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Iberospinus is a genus of possibly Baryonychine basal Spinosaurid[1], that lived in what is now Portugal, during the Early Cretaceous.[2]

Description

Skeletal reconstruction of Iberospinus, by Scott Hartman.

Iberospinus is a large-sized bipedal Carnivore, with the holotype specimen having been esimated to be about 9 meters in length.[3] The specimen includes: dentary, isolated teeth, scapula, ribs, a dorsal vertebra, neural arches, pubic shaft, 15 caudal vertebrae, calcanea, and one pedal ungual.

It is a medium sized spinosaurid diagnosable by: the dentary with only one foramen in the Meckelian sulcus and a straight ventral edge (not upturned), the presence of laminae in the pleurocelic depression of the medio-distal caudal vertebrae, the straight anterior rim of the scapula (acromion not protruding); the reduced acromial ridge of the scapula and the contact with coracoid occupying the entire ventral surface of it; the pubic apron being thick in almost the entire length of the pubis shaft, and the presence of a mound-like eminence in the proximal lateral part of the pubis.[4]

Classification

Phylogenetic analysis by Octávio Mateus and Darío Estraviz-López recovers Iberospinus natarioi outside of the clade formed by Suchomimus and Baryonyx, although other characters (like the teeth denticles) point towards an affinity with baryonychines. However several anatomical features also point to a likely of position of basal Spinosauridae. It is also suggested that Iberospinus, along with many other Iberian Spinosaur taxa, are to have originated from western Europe.[4]

Palaeoecology

Iberospinus was only one of the many other diverse Spinosaurid taxa of Iberia, having most likely coexisted with Camarillasaurus, Baryonyx, and Vallibonaventrix.

Sidenote about Iberia Spinosaurids

In spite of not being recognized as such, Spinosauridae has been known in Portugal since the 19th century thanks to the discovery of “Suchosaurus girardi’’ (Sauvage, 1897–1898). Shortly after the discovery of Baryonyx, a series of papers referred several isolated elements to this taxon from Spain, including a left maxilla and a partial vertebral column and forelimb. In addition, some isolated teeth and a hypertrophied manual ungual phalanx were attributed to baryonychine theropods along with several isolated teeth referred to spinosaurines. The first taxon of Spinosauridae described from the Iberian Peninsula, Vallibonavenatrix cani Malafaia et al., 2020, was established on the basis of cervical, dorsal, sacral, and caudal elements, with fragments of ribs, chevrons, and a relatively complete pelvic girdle; their analysis placed it within Spinosaurinae. Camarillasaurus cirugedae Sánchez-Hernández & Benton, 2012 was originally regarded as a ceratosaur but has now been suggested to be a megalosauroid, with probable spinosaurid affinities.

  • Specimen ML1190, the subject of this work, was first described in 2011 after its discovery by the amateur fossil collector Carlos Natário in 1999. It was originally referred by Mateus et al., 2011 to Baryonyx walkeri on the basis of the following dental characteristics: “Enamel surface with small (and nearly vertical) wrinkles, variable denticle size along the carinae, 6–7 denticles per millimeter, wrinkles forming a 45 degree angle near the carinae, and tooth root longer than crown”, although another autapomorphy of Baryonyx according to Sereno et al., 1998, a well-developed peg-and-notch scapular attachment to the coracoid, is also mentioned. This work also notes some differences with the holotype of Baryonyx, especially the mound-like eminence on the lateral surface of the proximal pubis
  • ML1190 was subjected to another study in 2017, when Waskow & Mateus studied histological samples from a rib attributed to the fossil. Their main conclusion regarding ML1190 was that this rib belonged to a fully mature individual of about 23–25 years of age when it died. It reached sexual maturity at about 13–15 years of age, despite the lack of fusion of the dorsal neural arches with the centrum by the time of its death.
  • More recently, ML1190 was included in a phylogenetic analysis by Arden et al., 2019 [44], in a matrix derived from that of Evers et al., 2015. This analysis recovered the specimen outside of the clade formed by Baryonyx or Suchomimus, due to the lack of the upturned anterior part of the dentary present in both aforementioned taxa.
  • In 2021, ML1190 was included in yet another two phylogenetic analyses. The first was a parsimony analysis that recovered the specimen as an indeterminate Baryonychinae and the second was a Bayesian analysis that found it to be grouped together with Baryonyx

Diet

A 2016 study by the Belgian palaeontologist Christophe Hendrickx and colleagues. They found that adult spinosaurs could displace their mandibular rami (halves of the lower jaw) sideways when the jaw was depressed, which allowed the pharynx (opening that connects the mouth to the oesophagus) to be widened. This jaw-articulation is similar to that seen in pterosaurs and living pelicans, and would likewise have allowed spinosaurids to swallow large prey such as fish and other animals. They also reported that the Portuguese Iberospinus (previously known and interpreted as Iberian Baryonyx specimens) fossils were found with direct association to Iguanodon teeth, and listed it along with other such associations as support for truly opportunistic feeding behavior seen in spinosaur species.[5]

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References

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