Currently, the temporal range of the Spinosauridae is commonly thought to be restricted to the Late Jurassic-Late Cretaceous. The earliest definite spinosaurid is Ostafrikasaurus crassiserratus from the Upper Dinosaur Member of the Tendaguru Formation in Tanzania. The Upper Dinosaur Member dates to the Upper Tithonian of the Late Jurassic (c. 148-145 Ma). The latest members of the clade are Oxalaia quilombensis from the Alcântara Formation of Brazil, Spinosaurus aegyptiacus from the Bahariya Formation of Egypt, and possibly Sigilmassasaurus brevicollus from the Kem Kem Compound Assemblage of Morocco. All of these formations date to the Lower Cenomanian of the Late Cretaceous (c. 100-97 Ma). However, more recent finds show that spinosaurids both originated earlier and became extinct later than previously thought.

MUPE HB-87



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Specimen MUPE HB-87, a possible spinosaurid tooth. Image courtesy of Serrano-Martinez et al. 2015.

In their 2015 paper “Isolated teeth from the Middle Jurassic of Niger and the early dental evolution of the Spinosauridae”, Serrano-Martinez et al. described four theropod teeth from the “Argiles de l’Irhazer” unit of the Irhazer Group of Niger. These four teeth were found associated with the holotype of the sauropod Spinophorosaurus (a taxon discussed more here). Three of the teeth, specimens MUPE HB-142, MUPE HB-118, and MUPE HB-125, were found to likely belong to an afrovenatorine megalosaurid (possibly Afrovenator from the overlying Tiourarén Formation). However, a fourth tooth, MUPE HB-87 was found to fall within spinosaurid morphospace. Serrano-Martinez et al. noted that this tooth showed characteristics of both megalosaurids and spinosaurids, marking it as a transitional form. The “Argiles de l’Irhazer” has been tentatively dated to the Bajocian-Bathonian of the Middle Jurassic (c. 170-166 Ma), which means MUPE HB-87 predates Ostafrikasaurus by over 20 million years. This new evidence pushes back the date of the emergence of the Spinosauridae, and supports a probable African origin for the group.

XMDFEC V0010



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A likely baryonychine spinosaurid tooth, specimen XMDFEC V0010. Scale bar equals 1 cm. Image courtesy of Hone et al. 2010.

Hone et al. reported the presence of a spinosaurid from the middle unit of the Majiacun Formation of China in their 2010 paper “A probable baryonychine (Theropoda: Spinosauridae) tooth from the Upper Cretaceous of Henan Province, China”. They determined that specimen XMDFEC V0010, a single tooth, belonged to a baryonychine spinosaur. This is the first occurrence of the Baryonychinae in Asia, and the first Late Cretaceous member of the clade. The middle unit of the Majiacun Formation has been dated to the Middle Santonian (c. 85 Ma), additionally making XMDFEC V0010 the latest known spinosaurid. The Spinosauridae were previously thought to have gone extinct due to the rise in sea levels and climate change during the Cenomanian-Turonian transition. It now appears that at least some members survived beyond this point. With the exception of possible spinosaur remains from the Maastrichtian Maevarano Formation of Madagascar, XMDFEC V0010 marks the last occurrence of spinosaurids in the fossil record.

Conclusion

Although the the temporal range of the Spinosauridae has before been Tithonian-Cenomanian (148-97 Ma), the discovery of specimens MUPE HB-87 and XMDFEC V0010 demonstrate otherwise. It should instead be extended by nearly 30 million years to Bajocian-Santonian (170-85 Ma). These fossils give tantalizing clues to both the origin and extinction of the spinosaurids. Future finds may indicate an even longer existence for this enigmatic theropod clade.

References

Hone, D.W.E., Xu, X. & Wang, D. (2010). A probable baryonychine (Theropoda: Spinosauridae) tooth from the Upper Cretaceous of Henan Province, China. Vertebrata PalAsiatica 48, 19-26.

9/17/2016

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