Postcranial Osteology Research Articles

The Picocoraciades (hoopoes, rollers, woodpeckers, and allies) from the early Eocene London Clay of Walton-on-the-Naze

We describe upupiform, coraciiform, and possible piciform birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). The material includes partial skeletons of a new species of a small upupiform bird, Waltonirrisor tendringensis, gen. et sp. nov., which is the earliest known representative of the Upupiformes. Three very similar species of stem group rollers are assigned to Laputavis robusta, Septencoracias morsensis, and S. simillimus, sp. nov. These species only differ in minor features, which raises the possibility that the taxon Sepencoracias Bourdon, 2016 is a junior synonym of Laputavis Dyke, 2001. A smaller stem group roller from Walton-on-the-Naze resembles the North American primobucconid species Primobucco mcgrewi. We also describe two species of a new genus-level taxon, Pristineanis, gen. nov., which shows close affinities to the North American “Neanis” kistneri and may be a stem group representative of the Piciformes. In many aspects of their postcranial osteology, the stem group Coracii from Walton-on-the-Naze, as well as the new taxon Pristineanis, resemble coeval Trogoniformes from this fossil site. Because trogons are the extant sister taxon of the Picocoraciades – the clade including the Upupiformes, Coraciiformes, and Piciformes –, the shared similarities are likely to be plesiomorphic for this latter clade. Early Cenozoic representatives of the Upupiformes and Coraciiformes were much smaller than their extant relatives, which suggests that the Picocoraciades are an avian example of Cope’s Rule that postulates a tendency for size increase in evolutionary lineages over time.

Cranial and postcranial anatomy of a juvenile baurusuchid (Notosuchia, Crocodylomorpha) and the taxonomical implications of ontogeny.

Baurusuchidae comprises a clade of top-tier terrestrial predators and are among the most abundant crocodyliforms found in the Adamantina Formation, Bauru Basin, Brazil (Campanian-Maastrichtian). Here, we provide a detailed description of the cranial and postcranial osteology and myology of the most complete juvenile baurusuchid found to date. Although the preservation of juvenile individuals is somewhat rare, previously reported occurrences of baurusuchid egg clutches, a yearling individual, and larger, but skeletally immature specimens, comprise a unique opportunity to track anatomical changes throughout their ontogenetic series. Its cranial anatomy was resolved with the aid of a three-dimensional model generated by the acquisition of computed tomography data, and its inferred adductor mandibular musculature was compared to that of mature specimens in order to assess possible ontogenetic shifts. A subsequent phylogenetic analysis included the scoring of Gondwanasuchus scabrosus, the smallest baurusuchid species known to date, to evaluate its phylogenetic relations relative to a known juvenile. We find considerable differences between juveniles and adults concerning skull ornamentation and muscle development, which might indicate ontogenetic niche partitioning, and also anatomical and phylogenetic evidence that G. scabrosus corresponds to a young semaphoront lacking mature cranial features.

Morphology, molecular systematics and phylogeography of the Spine-cheek Gudgeon, Eleotris acanthopomus (Teleostei: Eleotridae) from the north-western Indian Ocean

General morphology, cephalic sensory papillae pattern, postcranial osteology, phylogenetic placement, phylogeographic pattern, and distribution of Eleotris acanthopomus Bleeker, 1853 (Teleostei: Gobiiformes: Eleotridae) from the north-western Indian Ocean (Arabian Sea) are described. The cephalic papillae pattern follows the ‘open’ opercular pattern, and the cheek pattern ‘2.4’. The vertebral column includes 10 abdominal and 14–15 caudal vertebrae, for a total vertebral count of 24–25. Corroborating the morphological results, DNA barcoding based on mitochondrial COI confirmed that the specimens collected from the Arabian Sea coastal area are conspecific with E. acanthopomus from other Indo-Pacific localities. Eleotris acanthopomus from the Arabian Sea shows the closest phylogenetic relationship to E. pellegrini (11.9% K2P genetic distance). The presence of E. acanthopomus in the coastal area of the Arabian Sea represents the first record of this genus and species for the northern Indian Ocean and markedly expands its known geographical distribution range. A preliminary phylogeographic analysis of the newly collected E. acanthopomus haplotype from the Arabian Sea and archived haplotypes from other Indo-Pacific localities suggests that extensive dispersal occurs among regional populations, most probably during the pelagic larval stage.

Postcranial osteology of Beipiaosaurus inexpectus (Theropoda: Therizinosauria).

Beipiaosaurus inexpectus, from the Lower Cretaceous Yixian Formation (Sihetun locality, near Beipiao), Liaoning, China, is a key taxon for understanding the early evolution of therizinosaurians. Since initial publication in 1999, only the cranial elements of this taxon have been described in detail. Here we present a detailed description of the postcranial skeletal anatomy of the holotype specimen of B. inexpectus, including two never before described dorsal vertebrae from the anterior half of the series. Based on these observations, and comparisons with the postcranial skeleton of therizinosaurian taxa named since the most recent diagnosis, we revised the diagnostic features for B. inexpectus adding three new possible autapomorphies (PII-3 shorter than PIII-4, subequal length of the pre- and postacetabular portions of the ilium, and equidimensional pubic peduncle of ilium). Additionally, we also propose three possible synapomorphies for more inclusive taxa (Therizinosauroidea and Therizinosauridae) and discuss implications for evolutionary trends within Therizinosauria. The newly acquired data from the postcranial osteology of the holotype specimen of B. inexpectus sheds light on our understanding of postcranial skeletal evolution and identification of therizinosaurians.

Blind snakes beneath the surface: Continuing the legacy of Richard Thomas.

Blind snakes (Scolecophidia) are small-bodied, enigmatic burrowing reptiles with members found on all continents except Antarctica. This Special Issue on blind snakes honors and advances the foundational studies by a remarkable anatomist, Richard Thomas. Richard is currently one of the living herpetologists to have described the greatest number of herpetofauna species, including many blind snake taxa. Recent interest in scolecophidian research at several conferences led to the development of this Special Issue on blind snake anatomy. This issue spans a diversity of papers, from biographical accounts of Richard's life and works, to a brief history of scolecophidian anatomical studies and the benefits of computed tomography (CT) technology, to a variety of studies on the skull and post-cranial osteology, cranial and jaw biomechanics related to subterranean lifestyles, evolution, and systematics of blind snake taxa from around the globe. This Special Issue will hopefully serve as a valuable resource and contribution to the field of blind snake anatomy research, and a joyful reflection on the life and career of a herpetologist who mentored and inspired a new generation of researchers in this area.

Osteology of the enigmatic threadsnake speciesEpictia unicolorandTrilepida guayaquilensis(Serpentes, Leptotyphlopidae) with generic insights

Since the rearrangement of all leptotyphlopid species previously known as "Leptotyphlops" in Adalsteinsson et al. (2009)'s paper, several taxa have remained untested regarding their generic identity and have been assigned to different genera based on phenotypic data or, in some cases, without any clear justification. Most of the difficulties in assigning some leptotyphlopid taxa are due to their conserved external morphology, summed with a relatively small number of available specimens, which complicate the recognition of a unique combination of characters for their reasonable generic allocation. On the other hand, recent osteological studies-especially those on the skull-provide relevant data combinations for species assignment and even for the recognition of new genera. In this work, we have attempted to determine the generic allocation of Epictia unicolor and Trilepida guayaquilensis-both species currently known only by their holotype-based on a detailed description of cranial and post-cranial osteology. We confirm the assignment of E. unicolor to the genus Epictia despite the divergent configuration of cephalic shields. Based mainly on data from the skull, suspensorium, and cervical vertebrae but supported by external morphology as well as a redescription of the holotype, we propose the assignment of Trilepida guayaquilensis to the genus Epictia. This study provides not only detailed data on the osteology of Epictia, but also a first approach to the putative combination of osteological characters for the genus.

Postcranial osteology of the basally branching hadrosauroid dinosaur Tanius sinensis from the Upper Cretaceous Wangshi Group of Shandong, China

ABSTRACT Tanius sinensis was one of the first dinosaur species to be named from China. It was established on a partial skeleton recovered by a joint Sino-Swedish expedition in 1923. The fossils were excavated from Upper Cretaceous strata of the Jiangjunding Formation (Wangshi Group) in Shandong Province, and although their discovery dates back almost 100 years, they have not been reassessed in detail since their initial description in 1929. This omission is critical because T. sinensis is now recognized as one of the stratigraphically youngest non-hadrosaurid hadrosauroid taxa. Here, we re-evaluate the postcranial osteology of T. sinensis as a prelude to an anatomical and phylogenetic revision of the species. We examined the holotype and all currently referred specimens of T. sinensis first-hand, and identified a unique postcranial character state combination incorporating tall dorsal neural spines, a reduced postacetabular ridge on the ilium, a fully enclosed flexor tunnel formed by the distal condyles of the femur, and a lunate proximal end on metatarsal III. Comparisons with other species of Tanius confirm that: (1) T. chingkankouensis is a nomen dubium erected on non-diagnostic composite material; (2) T. laiyangensis was established on indeterminate hadrosaurid remains that are not attributable to Tanius; and (3) the anecdotal assignments of Bactrosaurus prynadai and Tsintaosaurus spinorhinus to Tanius cannot be substantiated. Close inspection of the holotype caudal vertebra further reveals a possible healed bite trace consistent with a prey–predator interaction. Lastly, our calculated average body mass estimate for T. sinensis of between 2091–3533 kg suggests that it was one of the largest non-hadrosaurid hadrosauroids.

A Monograph on the Osteology of Mesopotamian Spiny-tailed Lizards, Saara loricata (Blanford, 1874) (Sauria: Agamidae: Uromastycinae)

The species of the subfamily Uromastycinae are herbivorous burrowing lizards distributed from the African Sahara Desert to the Asian Thar Desert and across the Arabian Peninsula. Although osteological studies on Uromastycinae have a long history, a detailed description of the complete skeleton is lacking. We investigate the cranial and postcranial osteology of the Mesopotamian Spiny-tailed Lizard (Saara loricata, previously referred to Uromastyx). We studied articulated and disarticulated materials from five specimens and present a complete description of the bones of the species. Our study adds to the growing body of literature on the skeleton of agamid lizards. Unlike Uromastyx sensu stricto, in S. loricata no anterior premaxillary foramina exists on the anterior surface of the premaxilla, no contact exists between the frontal and the maxilla or premaxilla, the anterolateral processes of the frontal are unexposed in dorsal view so that the prefrontal and nasal are attached, and the pterygoid does not contact the vomer anteriorly and the quadrate posteriorly. Unlike its congener S. hardwickii, in S. loricata no anterior premaxillary foramen exists on the anterior surface of the premaxilla, a smaller ethmoidal foramen perforates the nasal, a well-developed, posteriorly extended socket-like notch is formed through anterior bifurcation of the jugal, an L-shaped suture line forms between the jugal and postorbital in dorsal view, and an interlocking suture between the surangular and dentary exists in S. loricata.

Postcranial Osteology of the First Early-Stage Juvenile Skeleton of Plateosaurus trossingensis (Norian, Frick, Switzerland)

Postcranial Osteology of the First Early-Stage Juvenile Skeleton of Plateosaurus trossingensis (Norian, Frick, Switzerland)

Darevskia parvula (Lantz & Cyren, 1913) ve Darevskia adjarica (Darevsky & Eiselt, 1980)'nın karşılaştırmalı iskelet osteolojisi (Squamata: Lacertidae)

A detailed description of cranial and postcranial osteology of Darevskia parvula and D. adjarica is provided osteological data for further comparative studies of other lizards. The descriptions and comparisons are based on 12 specimens, of which 10 adult and 2 juveniles for each species. Darevskia parvula and D. adjarica are highly conservative species and they have similar osteological features. The differences in the current study are the number of teeth for the cranial skeleton and the number of vertebrae for the postcranial. Darevskia parvula has a lower number of teeth than D. adjarica.

Descriptive osteology and patterns of limb loss of the European limbless skink Ophiomorus punctatissimus (Squamata, Scincidae).

The limbless skink Ophiomorus punctatissimus is a cryptozoic species found in the Peloponnese region of Greece and on the Greek island Kythira. To provide the first thorough description of the cranial and postcranial osteology of this species, both disarticulated specimens and X-ray computed tomographies of wet-preserved specimens were examined in detail. Resulting from this, an anatomical atlas of this species is provided. Two separate considerations, an evolutionary and an ecomorphological one, are made based on the observed adaptations related to limb loss in this skink. The structure of the girdles shows a particular pattern of reduction: whereas the pelvic girdle is mostly vestigial, the pectoral girdle is instead well developed, with all the elements typical of limbed lizards except for the actual limbs. This led us to hypothesize an asynchronous pattern of limb reduction during the evolution of this species, in which the hindlimbs regressed earlier than the forelimbs. Furthermore, considerations based on overall body morphology, osteology and the structure of the inner ear led to the recognition of this species as a burrowing ecomorph. In contrast to the morphology normally displayed in this ecomorph, O. punctatissimus is characterized by the retention of autotomic vertebrae in its tail. This is consistent with the habitats in which it lives, where active burrowing would be difficult because of the hard, rocky terrain. Instead, this skink hides among rocks on the surface and is, therefore, subject to greater predation risk.

Osteology of The Middle Eocene CeratomorphHyrachyus modestus(Mammalia, Perissodactyla)

ABSTRACT The middle Eocene ceratomorph Hyrachyus has been considered a pivotal genus in ceratomorph evolution, either as a transitional form from tapiroids to rhinocerotoids, giving rise to all later rhinocerotoids, or else as the sister taxon to other rhinocerotoids. Thus, Hyrachyus has been commonly chosen as an outgroup in phylogenetic analyses of rhinocerotoids. However, little has been published on the osteology of Hyrachyus, even though well-preserved craniodental and postcranial specimens of this taxon have been in collections for decades. Here, we describe and illustrate the cranial and postcranial osteology of Hyrachyus modestus, based mainly on the exceptionally preserved specimens housed at the American Museum of Natural History, specifically AMNH FM 12664. Our bone-by-bone description provides detailed information on the osteological morphology of Hyrachyus, which should be useful for phylogenetic analyses of both rhinocerotoids and perissodactyls in general, because it provides one of the mor...

The vertebrate fauna of the upper Permian of Niger—IX. The appendicular skeleton of Bunostegos akokanensis (Parareptilia: Pareiasauria)

ABSTRACTPareiasaurs were a group of herbivorous reptiles that lived during the middle to late Permian (˜265–252 Ma) in what is modern-day Europe, Asia, South America, and Africa. Field work in the Moradi Formation of northern Niger has produced multiple elements of the appendicular skeleton of the pareiasaur Bunostegos akokanensis. The considerable size disparity and morphological variation among the elements suggest that they represent ontogenetic stages ranging from relatively juvenile to adult. Here we present the first description of the scapulocoracoid, humerus, radius, ulna, pelvis, and femur of Bunostegos as well as some of the first ontogenetic data for postcranial osteology in pareiasaurs. As with the skull, numerous postcranial autapomorphies characterize Bunostegos, including laterally originating acromion process of the scapula; radius and ulna with continuous articular surface on humerus; paired crests on the olecranon process; ulna longer than humerus; pinched posterior margin of the acetabular rim; robust pelvic symphysis extending the length of the puboischiatic plate; lack of a distinct postaxial flange of the femur; and an elaborated femoral lateral condyle wrapping over the medial condyle. We incorporated data from the appendicular skeleton of Bunostegos into a revised phylogenetic analysis of pareiasaur relationships. The results of this analysis corroborate previous cranial analyses that place Bunostegos between Guadalupian taxa and the Lopingian velosaur subclade. Interestingly, several aspects of its postcranial anatomy suggest that Bunostegos possessed relatively upright forelimb posture, which would be unique among pareiasaurs and possibly Permian amniotes as a whole.SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP

A reassessment of Eocene parrotlike fossils indicates a previously undetected radiation of zygodactyl stem group representatives of passerines (Passeriformes)

In the past years, various Eocene fossil birds were described as stem group representatives of the zygodactyl Psittaciformes (parrots). These birds show quite disparate morphologies, which cast some doubt on the correct assignment of all of them to the psittaciform stem group. A reassessment of their affinities is further needed, because it was recently proposed that among extant birds, Psittaciformes and Passeriformes (passerines) form a clade and that passerines possibly derived from a zygodactyl ancestor. Here, phylogenetic analyses are performed, which for the first time also include representatives of the Zygodactylidae, the extinct zygodactyl sister taxon of the Passeriformes. The early Eocene Psittacopes was originally described as a stem group representative of Psittaciformes. However, none of the present analyses supported psittaciform affinities for Psittacopes and instead recovered this taxon in a clade together with zygodactylids and passerines. Also part of this clade are the early Eocene taxa Pumiliornis and Morsoravis, and it is detailed that Psittacopes and the long‐beaked and presumably nectarivorous Pumiliornis, with which it has not yet been compared, are very similar in their postcranial osteology. The present analysis corroborates the hypothesis of a zygodactyl stem species of passerines. To account for these results, Psittacopes is here assigned to a new higher‐level taxon and a new name is also introduced for the clade including Zygodactylidae and Passeriformes.

Cranial and vertebral morphology of the straight-billed Miocene phoenicopteriform bird Palaelodus and its evolutionary significance

Palaelodidae are the extinct sister taxon of flamingos (Phoenicopteridae). These Cenozoic birds are of significance for an understanding of flamingo evolution, because they have a short and straight beak and exhibit swimming adaptations, thus possibly bridging the morphological gap between flamingos and their closest extant relatives, the grebes (Podicipedidae). Palaelodus bones are very abundant in some fossil localities, but critical osteological details remained unknown, and for the first time more detailed descriptions of the neurocranium, quadrate, mandible, vertebrae, and pedal phalanges are given in the present study. Although the postcranial osteology of Palaelodus closely resembles that of extant flamingos, the skull is utterly different. The morphology of the mandible casts some doubt on previous assumptions that Palaelodus already evolved a filter feeding apparatus. The shape of the pedal phalanges supports swimming habits and differences in the vertebral column are described, which suggest a different feeding position than in extant flamingos. Derived features are identified, which are shared by flamingos, grebes, and some “gruiform” taxa, and which may constrain the candidate taxa for the closest extant relatives of flamingos and grebes.

Interplay between postcranial morphology and locomotor types in Neotropical sigmodontine rodents

Sigmodontine rats are one of the most diverse components of the Neotropical mammal fauna. They exhibit a wide ecological diversity and a variety of locomotor types that allow them to occupy different environments. To explore the relationship between morphology and locomotor types, we analyzed traits of the postcranial osteology (axial and appendicular skeletons) of 329 specimens belonging to 51 species and 29 genera of sigmodontines exhibiting different locomotor types. In this work, postcranial skeletal characters of these rats are considered in an ecomorphological study for the first time. Statistical analyses showed that of the 34 osteological characters considered, 15 were related to the locomotor types studied, except for ambulatory. However, character mapping showed that climbing and jumping sigmodontines are the only taxa exhibiting clear adaptations in their postcranial osteology, which are highly consistent with the tendencies described in many other mammal taxa. Climbing, digging and swimming rats presented statistically differences in traits associated with their vertebral column and limbs, whereas jumping rats showed modifications associated with all the skeletal regions. Our data suggest that sigmodontine rats retain an all-purpose morphology that allows them to use a variety of habitats. This versatility is particularly important when considering the lack of specialization of sigmodontines for a specific locomotor mode. Another possible interpretation is that our dataset probably did not consider relevant information about these groups and should be increased with other types of characters (e.g. characters from the external morphology, myology, etc.).

On the osteology of Tapejara wellnhoferi KELLNER 1989 and the first occurrence of a multiple specimen assemblage from the Santana Formation, Araripe Basin, NE-Brazil

The postcranial elements of two similar sized and juvenile individuals, along with a partial skull, are attributed to the Early Cretaceous pterosaur Tapejara wellnhoferi. The remains, recovered from a single concretion of the Romualdo Member, Santana Formation, NE-Brazil, represent the first account of multiple specimens having settled together and allow for a complete review of postcranial osteology in tapejarid pterosaurs. A comparison of long bone morphometrics indicates that all specimens attributed to the Tapejaridae for which these elements are known (i.e. Huaxiapterus, Sinopterus, Tapejara) display similar bivariate ratios, suggesting that Chinese and Brazilian taxa must have exhibited similar growth patterns. An unusual pneumatic configuration, whereby the humerus is pierced by both dorsally and ventrally located foramina, is observed within T. wellnhoferi, while the pneumatic system is inferred to have invaded the hindlimbs via the femur in all members of the Azhdarchoidea. The partial preservation of the endocranial cavity allows for a reconstruction of the tapejarid brain, where despite a small orbit with respect to skull size, the presence of large flocculi and ocular lobes indicate that Tapejara possessed both excellent balancing and visual systems as a consequence of its aerial lifestyle.

The postcranial osteology and phylogenetic position of the small ornithischian dinosaur Changchunsaurus parvus from the Quantou Formation (Cretaceous: Aptian–Cenomanian) of Jilin Province, north‐eastern China

Abstract: Ornithopods were the most important group of Cretaceous ornithischians and achieved high levels of abundance and taxonomic diversity. An understanding of the phylogeny, early evolution and diagnosis of the clade is hampered by a shortage of detailed anatomical descriptions of basal taxa. One of the most important basal ornithopod taxa discovered in recent years is Changchunsaurus parvus, from the Quantou Formation (‘middle’ Cretaceous) of Jilin Province, China, represented by excellent cranial and postcranial material. Here, we present the first description of the postcranial anatomy of the holotype specimen of Changchunsaurus and provide comparisons to other basal cerapodans and basal ornithopods. A phylogenetic analysis finds relationships amongst basal ornithopods to be extremely poorly resolved, but supports a sister‐group relationship between Changchunsaurus and Jeholosaurus shangyuanensis from the Yixian Formation (late Barremian–early Aptian) of Liaoning Province, China. Numerous characters distinguish the two taxa, supporting their generic distinction. The proposed sister‐group relationship suggests that an endemic clade of small‐bodied bipedal ornithopods existed in north‐east China during the Early to ‘middle’ Cretaceous.

Osteology of Lophiodon Cuvier, 1822 (Mammalia, Perissodactyla) and its phylogenetic implications

ABSTRACT Lophiodon is the best-known member of the Lophiodontidae, a family of Eocene Eurasian perissodactyls, in terms of its skull and postcranial skeleton. Previous studies have allied Lophiodontidae with either Tapiroidea or Chalicotherioidea. This study describes the cranial and postcranial osteology of Lophiodon with an emphasis on characters pertaining to the phylogenetic position of lophiodontids. Although cranial and postcranial remains of Lophiodon are known from European faunas, the skull and postcranial skeleton have not been well studied, and few non-dental characters have been used to investigate the relationships of this genus to other perissodactyls. Lophiodon displays a mosaic of cranial and postcranial features that could be interpreted as possible synapomorphies uniting it with either tapiroids or chalicotherioids. Data collected from these studies were incorporated into a phylogenetic analysis of a variety of perissodactyl taxa scored for characters of the skull, postcranial skeleton, and dentition. These data indicate that lophiodontids, as represented by Lophiodon, are the sister-taxon to Ceratomorpha (Tapiroidea plus Rhinocerotoidea). Chalicotherioids are paraphyletic and placed in a clade with palaeotheriids and brontotheres, a result that may be due to superficial similarities of the dentition. Thus, lophiodontids still belong in the Tapiromorpha, but cranial and postcranial evidence does not support a special relationship with either tapiroids or chalicotherioids. Unlike previous studies, the results also do not support a monophyletic Equoidea (Palaeotheriidae plus Equidae).

The postcranial osteology and phylogenetic position of the Middle Eocene Messelastur gratulator Peters, 1994—a morphological link between owls (Strigiformes) and falconiform birds?

ABSTRACT An articulated skeleton of Messelastur gratulator Peters, 1994, from the middle Eocene of Messel in Germany is described. This species was hitherto known from two skulls with associated vertebrae only, and has been tentatively classified in the Accipitridae (hawks). The new specimen shows that M. gratulator closely resembles the Lower Eocene Tynskya eocaena Mayr, 2000a, which is known from an articulated skeleton from the North American Green River Formation and isolated bones from the London Clay in England. Both species, M. gratulator and T. eocaena, are assigned to the new taxon Messelasturidae. The new specimen exhibits previously unknown osteological details bearing on the phylogenetic position of the Messelasturidae, most notably the absence of an ossified supratendineal bridge on the distal tibiotarsus. Cladistic analysis of 110 characters supports sister-group relationship between Messelastur and Tynskya, and shows the Messelasturidae to be the sister taxon of owls (Strigiformes). The clade (Messelasturidae + Strigiformes) is shown to be the sister group of the clade (Falconidae [falcons] + Accipitridae). Among the known fossil raptorial birds, the Messelasturidae most substantially differ from the extant taxa. They provide a morphological link between Strigiformes and Falconiformes (diurnal birds of prey), and support the highly disputed falconiform affinities of owls in combining derived tibiotarsus and tarsometatarsus characters of owls with a more plesiomorphic, 'falcon-' or 'hawk-like', skull morphology.