Allosaurus (fragilis or jimmadseni?) Specimen MOR 693 ("Big Al"):
When studying how many species of Allosaurus there were, I was able to find seven: A. fragilis, A. europaeus, A. jimmadseni, (?)A. tendagurensis, (?)A. amplus, A. lusasi, and A. maximus, which I, and David K. Smith (1998), thought of as being a large and robust species of Allosaurus. However, Chure and Loewen (2020) stated that there were only two species of Allosaurus from North America, and one species from Europe: Allosaurus fragilis and jimmadseni from North America, and A. europaeus from Europe. Now, Evers et al., (2020) says that there is, more than likely, only ONE species of Allosaurus WORLDWIDE! So my question is... how many species of Allosaurus are there!?
Three Species of Allosaurus?:
Allosaurus fragilis:
Allosaurus has NOT have a good history in terms of how many confirmed species there are. The first species discovered was Allosaurus fragilis, discovered by Othniel Charles Marsh in 1877. The holotype is named YPM 1930 (Paleofile) (Paul and Carpenter, 2010, pg. 53). Marsh says that the species is characterized by "hour-glass-shaped centra, biconcave vertebra with shallow cavities that ensure lightness, and slender feet bones," (Marsh, 1877, pg. 515-516).
Unfortunately, the holotype is not diagnostic enough to be considered as a definitive species, due to fragmentary remains. In 2010, paleontologists Gregory S. Paul and Kenneth Carpenter proposed to designate another specimen, USNM 4734, discovered from the same quarry as YPM 1930, to be the neotype. (Paul and Carpenter, 2010, "Abstract" and pg. 55). This hasn't officially taken place yet though (Evers et al., 2020, "Introduction," p.3).
Other theropods previously thought to be their own species, like Epanterias, Creosaurus, Labrosaurus, Camptonotus, Wyomingraptor, Madsenius, and Antrodemus, have been reassigned to Allosaurus fragilis. Other Allosaurus species from North America (like Allosaurus amplus and A. lucasi) are considered to be Allosaurus fragilis or Allosaurus indeterminate (Chure and Loewen, 2020, "Discovery and excavational history," p. 5). Even Allosaurus maximus, whom paleontologist David K. Smith proposed in 1998 (and I agreed with him), seems to be Allosaurus fragilis now. Allosaurus tendagurensis is considered to be a nomen dubium, since it is only based on a tibia.
As of right now, there are either one, or three, valid species of Allosaurus, with two being in North America and one in Europe.
Allosaurus jimmadseni:
Allosaurus jimmadseni was proposed by paleontologist David Chure in 2000 for his thesis. For a LONG time, it had quotation marks around its name because it wasn't officially described in a scientific paper (Theropod Database, "A. 'jimmadseni'"). However, Chure and Loewen (2020) have concluded that Allosaurus jimmadseni is definitive based on:
"(1) in lateral view, a row of neurovascular foramina pierce the medioventral wall of the maxillary antorbital fossa; (2) straight posteroventral jugal ramus of maxilla where it articulates with jugal; (3) laterodorsal margin of nasal “pinched” into low crest continuous from premaxilla to lacrimal; (4) posterior portion of dorsal surface of nasal cup-shaped, producing a median peak in region of nasofrontal contact; (5) relatively taller lacrimal horns than in Allosaurus fragilis; (6) jugal with relatively straight ventral margin and straight-to-slightly-curved outline in dorsal view; a well-developed distinct antarticular, and (7) axial intercentrum is rotated dorsally and has a flared rim in lateral view," ("Diagnosis").
This has been called into question by Evers et al., (2020), but I will talk about that later. The holotype is DINO 11541, which is based on a skull and most of the post-cranial skeleton. There are a few other specimens assigned to A. jimmadseni, with two notable specimens called "Big Al" and "Big Al 2" (Chure and Loewen, 2020, "Holotype" and "Referred material"). Allosaurus jimmadseni lived in North America alongside A. fragilis.
Allosaurus europaeus:
Allosaurus europaeus was discovered by Perez-Moreno et al., (1999), but it wasn't named A. europaeus until 2006 (Mateus et al., 2006, pg. 5). Aside from its geographical location, Mateus et al., (2006) says that A. europaeus is characterized by:
"jugal participation in the antorbital fenestra; maxilla forked posteriorly; truncated ventroposterior process of the maxilla; nasal with two pneumatic foramina (the anterior foramen twice the size of the posterior); posteroventral pro- jection of the jugal more than twice the posterodorsal projection; large an- terior surangular foramen; no lacrimal-maxillary contact; squamosal con- tacts the quadratojugal by a sigmoidal suture; squamosal projects ventrally into laterotemporal fenestra; lacrimal horn narrow in lateral view; large ventral projection of postorbital; rugose dorsal rim of the nasal; the occipi- tal condyles above the squamosal-quadratojugal contact; the anterior tip of quadratojugal is anterior to the laterotemporal fenestra; the lateral lamina of lacrimal is subtle; palatine contacts the pterygoid dorsoposteriorlly; and ventral tip of the postorbital reaches the lower rim of the orbit," (pg. 5).
Chure and Loewen (2020) kept A. europaeus as a separate species of Allosaurus, since its jugal, maxilla, and nasal differs from A. fragilis and A. jimmadseni (Figure 16) ("Conclusion"). In their conclusion, Chure and Loewen (2020) stated that there were only three species of Allosaurus that exist: A. fragilis, A. jimmadseni, and A. europaeus.
Allosaurus Skulls (Chure and Loewen, 2020, Figure 16):
Very soon after Chure and Loewen (2020) published their paper, Evers et al., (2020) publish their own on Allosaurus. They studied the skulls, in particular the jugals or cheek bones, of Allosaurus, and have concluded that there aren't any differences, whether or not they belonged to the same or different species of Allosaurus:
"Here, we use the taxon Allosaurus without species epithet due to the unsolved taxonomic issues. However, our observations are based on specimens that have been referred to both species, and we have not found any differences between those for the elements of interest," ("Introduction," p. 3).
This was also shown and stated in Figure 5, "Data from specimens of Allosaurus" p. 6, and in the "Conclusion." In Figure 5, the jugals for A. jimmadseni ("A" and "B"), A. fragilis ("C"), and A. europaeus ("D") all look the same.
Allosaurus Jugals/Cheek Bones (Evers et al., 2020, Figure 5) (A. jimmadseni are "A" and "B", A. fragilis is "C", and A. europaeus is "D"):
"...the new observations have implications for the diagnosis of the European A. europaeus (Mateus, Walen & Antunes, 2006; Fig. 5D) as a distinct species, for which the jugal participation in the antorbital fenestra was listed as one of the few autapomorphic characters that differentiate it from the North American species. Besides, the authors listed the absence of a lacrimal-maxilla contact as a further apomorphy, which is related to the former character. However, as pointed out above, this is only true for the lateral view, while a medial contact between both bones was almost certainly present. Unfortunately, this cannot be verified at the moment as the internal side of the skull is filled with matrix, but the consistent nature of this contact in regard to Allosaurus specimens examined for this study allow inferring the presence of this contact with high confidence. All other diagnostic features of A. europaeus have been questioned to be truly unique, and some have proven to be variably present in North American Allosaurus specimens (Malafaia et al., 2007). Therefore, a re-evaluation of the European species is necessary, as currently none of the originally proposed diagnostic features are uniquely present in the holotype of Allosaurus europeaus," ("Discussion," p. 3).
In their conclusion, it seems that there are no major differences in all of the Allosaurus skulls studied in the paper:
"The configuration of cheek bones does not vary between the examined specimens in Allosaurus, and our observations furthermore indicate that the European species A. europaeus did not differ in this regard from North American material," ("Conclusion").
But what's even more interesting is what Allosaurus' skull actually looked like. Based on their new findings, Evers et al., (2020) recreated what Allosaurus' skull really looked like:
Allosaurus MOR 693 ("Big Al") Skull Reconstruction (Evers et al., 2020):
Kenneth Carpenter came to this conclusion ten years earlier. In 2010, Carpenter said that the differences in the skull bones of multiple Allosaurus specimens seem to be "mostly isometric, with only a slight isometric trend in some of the bones... I view these as extreme variation rather than distinct taxon," (Carpenter, 2010, "Conclusion," p. 1). He also questioned "some autapomorphic characters used to define other theropod taxa," since they appear to be questionable and are a result of "ontogenetic and individual variation" ("Abstract"). It seems that a similar conclusion was decided on in Evers et al., (2020).
Paleontologist Mickey Mortimer has stated some similar points on her Theropod Database website, and on other bones said to have belong to other species of Allosaurus. She basically concluded that Allosaurus fragilis was the most valid species of Allosaurus, and other characteristics said to have been diagnostic only in other species of Allosaurus can be seen in other specimens of Allosaurus fragilis as well. Therefore, it seems that she came to the same conclusion as Carpenter (2010) and Evers et al., (2020). Therefore, I'll agree to consider Allosaurus fragilis as the only valid species of Allosaurus until further notice.
Update (5/3/20): It seems that Allosaurus "europaeus" was considered to be Allosaurus fragilis by some paleontologists before. Malafaia et al., (2007) and (2010) have argued that European fossils of Allosaurus belonged to Allosaurus fragilis (Malafaia et al., 2007, "Abstract") (Malafaia et al., 2010, pg. 202, "Conclusions," p. 2). They even said that A. "europaeus" was a synonym of A. fragilis (Malafaia et al., 2007, "Abstract").
Conclusion:
Based on Evers et al., (2020), Carpenter (2010), Mickey Mortimer from the Theropod Database, and now Malafaia et al., (2007) and (2010), it seems that Allosaurus fragilis is the only valid species of Allosaurus. The supposed different diagnostic characteristics seen in each species of Allosaurus seem to be found in other specimens of different species, and therefore there don't seem to be any differences in the species. Since Allosaurus fragilis was named first, I will consider all other "species" as Allosaurus fragilis until more information is published in the future. This includes "Allosaurus maximus," and even the nomen dubium "Allosaurus tendagurensis."
Links:
Allosaurus fragilis:
Othniel Charles Marsh (1877):
Paleofile ("Allosaurus"):
Paul and Carpenter (2010):
Other Theropods Assigned to Allosaurus fragilis, and Other Allosaurus Species Either Assigned to Allosaurus fragilis or Are Nomen Dubium:
Chure and Loewen (2020):
https://peerj.com/articles/7803/
Evers et al., (2020):
https://peerj.com/articles/8493/
Chure and Loewen (2020):
https://peerj.com/articles/7803/
Evers et al., (2020):
https://peerj.com/articles/8493/
Theropod Database:
("A. 'jimmadseni'"):
Chure and Loewen (2020):https://peerj.com/articles/7803/
Evers et al., (2020):
https://peerj.com/articles/8493/
(?)Allosaurus europaeus:
Perez-Moreno et al., (1999):
http://hazy.cs.wisc.edu/hazy/share/zifeipdf/10381/input_k2opt.pdf
Mateus et al., (2006) (pg. 5):
https://docentes.fct.unl.pt/sites/default/files/omateus/files/mateus_walen_antunes_-_2006_-_the_large_theropod_fauna_of_the_lourinha_formation__portugal__and_its_similarity_to_the_morrison_formation__with_a_description_of_a_new_species_of_allosaurus.pdf
Skulls:
Chure and Loewen (2020):
Evers et al., (2020):
https://peerj.com/articles/8493/
Malafaia et al., (2007) ("Abstract"):
Malafaia et al., (2010) (Pg. 202, "Conclusions," p. 2):
Osborn (1903):
http://digitallibrary.amnh.org/bitstream/handle/2246/1510//v2/dspace/ingest/pdfSource/bul/B019a31.pdf?sequence=1&isAllowed=y
Link 2:
http://digitallibrary.amnh.org/handle/2246/1510?show=full
Paleofile:
http://www.paleofile.com/Dinosaurs/Theropods/Allosaurus.asp
Chure and Loewen (2020) (Figure 16):
Evers et al., (2020) (Figure 5 and Figure 6):https://peerj.com/articles/8493/
Kenneth Carpenter (2010):
Theropod Database ("Allosaurus fragilis"):
https://www.theropoddatabase.com/Carnosauria.htm#Allosaurusfragilis
(?)Other Species:
(?)A. amplus:
Galton et al., (2015) ("Abstract;" "Discussion" pg. 330):
https://www.researchgate.net/publication/273334027_The_holotype_pes_of_the_Morrison_dinosaur_Camptonotus_amplus_MARSH_1879_Upper_Jurassic_western_USA_-_Is_it_Camptosaurus_Sauropoda_or_Allosaurus
(?)A. tendagurensis:
Rauhut (2005/2011) (pg. 209):
https://www.academia.edu/25456862/Theropod_dinosaurs_from_the_Late_Jurassic_of_Tendaguru_Tanzania
(?)A. lucasi:
Sebastian G. Dalman (2014):
