Thalassodromids Temporal range: Early-Late Cretaceous, 112–88 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Replica skeleton of Tupuxuara leonardii
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Pterosauria
Suborder:	†Pterodactyloidea
Clade:	†Azhdarchoidea
Family:	†Thalassodromidae Witton, 2009
Type species
†Thalassodromeus sethi Kellner & Campos, 2002
Genera
†Alanqa? †Argentinadraco? †Banguela? †Kariridraco †Leptostomia? †Thalassodromeus †Tupuxuara †Xericeps?
Synonyms
Thalassodrominae Kellner, 2007 Tupuxuaridae Martill, Bechly & Heads, 2007

Thalassodromidae (meaning "sea runners", due to previous misconceptions of skimming behavior; they are now thought to be terrestrial predators) is a group of azhdarchoid pterosaurs from the Cretaceous period. Its traditional members come from Brazil, which include the type genus Thalassodromeus, as well as Tupuxuara. Additionally, the recently named genus Kariridraco, also from Brazil, is another undisputed thalassodromid. However, other possible members also come from other places, including Morocco and Argentina.

The classification of Thalassodromidae is quite controversial and disputed. It was actually initially denominated Thalassodrominae, as a subfamily within the group Tapejaridae. However, opposing studies regarding its placement have argued that its members were more closely related to azhdarchids and dsungaripterids, while also elevating it to family level. As of the present day, the denomination Thalassodromidae is preferred in order to maintain naming consistency despite disagreements about classification.

The classification of thalassodromids is controversial. Its initial members included Thalassodromeus and Tupuxuara, which were assigned initially to the family Tapejaridae by Brazilian paleontologists Alexander Kellner and Diógenes de Almeida Campos. In 2007, the subfamily Thalassodrominae was coined by Kellner to group both members within Tapejaridae.^[1] However, several conflicting studies arose. They argued that both Thalassodromeus and Tupuxuara were more closely related to the family Azhdarchidae instead of the tapejarids. As early as 2003, paleontologist David Unwin created the group Neoazhdarchia to contain Tupuxuara and Azhdarchidae.^[2] This arrangement would later be supported by British paleontologists David Martill and Darren Naish, who deemed Tapejaridae to be paraphyletic (unnatural), and found both Thalassodromeus and Tupuxuara as sister taxa to Azhdarchidae.^[3] In 2008, Chinese paleontologist Lü Junchang and colleagues would use the term "Tupuxuaridae" to include both genera in their phylogenetic analysis, finding the group nested within Neoazhdarchia.^[4] In 2009, British paleontologist Mark Witton also concurred with the placement of Thalassodromeus and Tupuxuara within Neoazhdarchia. However, he noted that the term Thalassodrominae was created before Tupuxuaridae, so therefore it had naming priority. He elevated Thalassodrominae to family level to satisfy the hierarchy within Neoazhdarchia, thus creating the denomination Thalassodromidae.^[5]

On the other side, Kellner's classification model indicating a tapejarid identity for Thalassodromeus and Tupuxuara would also be supported by numerous studies, such as that of Brazilian paleontologist Felipe Pinheiro and colleagues in 2011,^[6] that of paleontologist Rodrigo Pêgas and colleagues in 2018,^[7] and that of Kellner and colleagues in 2019.^[8] In 2021, paleontologist Gabriela Cerqueira and colleagues named the new genus Kariridraco and found it to group with both Thalassodromeus and Tupuxuara, following a tapejarid identity, thereby using the denomination Thalassodrominae.^[9]

The cladogram below shows the phylogenetic analysis by Cerqueira and colleagues in 2021, in which they used Kellner's model of classification. Thalassodrominae would be grouped with the subfamily Tapejarinae within Tapejaridae.^[9]

In 2018, paleontologist Nicholas Longrich and colleagues recovered the pterosaurs Aerotitan and Alanqa as thalassodromids, but noted that their fossil remains of are fragmentary, so this assignment was only tentative.^[10] In a 2021 study, Pêgas and colleagues reassigned Aerotitan back to Azhdarchidae, corrobating its initial placement in its description. Alanqa was assigned to its own family, the Alanqidae, as the sister taxon of Keresdrakon. Alanqidae in turn was recovered as the sister taxon of Azhdarchidae.^[11]

Life reconstructions of the possible thalassodromids Argentinadraco (above) and Leptostomia (below)

In the same year, American paleontologist Brian Andres would also find an azhdarchid identity for Aerotitan. However, he found Alanqa as a thalassodromid, following Longrich and colleagues in 2018. He would also find the pterosaurs Argentinadraco, Leptostomia, and Xericeps within Thalassodromidae, expanding the family to six genera, including the traditional members Thalassodromeus and Tupuxuara. He would additionally utilize the term Thalassodrominae as a subfamily within Thalassodromidae in his phylogenetic analysis, in which he would include all thalassodromid genera except for Tupuxuara. This is a new arrangement for the group that has not appeared in any former study, whether in favor of a tapejarid or a neoazhdarchian identity. The results of his study are shown in the first cladogram below.^[12] In 2023, Pêgas and colleagues argued that despite the disagreements about the position of the group, the species contained within it have almost always been consistent (Thalassodromeus and Tupuxuara). Therefore, they deemed the difference in naming pattern undesirable. They favored the denomination Thalassodromidae to have consistency with other studies that used the same name. In their phylogenetic analysis, they supported a close relationship between the thalassodromids and the family Tapejaridae, thereby following the classification model established by Kellner. Both Thalassodromidae and Tapejaridae would form the larger group Tapejaromorpha. The results of their study are shown in the second cladogram below.^[13] Subsequent studies using Kellner's model would also employ the denomination Thalassodromidae instead of Thalassodrominae.^[14][15]