with just three new species being reported in each of the first two decades of the 20th century, and just one(!) in the 1960s."

In light of the data I presented in the comment I made in response to the original statement, the statement in the article is still wrong:

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"This cannot be correct. And as I think I demonstrate below, it is not.

1910s
Giraffatitan brancai (1914 as Brachiosaurus brancai; genus named in 1988 / 2009)
Dicraeosaurus hansemanni 1914
Dicraeosaurus sattleri 1914 (might be synonymous with the above)
Apatosaurus louisae 1915

1920s
Alamosaurus sanjuanensis 1922 (debatably a nomen dubium)
Amanzia greppini (1922 as Ornithopsis greppini; genus named in 2020)
Galeamopus hayi (1924 as Diplodocus hayi; genus named in 2015)
Rhoetosaurus brownei 1926
Malawisaurus dixeyi (1928 as Gigantosaurus dixeyi; genus named in 1993)
Antarctosaurus wichmannianus 1929
Laplatasaurus araukanicus 1929
Euhelopus zdanskyi (1929 as Helopus zdanskyi; genus named in 1956)

1930s
Aegyptosaurus baharijensis 1932 (arguably a nomen dubium but only because it was blown up in WWII)
Austrosaurus mckillopi 1933
Jainosaurus septentrionalis (1933 as Antarctosaurus septentrionalis; genus named in 1994/5)
Mongolosaurus halpodon[sic; my bad: haplodon] 1933 (arguably a nomen dubium)
Tienshanosaurus chitaiensis 1937 (arguably a nomen dubium)
Omeisaurus junghsiensis 1939

1940s
Sanpasaurus yaoi 1944 (arguably a nomen dubium)
Amygdalodon patagonicus 1947

1950s
Mamenchisaurus constructus 1954
Rebbachisaurus garasbae 1954
"Cetiosaurus" moghrebiensis 1954
Lusotitan atalaiensis (1957 as Brachiosaurus atalaiensis; genus named in 2013)
Lourinhasaurus alenquerensis (1957 as Apatosaurus alenquerensis; genus named in 1998)

1960s
"Brachiosaurus" nougaredi 1960
"Barosaurus" africanus var. gracilis 1961"

In light of the above alone, the dataset must be viewed as being flawed and/or incomplete. A thorough revision thereof must take place for the analysis conducted herein to have sufficient validity to be worth publishing."

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Dr Stephen F. Poropat

Deputy Director

Western Australian Organic and Isotope Geochemistry Centre

School of Earth and Planetary Sciences

Curtin University

Bentley, Western Australia

Australia 6102

https://stephenporopat.weebly.com/

[Mickey Mortimer]

Interesting Stephen. Here's his actual list from the supp info-

Diplodocoid Dicraeosaurus hansemanii 1914 Tanzania Jurassic 

Diplodocoid Apatosaurus louisae 1915 United-States Jurassic 

Lithostrotia Alamosaurus sanjuanensis 1922 United-States Cretaceous 

SauropBasal Rhoetosaurus brownie 1926 Australia Jurassic 

Lithostrotia ?Antarctosaurus? giganteus 1929 Argentina Cretaceous 

Lithostrotia Antarctosaurus wichmannianus 1929 Argentina Cretaceous 

Lithostrotia Laplatasaurus araukanicus 1929 Argentina Cretaceous 

Lithostrotia Magyarosaurus dacus 1932 Romania Cretaceous 

TitanosauriaBasal Aegyptosaurus baharijensis 1932 Egypt Cretaceous 

SomphoBasal Austrosaurus mkillopi 1933 Australia Cretaceous

SomphoBasal Mongolosaurus haplodont 1933 Mongolia Cretaceous 

EusauroBasal Teinshanosaurus chitaiensis 1937 China Jurassic 

EusauroBasal Omeisaurus junghsiensis 1939 China Jurassic 

SauropBasal Sanpasaurus yaoi 1944 China Jurassic 

Basal Amygdalodon patagonicus 1947 Argentina Jurassic 

Diplodocoid Rebbachisaurus garasbae 1954 Morocco Cretaceous 

EusauroBasal Mamenchisaurus constructus 1954 China Jurassic 

EusauroBasal 'Cetiosaurus' mogrebiensis 1955 Morocco Jurassic 

SomphoBasal Euhelopus zdanskyi 1956 China Cretaceous

Note Amygdalodon was incorrectly counted as non-sauropod. Otherwise, nougaredi is missing (probably correctly being considered indeterminate after Mannion et al., 2013), as is sattleri (maybe due to synonymy like you suggested), as is africanus var. gracilis (which I'd say is excusable if it was viewed as infrasubspecific; Bivens et al. 2025 argued it should be cited as 1989 anyway). But yes, this shows that neither Henderson's original or published statements match his data, with two 1910s species, five 1920s species, and zero 1960s species. Which is also odd because it shows it wasn't just hyperbole, since the actual count is lower than his statements for two of the decades.

But as your list shows, his actual data is also just misleading by not counting when the species itself was named if it was reassigned to a different genus. The previously stated method of "For the purposes of the present study, a species with a revised identification is considered to be `known' or `discovered' at the latest date that the revised name was established independent of whether it was a genus or species name change" is just really bad for the study's purpose. I could SORT of partially see it if the study were counting genera only and thus when e.g. Giraffatitan was split from Brachiosaurus, that would be newly recognized generic diversity. But as is, generic reassignments are due to the whims of when researchers restudy taxa, or when they find out a genus is preoccupied, not anything to do with where a species was discovered. So again to use Giraffatitan, it's historical significance of discovery is the 1909-1912 expedition to what's now Tanzania, not Paul's 1988 physiology paper that split it two decades before it was even generally recognized.

And it's not consistently followed, as I noted above. Looking at the theropod list for instance, Megapnosaurus rhodesiensis is listed as 1969 (should be 2001), Duriavenator hesperis is listed as 1974 (should be 2008), etc..

Mickey Mortimer

[John D'Angelo]

This strikes me as a particularly egregious example of the bad habit in dinosaur paleontology of not treating species as real taxa unless they’re in monotypic genera. Arguing that a species was "hidden" before it received its current genus assignment, or that "we finally gained a proper understanding of" a taxon upon it receiving its current genus assignment, doesn't make any sense to me. Surely one cannot argue that we had a "proper understanding" of Megalosaurus bucklandii in 1824 but didn't have a "proper understanding" of Giraffatitan brancai until 1988. I also note that Henderson’s list isn’t consistent whether species within the same genus are included: multiple species are listed for Apatosaurus and Mamenchisaurus but not Camarasaurus, Dicraeosaurus, Diplodocus, or Omeisaurus. So it’s not clear what criteria are being followed here. I think the most consistent approach would have been to do it by the publication date of the nominal species (which is a well-defined date), regardless of when its name-bearing type specimen was collected. Certainly, if Henderson is going to be talking about the number of species discovered in the 19th century, he should be dating their discovery date according to the naming of the species, not the date at which they got reassigned to a new genus, so his list of valid 19th century sauropodomorph species is missing at least Haestasaurus becklesii, Camarasaurus grandis, Camarasaurus lentus, Smitanosaurus agilis, and Neuquensaurus australis (plus a few other taxa that I hesitate to accept as valid). His list of valid 19th-century sauropodomorphs includes Atlantosaurus montanus for some reason, even though it is is pretty much universally agreed to be a nomen dubium (and in the unlikely event that the holotype proves to be diagnostic at the species level, there is a pretty good chance it would be the senior synonym of some other Morrison taxon, thus not representing an additional valid species). The list also includes Cetiosaurus brevis, Astrodon johnstoni, Ornithopsis hulkei, Titanosaurus indicus, and Dinodocus mackesoni, all of which are on thin ice at best.

(Side note: Cetiosaurus brevis Owen, 1842 is the senior objective synonym of Cetiosaurus conybeari Melville, 1849, the holotype of which is four caudal vertebrae that also form the lectotype of C. brevis, but not the senior objective synonym of Pelorosaurus conybeari Mantell, 1850, as Mantell explicitly considered “the humerus alone” as the basis for that taxon. The fact that he considered it “a great probability” that the vertebrae of C. brevis belonged to the same taxon, and reused the epithet conybeari, doesn't change that. Whether the holotype humerus of P. conybeari and lectotype caudal vertebrae of C. brevis represent the same individual or even the same biological species is unclear.)

Here’s my count of nominal species of sauropod named from 1900 to 1969 (cited in their original combination):

1900–1909 (8 nominal species, 6 taxonomically valid)
- Diplodocus carnegii Hatcher, 1901 (accepted)
- Elosaurus parvus Peterson & Gilmore, 1902 (accepted as Apatosaurus parvus or Brontosaurus parvus)
- Brachiosaurus altithorax Riggs, 1903 (accepted)
- Haplocanthus priscus Hatcher, 1903 (accepted as Haplocanthosaurus priscus)
- Haplocanthosaurus utterbacki Hatcher, 1903 (junior subjective synonym of Haplocanthosaurus priscus)
- Algoasaurus bauri Broom, 1904 (nomen dubium)
- Gigantosaurus africanus Fraas, 1908 (accepted as Tornieria africana)
- Gigantosaurus robustus Fraas, 1908 (accepted as Janenschia robusta)

1910–1919 (8 nominal species, 5 or 6 taxonomically valid)
- Brachiosaurus brancai Janensch, 1914 (accepted as Giraffatitan brancai)
- Brachiosaurus fraasi Janensch, 1914 (junior subjective synonym of Giraffatitan brancai)
- Dicraeosaurus hansemanni Janensch, 1914 (accepted)
- Dicraeosaurus sattleri Janensch, 1914 (accepted)
- Titanosaurus dacus Nopcsa, 1915 (accepted as Magyarosaurus dacus)
- Apatosaurus louisae Holland, 1916 (accepted)
- Apatosaurus minimus Mook, 1917 (species inquirenda)
- Uintasaurus douglassi Holland, 1919 (junior subjective synonym of Camarasaurus lentus)

1920–1929 (15 nominal species, 8 to 10 taxonomically valid)
- Alamosaurus sanjuanensis Gilmore, 1922 (accepted)
- Ornithopsis greppini Huene, 1922 (accepted as Amanzia greppini)
- Asiatosaurus mongoliensis Osborn, 1924 (nomen dubium)
- Diplodocus hayi Holland, 1924 (accepted as Galeamopus hayi)
- Rhoetosaurus brownei Longman, 1926 (accepted)
- Gigantosaurus dixeyi Haughton, 1928 (accepted as Malawisaurus dixeyi)
- Helopus zdanski Wiman, 1929 (accepted as Euhelopus zdanskyi)
- Antarctosaurus giganteus Huene, 1929 (species inquirenda)
- Antarctosaurus wichmannianus Huene, 1929 (accepted)
- Campylodon ameghinoi Huene, 1929 (nomen dubium)
- Laplatasaurus araukanicus Huene, 1929 (accepted)
- Loricosaurus scutatus Huene, 1929 (nomen dubium, possible junior synonym of Neuquensaurus australis)
- Titanosaurus robustus Huene, 1929 (species inquirenda, possible junior synonym of Neuquensaurus australis)
- Titanosaurus lydekkeri Huene, 1929 (nomen dubium)
- Titanosaurus valdensis Huene, 1929 (nomen dubium)

1930–1939 (8 or 9 nominal species, 7 taxonomically valid)
- Aegyptosaurus baharijensis Stromer, 1932 (accepted)
- Magyarosaurus hungaricus Huene, 1932 (accepted as Petrustitan hungaricus)
- Magyarosaurus transylvanicus Huene, 1932 (junior subjective synonym of Magyarosaurus dacus)
- Antarctosaurus septentrionalis Huene and Matley, 1933 (accepted as Jainosaurus septentrionalis)
- Austrosaurus mckillopi Longman, 1933 (accepted)
- Mongolosaurus haplodon Gilmore, 1933 (accepted)
- Tienshanosaurus chitaensis Young, 1937 (accepted)
- Antarctosaurus jaxarticus Riabinin, 1938 (nomen dubium or nomen nudum)
- Omeisaurus junghsiensis Young, 1939 (accepted)

1940–1949 (3 nominal species, 2 taxonomically valid)
- Titanosaurus falloti Hoffet, 1942 (nomen dubium)
- Sanpasaurus yaoi Young, 1944 (accepted)
- Amygdalodon patagonicus Cabrera, 1947 (accepted)

1950–1959 (8 nominal species, 4 to 6 taxonomically valid)
- Camarasaurus annae Ellinger, 1950 (junior subjective synonym of Camarasaurus lentus)
- Chiayusaurus lacustris Bohlin, 1953 (nomen dubium)
- Mamenchisaurus constructus Young, 1954 (accepted)
- Rebbachisaurus garasbae Lavocat, 1954 (accepted)
- Cetiosaurus mogrebiensis Lapparent, 1955 (species inquirenda)
- Apatosaurus alenquerensis Lapparent and Zbyszewski, 1957 (accepted as Lourinhasaurus alenquerensis)
- Brachiosaurus atalaiensis Lapparent and Zbyszewski, 1957 (accepted as Lusotitan atalaiensis)
- Omeisaurus changshouensis Young, 1958 (species inquirenda)

1960–1969 (2 nominal species, 0 taxonomically valid)
- Brachiosaurus nougaredi Lapparent, 1960 (nomen dubium)

- Rebbachisaurus tamesnensis Lapparent, 1960 (nomen dubium)

FWIW, my personal count is that of 539 nominal species of sauropodomorph (including 14 of uncertain or partial sauropodomorph affinities), there are 370 valid species and 35 species inquirendae. Seven of these species were named too recently to be included in this paper. My count is surprisingly close to Henderson's count of 366 (which would now be 373) despite some obvious differences in what we consider to be valid taxa.

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