| Iberospinus | |
|---|---|
 | |
| Skeletal diagram of the relatedBaryonyx, showing the known bones ofIberospinus in red (Scott Hartman) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Spinosauridae |
| Genus: | †Iberospinus Mateus & Estraviz-López,2022 |
| Species: | †I. natarioi |
| Binomial name | |
| †Iberospinus natarioi Mateus & Estraviz-López, 2022 | |
Iberospinus (meaning "Iberian spine") is an extinctgenus ofspinosauriddinosaur from theEarly Cretaceous (Barremian)Papo Seco Formation ofPortugal. The genus contains a single species,I. natarioi, known from several assorted bones belonging to one individual.Iberospinus represents one of five known spinosaurid taxa from the Iberian Peninsula, the others beingCamarillasaurus,Protathlitis,Riojavenatrix, andVallibonavenatrix.[1] It is important for its implications of the geographical origin ofSpinosauridae and the suggested presence of potentially semi-aquatic lifestyle earlier in the evolution of this clade.[2]
The firstfossil material was discovered in 1999, with additional expeditions from 2004 to 2008. After being described as a specimen ofBaryonyx in 2011,[3] it was realised to have been a unique species in 2019, with specimen ML1190 as theholotype.[4] Additional material was discovered in a June 2020 expedition, after whichIberospinus wasdescribed as a new genus and species in 2022 byOctávio Mateus andDarío Estraviz-López.[2]
Iberospinus is currently known fromdentary fragments,teeth, an incomplete rightscapula, partialdorsal andcaudal vertebrae,rib fragments, a partialpubis, two incompletecalcanea, and a pedalungualphalanx. All of the material belongs to one individual. Theholotype material represents one of the most complete spinosaurid specimens in the world.[2]
Of the generic name, "Iberospinus," "ibero" is derived fromIberia, a Roman name for the Iberian Peninsula, while theLatinspinus[ˈs̠piːnʊs̠] means spine, after the elongated neural spines of relatedspinosaurids. The specific name, "natarioi" honorsCarlos Natário, the discoverer of the holotype.[2]
Thedentary (lower jaw) ofIberospinus shows an intricate neurovascular system that would connect the teeth and the external foramina. A series of replacement teeth are also preserved in the dentary. Characteristics of the bones, especially in the tail and pedal ungual phalanx, indicate a possible semi-aquatic lifestyle, though the extreme features in some relatedspinosaurines are not seen.[2]
The followingautapomorphies distinguishIberospinus. The dentary bone contains a single foramen within theMeckelian sulcus and has a straight ventral edge instead of curved as in most other spinosaurids. Laminae are present in the pleurocoelic depression of the mediodistal tail vertebrae. The shoulder blade has a straight anterior rim without a protrudingacromion and a coracoidal contact occupying the entire ventral surface. The pubic apron is thick throughout the entire length of the pubic shaft. There is a mound-like eminence in the proximal lateral portion of thepubic bone.[2]
TheIberospinus fossil material was included inphylogenetic analyses before it received a scientific name. In 2019, Ardenet al. recovered it as aspinosaurid outside of theBaryonychinae and Spinosaurinae. They noted that the anterior end of the dentary is not strongly upturned, as one might expect to see in a baryonychine, despite it having been originally described as a specimen ofBaryonyx.[4] However, in their 2021 description of theWessex Formation baryonychinesCeratosuchops andRiparovenator, Barkeret al. recovered the material as thesister taxon toBaryonyx, with this clade as the sister taxon to the Ceratosuchopsini. Their results are shown in thecladogram below:[5]
In their description of Mateus & Estraviz-López (2022) recoveredIberospinus within the Spinosauridae, outside of both the Baryonychinae and the Spinosaurinae, similar to the results of Ardenet al. (2019). However, they explain that the fossil material shows some characteristics of baryonychines, suggesting a closer relation to the group. Acladogram after the describing authors is shown below:[2]
In their 2023 description ofProtathlitis, Santos-Cubedoet al. performed a phylogenetic analysis, recovering a taxonomic split between the Baryonychinae and Spinosaurinae, similar to the previous results of Mateus & Estraviz-López (2022). AlthoughIberospinus was not included in their analysis, they proposed that, due to similarities in anatomy, likely phylogenetic position, and age,Iberospinus may be either the sister taxon toCamarillasaurus, or possiblysynonymous with it.[6]
A 2017 histological study ofgrowth lines by the German palaeontologist Katja Waskow and Mateus found that specimen ML1190 had died between the age of 23 and 25 years old, and was close to its maximum size and skeletal maturity. This contradicted a younger age indicated by the neurocentral sutures not being fused, and the presence of both mature and sub-adult traits may be due topaedomorphosis (where juvenile traits are retained into adulthood). Paedomorphic traits may be related to swimming locomotion, as they have been suggested in other extinct animals thought to have been aquatic (such asplesiosaurs andtemnospondyls). The study also found that the animal had reached sexual maturity at the age of 13 to 15 years, due to a decrease in growth rate at this point.[7]
The Papo Seco Formation of Portugal whereIberospinus is known from is composed ofmarl, representing a lagoon environment. Other dinosaur remains from the area include fragments tentatively assigned toMantellisaurus, amacronarian sauropod, andMegalosaurus. Most of the bones ofIberospinus specimen ML1190 were damaged, and some scratches may be marks from small scavengers. The specimen's disarticulation indicates it was transported from a more-terrestrial environment (since many bones are missing), but those found were close together.[8][9]
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