What did Spinosaurus Look Like Part 2: Short Arms?

Originally, I came to the conclusion that Spinosaurus would've been a quadruped. This was due to the fact that Spinosaurus had long arms but short claws that were not robust, trace fossils of theropod arm and hand marks, and I kept getting a large center of mass for the animal. However, I noticed a pattern regarding a spinosauroid manual ungual from Ibrahim et al., (2020a) and the reconstructed Spinosaurus arm from DinoLab a few years back. It led me to a new possibility: Spinosaurus probably had short arms! If Spinosaurus was bipedal, then this is probably the best hypothesis to make it so.

I've learned over time to let go of my biases in order to get to the truth of a particular matter. It's been a gradual process with Spinosaurus, but it's better late than never. Let's suppose that Spinosaurus wasn't a quadruped. Let's agree that Spinosaurus' arms weren't capable of supporting its weight. Suppose that it's center of mass was shorter than its femoral length, allowing it to be a biped. These conclusions came from Sereno et al., (2022). However, we're also going to add Ibrahim et al., (2020a) and the reconstructed arm from DinoLab into the equation. Sereno et al., (2022) showed that about 90% of the arm for the reconstructed skeleton is a composite (then again, the whole skeleton is a composite). Only one phalange, and one manual ungual, came from the neotype. The phalange belongs on the second finger (Sereno et al., 2022) (Fabbri et al., 2022). The manual ungual is on the third digit, and it is very small (Fabbri et al., 2022). The phalange is elongated and skinny (Sereno et al., 2022) (Fabbri et al., 2022), just like the phalanges on the reconstructed arm from DinoLab. So far, so good! I also noted that, in my original post announcement about the DinoLab arm, I stated that the arm looked smaller than the arms on the reconstructed skeleton made by Ibrahim, Sereno, and co. It should be noted that the metacarpals (not shown), phalanges, and the radius and ulna (they are partially complete), are real material. The humerus is a "cast"/"articulated." There is also some criticism towards the third finger being way too long, but it's not conclusive. This comes from DinoLab on their Facebook post, and Paleontologist Roberto Diaz Sibaja from Facebook as well. Terry from DinoLab said that some paleontologists have verified the bones (that are real) to be conclusive (Facebook), so we seem to be on the right path here. I will also ignore the radius from Goo (2022) for now. 

DinoLab Spinosaurus arm (Facebook, 2021):

Compare the claws to the spinosauroid claw (NMC 41820) from Ibrahim et al., (2020a) (Figure 111A-B):

Full figure. Scale bar is 5 cm:

Description of NMC 41820 (Ibrahim et al., 2020a, Theropoda: Manual ungual morphotype 1):

Information on Spinosaurus arm from DinoLab (Facebook, 2021):

Another pic of the DinoLab arm (The Zone @91-3, 2021):

Pics of DinoLab arm from Twitter-X (2020):
First:

Second (Notice that the arm looks smaller here):

Spinosaurus' skeletal design by Sereno et al., (2022) (Figure 1). The neotype's bones are blue. The phalange in D is not from the neotype though. It's from the first digit, not the second. Scale bar for D is 3 cm:

Spinosaurus skeleton from Fabbri et al., (2022) (Figure 1). The red bones are from the neotype:

Close up of the hand. You can see phalange 2-1, and manual ungual 3, in red:

So in total, we have a Spinosaurus arm that consists of a (probable) small and stocky radius and ulna, slender manual phalanges, and small manual unguals that were not recurved as typically seen in the other spinosauroids like the baryonychinae. The humerus is unknown, but we can speculate that it was probably smaller than the one from DinoLab and shaped more akin to a baryonychinae. Taking all of this into account, one could speculate that Spinosaurus' arms were probably shorter than typically reconstructed. I would imagine that Spinosaurus could've taken the tyrannosaurid and carcharodontosaurid route: Evolve larger skulls that replaced the necessity to have long arms. In return, the forelimbs would be reduced in size. 

This is, by no means, the final say in the matter. There is something strange with the arms of Spinosaurus, which leads me to believe that they were probably not very useful to the animal in life. There are other factors that still go against a strictly bipedal Spinosaurus (see part 1 of this series). Until more bones are discovered (hopefully from the neotype specimen), I'll say that Spinosaurus could've been quadrupedal IF it had long arms. I can't see Spinosaurus dragging is arms across the ground while being bipedal. If it had short arms, then I will say that Spinosaurus was bipedal. 

Links:
Part 1:
https://psdinosaurs.blogspot.com/2023/03/what-did-spinosaurus-look-like-part-1.html
Ibrahim et al., (2020a):
https://zookeys.pensoft.net/article/47517/element/7/0/deltadromeus/
DinoLab:
1.) Instagram (Gramho):
https://gramho.com/media/2535465340537444071
2.) Facebook:
https://m.facebook.com/dinolabinc/posts/our-spinosaurus-arm-is-still-on-display-we-arent-sure-how-much-longer-we-are-goi/885524165571071/
3.) Twitter-X:
https://mobile.twitter.com/DinoLab_Inc/status/1322305140020269058
4.) The Zone @91-3:
-Photo:
https://images.app.goo.gl/FYeo7rjhQr6cPLja7
-Website:
https://www.thezone.fm/2020/09/02/geekout-dino-lab-spino-arm/
Sereno et al., (2022):
https://www.biorxiv.org/content/10.1101/2022.05.25.493395v1.full
Fabbri et al., (2022):
https://www.nature.com/articles/s41586-022-04528-0.epdf?sharing_token=rxUUwyZxDWQ24dJfwtIw89RgN0jAjWel9jnR3ZoTv0NEFj8DFZa3bazFWKdXldNTvT8T3daJQzYMUbPXaqso6c2KKBgthBeOpsV72_JOZHeSlOxZzzE9wUggHYItKT5ASyn5r0hTiRPfCQi_Cfe9RPf0tvCNFd3T4QXE2UU4r7wR-SYYL4_TSvBiBpniofeQoStgnv6yWzzkL81Gcy2g6hKT9nO8ozsufeY9DwX1VK-Vsw94pFBHTtBWnm2-q0bJ33Xx2cPSUh5t7T-nx3NDvtkT9MSkWBYPTw7aqWM5FRs%3D&tracking_referrer=www.sciencenews.org
Mr. Sibaja (Palaeos):
1.) Facebook Post:
https://m.facebook.com/PalaeosPag/photos/a.157631294723661/1059058504580931
2.) Blog:
https://palaeos-blog.blogspot.com/?m=0