High incidence of cervical ribs indicates vulnerable condition in Late Pleistocene woolly rhinoceroses

Increased incidences of cervical ribs in deer indicate extinction risk

Mammals as a rule have seven cervical vertebrae, a number which remains remarkably conserved. Occasional deviations of this number are usually due to the presence of cervical ribs on the seventh vertebra, indicating a homeotic transformation from a cervical rib-less vertebra into a thoracic rib-bearing vertebra. These transformations are often associated with major congenital abnormalities or pediatric cancers (pleiotropic effects) that are, at least in humans, strongly selected against. Based on data from Late Pleistocene mammoths (Mammuthus primigenius) and woolly rhinoceroses (Coelodonta antiquitatis) from the North Sea, we hypothesized that high incidences of cervical ribs in declining populations are due to inbreeding and/or adverse conditions impacting early pregnancies. In this study, we investigated the incidence of cervical ribs in an extinct Late Pleistocene megaherbivore, giant deer (Megaloceros giganteus) from Ireland and in the extant highly inbred Père David deer (Elaphurus davidianus) and in twenty other extant species. We show that the incidence of cervical ribs is exceptionally high in both the Irish giant deer and the Père David deer and much higher than in extant outbred deer. Our data support the hypothesis that inbreeding and genetic drift increase the frequencies of maladaptive alleles in populations at risk of extinction. The high incidence of cervical ribs indicates a vulnerable condition, which may have contributed to the extinction of megaherbivore species in the Late Pleistocene. We argue that cervical rib frequency may be a good proxy for extinction risk in inbred populations.

Morphology of the Ventral Process of the Sixth Cervical Vertebra in Extinct and Extant Equus: Functional Implications

In this study, we examined the ventral process of C6 in extinct and extant Equus (sister taxa to Equus ferus caballus only) with the purpose of describing normal morphology and identifying anomalous variations relevant to recent studies describing a congenital malformation in E. ferus caballus. Overall, 83 specimens from 9 museums and 3 research/educational facilities were examined, totalling 71 extinct specimens from 12 species and 12 extant specimens from 5 species. The lateral view revealed that a large convexity exists in the ventral process between the cranial ventral tubercle (CrVT) and the caudal ventral tubercle (CVT) in the earliest ancestor, Hyracotherium grangeri, from 55 mya, which receded throughout the millennia to become a smaller convexity in E. ferus caballus and the sister taxa. The CrVT is visibly shorter and narrower than the CVT, with a constricted section directly ventral to the transverse process, essentially demarcating the CrVT and CVT. No congenital malformations were evident. As the ventral process of C6 is an integral component for muscle attachment in supporting the head/neck during posture and locomotion, this would indicate that the caudal module in the cervical column might be compromised when a partial or complete absence of the CVT is detected via radiographs in modern E. ferus caballus.

Breaking the constraint on the number of cervical vertebrae in mammals: On homeotic transformations in lorises and pottos

Mammals almost always have seven cervical vertebrae. The strong evolutionary constraint on changes in this number has been broken in sloths and manatees. We have proposed that the extremely low activity and metabolic rates of these species relax the stabilizing selection against changes in the cervical count. Our hypothesis is that strong stabilizing selection in other mammals is largely indirect and due to associated pleiotropic effects, including juvenile cancers. Additional direct selection can occur due to biomechanical problems (thoracic outlet syndrome). Low metabolic and activity rates are thought to diminish these direct and indirect effects. To test this hypothesis within the primates, we have compared the number of cervical vertebrae of three lorisid species with particularly low activity and metabolic rates with those of more active primate species, including with their phylogenetically closest active relatives, the galagids (bushbabies). In support of our hypothesis, we found that 37.6% of the lorisid specimens had an abnormal cervical count, which is a higher percentage than in the other nine primate families, in which the incidence varied from zero to 2.2%. We conclude that our data support the importance of internal selection in constraining evolvability and of a relaxed stabilizing selection for increasing evolvability. Additionally, we discuss that there is no support for a role of the muscularized diaphragm in the evolutionary constraint.

Rarity of congenital malformation and deformity in the fossil record of vertebrates - A non-human perspective

OBJECTIVE

A malformed pectoral joint of the middle Devonian antiarch fish Asterolepis ornata is described, and a survey of congenital malformations in the fossil record is provided.

MATERIALS

The specimen of A. ornata (MB.f.73) from Ehrman in Latvia, stored at the Museum für Naturkunde Berlin, Germany.

METHODS

A. ornata was macroscopically and radiologically investigated, and the overview on congenital malformation was based on an extensive literature survey.

RESULTS

In the deformed joint of A. ornata, the articular surfaces and muscle attachment sites are greatly reduced, indicating restricted mobility. Congenital malformations can be found since the middle Silurian and affect all groups of vertebrates, but they are rare. Teeth and the vertebral column are the most commonly affected anatomical regions, and the mechanisms causing these malformations probably remained the same through geological time.

CONCLUSIONS

Micro-CT of the deformed joint shows no disturbance of the normal trabecular pattern and no evidence of trauma or disease, suggesting a congenital hypoplasia, although an acquired deformity cannot be ruled out completely.

SIGNIFICANCE

Congenital malformations, even those that are rare, were part of the common history of vertebrates for more than 400 million years.

LIMITATIONS

Epidemiologic measures like incidence and prevalence usually cannot be applied to define rare diseases in the fossil record.

SUGGESTIONS FOR FURTHER RESEARCH

A broadly based analysis of species of fossil vertebrates with numerus recovered specimens (e.g. many bony fishes, amphibians, certain dinosaurs) might statistically affirm the occurrence of malformations and possible correlations with the paleoenvironment.

Vertebral Formulae and Congenital Vertebral Anomalies in Guinea Pigs: A Retrospective Radiographic Study

Simple Summary

Guinea pigs are popular pets, but there is still a lack of information about their morphology. Variable morphology of the vertebral column can lead to incorrect localization of spinal diseases or the site of surgical intervention. This study aimed to determine the numerical variants of vertebral column and prevalence, localization, and type of congenital anomalies of the vertebral column. Vertebral column radiographs were reviewed in 240 guinea pigs, and nine numerical variants of the vertebral column were noticed. The most common vertebral formula, seven cervical, 13 thoracic, six lumbar, four sacral, and five to seven caudal vertebrae, was found in 75% of guinea pigs. Congenital anomalies were also found as incidental findings in 12.5% of guinea pigs, mostly in the thoracolumbar and lumbosacral regions. The most common congenital anomalies were a variable morphology of the last pair of ribs in the thoracolumbar region and transitional vertebra with a mixed morphological characteristic of lumbar and sacral vertebrae in the lumbosacral region. The cervical region was the least common region for congenital anomalies of the vertebral column. Our results contribute to the knowledge of clinical morphology in guinea pigs applicable in both, research and clinical practice.

Abstract

The objectives of this retrospective study of 240 guinea pigs (148 females and 92 males) were to determine the prevalence of different vertebral formulae and the type and anatomical localization of congenital vertebral anomalies (CVA). Radiographs of the cervical (C), thoracic (Th), lumbar (L), sacral (S), and caudal (Cd) part of the vertebral column were reviewed. Morphology and number of vertebrae in each segment of the vertebral column and type and localization of CVA were recorded. In 210/240 guinea pigs (87.50%) with normal vertebral morphology, nine vertebral formulae were found with constant number of C but variable number of Th, L, and S vertebrae: C7/Th13/L6/S4/Cd5-7 (75%), C7/Th13/L6/S3/Cd6-7 (4.17%), C7/Th13/L5/S4/Cd6-7 (2.50%), C7/Th13/L6/S5/Cd5-6 (1.67%), C7/Th12/L6/S4/Cd6 (1.25%), C7/Th13/L7/S4/Cd6 (1.25%), C7/Th13/L7/S3/Cd6-7 (0.83%), C7/Th12/L7/S4/Cd5 (0.42%), C7/Th13/L5/S5/Cd7 (0.42%). CVA were found in 30/240 (12.5%) of guinea pigs, mostly as a transitional vertebra (28/30), which represents 100% of single CVA localised in cervicothoracic (n = 1), thoracolumbar (n = 22) and lumbosacral segments (n = 5). Five morphological variants of thoracolumbar transitional vertebrae (TTV) were identified. Two (2/30) guinea pigs had a combination of CVA: cervical block vertebra and TTV (n = 1) and TTV and lumbosacral transitional vertebra (LTV) (n = 1). These findings suggest that guinea pigs’ vertebral column displays more morphological variants with occasional CVA predominantly transitional vertebrae.

Cervical ribs in human early life: morphological variability and first identification as a morbidity criterion in a past population

Despite the medical literature on supernumerary cervical ribs in extant adult samples, little is known about their development and occurrence in early infancy. The documentation of cervical ribs in modern samples of fetuses and neonates is indeed affected by ethical as well as technical limitations. The aim of the present study was to investigate their frequencies and morphological variability in the first known archaeological collection of very young children with this anatomical variant. The study sample comes from the 8B-51 necropolis on the Saï island (Sudan) and dates to the Classic Kerma Period (XVIIIe-XVIe centuries BC). It consists of 64 individuals deceased between 24 weeks of amenorrhoea and 2 years of age. Bilateral or unilateral cervical ribs were found in 27 individuals. A total of 43 cervical ribs were identified, 38 of which are fully preserved. According to these observations, at least 42% of the individuals have unilateral or bilateral cervical ribs, with an average maximum length of < 1 cm. This frequency is very high compared to those observed in contemporary adult samples (up to 3%). First, the comparison of our results with biological and genetic research demonstrating the link between the occurrence of cervical ribs and a reduced chance of survival during infancy allows the first identification of this trait as an indicator of morbidity in an archaeological collection, a morbidity to which a genetic homogeneity or even endogamy could contribute. Second, the number of ribs studied makes it possible to propose a morphological classification based on the general shape and the shape of the articular facets, classification that can be used tos refine the analyses of the trait in future samples.

Development and Evolutionary Constraints in Animals

We review the evolutionary importance of developmental mechanisms in constraining evolutionary changes in animals—in other words, developmental constraints. We focus on hard constraints that can act on macroevolutionary timescales. In particular, we discuss the causes and evolutionary consequences of the ancient metazoan constraint that differentiated cells cannot divide and constraints against changes of phylotypic stages in vertebrates and other higher taxa. We conclude that in all cases these constraints are caused by complex and highly controlled global interactivity of development, the disturbance of which has grave consequences. Mutations that affect such global interactivity almost unavoidably have many deleterious pleiotropic effects, which will be strongly selected against and will lead to long-term evolutionary stasis. The discussed developmental constraints have pervasive consequences for evolution and critically restrict regeneration capacity and body plan evolution.