PALEONTOLOGY IN FEBRUARY, 2025

ABSTRACT

A considerable number of azhdarchid pterosaur fossils have been recovered from Maastrichtian deposits of North America. Historically, most of these specimens have been referred to Quetzalcoatlus based on a preliminary understanding of the genus. Further study of Quetzalcoatlus and other azhdarchids has increased our understanding of the anatomy and diversity of the clade, and warrants reappraisal of specimens previously referred to this genus. Here we redescribe an azhdarchid cervical vertebra recovered from the Maastrichtian Hell Creek Formation of Montana, U.S.A. Digitization of this specimen via laser scanning allows a more detailed assessment and reconstruction of this specimen’s morphology, revealing both unique characters and unique character combinations. We therefore assign this specimen to a new genus and species of medium-sized azhdarchid, Infernodrakon hastacollis gen. et sp. nov. Phylogenetic analysis recovers Infernodrakon as more closely related to Arambourgiania than to Quetzalcoatlus. Review of Maastrichtian azhdarchid material from North America reveals a high diversity despite the relatively fragmentary fossil record for this clade.

LINK(S)

https://www.tandfonline.com/doi/full/10.1080/02724634.2024.2442476

ABSTRACT

The mid-Pliocene Warm Period (mPWP; 3.26–3.02 Ma) is an interval often suggested as a potential analogue of the near future climate and fate of the Greenland Ice Sheet (GIS). Here, neodymium and lead isotopes from marine sediment cores collected off the southern Greenland margin suggest pulses of intense glacial erosion of Precambrian terranes during this interval, while grain size data indicate a reduction in the strength of contour currents, both following a near obliquity cycle (~41 ka) pacing. These cold spells were thus sufficiently intense to trigger recurrent ice growth over Greenland, even under the high atmospheric CO2 concentration (~400 ppmV) of the interval, before the intensification of the Northern Hemisphere Glaciation (~2.7 Ma). However, the mPWP was marked by a low amplitude in the axial tilt oscillation of the Earth, thus lesser variations in summer insolation at high latitudes than in the present era. Therefore, although it may offer some similarities with the future of the Earth’s climate, the mid-Pliocene cannot be seen as a genuine analogue for predicting the fate of the GIS.

LINK(S)

https://www.nature.com/articles/s41467-025-56996-3

https://www.nature.com/articles/s41467-025-56996-3.pdf

ABSTRACT

The Compsognathidae was originally considered an early-diverging clade of coelurosaur theropods. However, recent study suggests that Compsognathidae is not monophyletic. Here, we describe two new compsognathid-like species, Sinosauropteryx lingyuanensis sp. nov. and Huadanosaurus sinensis gen. et sp. nov. from the Lower Cretaceous Yixian Formation of Dawangzhangzi (Lingyuan, western Liaoning, China). The phylogenetic results indicate that all compsognathid-like theropods from the Early Cretaceous Jehol Biota form a monophyletic group Sinosauropterygidae nested among early-diverging coelurosaurs. Morphological comparison between various species of sinosauropterygids from the Early Cretaceous of Northeast China, combined with the phylogenetic results, suggests that at least three distinct hunting strategies were present among coeval species. The diversification of theropods should be attributed to the landscape caused by the North China craton destruction.

LINK(S)

https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr/nwaf068/8030555

ABSTRACT

The Hațeg Basin and surrounding areas in Transylvania, western Romania, have been a hotspot for research on vertebrate faunas of the Late Cretaceous European Archipelago. One of the historically earliest titanosaurian sauropod dinosaurs to be discovered, the ‘dwarfed’ species Magyarosaurus dacus comes from lower Maastrichtian deposits in this basin; however, this species has been neglected, with no modern treatment of its anatomy, taxonomy or phylogenetic affinities. Via detailed anatomical study of historical and undescribed remains, combined with archival data, we identify shared autapomorphies that link multiple partial skeletons. Our analysis of hundreds of specimens (including >20 monospecific assemblages) enables the stabilization of the type species Magyarosaurus dacus. We propose the presence of three additional, but only partly contemporaneous taxa – Paludititan nalatzensis, Petrustitan (‘Magyarosaurus’) hungaricus n. gen. and Uriash kadici n. gen. n. sp. (the latter being amongst the largest known sauropods of the Late Cretaceous European Archipelago). We present a new phylogenetic analysis (152 taxa scored for 570 characters), with implications for broader titanosaurian evolutionary relationships and biogeography: Magyarosaurus is recovered either as a member or a close relative of Saltasauridae; Paludititan has affinities with Lognkosauria, along with the contemporaneous Lohuecotitan; Petrustitan is most closely related to South American early diverging eutitanosaurian taxa; and Uriash also shares affinities with Gondwanan taxa. Our findings strengthen the hypothesis that latest Cretaceous European titanosaurs belonged to Gondwanan lineages that invaded the former area during the Barremian–Albian. We interpret the presence of body-size disparity as either evidence that large-bodied taxa were ecologically excluded from body-size reduction by competition with small-bodied titanosaurs, or that dwarfing occurred stratigraphically earlier among several lineages and the small-bodied titanosaurs on Hațeg Island are the descendants of existing dwarfed ancestors. Finally, we find no indication of a body size-related titanosaurian turnover in the uppermost Cretaceous of the Transylvanian area.

LINK(S)

https://www.tandfonline.com/doi/full/10.1080/14772019.2024.2441516

https://www.tandfonline.com/doi/epub/10.1080/14772019.2024.2441516?needAccess=true

ABSTRACT

The Early Cretaceous non-avian theropod body fossil record of Victoria, Australia dominantly comprises isolated dental and postcranial remains. Numerous specimens have been collected from both the upper Strzelecki Group (upper Barremian–lower Aptian) and Eumeralla Formation (upper Aptian–lower Albian), yet theropod diversity in each unit remains poorly resolved. In both deposits, specimens pertaining to Megaraptoridae—a clade seemingly endemic to South America and Australia in the Cretaceous—are most frequently encountered. However, evidence of other typically common Gondwanan theropod groups, including Abelisauridae and Carcharodontosauria, has remained unknown. Herein, we describe five new theropod specimens: three tibiae, and two articulated caudal vertebrae with haemal arches, from the upper Strzelecki Group; and a single tibia from the Eumeralla Formation. Two of these tibiae—one each from the upper Strzelecki Group and the Eumeralla Formation—provide the first evidence for Carcharodontosauria in Australia. Two megaraptorid specimens from the upper Strzelecki Group—a tibia, and two caudal vertebrae with haemal arches—demonstrate that this clade had achieved large body size at the time of its first appearance in the fossil record. A tibia from the upper Strzelecki Group is interpreted to represent the Gondwanan dromaeosaur clade Unenlagiinae. Collectively, the new theropod remains described herein strengthen the evidence for mid-Cretaceous faunal interchange between Australia and South America across Antarctica, and highlight the presence of carcharodontosaurians and unenlagiines at high latitudes in the late Early Cretaceous.

LINK(S)

https://www.tandfonline.com/doi/full/10.1080/02724634.2024.2441903

https://www.tandfonline.com/doi/epdf/10.1080/02724634.2024.2441903?needAccess=true

ABSTRACT

Recent macroevolutionary studies predict a diversification of early birds during the Jurassic period, but the unquestionable Jurassic bird fossil record is limited to Archaeopteryx, which has also been referred to deinonychosaurian dinosaurs by some analyses. Although they have feathered wings, the known Jurassic birds are more similar to non-avialan theropods in having the ancestral long reptilian tail. This is in stark contrast to most Cretaceous and crownward taxa, which have a short tail that terminates in a compound bone called the pygostyle. Here we report on the oldest short-tailed avialan, Baminornis zhenghensis gen. et sp. nov., from the recently discovered Late Jurassic Zhenghe Fauna, which fills a noticeable spatio-temporal gap in the earliest branching avialan fossil record. B. zhenghensis exhibits a unique combination of derived ornithothoracine-like pectoral and pelvic girdles and plesiomorphic non-avialan maniraptoran hand, demonstrating mosaic evolution along stem avialan line. An avialan furcula collected from the same locality is referrable to ornithuromorphs on the basis of our morphometric and phylogenetic analyses. These newly discovered fossils demonstrate the early appearance of highly derived bird features, and together with an anchiornithine fossil from the same locality, they suggest an earlier origin of birds and a radiation of early birds in the Jurassic.

LINK(S)

https://www.nature.com/articles/s41586-024-08410-z

ABSTRACT

A new crocodylomorph taxon, Pattisaura gracilis, is described based on an associated partial skeleton from the Upper Triassic Dockum Group of northwest Texas. Pattisaura gracilis represents a non-crocodyliform crocodylomorph and can be characterized mainly by a set of character states from the skull, vertebral column, pelvis, and osteoderms. The discovery of P. gracilis expands the distribution range of non-crocodyliform crocodylomorphs in North America. P. gracilis may be closely related to Redondavenator quayensis from northeast New Mexico. With addition of P. gracilis, our phylogenetic analysis does not support the monophyly of Sphenosuchia and the presence of an Argentinian clade, a purely North American clade, or a Middle to Late Jurassic Hallopodidae among non-crocodyliform crocodylomorphs but confirms the closest relationship of Almadasuchus to Crocodyliformes and partly supports the existence of Solidocrania with Hallopus victor as its most basally branching member.

LINK(S)

https://www.tandfonline.com/doi/full/10.1080/02724634.2024.2446604?src=

ABSTRACT

Patagorhacos terrificus is a phorusrhacid bird known from the early Miocene of Río Negro province, northern Patagonia. Originally based on the distal end of a quadrate bone, and a referred fragmentary ulna, its affinities were considered dubious by some authors, who also regarded it as Aves incertae sedis. The aim of present contribution is to report two new specimens of Patagorhacos that include valuable anatomical information, including the proximal end of femur, tibiotarsus and proximal and distal end of tarsometatarsus, among others. These new specimens indicate without any doubt that Patagorhacos belongs to phorusrhacid birds, and that it is a valid taxon that can be distinguished from other similar-sized taxa, such as Patagornis and Hermosiornis. With this new information at hand, a new phylogenetic analysis of phorusrhacid birds is performed. This analysis constitutes the most complete dataset known for phorusrhacids (25 taxa and 206 characters) and unambiguously nests Patagorhacos among phorusrhacids. It also lends support to the hypothesis that the loss of flight and acquisition of gigantism among phorusrhacids occurred only once. The North American and European Bathornis and Ameghinornis resulted as the successive sister taxa to Phorusrhacidae, indicating a complex biogeographical scenario.

LINK(S)

https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2458127

ABSTRACT

Plesiosaurs are an iconic group of Mesozoic marine reptiles with an evolutionary history spanning over 140 million years (Ma). Their skeletal remains have been discovered worldwide; however, accompanying fossilized soft tissues are exceptionally rare. Here, we report a virtually complete plesiosaur from the Lower Jurassic (∼183 Ma) Posidonia Shale of Germany that preserves skin traces from around the tail and front flipper. The tail integument was apparently scale-less and retains identifiable melanosomes, keratinocytes with cell nuclei, and the stratum corneum, stratum spinosum, and stratum basale of the epidermis. Molecular analysis reveals aromatic and aliphatic hydrocarbons that likely denote degraded original organics. The flipper integument otherwise integrates small, sub-triangular structures reminiscent of modern reptilian scales. These may have influenced flipper hydrodynamics and/or provided traction on the substrate during benthic feeding. Similar to other sea-going reptiles, scalation covering at least part of the body therefore probably augmented the paleoecology of plesiosaurs.

LINK(S)

https://www.cell.com/current-biology/fulltext/S0960-9822(25)00001-6

https://www.cell.com/action/showPdf?pii=S0960982225000016

ABSTRACT

Giant short-faced bears (Arctodus simus) were the largest carnivoran of Pleistocene North America and are one of the most extensively studied extinct megafaunal species from the continent. Smaller and larger forms of A. simus have previously been recognized and are sometimes considered subspecies (A. s. simus and A. s. yukonensis, respectively). However, researchers have also proposed that this size variation is primarily the result of sexual dimorphism. We sequenced 31 mitogenomes of A. simus from locations ranging from Alaska to New Mexico. Our results revealed a lack of phylogeographic structure in A. simus, as well as low genetic diversity and relatively recent mitochondrial diversification. These observations may either represent population bottlenecks during the Late Pleistocene or simply a naturally low effective population size resulting from a dispersed population and low population density. We found no evidence for genetic differences among our samples, which were compatible with the previously proposed A. simus subspecies. In contrast, all large specimens to which we could assign a sex using genetic data were male, whereas the small specimens in our dataset were all female, supporting the hypothesis that A. simus size variation can be explained by sexual dimorphism.

LINK(S)

https://academic.oup.com/zoolinnean/article-abstract/203/2/zlaf001/8002103

ABSTRACT

Fossils representing Cretaceous lineages of crown clade birds (Aves) are exceptionally rare but are crucial to elucidating major ecological shifts across early avian divergences. Among the earliest known putative crown birds is Vegavis iaai, a foot-propelled diver from the latest Cretaceous (69.2–68.4 million years ago) of Antarctica with controversial phylogenetic affinities. Initially recovered by phylogenetic analyses as a stem anatid (ducks and closely related species), Vegavis has since been recovered as a stem member of Anseriformes (waterfowl), or outside Aves altogether. Here we report a new, nearly complete skull of Vegavis that provides new insight into its feeding ecology and exhibits morphologies that support placement among waterfowl within crown-group birds. Vegavis has an avian beak (absence of teeth and reduced maxilla) and brain shape (hyperinflated cerebrum and ventrally shifted optic lobes). The temporal fossa is well excavated and expansive, indicating that this bird had hypertrophied jaw musculature. The beak is narrow and pointed, and the mandible lacks retroarticular processes. Together, these features comprise a feeding apparatus unlike that of any other known anseriform but like that of other extant birds that capture prey underwater (for example, grebes and loons). The Cretaceous occurrence of Vegavis, with a feeding ecology unique among known Galloanserae (waterfowl and landfowl), is further indication that the earliest anseriform divergences were marked by evolutionary experiments unrepresented in the extant diversity.

LINK(S)

https://www.nature.com/articles/s41586-024-08390-0

ABSTRACT

Mosasaurid teeth are abundant in the fossil record and often diagnostic to low taxonomic levels, allowing to document the taxonomic diversity and ecological disparity through time and with fewer biases than in other marine reptiles. The upper Maastrichtian Phosphates of Morocco, with at least fifteen coeval species representing a wide range of sizes and morphologies, undoubtedly represent the richest outcrop in the world for this clade of iconic Mesozoic squamates and one of the richest known marine tetrapod assemblages. Until now, the methods used to link tooth morphology to diets in marine amniotes were mainly qualitative in nature. Here, using the dental morphology of mosasaurids from Morocco, we combine two complementary approaches—a thorough comparative anatomical description and 2D/3D geometric morphometry—to quantitatively categorize the main functions of these teeth during feeding processes and infer diet preferences and niche-partitioning of these apex predators. Our results from combining these two approaches show the following: (1) Mosasaurids from the upper Maastrichtian Phosphates of Morocco occupy the majority of dental guilds ever colonized by Mesozoic marine reptiles. (2) As seen elsewhere in the Maastrichtian, mosasaurines dominate the regional mosasaurid assemblage, exhibiting the greatest taxonomic diversity (two-thirds of the species) and the largest range of morphologies, body sizes (2 m to more than 10 m) and ecological disparities (participating in nearly all predatory ecological guilds); strikingly, mosasaurines did not developed flesh piercers and, conversely, are the only ones to include durophagous species. (3) Halisaurines, though known by species of very different sizes (small versus large) and cranial morphologies (gracile versus robust), maintain a single tooth shape (piercer). (4) Plioplatecarpines were medium-size cutters and piercers, known by very morphologically diverging species. (5) Tylosaurines currently remain scarce, represented by a very large generalist species; they were largely replaced by mosasaurines as apex predators over the course of the Maastrichtian, as observed elsewhere. Also, when comparing tooth shapes with body sizes, the largest taxa (>8 m long) occupied a restricted area of tooth shapes (generalist, durophagous), whereas small and medium-sized species (<8 m long) range across all of them (generalists, durophagous, cutters, piercers). In other words, and probably related to the specificities and advantages of biomechanical resistance, apex predators are never dedicated piercers, micro-predators are conversely never generalists, and meso-predators show the widest range of dental adaptations. These diversities and disparities strongly suggest that Tethyan mosasaurids evolved strong niche-partitioning in the shallow marine environment of the upper Maastrichtian Phosphates of Morocco. Such a high diversity sensu lato just prior to the K/Pg biological crisis suggests that their extinction was rather sudden, though the exact causes of their extinction remain unknown. Finally, Gavialimimus Strong et al., 2020 is systematically reassigned to Gavialimimus ptychodon (Arambourg, 1952), and an emended diagnosis (for teeth and dentition) is proposed for this species.

LINK(S)

https://www.mdpi.com/1424-2818/17/2/114

ABSTRACT

The Lufeng Formation of Lufeng City, Yunnan Province, China, is one of the most important sedimentary units for understanding the evolution of the Early Jurassic sauropodomorph dinosaurs. Here, a new species of the early-diverging sauropodomorph Xingxiulong from the Lower Jurassic Lufeng Formation is erected on the basis of a postcranial skeleton. Xingxiulong yueorum, sp. nov. is distinguished from Xingxiulong chengi by possessing a pendant-shaped fourth trochanter with distal termination, an astragalus with almost straight dorsal margin of the posterior surface, and pedal digit V with two phalanges. A phylogenetic analysis supports the monophyly of genus Xingxiulong. Both the two species of Xingxiulong have four sacral vertebrae, which are typically associated with the late-diverging sauropodiforms and sauropods, suggesting a complex early evolution within the sauropodomorphs. This discovery adds to the diversity of the sauropodomorphs from the Lufeng Formation and contributes to our understanding of the intricate patterns characterising the early evolution of sauropodomorphs in Asia.

LINK(S)

https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2458130