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There is such a long time I don't do one of this, but here it goes... a little text on everyone favorite drama series "Spinodrma". Note this was wrote for discord, I am just adapting and posting it here because it ended up too big there. I know I should have done a better job referencing the papers quote during the text, but this took me five hours and a bit more just for formatting from Deviant Art.

The Two Kem-Kem Spinosaurids

This part of the journal contains a summary of the argumentation and conclusion, complemented with some personal comments, to the presence of a second spinosaurid in the Kem Kem beds.

Rostra

Out of the characters distinguishing the rostral morphotypes, only “ventral premaxillary profile in lateral view” is kinda good, it has decent states, but is affected by distortion. The others are not totally bad characters, however they have poorly differentiated states and are affected by the taphonomical distortion and crushing of morph-B rostrum. The nares character is actually bad since it is based on a specific shape difference of a small feature; its states are not that differentiable thus it probably is not phylogenetically informative.

I would also like to note that when commenting on the same topic with the Kem-Kem monograph data I was not sure about the rostra state as it was very briefly discussed. This provides a more comprehensive discussion on the topic, the Not-Spinosaurus rostrum that I talked about there is not the same Not-Spinosaurus rostrum here. The one in the monograph is from Niger and the one in Lakin and Longrich, 2019 is from Morocco.

Frontals

Even if the discussion in the new paper is more comprehensive, I actually do prefer the discussion presented in the monograph as it is more objective. The rest of this topic is an adapted version of the previous text.

There are two Not-Spinosaurus frontals.

• The first one (Arden et al., 2019, Fig2) is proposed in the monograph to be a frontoparietal, said to be clearly not a spinosaurid, proposed to resemble the condition present in a marine crocodyliform. The parietal portion is long and has an expansive supratemporal fossa while spinosaurids like Baryonyx, Suchomimus and Irritator have short parietals and small supratemporal fossa.

• The second one (Arden et al., 2019, Fig3) is proposed to be a carcharodontosaurid in the monograph, while proposed to be either a carcharodontosaurid or an abelisaurid in the taxonomy paper based on its ratios. The frontals are described as broad, having a marked median crest and lacking a deep embayment on each side for the prefrontals. In the monograph, it is said to be an “unusual” condition for spinosaurids, however the usual spinosaurid condition is not made explicit nor why this specimen better fits a carcharodontosaurid, this information, once more, isn't clear in the taxonomy paper.

There is a huge text on sexual/ontogenetic variation explaining the different ratios if the second frontal is actually a spinosaurid, I do think it was a good idea to present this discussion even if I don’t think it is super relevant because the identity of this frontal is not conclusive. Its most notable point refers to the projection of the orbit being highly variable in semi-aquatic taxa as corcs and hippos, the projection of the orbit is something related to acquisition to semi-aquatic habits, therefore such comparison is valid for explaining the variability.

However, the part regarding size variation and sexual dimorphism across semi-aquatic animals is not as good, as those factors quite variable on modern species across multiple groups and there is no reason to believe semi-aquatic habit has to do with acquisition of sexual dimorphism. They should have sticked with just the theropod comparison part and argue it is cause by individual dimorphism, as detection of sexual dimorphism in dinosaurs is something very tenuous.

The conclusion that the differences of the specimens being regular variation within a single taxon presented in the new paper is not that good because there is no guideline for how different they would need to be to represent distinct taxa. In my opinion the frontal with questionable spinosaurid identity should not be used in Spinosaurus taxonomical discussions, as we are not certain if it is one. The question if it is Spinosaurus aegyptiacus or another spinosaurid should only be addressed if it actually gets confirmed to be a spinosaurid.

Quadrates

The Not-Spinosaurus quadrate is indeed distinct from Spinosaurus aegyptiacus quadrate and has some unambiguous spinosaurid synapomorphies. In addition, it has traits suggesting a condition possibly similar to Irritator's (plesiomorphic or apomorphic nature of those is unknown). Only a third of the original bone is preserved so they are not sure if this is variation is significant, as quadrates outside Kem-Kem are poorly sampled. This is by far the best evidence for a second taxon, but the fragmented nature of a single element is understandable that they decide it alone is not unambiguous evidence for a second taxon in the area. I am not sure if this specimen was referred to Spinosaurus aegyptiacus by this paper but IMO it should be treated as Spinosauridae indet.

Teeth

I am getting quite tiered, so let’s make this simple EVERYONE ALREADY KNOW TEETH ARE NOT GOOD TO DIAGNOSIS LOWER LEVELS OF DINOSAURS TAXONOMY. Overall conclusion by the authors is that differences in isolated teeth can be due to different positions on the tooth row, and because the cause of the subtle differences is unknown they should not be used for taxonomical differentiation between individual species.

Vertebrae or Sigilmassasaurus autapomorphies

1. Centroprezygapophyseal fossa – The vertebrae used for treating this as a distinguishing feature are from a different part of the cervical series. As there is significant change in cervical and anterior dorsal morphology on spinosaurids, exemplified by Suchomimus complete cervico-dorsal series, it is reasonable to treat this as variation across difference cervical elements and not between different species. In addition, two specimens 6th cervicals have identical morphology and one has almost no fossa and the other having a well-developed one, so it seems to be something variable across different individuals. If that wasn't enough, this feature varies within a single specimen, being more/less developed across left or right side of the same vertebra. It is an excessively dynamic feature to be used as an autapomorphy of mid-cretaceous spinosaurids.

2. Epipophyses – This is also a transitional feature across the cervical series, in addition to the “overhanging” condition being stated as a misinterpretation by Arden et al., 2015.

3. Neural spines – The cervicals used for this distinction are not from the same part of the axial series, the differences in those are probably due to their different position in the sequence, as common in basal-Tetanurae. In addition, the difference is exacerbated based on preservation artifacts in one of these specimens, proven by a better-preserved specimen.

4. Ventral rugose platform – As everyone know by this point this is also argued to be something variable across the cervical series of Spinosaurus and not something diagnostic of two different spinosaurid taxa.

The state of Oxalaia

The new paper also discuss the status of this taxon, reevaluating all its autapomorphies. The three rejected by Sales and Schultz, 2017 are also considered invalid autapomorphies here as they are shared with other spinosaurids. The two autapomorphies considered to be valid in 2017, the sculpted premaxillae and the tooth replacement one, are considered to be valid and too trivial respectively. This lefts Oxalaia with a single autapomorphy, not enough for validating taxonomic distinction, this leading Oxalaia quilombensis being lumped into Spinosaurus aegyptiacus.

However, my conclusion differs from the authors, as “too trivial” alone is not a good argument and a more detailed explanation on the reason for disregarding this feature would be neat. On the other hand, autapomorphies are not the single thing used for a diagnosis a. Using only the data from the ex-autapomorphies O.quilombensis does have a unique combination of characters (here UCC) not seen in other spinosaurids (one of those being its autapomorphy). More so, there is nothing clear to suggest it is Spinosaurus aegyptiacus, besides probably the character that supported sister relationship between MSNM V4047 and Oxalaia's type in Sales and Schultz, 2017. So if they consider it diagnosable as a unique taxonomical unity and do not provide shared characteristics to connect this specimen to S.aegyptiacus it should be Spinosaurinae indet. instead of getting lumped.

A phylogenetic analysis to test Oxalaia position would also be welcome, based on the recognition that the tooth replacement character being shared with Irritator/Angaturama. I also would note that the Gara Samani specimen believed to be Albian in age, older than the proposed age for Oxalaia, was recovered by Arden et al., 2019 as more related to S.aegyptiacus sensu Ibrahim than Oxalaia was to S.aegyptiacus, meaning S.aegyptiacus would have an uncommonly longer time range compared to other dinosaurs or it is being over-lumped.

Considering the fragmentary nature of O.quilombensis, it having a UCC and possible cladogenetic difference from S.aegyptiacus two paths can be taken: A – it is just Spinosaurinae indet. or B – it is its own unique taxonomical unity. I will stick to the same nomenclature I am using for the last years with this specimen being Spinosaurus quilombensis. Further research and new material may suggest a full lump of S.quilomebnsis into S.aegyptiacus or a “resurrection” of Oxalaia.

• Oxalaia’s UCC = “anterior projection of the maxillae between the premaxillae in the palatal region is very thin” + “possession of two replacement teeth associated with functional pm3” + “sculptured condition of the premaxillae”

Minor comments

• Everything argued on the Sigilmassasaurus case will probably be addressed by Evers and his group, as himself already mentioned disagreeing with something discussed in the monograph.

• Even if I provisionally agree with Ibrahim’s group conclusion on the taxonomy of Kem-Kem spinosaurids, the overall taxonomy of multiple theropods of North Africa and Northwest Brazil needs further study. Radioisotopic dating would be helpful; if Kem-Kem, Bahariya, Echkar and Alcântara could be precisely dated it would give and an exact time frame for the evolution of the proposed differences of their native. If they are all contemporaneous or if those different were to show up in different points and different populations, that meaning probably having taxonomical significance.

Summary of the paper

• Rostra -> differences probably related to distortion and crushing of morph-B

• Frontals -> messier, one stated to not be a spinosaurid with certainty in the monograph and the other having a questionable spinosaurid identity so they should not be used in the lower level taxonomical discussion.

• Quadrates -> there seems to be a specimen distinct from Spinosaurus aegyptiacus, but its fragmented nature is not enough to suggest a second taxon.

• Teeth -> differences may be related to different positions ontogeny, poor data overall makes use of teeth questionable for lower level taxonomy.

• Vertebrae -> autapomorphies poorly based on highly variable features, comparison of different vertebrae in the cervical series known to be variable in Spinosauridae or taphonomical distortions.

• Oxalaia -> has a single autapomorphy, not enough for recognition of a distinction, lumped into Spinosaurus aegyptiacus.

My conclusions:

• There may be a second Kem-Kem spinosaurid, there is no reason objecting its existence, but currently there is no specimen unambiguously support its existence. Everything about the different morphotypes is discussed in detail in the taxonomy paper, most had a good reason to be questioned and denied, except the quadrate (best evidence for a second taxon in the area).

• Sigilmassasaurus has a fragile diagnosis based on highly variable cervical features, others derived from possible misinterpretation of specific cervical elements position and distortion of certain features. I feel like the burden of prove is on Sigilmassasaurus defenders on why this difference would be valid and not explained by the reasons Ibrahim’s group proposes.

• Oxalaia's diagnosis suffered a heavy damage since its description. It still seems to have an UCC but its fragmented nature hampers its taxonomical distinction, and no good argumentation is provided for the lump into S.aegyptiacus proper. It should be considered either a distinct valid taxonomical unity or spinosaurinae indet. I’ll stick with my S.quilombensis.

Waaaay too much text and I hope formatation does not go to hell ... and of course it did.

Also noting I'm not a theropod person much less an expect, this post is not intended on being something to be taken too seriously for Spinodrama resolution, it is intended on being a summary of Smytha, Ibrahim and Martilla, 2020 and the other recent papers on North African Cenomanian spinosaurids that you can link to a friend that wants a general summary about this situation. Of course as I spend time reading the papers I took some conclusions that are added as commentary on their specific point and redressed in my conclusions.

Once more I'll state that this was made to be a Discord comment, a big one, but still a comment and not a "blog-post" as it was adapted here. That means I did not note all references I may be quoting here, the main papers addressed are present in the ref. list below.

Reference list:

Arden, Thomas MS, et al. "Aquatic adaptation in the skull of carnivorous dinosaurs (Theropoda: Spinosauridae) and the evolution of aquatic habits in spinosaurids." Cretaceous Research 93 (2019): 275-284.

Evers, Serjoscha W., et al. "A reappraisal of the morphology and systematic position of the theropod dinosaur Sigilmassasaurus from the “middle” Cretaceous of Morocco." PeerJ 3 (2015): e1323.

Ibrahim, Nizar, et al. "Geology and paleontology of the Upper Cretaceous Kem Kem Group of eastern Morocco." ZooKeys 928 (2020): 1.

Ibrahim, Nizar, et al. "Tail-propelled aquatic locomotion in a theropod dinosaur." Nature (2020): 1-4.

Lakin, Rebecca J., and Nicholas R. Longrich. "Juvenile spinosaurs (Theropoda: Spinosauridae) from the middle Cretaceous of Morocco and implications for spinosaur ecology." Cretaceous Research 93 (2019): 129-142.

Sales, Marcos AF, and Cesar L. Schultz. "Spinosaur taxonomy and evolution of craniodental features: Evidence from Brazil." PloS one 12.11 (2017).

Smyth, Robert SH, Nizar Ibrahim, and David M. Martill. "Sigilmassasaurus is Spinosaurus: a reappraisal of African spinosaurines." Cretaceous Research (2020): 104520.

Edits:

May 31st, 2020 - added couple other references, corrections on the text, italicized all scientific names that previously were not, minor work on text format without any significant changes to its content.