A new adult specimen of the basalmost ornithuromorph bird <i>Archaeorhynchus spathula</i> (Aves: Ornithuromorpha) and its implications for early avian ontogeny

<p>Most living birds characteristically grow rapidly and reach adult size within a year. Nevertheless, little is known about how such an advanced developmental strategy evolved despite many discoveries of early fossil birds. Here we assess the long-bone histology from a new adult specimen of <i>Archaeorhynchus spathula</i>, the basalmost taxon of Ornithuromorpha. Ornithuromorpha is the most inclusive clade containing extant birds but not the Mesozoic Enantiornithes. Histological analysis reveals that the cortex is composed of parallel-fibred bone with three lines of arrested growth, indicative of slow and annually interrupted growth for this taxon. Such bone histology is significantly different from that of other known basal ornithuromorphs, but resembles that of enantiornithines, which leads us to suggest protracted slow growth in the common ancestor of Ornithuromorpha and Enantiornithes. The fusion sequence of the tarsometatarsus between Enantiornithes and Ornithuromorpha has long been hypothesized to be different and regarded as indicative that enantiornithines are not close relatives of ornithuromorphs. Due to a lack of fossils recording early ontogenetic stages, little is known about the development of the tarsometatarsus in basal ornithuromorphs, making this hypothesis impossible to test. Here we show that the fusion sequence of the tarsometatarsus in <i>Archaeorhynchus</i> is similar to that of enantiornithines, and that the proximal-early fusion in tarsometatarsus represents a plesiomorphic trait for basal birds. Our findings also shed light on ontogenetic variation of sternal morphology, which highlights the importance of ontogeny in the taxonomic and phylogenetic study of early birds.</p

Convergent evolution of a mobile bony tongue in flighted dinosaurs and pterosaurs

<div><p>The tongue, with fleshy, muscular, and bony components, is an innovation of the earliest land-dwelling vertebrates with key functions in both feeding and respiration. Here, we bring together evidence from preserved hyoid elements from dinosaurs and outgroup archosaurs, including pterosaurs, with enhanced contrast x-ray computed tomography data from extant taxa. Midline ossification is a key component of the origin of an avian hyoid. The elaboration of the avian tongue includes the evolution of multiple novel midline hyoid bones and a larynx suspended caudal to these midline elements. While variable in dentition and skull shape, most bird-line archosaurs show a simple hyoid structure. Bony, or well-mineralized, hyoid structures in dinosaurs show limited modification in response to dietary shifts and across significant changes in body-size. In Dinosauria, at least one such narrow, midline element is variably mineralized in some basal paravian theropods. Only in derived ornithischians, pterosaurs and birds is further significant hyoid elaboration recorded. Furthermore, only in the latter two taxa does the bony tongue structure include elongation of paired hyobranchial elements that have been associated in functional studies with hyolingual mobility. Pterosaurs and enantiornithine birds achieve similar elongation and inferred mobility via elongation of ceratobranchial elements while within ornithurine birds, including living Aves, ossified and separate paired epibranchial elements (caudal to the ceratobranchials) confer an increase in hyobranchial length. The mobile tongues seen in living birds may be present in other flighted archosaurs showing a similar elongation. Shifts from hypercarnivory to more diverse feeding ecologies and diets, with the evolution of novel locomotor strategies like flight, may explain the evolution of more complex tongue function.</p></div

The M. branchiomandubularis (arrows) in birds and <i>Alligator</i>.

<p>(A)<i>Rhea americana</i> (USNM 615363), (B)<i>Dromaius novaehollandiae</i> (TMM M-14235), (C) <i>Nothura maculosa</i> (USNM 631209), (D)<i>Megapodius pritchardii</i> (USNM 319640), (E) <i>Phasianus colchicus</i> (TMM M-12000), (F)<i>Alligator mississippiensis</i> (TNHC specimen). The two portions of the muscle are indicated in Galliformes: ‘M. branchiomandubularis cranialis’ (mbm_a) and ‘caudalis’ (mbm_p).</p

The first enantiornithine bird from the Upper Cretaceous of China

<div><p>ABSTRACT</p><p>A new Late Cretaceous avian taxon, <i>Parvavis chuxiongensis</i>, gen. et sp. nov., is reported here based on an incomplete skeleton from Upper Cretaceous lake deposits in Yunnan Province, southern China. A phylogenetic analysis of 32 taxa and 242 morphological characters resulted in three most parsimonious trees, the strict consensus tree of which places <i>Parvavis chuxiongensis</i> within Enantiornithes. Histological study shows that the bones of <i>Parvavis</i> were composed of parallel-fibered bone tissue without lines of arrested growth, and indicated that growth rate had slowed but had not stopped at any stage prior to death. The bones also lack the rough surface texture seen in juvenile birds. Therefore, the new bird was probably close to adult body size at the time of death. However, the specimen is surprisingly small, highlighting the wide range of body sizes in Upper Cretaceous enantiornithines. The new specimen also represents both the first known bird from the Upper Cretaceous of China and the first Mesozoic bird from the south of China, and thus extends the temporal and geographic range of Mesozoic birds in China.</p> <p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at <a href="http://www.tandfonline.com/UJVP" target="_blank">www.tandfonline.com/UJVP</a></p> </div

Photograph (A) and camera lucida drawing (B) of the skull of IVPP V18687, and comparison of teeth morphological details of C, IVPP V18687;D, <i>Pengornis houi</i>; and E, <i>Eopengornis martini</i>, and lacrimals of F, IVPP V18687; and G, <i>Pengornis houi</i>.

<p>Abbreviations: an, angular; de, dentary; fr, frontal; hy, hyoid; ju, jugal; la, lacrimal; m, maxilla; na, nasal; oi, occipital region; pa, parietal; pm, premaxilla; pt, palatine; qj, quadratojugal; qu, quadrate. Scale bar equals 5 mm.</p

Episterno-hyoid and M. coracohyoideus muscle in <i>Alligator</i> and proposed homologous muscles in birds.

<p>(A)(B)<i>Alligator mississippiensis</i> (TMM M-12053), (C)(D)the homologous M. sternotrachealis in <i>Aythya americana</i> (TMM M-12682). (E)(F) show the M. tracheolateralis in <i>Aythya americana</i> (USNM 643741) and <i>Rhea americana</i> (USNM 615363) respectively; (G)(H)(I) show M. cricohyoideus in <i>Nothura machulosa</i> (USNM 631210), <i>Megapodius pritchardii</i> (USNM 319640) and <i>Aythya americana</i> (USNM 643741) respectively Abbreviations: ephc, episterno-hyoid complex; mch, M. cricohyoideus; mclh, M. cleidohyoideus; mtl, M. tracheolateralis, and mstt, M. sternotrachealis.</p

Measurements (mm) of IVPP V18687.

<p>Measurements (mm) of IVPP V18687.</p

DiceCT imaging of the head of <i>Dromaius novaehollandiae</i>.

<p>Individual cross-sections (A-D) from cranial to caudal region with targeted muscular and bony elements colored and labeled. Abbreviations: lar, larynx; mbm, M. branchiomandibularis; mcg, M. ceratoglossus; mge, M. genioglossus; mhys, M. hypoglossus; msh, M. stylohyoideus and M. serpihyoideus; mtl, M. tracheolateralis.</p

A New Species of Pengornithidae (Aves: Enantiornithes) from the Lower Cretaceous of China Suggests a Specialized Scansorial Habitat Previously Unknown in Early Birds

<div><p>We describe a new enantiornithine bird, <i>Parapengornis eurycaudatus</i> gen. et sp. nov. from the Lower Cretaceous Jiufotang Formation of Liaoning, China. Although morphologically similar to previously described pengornithids <i>Pengornis houi</i>, <i>Pengornis</i> IVPP V18632, and <i>Eopengornis martini</i>, morphological differences indicate it represents a new taxon of the Pengornithidae. Based on new information from this specimen we reassign IVPP V18632 to <i>Parapengornis</i> sp. The well preserved pygostyle of the new specimen elucidates the morphology of this element for the clade, which is unique in pengornithids among Mesozoic birds. Similarities with modern scansores such as woodpeckers may indicate a specialized vertical climbing and clinging behavior that has not previously been inferred for early birds. The new specimen preserves a pair of fully pennaceous rachis-dominated feathers like those in the holotype of <i>Eopengornis martini</i>; together with the unique morphology of the pygostyle, this discovery lends evidence to early hypotheses that rachis-dominated feathers may have had a functional significance. This discovery adds to the diversity of ecological niches occupied by enantiornithines and if correct reveals are remarkable amount of locomotive differentiation among Enantiornithes.</p></div

DiceCT imaging of the head of <i>Nothoprocta perdicaria</i>.

<p>Individual cross-sections (A-D) from cranial to caudal region with targeted muscular and bony elements colored and labeled. Abbreviations: lar, larynx; mbm, M. branchiomandibularis; mcg, M. ceratoglossus; mge, M. genioglossus; mhys, M. hypoglossus; msh, M. stylohyoideus and M. serpihyoideus; mtl, M. tracheolateralis; md, mandible.</p