Jesús Marugán-Lobón

The enantiornithes, a group of Mesozoic birds, have morphological features suggesting a precocial mode of development; however, their detailed physiological characteristics, particularly hatchling metabolic rates, have yet to be explored. Here, we retrodicted metabolic rates for four Lower Cretaceous enantiornithines: one hatchling, one adult from Las Hoyas, one early post-hatching juvenile and one post-juvenile individual from the Jehol Biota, using phylogenetic comparative analyses and a comprehensive dataset of extant birds spanning the altricial–precocial spectrum. By examining vascular density (related to resting metabolic rate (RMR)) and nutrient foraminal size (proportional to blood flow rate) as proxies, we inferred the metabolic scope of the hatchling enantiornithine and determined that it fell toward the precocial end of the altricial–precocial spectrum. The RMR values of the two enantiornithine chicks were retrodicted as 0.67 mlO2 h–1 g–0.93. The peak metabolic rate (PMR) retrodicted is twice the resting metabolism for the Las Hoyas hatchling. These results are consistent with a semi-precocial/precocial development characterized by independent locomotion by climbing using the wing claws soon after hatching. However, flapping flight may have been delayed, owing to incomplete ossification of the sternum, as observed in one hatchling specimen.

Giraffe ( Giraffa spp.) are among the most unique and charismatic extant animals, largely due to their distinct morphology. The evolutionary and developmental origin of ossicones is a key factor in giraffid biology, yet other features building their characteristic head physiognomy remain poorly studied. Here, we analysed the cranial diversity of extant Giraffa using a continent‐wide sample with a balanced sex ratio and ontogenetic growth series, using shape analysis (3D geometric morphometrics). Detailed comparisons showed significant differences in cranial morphology across the four Giraffa species, and in some cases also between subspecies of the same species. The analyses revealed that females reach adult cranial form at an earlier age (around 4 years old), while males continue growing until the eighth year, aligning with the onset of sexual maturity for each of the sexes. Multivariate methods unambiguously prompt significant covariation between skull parts. Such high covariation patterns indicate that Giraffa skull morphology largely evolves as a whole (i.e., morphologically integrated), even though parts of it (such as the ossicones) develop in different magnitudes. Considering their role in territorial and mating behaviours, we suggest that ossicone morphology influences the parapatric evolution of Giraffa through sexual selection. Palaeontological evidence shows that development of larger ossicones is a relatively recent trait for members of the genus Giraffa , with the cranial morphology of the southern giraffe ( Giraffa giraffa ) being the closest to that of the ancestral forms, possibly through plesiomorphy or paedomorphosis.

The fossil record of Early Cretaceous enantiornithine birds from the Iberian Peninsula is the most significant in the world outside of China. Despite its historical relevance, taxonomic diversity, and relative abundance, adult cranial remains had not been reported before. In this study, we describe a new enantiornithine species, Gorgonavis alcyone gen. et sp. nov. based on a disarticulated skull from the Early Cretaceous locality of Las Hoyas (129–126 Myr; Cuenca, Spain), the first adult cranial remains of a bird from this fossil site. Digital imaging of the µCT-scanned fossil remains shows that Gorgonavis is characterized by a slender and elongated rostrum in which teeth are restricted to the premaxillary corpus, a thin, edentulous maxilla, and a jugal bone with an elongated and strongly angled postorbital process. Despite the fragmentary nature of the holotype, comparative anatomy and phylogenetic analyses suggest the identification of the new species as a longipterygid, a distinct clade of Enantiornithes characterised by an elongated rostrum, a cranial configuration consistent with the new fossil . Gorgonavis represents the oldest occurrence of an enantiornithine with relative rostral elongation outside of the Jehol Biota. The new discovery suggests that some specialised early enantiornithine lineages had a broader geographical, and more ecologically diverse distribution than previously thought.

La presencia del tracto digestivo constituye una valiosa fuente de información para comprender las estrategias alimentarias de los organismos fósiles. Sin embargo, la preservación de tejido blando suele estar limitada a yacimientos con preservación excepcional, como el yacimiento español de Las Hoyas (Barremiense, Cretácico). La revisión de 1134 fósiles de teleósteos permitió identificar, en la cavidad abdominal, tejidos blandos atribuibles a distintos órganos internos y materia en digestión (consumulitos). De entre los órganos internos preservados, se encuentran diferencias estructurales entre los tractos digestivos de Rubiesichthys gregalis, Teleostei incertae sedis n. sp. 1 y Teleostei incertae sedis n. sp. 2. La morfología del tracto digestivo y la presencia de inclusiones en los consumulitos indican una dieta omnívora en los teleósteos de Las Hoyas, con relativa especialización hacia la digestión de grandes cantidades de materia orgánica, incluyéndose restos de otros peces y crustáceos. Estas interpretaciones matizan previas interpretaciones ecológicas sobre los teleósteos en el ecosistema. En paralelo, la identificación a nivel de tejido blando en dos especies distintas tradicionalmente agrupadas bajo la categorización de Teleostei incertae sedis indica que la relativa baja diversidad de teleósteos de Las Hoyas, en realidad, revela ciertas especializaciones anatómicas relevantes para la comprensión de estos linajes en el futuro.

Pterosaur tracks are relatively abundant in the Spanish fossil record and are especially localized in the Upper Jurassic of the Asturian coast and in the Lower Cretaceous of the Cameros Basin. All cases so far have been identified within the ichnogenus Pteraichnus . The Berriasian of the Cameros Basin is especially abundant in pterosaur ichnites, and, for this reason, the presence of seven ichnogenera had been proposed, about which, in general, there has not been a complete consensus among researchers. These ichnogenera were established according to normal procedure in paleoichnology, that is, with morphological characters, as well as considering several variables and meristic indexes. We provide a study on the variability of pterosaur handprints, focused on the Cameros Basin record, using shape analytical tools (geometric morphometrics). The results suggest that shape variability is continuous with respect to pterosaur handprint geometry. In consequence, there are no distinctive features that allow us to discriminate between them, even considering factors such as geological age or geographical origin. The shape of pterosaur manus prints remains very constant, suggesting a conservative evolution pattern of the module formed by the digits I, II and III, an important structure of the pterosaur arm for adequate quadrupedal locomotion on land.

The origin of flight in avian dinosaurs has been historically an ideal framework for proposing the evolutionary relationship between form and function in limb proportions under the hypothesis of specialized locomotor modules. However, other hypotheses suggest that the evolution of the forelimb and the hindlimb is strongly influenced by shared developmental constraints, entailing that limbs evolve in an integrated manner and keeping the scientific debate open. To assess this, we used an alternative morphometric approach to compare and statistically analyse limb morphological covariation in a phylogenetically broad context across non-avian maniraptoran theropods and modern birds. Our results show that the maniraptoran lineage shares a strong covariation between limb proportions, a pattern indicating that consistent morphological integration has constrained the forelimb and hindlimb evolutionary transformation. Different evolutionary grades within Maniraptora, both volant and non-volant lineages, display distinct and weaker covariation patterns, suggesting the emergence of independent evolutionary trends within such underlying patterns of integration. These findings are consistent with a developmental hypothesis in which the evolutionary transformation of limbs in maniraptoran dinosaurs was influenced by its serial homology, underscored by shared developmental programmes. Thus, limb evolution was not solely driven by modular (functional) specialization for flight.

Landmark-based geometric morphometric (GM) methods have become a standard in shape analysis. Superimposition of landmark constellations, referenced to the mean, is performed using the least squares criterion under the consensus framework of Generalized Procrustes Analysis (GPA). While effective, especially when combined with multivariate statistics, this approach also has limitations. Specifically, if there is localized variation (if a few landmarks are significantly displaced in relation to the others), the method homogenizes variation to perform an optimal fit that can spread variation randomly, yielding unrealistic results. This limitation has long been recognized and discussed in the literature—especially paleontological—proposing methods based on repeated medians that help checking for such localized variation in landmark constellations. However, the broad establishment of GPA has led to their neglect, potentially compromising interpretations in studies of allometry, integration, and modularity. Two real life examples, one biological (spiders) and one paleobiological (pterosaur skulls), are used to illustrate what "localized variation" means and the effect it can have on the structure of Procrustes shape data, and consequently, on further statistical analyses. The intended message is that median-based resistant methods for landmark superimposition should be re-implemented

The West African giraffe Giraffa camelopardalis peralta , the rarest giraffe subspecies, is one of the least studied taxa of the African megafauna in terms of anatomy, physiology, and taxonomy due to the limited material hosted in museum collections. Here, we discuss specific morphological features of the holotype of this subspecies, re‐evaluate its diagnostic characteristics and expand our knowledge of the morphology of the taxon with the addition of specimens collected in the wild. Our results show that G. c. peralta is not a subspecies of ‘gigantic’ proportions, as indicated in previous studies. This misunderstanding arose from the misidentification of the holotype specimen (NHMUK‐ZD‐1898.2.19.1) as a female instead of a male. The only other G. c. peralta specimen, which is hosted in the same collections in the Natural History Museum of London (NHMUK‐ZD‐1904.11.2.2), is a male of morphology and size much closer to that of an average G . camelopardalis male. Our findings show that in comparison to other giraffe subspecies the dimensions of G. c. peralta are as metrically expected and reveal preliminary evidence of the strongest sexual size dimorphism in the genus Giraffa . We further suggest that the holotype should be relabeled as a male. The evolutionary history and the phylogenetic position of G . c . peralta are discussed, favoring the mixing‐isolation‐mixing pattern with the Kordofan giraffe ( G. c. antiquorum ).

The Karoo Basin of South Africa is renowned for its abundance and diversity of therapsid fossils. Among the most ubiquitous and persistent of the Permian fauna is the small herbivorous dicynodont Diictodon feliceps . Intraspecific variation in Diictodon is historically confounding, and while ontogeny is frequently cited as a potential source of variation, observable developmental changes have never been calibrated. The present study revisits this issue, comparing three-dimensional landmark configurations of 82 Diictodon crania to investigate the association between shape, size and dimorphism. Beyond the statistically significant relationship between shape and allometry, our results determine the shape differences between juvenile and adult skulls of Diictodon , aligned with common craniofacial features documented in other tetrapod taxa. Functionally, these changes are attributed to development of the jaw musculature for feeding on larger, tougher plant matter during later ontogeny. Cranial morphological variation owing to sexual dimorphism is negligible, but distinct differences are noted in the allometric trajectories of each morphotype. A component of non-allometric variation cannot be accounted for, and we propose that this represents natural variation, rather than an artefact of taphonomic deformation.

The Lower Cretaceous fossil site of Las Hoyas (Cuenca, Spain) has yielded the richest Cretaceous avifauna of the European continent. We describe a new fossil (MUPA-LH-33333) of an enantiornithine bird from this locality. This specimen consists of a partially articulated skeleton preserving portions of the vertebral column, both girdles and limbs, ribs and sternum; it also preserves patches of soft tissues including remigial feathers and integumentary structures belonging to the postpatagium. MUPA-LH-33333 shares dimensions and some anatomical features with the holotype of Concornis lacustris, a species previously described from Las Hoyas. However, the new specimen shows differences especially in the coracoid and the sternum, suggesting the presence of a different morphotype closely related to C. lacustris. Nevertheless, the poor preservation prevents asserting that it represents a new species. Histological evidence from its long bones indicates that is subadult or adult and that early fast rates followed by slower and protracted cyclical phases took place during its growth, a previously unnoticed pattern in Lower Cretaceous enantiornithines. This new finding supports the hypothesis that enantiornithines regularly inhabited the Las Hoyas wetland, making this site a hotspot for enhancing our understanding of the evolution and life history of these Cretaceous birds.