Friday, July 24, 2020

The Arguable Identity of Paraxenisaurus

Hi everyone.  In light of Cau's recent post on the supposed new Mexican deinocheirid "Paraxenisaurus normalensis" (Serrano-Brañas et al., 2020), I figured I'd check the taxon out to see what I thought.

The first thing you might note are the quotation marks surrounding its name, as this is yet another example of authors not including an lsid or reference to ZooBank in their electronic descriptions.  ICZN Article 8.5.3. states names published electronically must "be registered in the Official Register of Zoological Nomenclature (ZooBank) (see Article 78.2.4) and contain evidence in the work itself that such registration has occurred", and the pre-print is said to be in preparation for Volume 101 of Journal of South American Earth Sciences, cited as August 2020.  Thus it gets to join the ranks of "Thanos" and "Trierarchuncus"as theropods that will eventually be validly named this year.  But at least it's not stuck in the purgatory of twelve Scientific Reports Mesozoic theropods, which will never be physically published and thus will remain invalid unless outside action is taken.

One of the big takeaways from Cau's blogpost is that "I am doubtful about the possibility of referring these elements [the paratypes] to the same species of the holotype, since there are very few superimposable elements among the three specimens. Therefore, there is a risk that Paraxenisaurus , - understood as the sum of all three specimens - is a chimera."  After reading the paper, Andrea REALLY undersold this critique.  Here are the specimen materials lists, with the overlapping elements highlighted in matching colors-

(BENC 2/2-001; proposed holotype) proximal manual phalanx II-2 or III-3, partial astragalocalcaneum, partial metatarsal II, phalanx II-1 (115 mm), proximal phalanx II-2, partial metatarsal III, proximal phalanx III-3, distal metatarsal IV, phalanx IV-1 (104 mm), phalanx IV-3 (67 mm), phalanx IV-4 (45 mm), partial pedal ungual IV
(BENC 1/2-0054) distal metacarpal I, proximal phalanx I-1, partial manual ungual I, distal metacarpal II, distal phalanx II-2
(BENC 1/2-0091) several proximal caudal central fragments (66, 75, 76 mm), proximal metacarpal II, partial metacarpal III, distal femur (155 mm trans), distal metatarsal IV
(BENC 1/2-0092) several distal caudal vertebrae (70, 71 mm)
(BENC 30/2-001) pedal ungual II, pedal ungual III

As you can see, there's only one strict overlap, with BENC 1/2-0091 sharing a distal metatarsal IV with the proposed holotype, found ~14 kilometers away.  The paper lists no proposed apomorphies or unique combination of characters for distal metatarsal IV, and indeed the description states they preserve largely non-overlapping portions-

"In the holotype, the distal articular surface is fragmented (Figures 11a1 and 11a2); but in the referred specimen (BENC ½-0091), this surface is nicely preserved and has a non-ginglymoid outline (Figures 11b1 and 11b2). The medial condyle is mostly preserved in the holotype (Figure 11a3), but in the referred specimen it is completely broken (Figure 11b3). Conversely, the lateral condyle is broken in the holotype (Figure 11a4), but is well preserved in the referred specimen (Figure 11b4). Collateral ligament fossae are well developed on both condyles and have approximately the same size and depth (Figures 11a3 and 11b4). In cross-section, the shaft of metatarsal IV near the distal end is thicker dorsoventrally than wide."

Needless to say, metatarsal IV has a shaft which is deeper than wide in all ornithomimosaurs, and the preserved ligament fossae are on opposite sides in each specimen (medial in proposed holotype, lateral in 1/2-0091).  Below is a figure comparing the two Mexican specimens with Ornithomimus velox, with 1/2-0091 flipped so that all are comparable as left elements.  I don't see anything the "Paraxenisaurus" specimens have in common that could diagnose a taxon.

Left distal metatarsal IV of (left to right) intended "Paraxenisaurus normalensis" holotype BENC 2/2-001, intended "Paraxenisaurus normalensis" paratype BENC 1/2-0091 (right element flipped), and Ornithomomus velox holotype YPM 542 in (top to bottom) dorsal, lateral, ventral and medial views ("Paraxenisaurus" after Serrano-Brañas et al., 2020; Ornithomimus after Claessens and Loewen, 2016).

While no other elements are exactly matched, referred specimen BENC 30/2-001 does include pedal unguals II and III, while the intended holotype has pedal ungual IV.  These are again from different localities, although closer this time (~2.8 km), and this time we have characters listed in the diagnosis- 

"(9) distinctively broad and ventrally curved pedal unguals that angled downward with respect to the proximal articular surface and depending on the digit, the proximodorsal process becomes slightly enlarge and changes its position from nearly horizontal to mostly vertical, adopting a lipshaped appearance; and (10) pedal unguals with a rounded, large foramen on the medial side* and a deep ventral fossa that surrounds a strongly developed, ridge-like flexor tubercle."

Pedal unguals of (left to right) intended "Paraxenisaurus normalensis" paratype BENC30/2-001 right digit II, right digit III and intended "Paraxenisaurus normalensis" holotype BENC 2/2-001 left digit IV in (top to bottom) right, left, proximal and dorsal views (after Serrano-Brañas et al., 2020).  Green lines point to supposedly natural median foramen

Ventral curvature is plesiomorphic, the unguals of BENC 30/2-001 are not broader than other ornithomimosaurs', and ventral angling with the proximal end held vertically is common in theropods and present in e.g. Garudimimus and Beishanlong.  The proximodorsal process "changing its position" is using a difference between 30/2-001's mostly horizontal processes and the intended holotype's more vertical process as character, which in itself presupposes they are the same taxon.  The ventral fossa surrounding a ridge-like flexor tubercle is also present in Harpymimus, Garudimimus, Beishanlong and large Dinosaur Park unguals (NMC 1349, RTMP 1967.19.145) and is not shown in the intended holotype but is claimed to be "partially broken."  This leaves the medial foramen, which might be a valid character in unguals III and IV (II is damaged in that area), but might also be taphonomic, as there are many other small circular areas of damage (e.g. center of proximal surface of ungual IV).  While the two unguals in 30/2-001 are similar to each other, that of the intended holotype is more strongly curved, has that smaller more dorsally angled proximodorsal process, is wider in proximal view, and lacks the expanded ventral half characteristic of ornithomimosaurs that is present in the other specimen.  But even if these two pedal unguals are correctly referred, they are all that's present in specimen BENC 30/2-001.  So they get us nowhere in determining caudal, manual (besides proximal manual phalanx II-2 or III-3) or femoral morphology.

The final issue I noticed was the emphasis on "Paraxenisaurus" having a first pedal digit.  This would ironically be unlike Deinocheirus, but plesiomorphically shared with Nedcolbertia, "Grusimimus", Garudimimus, Beishanlong, Archaeornithomimus and Sinornithomimus.  The character state is based on metatarsal II, where "a facet on the posterior surface of the distal quarter of this shaft, indicates the presence of an articulation area for metatarsal I." The figure shows a longitudinal groove extending down the posterior center of distal metatarsal II, which as anyone who has scored taxa for Clarke's bird matrix could tell you, is not how non-birds attach their hallux to the metatarsus.  Hattori (2016) for instance writes in Allosaurus "there is no attachment scar corresponding to the metatarsal I fossa on either medial or plantar aspect of MT II" and in Citipati "there is no obvious attachment scar of MT I on either medial or plantar aspect of MT II."  Serrano-Brañas et al. state "in Garudimimus brevipes ... the attachment site is also placed in the same area as in Paraxenisaurus normalensis", but the feature in Garudimimus is a raised scar with sharp medial demarcation from the shaft.  As Middleton (2003) recognized, this scar is for the m. gastrocnemius, specifically the m. gastrocnemius pars medialis (Carrano and Hutchinson, 2002), and I'll note it's present even in Gallimimus which lacks pedal digit I (Osmolska et al., 1972: Plate XLIX Fig. 1b).  "Paraxenisaurus"'s groove is then more likely to be the m. flexor digitorum longus II tendon, which "passed through the ventral groove in its respective metatarsal to insert serially on each of the pedal phalanges" in e.g. Tyrannosaurus (Carrano and Hutchinson, 2002).  

Left metatarsal II in ventral view of (left to right) intended "Paraxenisaurus normalensis" holotype BENC 2/2-001 (after Serrano-Brañas et al., 2020; yellow arrow points to supposed articulation for metatarsal I), Garudimimus brevipes holotype IGM 100/13 (after Kobayashi and Barsbold, 2005; line points to supposed articulation for metatarsal I), Gallimimus bullatus ZPAL MgD-I/94 (after Osmolska et al., 1972), and Tyrannosaurus rex FMNH PR2081 (after Brochu, 2003).

What exactly is "Paraxenisaurus"?  Comparison is hindered by the specimens being figured mixed together, and the figures are not in numerical order in the preprint, being shown in the order of- 1, 10-19, 2, 20-23, 3-9.  In addition, the scale bars vary within the same figure (e.g. phalanx IV-1 is proximally ~61 mm wide in figure 14a but ~93 mm wide in figure 14e) and the listed measurements are different yet (e.g. IV-1 is listed as 83 mm wide).  Thus any composite reconstruction is necessarily approximate.  The supposed manual element is too fragmentary to give much information, but it is of the appropriate size and shape to be a proximal pedal phalanx I-1.  This would make more sense preservationally since the other material preserved in the specimen is all from the tarsus and pes.  It's a shame the astragalocalcaneum is not described better or figured in more views, as the dorsal (= proximal?) perspective has many broken surfaces and edges, so that e.g. the small calcaneum might be preservational.  The fused proximal tarsals are like ceratosaurs, deinocheirids (Deinocheirus plus Hexing), alvarezsaurids and caenagnathids.  Having any sense of the ascending process morphology could tell us much.  Metatarsal II is not obviously deeper than wide, unlike ornithomimosaurs (except Harpymimus; unreported in deinocheirids), but like carcharodontosaurids, therizinosauroids, some oviraptorids and velociraptorines.  The proximal outline of metatarsal III would at first glance appear to be the strangest thing about this material, being reconstructed as strictly dorsoventrally oval unlike all(?) other theropods.  Tilting it and adding a posterior tapered tip results in a close match to Majungasaurus however (see figure below).  If it is an unreduced proximal metatarsal III, tyrannosauroids, most ornithomimosaurs, alvarezsauroids and pennaraptorans would be excluded.  Proximal phalanx II-2 lacks a proximoventral heel, so is not from a deinonychosaur.  The pedal phalanges are too elongate to be therizinosauroid, and the pedal ungual is too broad.  Phalanges are not as dorsoventrally compressed as Mapusaurus, and as noted above they lack the ventrolateral shelves found in ornithomimosaurs.  Abelisaurid phalanges seem similar however.  I wonder if we have a case like Camarillasaurus or probably Dandakosaurus involving misidentified elements making the specimen seem stranger than it really was, with so many edges of supposed metatarsal III dotted to indicate incompleteness that it could actually be metatarsal II or IV.  Certainly nothing connects this specimen with Deinocheirus.  As per the numerous errors illustrated by Hartman et al. (2019) nobody should trust Choiniere et al.'s scorings in any case.  The Lori matrix recovers "Paraxenisaurus" as a ceratosaur closest to Aucasaurus as far as taxa with well preserved feet are concerned, but also doesn't include characters particular to ceratosaurs and isn't great with pedal characters in general.  So I would place the specimen as Neotheropoda incertae sedis (or even indet.) pending a better description of the tarsus and of the real bone surfaces on supposed proximal metatarsal III. 

Pes of "Paraxenisaurus normalensis" holotype (center) in dorsal view compared to Majungasaurus crenatissimus composite (left) and Deinocheirus mirificus referred specimen IGM 100/127 (right).  Colored proximal view of "Paraxenisaurus" is after Serrano-Brañas et al., with reoriented metatarsal III as per my interpretation shown above that.  Note "Paraxenisaurus" elements were scaled using their scale bars, whereas scaling to listed measurements results in different proportions, so those should be seen as approximate.  "Paraxenisaurus" after Serrano-Brañas et al. (2020), Majungasaurus after Carrano (2007) and Deinocheirus after Lee et al. (2014).

References- Osmólska, Roniewicz and Barsbold, 1972. A new dinosaur, Gallimimus bullatus n. gen., n. sp. (Ornithomimidae) from the Upper Cretaceous of Mongolia. Palaeontologica Polonica. 27, 103-143.
Carrano and Hutchinson, 2002. Pelvic and hindlimb musculature of Tyrannosaurus rex (Dinosauria: Theropoda). Journal of Morphology. 253, 207-228.

Brochu, 2003. Osteology of Tyrannosaurus rex: Insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. Society of Vertebrate Paleontology Memoir. 7, 138 pp.

Middleton, 2003. Morphology, evolution, and function of the avian hallux. PhD thesis, Brown University. 147 pp.

Carrano, 2007. The appendicular skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. In Sampson and Krause (eds.). Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. SVP Memoir 8, 164-179.

Lee, Barsbold, Currie, Kobayashi, Lee, Godefroit, Escuillie and Tsogtbaatar, 2014. Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus. Nature. 515, 257-260.

Kobayashi and Barsbold, 2005. Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia. Canadian Journal of Earth Sciences. 42(9), 1501-1521.

Claessens and Loewen, 2016 (online 2015). A redescription of Ornithomimus velox Marsh, 1890 (Dinosauria, Theropoda). Journal of Vertebrate Paleontology. 36(1), e1034593.

Hattori, 2016. Evolution of the hallux in non-avian theropod dinosaurs. Journal of Vertebrate Paleontology. 36(4), e1116995.

Hartman, Mortimer, Wahl, Lomax, Lippincott and Lovelace, 2019. A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ. 7:e7247.

Cau, 2020 online.

Serrano-Brañas, Espinosa-Chávez, Maccracken, Gutiérrez-Blando, de León-Dávila and Ventura, 2020. Paraxenisaurus normalensis, a large deinocheirid ornithomimosaur from the Cerro del Pueblo Formation (Upper Cretaceous), Coahuila, Mexico. Journal of South American Earth Sciences. 101, 102610.


  1. Random unrelated bits of likely indeterminate neotheropod? I'm impressed, that's some next level shit even for nowadays. Truly we live in the Second Bone Wars.

  2. "Paraxenisaurus" (scored uniquely from the type material) is currently the OTU the pruning of which most improves the resolution in my analysis.

  3. How did this survive peer review? This reminds me of Cope cobbling together "Monoclonius" based on various bones collected at several sites. How can it NOT be a chimaera?!

    1. It's not even the worst part of the paper. If you look at the characters used to justify placing "Paraxenisaurus" in Deinocheiridae, they are ones plesiomorphically present in most Mesozoic theropods and scored that way in the matrix-

      "In particular, within the Deinocheiridae family, Paraxenisaurus normalensis shares the following synapomorphies with Deinocheirus mirificus: [...] unenclosed lateral grooves of manual ungual I in ventral view [Char 421(0)], an astragalus with indistinct or poorly separated condyles [Char 530(0)], and a dorsoventrally thicker shaft of metatarsal IV in cross-section [Char 558(0)]."

      These don't even map to Deinocheiridae in the cladogram, so did the authors misread their tree?

  4. Why the authors concluded that Paraxenisaurus is actually a Deinocheirid.

    First off, we know Paraxenisaurus is an Ornithomimosaur and not a Therizinosaur because of the Metatarsal II and its anchor point for digit I. As it has a rather small digit I anchor point unlike Therizinosaurs which have a digit I that reaches the ground. Also if we see refered specimen BENC ½-0054 and its manual ungual I-2, at the base we see apart from the median keel, the flexor tubercle which presents striking similarities between Beishanlong, a member of Deinocheiridae, and doesn't ressemble in the slightest to any therizinosaur claw.
    By also looking at the caudal vertebrae of refered specimen BENC ½-0091 we can compare them to that of Therizinosaurs, and they share no resemblance at all. Paraxenisaurus' caudal vertebrae lack pneumatic phoramen, which are present in Therizinosaurs. Besides the overall pneumaticity of the vertebrae, Paraxenisaurus presents typical porous tissue, while Therizinosaurs present a highly pneumatic porous tissue.
    Secondly, we can know that Paraxenisaurus is actually a Deinocheirid from characteristic of the manual ungual I-2, and the metatarsals, pedal phalanges and pedal unguals. The metatarsals unlike ornithomimid ornithomimosaurs present the anchor point for a hallux, just like Beishanlong and Garudimimus, both Deinocheirid ornithomimosaurs (Deinocheirus does not have this characteristic as it is a much more derived form of deinocheiridae).

    1. Now, you could make the argument that the metatarsals of Paraxenisaurus share the same characteristics with Tyrannosaurids and some Tyrannosauroids but here is where the pedal phalanges and unguals come to play.
      The pedal phalanges of Paraxenisaurus show us a pedal morphology that is unlike ornithomimid ornithomimosaurs yet again, which is for supporting massive weight and not exactly designed for running, once again comparable with the ones of Beishanlong, a Deinocheirid ornithomimosaur.
      There are other morphological differences in the pedal phalanges of Paraxenisaurus that are also different compared to those seen in Tyrannosauridae and Tyrannosauroidea, but which are shared among Ornithomimosauria. Paraxenisaurus has gently arched pedal phalanges with flattened dorsal surfaces and projecting ventral processes in proximal view, as well as shortened pedal phalanges in digit IV. In contrast, the pedal phalanges seen in tyrannosaurids and some tyrannosauroids are mediolaterally pinched, lack the proximally projecting processes and are more elongated.
      And the time frame frame and geographic position also helps us identifying its true identity. It is very unlikely for it to be a basal Ornithomimosaurs, like Andrea Cau suggested, as he said that ii would be closely related to Nqwebasaurus, a basal Ornithomimosaur from Africa that lived 145 - 140 million years ago, when Paraxenisaurus lived 72 million years ago in what is now Mexico, which was at the time part of southern Laramidia. There was never any connection between Africa and Mexico at any point in the Cretaceous. If anything, the existence of Paraxenisaurus as a Deinocheirid further supports the idea of a faunal exchange between Asia and North America in the Cretaceous period. As Therizinosaurs, which originated in North America and then went and populated Asia, and Ceratopsians and Tyrannosaurs, which originated in Asia and went to North America.

    2. And lastly, for the claims that it is a chimeric dinosaur.
      There is the Holotype:
      BENC 2/2–001, and preserves Partial manual phalanx II-2 or III-3, 40 Partial astragalus, Partial calcaneum, Partial metatarsal II, Proximal end metatarsal III, Distal end metatarsal III, Partial metatarsal IV , Pedal phalanx II-1, Partial pedal phalanx II-2, Partial pedal phalanx III-3, Pedal phalanx IV-1, Pedal phalanx IV-3, Pedal phalanx IV-4, and Pedal ungual IV-5.
      Then there are four refered specimens:
      Specimen BENC ½-0054, which preserves Partial metacarpal I, Partial metacarpal II, Partial phalanx I-1, Partial phalanx II-2 and Partial manual ungual I-2.
      Specimen BENC ½-0091, Partial metacarpal II, Proximal end metacarpal III, Distal end metacarpal III, Partial anterior caudal vertebra (centrum), Anterior caudal vertebra (centrum), Anterior caudal vertebra (centrum), Anterior caudal vertebra (centrum), Partial femur and Partial metatarsal IV
      Specimen BENC ½-0092, Posterior caudal vertebra and Posterior caudal vertebra.
      Specimen BENC 30/2–001, Pedal ungual II-3 and Pedal ungual III-4.
      Why were these specimens collected and described together? Well, all of these remains are from the Cerro del Pueblo formation in Mexico, which dates to 72 million years ago. In the Cerro del Pueblo formation there have been countless reports of Ornithomimosaurs throughout the years, from the nomen nudum "Saltillomimus rapidus" to other typical Ornithomimid Ornithomimosaurs. Although BENC 2/2–001, BENC ½-0054, Specimen BENC ½-0091, Specimen BENC ½-0092 and Specimen BENC 30/2–001 were the exception. These specimens were unlike the slim and graceful individuals recollected throughout the Cerro del Pueblo formation, these were big and robust remains. It is much more likely that these remains belonged to one species of giant Ornithomimosaur rather than several giant Ornithomimosaurs sharing the same ecosystem plus coexisting with the smaller Ornithomimids and Hadrosaurs from the formation, like Velafrons and Latirhinus.
      I hope explained myself thoroughly, and hoped to clear that issue on the matter.
      Thus concluding that Paraxenisaurus is a Deinocheirid.

      Thank you for reading.

      Claudia Inés Serrano-Brañas, Belinda Espinosa-Chávez, S. Augusta Maccracken, Cirene Gutiérrez-Blando, Claudio de León-Dávila, José Flores Ventura (2020).
      Paraxenisaurus normalensis , a large deinocheirid ornithomimosaur from the Cerro del Pueblo Formation (Upper Cretaceous), Coahuila, Mexico. Journal of South American Earth Sciences 102610: doi: 10.1016 / j.jsames.2020.102610

      Hedrick, B. P., Zanno, L. E., Wolfe, D. G. & Dodson, P. The slothful claw: osteology and taphonomy of Nothronychus mckinley i and
      N. graffami (Dinosauria: Theropoda) and anatomical considerations for derived therizinosaurids. PloS one 10, e0129449 (2015)

      Choiniere, J. N., Forster, C. A. & de Klerk, W. J. New information on Nqwebasaurus thwazi, a coelurosaurian theropod from the Early Cretaceous Kirkwood Formation in South Africa. J. Afr. Earth Sci. 71–72, 1–17. https :// arsci
      .2012.05.005 (2012).

      H. E., R., & K., C. (2014). Dinosaurs and Other Reptiles from the Mesozoic of Mexico. Erscheinungsort nicht ermittelbar: Indiana University Press.
      Cau, A., PhD. (2020, April 26).

      Paraxenisaurus: Un deinocheiride messicano? Retrieved September 16, 2020, from
      Mortimer, M. (2020, July 24). The Arguable Identity of Paraxenisaurus. Retrieved September 16, 2020, from

    3. Hi. Thanks for the detailed comment.

      First, I agree with the paper that the paratypes are all ornithomimosaurs, although I think a couple elements are misidentified.

      Second, I agree the holotype is not a therizinosauroid, as I wrote "The pedal phalanges are too elongate to be therizinosauroid, and the pedal ungual is too broad." And if proximal metatarsal III is correctly identified, it's not a tyrannosauroid since it is unreduced.

      But, I don't see any reason the holotype is an ornithomimosaur. The shape of proximal metatarsal III is unlike even Deinocheirus, where it is narrow in the middle and concave laterally, but is like Majungasaurus as I showed above. Also the holotype pedal ungual is not like 30/2-001 or other ornithomimosaurs (e.g. McFeeters et al., 2018), being broad and not having the proximoventral spurs.

      So why couldn't the holotype be an abelisaur? They are big and robust, have small pedal digits I, distally shortened phalanges on pedal digit IV, etc., and match the time period. The only real problem is being in North America, but Mexico was close to South America and likely separated only by a couple series of small islands (, Mexican Labocania is like carcharodontosaurs, North American alvarezsaurids may be phylogetically intermediate between South American and Asian ones (Hartman et al., 2019), and titanosaurs like Alamosaurus are only found in the southern part of North America so may be from South America.

      If you're a coauthor of the Paraxenisaurus description, would you be able to send me additional images of the astragalocalcaneum?

    4. H. E., R., & K., C. (2014). Dinosaurs and Other Reptiles from the Mesozoic of Mexico. Erscheinungsort nicht ermittelbar: Indiana University Press.

      That part in the middle is German, funnily enough, and means "place of publication indeterminable".

      ...which is of course wrong, and I honestly have no clue why anybody cares. The time when it made sense to say that a book was published in one particular place ended several decades ago.

    5. Thank you David Marjanović, for pointing out an oversight in my references, I thought for a moment you would add something to this debate or maybe point out a flaw in my conclusions or ask a question, but no.

  5. Hello Mickey Mortimer,
    I'm glad you took time out of your day to respond to my comment, I am grateful for your feedback and for encouraging scientific discourse regarding this rather controversial specimen.
    Sorry for not responding any earlier, I had forgotten I had commented and hadn't seen your response. I will soon be posting my response to it being an Abelisaur, as recent evidence regarding Paraxenisaurus has been brought to light in a recent interview with some of the Authors of the description.

    1. Ms. Mortimer, I would encourage you to write a scientific article to bring all of this controversy to the authors attention, as they could reply with an actual response as authors of the Paraxenisaurus description. Regarding the astragalocalcaneum, I am not a coauthor, if I were, I would’ve done things very differently regarding the description, and sadly I was not able to find more photos of the astragalocalcaneum. Although I belive Thomas Holtz, theropod expert said there were no errors with the identifications of the animal, as he even shared the article on FaceBook and even congratulated Ms. Serrano-Brañas on the incredible discovery.

  6. Claims regarding Paraxenisaurus being an Abelisaurid.

    In the Cerro del Pueblo formation it would be rather implausible to see both Abelisaurids and Tyrannosaurids coexisting without any problems for the ecological niche. As both would be competing for the same ecological niche of big carnivorous predators. In fact, there has been a lot of Tyrannosaurid and Tyrannosauroid remains uncovered, such as teeth, claws, phalanges and much more, and yet no evidence so far of any Abelisaur remains, not even teeth. [1]

    1. Paraxenisaurus’ unguals do not share characteristics with those of Abelisaurids, as they are not as curved as you would expect in a solely carnivorous nor are congruent with the idea for it to be an Abelisaur. For example, the proximodorsal process of Paraxenisaurus holotype’s ungual claw (BENC 2 /2–001) is not even similar to the proximodorsal process of Abelisaurs, for example ( We can clearly see that this Abelisaurids proximodorsal process is lowered/downturned in lateral view, while Paraxenisaurus’ proximodorsal process is lifted/upturned in lateral view. It is also quite distinct from that of Paraxenisaurus in dorsal view. Compare the proximal part of the ungual of both Paraxenisaurus and any Abelisaurid, and lastly it is asymmetrical in proximal view, giving it yet again a distinct shape than that of Paraxenisaurus. [2] [3] [4]

    2. For the Semi-ginglymoid articulation of the distal end of metatarsal III we can see striking similarities with other Ornithomimosaurs, such as the other Mexican Ornithomimosaur Tototlmimus packardensis (, or better yet, Deinocheirid Ornithomimosaurs, such as Beishanlong ( and Garudimimus ( See Figure 15). We can see the similarities in the shape of the distal end of Metatarsal III and the Semi-ginlymoid articulation as seen in Paraxenisaurus. Now to comparing the distal end of metatarsal III of the abelisaurid Majungasaurus ( to that of Paraxenisaurus, they do not share similar looking Semi-ginglymoid articulations. Using these as evidence suggests that Paraxenisaurus was not an Abelisaurid, but more likely a Ornithomimosaur, quite possibly, a deinocheirid, because of the appearance of the hallux anchor point in metatarsal II. [3] [4] [5] [6] [7]

    3. A new detail added to the Paraxenisaurus dilemma was that on December 7th, 2020. Claudia Inés Serrano-Brañas, main author of the description of Paraxenisaurus, gave a speech about the Cerro del Pueblo formation, and in a segment, talking about Paraxenisaurus normalensis itself. She mentioned that the Holotype, as well as the paratypes all were found in the same type of environment. Giving her a reason to think that all of the referred specimens belonged to the same species. A heavily built, bulky, non-graceful, Ornithomimosaur that presents deinocheirid like characteristics (stiff distal end of the tail (referred specimen BENC ½-0092), manual ungual I-2 which presents at the base apart from the median keel, the flexor tubercle with sulcus, producing 2 grooves which present striking similarities with the deinocheirid Beishanlong (referred specimen BENC ½-0054), Metatarsal II with it’s anchor point for the hallux and metatarsal III which as discussed above, looks much more like an ornithomimosaur metatarsal than an Abelisaur (Holotype BENC 2 /2–001), plus other fragments and bones suggesting a similar body plan of a heavyweight deinocheirid ornithomimosaur) living in the same environment. [8]


    4. Presenting said evidence indicates a high likelihood of all of these specimens (BENC 2/2–001, BENC ½-0054, BENC ½-0091, BENC ½-0092, BENC 30/2–001) belonging to the same genus and species of Ornithomimosaur dinosaur, as all remains were found in the same environment and suggest a similar, if not the same animal.

      I hope you had a pleasant read and thank you for taking your time reading this. I hope I explained myself thoroughly, and hoped to clear that issue on the matter, again.

      Thus concluding that Paraxenisaurus is a Deinocheirid.


      [1] H. E., R., & K., C. (2014). Dinosaurs and Other Reptiles from the Mesozoic of Mexico. Erscheinungsort nicht ermittelbar: Indiana University Press.
      Cau, A., PhD. (2020, April 26).

      [2] Maganuco, Simone & Cau, Andrea & Pasini, Giovanni. (2008). New information on the abelisaurid pedal elements from the Late Cretaceous of NW Madagascar (Mahajanga Basin).. Atti della Società Italiana di Scienze Naturali e del Museo Civico di Storia Naturale in Milano. 149. 239-252.

      [3] New information on the abelisaurid pedal elements from the Late Cretaceous of NW Madagascar (Mahajanga Basin). - Scientific Figure on ResearchGate. Available from: [accessed 23 Dec, 2020]

      [4] Carrano, Matthew. (2007). The appendicular skeleton of Majungasaurus crenatissimus (Theropoda: Abelisauridae) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology. 27. 163-179. 10.1671/0272-4634(2007)27[163:TASOMC]2.0.CO;2.

      [5] Kobayashi, Yoshitsugu & Barsbold, Rinchen. (2011). Reexamination of a primitive ornithomimosaur, Garudimimus brevipes Barsbold, 1981 (Dinosauria: Theropoda), from the Late Cretaceous of Mongolia. Canadian Journal of Earth Sciences. 42. 10.1139/e05-044.

      [6] Tsogtbaatar Chinzorig, Yoshitsugu Kobayashi, Khishigjav Tsogtbaatar, Philip J. Currie, Mahito Watabe, and Rinchen Barsbold. 2017/12/01. First Ornithomimid (Theropoda, Ornithomimosauria) from the Upper Cretaceous Djadokhta Formation of Tögrögiin Shiree, Mongolia 10.1038/s41598-017-05272-6

      [7] Makovicky Peter J., Li Daqing, Gao Ke-Qin, Lewin Matthew, Erickson Gregory M. and Norell Mark A. 2010A giant ornithomimosaur from the Early Cretaceous of ChinaProc. R. Soc. B.277191–198

      [8] Serrano Brañas, C. I., 2020. “La Formación Del Cerro Del Pueblo: Un Extraordinario Ecosistema Ancestral.” December 7th, 2020.

      Mortimer, M. (2020, December 23). The Arguable Identity of Paraxenisaurus. Retrieved December 23, 2020 from