More Like this

1. Cetacean Orbital Muscles: Anatomy and Function of the Circular Layers

   https://doi.org/10.1002/ar.24278  

   Meshida, Keiko ; Lin, Stephen ; Domning, Daryl P. ; Reidenberg, Joy S. ; Wang, Paul ; Gilland, Edwin ( November 2019 , The Anatomical Record)

   Dissections of cetacean orbits identified two distinct circular muscle layers that are uniquely more elaborate than the orbitalis muscles described in numerous mammals. The circular orbital muscles in cetaceans form layers that lie both external and internal to the rectus extra ocular muscles (EOMs). A cone‐shaped external circular muscle (ECM) that invests the external surface of the rectus EOMs was found in all cetacean specimens examined. The cetacean ECM corresponds generally to descriptions of themusculus orbitalisin various mammals but is more strongly developed and has more layers than in noncetaceans. A newly identified internal circular muscle (ICM) is located internal to the rectus EOMs and external to the retractor bulbi (RB). The RB is massive in cetaceans and is encased in a connective tissue layer containing convoluted bundles of blood vessels. The most robust ECM and ICM layers were in sperm whale (Physeter macrocephalus) where they form complete rings. Surprisingly, histological analysis showed the sperm whale ECM to contain both smooth and striated (skeletal) muscle layers while the ICM appeared to contain solely skeletal muscle fibers. The extreme development of the ECM (orbitalis) and RB suggest a co‐evolved system mediating high degrees of protrusion and retraction in cetaceans. We know of no homolog of the ICM but its function seems likely related to the complex vascular structures surrounding and deep to the retractor muscle. Skeletal muscle components in orbital circular muscles appear to be highly derived specializations unknown outside of cetaceans. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1792–1811, 2020. © 2019 American Association for Anatomy

    

   more » « less
2. Getting into Shape: Limb Bone Strength in Perinatal Lemur catta and Propithecus coquereli

   https://doi.org/10.1002/ar.24045  

   Young, Jesse W. ; Jankord, Kathryn ; Saunders, Marnie M. ; Smith, Timothy D. ( December 2018 , The Anatomical Record)

   Functional studies of skeletal anatomy are predicated on the fundamental assumption that form will follow function. For instance, previous studies have shown that the femora of specialized leaping primates are more robust than those of more generalized primate quadrupeds. Are such differences solely a plastic response to differential loading patterns during postnatal life, or might they also reflect more canalized developmental mechanisms present at birth? Here, we show that perinatalLemur catta, an arboreal/terrestrial quadruped, have less robust femora than perinatalPropithecus coquereli, a closely related species specialized for vertical clinging and leaping (a highly unusual locomotor mode in which the hindlimbs are used to launch the animal between vertical tree trunks). These results suggest that functional differences in long bone cross‐sectional dimensions are manifest at birth, belying simple interpretations of adult postcranial form as a direct record of loading patterns during postnatal life. Despite these significant differences in bone robusticity, we find that hindlimb bone mineralization, material properties, and measures of whole‐bone strength generally overlap in perinatalL. cattaandP. coquereli, indicating little differentiation in postcranial maturity at birth despite known differences in the pace of craniodental development between the species. In a broader perspective, our results likely reflect evolution acting during prenatal ontogeny. Even though primates are notable for relatively prolonged gestation and postnatal parental care, neonates are not buffered from selection, perhaps especially in the unpredictable and volatile environment of Madagascar. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 303:250–264, 2020. © 2018 American Association for Anatomy

    

   more » « less
3. Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition

   https://doi.org/10.1002/ar.24046  

   Tapanila, Leif ; Pruitt, Jesse ; Wilga, Cheryl D. ; Pradel, Alan ( December 2018 , The Anatomical Record)

   Sharks of Late Paleozoic oceans evolved unique dentitions for catching and eating soft bodied prey. A diverse but poorly preserved clade, edestoids are noted for developing biting teeth at the midline of their jaws.Helicoprionhas a continuously growing root to accommodate >100 crowns that spiraled on top of one another to form a symphyseal whorl supported and laterally braced within the lower jaw. Reconstruction of jaw mechanics shows that individual serrated crowns grasped, sliced, and pulled prey items into the esophagus. A new description and interpretation ofEdestusprovides insight into the anatomy and functional morphology of another specialized edestoid.Edestushas opposing curved blades of teeth that are segmented and shed with growth of the animal. Set on a long jaw the lower blade closes with a posterior motion, effectively slicing prey across multiple opposing serrated crowns. Further examples of symphyseal whorls among Edestoidae are provided from previously undescribed North American examples ofToxoprion,Campyloprion,Agassizodus, andSinohelicoprion. The symphyseal dentition in edestoids is associated with a rigid jaw suspension and may have arisen in response to an increase in pelagic cephalopod prey during the Late Paleozoic. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 303:363–376, 2020. © 2018 American Association for Anatomy

    

   more » « less
4. The Frontoparietal Fossa and Dorsotemporal Fenestra of Archosaurs and Their Significance for Interpretations of Vascular and Muscular Anatomy in Dinosaurs

   https://doi.org/10.1002/ar.24218  

   Holliday, Casey M. ; Porter, William Ruger ; Vliet, Kent A. ; Witmer, Lawrence M. ( July 2019 , The Anatomical Record)

   The attachments of jaw muscles are typically implicated in the evolution and shape of the dorsotemporal fenestra on the skull roof of amniotes. However, the dorsotemporal fenestrae of many archosaurian reptiles possess smooth excavations rostral and dorsal to the dorsotemporal fossa which closely neighbors the dorsotemporal fenestra and jaw muscle attachments. Previous research has typically identified this region, here termed the frontoparietal fossa, to also have attachment surfaces for jaw‐closing muscles. However, numerous observations of extant and extinct archosaurs described here suggest that other tissues are instead responsible for the size and shape of the frontoparietal fossa. This study reviewed the anatomical evidence that support soft‐tissue hypotheses of the frontoparietal fossa and its phylogenetic distribution among sauropsids. Soft‐tissue hypotheses (i.e., muscle, pneumatic sinus, vascular tissues) were analyzed using anatomical, imaging andin vivothermography techniques within a phylogenetic framework using extant and extinct taxa to determine the inferential power underlying the reconstruction of the soft tissues in the skull roofs of dinosaurs, pseudosuchians, and other reptiles. Relevant anatomical features argue for rejection of the default hypothesis—that the fossa was muscular—due to a complete lack of osteological correlates reflective of muscle attachment. The most‐supported inference of soft tissues is that the frontoparietal fossa contained a large vascular structure and adipose tissue. Despite the large sizes and diverse morphologies of these fossae found among dinosaur taxa, these data suggest that non‐avian dinosaurs had the anatomical foundation to support physiologically significant vascular devices and/or vascular integumentary structures on their skull roofs. Anat Rec, 303:1060–1074, 2020. © 2019 Wiley Periodicals, Inc.

    

   more » « less
5. Functionally Driven Modulation of Sarcomeric Structure and Membrane Systems in the Fast Muscles of a Copepod ( Gaussia princeps )

   https://doi.org/10.1002/ar.23966  

   Glaser, Nosta ; Iyer, Ramesh ; Gilly, William ; Franzini‐Armstrong, Clara ( November 2018 , The Anatomical Record)

   Muscles of the mesopelagic copepodGaussia princeps(Arthropoda, Crustacea, Calanoida) are responsible for repetitive movements of feeding and swimming appendages that are too fast to be followed by eye. This article provides a comparative functional and ultrastructural description of five muscles that have different contraction speeds and are located within different anatomical sites. All are very fast, as indicated by a thick:thin filament ratio of 3:1 and sarcomere lengths that vary between 1 and 3 μm. Measured lengths of thin and thick filaments indicate classification of the muscles into three distinct groups (short, medium, and long) and predict a difference in speed of up to threefold between fibers with the shortest and longest sarcomeres. Indeed, the kicking movement of the posterior legs (with the shortest sarcomere length) is approximately threefold faster than the simultaneous back‐folding of the antennae (with the longest length). Thus, a specific relationship between speed of movement and sarcomere length is established, and we can use the latter to predict the former. Regulatory systems of contraction (sarcoplasmic reticulum [SR] and transverse [T] tubules) match the different contractile properties, varying in frequency of distribution and overall content in parallel to sarcomere variations. All muscles from appendages and body musculature show a unique disposition of contractile material, SR, and T tubules found only in copepod muscles; muscle filaments are grouped in large supermyofibrils that are riddled with frequent cylindrical shafts containing SR and T tubules. This arrangement insures a high spatial frequency of regulatory components. Anat Rec, 301:2164–2176, 2018. © 2018 Wiley Periodicals, Inc.

    

   more » « less